ABSTRACT. The achievement of ignition on the National Ignition Facility in 2022 demonstrated the fundamental feasibility of controlled thermonuclear fusion in the laboratory for energy gain, and was the first major hurdle in efficiently harvesting fusion energy through inertial fusion energy (IFE). Excitement has been growing worldwide, with notable activity in the public and private sectors. To make IFE commercially viable, however, there are still significant scientific, engineering, workforce, and economic hurdles. This talk will review the advancements that made the ignition breakthrough possible, provide an overview of the international IFE landscape, and describe the remaining gaps and challenges that must be solved to realize IFEl aser inertial fusion as a path for clean energy and energy security.

ABSTRACT. Laser-plasma-based wakefield accelerators are changing the scientific landscape bringing on new hopes for high energy physics, compact light sources, and societal applications. Many of these applications critically require the precise characterization of the plasma wakefield that largely affects the bunch’s quality they provide. Advanced diagnostics of such highly transient, microscopic bunch and field structures, however, remains very challenging. After introducing the context and the status of this research, I will shortly explain the physical processes that are involved in plasma accelerators, I then will report on recent major results that demonstrate for the first time the real-time visualization of laser-driven nonlinear relativistic plasma wave[1], its transition to electron-driven wakefield [2] and the femtosecond microscopy of relativistic electron bunch [3].

This will be followed by a short review of the most mature applications including the status of our EIC project ebeam4therapy [4].

[1] Y. Wan, O. Seeman, S. Tata, S. Smarstev, I. Andriyash, E. Kroupp, and V. Malka, Nature Physics (2022), https://doi.org/10.1038/s41567-022-01717-6

[2] Y. Wan, S. Tata, O. Seemann, EY Levine, S Smartsev, E Kroupp, V Malka, Science Advanced eadj3595 (2024)

[3] Y. Wan, S. Tata, O. Seemann, EY Levine, S Smartsev, E Kroupp, V Malka, Light: Science & Applications 12 (1), 116 (2023)

[4] https://ebeam4therapy.eu

ABSTRACT. Plasma in a gas phase forms in a free space or in a container, and its shapes and motions have attracted much scientific attentions for decades. In the outer space, it exists magnetohydrodynamically in rich forms in the background of the external magnetic fields. Fusion plasma in a reactor is produced in a large vacuum vessel to configure its form to maximize its energy output, keeping its stability. Low-temperature plasmas, which are industrial tools as well as fundamental scientific models, have been reported in many shapes under elaborate controls since they play various roles with specific aims in non-equilibrium states, such as light sources, material processing, and medical treatments. For instance, we reported plasma photonic crystals and plasma metamaterials, which have spatial periodicstructure and work as microwave regulators [1,2]. In another study, a filter-like thin plasmasheet is equivalent to a controllable chemical filter [3]. Although they are deliberately designed to optimize their functional outputs, in some cases we have no ideas on scientific principles in its spatial design since they are fixed after simple trial-and-error procedures.

In this study, using our previous research results [1-4] and other relevant scientific achievements, we revisit relationships between functions of low-temperature plasmas and their shapes. Recently, we experimentally developed a maze-solver based on plasma channel expansion [4] and examined such phenomena using Boltzmann-Gibbs (thermodynamical) and Shannon (information) entropies. From this point of view, we can reconsider functions of plasma shapes in our previous research results such as plasma metamaterials and plasmachemical filters, both of which possessed designed shapes for specific purposes in non-equilibrium states. A clue to overall understanding of functions and shapes may be given by entropy estimation, and low-entropy states will be of benefit to improved functions.

Acknowledgements. This work was partly supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology(MEXT/JSPS KAKENHI) with Grant Nos. JP JP22K18704 and JP24H00036.

[1] O. Sakai, et. al., Plasma Sources Sci. Technol. 21, 013001 (2012)

[2] O. Sakai, et. al., Plasma Phys. Contr. Fusion 59, 014042 (2017)

[3] O. Sakai, et. al., Thin Solid Films 519, 6999 (2011)

[4] O. Sakai, et. al., PLoS One 19, e0300842 (2024)

ABSTRACT. COMPASS-U is a new tokamak which is currently under construction at the Institute of Plasma Physics of the Czech Academy of Sciences in Prague [1]. Its relatively small size (R = 0.9 m, a = 0.27 m), compared to other existing or planned tokamaks, combined to a high magnetic field (5 T) and a high plasma current (2 MA) makes it very challenging to design, especially its plasma-facing components. Indeed, the thermal energy confined in the plasma needs to be extracted on a limited area in the divertor yielding extremely high energy flux densities, few times higher than the ones met at the surface of the Sun. The large magnetic pressure needed to keep the hot plasma far away from the wall can be, in case of a sudden loss of confinement so-called ‘disruptions’, accidentally transferred to in-vessel components in a fraction of millisecond, yielding large electromagnetic (EM) JxB forces, ranging from several tens of kN on some tiles up to 4 MN on the vacuum vessel [2]. COMPASS-U being aunique new machine, these loads cannot be estimated from previous experiments and need to be determined.

This contribution describes how plasma physics considerations are used for engineering purposes in order to design the plasma-facing components of a tokamak. Design requirements are driven by the physics to be investigated. The large variety of foreseen plasma scenarios and magnetic equilibria, for investigating different types of physics, adds to the challenge as a single first wall configuration must cope with abroad range of completely different constraints. The different loads are estimated from scaling laws derived from multi-machine databases, simulations and extrapolation from existing devices. As an example, heat loads at the divertor targets follow the Eich’s lawand profiles [3]. It yields for COMPASS-U a power fall-off length in the edge plasma close to the wall of λ_q^omp ~1 mm and consequently steady-state energy flux densities upto 100 MW/m² if no mitigation is applied. Other type of thermal loads, more transient but more powerful, have to be also considered, e.g., runaway electrons with energy in the range 100-300 kJ or edge localized modes, adding to the risk of melting the tungsten tiles. During disruptions, the different currents induced (eddy) and flowing (halo) into the structures due to the temporal variation of magnetic field, caused by vertical displacements and by the plasma current quench, are determined using an EM model based on finite element modeling and multi-machine databases created for ITER under the International Tokamak Physics Activity [4].

[1] P. Vondracek et al., Fusion Eng. and Design 169 (2021) 112490

[2] J. Hromadka et al., Fusion Eng. and Design 167 (2021) 112369

[3] T. Eich et al., Physical Review Letters 107 (2011) 215001

[4] N.W. Eidietis et al., Nuclear Fusion 55 (2015) 063030

ABSTRACT. The erosion of tungsten (W) by fast deuterium (D) atoms from charge-exchange reactions, predicted to be the dominant cause of the observed W radiation in most JET ITER-like-wall plasmas [1], is determined by the co-dependent energy and angular distributions and the flux of incident D atoms. Monte Carlo simulations using conventional histogram binning methods compromise between high resolution and low stochastic noise. In contrast, tallying functional expansion coefficients of the angular spectrum for each energy bin provides both arbitrarily high angular resolution and reduced Monte Carlo noise compared to angular histogram binning.

EIRENE simulations of JET L-mode and H-mode plasmas using newly implemented functional expansion tallies with a Legendre polynomial basis indicate that the most common D impact angles near the JET low-field side divertor entrance are in the range of 60° to 85° to the surface normal at impact energies (E) of 100 to 700 eV and 30° to 50° at E > 1 keV. The predicted W sputtering due to atoms and the W density in the core plasma is increased by up to one-third due to the energy-resolved angular spectra, compared to the total energy-independent angular spectrum and to earlier simulations [1] which assumed a constant impact angle of 60°. As the atomic D flux density decreases with higher impact energy, the increased W sputtering yield due to larger impact angles at 250 eV < E < 700 eV is more significant than the reduced W yield due to more perpendicular angles at E > 1 keV.

[1] H. Kumpulainen, et. al., Plasma Physics and Controlled Fusion 66, 055007 (2024)

ABSTRACT. We present experimental results from the Raman Amplification experimental platform at the University of Rochester’s Laboratory for Laser Energetics (LLE). This platform explores Raman amplification in a unique parameter space which includes a multi-joule pump and an adjustable-energy seed with intensities exceeding 1 x 10¹⁵ W/cm². Initial experiments have demonstrated single-pass Raman amplification in multiple focal configurations with energy gain factors as high as 30x and record efficiencies as high as 11.7%. Amplification factor and efficiency scalings with plasma density, focal geometry, pump energy, and seed energy are presented. The impact of propagation of both the pump and seed lasers on the amplification process is explored.  This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number DE-NA0004144, the U.S. Department of Energy under Awards DE-SC0021057 and DE-SC0016253.

