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The mixing process of the cathodic jets is an important connection between the metal surface and the plasma arc column, which helps to understand the diffusion mechanism of the vacuum arc and guides the vacuum switch design. The interaction process of double cathode jets is simulated using a 3D magnetohydrodynamic method. This study analyzes the evolution of plasma parameters as the double cathode jets transition from a separated state to a mixed state. The results indicate that a mixed single-peaked jet ultimately forms at the exit when the double cathode jets are present at the inlet of the cathode surface. The transition from the separated state to the mixed state occurs further away from the cathode surface as the inlet current density of the jets increases from 3 to 5 × 109 A/m2. Additionally, the asymmetry in the current density of the double cathode jets causes the peaks of the mixed single-peak current density and ion temperature to be skewed toward the direction of the lower inlet current density. In cases where the inlet current direction is asymmetric, the peaks shift toward the direction where the inlet current is perpendicular to the cathode surface. Furthermore, the outward expansion acceleration trend of the plasma aligns well with the results from single-jet numerical simulations. [ABSTRACT FROM AUTHOR]

We investigate the dynamics of plasma-based acceleration processes with collisionless particle dynamics and non-negligible thermal effects. We aim at assessing the applicability of fluid-like models, obtained by suitable closure assumptions applied to the relativistic kinetic equations, thus not suffering from statistical noise, even in the presence of a finite temperature. The work here presented focuses on the characterization of pressure anisotropies, which crucially depend on the adopted closure scheme, and hence are useful to discern the appropriate thermal fluid model. To this aim, simulation results of spatially resolved fluid models with different thermal closure assumptions are compared with the results of particle-in-cell simulations at changing temperature and amplitude of plasma oscillations. [ABSTRACT FROM AUTHOR]

The EuPRAXIA EU project is at the forefront of advancing particle accelerator research and the development of photon sources through innovative plasma acceleration approaches. Within this framework, the EuAPS project aims to exploit laser wakefield acceleration to build and operate a betatron radiation source at the INFN Frascati National Laboratory. The EuAPS source will provide femtosecond X-ray pulses in the spectral region between about 1 and 10 keV, unlocking a realm of experimental ultrafast methodologies encompassing diverse imaging and X-ray spectroscopy techniques. This paper presents a description of the EuAPS betatron source, including simulations of the photon beam parameters, outlines the preliminary design of the dedicated photon beamline, and provides an insightful overview of its photon science applications. [ABSTRACT FROM AUTHOR]

After leaving the Sun’s corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. Alfvén waves are perturbations of the interplanetary magnetic field that transport energy. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecraft to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the plasma between the outer edge of the corona and near the orbit of Venus, along with the presence of large-amplitude Alfvén waves. We calculate that the damping and mechanical work performed by the Alfvén waves are sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere. [ABSTRACT FROM AUTHOR]

Efficient laser-driven plasma acceleration of ion beams requires precision control of the target–plasma profile, which is crucial to optimize the laser energy transfer. Along the laser propagation direction, this can be achieved by tailoring the temporal structure of the laser pulse. We show for the first time that frequency-doubling of a short pulse (hundreds-femtosecond range) petawatt-class mixed-glass laser system, which results in temporal intensity contrast enhancement, enables surface and volumetric laser–energy coupling, and the acceleration of proton beams from few-nanometer-thick foil targets. Experimentally, maximum ion energies and laser-to-proton energy conversion efficiencies were found to be both maximized at optimum laser and target conditions manifested when the normalized target density nearly equalizes the normalized laser vector potential, which is in agreement with theory and simulations. These signatures are recognized as a unique indication of the interaction between ultra-intense laser pulses with high temporal intensity contrast and ultra-thin nanometer-scale targets. Transverse modulations of accelerated proton beams in the form of bubble- and ring-like structures measured in the thinnest targets provide additional evidence of volumetric laser-driven particle acceleration regimes and transitional features in ultra-thin foil targets specific to laser–plasma interactions characterized by a high temporal intensity contrast. These results open avenues in the generation of high contrast laser pulses from short-pulse-femtosecond petawatt mixed-glass laser systems and demonstrate the feasibility of this technique for applications requiring high laser intensity contrast with high efficiency. [ABSTRACT FROM AUTHOR]

Plasma wakefield acceleration revolutionized the field of particle accelerators by generating gigavolt-per-centimeter fields. To compete with conventional radio-frequency (RF) accelerators, plasma technology must demonstrate operation at high repetition rates, with a recent research showing feasibility at megahertz levels using an Argon source that recovered after about 60 ns. Here we report about a proof-of-principle experiment that demonstrates the recovery of a Hydrogen plasma at the sub-nanosecond timescale. The result is obtained with a pump-and-probe setup and has been characterized for a wide range of plasma densities. We observed that large plasma densities reestablish their initial state soon after the injection of the pump beam (< 0.7 ns). Conversely, at lower densities we observe the formation of a local dense plasma channel affecting the probe beam dynamics even at long delay times (> 13 ns). The results are supported with numerical simulations and represent a step forward for the next-generation of compact high-repetition rate accelerators. The authors report about a proof-of-principle experiment that demonstrates the recovery of a Hydrogen plasma accelerator at the sub-nanosecond timescale. The result is obtained with a pump-andprobe setup and represent a step forward for the next-generation of compact high-repetition rate plasma-based accelerators. [ABSTRACT FROM AUTHOR]

Introduction. One of the directions of development of plasma technologies consists in the formation of gas-metal plasma formations and throwing them to a certain distance. Known thrusters of plasma formation either have an electrode system that is prone to erosion, or a discharge system in a solid dielectric substance in which ablation occurs, or a complex gas-dynamic system with fuel supply. They do not provide acceleration of plasma formation in the atmosphere for a significant distance. Purpose. A theoretical and experimental study of electromechanical and thermophysical processes in a plasma thruster, which ensures the formation of a plasma formation due to thermal ionization by an induced current in a thin conductor layer during a high-voltage discharge on an inductor and the accelerating of a plasma formation in the atmosphere for a significant distance. Methodology. The proposed concept of a plasma thruster, in which the inductor inductively interacts with a combined armature, which includes an aluminum armature in the form of a thin (0.5-1 μm) foil, a copper armature made of a thicker foil (35-50 μm).On the basis of a mathematical model that takes into account the uneven distribution of currents in the inductor and conductive armatures, the features of the process of acceleration the combined armature in the atmosphere were established and experimental studies were carried out. Results. The electromechanical and thermal characteristics of the plasma thruster were calculated. It was established that the choice of the thickness of the dielectric layer of the armature, to which the aluminum and copper armatures are attached, is determined by the energy balance between the heating temperature of the aluminum armature and the electromechanical indicators of the thrower. Scientific novelty. It was experimentally established that the greatest density and homogeneity is observed in the middle of the plasma formation, which has the shape of a torus, moving away from the dielectric sheet on which the aluminum armature was located. As the voltage of the capacitive energy storage increases, the induced current density in the armature increases and the plasma formation becomes more uniform. Practical value. In comparison with the experimental results, the calculated current in the inductor coincides both in shape and in magnitude with an accuracy of 7 %. The biggest difference between the calculated and experimental currents of the inductor occurs when the aluminum armature is thermally destroyed. The transition of an aluminum armature into a plasma formation depends significantly on the voltage of the capacitive energy storage. References 26, figures 16. [ABSTRACT FROM AUTHOR]

