In this work, we investigate the dynamics of particles accelerated by electromagnetic wave pulses under the effects of a radiation reaction as described by the Landau–Lifshitz model. The radiation reaction breaks the invariant used to predict both the critical carrier amplitude required for efficient particle acceleration and the particle’s final ejection velocity. Moreover, it alters the dynamical regimes predicted by models that neglect it. Numerical simulations of single-particle dynamics, performed using both the full dynamical equations and the canonical averaged formulation, support the analytical results.

Bridging the spatiotemporal scales of magnetic seed field generation and subsequent dynamo amplification in the weakly collisional intracluster medium presents an extreme numerical challenge. We perform collisionless turbulence simulations with initially unmagnetised electrons that capture both magnetic seed generation via the electron Weibel instability and the ensuing dynamo amplification. Going beyond existing pair-plasma studies, we use an ion-to-electron mass ratio of $100$ for which we find electron and ion dynamics are sufficiently decoupled. These simulations are enabled by the 10-moment collisionless fluid solver of Gkeyll, which evolves the full pressure tensor for all species. The electron heat-flux closure regulates pressure isotropisation and effectively sets the magnetic Reynolds number. We investigate how the strength of the closure influences the transition between a regime reminiscent of previous kinetic pair-plasma simulations and a regime exhibiting dynamo behaviour qualitatively similar to magnetohydrodynamics.

In toroidal confinement systems, the scrape-off layer (SOL) magnetic field exhibits characteristics analogous to those of a magnetic mirror configuration, particularly in the edge plasma region. Therefore, linear plasma devices have advanced divertor simulation studies. To further promote divertor simulation studies, a new divertor simulator, ‘Pilot GAMMA PDX-SC (PGX-SC)’ has been developed, incorporating a pair of superconducting coils that generate a simple magnetic mirror configuration. An electrode-biasing system was installed on the PGX-SC to regulate the plasma potential. The system comprises three concentric basing plates installed at the east end of the main chamber of PGX-SC, in conjunction with a DC-stabilised power supplies for each basing plate. This system can also measure the floating potentials and electrode currents by connecting a resistor to each plate in the absence of an external power supply. Preliminary experiments were conducted to investigate the effect of plasma by applying a bias to the electrode plates. Applying a voltage to the inner electrode increased the plasma potential at the outer electrode. This result suggests the feasibility of controlling the peripheral plasma potential using concentric biasing plates. When voltage was applied to the outer electrode, the amplitude of the fluctuating current decreased. These results collectively indicate the capability of plasma control employing concentric biasing plates.

Phase-space electron holes, recognised as fundamental nonlinear electrostatic structures in space plasmas, have recently been detected near the mantle boundary of the Venusian magnetosheath by both the Parker Solar Probe (PSP) and the Pioneer Venus Orbiter (PVO). To understand their origin and characteristics, we develop a hydrodynamic model coupled with reductive perturbation theory that incorporates a small population of non-isothermal trapped electrons together with the dynamical effects of solar-wind ions and electrons. This formulation yields a generalised Schamel–Korteweg de Vries equation supporting two distinct classes of nonlinear electrostatic modes: solitary waves and double layers. Using parameter ranges constrained by in situ measurements – including relative densities, drift velocities and temperature ratios – we conduct a detailed parametric investigation of both structures. For the solitary-wave solutions, the model predicts electric field amplitudes of ${\sim} 20$ mV m–1, temporal scales of ${\sim} (2.5{-}4.5)\,$ms and characteristic frequencies of ${\sim} (0.31{-}5.6)$ kHz. The double-layer solutions exhibit fields of ${\sim} 18$ mV m–1, durations of ${\sim} 4.5\,$ms and frequencies of ${\sim} (0.63{-}1.6)$ kHz. These results are in strong agreement with PSP and PVO observations, which report electrostatic fluctuations near 5.4 kHz with amplitudes of ${\sim} 20$ mV m–1. The present analysis therefore provides a consistent physical interpretation of electron-hole structures in the Venusian magnetosheath and highlights their role in mediating kinetic processes at unmagnetised planetary boundaries.

