ABSTRACT. Generating a powerful and quasistatic magnetic field within the confines of a tabletop laboratory experiment has proven to be a persistent challenge. Magnetized high energy density physics through such experiments presents significant opportunities for exploring and studying several terrestrial as well as astrophysical phenomena, apart from controlling relativistic electron transport, directly relevant for fusion schemes.

Here we demonstrate that the modest magnetic field (0.1 tesla) in a common, readily available Neodymium magnet excited by an ultra-intense, femtosecond laser pulse leads to the generation and amplification of axial quasistatic magnetic field to megagauss levels lasting a few picoseconds. The experimental findings are strongly supported by particle-in-cell simulations, which not only validate the observations but also unveil a potential dynamo mechanism responsible for the enhancement and amplification of the axial magnetic field [1].

We also experimentally demonstrate that this modest (0.1 Tesla), static magnetic field guides 100s keV-MeV energy, mega-ampere electron pulses over macroscopic distances.These pulses, driven by an ultrahigh intensity, femtosecond laser, propagate like a beam a distance as large as 5 mm in a high Z target (neodymium), their collimation improved, and flux density enhanced nearly by a factor of 3 [2]. Unlike the previous studies that used 100s Teslaor kilotesla fields [3,4], our studies may prove more amenable for fast electron beam-driven radiation sources, fast ignition of laser fusion, and laboratory astrophysics.

[1] Anandam et al., (in preparation)

[2] Anandam et al., arXiv:2311.06884 (2023)

[3] H.-b. Cai, S.-p. Zhu, and X. T. He, Physics of Plasmas, 20, 072701 (2013)

[4] M. Bailly-Grandvaux, et al., Nature Communications, 9, 102 (2018)

ABSTRACT. Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black-hole and neutron-star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with electron-positron pairs. Their role in the dynamics of such environments is in many cases believed to be fundamental, but their behaviour differs significantly from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies, which are rather limited. Here we present the first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN's Super Proton Synchrotron (SPS) accelerator. We show that the characteristic scales necessary for collective plasma behaviour, such as the Debye length and the collisionless skin depth, are exceeded by the measured size of the produced pair beams. In the first application of this experimental platform, the stability of the pair beam is studied as it propagates through a meter-length plasma, analogous to TeV γ-ray induced pair cascades in the intergalactic medium. It has been argued that pair beam instabilities disrupt the cascade, thus accounting for the observed lack of reprocessed GeV emission from TeV blazars. If true this would remove the need for a moderate strength intergalactic magnetic field to explain the observations. We find that the pair beam instability is suppressed if the beam is not perfectly collimated or monochromatic, hence the lower limit to the intergalactic magnetic field inferred from γ-ray observations of blazars is robust.

ABSTRACT.  Joydeep Ghosh1,2, M. B. Chowdhuri1, Aman Gauttam1, N. Ramaiya1, BharatHedge1,2, Kaushlender Singh1,2, Suman Dolui1,2, Ashok Kumawat1,2, Dipexa Modi3, SoumitraBanerjee1,2, Injamul Houqe1,2, Komal1,2, Harshita Raj1,2, K. A. Jadeja1, Ankit Patel1, PramilaGautam1, Utsav1, K. Shah4, G. Shukla1, N. Yadava5, Tanmay Macwan6, S. Patel3, LaxikantaPradhan1, Suman Aich1, A. Kanik7, Rohit Kumar1,2, Priyanka Verma1, K.M. Patel1, KalpeshGadoliya1, R. L. Tanna11Institute for Plasma Research, Bhat, Gandhinagar, Gujarat 382 428, India2Homi Bhabha National Institute, Training School Complex, Mumbai 400094, India3 Pandit Deendayal Petroleum University, Raisan, Gandhinagar, Gujarat 382007, India4Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543,USA5Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831, USA6Physics and Astronomy Department, University of California, Los Angeles, California90098, USA7University of Petroleum & Energy Studies, Dehradun 248007, India

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In both Hydrogen & Deuterium discharges, intrinsic toroidal rotation has been observed using Doppler shifts in spectral lines of the main impurity ions (C5+ ions, emitting at 529.05nm) in ADITYA-U tokamak without applying any external torque to the plasma. Inpurely Hydrogen discharges, intrinsic toroidal rotation reverses its direction from counter-current to co-current on increasing the plasma current beyond a certain threshold value. However, this intrinsic toroidal rotation (measured in the edge region) is observed to damp to zero as soon as the edge electron density is increased [1]. In Hydrogen discharges, E×B driftvelocity is found to drive the observed intrinsic toroidal rotation in the edge region of ADITYA-U. A recent and a new study of the isotopic effect is performed on the intrinsic toroidal rotation in ADITYA-U tokamak, which will be discussed in this paper.