The recently demonstrated concept of the plasma photocathode, whereby a high-brightness bunch is initialized by laser ionization within a plasma wakefield acceleration bubble, is informally referred to as Trojan Horse wakefield acceleration. In a similar vein, the dielectric Trojan Horse concept incorporates a dielectric-lined waveguide to support a charged particle beam-driven accelerating mode and uses laser initiated ionization of neutral gas within the waveguide to generate a witness beam. One of the advantages of the dielectric Trojan Horse concept is the reduced requirements in terms of timing precision due to operation at a lower frequency. In this paper, we present experimental results on the generation and characterization of a four-bunch drive train for resonant excitation of wakefields in a cylindrical dielectric waveguide conducted at the Argonne Wakefield Accelerator facility. The results lay the foundation for the demonstration of a plasma photocathode scheme within a dielectric wakefield accelerating structure. Modifications to improve capture efficiency with improved beam transmission are suggested as well. [ABSTRACT FROM AUTHOR]

Beam stability and timing jitter in modern linear accelerators are becoming increasingly important. In particular, if a magnetic or radio-frequency (RF) compression regime is employed, the beam time of arrival jitter at the end of the linac can be strictly correlated with the phase noise of the accelerating fields of the RF structure working off-crest. For this reason, since 2008, an RF fast-feedback technique, which acts within each RF pulse, has been successfully employed at LNF-INFN (Laboratori Nazionali di Frascati dell'Istituto Nazionale di Fisica Nucleare) in the SPARC_LAB (Sources for Plasma Accelerators and Radiation Compton with Laser And Beam) facility on S-band (2856 MHz) klystrons powered by pulse-forming network (PFN) modulators, as reported in this paper. However, in order to meet the more stringent requirements of plasma wakefield acceleration schemes, some upgrades to this feedback system have been recently carried out. The first prototype has been experimentally tested on a C-band (5712 MHz) klystron, driven by a solid-state modulator, in order to investigate the possibility for additional improvement resulting from the inherently more stable power source. In this paper, the design, realization and the preliminary measurement results obtained at SPARC_LAB after such upgrades will be reviewed. [ABSTRACT FROM AUTHOR]

Dust populations in space plasmas are often described by a size distribution function, generally a power law distribution. In view of that, we include this feature in the kinetic description of a homogeneous magnetized dusty plasma with electrically charged immobile dust grains, in order to study its effects in the propagation and damping of Alfvén waves. The dispersion relation is numerically solved using parameters typically found in the dust-driven stellar winds of carbon-rich stars and in Earth's auroral acceleration region, two space systems with unalike plasma parameters and in which Alfvén waves are known to play important roles in the plasma acceleration and heating processes. We show that the characteristics of the normal modes, namely the ion cyclotron and whistler modes, will change when one considers a power law distribution of dust sizes in the theory, as compared to a mono-sized dust population; and that these differences will depend on the exponent p of the power law, which alters the plasma charge imbalance between electrons and ions. We also notice that power-law distribution functions will modify the waves' damping rate values. In particular, we show that in a stellar wind environment the ion cyclotron mode at very small wavenumber decreases with the reduction of p , while for higher wavenumber the damping of this mode increases with the reduction of p. For the Earth's magnetosphere, the results obtained show that the wave damping increases with the decrease of p for all wavenumbers, for the parameters considered in the analysis. [ABSTRACT FROM AUTHOR]

Laser Wakefield Acceleration (LWFA) has emerged as a groundbreaking approach for generating ultra-high energy electron beams over short distances, revolutionizing the field of particle acceleration. In this paper, we investigate the novel concept of employing sin-Gaussian laser pulse for enhanced LWFA performance. sin-Gaussian pulses combine the advantageous features of both sinusoidal and Gaussian pulse shapes, offering unique opportunities for generating the plasma wakefield and optimizing electron acceleration. We present a comprehensive theoretical analysis of the interaction between a sin-Gaussian laser pulse and an underdense plasma medium, elucidating the intricate dynamics of the wakefield excitation and electron acceleration. Through analytical study, we demonstrate that the sin-Gaussian pulse configuration leads to a significant energy gain (Maximum gain of 2.06 GeV with chosen parameters) for plasma electrons. Furthermore, we explore the effects of varying key parameters such as the laser electric field amplitude and beam waist on the acceleration performance. Our findings reveal the underlying physics governing the interplay between these parameters and the resulting electron energy spectra for LWFA outcomes. [ABSTRACT FROM AUTHOR]

Kinetic simulations of relativistic turbulence have significantly advanced our understanding of turbulent particle acceleration. Recent progress has highlighted the need for an updated acceleration theory that can account for particle acceleration within the plasma's coherent structures. Here, we investigate how intermittency modeling connects statistical fluctuations in turbulence to regions of high-energy dissipation. This connection is established by employing a generalized She–Leveque model to characterize the exponents ζ p for the structure functions S p ∝ l ζ p . The fitting of the scaling exponents provides us with a measure of the codimension of the dissipative structures, for which we subsequently determine the filling fraction. We perform our analysis for a range of magnetizations σ and relative fluctuation amplitudes δ B 0/ B 0. We find that increasing values of σ and δ B 0/ B 0 allow the turbulent cascade to break sheetlike structures into smaller regions of dissipation that resemble chains of flux ropes. However, as their dissipation measure increases, the dissipative regions become less volume filling. With this work, we aim to inform future turbulent acceleration theories that incorporate particle energization from interactions with coherent structures within relativistic turbulence. [ABSTRACT FROM AUTHOR]