We investigate plasma wake generation via Compton scattering from photon bursts in the Thomson regime, a non-ponderomotive process relevant when the photon wavelength is shorter than the interparticle distance. In this regime, electrons can reach relativistic velocities. We extend linear theory to the nonlinear regime, showing that plasma waves can reach the wave-breaking limit. Perfectly collimated drivers produce wakes propagating at the speed of light, allowing electron phase-locking (limited by driver depletion). Non-collimated drivers induce subluminal phase velocities, limiting acceleration via dephasing. Two-dimensional simulations reveal unique transverse fields compared with laser wakefields, with a DC magnetic field leading to consistent focusing. The work considers observational prospects in laboratory and astrophysical scenarios such as around highly luminous compact objects (e.g. pulsars, gamma-ray bursts) interacting with tenuous interstellar or intergalactic plasmas, where conditions favour Compton-dominated wakefield acceleration.

Axisymmetric cylindrical configurations of the magnetic field are used to confine and guide plasmas in fusion and electric propulsion devices, where plasma equilibria are established as a balance between plasma pressure, magnetic stress (pressure) and inertial forces due to azimuthal plasma rotation and axial flow rotation. Most generally, in an axially inhomogeneous case, plasma rotation and azimuthal magnetic field are related via Alfvén wave type coupling. We show that, for a special case of a current-free nozzle and, therefore, absence of the azimuthal plasma rotation, the plasma flow along the magnetic surface can be analysed independently of the exact shape of the magnetic surface. The velocity of the transonic plasma flow is determined by the magnitude of the magnetic field on the magnetic surface, while the actual shape of the magnetic surface is determined by the solution of the generalised Grad–Shafranov equation that includes the inertial forces. These analytical results are confirmed with numerical simulations that highlight the contribution of the inertial forces to plasma acceleration and equilibrium. Implications for the flows in the magnetic nozzle for the electric propulsion and open mirrors for fusion are discussed.

In this study, a radiative divertor simulator was developed using the linear magnetic mirror device KAIMIR, considering the center chamber as the upstream scrape-off layer and the expander chamber as the downstream region. To achieve divertor-relevant conditions, the gas feed system of the KAIMIR device was upgraded to increase the particle flux at the downstream region. In addition, a differential pumping system using a skimmer structure was implemented to enable independent control of the neutral pressure between the upstream and downstream regions by reducing the vacuum conductance between the chambers. With this system, a neutral pressure up to 70 mTorr was achieved in the expander chamber while maintaining plasma characteristics in the center chamber. Simulations were then conducted, where non-monotonic behaviour of the ion saturation current and line-integrated density was observed with increasing neutral pressure in the expander chamber, suggesting a transition from attached to detached plasma regimes. Visible emission profiles from fast camera measurements revealed enhanced recombination emission and the formation of localised low-temperature plasma near the downstream region. These results demonstrate that the upgraded KAIMIR device provides a controllable linear divertor simulator suitable for the investigation of radiative and detached divertor plasma physics in a linear configuration.

Axial plugging is a critical challenge for fusion in open-ended magnetic confinement systems. Unlike simple magnetic mirrors, which suffer from direct axial flow, multi-mirror systems utilise a series of aligned magnetic cells to suppress plasma loss; however, the resulting confinement still requires additional plugging to reach Lawson criterion levels. In Miller et al. (Phys. Plasmas, 2023, vol. 30, p. 072510), it was found that applying a travelling and rotating electric field in multi-mirror machines can significantly suppress axial loss due to a selectivity effect induced by the Doppler shift of the ion cyclotron resonance. However, this method is energetically expensive and vulnerable to plasma screening effects. Here, we show that using a travelling, rotating magnetic field can achieve comparable plugging effectiveness while offering better penetration and lower energy costs. Two limiting scenarios, with and without an induced electric field, were considered. The confinement enhancement is calculated using a semi-kinetic rate-equation model, in which the rate coefficients are determined from single-particle simulations. While both scenarios exhibit significant confinement enhancement, the scenario without an induced electric field is much more energetically efficient, as it relies on phase-space mixing rather than on energy deposition in the escaping particles. The decoupling of confinement from plasma collisionality enables fusion conditions in the central cell while allowing affordable and efficient confinement enhancement in the multi-mirror sections.

Collisionless zonal flow (ZF) saturation is analytically investigated using a reduced two-field fluid model for ion temperature gradient-driven turbulence subject to a three-wavevector, five-mode truncation that includes the interaction of an unstable mode, the ZF and a stable mode. Using weak-turbulence closure theory, a wave kinetic equation (WKE) is derived describing the temporal evolution of the ZF energy spectrum for this system according to linear and nonlinear dynamics. The terms in the nonlinear time evolution operator, which describe resonant energy transfer among triads of fluctuations, are expressed as matrices whose elements are arithmetic combinations of the linear eigenvalues of the individual modes participating in a given interaction. In the collisionless limit, the matrices characterising ZF drive and damping become highly symmetric, and conditions are found for spectral saturation in this regime. A set of stationary solutions to the WKE are found that describe a state of turbulence in which the nonlinearly driven stable modes reach identical levels as the linearly driven unstable modes, producing identical rates of up- and down-gradient thermal energy transport at each fluctuation length scale. Generalisation to the non-truncated system is briefly discussed.

