ABSTRACT. With the world’s energy needs expected to rise by a factor of at least 4-5 until the end of the 21st century, and all existing options to cover these demands known to be subject to various disadvantages and limitations, fusion energy provides an attractive additional opportunity. As we edge closer to realizing practical fusion power, the integration of advanced computational tools becomes essential. This talk will explore the concept and development of digital twins inthe context of fusion systems, highlighting their potential to revolutionize the design, optimization, and operation of fusion reactors.

Digital twins – virtual replicas of physical systems – enable real-time monitoring andsimulation, providing a dynamic and predictive insight into system behavior under various conditions. For fusion systems, digital twins can simulate plasma behavior, reactor materials, and subsystems, facilitating enhanced plasma operation and control strategies, thus significantly reducing downtime and operational costs.

The talk will cover the foundational elements required to develop digital twins for fusion systems, including multi-fidelity modeling, data integration, and advanced algorithms for real-time data processing and decision-making. Emphasis will be placed on the challenges unique to fusion systems, such as the complex and highly nonlinear nature of plasma dynamics. Case studies of ongoing projects and collaborations in the fusion research community will be presented to illustrate the practical applications and benefits of digital twins.

The talk will also address future directions, emphasizing the role of artificial intelligence andmachine learning in enhancing the predictive capabilities of digital twins. By leveraging these technologies, we can accelerate the path to achieving reliable and economically viable fusion energy.

ABSTRACT. The characterization of the statistical properties of solar-wind turbulence is a major challenge in solar plasma physics. Satellite observations have shown that solar-wind-plasma turbulence displays a fluid energy spectrum with an inertial range with a scaling exponent that is consistent with -5/3, which follows from the Kolmogorov hypotheses of 1941(henceforth K41). By contrast, the magnetic-energy spectrum displays two different scaling ranges (the first and second inertial ranges): (i) the first inertial range is consistent with the K41 power; (ii) the second inertial range is characterised by an exponent that lies in the range[-4,-1]. Furthermore, solar-wind-turbulence has also been analyzed to uncover (a) intermittency and multiscaling of velocity and magnetic-field structure functions and (b) the alignment of velocity and magnetic-field fluctuations. One study has found structure–function multiscaling (simple scaling), in the first (second) inertial range. We examine the statistical properties of three-dimensional (3D) Hall magnetohydrodynamics (HMHD) turbulence by carrying out high-resolution pseudospectral direct numerical simulations. We explore the dependence of 3D HMHD turbulence on the Reynolds number Re and the ion-inertial scale.We present several statistical properties of 3D HMHD turbulence, which we also compare with their counterparts for 3D MHD turbulence and solar-wind turbulence by calculating (a) the temporal evolution of the energy-dissipation rates and the energy, (b) the wave-number dependence of fluid and magnetic spectra, (c) the probability distribution functions of the cosines of the angles between various pairs of vectors, such as the velocity and the magnetic field, and (d) various measures of the intermittency in 3D HMHD turbulence

ABSTRACT. Ye.O.Kazakov1, K.Crombé1,2, D.Hartmann3, D.Castaño-Bardawil1, D.Lopez-Rodriguez1,2,I.Stepanov1, M.Verstraeten1, M.Vervier1, B.Schweer1, A.Dinklage3, T.Fornal4, D. Gradic3, M.Gruca4,K.P.Hollfeld5, J.P.Kallmeyer3, I.Ksiazek6, A.Krämer-Flecken7, M.Kubkowska4, Ch.Linsmeier7, F.Louche1,O.Neubauer7, D.Nicolai7, G.Offermanns5, G.Satheeswaran7, L Syrocki4, M.Van Schoor1, R.C.Wolf3, theTEC team1,7and W7-X team81Laboratory for Plasma Physics, Royal Military Academy, TEC Partner, Brussels, Belgium2Department of Applied Physics, Gent University, Belgium3Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, D-17491 Greifswald, Germany4 Institute of Plasma Physics and Laser Microfusion, 23 Hery Str., 01-497 Warsaw, Poland5Zentralinstitut für Engineering, Elektronik und Analytik – Engineering und Technologie, (ZEA-1),6Institute of Physics, Opole University, ul. Oleska 48, 45-052 Opole, Poland7Institut für Energie- und Klimaforschung / Plasmaphysik (IEK-4), Trilateral Euregio Cluster (TEC) Partner,Forschungszentrum Jülich, D-52435 Jülich, Germany8See the author list of the paper by T.Sunn Pedersen et al., Nucl. Fusion 62 (2022) 04202

%SVL fiox authors

The superconducting stellarator Wendelstein 7-X (W7-X) at the Max-Planck-Institutein Greifswald began operation in 2015. To demonstrate efficient confinement of energetic alpha particles, which will be essential for a future Helias fusion reactor, W7-X requires a population of fast ions with energies ranging from 80 to 100 keV in the core of high-density plasmas. This can be achieved with Ion Cyclotron Resonance Heating (ICRH) using minority heating of H in ⁴He and D plasmas, as well as the three-ion scenarios of ⁴He-(³He)-H and D-(³He)-H.

The ICRH antenna for W7-X consists of two poloidal straps. Each strap is terminated by a pre-matching capacitor at one end and short-circuited at the other, with RF power fed atan intermediate position along the straps. The antenna's shape is tailored to match the 3D shapeof the Last Closed Magnetic Surface (LCMS) in the standard magnetic field configuration of W7-X, resulting in variable curvature in both toroidal and poloidal directions over the plasma-facing surface [1]. The antenna can also be moved radially up to 35 cm, and a gas puffingsystem is incorporated to inject gas in the region between the scrape-off layer (SOL) and the LCMS to locally improve coupling. The full system was commissioned on W7-X plasmas in February and March of 2023. During these experiments, only one of the two straps was powered due to a faulty pre-matching capacitor and vacuum feedthrough, resulting in operation with k|| ~0.

Two significant milestones were achieved: operation at high power levels (up to 700kW) and the generation of a target plamsa using ICRH alone at magnetic fields below the usual 2.5 T, where the 140 GHz ECRH system is not resonant. In these experiments, the standard magnetic configuration in W7-X was used, the LCMS was positioned 17 cm from the first wall, and the distance between the antenna and the LCMS ranged from 3 to 10 cm. Despite the unfavourable heating conditions, k_|| ~0, there was a clear increase in the plasma stored energy at constant electron density, consistent with an increase in ion temperature.The Faraday screen is omitted in this antenna design, based on extensive experience with TEXTOR [2]. No edge interaction was observed. Small levels of Cu and C impurities where observed with VUV and Soft X-ray diagnostics. In plasma start-up experiments at 1.7T, plasmas were sustained for the full duration of the ICRH pulse with approximately 300 kWRF power.

[1] J.Ongena et al., Physics of Plasmas 21, 061514 (2014)

[2] R. Van Nieuwenhove et al., Nucl. Fusion 32 (1992) 1913

ABSTRACT. The Alfvén instability nonlinearly excited the energetic-particle-driven geodesic acoustic mode on the ASDEX-Upgrade tokamak, as demonstrated experimentally [1-5]. The mechanism of the energetic-particle-driven geodesic acoustic mode excitation and the mode nonlinear evolution is not yet fully understood. In the present work, a first-principles simulation using the MEGA code [6] investigated the mode properties in both the linear growth and nonlinear saturated phases [7,8]. The simulation parameters and the equilibrium data are based on the realistic experiment, that is shot #34924 of ASDEX-Upgrade at t = 1.9 s. Here we show that the simulation successfully reproduced the excitation and coexistence of these two modes, and agreed with the experimental results well. The mode frequencies of these two modes are about 100 kHz and 50 kHz, respectively. In addition, the simulation reveals a radially inward energetic particle redistribution during mode activities, consistent with the experimental findings. Conclusive evidence showed that the resonance overlap is the excitation mechanism of the energetic-particle-driven geodesic acoustic mode. In the linear growth phase, energetic particles that satisfied different resonance conditions excited the Alfvén instability, which then caused energetic particle redistribution in phase space. These redistributed energetic particles caused resonance overlap, exciting the energetic-particle-driven geodesic acoustic mode in the nonlinear phase. The above process was demonstrated in toroidal canonical momentum P_φ and energy E phase space, and the time evolution of energetic particle distribution ftotal and δf are investigated in detail.