The Juno spacecraft had previously observed intense high frequency wave emission, broadband electron and energetic proton energy distributions within magnetic flux tubes connected to Io, Europa, Ganymede, and their wakes. In this work, we report consistent enhancements in <46 keV energy proton fluxes during these satellite flux tube transit intervals. We find enhanced fluxes at discrete energies linearly separated in velocity for proton distributions within Io wake flux tubes, and both proton and electron distributions within Europa and Ganymede wake flux tubes. We propose these discrete enhancements to be a result of resonances between particles' bounce motion with standing Alfvén waves generated by the satellite‐magnetosphere interaction. We corroborate this hypothesis by comparing the bounce and field‐line resonance periods expected at the satellites' orbits. Hence, we find bounce‐resonant acceleration is a fundamental process that can accelerate particles in Jupiter's inner magnetosphere and other astrophysical plasmas. Plain Language Summary: The passage of the Galilean moons‐ Io, Europa, Ganymede, and Callisto, perturbs the plasma flow in Jupiter's magnetosphere, creating waves that travel from the moon and reflect off Jupiter's ionosphere. These waves have been proposed to accelerate charged particles, and such accelerated particles had been observed by the Juno spacecraft during its passage through magnetic field lines connected to the satellite wakes. In this work, we find instances when this acceleration occurs selectively at specific energies that have constant separation in speed. We propose that this selective acceleration is due to resonance between particle bounce motion and the waves arising from the satellite wake perturbation. Bounce‐resonant acceleration is a promising fundamental process which can accelerate particles in Jupiter's inner magnetosphere and other plasma systems with similar geometries. Key Points: Proton and electron flux enhancements in satellite and wake flux tubes often occur at discrete energies linearly separated in speedBroadband proton flux enhancements at <46 keV energies were also observed within satellite flux tube crossingsParticles can be accelerated via resonance between bounce motion and standing Alfvén waves generated by moon‐magnetosphere interactions [ABSTRACT FROM AUTHOR]

The laser wakefield acceleration (LWFA) scheme is now a superb and potent instrument for industry, medicine, fusion, and other uses. With the aid of this technique, high-quality electron beams can be generated, which might eventually be employed to create small, portable X-ray sources. Using a linearly polarized Gaussian laser pulse, the present work focuses on examining electron acceleration in an under-dense plasma having a ramp profile with different density-hill widths. Two-dimensional Fourier–Bessel Particle-In-Cell simulation (2D-FBPIC) code shows that optimizing the laser parameters and plasma density profile maximizes the energy gain and minimizes the normalized rms emittance in the x, y directions inside the plasma bubble. For 10 and 90 μ m density-hill widths, respectively, the optimal emittance value is reported to be ϵ x ∼ 3.10 mm.mrad in the x-direction and ϵ y ∼ 2.63 mm.mrad in the y-direction. At a density-hill width of 90 μ m , it is also observed that the charge trapped inside the bubble is 44.91 pC. With this density-hill width and a plasma channel length of 3.84 mm, our simulation findings show an energy gain of 0.38 GeV to the electron-bunch accelerated inside the bubble. [ABSTRACT FROM AUTHOR]

Plasma toroidal rotation acceleration in the co-current direction introduced by the n = 1 (toroidal mode number) static resonant magnetic perturbation (RMP) has been observed in the EAST tokamak. It strongly depends on the RMP coil configuration, which is manifested by its dependence on δ ϕ U L (phase difference between upper and lower coils) and RMP current. Modeling results from NTVTOK based on the linear plasma response modeled by MARS-F shows that the Neoclassical Toroidal Viscosity (NTV) torque is in the co-current direction because of the dominant contribution from electrons with the condition that the electron normalized collisionality is much lower than that of ions in this experiment. The modeled dependence of core integrated NTV torque modulated by the magnitude of core magnetic perturbation on δ ϕ U L is consistent with the experimental observations. Threshold condition related to normalized collisionality to achieve the transition from rotation braking to acceleration is obtained in the NTV modeling and agrees well with experimental observations. It is shown in the modeling that the discharges with rotation acceleration are located at the regime that electron contribution to NTV is dominant and the torque is in co-current direction, while others with rotation braking are located at the regime that ion contribution to NTV torque is dominant and the torque is in countercurrent direction. Though the modeling results are in qualitative agreement with the experimental results, there is quantity difference between the modeled NTV torque based on linear plasma response and the experimental values. Possible reason is that the 3D fields are underestimated by linear modeling, particularly in the case of RMP field penetration, as demonstrated by the RMP current threshold for the rotation acceleration observed in the experiments. [ABSTRACT FROM AUTHOR]

We have recently proposed a new technique of plasma tailoring by laser-driven hydrodynamic shockwaves generated on both sides of a gas jet [Marquès et al., Phys. Plasmas 28, 023103 (2021)]. In a continuation of this numerical work, we study experimentally the influence of the tailoring on proton acceleration driven by a high-intensity picosecond laser in three cases: without tailoring, by tailoring only the entrance side of the picosecond laser, and by tailoring both sides of the gas jet. Without tailoring, the acceleration is transverse to the laser axis, with a low-energy exponential spectrum, produced by Coulomb explosion. When the front side of the gas jet is tailored, a forward acceleration appears, which is significantly enhanced when both the front and back sides of the plasma are tailored. This forward acceleration produces higher-energy protons, with a peaked spectrum, and is in good agreement with the mechanism of collisionless shock acceleration (CSA). The spatiotemporal evolution of the plasma profile is characterized by optical shadowgraphy of a probe beam. The refraction and absorption of this beam are simulated by post-processing 3D hydrodynamic simulations of the plasma tailoring. Comparison with the experimental results allows estimation of the thickness and near-critical density of the plasma slab produced by tailoring both sides of the gas jet. These parameters are in good agreement with those required for CSA. [ABSTRACT FROM AUTHOR]

Particle-driven plasma wakefield acceleration (PWFA) exploits the intense wakefields excited in a plasma by a high-brightness driver beam in order to accelerate a trailing, properly delayed witness electron beam. Such a configuration offers notable advantages in achieving very large accelerating gradients that are suitable for applications in particle colliders and photon production. Moreover, the amplitude of the accelerating fields can be enhanced by resonantly exciting the plasma using a multi-pulse driver beam with a proper time structure. Before the injection into the plasma stage, the pulsed electron beam, conventionally termed the comb beam, is usually produced and pre-accelerated in a radio-frequency (RF) linear accelerator (linac). In this pape, we discuss challenging aspects of the dynamics that comb beams encounter in the RF injector stage preceding the plasma. In particular, the examples we analyze focus on the use of velocity bunching to manipulate the time structure of the beam and the impact of dipole short-range wakefields on the transverse emittances. Indeed, both processes crucially affect the phase space distribution and its quality, which are determinant features for an efficient acceleration in the plasma. In addition, the analyses we present are performed with the custom tracking code MILES, which utilizes semi-analytical models for a simplified evaluation of wakefield effects in the presence of space charge forces. [ABSTRACT FROM AUTHOR]