ABSTRACT. ExawaE or zeEawaE laser pulses can be groundbreaking scientfic tools for uncovering the mysteries of our universe. These high-power laser pulses enable experimental studies of phenomena such as vacuum boiling and pair-production, Hawking radiation, and quantumgravity, holding great potential for advancing our understanding of nature. However, the currently available CPA technology is stuck at petawaE level, mainly due to the material breakdown of compression gratings and alternative solutions are yet to come from conventional optics. Plasma, being in a state of matter already broken down, can endure highly intense laser fields without damage. Its resilience to strong fields, coupled with its optically dispersive properties, makes plasma an ideal medium for manipulating high-power laser pulses. In this presentation, I will present a recently devised novel concept for pulse compression using adensity gradient, high density plasma. The point of the new idea is generating reflection path difference of photons of a chirped pulse using a near-critical, gradient densit plasma. As the higher frequency photons take longer reflection path deeper into the plasma, the photons in the tail of a negatively chirped pulse can catch up those in the pulse front, resulting inconcentration of the photons into a narrow region. So far this idea is still in theoretical and modelling level, but it has been already published to Nature Photonics in 2023 [1], and experimental proof-of-principle is in progress. In theoretical point of view, combining different plasma optics ideas with the original density gradient idea is being studied. Here I present the status of the research and future vision of this innovative concept, providing comparison of characteristics of previous plasma-based schemes such as Raman, Brillouin and plasma gratings.These advancements can be crucial steps toward realizing compact, exawaE, or zeEawaE laserpulses.

[1] Hur et al., Laser pulse compression by a density gradient plasma for exawaE to zeEawaElasers, Nature Photonics 17, 1074 (2023).

ABSTRACT. A quasilinear plasma transport theory that incorporates Fokker-Planck dynamical friction (drag) and pitch angle scattering is self-consistently derived from first principles for an isolated, marginally-unstable mode resonating with an energetic minority species. It is found that drag fundamentally changes the structure of the wave-particle resonance, breaking its symmetry and leading to the shifting and splitting of resonance lines. In contrast, scattering broadens the resonance in a symmetric fashion. Comparison with fully nonlinear simulations shows that the proposed quasilinear system preserves the exact instability saturation amplitude and the corresponding particle redistribution of the fully nonlinear theory. Even in situations in which drag leads to a relatively small resonance shift, it still underpins major changes in there distribution of resonant particles. This novel influence of drag is equally important in plasmas and self-gravitating systems. In fusion plasmas, the effects are especially pronounced for fast-ion-driven instabilities in tokamaks with low aspect ratio or negative triangularity, as evidenced by past observations. The same theory directly maps to the resonant dynamics of the rotating galactic bar and massive bodies in its orbit, providing new techniques for analyzing galactic dynamics and for constraining candidates of dark matter particles.

[1] V. N. Duarte et al, Phys. Rev. Lett. 130, 105101 (2023).

[2] C. Hamilton et al, Astrophys. J. 954, 12 (2023).

ABSTRACT. Accreting neutron stars (ANS) are unique cosmic laboratories for studying the exotic plasma phenomena. ANS are characterised by strong surface gravity ~10¹⁴ cm/s² and a widerange of strong dipole magnetic fields ~10⁸-10¹⁴ Gauss and have a binary companion that feeds the ANS with matter, often creating the accretion disk (AD) [1]. We consider the simplest caseof steady-state mass accretion and find intriguing solutions by applying the well-known MHD model.

The large magnetic field causes the ions and electrons to flow along the field lines, given in this case by the dipole approximation [2]. A slowly rotating ANS is considered, withits magnetic axis aligned with the rotation axis for simplicity. We show that for a givenaccretion rate, the conservation laws define boundaries of parameter-space where meaningful solutions can be found. It is also seen that the region near the poles, where the plasma gets concentrated, has an incredibly small thickness in the θ-direction. As the highly conducting plasma, attached to the converging magnetic field lines of increasing strengths, is channelled to the polar region of the neutron star acquires remarkably high densities and, in most cases,remains sub-alfvenic [3]. As the plasma continues to move further towards the ANS poles, the gravity and the magnetic field topology causes a compression of the plasma [2]. Diamagnetic effects due to a sharp radial pressure gradient cause a toroidal sheet to form on the outer and inner sides of the envelope defined by field lines binding the accretion disk. A weak electrical resistivity is enough to drive a significant poloidal current in the ANS magnetosphere. Finally, the conditions that may mark the onset of ideal and resistive MHD instabilities are delineated.

[1] J. Frank, A. R. King, D. J. Raine, and J. Shaham, “Accretion Power in Astrophysics, ”Physics Today, vol. 39, no. 10. Cambridge University Press (CUP), pp. 124–126, 2002.doi: 10.1063/1.2815178.

[2] K. Singh and I. Chattopadhyay, “Study of magnetized accretion flow with coolingprocesses,” Journal of Astrophysics and Astronomy, vol. 39, no. 1, pp. 1–9, 2018, doi:10.1007/s12036-017-9500-7.

[3] P. Ghosh, Rotation and Accretion Powered Pulsars. WORLD SCIENTIFIC, 2007. doi:10.1142/4806.

ABSTRACT. For the benefit of accurate and precise plasma parameter inference in the upcoming DEMO demonstration fusion reactor, we aim to leverage the probabilistic framework of Bayesian inference. This framework provides a modular way of combining complementary diagnostics and delivers distributions for the plasma parameters of interest. Using prior physical knowledge of the expected plasma current density distribution, together with forward models to find the theoretical diagnostic measurements, we can infer the most probable plasma current density distribution and its covariance function derived from the diagnostic measurements and their uncertainties. From this, we calculate the plasma current, centroid position, and shape.

The inference is based on multiple diagnostics: pick-up coils, flux loops, and saddle coils. They are external diagnostics and therefore do not provide internal information of the plasma. Nonetheless, it has been shown that using a Gaussian process and a well-informed prior distribution, one can reconstruct the current density distribution and poloidal flux distribution with relatively good agreement [1]. The disagreement between the current density distribution and the ground-truth distribution increases rapidly towards the plasma centre, yet there remains aqualitative agreement. The reconstructed plasma boundary remains reliable, though the error on the poloidal flux distribution becomes quite large towards the centre [2].

In addition, we employed Bayesian experimental design (BED) to study the optimal amount and distribution of tangential and normal pick-up coils, complying with the DEMO design restrictions. BED aims to maximize a utility function, specifically the Shannon entropy, which in our case meant achieving D-optimality or maximizing the determinant of the Fisher information matrix of the plasma parameters.

Acknowledgements. J. De Rycke acknowledges the Research Foundation - Flanders (FWO) via PhD grant1SH6424N

[1] Z. Liu, et al., Plasma Phys. Control. Fusion 64, (2022).

[2] J. De Rycke, et al., EFDA_D_2R2765, idm.euro-fusion.org/?uid=2R2765, (2023).

ABSTRACT. TBA

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ABSTRACT. Collisions between charged and neutral particles in plasma can lead to energy and momentum transfer, which can affect plasma temperature and density profiles. Understanding and controlling these transport properties is necessary to achieve and maintain the conditions required for nuclear fusion reactions to occur in a tokamak.

In this study, we investigate collision frequency and energy transfer between electrons and Helium atoms. The interaction between an incoming electron and He atom was studied by the optical potential method, which consists of three interaction potentials accounting for various effects. Momentum-transfer cross section and phase shifts are found using the partial wave expansion and the variable phase approach, respectively.

The resulting effective frequency has a maximum depending on the energy. The experimental data found in the literature are consistent with the detected maximum. At energies lower than the maximum energy, our results coincide with other works. Energy transfer calculations for the energy values above the detected maximum showed that temperature equalization between helium and electron occurs more slowly than has been known.Large tokamaks, including JET and JT-60U, also produce electron-positron pairs in plasma, where collisions between several MeV runaway electrons and thermal particles can produce up to 1014 positrons. How many positrons are generated depending on the energy ofthe runaway electrons, the differential production rate can be calculated using the runaway electron distribution and the Coulomb logarithm.

Acknowledgments. This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP AP19679536)

ABSTRACT. The transition from the L-mode to H-mode confinement in stellarators is triggered by a sudden local increase of the radial electric field, E_r, which in turn reduces the fluctuation amplitudes and consequently suppresses the turbulence. The H mode is achieved only when certain thresholds in the control parameters are exceeded. In the case of biased H modes, the transition is obtained only when the bias voltage applied to the probe exceeds a critical value. In this work we study the biased H mode using a transport model that includes neoclassical and turbulent contributions [1]. The biasing electrode is assumed to produce a localized radial current which in turn affects the ambipolar radial electric field E_r. The sharp local changein Er triggers the confinement improvement around the edge region, by suppressing turbulent fluctuations due to the shear of the poloidal ion velocity. For the anomalous transport we use the balooning approximation including the stabilizing effect of the E × B shear. Starting from experimental profiles, the simulations are carried out using the ASTRA transport code [2] exploring different scenarios, in time and in space, with positive and negative bias. The results of the simulated radial electric field, electric potential and poloidal ion velocity are confronted with experimental data.