[1] Ph. Lauber, et. al., presented at 27th IAEA Fusion Energy Conference, Gandhinagar, India,2018)

[2] P. Poloskei, et. al., presented at 44th EPS Conference on Plasma Physics, Belfast, UK,2017)

[3] F. Vannini, et al., Nuclear Fusion 62, 126042 (2022)

[4] G. Vlad, et al., Nuclear Fusion 61, 116026 (2021)

[5] B. Rettino, et al., Nuclear Fusion 62, 076027 (2022)

[6] Y. Todo, et al., Plasma Physics and Controlled Fusion 63, 075018 (2021)

[7] H. Wang, et. al., presented at 29th IAEA Fusion Energy Conference, London, UK, 2023)

[8] H. Wang, et al., Nuclear Fusion 64, 076015 (2024)

ABSTRACT. Understanding the transport and losses of particles in tokamaks is crucial for operating future fusion reactors in particular for energetics particles, as they can be expelled before being able to deposit their energy in the tokamak core. Focusing on energetic trapped particles, they can destabilize the so called fishbone instability[1, 2, 3] that finally induces their transport. Indeed, the resonant interaction between the toroidal precessional motion of particles and the low-frequency kink mode [2, 4] leads to a growing fishbone instability in the core of the tokamak. Those energetic particles can be generated by heating systems in D-D experiments, for instance, or correspond to the population of particles with a velocity mainly perpendicular to the ambient magnetic field in D-T experiments. In this work, we first present a model coupling a reduced MagnetoHydroDynamics model incylindrical geometry, for the thermal plasma, with a kinetic description for the trapped energetic particles. The numerical work takes advantage of reduced MagnetoHydroDynamic code, AMON [5], developed at the PIIM laboratory, to which we added a gyro- and bounce-averaged Vlasov equation for the energetics particles. We ran linear simulations, using a small resistivity and different amounts of energetic particles for investigating the development of the fishbone instability close and far to the threshold [6], checking for the correct growth rate of the mode and the eigenfunction profiles. Non-linear simulations have been performed focusing on the saturation of the fishbone instability and the induced transport, by checking the phase space dynamics of the energetics particles.

[1] R.B. White, et al., Physical review letters 62, 539 (1989)

[2] B. Coppi, et al., Physical review letters 57, 2272 (1986)

[3] B. Coppi, et al., Physics of Fluids B:Plasma Physics 2, 927-943 (1990)

[4] R.B. White, et al., Reviews of Modern Physics 58, 183 (1986)

[5] M. Muraglia, et al., Nuclear Fusion 57, 072010 (2017)

[6] M. Idouakass, et al., Physics of Plasmas 23, 102113 (2016)

ABSTRACT. For modern plasma processing, there is a need to perform kinetic simulations of large plasma devices using the particle-in-cell (PIC) technique due to relative ease of implementing the method, and that it can be parallelized effectively over many processors and accelerated on GPUs. At PPPL we have developed two codes EDIPIC-2D and LTP-PIC-3D. EDIPIC-2D is an open-source code that includes features for simulations of practical devices and has been used for modelling of several plasma devices. LTP-PIC-3D is a high-performance scalable PIC code which incorporates best programming practices and multi-level parallelism. This code was upgraded to operate efficiently on the latest CPU/GPU architectures for additional performance improvements. Energy conserving or implicit methods were implemented to speed up simulations [1]. Effects of numerical noise in simulations using PIC code need to be analysed and considered [2]. These codes have been applied to study plasma processing applications, such as capacitively coupled plasmas [3], electron beam produced plasmas [4], inductively coupled plasmas, and hollow cathode discharges. To model surface processeswe used a combination of quantum chemistry methods and molecular dynamics [5].

Acknowledgements. Supported by the US Department of Fusion Energy Science.

[1] H. Sun, et al, Phys. Plasmas 30, 103509 (2023); A.T. Powis, et al, Phys. Plasmas 31, 023901 (2024).

[2] S. Jubin et al, Phys. Plasmas 31, 023902 (2024);

[3] L. Xu, et al, Plasma Scie. and Technol. 32, 105012 (2023), A. Verma, et al, ibid 33 035003 (2024); S. H.Son, et al, Appl. Phys. Lett. 123, 232108 (2023); S. Sharma, Phys. Plasmas 29, 063501 (2022);

[4] S. Rauf, et al, Plasma Scie. and Technol. 32, 055009 (2023);

[5] O. D. Dwivedi, et al, J. Vac. Scie. & Technol. A 41, 052602 (2023); Y. Barsukov, et al, Nanotechnology 32,475604 (2021); S. Jubin et al, Front. Phys. 908694 (2022); A. Rau et al, Front. Phys. 933494 (2022).

ABSTRACT. Surface modification of polymers is essential for tuning their surface properties, opening a myriad of applications across various technological areas. ECR plasma is one of the technologies used for surface treatment of polymers. However, various ECR plasma system parameters affect the plasma behavior and the plasma energy required to tune the surface of polymers. Therefore, in this study, COMSOL Multiphysics-based Finite Element Analysis [1,2] was utilized to investigate various crucial plasma parameters as a function of microwave power, pressure, and magnetic field strength. Variations in the resonance zone and properties such as ionization rate, electron mobility, mean plasma electrical conductivity, electron temperature, electron density, etc., were predicted. Further, the parameters were experimentally measured [3] and validated. The results demonstrated good agreement with experimental data. This study provides valuable insights for optimizing plasma parameters for various applications of ECR plasma, such as polymer surface modification, surface grafting, and applications in space and biomedical fields.

Acknowledgments. SSS would like to express my sincere gratitude to Mahatma Jyotiba Phule Research and Training Institute (MAHAJYOTI), Nagpur, India, For their Financial support. Their assistance was crucial in enabling the progress and completion of this work.

[1] Zhang Bin et al., Thin solid Films,714, (2020)

[2] M. Asadi Aghbolaghi et. al., AIP advances,14(3), (2024).

[3] More et. al., Review of Scientific Instruments,89(1),2018.

Acknowledgments. SSS would like to express my sincere gratitude to Mahatma Jyotiba Phule Research andTraining Institute (MAHAJYOTI), Nagpur, India, For their Financial support. Their assistancewas crucial in enabling the progress and completion of this work.

ABSTRACT. Magnetic reconnection – a fundamental collective plasma process of violent reorganization of the magnetic-field topology and associated rapid release of magnetic energy– is ubiquitous in many space and astrophysical plasma environments, powering intense high-energy flares. However, under the extreme physical conditions encountered around neutron stars and black holes, reconnection takes place in an exotic radiative relativistic regime, where particles energized by magnetic-energy release to relativistic energies emit copious amounts of synchrotron and/or inverse-Compton radiation. The resulting radiative losses feedback on the reconnection process, altering its dynamics and energetics and suppressing nonthermal particle acceleration. Under even more extreme conditions, QED processes like pair creation come into play, leading to a nontrivial self-regulating regime where the reconnection layer creates its own plasma. In this talk I will review the recent advances in our understanding of this fascinating radiative relativistic reconnection regime made possible by novel first-principles radiative-QED particle-in-cell numerical simulations in combination with analytical theory.

ABSTRACT. The Magnetospheric Multiscale Spacecraft (MMS) identified electrostatic solitary wave (ESW) signatures associated with localized bipolar electric field pulses in there connection jet region located in Earth's magnetotail [1]. Those observations unveiled the presence of two counter streaming ion (proton) beams and hot electrons [1], thus suggesting apossible link between the generation of nonlinear waves and counterpropagating cold ion beams within the jet. ESW observed in the magnetosphere [2] are known to be affected by energetic particles, a common occurrence in various Space environments and in particular in the solar wind, associated with long-tailed non-Maxwellian distributions [3].

Inspired by the above observations [1] and following up on subsequent studies [4-5],we have developed a three-component plasma model consisting of two counterstreaming proton beams and suprathermal electrons, in order to investigate the occurrence of electrostatic waves in the Earth’s reconnection jet region. A thorough study reveals a number of possibilities, including predictions of subsonic pulse-shaped solitary waves -associated with the slow ion-acoustic mode- occurring only at a certain threshold in the beam speed (value)[6]. Subsonic shock-shaped structures have also been shown to exist in the presence of weak dissipation [7]. Subsonic electrostatic excitations are not possible in the absence of a beam.