Modeling plasma accelerators is a computationally challenging task and the quasi-static particle-in-cell algorithm is a method of choice in a wide range of situations. In this work, we present the first performance-portable, quasi-static, three-dimensional particle-in-cell code HiPACE++. By decomposing all the computation of a 3D domain in successive 2D transverse operations and choosing appropriate memory management, HiPACE++ demonstrates orders-of-magnitude speedups on modern scientific GPUs over CPU-only implementations. The 2D transverse operations are performed on a single GPU, avoiding time-consuming communications. The longitudinal parallelization is done through temporal domain decomposition, enabling near-optimal strong scaling from 1 to 512 GPUs. HiPACE++ is a modular, open-source code enabling efficient modeling of plasma accelerators from laptops to state-of-the-art supercomputers. Program summary: Program Title: HiPACE++ CPC Library link to program files: https://doi.org/10.17632/zh3rc7hvrm.1 Developer's repository link: HiPACE++ GitHub repository Licensing provisions: BSD 3-clause Programming language: C++ Nature of problem: Modeling plasma accelerators is a computationally challenging task requiring nanometer-scale resolutions over meter-scale propagation distances. The quasi-static particle-in-cell method enables high-fidelity simulations of this strongly non-linear process, but these simulations can be very expensive. Solution method: The quasi-static particle-in-cell algorithm is modified to enable efficient utilization of accelerated hardware, in particular with GPU computing, reducing the cost of simulations by orders of magnitude. A novel longitudinal parallelization enables excellent strong scaling of this method up to hundreds of GPUs. Reference: 10.5281/zenodo.5358483

We present experimental results on the formation and evolution of current sheets in two-dimensional magnetic configurations with an X-type null line. Typical features of both the initial magnetic field and the current sheet are their symmetry properties. The experiments were carried out using the CS-3D setup. The formation of a current sheet occurs just after the magneto-sonic wave converges at the null line; then, both the electric current and plasma become compressed in a planar 2D sheet, which accumulates an excess of magnetic energy. The excitation of the Hall currents, which build up the out-of-plane magnetic fields inside the 2D current sheet, brings about the modification of the sheet structure. As a result, the magnetic fields and plasma currents become 3D. The dynamic plasma processes give rise to additional current sheet deformations, which are caused by the excitation of inverse currents at the side edges of the sheet. As a consequence, the out-of-plane magnetic fields are reversed, and strong Ampère's forces of the opposite directions come into play. These forces slow down the previously accelerated high-speed plasma flows so that the flows become limited in time and space. [ABSTRACT FROM AUTHOR]

A comprehensive characterization of lattice Boltzmann (LB) schemes to perform warm fluid numerical simulations of particle wakefield acceleration (PWFA) processes is discussed in this paper. The LB schemes we develop hinge on the moment matching procedure, allowing the fluid description of a warm relativistic plasma wake generated by a driver pulse propagating in a neutral plasma. We focus on fluid models equations resulting from two popular closure assumptions of the relativistic kinetic equations, i.e., the local equilibrium and the warm plasma closure assumptions. The developed LB schemes can, thus, be used to disclose insights on the quantitative differences between the two closure approaches in the dynamics of PWFA processes. Comparisons between the proposed schemes and available analytical results are extensively addressed. [ABSTRACT FROM AUTHOR]

Research on plasma accelerators for high-energy colliders has rapidly progressed over the past few decades. Plasma acceleration with a high repetition rate will enable higher collider luminosity, but results in a heated plasma. This study investigates two phenomena—beam breakup instability and ion motion—in the nonlinear blowout regime in plasma accelerators and how the plasma temperature affects them. It was found that increasing the plasma temperature enhances the beam breakup instability by reducing the blowout radius while suppressing the on-axis ion-density spike caused by ion motion. This imposes a stringent demand on alignment tolerances, but it offers promising prospects for mitigating ion motion. [ABSTRACT FROM AUTHOR]

Ambipolar electric field is formed in the expanding plasma of the small radio frequency plasma thruster using a cusp-shaped magnetic field. A highly energized group of ion energy distribution function is observed in the z-direction, indicating the presence of axial ion acceleration downstream the magnetic nozzle owing to the electric field. The mean velocity profile of the beam ions along the z axis is evaluated using the energy distribution functions along the z axis. The high axial ion velocity profile stretches downstream, although the evaluated dimensionless velocity profile is lower than that calculated using quasi-one-dimensional models. It is suggested that ion momentum loss can result from ion-neutral collision, leading to beam divergence in the magnetic nozzle of the proposed small thruster. [ABSTRACT FROM AUTHOR]

Solar flare electron acceleration is an efficient process, but its properties (mechanism, location) are not well constrained. Via hard X-ray (HXR) emission, we routinely observe energetic electrons at the Sun, and sometimes we detect energetic electrons in interplanetary space. We examine if the plasma properties of an acceleration region (size, temperature, density) can be constrained from in situ observations, helping to locate the acceleration region in the corona, and infer the relationship between electrons observed in situ and at the Sun. We model the transport of energetic electrons, accounting for collisional and non-collisional effects, from the corona into the heliosphere (to 1.0 au). In the corona, electrons are transported through a hot, over-dense region. We test if the properties of this region can be extracted from electron spectra (fluence and peak flux) at different heliospheric locations. We find that cold, dense coronal regions significantly reduce the energy at which we see the peak flux and fluence for distributions measured out to 1.0 au, the degree of which correlates with the temperature and density of plasma in the region. Where instrument energy resolution is insufficient to differentiate the corresponding peak values, the spectral ratio of [7–10) to [4–7) keV can be more readily identified and demonstrates the same relationship. If flare electrons detected in situ are produced in, and/or transported through, hot, over-dense regions close to HXR-emitting electrons, then this plasma signature should be present in their lower-energy spectra (1–20 keV), observable at varying heliospheric distances with missions such as Solar Orbiter. [ABSTRACT FROM AUTHOR]