[1] B.A. Carreras, et. al., Physics of Fluids B 3, 1438 (1991)

[2] G. V. Pereverzev, et. al., ASTRA: an Automated System for TRansport Analysis, Max Plank Institut fur Plasmaphysik, Rep. IPP 5/98, Garching (2002)

ABSTRACT. The plasma turbulence dependence with the equilibrium density profile and externally imposed electric fields was investigated in Texas Helimak [1], a toroidal plasma device suitable for turbulence studies with flexible configurations regarding the equilibrium magnetic field and electrostatic biasing. In Texas Helimak stable plasma discharges are obtained using ECRH resonant heating whose maximum absorption position depends on the magnetic field intensity. The turbulence is measured simultaneously by 96 Langmuir probes selected among the more than 700 available ones. Also, it is possible to impose the electrostatic potential in some radial regions, by connecting a DC power device in one of the four bias plate sets. Initially, with all the bias plates grounded, the magnetic field intensity was changed by selecting the coils current into 36 different values (one per discharge), which makes the density peak position vary by almost half of the machine radial extension. The turbulence level profile follows the density profile changes. Moreover, by comparing the turbulence radial profiles with the density peak positions, it is possible to see that the turbulence level is enhanced in the negative density gradient side of the peak, as predicted for ideal interchange modes [2]. Furthermore, when considering discharges with just one of the bias plates polarized (the others grounded), we observed strong changes in the density radial profiles for both positive and negative bias values due to biasing, with the peak displacement in different directions depending on the bias signal: the peak is moved out of the bias plate incase of negative bias and in the opposite direction with positive biasing. The turbulence level and the density radial profiles follow similar trends in general, but the link between them is not so clear as in discharges without biasing.

Work supported by FAPESP, grant 2018/03211-6, and CNPq, grant 420175/2023-7.

[1] K.W. Gentle and H. He, Plasma Sci. Technol. 10, 284 (2008)

[2] D.L. Toufen et al., Phys. Plasmas 29, 042303 (2022)

ABSTRACT. Two dimensional (X-Y plane) Particle-In-Cell (PIC) simulation were performed using EPOCH [1] to study the evolution of plasma microdroplet irradiated by a laser pulse. The laser wavelength of 800nm, FWHM pulse duration of 25 fs and spot size of 19 micron were chosen. The target plasma droplet of diameters 15, 30, and 60 microns were chosen. The laser intensity was non-relativistic with a₀ = 0.5. The plasma density in the microdroplet hada gradient from zero to 10 n_c (nc being the critical density) over a region of two microns. In the simulation the laser propagates along the X axis and its transverse profile is centered about Y = 0 and is incident normal to the target. At Y = 0 the electric field of the laser is transverse to the surface of the target. At all other Y locations, due to the curvature of the target, an electric component normal to the surface exists. This component of the electric field extracts the electrons out of the target (Fig1a) following the well-known vacuum heating process. The electrons acquire certain amount of energy irreversibly from the laser during this phase. The gain in kinetic energy of the electrons is apparent from the initial rise seen in average particle energy (APE) in Fig.1 a. Thereafter, two additional phases of energy increment are observed. It should be noted that the two subsequent phases occur after the laser pulse has left the simulation box. The energy acquired during these phases is a result of collision between the two surface waves (excited by the laser as it grazes through the targetsurface Fig.1a) which traverse the top and bottom hemispheres to collide at the diametrically opposite point (Fig 1b). In addition, electrons from the bulk also arrive here. The collision of the two surface and the bulk disturbances lead to irreversible gain of the electron energy. Thus the second phase of growth in energy corresponds to this collision, the third happens at the time when the three colliding disturbances reverse their direction and again hit each other at the other side of the target (Fig 1c). A detail understanding of this process will be provided.

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Figure 1. Temporal evolution of electric field, average paricle energy and electrons for laser interacting with plasma microdroplets.

[1]T. D. Arber et al., Plasma Phys. Control. Fusion, vol. 57, no. 11,p. 113001, 2015.

[2]N. A. Ebrahim, et al., Phys. Rev. Lett., vol. 45, no. 14, p 1179, 1980.

[3]T. J. M. Boyd, Plasma Phys. Control. Fusion, vol. 28, p. 1887, 1987.

ABSTRACT. In fundamental particle physics experiments, energy requirements have become difficult to achieve in circular accelerators. Linear wakefield devices appear as a modern solution to produce particles of very high energies: plasma wakefield accelerators provide significantly higher E-fields to accelerate particles than conventional linear particle accelerators. However, to achieve these high electric fields, the plasma medium must have a large electron plasma density to create strong gradients. It is known that helicon plasma discharges achieve very high electron plasma densities, allowing the system to acquire the necessary density magnitudes for accelerator purposes [1].

This study aims to understand helicon wave propagation and dissipation in plasma wakefield systems, as well as the influence of different antenna geometries on the efficiency of helicon wave excitation. Furthermore, the evolution of the radial plasma density gradient on the efficiency of coupling to the helicon wave will be studied.

The research plan consists of performing a theoretical analysis with a full-wave simulation using the finite-difference time-domain (FDTD) 3D code FOCAL, which solves Maxwell’s equations coupled to the fluid equation of motion for electrons in a cold magnetized plasma [2]. In parallel, computational simulations are made using the COMSOL Multiphysics code package. The simulations will be applied to the linear plasma device VINETA.75, located at the University of Greifswald. The device’s geometry will be implemented in the numerical modelsas a first step. It is then planned to compare the results with measurements of the wavefield sin VINETA.75. Also, external cooperation is made with the teams in the MAP device at the University of Wisconsin-Madison, and the PROMETHEUS-A and AWAKE experiments at CERN[3].

Acknowledgements. This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - project number 517709182.

[1] O. Schmitz, et al., Plasma Sources Science and Technology 29, 045008 (2020)

[2] A. Köhn-Seemann, et al., Plasma Physics and Controlled Fusion 60, 075006 (2018)

[3] B. Buttenschön, et al., Plasma Physics and Controlled Fusion 60, 075005 (2018)

ABSTRACT. The experiment was conducted using the PLASGAS plasma reactor, which has an internal volume of 200 liters and utilizes the Hybrid Water Stabilized Plasma torch. The characteristics of the Hybrid Water/Gas DC Arc Plasma Torch and the PLASGAS reactor are detailed by Hrabovský et al. [1] and Fathi et al. [2], respectively. Previously, this system has been employed for the pyrolysis of methane [3] and natural gas [4]. In this study, however, we investigate methane pyrolysis by adding Nickel Oxide powder as a catalyst. This experiment introduced a 100 SLM methane feed into the reactor, with plasma power set at110 kW. The resulting gas composition was 86.5 vol% hydrogen and 12.1 vol% carbonmonoxide, with only 1.2 vol% methane remaining unconverted and 0.1 vol% acetylene produced. In addition to hydrogen production, a solid carbon-nickel (core-shell) structure nanocomposite material was synthesized. XRD and EDX analysis confirmed that the nickeloxide was reduced to zero-valent nickel nanoparticles with particle sizes less than 50 nm. TheTEM images of the produced composite material are shown below.

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[1] M. Hrabovsky et al., “Properties of hybrid water/gas dc arc plasma torch,” IEEE Trans. Plasma Sci., vol. 34, no. 4 III, pp. 1566–1575, 2006.

[2] J. Fathi et al., “Multiple benefits of polypropylene plasma gasification to consolidate plastic treatment, CO2 utilization, and renewable electricity storage,” Fuel, vol. 368, no.April, 2024.

[3] A. Mašláni et al., “Pyrolysis of methane via thermal steam plasma for the production ofhydrogen and carbon black,” Int. J. Hydrogen Energy, no. xxxx, 2020.

[4] A. Mašláni et al., “Impact of natural gas composition on steam thermal plasma assisted pyrolysis for hydrogen and solid carbon production,” Energy Convers. Manag., vol. 297,no. October, 2023.

ABSTRACT. %SVL correct title

The Earth’s magnetic field has variations both in the time and spatial domains, which are due to the internal dynamics of the Earth’s core, the forcing by external sources like the solar wind, or fluctuations induced by coupling between neighbouring regions. This leads to various levels of correlations between magnetic field readings on the Earth’s surface, which map the interplay of these factors across multiple time and space scales. In this work, we propose to describe and study this complex dynamics of spatiotemporal correlations by means of tools derived from graph theory and complex networks, which have shown to be useful to describe the behavior of various systems of geophysical interest [1, 2, 3]. In particular, we study the evolution of magnetic field measurements on the Earth’s surface along the 23rd solar cycle.