Acknowledgements. Authors KS and IK acknowledge financial support from Khalifa University’s Space and Planetary Science Center under grant No. KU-SPSC-8474000336. KS and IK also thank KU for support via grant CIRA-2021-064/8474000412.

[1] C. M. Liu et al., “Ion‐beam‐driven intense electrostatic solitary waves in reconnection jet,” Geophys. Res. Lett., 46, 12702 (2019).

[2] D.B. Graham, Y.V. Khotyaintsev, A. Vaivads, Andre M., “Electrostatic solitary waves and electrostatic waves at the magnetopause,” Geophys. Res. Lett. 42, 215 (2015).

[3] G. Livadiotis, “Kappa Distributions - Theory and Applications in Plasmas” (Amsterdam, Elsevier, 2017).

[4] G. S. Lakhina, S. V. Singh, R. Rubia, “A new class of ion-acoustic solitons that can exist below critical Mach number,” Phys. Scr., 95, 105601 (2020).

[5] F. Verheest, M. A. Hellberg, “Fast and slow beam mode ion-acoustic solitons in plasma swith counterstreaming cold protons,” Phys. Scr., 96, 045603 (2021).

[6] K. Singh, S. S. Varghese, F. Verheest, I. Kourakis, “On the existence of subsonic solitary waves associated with reconnection jets in Earth's magnetotail,” Astrophys. J., 957, 96 (2023).

[7] K. Singh, F. Verheest, I. Kourakis, “Evolution of Subsonic Shock Waves Associated with Reconnection Jets in Earth's Magnetotail,” Astrophys. J., 966, 203 (2024).

ABSTRACT. Gyrokinetics is a powerful theoretical framework based on which a large number of analytical and numerical studies on microinstabilities and turbulent processes in magnetized plasmas have been done. This work consists of two parts of our recent theoretical andsimulation studies on gyrokinetic turbulence. In the first part, a variational principle is used to derive governing equations of electromagnetic turbulent gyrokinetic plasma systems with conservation properties favorable for long-time global gyrokinetic transport simulation of high beta plasmas. Then, the invariance of the Lagrangian of the system under an arbitrary spatial coordinate transformation is used to derive the local momentum balance equation in which effects of collision and source terms are included [1]. In a way analogous to the derivation of the energy-momentum tensor in the theory of general relativity, the variational derivative of the Lagrangian density with respect to the metric tensor is taken to directly obtain the symmetric pressure tensor which describes both collisional and turbulent momentum transport processes. The derived symmetric pressure tensor is useful for treating momentum conservation in symmetric magnetic configurations. In the second part, the effects of turbulence on energy exchange between electrons and ions are investigated. Although the effect of turbulent energy exchange has not been considered significant in previous studies, it is anticipated to have a greater impact than collisional energy exchange in low collisional plasmas such as those in future fusion reactors. It is shown from gyrokinetic simulations that the energy exchange due to the ion temperature gradient (ITG) turbulence mainly consists of the cooling of ions in the grad B-curvature drift motion and the heating ofelectrons streaming along a field line [2]. The ITG turbulence transfers energy from ions to electrons regardless of whether ions or electrons are hotter, which is in marked contrast to theenergy transfer by Coulomb collisions. This implies that the ITG turbulence should be suppressed from the viewpoint of sustaining the high ion temperature required for fusion reactions since it prevents energy transfer from alpha-heated electrons to ions as well as enhancing ion heat transport toward the outside of the reactor. Furthermore, linear and nonlinear simulation analyses confirm the feasibility of quasilinear modeling for predicting the turbulent energy exchange in addition to the particle and heat fluxes.

[1] H. Sugama, Phys. Plasmas 31, 042303 (2024).[2] T. Kato, H. Sugama, T.-H. Watanabe, M. Nunami, “Energy exchange between electronsand ions in ion temperature gradient turbulence,” arXiv:2402.12748 (2024); submittedto Phys. Plasmas.

ABSTRACT. The phenomena of layering in turbulent mixing processes is observed in a variety of physical systems, including magnetically confined plasmas. In this case, layering isconnected with the so-called ExB staircase, which is a series of mixing zones interspersed by shear layer mini-barriers. Staircase formation can result from inhomogeneous mixing. This basic experiment addresses some of the key questions in layering and staircase dynamics, such as deviation from marginality and the percolation of density and thermal mixing.

In this work, we investigate layering and staircase dynamics using a melting vortexlattice (or fluctuating cellular array), which intrinsically drives inhomogeneous mixing[1]. To accomplish this, a vortex array is created in a large linear magnetized plasma device (LAPD) that is designed to have a system of tangent eddies, thus forming a staircase structure which can exhibit “melting” through the interaction of neighboring cells in the lattice. To create the vortex lattice in the LAPD experiment, a smaller lanthanum hexaboride (LaB6) cathode source is placed at the opposite end of the device relative to the main discharge large area LaB6 cathode. A carbon mask containing a patterned array of holes is placed in front of this smaller cathode. When this smaller cathode is biased to a mesh anode in front of the main discharge cathode, a stream of electrons flows through the lattice of holes in the mask and current channels are created in the pattern of the mask. The lattice of filaments that form has finite axial extent and the filament length is controlled by adjusting the magnitude of thebiasing voltage. The initial experiments were carried out using a 3x3 square lattice of cells. Langmuir probes were used to make cross-field planes of density, temperature, and plasmapotential.

The results indicate the establishment of a dynamical vortex lattice with local and global vortical azimuthal and axial flows. In the near field region of the lattice, the local plasma potential forms a well, which induces ExB differential rotation of the lattice resulting in azimuthally symmetric inhomogeneous boundary layers that are on the scale of the gaps in the initial lattice structure. A series of mixing layers is interspersed with the boundary layers and cross-field diffusion begins to reduce the gradients. A spectral analysis of the gradient-driven fluctuations and their relation to the diffusivity, as well as the coupling of this spinning lattice structure to the background plasma will be presented.

[1] F.R. Ramirez and P.H. Diamond, Physical Review E 109, 025209 (2024)

ABSTRACT. MHD instabilities are of considerable fundamental and practical importance formagnetic fusion plasmas, since they are believed to set limits on the achievable plasma pressure and current density, sometimes even leading to the termination of the plasma discharge. An eigenvalue and an initial value MHD codes in toroidal geometry have been developed to facilitate the related numerical investigations in understanding MHD stability in tokamak plasmas, since the exact solutions are impossible to analytically obtain due to the complexity of toroidal geometry.

A new full MHD eigenvalue code SCELT (Symbolic Computation aided Eigenvalue and Linear code for Tokamak) has been constructed by utilizing the symbolic computation technique for the first time [1]. A symbolic vector analysis module is first developed to conduct the automatic derivation of the tedious linearized full MHD equations in the magnetic flux coordinate system. And an automatic numerical discretization module is developed to implement the automatic numerical discretization. The reliability of the new full MHD eigenvalue code developed with help of these two modules is verified by the internal kink mode and tearing mode tests. This new method has the advantage to dramatically reduce the manpower and to avoid possible errors in code development. The feasibility and advantage of the methodology also has been further demonstrated by solving the more difficult challenge of MHD continua, i.e. global Geodesic Acoustic Modes (GAM), which ordinarily come with spatial singularities [2].

Also, a new initial value full MHD code using discontinuous Galerkin (DG) and Weighted Essentially Non-Oscillatory (WENO) methods has been developed to solve the conservative perturbed MHD equations in toroidal geometry [3]. A triangular mesh based on the flux of the fixed boundary equilibrium in the poloidal plane and a uniformly division in toroidal direction were adopted during the code development. The code was linearly tested by performing the linear calculations of the internal kink mode and tearing mode. Nonlinear simulations of the resistive internal kink mode and tearing mode are also carried out.

Acknowledgments: This work is supported by the National Natural Science Foundation of China under Grant Nos. 12075282 and 11775268. The numerical calculations in this paper were performed on ShenMa High Performance Computing Cluster in Institute of Plasma Physics, Chinese Academy of Sciences and Hefei Advanced Computing Center.