MIDAS-1D2V is a plasma simulation code for axially symmetric open traps. It solves the non-stationary kinetic equation for the ion distribution function, accounting for Coulomb collisions. This paper presents two key modifications to the model. The first modification enables the calculation of fusion reactions in the plasma, with charged reaction products treated as an additional source term in the kinetic equation. The second modification incorporates beam capture dynamics, including ionisation and charge-exchange processes. Both modifications have been implemented for hydrogen isotopes.

Using a two-fluid approach, we consider the properties of relativistically nonlinear (arbitrary $a_0$), circularly polarised electromagnetic waves propagating along a magnetic field in electron–ion and pair plasmas. Dispersion relations depend on how wave intensity scales with frequency, e.g. $a_0 (\omega )$. For superluminal branches, the nonlinear effects reduce the cutoff frequency, while the general form of the dispersion relations $\omega (k)$ remains similar to the linear case. For subluminal waves, whistlers and Alfvén, a new effect appears: dispersion curves effectively terminate at finite $\omega ^\ast {-} k^\ast$, where the group velocity becomes zero. Qualitatively, subluminal modes with fluctuating electric field larger than the guide field, $E_w (\omega ) \geqslant B_0$, cannot propagate. In extended systems, e.g. within magnetospheres of neutron stars, this leads to opening of the magnetosphere by a strong wave.

By a detailed comparison of leaky magnetohydrodynamic waves in coronal magnetic flux tubes with leaky electromagnetic waves in dielectric media, it is shown that the latter kind may be called quasi-normal modes, since they can be regularised by a normalisation which systematically cuts off the contribution of the external homogeneous region, whereas such a possibility is forbidden for the former kind by the conservation of magnetic flux. Consequently, leaky magnetohydrodynamic waves cannot be systematically applied to coronal seismology, i.e. to the inverse spectral problem of determining the different equilibrium distributions of the fields by comparing the spectra they produce with the observed ones.

An overview of new experimental results obtained at the GOL-NB multiple-mirror trap over the past two years is presented. The main scientific objectives of GOL-NB are the direct demonstration of the multiple-mirror confinement efficiency with hydrogen plasma. The device has a configuration that simulates, at reduced plasma parameters, the configuration of a reactor-class facility with a central gas dynamic trap and sections with a strong magnetic field attached to it, which can be turned on both as long solenoids or as multiple mirrors. Plasma is heated by 1 MW neutral beam injection. The following elements are discussed in the paper: magnetohydrodynamic (MHD) stability, plasma parameters in the central trap, neutral beam trapping and fast ion spectrum, comparison of the multiple-mirror and solenoidal configurations at high collisionality, and measures for the reduction in neutral density. The main goals of the experiments were plasma properties characterisation in the central trap and studies of plasma flow in the strong-field sections. We also introduce two new systems for additional plasma heating, a low-energy electron beam mounted at the exit plasma receiver and a 13.56 MHz ICRH system, which is under tests at several kilowatts of input power.

The Gas Dynamic Trap (GDT) facility at the Budker Institute of Nuclear Physics continues experimental studies in support of the Gas-Dynamic Multiple-Mirror Trap (GDMT) project – a prospective neutron source and thermonuclear reactor concept based on open-ended magnetic confinement. During the 2024–2025 upgrade campaign, key engineering systems and diagnostic suites were substantially modernised to address critical physics and technology challenges for the GDMT development. Three key research and development directions were pursued. First, a conductive wall stabilisation system was designed to suppress magnetohydrodynamic (MHD) instabilities at high plasma beta. Second, a new second-harmonic X-mode electron cyclotron resonance heating (ECRH) system operating at 54.5 GHz with 0.8 MW power was commissioned. Preliminary experiments demonstrated increased electron temperature compared with non-ECRH heated plasmas. Third, proof-of-principle experiments on bulk plasma fuelling using a Marshall gun injector were successfully performed, supporting further development towards a high-repetition-rate injector. These results provide essential experimental validation and technological groundwork for the GDMT project, demonstrating progress towards high-beta plasma operation, efficient heating schemes and particle balance control in open magnetic traps.