Based on records by 59 magnetometers during the 23rd solar cycle [4], we define a complex network where nodes are points on the Earth’s surface (magnetometers), and their connections represent the degree of similarity between the time series observed at those points. Our results show that there is a correlation between the evolution of network community structure and geomagnetic activity. In addition, we study the dependence of the results of the methods used to define the similarity between time series (and, therefore, to define the connection between nodes), in order to establish the best possible sensitivity for the community structure with respect to the geomagnetic activity, as measured by the Dst index and the sunspots number. We show that the choice of similarity method is not as relevant as the choice of the correlation threshold which determines whether two nodes are actually connected or not. Our work suggests that analysis of the Earth’s magnetic field variations using complex network and community structure analyses, can be useful to understand the geomagnetic activity along the solar cycle.

Acknowledgements. This project has been financially funded by FONDECyT, grant number 1242013 (VM).

[1] L. Orr, S. C. Chapman, J. W. Gjerloev, and W. Guo, Network community structure of substorms using SuperMAG magnetometers, Nuovo Cim. 12, 1842, 2021.

[2] S. Lu, H. Zhang, X. Li, Y. Li, C. Niu, X. Yang, and D. Liu, Complex network descriptionof the ionosphere, Nonlinear Proc. Geophys. 25, 233–240, 2018.

[3] A. Najafi, A. H. Darooneh, A. Gheibi, and N. Farhang, Solar flare modified complex network, Astrophys. J. 894, 66, 2020.

[4] World Data Center for Geomagnetism, Kyoto,http://wdc.kugi.kyoto-u.ac.jp/dstdir/dst2/onDstindex.html.

ABSTRACT. The Sun and its behavior are studied by means of complex networks. The complex network was built using the Horizontal Visibility Graph (HVG) algorithm. This method maps time series into graphs in which every element of the time series is considered as a node and a visibility criterion is defined in order to connect them [1]. The HVG method has been widely used to analyze various systems such as pulsating variable stars [2], solar activity [3, 4] and blazars [5]. Using this method, we construct complex networks for magnetic field and sunspots time series encompassing four solar cycles, and various measures such as degree, clustering co-efficient, betweenness centrality and eigenvector centrality were calculated. In order to study the system in several time scales, we perform both a global, where the network contains information on the four solar cycles, and a local analysis, involving moving windows. Our results suggest that complex networks can provide a useful way to follow solar activity, and reveal new features on solar cycles.

[1] Lucas Lacasa, et al., Proc. Natl. Acad. Sci. 105, 4972-4975 (2008)

[2] Víctor Muñoz and N. Elizabeth Garcés, PLoS ONE 16, e0259735 (2021)

[3] Víctor Muñoz and Eduardo Flández, Entropy 24, 753 (2022)

[4] Tomás Zurita-Valencia and Víctor Muñoz, Entropy 25, 342 (2023)

[5] Belén Acosta-Tripailao, et al., Entropy 24, 1063 (2022)

ABSTRACT. The radiation pressure and strong magnetic fields are prominent in the structures of Rayleigh-Taylor (R-T) instability in the interior of white dwarfs. We have investigated the radiation pressure-driven R-T instability in a compressible and magnetized ultra-relativistic degenerate strongly coupled plasma. The equation of state has been derived for such systems incorporating ultra-relativistic degenerate electrons with their radiation pressure and ion gas compressibility. The dispersion relation of the density gradients driven R-T instability is analyzed using the generalized hydrodynamic (GH) fluid model in the strongly  coupled and weakly coupled limits [1]. We assumed the electron fluid is inertialess, ultra-relativistic degenerate and weakly coupled while the ion fluid is non-degenerate and strongly coupled [2].

It is observed that the R-T instability criterion has been modified significantly due to radiation pressure, ion gas compressibility and degeneracy parameter. In the kinetic limit, the instability region is shorter than the hydrodynamic limit due to the dominance of plasma frequency over the viscoelastic relaxation frequency. The outcomes are explored in analyzing the development of R-T instability in the strongly magnetized carbon-oxygen white dwarfs. The radiation pressure, electron temperature and ion density strongly suppress the growth rate of the R-T instability in the interior of white dwarfs. The strong magnetic fields introduce asymmetry to the system by destabilizing the R-T unstable modes. The present results are also useful for understanding the R-T instability in the star formation and dense plasmas in inertial confinement fusion in some limiting cases.

[1] P. K. Kaw and A. Sen, Phys. Plasmas 5,3552(1998).

[2] Ravinder Bhambhu and R. P. Prajapati, Phys. Plasmas 30, 042114 (2023)

ABSTRACT. There has been significant interest lately in the study of Electromagnetic (EM) wavesinteracting with magnetized plasmas. The variety of resonances and the existence of several pass and stop bands in the dispersion curve for different orientations of the magnetic field offer new mechanisms of EM wave energy absorption [1,2,3]. However, earlier studies have beeninvestigated only special cases of magnetized plasma geometry (e.g. RL mode (k ∥ B_ext  ($theta$ =0 ) or X-mode k ⊥ B_ext ($theta$ = $pi$/2) configuration). In these cases, EM wave get absorbedat their respective resonances (e.g. for $theta$ = 0 electron cyclotron resonance (_$omega$EM = _$omega$erc),and for $theta$ = $pi$/2, upper hybrid resonance ( _$o,mega$EM = _$omega$uh)). We consider here the case of EM wave propagation at an oblique angle with respect to B_ext. We tailor the magnetic field inhomogeneity such that the EM wave pulse encounters resonance layer (n² → ∞) within the plasma. A 2-D Particle - In - Cell (PIC) simulation using the OSIRIS 4.0 platform has been carried out for this particular case. A significant enhancement in absorption leading to almost complete absorption of laser energy by the plasma have been observed (Fig.1). A detailed study characterizing the role of external magnetic field profile, EM wave intensity, etc., has also been carried out.

%SVL insert figure and fix equations

[1] S. Maity, et al, Phys. Rev. E 105, 055209 (2022)

[2] R. Juneja, et al, Plasma Physics and Controlled Fusion 65, 095005 (2023)

[3] A. Vashistha, et al, New Journal of Physics 22, 063023 (2020).

ABSTRACT. The Gardner equation is a combination of the KdV equation (with quadratic non-linearity having constant coefficient B) and the modified KdV equation (with cubic non-linearity and constant coefficient C). For consistency, whereas C is of order one B should be very small, given the expansions used in the derivation of all KdV-like evolution equations. If B were of order one, the quadratic term would prevail over the cubic term, which could then be neglected. The sign of B is irrelevant because if B<0 the Gardner equation can be rescaled to the case B>0. The sign of C, however, is quite important. Even though the Gardner equation is fully integrable for both positive and negative C, the usual soliton solutions can only be generated for C>0, which is of crucial importance should one want to study the collisions of solitons. A multispecies plasma model should therefore be detailed enough that the compositional parameters allow for a tiny B and a positive C. This aspect has been over-looked or neglected by several authors using the Gardner equation in their analysis, mostly due to the complexity of the plasma compositional parameters. In essence, a simple ion-electron plasma does not have enough compositional flexibility to go beyond the KdV equation.

It will be shown on a relevant dusty plasma model [1], comprising cold negative dust grains, Maxwellian electrons and nonthermal protons, that it is indeed possible to have B close to zero, while C>0. When B gets larger, C can become negative, but in that case the absolute value of B is larger than that of C, leading to a regime where the relevant equation is the KdV, not the Gardner equation. In between, there is a region where the compositional parameter scan be adjusted such that, e.g., B=0.01 and C=0.35. In the theoretical studies of nonlinear electrostatic plasma waves there is another method, namely Sagdeev’s pseudopotential analysis, where the Poisson equation is integrated leading to an “energy integral,” with full nonlinearities but requiring a numerical integration of the Poisson equation to produce the profiles. The case of B=0.01 and C=0.35 will be discussed via the two approaches (Gardner and Sagdeev), and the results compared. Discrepancies might indicate the limits of the Gardner approach at higher amplitudes, given that in reductive perturbation theory the expansions limit the nonlinearities to the quadratic or cubic terms.

[1] F. Verheest and S. R. Pillay, Phys. Plasmas 15, 013703 (2008)

ABSTRACT. Landau damping is a captivating phenomenon, manifested as wave dissipation (damping) occurring – despite the absence of inter-particle collisions – due to resonant interactions between waves and particles [1]. Focusing on the ubiquitous presence of charged dust in space and in laboratory plasma environments [2], one may wonder how Landau damping may affect the propagation of electrostatic solitary waves (ESWs) and associated instabilities in space and astrophysical environments [3]. This investigation explores the effect of Landau damping on nonlinear dust-ion-acoustic waves (DIAWs) in a dusty plasma composed of inertial ions, energetic (suprathermal) electrons, and immobile dust. A cold-ion fluid model, coupled to a Vlasov-type kinetic equation for the electron dynamics, has been adopted. A kappa-distribution [4, 5] is assumed as equilibrium state for the electrons, in account of the non-Maxwellian particle behavior observed in Space [5].