[1] J. Ma and W. Guo, Computer Physics Communications 278 108412 (2022)

[2] W. Guo and J. Ma, Plasma Phys. Control. Fusion 66 035005 (2024)

[3] J. Ma, et. al, Computer Physics Communications 299 109139 (2024)

ABSTRACT. The vast majority of ITER plasma boundary simulations have focused on the divertor phase since it is under these conditions that the principal plasma performance objectives will be achieved. However, as in all tokamaks, every ITER plasma pulse will have to pass through a current ramp-up phase, which, in common with many devices will take place in ITER in limiter configuration on the central column[1]. As for the rest of the main chamber first wall (FW), the central column will consist of FW panels (FWP) protecting the blanket shield blocks, with each panel shaped toroidally to ensure protection of leading edges between adjacent panels. This shaping leads to localized power deposition due tomagnetic field line shadowing. Analysis based on 3D field line tracing coupled with a very simple, non-dissipative description of the scrape-off layer (SOL) parallel heat flow profile, q_||(r) has shown that under some conditions (depending on plasma current, heating power and the degree of radial misalignment between FWP’s), heat loads during the limiter ramp-up can approach, or even exceed the stationary values for which the panels are rated.

Given the potential for FWP power flux overload, it is important to assess the degree of conservatism introduced by the simplified SOL model employed in field line tracing study. A first step in such anassessment is reported here in which a 3D plasma transport study is performed using the coupled plasma-neutral transport code EMC3-Eirene, taking into account the full 3D FW CAD geometry from which an appropriate EMC3-Eirene numerical grid is constructed and a large enough portion of the full torus is simulated to fully capture all shadowing effects. Radial profiles of transport coefficients are chosen such that q_||(r) at the outside midplane (OMP) closely follows the double exponential profile used to determine the optimum FWP toroidal shaping [1,2]. First simulations are reported for a fixed, slightly elongated magnetic equilibrium at I_p ~2 MA, B_T = 5.3 T with varying SOL input power and OMP separatrix density, chosen on the basis of DINA code ramp-up simulations. These are similar parameter sets to those chosen for a companion 2D SOLPS-ITER study of ITER limiter start-up, though this latter work includes impurity evolution from the limiter surface, while there the focus is on pure hydrogen simulations. The key first conclusion from this work is that at the low densities (and hence high SOL Te) required for limiter start-up on ITER, dissipation due to hydrogenic radiation alone is negligible and the EMC3-Eirene deposited power distributions are similar to those obtained from the simple field line tracing approach. To provide a more quantitative assessment of the real reduction in power loading to be expected compared with the simple engineering treatment will require impurity release and transport to be included.

[1] R. A. Pitts et al., Nucl. Fusion 62 (2022) 096022

[2] M. Kocan et al 2015 Nucl. Fusion 55 033019

ABSTRACT. Nowadays, plasma-assisted nitrogen fixation (NF) processes have been demonstrated as ahighly promising alternative to the environmentally impacting Haber-Bosch process. Therefore, the community develops numerous attempts to optimize these processes in term of energy cost and yield. Among the various plasma technologies, atmospheric gliding arc plasmas (GAP) is found to suit well thanks to their warm feature and the significant molecular vibrational excitation they allow. In this contribution, we overview our recent experimental efforts to contribute towards a better understanding of this plasma technology for nitrogen fixation into NO_x.

In this context, the present work will specifically evaluate a gliding arc plasma operating with N₂ and O₂ at atmospheric pressure and more precisely on the study of the electrical (arc) stability of the process, and on the resultant benchmarking of the plasma-based nitrogen fixation process from a techno-economic perspective.

Considering the electrical stability of the studied process, the conventional approach of introducing external resistors to stabilize the arc is challenged by studying both the performance and the stability of the plasma replacing the external resistor with an inductor. From this work, we conclude that similar stabilization results can be obtained while significantly lowering the overall energy cost, which decreased from up to a maximum of 7.9 MJ/mol N to 3 MJ/mol N. Then, considering these results, we evaluate to which extent a hypothetical small-scale fertilizer production facility based on a rotating gliding arc plasma for nitrogen fixation can be a local competitive alternative for the Haber-Boschprocess. This is done by proposing a comparative model to understand how capital expenditures, gas price, CO2 allowances, levelized cost of energy, and transport costs affect the fertilizer production costs. The model highlights how, with the current best available technology, plasma-based nitrogen fixation, while being an interesting alternative for the synthesis of NO_x, still requires a more efficient use of H₂ for a direct production of NH₃ .

Acknowledgements. This research is supported by the FNRS project “NITROPLASM”, EOS O005118F.

ABSTRACT. In this work, miniaturized Plasma Focus (PF) technology, based on scaling laws for PF devices, is utilized to design and construct a pulsed plasma thruster for CubeSat nanosatellites. After the pinch phase in PF devices, a plasma shock appears, traveling at speeds of approximately 10⁵m/s, independent of the energy of the device. The ejected mass scales with the energy of the device; for a device operating at 400 J, the ejected mass is approximately 10⁻¹⁰ kg [1].Theoretical estimations suggest that a pulsed plasma thruster (PPT) based on PF technology, operating at 1 J, will generate impulses ranging from fractions of μNs to several μNs per pulse [2].

It is important to note that while PF devices operate at millibar pressures, a PPT operates in orbit under vacuum conditions, where plasma is generated through the ablation of insulating material, typically PTFE.

A pulsed plasma thruster was constructed using a small capacitor of 1.5 μF, 2 kV (3 J stored energy), with dimensions of 50 mm x 45 mm x 30 mm and a weight of 115 g. This capacitor is charged using a voltage multiplier rated at 6 W, Vin = 12 V, Vout = 2 kV, with dimensions of 57mm x 28 mm x 12 mm and a weight of 37 g. The plasma gun weighs approximately 2 g. Consequently, the total weight and volume of the PPT system are around 150 g and 100 cm³. To measure the impulse, a new thrust stand based on a single-point load cell was developed. The calibration of the load cell, along with the associated electrical signals and PPT assembly, is analyzed.

Acknowledgements. This work is supported by ANID FONDECYT Regular 1211695.

[1] Soto, L., Pavez, C., Moreno, J., Inestrosa-Izurieta, M. J., Veloso, F., Gutiérrez, G., ... &Delgado-Aparicio, L. F. (2014). Characterization of the axial plasma shock in a table top plasma focus after the pinch and its possible application to testing materials for fusion reactors. Physicsof Plasmas, 21(12).

[2] Soto, L., Pavez, C., Pedreros, J., Jain, J., Moreno, J., San Martín, P., Castillo, F., Zanelli,D. & Altamirano, L. (2024). Development of a Miniaturized 2 Joule Pulsed Plasma Source based on Plasma Focus Technology: Applications in Extreme Condition Materials and Nanosatellite Orientation. Micromachines, in press.

ABSTRACT. Due to their unique properties, polymer nanoparticles (PNPs) have found their application in photonics, drug delivery, sensing, environmental remediation, and more. Numerous chemical methods have been developed for their synthesis, which normally require the use of solvents, are time-consuming, and costly. Therefore, there is still a need for environmentally sustainable, efficient, and time-saving methods for the synthesis of PNPs [1]. One such method is magnetron sputtering, a quite straight-forward process with high deposition rates, yielding nanoparticles of very high purity, and allowing the tailoring of particle size distributions [2]. However, despite the high potential of this method in developing PNPs, most existing studies have primarily focused on the production of metal nanoparticles. To address this gap, we present, for the first time, the solvent-free synthesis of polystyrene (PS) nanoparticles via a radiofrequency (RF) magnetron-based gas aggregation cluster source (GAS).