The high longitudinal electric fields generated in plasma wakefields are very attractive for a new generation of high gradient plasma based accelerators. On the other hand, the strong transverse fields increase the demand for a proper matching device in order to avoid the spoiling of beam transverse quality. A solution can be provided by the use of a plasma ramp, a region at the plasma injection/extraction with smoothly increasing/decreasing plasma density. The transport of a beam inside a plasma ramp, beside its parameters, depends on the profile of the ramp itself. Establishing the transfer matrix for a plasma ramp represent a very useful tool in order to evaluate the beam evolution in the plasma. In this paper a study of a cosine squared ramp is presented. An approximate solution of the transverse equation of motion is evaluated and exploited to provide a simple transfer matrix for the plasma ramp. The transfer matrix is then employed to demonstrate that this kind of ramp has the effect to minimize the emittance growth due to betatron dephasing. The behavior of a squared cosine plasma ramp will be compared with an experimentally measured plasma ramp profile in order to validate the applicability of the transfer matrix to real cases. [ABSTRACT FROM AUTHOR]

• On-orbit non-intrusive perturbation measurement of Hall effect thrusters. • 10 kHz to 100 kHz analysis better than full frequency domain. • Perturbation signal amplified by scatter numbers in the far-zero region. • The physical core represented by the scatter numbers is the dwell time. • Dwell time is mainly related to breathing oscillations. The failure of Hall effect thruster (HET) is usually the result of the accumulation of several tiny abnormal disturbances during operation. Timely and accurate early warning of perturbations is an important guarantee for the normal operation of thrusters. In this study, when the perturbation rate of HET signal (anode voltage or anode flow rate) is −4% to 4%, the time scale signal of breathing oscillation (BO) in the frequency range of 10 kHz to 100 kHz is statistically analyzed. Experiments show that when the signal is perturbed, the balance between ionization and acceleration of plasma in the discharge channel is destroyed, resulting in the dwell time of the wave peaks and valleys of BO in the far-zero region with the perturbation law, which visually shows that the number of scattered points at the corresponding current value changes regularly. According to the above statistical characteristics, this paper proposes a new condition monitoring index, namely the number of scattered points in the wave peaks side of the far-zero point area, and designs a perturbation indicator for the operating condition of the HET. Compared with direct monitoring of discharge current in engineering, this indicator can amplify the influence of the perturbation signal on BO, and has better identification and accuracy. Meanwhile, the indicator does not use invasive measurement and complex equipment, and is promising to be applied to the monitoring and diagnosis of the perturbation operation state of the on-orbit thruster. [ABSTRACT FROM AUTHOR]

The paper [R.T. Sandberg and A. G. R. Thomas, Phys. Rev. Lett. 130, 085001 (2023)] proposed a scheme to generate ultrashort, high energy pulses of XUV photons through dephasingless photon acceleration in a beam-driven plasma wakefield. An ultrashort laser pulse is placed in the plasma wake behind a relativistic electron bunch so that it experiences a density gradient and therefore shifts up in frequency. Using a tapered density profile provides phase-matching between the driver and witness pulses. In this paper, we study via particle-in-cell simulation the limits, practical realization, and 3D considerations for beam-driven photon acceleration using the tapered plasma density profile. We study increased efficiency by the use of a chirped drive pulse, establishing the necessity of the density profile shape we derived as opposed to a simple linear ramp, but also demonstrating that a piecewise representation of the profile—as could be experimentally achieved by a series of gas cells—is adequate for achieving phase matching. Scalings to even higher frequency shifts are given. [ABSTRACT FROM AUTHOR]

It is shown by numerical simulations that, if a laser pulse from the eXawatt Center for Extreme Light Studies (Sarov) is used as a driver for a laser wakefield accelerator, an electron bunch with a charge of 50 pC can be accelerated to energy of 100 GeV with an energy spread of less than 1%. To this end, it is necessary to form a plasma channel 70 m long with a characteristic radius of 200 μm and a plasma density of 3 × 1015 cm–3 on the axis. In a denser plasma, the acceleration rate is higher, but the acceleration length and the resulting energy are smaller. The accelerator parameters can be numerically optimized using a quasistatic model describing the laser pulse in terms of its envelope, which reduces the computation time by several orders of magnitude as compared to complete models. [ABSTRACT FROM AUTHOR]

Laser-driven electron acceleration in underdense plasma is a promising route towards the realization of reliable sources of relativistic electrons in the 0.1–1 GeV energy range. Generation of such electron bunches at high repetition rates is hindered by the limited energy per pulse, which inevitably results in very short pulse duration and tight focusing. Compressing the laser energy in time and space allows scientists to use higher plasma density to drive wakefieds, which in turn results in enhanced diffraction and dispersion of the broadband laser pulse. These features make difficult to control the acceleration in the plasma wave and to improve the beam quality. Here we propose a mm-long three-stage acceleration scheme, which allows for tunable injection and optimal acceleration of high-quality electron bunches. The full interaction length is modeled by 3D particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

Plasma acceleration is considered a prospective technology for building a compact multi-TeV electron–positron collider in the future. The challenge of this endeavor is greater for positrons than for the electrons because usually the self-generated fields from laser–plasma interaction are not well-suited for positron focusing and on-axis guiding. In addition, an external positron source is required, while electrons are naturally available in the plasma. Here, we study electron–positron pair generation by an orthogonal collision of a multi-PW laser pulse and a GeV electron beam by the nonlinear Breit–Wheeler process. We studied conditions favorable for positron deflection in the direction of the laser pulse propagation, which favors injection into the plasma for further acceleration. We demonstrate using the OSIRIS particle-in-cell framework that the radiation reaction triggered by ultra-high laser intensity plays a crucial role in the positron injection. It provides a suppression of the initial transverse momentum gained by the positrons from the Breit-Wheeler process. For the parameters used in this work, the intensity of at least 2.2 × 10 23 W / cm 2 is needed in order to inject more than 1% of positrons created. Above this threshold, the percentage of injected positrons rapidly increases with intensity. Moreover, subsequent direct laser acceleration of positrons in a plasma channel, using the same laser pulse that created them, can ensure a boost of the final positron energy by a factor of two. The positron focusing and guiding on the axis is provided by significant electron beam loading that changes the internal structure of the channel fields. [ABSTRACT FROM AUTHOR]

A H2/O2 electro-chemical hybrid thruster with a novel design for efficient coupling of hydrogen–oxygen detonation combustion and plasma acceleration is constructed and tested. The comprehensive effects of various parameters, such as the delay time, the background pressure, the capacitance, the external magnetic field, and the propellant mass flow rate, on the performance of the thruster have been explored in single-pulse mode. Several strategies for enhancing the efficiency have been proposed. It is found that, by adding an external magnetic field and decreasing the storage capacitor under the low pressure of 30 Pa and higher single-pulse gas intake at appropriate delay time, the average thrust and efficiency can be enhanced up to 73.2 mN and 15.58%, respectively. In addition, the maximal specific impulse of 676 s is also achieved. The results strongly indicate the great potential of the proposed electro-chemical hybrid thruster in achieving large thrust and high-level specific impulse. [ABSTRACT FROM AUTHOR]