A multiscale perturbation technique has been adopted and shown to lead to an evolution equation in the form of a modified Korteweg–de Vries (KdV) equation that incorporates adissipative term, representing kinetic (Landau) damping [6]. Exact analytical solutions have been obtained, representing solitary waves undergoing amplitude decay over time. The combined parametric effect of Landau damping, non-Maxwellian electron statistics (via the kappa parameter) and dust density on the characteristics of DIAWs has been examined. The results of this investigation aim at generalizing earlier work [6, 7] by shedding some light on the dynamics of nonlinear waves in various space and astrophysical dusty environments [2,3].

Acknowledgments. Authors KS and IK also acknowledge financial support from Khalifa University’s Space and Planetary Science Center under grant No. KU-SPSC-8474000336. All authors gratefully acknowledge financial support from Khalifa University of Science and Technology, Abu Dhabi UAE via the (internally funded) project FSU-2021-012/8474000352and from a CIRA (Competitive Internal Research) award (CIRA-2021-064/8474000412).

[1] D. D. Ryutov, Plasma Phys. Contro. Fusion 41, A1–A12 (1999).

[2] P. K. Shukla & A. A. Mamum, Introduction to Dusty Plasma Physics (IoP, Bristol, 2002).

[3] C. K. Goertz, Rev. Geophys. 27, 271 (1989).

[4] G. Livadiotis, Kappa distributions: Theory & Applications in Plasmas (Elsevier, Amsterdam, 2017).

[5] V. Pierrard & M. Lazar, Solar Phys., 267, 153 (2010).

[6] E. Ott, & R. N. Sudan, Phys. Fluids, 12, 2388 (1969).

[7] H. Mushtaq, K. Singh and I. Kourakis, Nonlinear Ion-Acoustic Waves with Landau Damping in Non-Maxwellian Space Plasmas: on the Role of Suprathermal Electrons, submitted to Scientific Reports (Springer); under review (2024).

ABSTRACT. Electrostatic solitary waves (ESWs) are an ubiquitous occurrence in plasmas in the laboratory [1] and in Space [2], where they are observed widely in relation with bipolar electric field structures recorded by missions in planetary magnetospheres [3]. Their theoretical modeling represents a long standing challenge for theoreticians and experimental researchers alike. Even though an analytical framework has been established for the modeling of ESWs since the pioneering work of Sagdeev and coworkers [4] since decades ago, that framework provides “static” predictions of the solitary wave profile and provides no information on their propagation characteristics under realistic conditions. In particular, although the Sagdeev (pseudopotential) method -- and its small-amplitude Korteweg – de Vries (KdV) counterpart [5]-- successfully reproduce(s) the expected waveforms (i.e. a pulse for the ES potential and a bipolar form, in general, for the E-field), the (expected, but still not verified) soliton properties of the resulting -numerical- solutions from the Sagdeev formalism have not been analyzed.

We have undertaken a study of the dynamics of electrostatic pulses, from first principles. Based on a basic fluid model as a starting point, we have performed a series of numerical (fluid) simulations, in order to investigate the stability of electrostatic pulses and their interaction properties. Various propagation scenaria have been considered, and the pulses’ stability and (anticipated) soliton characteristics have been benchmarked. Solutions near the acoustic speed appear to be “KdV-like” (as expected), while strongly superacoustic (supersonic) pulses are characterized by a different amplitude-velocity relation but still possess the expected stability properties, throughout propagation and mutual interaction.

Acknowledgements. A.B. acknowledges support from the Ministerio de Economía y Competitividad of Spain (Grant No. PID2021-125550OBI00). Author IK acknowledges financial support from Khalifa University’s Space and Planetary Science Center under grantNo. KU-SPSC-8474000336 and also via grant CIRA-2021-064/8474000412.

[1] L. Romagnani et al, Phys. Rev. Lett. 101, 025004 (2008).

[2] S.S. Varghese et al, Sci Rep. 12 (1), 18204 (2022).

[3] D. B. Graham et al, J. Geophys. Res. (Space Phys.) 121 (4), 3069 (2016); B. Kakad et al,Astrophysical Journal 934 (2), 126 (2022).

[4] R. Z. Sagdeev, Rev. Plasma Phys., Vol. 4 (M. A. Leontovich, Ed..; New York: ConsultantsBureau) (1966), p. 52; F. Verheest & M.A. Hellberg, Electrostatic solitons and Sagdeev pseudopotentials in space plasmas: Review of recent advances, in: Handbook of Solitons: Research, Technology and Applications, NOVA Publ. (2008).

[5] Thierry Dauxois and Michel Peyrard, Physics of Solitons (Cambridge Univ. Press, 2006).

ABSTRACT. Electrostatic wavepacket modulation in plasmas is a widely studied nonlinear phenomenon: it is manifested as the variation (“modulation”) of a wavepacket’s harmonic amplitude in space and time, and may be attributed to various processes, such as self-modulation (self-interaction), cross-modulation, wave-wave interaction or due top ponderomotive processes [1, 2]. Modulated envelope (amplitude) dynamics is known to be described efficiently by a nonlinear Schrodinger (NLS) type equation [3], a nonlinear PDE that models the envelope’s evolution in space and time, in a slowly-varying amplitude approximation. In a fluid-plasma theoretical context, the NLS equation can be derived from a fluid model by means of a multiple scales technique [1,2,4]. Stability analysis may be performed, leading to predictions for modulational instability occurrence, a mechanism often postulated as a precursor state to freak wave (rogue wave) formation [2,4].

We have earlier undertaken a study of the modulational dynamics of an electrostatic wavepacket, from first principles [5]. Based on a cold-ion fluid model as a starting point, incorporating a phenomenological damping term in account of collisions, we have derived an NLS equation characterized by a complex-valued nonlinearity coefficient Q and a real dispersion coefficient P. The imaginary part of Q is thus associated with nonlinear dissipation of the envelope, as it results in a “damping” force that breaks the integrability of the NLS eq. and results in amplitude decay. Based on (and inspired by) [6], where numerical simulations revealed extreme wave events for the damped and forced NLS equation, we have performed a series of computer simulations in order to investigate the (in)stability and the evolution of an initial condition in the form of an envelope soliton (i.e. an exact solution of the unperturbed NLS eq.). Different possibilities have been explored, namely including the option of stabilizing the envelope pulse by imposing an ad hoc external forcing term to counteract dissipation.

Acknowledgements: One of us (NL), currently with IAT/ADPoly, was with Khalifa University during the early stages of this work. IK acknowledges financial support from Khalifa University via grants CIRA-2021-064/8474000412 and No. KU-SPSC-8474000336(Space and Planetary Science Group)

[1] I. Kourakis and P. K. Shukla, Nonlinear Processes in Geophysics 12, 407 (2005).

[2] N. Lazarides et al, Scientific Reports (Springer Nature) 14, 2150 (2024).

[3] Thierry Dauxois and Michel Peyrard, Physics of Solitons (Cambridge Univ. Press, 2006).

[4] M. McKerr, I. Kourakis & F. Haas, Plasma Phys. Cont. Fusion 56, 035007 (2014).

[5] I. Kourakis et al, work in progress (unpublished work).

[6] G. Fotopoulos et al, Comm. Nonlinear Science & Numerical Simulation 82, 105058 (2020).

ABSTRACT. Pedestal turbulence manifests as electron temperature fluctuations while the electron transport barrier remains intact until an edge-localized mode (ELM) crash occurs. Considering the crucial role of pedestal turbulence in the evolution and collapse of the pedestal, this study investigates the microscopic spatial structure and dynamics of these temperature fluctuations to elucidate the role of pedestal turbulence in the electron transport barrier [1,2]. We comprehensively compared electron temperature fluctuations observed during pedestal evolution under various instability conditions, explaining the role of pedestal turbulence in both the evolution and collapse phases. A novel diagnostic method was employed to enhance the turbulence characteristics in the KSTAR pedestal [3]. Utilizing a newly developed high-speed digitizer, we measured broadband electron cyclotron emission (ECE) to precisely observe high-frequency pedestal turbulence during both inter-ELM crash and resonant magnetic perturbation (RMP)-driven ELM suppression. Detailed comparisons with the characteristics of various instabilities revealed that the micro-tearing mode is associated with pedestal evolution and collapse. Conversely, the turbulence characteristics during ELM suppression align moreclosely with interchange modes, suggesting that turbulence-driven transport can induce distinct pedestal structures and ELM dynamics. To evaluate the impact of these turbulent fluctuations on pedestal evolution and collapse, we calculated the quadratic transfer function (QTF) [4]. The QTF results indicate that during the inter-ELM crash period, pedestal energy in nonlinearly transferred from turbulent eddies to magnetohydrodynamic (MHD) modes, causing the modestructure to expand radially. However, during RMP-driven ELM suppression, dominant modes do not grow due to energy exchange among turbulent eddies within the pedestal.