A PS target with a 81 mm diameter and 4 mm thickness is bombarded by high-energy plasma species, mainly ions, leading to the ejection of atoms, molecules, or molecular fragments from the target. The ejected species then travel and condense onto surrounding surfaces [2]. The PNPs were synthesized under constant pressure of 164 Pa in the aggregation chamber and a constant flow of 40 sccm of argon with a reaction time of 30 minutes. The effect of power on the PNPs’ characteristics was investigated across a range of power levels: 40, 60,and 80 W. The PNPs synthesized at lower power (40 W) exhibited spherical morphology with a diameter of approximately 100 nm, while higher powers (60 and 80 W) led to a cauliflower-like morphology marginally larger than the 40 W particles. Despite variations in morphology, Fourier-transform infrared (FT-IR) spectroscopy revealed a consistent preservation of the aromatic structure, evidenced by characteristic vibrational modes of the styrene ring with the out-of-plane bending vibration at 669 cm-1, C-C in-plane stretching [3], and various vibration bands associated with symmetric C-H stretching vibration of the methyl group (-CH3) at 2871and 2958 cm^-1, indicating substantial branching of the polymer [4]. For further comprehensive analysis, X-ray photoelectron spectroscopy (XPS) will be employed to provide insight into the elemental composition of the PNPs. Due to particles appearing transparent in the images obtained from scanning electron microscopy (SEM), ultraviolet-visible (UV-VIS) spectroscopy will also be performed to elucidate optical properties and the potential application of the synthesized PNPs in optoelectronic devices.

[1] Adhikari, C., Polymer nanoparticles-preparations, applications and future insights: Aconcise review. Polymer-plastics technology and materials, 2021. 60(18): p. 1996-2024.

[2] Kylián, O., et al., Magnetron sputtering of polymeric targets: From thin films to heterogeneous metal/plasma polymer nanoparticles. Materials, 2019. 12(15): p. 2366.

[3] Brijmohan, S.B., et al., Synthesis and characterization of cross-linked sulfonated polystyrene nanoparticles. Industrial & engineering chemistry research, 2005. 44(21):p. 8039-8045.

[4] Choudhury, A., et al., Studies of physical and chemical properties of styrene-based plasma polymer films deposited by radiofrequency Ar/styrene glow discharge. Progressin Organic Coatings, 2011. 70(2-3): p. 75-82.

ABSTRACT. Particle contamination control for particles down to submicron sizes is a crucial aspect of semiconductor processing and etching technologies. In recent times this aspect has also become crucial for the lithographic patterning process with the introduction of extremeultraviolet (EUV) lithography which uses highly energetic EUV photons (13.5 nm, 92 eV). One of the side effects of this development is the generation of EUV-induced plasma due to the interactions of highly energetic EUV photons with low pressure (1–10 Pa) background hydrogen gas. The lithography machines operate in pulsed mode with EUV pulses of < 100 nsin every 20 μs. The spatial and temporal evolution of the EUV induced plasmas has been investigated using 3D particle-in-cell (PIC) model. This shows the EUV light beam creating the plasma in < 100 ns (Fig.1a), whereafter it spreads and decays in the remaining 19.9 μs afterglow (Fig. 1b). This also impacts the particle contaminants: they become positive withinthe EUV beam due to the photoelectric effect and they become negative outside and after the beam passage due to EUV-induced plasma. The location of charged particles during the EUV pulse and in the afterglow is shown below in Fig. 1(c-d) . The multi-pulse population dynamics of charged particles is shown in Fig. 1e. This shows a peaked increase in positive particle population during every EUV pulse and a steady increase of negative particle population during multiple afterglows.

%SVL insert figure

Figure 1: Spatial distribution profile of electron density at Reticle Mini-Environment within ASML lithographymachine is shown (a) within EUV pulse (< 100 ns) and (b) after pulse (100 ns - 20 $\mu$ s) in the afterglow condition.(c-d) The typical population characteristics of 100 nm charged (positive: red and negative: blue) particles are shown in the two regimes mentioned in (a-b). For multi-pulse scenario, the population dynamics of charged and neutral particles are shown in (e). The population of neutral particle decreases over time at the expense ofnegatively charged particle generation. However, the population of positively charged particle remains steady over time.

Reference:

“Particle charging during pulsed EUV exposures with afterlow effect”, M.Chaudhuri, L.C.J. Heijmans, M. van de Kerkhof, P. Krainov, D. Astakhov and A. M.Yakunin, Plasma Sources Sci. Technol. 32, 095005 (2023)

ABSTRACT. One of the fundamental problems in space physics is the solar wind expansion and its interaction with different physical processes, e.g., collisions, wave turbulence or self-generated instabilities, conditioning the plasma dynamics. The expansion of the solar wind has been commonly described by the double adiabatic invariants or CGL theory [1], including the approach with the so-called Expanding Box Model (EBM) [2,3]. Despite the contributions made in the last decades, much remains to be understood and a realistically model, which includes plasma cooling and heating effects due to expansion concurring with other physical processes, is still an open problem. Our study introduces a new theoretical formalism to solve the CGL equations in an expanding framework, a significant step towards understanding what the expansion of the plasma entails but also what it implies. Our primary objective is to isolate the expanding effects and how they affect the conservation of double adiabatic invariants, the key aspect of the CGL theory.

To address the plasma expansion, we employed the Expanding Box Model transformations coupled with the ideal-MHD formalism used for CGL theory. This model provides a unique system of reference co-moving with the solar wind, allowing for the incorporation of transverse expansion into the double adiabatic equations. By following the same approximations and assumptions as in EBM and CGL theory, we developed a CGL-like description in which the expansion modifies the conservation of the double adiabatic invariants. Our results show that the double adiabatic equations are no longer conserved if plasma cooling is introduced through the EBM, with explicit dependence on expanding parameters, magnetic field profiles, and velocity gradients. Solving the equations for different magnetic field and density profiles (obtained self-consistently through the equations), we compute the evolution of anisotropy and plasma beta, which deviates from CGL predictions and empirical observations [4]. This deviation is attributed to the plasma cooling effect induced by the Expanding Box Model. Results suggest that heating mechanisms play an even major role in counteracting plasma coolingduring expansion.

[1] Chew, G., Goldberger, M., & Low, F. 1956, Proc. R. Soc. Lond,692 236, 112.

[2] Velli, M., Grappin, R., & Mangeney, A. 1992, AIP Conf. Proc., 757 267, 154.

[3] Grappin, R. & Velli, M. 1996, J. Geophys. Res., 101, 425.

[4] Marsch, E., Ao, X.-Z., & Tu, C.-Y. 2004, J. Geophys. Res. Space 730 Phys., 109.

ABSTRACT. In this work solar cycles 21 to 24 were studied using complex network analysis. A network was constructed for each of the four solar cycles, where the nodes correspond to theactive regions of the Sun that emanate flares, and on the other side, the connections correspond to the time sequence of solar flares. A similar network construction method is found in Ref. [1], following previous analyses for earthquake networks [2, 3]. In this way, we have constructed a directed network where we have also allowed self-connections. We calculate the incoming degree for each node, and subsequently the degree distribution, finding that for each solar cycle, the degree distribution obeys a power law, suggesting a preference of flares to appear incorrelated active zones. Additionally, we found a variation in the characteristic exponent for each cycle, being higher in the even cycles than in the odd cycles. By means of a more detailed analysis based on moving 11-year networks, we find that the characteristic exponent varies with a period of approximately 22 years [4], which suggests that complex networks may provide information about the Hale cycle [5].

Acknowledgments. This research was funded by FONDECyT grant number 1242013 (V.M.), and supported by ANID PhD grant number 21210996 (E.F.) and ANID PhD grant number 21231335 (A.Z). We are grateful to SDO Data supplied courtesy of the SDO/HMI consortia. We also thank to Space Physics Data Facility, NASA/Goddard Space Flight Center.

[1] V. Muñoz and E. Flández, Entropy 24, 753 (2022).

[2] S. Abe and N. Suzuki, Europhys. Lett. 65, 581 (2004).

[3] S. Abe, D. Pastén, and N. Suzuki, Phys. A 390, 1343-1349 (2011)

[4] P. Charbonneau, S. W. McIntosh, H.-L. Liu, and T. J. Bogdan, Solar Physics 203, 321(2001).

[5] M. N. Gnevyshev and A. I. Ohl, A. Zh. 25, 18 (1948).

