The Helicon-Cathode(HelCat) device is a medium-size linear experiment suitable for a wide range of basic plasma science experiments in areas such as electrostatic turbulence and transport, magnetic relaxation, and high power microwave (HPM)-plasma interactions. The HelCat device is based on dual plasma sources located at opposite ends of the 4 m long vacuum chamber – an RF helicon source at one end and a thermionic cathode at the other. Thirteen coils provide an axial magnetic field B ⩾ 0.220 T that can be configured individually to give various magnetic configurations (e.g. solenoid, mirror, cusp). Additional plasma sources, such as a compact coaxial plasma gun, are also utilized in some experiments, and can be located either along the chamber for perpendicular (to the background magnetic field) plasma injection, or at one of the ends for parallel injection. Using the multiple plasma sources, a wide range of plasma parameters can be obtained. Here, the HelCat device is described in detail and some examples of results from previous and ongoing experiments are given. Additionally, examples of planned experiments and device modifications are also discussed.

The Culham Thesis Prize is awarded annually to the nominee who has displayed an excellence in the execution of the scientific method as witnessed by the award of Doctor of Philosophy in Plasma Science from a UK or Irish university. The thesis content should exhibit significant new work and originality, clearly driven by the nominee, be well explained and demonstrate a good understanding of the subject. The prize is awarded at the Institute of Physics Plasma Physics Group Spring Conference and the prize winner gives an invited talk about their thesis work. The prize is sponsored by Culham Centre for Fusion Energy.

Copper activation was used to characterize high-energy proton beam acceleration from near-critical density plasma targets. An enhancement was observed when decreasing the target density, which is indicative for an increased laser-accelerated hot electron density at the rear target-vacuum boundary. This is due to channel formation and collimation of the hot electrons inside the target. Particle-in-cell simulations support the experimental observations and show the correlation between channel depth and longitudinal electric field strength is directly correlated with the proton acceleration.

We present simulations that demonstrate the production of quasi-monoenergetic proton bunches from the interaction of a CO2 laser pulse train with a near-critical density hydrogen plasma. The multi-pulse structure of the laser leads to a steepening of the plasma density gradient, which the simulations show is necessary for the formation of narrow-energy spread proton bunches. Laser interactions with a long, front surface, scale-length (≫ c/ωp) plasma, with linear density gradient, were observed to generate proton beams with a higher maximum energy, but a much broader spectrum compared to step-like density profiles. In the step-like cases, a peak in the proton energy spectra was formed and seen to scale linearly with the ratio of laser intensity to plasma density.

BOUT++ is a 3D nonlinear finite-difference plasma simulation code, capable of solving quite general systems of Partial Differential Equations (PDEs), but targeted particularly on studies of the edge region of tokamak plasmas. BOUT++ is publicly available, and has been adopted by a growing number of researchers worldwide. Here we present improvements which have been made to the code since its original release, both in terms of structure and its capabilities. Some recent applications of these methods are reviewed, and areas of active development are discussed. We also present algorithms and tools which have been developed to enable creation of inputs from analytic expressions and experimental data, and for processing and visualisation of output results. This includes a new tool Hypnotoad for the creation of meshes from experimental equilibria. Algorithms have been implemented in BOUT++ to solve a range of linear algebraic problems encountered in the simulation of reduced Magnetohydrodynamics (MHD) and gyro-fluid models: A preconditioning scheme is presented which enables the plasma potential to be calculated efficiently using iterative methods supplied by the PETSc library (the Portable, Extensible Toolkit for Scientific Computation) (Balay et al. 2014), without invoking the Boussinesq approximation. Scaling studies are also performed of a linear solver used as part of physics-based preconditioning to accelerate the convergence of implicit time-integration schemes.

The Weibel/filamentation instability is known to play a key role in the physics of weakly magnetized collisionless shock waves. From the point of view of high energy astrophysics, this instability also plays a crucial role because its development in the shock precursor populates the downstream with a small-scale magneto-static turbulence which shapes the acceleration and radiative processes of suprathermal particles. The present work discusses the physics of the dissipation of this Weibel-generated turbulence downstream of relativistic collisionless shock waves. It calculates explicitly the first-order nonlinear terms associated to the diffusive nature of the particle trajectories. These corrections are found to systematically increase the damping rate, assuming that the scattering length remains larger than the coherence length of the magnetic fluctuations. The relevance of such corrections is discussed in a broader astrophysical perspective, in particular regarding the physics of the external relativistic shock wave of a gamma-ray burst.

We start from a Mattor–Parker system and its generalization to include diffusion and derive the Random Phase equations. It is shown that the same type of fluid closure holds in the coherent and turbulent regimes. This is due to the fact that the Random Phase levels (1/I1 = 1/I2 + 1/I3), where Ij is the intensity of wave packet ‘j’, are attractors for the wave dynamics both in the coherent and incoherent cases. Focus here is on the wave dynamics with phase velocities varying due to nonlinear frequency shifts. Thus a Maxwellian distribution function is kept in all cases.