[1] J. Lee, et. al., Phys. Rev. Lett. 117, 075001 (2016)

[2] J. Lee, et. al., Nucl. Fusion 59, 066033 (2019)

[3] M.H. Kim, et. al., Nucl. Fusion 60, 126021 (2020)

[4] P. Manz, et. al., Phys. Rev. Lett. 103, 165004 (2009)

ABSTRACT. A Pulsed Plasma Accelerator (PPA) with coaxial electrodes system, is being used to produce ahigh speed (several km/s), high density (~ 10²⁰/m³) Hydrogen plasma stream by applying powerfrom a 200 kJ Pulsed Power System (PPS). The PPS, which consists of two modules capacitor banks, can be charged up to 15 kV to achieve 200 kJ of energy. This PPS generates a peak discharge current of 100 kA for a half time period of 500 μs. A gas injection valve is used to supply the requisite gas during the application of high voltage discharge pulse in between the two electrodes. The high voltage thus applied breaks down the gaseous medium in between the electrodes to form plasma sheet which is driven by the JxB force towards the open end of the electrodes to form a high-density plasma stream. In this work, the high speed Hydrogen plasmastream is allowed to fall on Tungsten substrates placed at a distance of 10 cm from the end of the electrodes. The measured heat energy density of the Hydrogen stream at this position is 0.205 MJ/m² while it increases up to 0.224 MJ/m² under an influence of 0.1 Tesla external magnetic field. The plasma matter interaction at this condition creates blister formation to the surface of Tungsten material for single exposure. However minor and major cracks, displacement of cracked surface, dust formation, re-deposition are observed in scanning electron micrograph for surface exposed for 15 times to the same plasma stream. The interaction due to the heat energy density of plasma stream on Tungsten material in this work resembles either a mitigated or lower energy type-I Edge Localized Mode (ELM) [1] and the reported results are highly relevant for fusionreactor.

[1] G. Sinclair, et. al., Scientific Reports 7, 1, (2017)

ABSTRACT. Taking the lead in developing, collecting, curating, modeling, and making accessible online a repository for fundamental data characterizing novel materials that can with standenormous heat and neutron exposure is important for controlled fusion energy and the design basis for a fusion pilot plant (FPP). The RM3FD is envisioned as a partnership for open accessof high-value, high-effort, fully referenced, intellectual property for mutually shared,straightforward to implement, and as a benefit toward commercial fusion energy development.

We are motivated to form an association for the repository, management, and modeling of materials fundamental data to address the recognized need for such a community data archive both for modeling consistency and for improved transparency in interpreting experiments. Resources of the envisiged RM3FD association could include annual membership dues, public or private donations and grants, and income from services rendered by the association. One model for this endeavor is the LXCat endeavor [1] (www.lxcat.net) for the low-temperature plasma science community. The objective of this presentation is to recruit interest in facilitating the exchange of data and numerical tools for modeling Plasma-Materials Interfaces in Advanced Materials and Fusion Nuclear Science, Engineering, & Technology. Interested partners are welcome to join the effort as stakeholders (users, contributors, advisors, and leaders within the association.in advancing a proposal to government agencies.

Notional objectives:

-- Encourage the exchange and the open access of fundamental data via the internet.

-- Develop tools to facilitate the exchange of on-line data.

-- Contribute to the collection and evaluation of data.

-- Communicate with international fusion-materials community.

-- Appeal to the Modeling for Fusion Materials Fundamental Data Network/Forum.

-- Encourage open access of numerical tools for predictive modeling & analysis.

-- Contribute to the standardization of formats for storing of and exchanging of data

[1] Pitchford, L., et al., LXCat: Web-Based Platform for Data Needed for Modeling Low Temperature Plasmas, Plasma Process., in Special Issue on Numerical Modeling of Low‐Temperature Plasmas for Various Applications, Polym. 2017, 14, 1600098.

ABSTRACT. Reducing the heat load on divertor plates is crucial for the development of a magnetic confinement plasma fusion power reactor. To achieve this goal, the formation of detached plasma through plasma-gas interaction is a promising method, and accurate modeling of detached plasmas is essential for designing DEMO reactors. In this study, we constructed a digital twin by comparing detached plasma experiments conducted using a linear plasmamachine with simulations integrating calculation codes for plasma transport, neutral transport, and collisional radiative processes. This presentation describes the results of both the experiments and simulations on linear detached plasma.

The linear plasma machine NAGDIS-II is used for the experiments [1]. This device can produce steady and high-density plasmas exceeding 10¹⁹ m^-3 using DC discharges. LaserThomson scattering measurements are installed in the upstream and downstream regions [2], and a 2D-driven spectroscopic and electrostatic measurement system is located downstream. The importance of the role of volume recombination as a particle loss process in detached recombining plasmas has been experimentally demonstrated, mainly using helium plasmas.The two-dimensional (2D) spatial structure of detached recombining plasmas, where the electron-ion recombination (EIR) is dominant, has also been clarified [3]. Furthermore, in the recombining region, the increase in plasma fluctuation and the associated increase in radial transport and structural changes have been revealed by time-space resolved 4D tomographyusing an electrostatic probe and a high-speed camera [4].

For hydrogen isotope plasmas, the competing processes of molecular assisted recombination (MAR) associated with excited hydrogen molecules and EIR have been investigated in detail. In deuterium plasmas, a transition from MAR to EIR is observed with increasing gas pressure [5]. Furthermore, comparative experiments between hydrogen and deuterium plasmas have been carried out, and isotope effects have been observed in which MAR is dominant in hydrogen plasmas compared to deuterium plasmas.To reproduce the above experimental results, a simulation code (DISCOVER: Detached plasma Integrated Simulation COde with Various Elastic/ inelastic Reactions), which integrates fluid, neutral and collisional radiative codes (including atomic and molecular species), has been developed by considering the transport of excited atoms and molecules generated by volume recombination and wall recycling.

Acknowledgement. This work was supported by JSPS KAKENHI Grant Numbers (20H00138, 22H01203, 24H00201).

[1] N. Ohno et al., Nucl. Fusion 41 (2001) 1055.

[2] S. Kajita et al., Plasma Sources Sci. Technol. 28 (2019) 105015

.[3] N. Ohno et al., Nuclear Materials and Energy 19 (2019) 458-462.

[4] H. Tanaka et al., Scientific Reports 14 (2024) 9329.

[5] J. Shi et al., Physica Scripta 98 (2023) 115605.

ABSTRACT. First-principles kinetic simulations have long been indispensable tools for advancing our understanding of plasma physics. With the advent of increasing computational power, these simulations can now tackle larger and more complex problems than ever before. However, as the size of these simulations grows, so too does the volume of data they generate, presenting new challenges in data analysis and interpretation. Scientific Machine learning (SciML) is emerging as a powerful solution to these challenges, offering new ways to harness and analyze the vast datasets produced by fully kinetic simulations. Beyond data analysis, the computational underpinnings of SciML also present new opportunities to innovate in the way we tackle computational problems in plasma physics.

In this talk, I will explore some of the avenues my group is pursuing at the intersection of kinetic simulations and SciML. First, I will discuss how SciML can be employed to derive accurate yet simplified dynamical models of plasmas directly from the data of first-principles particle-in-cell simulations. These approaches hold the potential to create new theoretical frameworks and computationally efficient simulation models of plasmas. Additionally, I will discuss how computational methods from SciML, such as physics-informed neural networks, can be applied to solve complex inverse problems in plasma physics, including the full state reconstruction of plasmas from partial measurements/observations. Here, first-principles kinetic simulations serve as numerical experiments, providing the data necessary to understand both the potential and limitations of these innovative computational techniques, and to guide their development for plasma physics.

ABSTRACT. The Earth's magnetic field undergoes constant perturbations caused by the solar wind, a stream of ions and electrons originating from the Sun. Understanding the dynamics of the solar wind driven magnetosphere is crucial, particularly as our modern society becomes increasingly dependent on technology that is susceptible to these phenomena. With the approach of the peak of the current solar cycle, it becomes imperative to anticipate potential disruptions to our magnetosphere and take precautionary measures to mitigate potential damage to our technologies. 

In an effort to characterize the dynamics of the solar wind-magnetosphere-ionosphere system (SWMI), numerous geomagnetic indices (GI) have been introduced. One noteworthy index, DST, has been constructed to characterize the magnetic field fluctuations in the equatorial regions at the Earth's surface, aiming to capture the effects of the ring current at ground level with an hourly temporal resolution. 