ABSTRACT. Vasily Kiptily7, Jef Ongena1, Hajime Urano7, Maiko Yoshida7,JET Contributors* and the EUROfusion Tokamak Exploitation Team**

1 Laboratory for Plasma Physics, LPP-ERM/KMS, Brussels, Belgium

7  United Kingdom Atomic Energy Authority, CCFE, Culham Science Centre, Abingdon, UK

%SVL edit author list

Mixed D-³He plasmas provide an opportunity to generate alpha particles with birth energies of 3.6 MeV without using tritium in a fusion device. The cross-section of the D-³He fusion reaction peaks at deuterium energies of ~450 keV. Recently, in preparation for alpha particle diagnostics in the DTE2 and DTE3 campaigns, dedicated alpha particle experiments wereconducted at JET [1]. These experiments utilized a combination of ICRF and NBI heating systems to generate the necessary high-energy deuterons. The resulting alpha production rate of ~1-2x10¹⁶ s^-1 enabled not only high-quality measurements of alpha particles [2], but also the observation of plasma instabilities driven by fusion-born alphas [3].

JT-60SA, the world-largest superconducting tokamak, will play a crucial role insupporting ITER and DEMO. It is equipped with a powerful NBI system, including both P-NBI and N-NBI, capable to deliver fast deuterons with energies up to 500 keV [4]. These characteristics make JT-60SA ideal for alpha-particle experiments in D-³He plasmas(there will be no tritium in JT-60SA to explore D-T fusion-born alphas), similar to thoseconducted at JET with a combination of P-NBI and ICRF systems. Following the closure of JET, JT-60SA is currently a unique tokamak for experimental studies of MeV-range fast ions and their impact on plasma confinement in large-scale tokamaks.

This proposed talk will first discuss recent JET experiments in D-³He plasmas, designed to prepare for future comparison experiments at JT-60SA. Specifically, in some of JET pulses discussed in this contribution, fast ions were deliberately generated off-axis, simulating the conditions expected with N-NBI ions at JT-60SA. We will proceed with discussing modeling results for a dedicated fast-ion scenario for alpha-particle studies in JT-60SA plasmas.The modeling shows that an alpha production rate of approximately 2-3x10¹⁶ s^-1 can beachieved with the high-power N-NBI system on JT-60SA at moderate ³He concentrations of 10-15%, surpassing the alpha production rate observed in D-³He plasmas on JET.The talk will conclude with a discussion on how future fast-ion experiments at JT-60SA can support the ITER rebaseline [5], particularly the development of alpha-particle diagnostics. This is a complex task, as most efforts have focused on exploiting alpha particle measurements using nuclear reactions between alpha particles and ⁹Be impurities. Due to the recent ITER decision to use a full-W wall, a new technique must be developed. We will present a proposed solution and explain how JT-60SA can contribute to this development.

[1] Ye.O. Kazakov et al., Phys. Plasmas 28, 020501 (2021)

[2] E. Panotin et al., Rev. Sci. Instrum. 92, 053529 (2021)

[3] V.G. Kiptily, Ye.O. Kazakov et al., Plasma Phys. Control. Fusion 64, 064001 (2022)

[4] JT-60SA Research Plan “Research Objectives and Strategy” (2018)

[5] A. Loarte et al., ‘The new ITER Baseline, Research Plan and Open R&D issues’ (2024)

* See the author list of “Overview of T and D-T results in JET with ITER-like wall” by C.F. Maggi et al., to be publishedin Nuclear Fusion Special Issue from the 29th Fusion Energy Conference (London, UK, 2023)

** See the author list of “Progress on an exhaust solution for a reactor using EUROfusion multi-machine capabilities”by E. Joffrin et al., to be published in Nuclear Fusion Special Issue from the 29th Fusion Energy Conference (London, UK, 2023)

ABSTRACT. Establishment of a refuelling method is an important issue for controlling nuclear fusion reactors. But, in DEMO-class high-temperature plasmas, a pellet injection reaches only up to 80-90% of the minor radius so that the central density peaking depends on particle pinch, making the prediction difficult. While turbulent particle transport has been studied based on local gyrokinetic models, it is also important to study global physics including the mean flow and the related neoclassical process. The global simulation is also meaningful to investigate impurity transport [1, 2] such as core Helium ash exhaust and edge impurity accumulation.

Based on this motivation, we perform flux-driven ITG/TEM simulations in the presence of ion/electron heating by means of the full-f electrostatic version of our global gyrokinetic code GKNET with a hybrid kinetic electron model [3]. This version enables us to precisely consider the self-consistent mean E_r determined by the radial force balance with the pressure and poloidal/toroidal flow profiles controlled by external source and sink. The global gyrokinetic ambipolarity condition can be also precisely treated so that we can investigate the physical mechanism of particle transport caused not only by non-axisymmetric ExB drift but also by axisymmetric ExB  and magnetic drifts which is responsible for the interactions between turbulent and neoclassical transport.

It is found that ion heating can drive turbulent ion particle pinch by ExB  drift (n ≠ 0) because the negative thermo-diffusion term becomes dominant. Turbulent electron particle pinch is also driven in the case with electron heating. Such an electron particle pinch can trigger an ambipolar field, leading to up-down asymmetric density perturbations and resultant ion particle pinch by not only magnetic drift but also ExB drift (n = 0) [4]. It suggests that a density peaking of bulk ions due to turbulent fluctuations can be achieved by sufficiently strong both ion and electron heating. It also implies that a scale separation between neoclassical and turbulent transport process is not satisfied and their interactions become essential, when the macroscopic structure changes on a turbulence time scale shorter than a collision time scale. We also perform flux-driven ITG/TEM simulation for deuterium, helium, electron and find that both helium ash exhaust and fuel supply can be achieved simultaneously by the similar mechanism discussed above.

In this talk, we will report the heating condition as well as the interaction between helium and bulk ion and electron transport in details.

[1] D. Estève et al., Nucl. Fusion 58, 036013 (2018).

[2] Y. Idomura et al., Phys. Plasmas 28, 012501 (2021).

[3] K. Imadera and Y. Kishimoto, Plasma Phys. Control. Fusion 65, 024003 (2023).

[4] K. Imadera et al., submitted to Nucl. Fusion.

ABSTRACT. Fusion-produced alpha particles have to be well confined in order to maintain the plasma at thermonuclear temperatures. But the presence of magnetic perturbations which can be produced by instabilities of various kinds, modify the magnetic structure of the confinement device and hence the transport properties of fast particles. In previous works we have analyzed the transport of fast ions across the region where a magnetic island is present comparing the predictions from a guiding center description and the full orbit ion trajectory [1]. That study is limited to the ion energies in the range of NBI heating, from 10 to 50 keV and it is found that the full orbit outflows are larger that those predicted by guiding center transport [2]. In addition, we study the transport of alpha particles with birth energies in the MeV range. The alphas are born in the plasma center and cross an island chain located at about the midradius. The analysis is done using a guiding center code (GCAF) and the full orbit code (KORC) for the case of a mid size tokamak. Resonance effects are found to be important for the particles to cross the island region, regarding the island width and the particle Larmor radius. In addition, for rotating islands, the rotation frequency has a resonant effect on the particle flow when it is of the order of the transit frequency or the trapping frequency. The study with the guiding center code can also be applied to the case of a stellarator with single helicity in order to estimate the non axisymmetric effects on the transport.

[1] Martinell J J, Carbajal L, Saavedra R 47th EPS Plasma Conference, P3.1083 (2021)

[2] Martinell J J, Carbajal L, 48th EPS Plasma Conference, P5b.125 (2022)

ABSTRACT. The progress has been reported [1-3] toward realizing a high-performance caesium(Cs)-free negative-ion source based on volume production in the magnetized sheet plasma device TPDsheet-U. In the experiments, H− ions have been successfully extracted from sheet plasma by using single-aperture grids when argon gas is added to hydrogen plasma at the external magnetic field strength of 38 mT. The experimental results with the single-aperture grid show that the performance of negative hydrogen ion current density (JC(H-)) of Cs-freeH− ion beam in TPD sheet-U is about one-fourth of that of Cs-containing H− ion sources in the negative-ion neutral-beam injector for ITER (NNBI) [4]. (i) The JC(H-) was ~7.5 mA/cm2 atan extraction voltage of 10 kV, a discharge current Id of 90 A, and a gas pressure of 0.3 Pa without argon. (ii) Co-extracted electrons JEG(e) are successfully suppressed by setting a softmagnetic filter (SMF) on plasma grid. The JEG(e)/JC(H-) ratio has been reduced to below 1.0 for a single-aperture grid with the SMF.