The electric field driven acceleration of plasma ions is an intrinsic effect in laser-induced plasma plumes and is responsible for the generation of high-energy ions. At high laser fluences (≥ 2 J/cm2), multiply charged ions are formed and affect the plume expansion dynamics. In this paper, we used kinetic energy-resolved mass spectrometry to investigate the relative abundance and kinetic energy distributions of singly- and doubly-charged ions produced by KrF-laser ablation of nine different oxide targets. The doubly charged metal ions with a lower mass-to-charge (m/z) ratio show narrow energy distributions at high average kinetic energies coinciding with the cutoff energies for the singly-charged ion distributions. The observation suggests that the recombination of higher charged ions plays a prominent role in the formation of the high-energy tail for singly-charged ions. The results are discussed in terms of component volatility and a dynamic double layer, where ions with different m/z values experience different accelerations. [ABSTRACT FROM AUTHOR]

Collimation control of energetic plasma beams is crucial in the laser–plasma field. In this paper, we report on a self-collimated acceleration scheme for a plasma beam using an ultra-intense Laguerre–Gaussian (LG) laser irradiating a solid target. Three-dimensional (3D) particle-in-cell simulations show that a plasma beam with a high current density is stably formed by the radiation pressure of the hollow LG laser. The initial interaction of LG laser with solid target can be approximately researched by a deformable mirror model. Under the effect of the ponderomotive force of the LG laser, the plasma converges in the center axis to form a narrow beam. An elongated strong-magnetic tunnel (B ∼ 2 kT) is self-generated around the plasma beam, capable of trapping some electrons in a region with a radius of less than 500 nm (r < 500 nm). Compared with the case driven by the conventional Gaussian laser, the beam radius size is dramatically reduced from the microscale to hundreds on the nanoscale. The beam density is increased by at least ten times. Such an interesting scheme can provide a feasible and efficient way to achieve and enhance the collimation of energetic particle beams, which may benefit the general applications of fast ignition in inertial fusion, radiotherapy, realization of high-energy density states, and so on. [ABSTRACT FROM AUTHOR]

Particle-driven plasma wakefield acceleration (PWFA) exploits the intense wakefields excited in a plasma by a high-brightness driver beam in order to accelerate a trailing, properly delayed witness electron beam. Such a configuration offers notable advantages in achieving very large accelerating gradients that are suitable for applications in particle colliders and photon production. Moreover, the amplitude of the accelerating fields can be enhanced by resonantly exciting the plasma using a multi-pulse driver beam with a proper time structure. Before the injection into the plasma stage, the pulsed electron beam, conventionally termed the comb beam, is usually produced and pre-accelerated in a radio-frequency (RF) linear accelerator (linac). In this pape, we discuss challenging aspects of the dynamics that comb beams encounter in the RF injector stage preceding the plasma. In particular, the examples we analyze focus on the use of velocity bunching to manipulate the time structure of the beam and the impact of dipole short-range wakefields on the transverse emittances. Indeed, both processes crucially affect the phase space distribution and its quality, which are determinant features for an efficient acceleration in the plasma. In addition, the analyses we present are performed with the custom tracking code MILES, which utilizes semi-analytical models for a simplified evaluation of wakefield effects in the presence of space charge forces.

Magnetic reconnection is known as an essential process to convert stored energy of magnetic field into the kinetic, thermal energy of plasma and the acceleration of charged particles in astrophysical and space plasmas. In this paper, we investigate some features of test particle acceleration during spine reconnection with an asymmetric current sheet. To do so, we study first the acceleration features of a test-particle and then discuss acceleration of a randomly injected population of 10,000 protons in the vicinity of a null point with input parameters for the solar corona. It is shown that protons are accelerated up to tens of keV and even higher kinetic energies, either along the spine axis or on the fan surface along specified lines. Also, we discuss the variation of energy spectra for different strengths of the electric and magnetic field amplitudes. [ABSTRACT FROM AUTHOR]

A thin current sheet in the Earth's magnetotail with characteristic thickness of one to several proton gyroradii is often observed during magnetospheric disturbances named substorms, when a relatively thick current configuration in the magnetotail is narrowed to an extremely small thickness and then can spontaneously be destroyed. The current-sheet destruction is usually accompanied by such active processes as plasma acceleration and heating, as well as generation of an induced electric field and magnetohydrodynamic waves. In this paper, we developed and investigated a model of formation of a thin current sheet in which, along with protons, we have taken into account single-charged oxygen ions coming from the ionosphere into the magnetotail current sheet during magnetically active periods. The aim of this simulation is to study the peculiarities of thin current-sheet formation in two-component plasma and investigate its structure. It is shown that equilibrium configuration can have some characteristic properties. In particular, if the system consists only of protons or heavy ions, single-scale current equilibrium supported by quasi-adiabatic particles is formed. When a current sheet is formed in plasma that consists of a mixture of protons and oxygen ions in comparable concentrations, a current sheet can be formed with heavy ions as current carriers and chaotic proton trajectories that make a negative contribution to the current, due to which the current-density profile becomes bifurcated with the minimum at the center and maxima at the periphery of the sheet. The results may be useful for the interpretation of observational data in the Earth's magnetotail. [ABSTRACT FROM AUTHOR]

In this theoretical study on an exploding foil initiator (EFI), the sequential events in an EFI system were numerically modeled and investigated from metallic bridge burst by ohmic heating and flyer acceleration by plasma expansion to explosive detonation by high-speed flyer impact. The EFI system modeling employed mass, momentum, and energy conservation coupled with the resistance–inductance–capacitance circuit equation of the initiation circuit and plasma property calculations of highly dense metallic plasma as well as a semi-empirical detonation model. The aim was to predict transient bridge behavior, flyer velocity, and detonation initiation threshold. Through comparisons and verifications with measured data from several existing EFI firing tests, the present system model was shown to predict bridge burst and flyer velocity very well. The numerical results indicated two different thresholds of charging voltage for flyer creation out of plastic film and impact detonation of explosive charge to be quite consistent with the measurements. The system behaviors in three different ranges of charging voltage were discussed in terms of discrete nature of this high-voltage explosive charge initiator. [ABSTRACT FROM AUTHOR]