In this context, we adapt a machine learning approach [1] designed specifically as a system science discovery technique to study this system. First, given that the magnetosphere is a high dimensional system driven by a turbulent solar wind, we take advance of the complexity of the SWMI interaction to construct an ensemble of neural net models, starting from a diverse set of seeds. Second, we optimize the models in terms of the iterated error, instead of the standard one step error. In addition, we try to identify what are the Robust Solar Wind Drivers that affect the system. By combining these strategies, we are able to construct diverse system science models that intend to concentrate on the relevant dynamics and drivers of the system. It unveils interesting insights into how to achieve an enhanced adaptability across distinct stages of a storm. For example, our results indicate that iterated models show improvements when employing iterative optimization compared to the one-step approach. 

Additionally, the construction of a diverse set of models that consider robust solar wind drivers suggest that this approach could be use to study the magnetosphere as a dynamically driven multi scale system with interconnected subsystems, and how to forecast their behavior. Additionally, it introduces an innovative interdisciplinary approach that provides valuable clues about the inner workings of neural networks.

[1] S. Blunier, B. Toledo, J. Rogan, J. A. Valdivia, A Nonlinear System Science Approachto Find the Robust Solar Wind Drivers of the Multivariate Magnetosphere, Published inSpace Weather, 19, e2020SW002634, 2021, https://doi.org/10.1029/2020SW002634

ABSTRACT. F. P. Orsitto2, G. Pucella2, S. Gabriellini3, F. Auriemma4, M. Baruzzo2, J.Bernardo5, A. Burckhart6, C. Challis1, R. Dumont7, N. Hawkes1, D. Keeling1, D. King1, J.Mailloux1, A. Patel1, C. Piron2, C. Sozzi4, V. K. Zotta3, JET Contributors* and theEUROfusion Tokamak Exploitation Team**1UKAEA Culham Campus, Abingdon, UK - 2ENEA C. R. Frascati, Frascati, Italy -3Università di Roma ‘La Sapienza’, Roma, Italy – 4CNR ISTP, Milano, Italy - 5IST, Lisboa,Portugal - 6IPP, Garching, Germany - 7CEA Cadarache, France* See the author list of C.F. Maggi et al. 2024 Nucl. Fusion(https://doi.org/10.1088/1741-4326/ad3e16)** See the author list of E.H. Joffrin et al 2024 Nucl. Fusion (https://doi.org/10.1088/1741-4326/ad2be4)

%SVL update authorlist

The integrated commissioning of JT-60SA tokamak was successfully completed in 2023 and the initial research phase of the machine is foreseen to start in 2026. The different operational scenarios envisaged for the extended research phase include a high current (5.5 MA / 2.25 T) inductive scenario, an advanced inductive scenario (3.5 MA / 2.28 T) and a fully non-inductive,high βN scenario for advanced tokamak operation (2.3 MA / 1.72 T) and they will be developed progressively starting from lower plasma currents.

In support of the scenario development activity to be carried out on JT-60SA, and based on previous exploration of the hybrid and advanced tokamak scenarios, JET has performed experiments aiming at establishing a scenario with dimensionless parameters between the JT-60SA advanced inductive and fully non-inductive scenarios.

In particular, deuterium plasmas were realized at toroidal magnetic field B_T = 1.7, 2.0 and 2.4T, plasma current I_p = 1.4 MA, elongation k = 1.6, triangularity δ ≈ 0.4, q₉₅=3.5-4.5, and q₀ at the start of the main heating phase >1.2, with NBI power P_NBI = 16-25 MW. A small subset of the deuterium plasmas obtained was replicated also in deuterium and tritium during the DTE3 experimental campaign to explore possible isotope effects.

Emphasis was placed to obtain plasmas with the highest possible β_N, while maintaining a mild MHD activity not to dramatically affect the confinement and guarantee the possibility of studying these plasmas from the transport point of view.

Main characteristics of the scenario developed on JET were: good confinement properties and relatively high β_N values for input NBI power of 20 MW (β_N>3.5 for1.7 T / 1.4 MA); good control of q₀ at the beginning of the main heating phase by tuning the NBI starting time t_0,NBI depending on the toroidal magnetic field value, as investigated in JET hybrid and advancedscenarios; maximum β_N ≈ 2.5-2.7 with relatively mild/stable MHD in the hybrid-advanced scenario at B_T = 2.4 T and q₀>1.

In this talk we review some aspects of the JT-60SA research plan, especially from the scenario development point of view, and present the main experimental results in support of the JT-60SA experimental exploitation showing that the scenarios developed on JET can approach theJT-60SA parameter space (especially in the initial operation phase) and some initial transport analysis showing that existing transport models such as Bohm/gyro-Bohm, QuaLiKiZ and CDBM can reproduce reasonably well the JET experiments.

ABSTRACT. A key challenge in magnetically confined fusion of high-temperature plasmas is that plasmas tend to be unstable and become turbulent, causing anomalous transport and confinement degradation. However, novel plasma self-organization can emerge spontaneously, playing a vital role in plasma confinement and advanced scenarios. For instance, when a heating input power exceeds a critical power threshold, the transition from a low-confinement mode (L-mode) to a high-confinement mode (H-mode) occurs spontaneously, where plasmas organize themselves into an ‘ordered’, high-confinement state. While reproduced in different fusion devices, its triggering mechanisms and causality relations are not fully understood. Furthermore, turbulence characteristics in the L and H modes are very variable, often with highly time-varying RMS values of fluctuating density and turbulence velocity. On the otherhand, the H-mode is subject to quasi-periodic edge-localized modes (ELMs), which can potentially cause significant damage to wall-facing materials. Despite successful experimentsof ELM suppression and mitigation, e.g., by using resonant magnetic perturbations (RMPs), what is necessary for successful control is not fully understood.

To address this, I discuss a statistical analysis method [1-4] to shed light on fundamental mechanisms involved in accessing high-confinement or other advanced improved confinement states. I show the limitations of a naïve picture of bifurcation in a deterministic system based on a mean-field type theory and elucidate how plasma statistical properties change over the L-H transition. In particular, stochastic noises produce random trajectories and phase mixing, leading to uncertainty in power threshold [1] and ELM suppression [2]. Ielucidate self-regulation and causal relations by information geometry [3,4] that works better than other popular entropy-based methods (e.g., transfer entropy). Some of the theoretical findings are supported from the L-H transition experimental data analysis [5]. We discuss implications for understanding other advanced operation scenarios.

Acknowledgements. This research is supported by Brain Pool Program funded by the Ministry of Science and ICT through the National Research Foundation of Korea (RS-2023-00284119) and EPSRC grants (EP/W036770/1, EP/R014604/1).

[1] E Kim & AA Thiruthummal, Entropy 26, 1 (2023)

[2] E Kim & R Hollerbach, Royal Soceity Philosophical transactions A, 381, 20210226(2023)

[3] E Kim, Entropy 23, 1393 (2021)

[4] E Kim, A-J Guel-Cortez, Entropy 23, 1087 (2021)

[5] H Farre-Kaga, Y Andrew, J Dunsmore, E Kim, et al, Euro Phys Lett. 142, 64001 (2023)

ABSTRACT. New aspects of fusion plasma physics such as role of magnetic configuration for edge confinement and heating effects in core confinement will be a basis for the testof ignition in magnetic fusion. Performance data (n $tau$_E T_i) and confinement scaling ($tau$_E) in the past half a century is discussed through critical analysis. These new findings are used to project the most probable ignition test device (tokamak device with V_p ~200m³) with the presently available engineering to demonstrate sustainment of T_i≫10keV fusion plasma through sufficient $alpha$-particle heating.

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ABSTRACT. The study of plasma instabilities is essential for understanding various astrophysical phenomena and advancing laboratory astrophysics. This presentation focuses on recent advancements in using lasers to generate unstable plasma conditions, both in non-magnetized and magnetized scenarios, leveraging anisotropic heating in laser-plasma interactions and the generation of ring-shaped momentum distribution functions during laser-ionization of a neutral gas.

We first delve into the generation of anisotropic momentum distributions due to stimulated Raman scattering (SRS) in laser-plasma interactions [1]. We use a combination of theoretical predictions and particle-in-cell (PIC) simulations to explore regimes in which SRS will cause strong anisotropies due to trapping and wave breaking of the small wavelength plasma waves resulting from the SRS near back-scattered modes. This anisotropy is a source for the Weibel instability [2]. We show how this configuration may help to better understand the long-time evolution of the generated magnetic field filaments.

The second part is dedicated to the electron cyclotron maser (ECM) instability in laser-ionized magnetized plasmas [3]. Recent results have shown that laser ionization can also generate plasmas unstable to the Weibel instability [4]. Here, we extend this approach by using circularly polarized lasers to ionize plasmas in the presence of a guiding field, creating long-lived ring-shaped momentum distributions. This configuration allows the growth of the ECM in a controlled laboratory environment, simulating conditions found in space and astrophysical plasmas. This is a very timely topic, as ring-shaped momentum distributions have been recently discovered to be a general feature of the Vlasov dynamics in regimes where radiation cooling is relevant [5-6].