The basic studies have been carried out extensively in order to understand themechanisms of volume production of H− ions in the magnetized sheet plasma and its dependences on gas pressure, magnetic field strength and grid structures.

[1] K.Hanai, et. al., Fusion Eng. Des. 146 (2019) 2721.

[2] K.Kaminaga, et. al., Rev. Sci. Instrum. 91 (2020) 113302.

[3] K.Kaminaga, et. al., Fusion Eng. and Des. 168 (2021) 112676.

[4] A.Tonegawa, et. al., Nucl. Fusion 61 (2021) 106030.

ABSTRACT. Thermal plasma offers great opportunity for processing of wide range of materials. For instance, different wastes can be efficiently decomposed into individual elements and as aresult, valuable products can be obtained. One of such products is hydrogen, which is abundant in principle everywhere, its efficient large-scale production is inevitable for industry or as a fuel, but at the same time hydrogen production is still considered as a challenge. Indeed, hydrogen technologies are a very rapidly evolving field and there is a great demand for alternative methods of hydrogen production. At present, most hydrogen is produced with CO₂ as a by-product, namely by fossil fuels reforming. The fossil reserves of hydrocarbons/methane/natural gas are still huge, but their processing by currently used methods is apparently unsustainable. Research teams and petrochemical companies around the world are working intensively on this issue, and new technological solutions can be expected in the near future. In general, we can see in every day’s life that the way in which energy is produced and used changes fundamentally.

This contribution presents the overview of the research related to the production of hydrogen from methane (or natural gas) and other hydrocarbons using thermal plasma. The hydrogen produced this way is categorized as a turquoise hydrogen and can be considered as acomplementary to the well-known green and blue hydrogen production ways [1]. Produced hydrogen is characterized by high purity and at the same time we address the possibility ofusing the residual solid carbon, which can have a wide range of parameters. This is clearly the critical issue connected with turquoise hydrogen production, because once the produced solid carbon finds reasonable market, then the hydrogen produced this way becomes meaningful and competitive to other technologies. As an example from our laboratory research, we present the steam thermal plasma with very high enthalpy and low mass flow rate produced in the direct current arc discharge, which is in direct contact with water vortex surrounding the arc column[2, 3]. This thermal plasma source is attached to the reactor with internal volume 200 l, where interaction of the hydrocarbon flow with the plasma takes place. Results include characterization of the gaseous and solid product of the reaction. Both hydrogen and carbonare analysed with the intent of wide range of different applications and at the same time, almost zero CO2 (or other greenhouse gases) production.

[1] J. Diab, L. Fulcheri, V. Hessel, V. Rohani, M. Frenklach, Why turquoise hydrogen will bea game changer for the energy transition, Int. J. Hydrogen Energy 47 (2022) 25831-25848.

[2] A. Mašláni, M. Hrabovský, P. Křenek, M. Hlína, S. Raman, V. S. Sikarwar, M. Jeremiáš, Pyrolysis of methane via thermal steam plasma for the production of hydrogen and carbon black, Int. J. Hydrogen Energy 46 (2021) 1605-1614.

[3] A. Mašláni, M. Hlína, M. Hrabovský, P. Křenek, V. S. Sikarwar, J. Fathi, S. Raman, S.Skoblia, O. Jankovský, A. Jiříčková, S. Sharma, T. Mates, R. Mušálek, F. Lukáč, M. Jeremiáš, Impact of natural gas composition on steam thermal plasma assisted pyrolysis for hydrogenand solid carbon production, Energ. Convers. Manage. 297 (2023) 117748

ABSTRACT. A large amount of manure and its irrational use negatively affect the environment. By using plasma processing of manure, it is possible to enhance the process of obtaining synthesis gas (CO+H2) and increase plant productivity by 150–200 times over biomass fermentation. Plasma processes are characterized by high temperatures, which greatly reduce waste processing time. This paper examines the plasma processing of biomass using the example of dried mixed animal manure (dung with a moisture content of 30%). Characteristic composition of dung, wt.%: Н2О – 30, С – 29.07, Н – 4.06, О – 32.08, S – 0.26, N – 1.22, P2O5 – 0.61, K2O– 1.47, СаО – 0.86, MgO – 0.37.

The thermodynamic code TERRA was used to analyze the plasma gasification and pyrolysis of dung. The calculations were conducted in the temperature range of 300 to 3,000K and pressure 0.1 MPa for the following thermodynamic systems: 100% dung + 25% air (plasma gasification) and 100% dung + 25% nitrogen (plasma pyrolysis). At a temperature of 1,500 K, which provides complete gasification of dung carbon, the maximum yield of combustible components, and decomposition of toxic furan, dioxin, and benz(a)pyrene, the following composition of gas was obtained, vol.%: СО – 29.6, Н2 – 35.6, СО2 – 5.7, N2 – 10.6,H2O – 17.9 (gasification); СО – 30.2, Н2 – 38.3, СО2 – 4.1, N2 – 13.3, H2O – 13.6 (pyrolysis). Gasification and pyrolysis of dung require 1.28 and 1.33 kWh/kg of specific energy, respectively.

A reactor with a capacity of 50 kg/h with a 100 kW plasma torch was used to processdung experimentally. The dung was gasified in an air (or nitrogen during pyrolysis) plasma jet, which provided a mass-average temperature in the reactor volume of at least 1,600 K. Organic matter was gasified, and inorganic matter was melted. For pyrolysis and gasification of dung, the specific energy consumption was 1.5 kWh/kg and 1.4 kWh/kg, respectively. The maximum temperature in the reactor reached 1,887 K. A gas of the following composition was obtained, vol.%: СO – 25.9, H2 – 32.9, СO2 – 3.5, N2 – 37.3 (pyrolysis in nitrogen plasma); СO – 32.6,H2 – 24.1, СO2 – 5.7, N2 – 35.8 (air plasma gasification). The specific heat of combustion of the combustible gas formed during pyrolysis and plasma-air gasification of agricultural waste was 10,500 and 10,340 kJ/kg, respectively. Comparison of the integral indicators of dungplasma processing showed satisfactory agreement between the calculation and experiment.

ABSTRACT. Atmospheric pressure plasmas (APPs) in contact with liquid, which are defined as “gas-liquid interfacial plasmas (GLIPs)”, are widely used in chemical [1], medical [2], agricultural[3,4], and public health fields [5]. In these applications of GLIPs, the reactive species generated by the plasma in the gas and liquid phases, especially those with short lifetimes, are considered to play an important role.

The purpose of this study is to control the generation of short-lived reactive species using several lab-made GLIP devices, to measure them precisely, and to elucidate their chemical reaction mechanisms [6,7]. For this purpose, GLIP experiments using high-speed liquid-column flow [8] are conducted to investigate in detail the spatio-temporal dynamics of the short-lived reactive species in the liquid phase irradiated by a helium plasma. As a result,very fast decay (a half-life of ~ 0.1 msec) of OH radical was detected for the first time and explained with a numerical model assuming surface-localization of OH radical.

Furthermore, we are trying to measure not only OH radicals but also short-lived reactive nitrogen species (RNS). To achieve this purpose, we attempted to measure short-lived RNS, which are precursors of long-lived RNS such as nitrate and nitrite, using the GLIP system equipped with the high-speed liquid column flow. As a result, we have successfully measured the time decay of precursors of RNS using the reagent p-HPA (p-hydroxyphenylacetic acid), as cavenger of nitrite and nitrate precursors. The nitrite precursors were detected whereas nitrate precursors were below the detection limit, and the half-life of nitrite precursors was approximately 3 ms, which is obviously longer than 0.1 ms of OH. The results, such as the fact that only the precursor of nitrite decayed with time, led to the conclusion that the precursor of the reactive nitrogen species detected in the present study was N₂O₃. These findings will contribute to the fully controlled generation of short-lived reactive species at the plasma-liquid interface, and the resulting selectively generated short-lived reactive species will be extended to a wide range of applications in environmental science, plant science, drug discovery science, material science, and other fields.

[1] T. Chida, K. Hiromori, N. Shibasaki-Kitakawa, S. Sasaki, T. Kaneko, and A. Takahashi,Plasma Process. Polym. 21, e2300163 (2023).