When two magnetic nozzles with opposite polarity are placed side by side, a 'magnetic arch' (MA) is formed, which connects the field lines of each nozzle into a closed-line configuration. The plasma expansion and acceleration in this magnetic topology are relevant for clusters of electrodeless plasma thrusters, as well as novel, non-cylindrical thruster architectures. A collisionless, quasineutral, two-fluid model of the plasma expansion in a MA, is introduced. The plasma properties (density, electron temperature, electrostatic potential, ion velocity, electric currents) in the 2D planar and zero plasma-beta limit are analyzed, and the magnetic thrust density is discussed. It is shown that the ions coming out of the two nozzles meet on a shock-like structure to form a single beam that propagates beyond the closed lines of the applied magnetic field, generating magnetic thrust. A small magnetic drag contribution comes from the final part of the expansion. The plasma-induced magnetic field is then computed self-consistently for non-zero plasma-beta expansions, showing that it stretches the MA in the downstream direction and helps reduce that drag contribution. Finally, the limitations of the present model are discussed. [ABSTRACT FROM AUTHOR]

Plasma accelerators that form high-speed plasma jets due to the force action of their own magnetic field operate at high currents. Because of that, current spots with a high current density may occur on their electrodes, which lead to erosion of the electrodes and limit their life-time. In this work, the current modes of a plasma accelerator were investigated both without current spots and with current spots on the electrodes. In the latter case, the dynamics of current spots in the course of plasma acceleration was explored. This issue was studied by the example of a high-current (I ≤ 25 kA) pulse discharge created between two long (l = 30 cm) and parallel stainless-steel electrodes of cylindrical shape of 10 mm in a diameter. Two distances between the cylinders' axes, h = 30 and 22 mm, were used. Two discharge zone configurations were investigated. In one of them, the discharge zone is not confined by side dielectric walls. In other one, the discharge zone is confined with transparent dielectric walls spaced by 12 mm. The high-current discharge was studied in nitrogen and helium at moderate pressures from P = 4 to 50 Torr. The high current was provided due to the discharging of a capacitor battery C = 1000 µF charged up to the voltage U ≤ 5 kV. At the very beginning, the discharge was initiated locally at one end of the electrodes, and then the formed plasma quickly moves toward the opposite end under strong force influence of its own magnetic field. Eventually, plasma clot is flying out of the discharge zone. [ABSTRACT FROM AUTHOR]

Acceleration of laser-induced plasma created as a result of three-step photoionization of atomic vapor by pulsed radiation of dye lasers pumped by copper-vapor lasers is studied experimentally. The acceleration was achieved due to the alternating magnetic field appearing upon propagation of a current pulse through an inductor located in direct proximity from the area of laser protoionization of atomic lutetium vapor. [ABSTRACT FROM AUTHOR]

Energy-frontier TeV colliders based on plasma accelerators are attracting much attention due to the recent achievements in multi-stage laser acceleration as well as the remarkable advances in electron- and proton-driven plasma accelerators. Such colliders may suffer a fundamental energy loss due to the radiation reaction (RR) effect, as the electrons lose energy through betatron radiation emission. Although the RR may not be critical for low-energy accelerators, it will exert limitations on TeV-class plasma-based colliders that need to be considered. In this paper, we have provided an extensive study of the RR effect in all pathways toward such colliders, including multi-stage plasma acceleration driven by the state-of-the-art lasers and the relativistic electron beam as well as the single-stage plasma acceleration with the energetic proton beams available at the CERN accelerator complex. A single-particle Landau–Lifschitz approach is used to consider the RR effect on an electron accelerating in the plasma blow-out regime. The model determines the boundaries where RR plays an energy limiting role on such colliders. The energy gain, the radiation loss, and the validity of the model are numerically explored. [ABSTRACT FROM AUTHOR]

Context. The energy release in eruptive flares and the kinematics of the associated coronal mass ejections (CMEs) are interlinked and require favorable observing positions as both on-disk and off-limb signatures are necessary to characterize these events. Aims. We combine observations from different vantage points to perform a detailed study of a long duration eruptive C7 class flare that occurred on 17 April 2021 and was partially occulted from Earth view. The dynamics and thermal properties of the flare-related plasma flows, the flaring arcade, and the energy releases and particle acceleration are studied together with the kinematic evolution of the associated CME in order to place this long duration event in context of previous eruptive flare studies. Methods. We use data from the Spectrometer-Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter to analyze the spectral characteristics, timing, and spatial distribution of the flare X-ray emission. Data from the Extreme Ultraviolet Imager (EUVI) onboard the Solar TErrestrial RElations Observatory-Ahead (STEREO-A) spacecraft are used for context images as well as to track the ejected plasma close to the Sun. With Atmospheric Imaging Assembly extreme ultraviolet (EUV) images from the Solar Dynamics Observatory, the flare is observed off-limb and differential emission measure maps are reconstructed. The coronagraphs onboard STEREO-A are used to track the CME out to around 8 R. Results. The flare showed hard X-ray (HXR) bursts over the duration of an hour in two phases lasting from 16:04 UT to 17:05UT. During the first phase, a strong increase in emission from hot plasma and impulsive acceleration of the CME was observed. The CME acceleration profile shows a three-part evolution of slow rise, acceleration, and propagation in line with the first STIX HXR burst phase, which is triggered by a rising hot (14 MK) plasmoid. During the CME acceleration phase, we find signatures of ongoing magnetic reconnection behind the erupting structure, in agreement with the standard eruptive flare scenario. The subsequent HXR bursts that occur about 30 min after the primary CME acceleration show a spectral hardening (from 7 to 4) but do not correspond to further CME acceleration and chromospheric evaporation. Therefore, the CME-flare feedback relationship may only be of significance within the first 25 min. of the event under study, as thereafter the flare and the CME eruption evolve independently of each other. [ABSTRACT FROM AUTHOR]

We report on the development of a compact, gas-filled capillary plasma source for plasma accelerator applications. The one-body sapphire capillary was created through a diamond machining technique, which enabled a straightforward and efficient manufacturing process. The effectiveness of the capillary as a plasma acceleration source was investigated through laser wakefield acceleration experiments with a helium-filled gas cell, resulting in the production of stable electron beams of 200 MeV. Discharge capillary plasma was generated using a pulsed, high-voltage system for potential use as an active plasma lens. A peak current of 140 A, corresponding to a focusing gradient of 97 T/m, was observed at a voltage of 10 kV. These results demonstrate the potential utility of the developed capillary plasma source in plasma accelerator research using electron beams from a photocathode gun. [ABSTRACT FROM AUTHOR]