By bridging these two studies, we aim to provide a comprehensive overview of our recent work in the generation and study of unstable plasmas.

[1] T. Silva et al., Physical Review Research 2, 023080 (2020)

[2] E. S. Weibel, Physical Review Letters 2, 83 (1959)

[3] T. Silva et al., in preparation

[4] P. J. Bilbao and L. O. Silva, Physical Review Letters 130, 165101 (2023)

[5] C. Zhang et al., Science Advances 5, eaax4545 (2019)

[6] P. J. Bilbao et al., Physics of Plasmas 31, 052112 (2024)

ABSTRACT. Ultra-intense, femtosecond laser pulses can produce hot, dense plasma and thereby generate intense shock waves. In the present study, we use extreme contrast pulses exhibiting an interesting consequence as the cold target is nanometric close to the probe critical surface.The cold target explodes under the influence of the intense pump pulse, driving a strong shock outward into the plasma, where it is witnessed by changes in the probe reflectivity and Doppler shift [1-3].

A detailed understanding of the critical surface motion of high intensity laser produced plasma is a very crucial parameter for understanding the interaction [1]. Experimentally resolving the ultrafast dynamics of high intensity laser driven plasma at both the relevant length scales and timescales simultaneously is challenging mainly due to the lack of diagnostic approach. Here, we present a novel technique based on pump-probe Dopplerspectrometry to map spatially and temporally the ultrafast dynamics of hot-dense plasma generated by femtosecond, relativistic laser pulses [2,3]. Our technique offers hundreds of femtoseconds time resolution simultaneously with a few micrometers spatial resolution across the transverse length of the plasma. The experiment was carried out using the TIFR150 TW laser system. The extreme contrast laser pulses are generated by converting the mainlaser pulses to second harmonic (400 nm) with peak intensity of [4]. Anormally incident time-delayed probe pulse reflected from its critical layer experiences achange in its wavelength due to the motion of the critical layer. Measuring the time dependent Doppler shifts at different locations across the probe pulse, we obtain two-dimensional velocity maps of the probe-critical plasma layer at ultrafast timescales [Fig. 1].The time and spatial resolution offered by the proposed technique could be improved using ashort duration probe pulse and increasing number of detection channels respectively. Early time measurements using this technique provide very important information about shockwave generation and propagation in dense medium [2,3].

%SVL: Add figure! Figure 1: Spatially resolved Doppler shifts and corresponding velocity maps.

[1] P. K. Kaw, Reviews of Modern Plasma Physics 1, 2 (2017).

[2] K. Jana, A. D. Lad, et al., Physical Review Research 3, 033034 (2021).

[3] K. Jana, A. D. Lad, et al., AIP Advances 12, 095112 (2022).

[4] C. Aparajit, et al., Applied Physics Letters 123, 141108 (2023).

ABSTRACT. Particle-In-Cell (PIC) simulations using the OSIRIS4.0 platform have been carried out to study the interaction of the laser pulse with an overdense plasma threaded by an inhomogeneous external magnetic field. The external magnetic field orientation is chosen to be along the laser magnetic field. The strength of the magnetic field at the plasma edge is such that the EM wave frequency lies inside the pass band, where the group velocity has a significant value. It enables the wave to enter the bulk plasma. The external magnetic field is then spatially tailored appropriately to have the LH resonance ata desired spatial location inside the plasma. This study demonstrates that the EM wave pulse comes to a standstill at the location of the resonance. The wave pulse is observed to break down subsequently, and the energy consequently goes dominantly to the local plasma ions. The absorption is significantly enhanced compared to the case in which the magnetic field profile was homogeneous [1, 2]. The dependence of absorption on the choice of magnetic field profile, the laser intensity, etc., will also be presented.

[1] Vashistha, Ayushi, et al. "A new mechanism of direct coupling of laser energy to ions."New Journal of Physics 22.6 (2020): 063023.

[2] Juneja, Rohit, et al. "Ion heating in laser interacting with magnetized plasma." Plasma Physics and Controlled Fusion 65.9 (2023): 095005.

ABSTRACT. In 1994 the research field of dusty plasmas changed fundamentally due to the discovery of the crystallization of dusty plasmas in the laboratory [1-3]. Before, dusty plasmas where mainly discussed theoretically concerning the interaction of dust particles with plasma in space, including interstellar clouds, circumstellar and protoplanetary accretion discs, nova ejecta, and planetary magnetospheres. In the late 80ies and early 90ies of the last century laboratory research in low-temperature plasmas started since dust particle growth became one of the leading problems in plasma processing industry. With the discovery of the so-called plasma crystals a new research field in classical condensed matter physics was born – a topic merging plasma and solid-state physics. One of the main properties of this new state of matter is the investigation of fluid and solid processes on the most fundamental – the kinetic – level due to the individual observation of the dust particles forming liquid and crystalline structures.

Gravity strongly affects micronsized dust particles and leads to their sedimentation. In Earth-bound labs 2-dimensional plasma crystals can be formed and investigated by e.g. levitating the charged dust particles in the sheath electric field. For the formation of large 3-dimensional systems microgravity experiments are necessary and have been performed in parabolic flights, sounding rockets and onboard the International Space Station ISS. The latter generated a longstanding program on the ISS over more than 20 years up to now. In this presentation I will review the research over the last 30 years by showing some of the highlight topics of plasma crystal research.

[1] H. Thomas et al., Phys. Rev. Lett. 73, 652 (1994)

[2] J.H. Chu et al., Phys. Rev. Lett. 72, 4009 (1994)

[3] Y. Hayashi et al., Jpn. J. Appl. Phys. 33, L804 (1994).

ABSTRACT. In this work, the impact of galactic cosmic rays (CRs) in terms of CR pressure andparallel CR diffusion is studied on the low-frequency magnetohydrodynamic (MHD) waves and linear gravitational instability in the typical dusty plasma environment of molecular clouds (MCs). The dusty fluid model is formulated by combining the equations of the magnetized electrons/ions and dust particles, including the CR effects. The interactions between CR fluid and gravitating magnetized dusty plasma have been studied with the help of modified dispersion properties of the MHD waves and instabilities using the hydrodynamic fluid–fluid (CR–plasma) approach. CR diffusion affects the coupling of CR pressure-driven mode with dust-Alfvén MHD mode and causes damping in the MHD waves. It persists in its effect alongthe direction of the magnetic field and is diminished across the magnetic field. The phase-speed diagram shows that for super-Alfvénic wave, the slow mode becomes the intermediate Alfvén mode.

The fundamental Jeans instability criterion remains unaffected due to CR effects, but in the absence of CR diffusion, the effects of dust-acoustic speed and CR pressure-driven wavespeed are observed in the instability criterion. It is found that CR pressure stabilizes while CR diffusion destabilizes the growth rates of Jeans instability and significantly affects the gravitational collapse of dusty MCs. The charged dust grains play a dominant role in the sub-Alfvénic and super-Alfvénic MHD waves and the collapse of MCs, triggering gravitational instability. The consequences have been discussed to understand the gravitational instability in the dense photodissociation regions of dusty MCs [2].

[1] Ram Prasad Prajapati, Month. Not. Roy. Astron. Soc., 510, 2127 (2022).

[2] Pallab Boro and Ram Prasad Prajapati, Month. Not. Roy. Astron. Soc., 522, 1752 (2023).

ABSTRACT. Shocks in the interstellar medium occur as a result of a variety of phenomena, e.g. protostellar outflows, supernovae and cloud-cloud collisions. In dense, molecular clouds the ionisation fraction of the plasma is low and the magnetic fields threading the clouds can be significant. This results in the shocks from the bipolar outflows of young stellar objects being C-type, meaning there is a smoothing effect on the discontinuities in the fluid parameters through the shock. These shocks are important for the generation of molecules such as SiO which are otherwise heavily depleted into dust grains in these regions. The destruction of dust grains in shocks can occur due to gas-grain sputtering and grain-grain collisions, in which the grains undergo shattering and vaporisation. These processes can be modelled in a MHD code by taking different sizes of grains to be individual fluids. However, it is more realistic to incorporate the grain size distribution which is then followed through the shock.The novelty of the method presented here is that the distribution within each bin is taken into account, either using a piecewise linear or power law approach. Numerical tests show that the results closely follow the analytic solutions even for small numbers of size bins when using the power law approach. The piecewise linear method is accurate for large numbers of bins, but is inadequate in comparison to the power law method for small numbers of bins.This method can be implemented into any HD/MHD code in which changes in the dust grain size distribution occur.