[2] S. Sasaki, Y. Zheng, T. Mokudai, H. Kanetaka, M. Tachikawa, M. Kanzaki, and T. Kaneko,Plasma Process. Polym. 17, e1900257 (2020).

[3] K. Shimada, K. Takashima, Y. Kimura, K. Nihei, H. Konishi, and T. Kaneko, PlasmaProcess. Polym. 17, e1900004 (2020).

[4] S. Takeshi, K. Takashima, S. Sasaki, A. Higashitani, and T. Kaneko, Plasma Process.Polym. (2024) in press.

[5] S. Sasaki, S. Osana, T. Kubota, M. Yamaya, H. Nishimura, R. Nagatomi, and T. Kaneko,J. Phys. D. Appl. Phys. 55, 295203 (2022).

[6] Y. Kimura, K. Takashima, S. Sasaki, and T. Kaneko, J. Phys. D: Appl. Phys. 52, 064003(2019).

[7] T. Kaneko, K. Takashima, and S. Sasaki, Plasma Chem. Plasma Process. (2024) in press.

[8] K. Takeda, S. Sasaki, W. Luo, K. Takashima, and T. Kaneko, Appl. Phys. Express 14,056001 (2021).

ABSTRACT. The understanding of plasma turbulence is pivotal to describe several interesting features in both laboratory and space plasmas. For fluctuation length scales sufficiently larger than the ion inertial length scale, a plasma is described by magnetohydrodynamics (MHD), which is the simplest mono fluid model of plasma. However, space plasmas are often weakly collisional with sufficiently high thermal pressure and hence are associated with fluctuations with length scales sufficiently smaller than the ion inertial length scales. The corresponding fluctuations time scale is subsequently much smaller than the ion gyroperiod. In such a regime, the ions are practically immobile and the plasma can be described using electron magnetohydrodynamics (EMHD) where the electron fluid is primarily carrying both the inertia and the current while colliding with neutralizing medium of immobile ions.

Since the ion fluid velocity is negligible, the current (J) and the electron fluid velocity (v_e) are related as J = −nev_e. In addition, the electron fluid is assumed to be incompress-ible such that ∇ · v_e = 0. Similar to ordinary magnetohydrodynamics, here too we neglect the displacement current (∂ E/∂t) assuming non-relativistic fluid velocities and the resultinggoverning equation for inviscid electron MHD becomes [1] ∂∂td2e ∇2B − B = ∇ × ve × d2e ∇2B − B (1) which is simply a frozen-in field equation for d2e ∇2B − B in the electron fluid with velocity v_e with d_e = c/ω_pe = (m_e/μ₀n_e²)^1/2 being the electron inertial length. The total energy E, the sum of the kinetic energy of the electron fluid and the magnetic energy i.e.E =Z 12ρev2e + B22μ0dτ, is an inviscid invariant of EMHD and hence is expected to show universal turbulent cascade.

In this work, we derive a compact exact relation where we express the average energy cascade rate ε in terms of two point increments of field variables and is written as⟨δ [ve × (ρeωe − neB)] · δ ve⟩ = 2ε, (2) where ω is the electron fluid vorticity. By using the condition of vanishing cascade [2], it has been shown that the flow relaxes towards a pressure-balanced relaxed state given by v_e ×(ρ_eω_e − neB) = ∇p_e. The universal cascade and the relaxation are also numerically studied by the help of direct numerical simulations.

%SVL correct equations

[1] A. Das and P. Kaw, Physics of Plasmas 8, 10 (2001)

[2] S. Banerjee, A. Halder and N. Pan, Physical Review E Letters 107, L043201 (2023)

ABSTRACT. Hall magnetohydrodynamics (HMHD) is a single fluid plasma model often employed to study sub-ion scale plasma dynamics. Unlike ordinary MHD, HMHD system allows a finite difference between ion and electron fluid velocities. The Hall effect is modelled in the induction equation by adding a nonlinear term −di∇∇∇ × ( jjj × bbb) where di is the ion inertial length, bbb is the magneticfield (normalized to a velocity) and jjj = ∇∇∇ × bbb. Therefore the Hall effect becomes important for length scales comparable or smaller than di.

In a turbulent plasma, the Hall effect plays a pivotal role by introducing a novel backscatter of magnetic energy which is found to be important for dynamo growth of magnetic field. By decomposing the Hall term in two parts namely di( jjj · ∇∇∇)bbb and −di(bbb · ∇∇∇) jjj one can separately measure the contributions of bbb and jjj-field to the dynamo action [1]. Along with the backscatter, the Hall effect is believed to introduce non-locality in the scale-to-scale energy transfer process [2]. In our current work [3], using data from simulation with 5123 grid points, we numerically investigate the locality of the energy transfer for two parts of the Hall term separately.

%SVL: add figure Figure 1: Shell-to-shell transfer rates for bbb-to-bbb (left panel) and jjj-to-bbb (right panel) transfers.

Fig. (1) shows the shell-to-shell transfers rates for the two parts mentioned before where T x, ym, n signifies net transfer rate from shell n of y-field to shell m of x-field. For all the shells, it is found that bbb-to-bbb channel shows strong local inverse cascade and weak non-local forward cascade (Fig. 1a). In contrast, for scales greater than di (corresponding to shell number 11)jjj-to-bbb channel shows weak inverse cascade both locally and nonlocally (Fig. 1b). However, for length scales smaller than di, the jjj-to-bbb transfer become strongly local and forward in nature. A phenomenological explanation is also provided based on the power spectra of bbb and jjj.

[1] A. Halder et. al., Phys. Rev. Fluids 8, 053701 (2023).

[2] Mininni et. al., J. Plasma Phys. 7, (2007).

[3] A. Halder et. al., manuscript in preparation, (2024)

%SVL: get expressions correct in final version

ABSTRACT. Turbulence in classical fluids is characterized by persistent structures that emerge from the chaotic landscape. We investigate the analogous process in fully kinetic plasma turbulence by using high-resolution, direct numerical simulations in two spatial dimensions. We observe the formation of long-lived vortices with a profile typical of macroscopic, magnetically dominated force-free states. Inspired by the Harris pinch model for inhomogeneous equilibria, we describe these metastable solutions with a self-consistent kinetic model in a cylindrical coordinate system centered on a representative vortex, starting from an explicit form of the particle velocity distribution function. Such new equilibria can be simplified to a Gold–Hoyle solution of the modified force-free state [1]. Turbulence is mediated by the long-lived structures, accompanied by transients in which such vortices merge and form self-similarly new metastable equilibria. This process can be relevant to the comprehension of various astrophysical phenomena, going from the formation of plasmoids in the vicinity of massive compact objects to the emergence of coherent structures in the heliosphere.

[1] T. Gold and F. Hoyle, Monthly Notices of the Royal Astronomical Society 120, 89 (1960)

ABSTRACT. The study of magnetically confined fusion involves complex physics that spans disparate time and length scales, requiring diverse simulation strategies ranging from magnetohydrodynamics (MHD) to particle-based models. While single-fluid MHD simulations are computationally efficient, they fail to capture critical phenomena at smaller scales. Conversely, particle-based methods, though accurate, are computationally prohibitive for full-domain simulations. The two-fluid MHD model provides a middle ground, significantly reducing computational complexity while preserving essential physical details lost in standard MHD models.

This work introduces novel algorithms for solving the two-fluid MHD equations using a finite volume approach, with a focus on enhancing simulation efficiency. Key innovations include relaxing the time step restrictions imposed by the speed of light constraint through an implicit Maxwell solver, and the use of a locally implicit treatment for stiff source terms. These advancements allow for larger time steps and reduced computational costs without sacrificing accuracy.

Additionally, this study extends the multi-physics approach to capture plasma-wall interactions using a rigid body ghost fluid method, enabling the simultaneous simulation of plasma and material interactions within a unified computational domain. The implemented algorithms are highly parallelized and validated against established benchmarks, including shock-capturing problems, magnetic reconnection scenarios, and the demonstration of two-fluid effects. The results show a significant reduction in computational time compared to traditional fully explicit methods, highlighting the potential of these new approaches to accelerate the development of efficient and accurate plasma simulations for nuclear fusion research.