An applied field magnetoplasmadynamic thruster (AF-MPDT) is one of the most promising electric engines for the space missions with high thrust. However, the acceleration mechanisms in AF-MPDTs are complicated because of the application of the magnetic nozzle, which limits the performance improvement of the thrusters. The discharge currents may flow out of the discharge chamber because of the magnetic nozzle, which was neglected in previous research studies about the acceleration mechanisms in AF-MPDTs. A model based on the MHD equations has been established to investigate the contribution of outflow currents to the plasma acceleration. The accuracy of the model has been proved by the comparison of the calculated thrust and the experimental data. The performance of the argon-fed AF-MPDT is measured by a target thrust stand. The dominant acceleration mechanism of the AF-MPDTs is the plasma expansion in the magnetic nozzle when the magnetic fields are less than 0.2 T. The primary thermal energy source of the AF-MPDTs is the Joule heating when the magnetic fields are lower than 0.1 T. The viscous heating due to the outflow currents will be dominant when the magnetic fields are higher. An AF-MPDT without a discharge chamber is proposed to improve the performance. Compared with the conventional AF-MPDT, the new structure may provide an average 15% increase in performance at the same condition. [Display omitted] • The influences of outflow currents on plasma acceleration are studied. • Higher outflow currents are beneficial for plasma acceleration in AF-MPDTs. • The plasma expansion is the dominant acceleration mechanism in AF-MPDTs. • An AF-MPDT without a discharge chamber is proposed for performance improvement. [ABSTRACT FROM AUTHOR]

The quasistatic approximation (QSA) is an efficient method of simulating laser- and beam-driven plasma wakefield acceleration, but it becomes imprecise if some plasma particles make long longitudinal excursions in a strongly nonlinear wave, or if waves with non-zero group velocity are present in the plasma, or the plasma density gradients are sharp, or the beam shape changes rapidly. We present an extension to QSA that is free from many of its limitations and retains its main advantages of speed and reduced dimensionality. The new approach takes into account the exchange of information between adjacent plasma layers. We introduce the physical model, describe its numerical implementation, and compare the simulation results with available analytical solutions and other codes. [ABSTRACT FROM AUTHOR]

This investigation presents a model based on the nonlinear coupling of waves for studying electron acceleration in laser-produced plasma. The impact of the localized structures formation and turbulence generation on electron acceleration is investigated via a second-order Fermi acceleration mechanism. For this purpose, the dynamical coupled equations of the extraordinary mode laser and the upper hybrid wave are formulated by taking into account relativistic and ponderomotive nonlinearity. These coupled equations are solved by laboratory simulations using pseudo-spectral and finite difference methods. The simulation results show the turbulent wavenumber spectrum associated with the localization of the laser beam. The power-law scaling of turbulence generation has been utilized to study the formation of the thermal tail of energetic electrons, which may be responsible for the acceleration of the electrons. A fractional diffusion method has been exploited to determine electron acceleration. This study also provides a simplified model for a better understanding of the nonlinear progression of the laser beam during propagation inside the magnetized plasma. [ABSTRACT FROM AUTHOR]

Plasma wakefield accelerators can be driven either by intense laser pulses (LWFA) or by intense particle beams (PWFA). A third approach that combines the complementary advantages of both types of plasma wakefield accelerator has been established with increasing success over the last decade and is called hybrid LWFA→PWFA. Essentially, a compact LWFA is exploited to produce an energetic, high-current electron beam as a driver for a subsequent PWFA stage, which, in turn, is exploited for phase-constant, inherently laser-synchronized, quasi-static acceleration over extended acceleration lengths. The sum is greater than its parts: the approach not only provides a compact, cost-effective alternative to linac-driven PWFA for exploitation of PWFA and its advantages for acceleration and high-brightness beam generation, but extends the parameter range accessible for PWFA and, through the added benefit of co-location of inherently synchronized laser pulses, enables high-precision pump/probing, injection, seeding and unique experimental constellations, e.g., for beam coordination and collision experiments. We report on the accelerating progress of the approach achieved in a series of collaborative experiments and discuss future prospects and potential impact. [ABSTRACT FROM AUTHOR]

Laser plasma accelerators (LPAs) have become one of the frontiers of the accelerator community, mainly because they promise orders of magnitude improvement in the accelerating gradient. However, the energy stability and spread of the high-charge bunched beams (e.g. several hundred pC per bunch) from LPAs still strongly limit their application. In this work, we propose a novel method utilizing magnetic chicanes combined with both active and passive plasma dechirpers to simultaneously reduce the central energy deviation and the energy spread of high-charge bunched beams from LPAs. Start-to-end simulations demonstrate that the central energy deviation and the energy spread of approximately 500 pC bunches can be simultaneously reduced from approximately 2% and 1.2% to 0.1% and 0.5%, respectively, while maintaining almost perfect transmission efficiency (above 97%).

We present experimental results on the formation and evolution of current sheets in two-dimensional magnetic configurations with an X-type null line. Typical features of both the initial magnetic field and the current sheet are their symmetry properties. The experiments were carried out using the CS-3D setup. The formation of a current sheet occurs just after the magneto-sonic wave converges at the null line; then, both the electric current and plasma become compressed in a planar 2D sheet, which accumulates an excess of magnetic energy. The excitation of the Hall currents, which build up the out-of-plane magnetic fields inside the 2D current sheet, brings about the modification of the sheet structure. As a result, the magnetic fields and plasma currents become 3D. The dynamic plasma processes give rise to additional current sheet deformations, which are caused by the excitation of inverse currents at the side edges of the sheet. As a consequence, the out-of-plane magnetic fields are reversed, and strong Ampère’s forces of the opposite directions come into play. These forces slow down the previously accelerated high-speed plasma flows so that the flows become limited in time and space.

In the field of beam driven acceleration of particles in plasma wakefields (PWFA), the source of the plasma medium is a crucial part of the accelerator setup. Gas discharges have proven to be a reliable and simple type of a plasma source in past experiments. Nevertheless, especially in plasma cells that aim for peak density in the range of 10 15 cm − 3 , physical apertures around 10 mm, and lengths of up to several meters, the stability of the discharge ignition and the pulse current waveform is limiting the applicability. We show successful mitigation of these jitters in a 0.1 m argon gas discharge cell, operating at maximum densities of ≤ 10 16 cm − 3 by optimisation of the cell design and the discharge current pulse circuit. [ABSTRACT FROM AUTHOR]