[1] Ankit Kumar et al 2024 Nucl. Fusion (DOI: https://doi.org/10.1088/1741-4326/ad4c5a,Accepted Manuscript Title: Effect of impurity seeding on edge toroidal rotation in ADITYA-U tokamak)

ABSTRACT. Intense ultrashort pulse lasers generate relativistic electrons when the intensity reaches relativistic scales, 10¹⁸ Wcm^-2 for 800nm pulses. This requires Terra watt class lasers that are complex, cumbersome, expensive and deliver typically 10 pulses per second. While the electron/x-rays/proton beams generated from such system have shown a lot of promise, developing applications on such systems is very challenging. I will talk about experiments where even at a 1/100th of laser intensity, it is feasible to generate relativistic electron beam of 1 MeV energy with multi kHz few mJ/pulse lasers. We show that plasma wave instabilities generated and manipulated  with suitable targetry is the underlying mechanism. The source size of the short pulse electron beam is amenable for x-ray radiography and shadowgraphy

ABSTRACT. Plasma optics are promising new tools to guide, shape, or even amplify ultrahigh-power, ultrashort laser pulses [1]. They have the unique potential to liberate ultrafast laser technology from the strong limitations posed by optical damage in conventional optical elements and so further increase the peak power of state-of-the-art lasers. However, the plasma is inherently dynamic, highly complex, and challenging to control, so it can easily degrade the spatio-temporal structure of the optical pulse. Therefore, to design and operate plasma optics, a precise characterization of the complex spatio-temporal and spatio-spectral profile of the laser pulse and the instantaneous dynamics of the plasma surface is highly desired. Furthermore, as ultra high-power laser systems have a low repetition rate down to single-shot operation, this spatio-temporal characterization is mandatory on a single-shotbasis. This was not demonstrated before, so it represents a serious gap.

Here, we present three-dimensional (3D) spatio-temporal measurements of such pulses based on spectral interferometry [2,3]. We measure the complex space-time distortions induced in the laser pulses by relativistic plasma while simultaneously capturing the underlying plasma dynamics, all in a single shot. This all-optical technique can capture 3D spatio-temporal couplings within pulses at ultra-high peak powers, enabling further progress in ultra-high-intensity laser and plasma technologies.

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[1] C. Riconda, et. al., Matter Radiation at Extreme 8, 023001 (2023)

[2] A. Dulat, et al., arXiv: 2310.11027 (2023)

[3] A. Dulat, et al., Optics Letter 47, 5684 (2022)

ABSTRACT. In this work, we use two-fluid simulations to investigate the nonlinear regime of the electrojet plasma instabilities responsible for the formation of electron density irregularities in the ionospheric E region [1]. We employ a 2-D model of partially ionized plasma, originally developed in [2] for studying E×B plasma discharges. The model unifies closely related plasma instabilities, such as the Simon-Hoh/gradient-drift, Farley-Buneman and lower-hybrid instabilities, and captures multiscale effects, including electron inertia and finite-Larmor-radius effects. We report on the development of secondary nonlinear instabilities and formation of large-scale plasma structures (the inverse cascade processes) leading to the nonlinear saturated state. We demonstrate that these large-scale structures play a crucial role in the development of the electrojet plasma turbulence. A comparison of computational results with experimental data is provided.

Acknowledgements. This work is partially supported by funding from the Natural Sciences and Engineering Council of Canada (NSERC), University of Saskatchewan Research grant 421980 to AVK, computational resources from the Digital Research Alliance of Canada, and Simons Collaboration on Hidden Symmetries and Fusion Energy.

[1] Hassan, Ehab, et al. "Multiscale equatorial electrojet turbulence: Baseline 2‐D model."Journal of Geophysical Research: Space Physics 120.2 (2015)

[2] Smolyakov, A. I., et al. "Fluid theory and simulations of instabilities, turbulent transportand coherent structures in partially-magnetized plasmas of discharges." Plasma Physics andControlled Fusion 59.1 (2017)

ABSTRACT. Observations conducted in Titan's ionosphere have unveiled the presence of various ions possessing either positive or negative charge [1] along with different blends of electron populations (at different altitudes) practically following a Maxwell-Boltzmann distribution[2]. From a fundamental (theoretical) point of view, it is well established that the coexistence of ions with opposite charges leads to novel phenomena, notably including the possibility of polarity reversal in localized modes, such as electrostatic solitary waves.

In this work, we shall thoroughly investigate the potential occurrence of ion-acoustic solitary waves in the ionospheric plasma of Titan. A bi-ion plasma-fluid model with two electron populations (with different temperatures) in the background has been adopted as a starting point to explore the nonlinear propagation features of ionic scale electrostatic solitary waves that may occur in Titan’s ionosphere from first principles. We have employed nonlinear (multiscale) perturbation techniques, in an effort to reduce the fluid model to a nonlinear evolution equation governing the electrostatic potential. Considering different plasma compositions, including critical configurations where the nature of nonlinearity is known tochange [3], different partial-differential equations have been obtained, incorporating quadraticor cubic nonlinearity as well as combinations thereof, thus describing diverse scenarios for the solitary wave propagation characteristics. The parametric influence of the plasma composition, in terms of the relative electron concentration (cool-to-hot electron density) and the relative (negative-to-positive) ion density, on the solitary wave features has been investigated. Different possibilities have been predicted, including positive and negative polarity pulses and double layers, whose characteristics (amplitude, width, polarity) dependon the plasma configuration.

Our theoretical findings should provide valuable insight into the criteria for existence and the dynamics of electrostatic solitary wave structures occurring in Titan's ionosphere, with an ambition to contribute to the prediction and interpretation of future observations.

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

[1] A. J. Coates, et al., Geophysical Research Letters, 34, L22103 (2007).

[2] A. Chatain, et al., Journal of Geophysical Research: Space Physics, 126, 1 (2021).

[3] F. Verheest, J. Plasma Phys. 39, 71 (1988); ibid, 81, 905810605 (2015).