Cross sections in the very low energy range are also represented by the modified effective-range theory (MERT) for low-energy electron scattering from the rare gas (argon). Simulations using published (theoretical) phase shifts indicate that extended versions of the standard effective-range theory with four adjustable parameters are required to give an adequate description of the phase shifts for argon. A four-parameter MERT fit gives a good representation of a recent electron–argon (e-Ar) total cross section experiment at energies less than 10.0 eV. Cross section Q(l) (E) for collision in dilute gases is given for any order l. Here Q(l) (E) are presented for l = 1. . .6. We present calculations for the elastic cross sections for electron scattering from argon. The improvement in the agreement between our theoretical calculations and the experimental measurements in the case of argon in scattering calculations are showed. Differential scattering experiments have been performed for the systems e-Ar in the energy range E = 0–10 eV and the angular range θ = 0–20° using a crossed-beam arrangement. Differential and integrated cross sections for the elastic scattering of low- and intermediate-energy (0–50 eV) electrons by argon atoms are calculated. For each impact energy, the phase shifts of the lower partial waves are obtained exactly by numerical integration of the radial equation. Transport coefficients of argon plasma are requested exactly, which is why we calculated the average collision cross sections for s = 1. . .11, l = 1. . .6.

Runaway electrons in tokamaks can cause serious damage to the first wall of the reactor and decrease its life time. Also, hard x-ray emission generated from high energy runaway electrons lead to the plasma energy loss. Therefore, suggesting methods to minimize runaway electron in tokamaks are very important. Applying external resonant field is one of the methods for controlling the Magneto Hydrodynamic (MHD) activity. Relation between the MHD activity and runaway electrons has already been studied (Jaspers et al. 1994; Ghanbari et al. 2012) Jaspers, R., et al. 1994 Phys. Rev. Lett.72, 4093; Ghanbari, M. R., et al. 2012a Phys. Scr.83, 055501. Present study attempts to investigate the effects of limiter biasing and Resonant Helical magnetic Field (RHF) on the generation of runaway electrons. For this purpose, plasma parameters such as plasma current, MHD oscillation, loop voltage, emitted hard x-ray intensity, Halpha impurity, safety factor in the presence and absence of external fields, were measured. Frequency activity was investigated with FFT analysis. The results show that applying resonant fields can control the MHD activity, and then hard x-ray emitted from the runaway electrons.

Fluid simulations are used to investigate a multi-component magnetized dusty plasma sheath. The model consists of positive ions, dust grains, and two species of electron populations. These electrons are assumed to be a sum of two Maxwellian distributions with two different temperatures (cold and hot). According to multi-fluid equations and some dimensionless variables, the dimensionless equations are obtained and solved numerically. The effect of the presence of the hot electrons in the sheath is examined. A significant change is observed in the quantities characterizing the sheath with respect to one species electrons (cold) assumption.

The probe intended for the characterization of cold plasma is introduced. The probe allows the estimation of Debye length of cold plasma. The probe is based on the pronounced modification of surface properties (wettability) of polymer films by cold plasmas. The probe was tested with the cold radiofrequency inductive air plasma discharge. The Debye length and the concentration of charge carriers were estimated for various gas pressures. The reported results coincide reasonably with the corresponding values established by other methods. The probe makes possible measurement of characteristics of cold plasmas in closed chambers.

Nonlinear interaction between Langmuir waves and Electron Acoustic Wave (EAW) is being studied in a warm magnetized plasma in presence of two intermingled fluids, hot electrons, and cold electrons while ions forming static background. Two-fluid, two-timescale theory is performed to derive modified Zakharov's equations in a magnetized plasma. These coupled equations describe low-frequency response of electron density due to high-frequency electric field along with magnetic field perturbations. Linear analysis shows coupling between acoustic mode, upper hybrid mode, and cyclotron modes. These modes are found to be modified due to the presence of two electron components. These equations are significant in the context of weak and strong turbulence.

The paper reports a new electrostatic-confinement-based fusion approach, where a new non-equilibrium distribution function for an ion-beam compressed by an external electric force has been derived. This distribution function allows the system to possess appreciably low and insignificant thermal energy irrespective of the energy per particle. The spread of energy among particles in the non-equilibrium state is attributed to collisions in the presence of external force, whereas for equilibrium, the spreading of energy is due to the absence of force. The reactivity for a deuterium--deuterium fusion, using the proposed distribution function, has been computed. It is shown that for initiating fusion among the particles, the fusion time is comparable with the energy confinement time of ions for beam energy greater than 160 keV. The estimated energy gain factor Q (ratio of the output fusion power to the power consumed by the system) is around 12 for beam energy 170 keV and ion density 1015 cm−3. The energy loss due to particle scattering is estimated and is taken into consideration for the estimation of energy gain. An outline of a conceptual model of a device is proposed in accordance with the proposed theory and the device is not similar to the one used conventionally in Inertial Electrostatic Confinement systems based on collisions of a beam with a reflex beam or with background gas or plasma.

It is widely held that the Nernst effect can drive instability in un-magnetised laser-plasmas by laterally compressing seed B-fields arising from the field-generating thermal instability [Tidman & Shanny, Phys. Fluids, 12:1207 (1974)]. Indeed, for wavelike perturbations, differential compression by the Nernst mechanism is thought to be most pronounced in the limit of low wave-number k → 0, and is considered particularly important given that it can ostensibly lead to instability when the more usual field-generating mechanism is stable. However, as part of a recent article [Bissell et al., New J. Phys., 15:025017 (2013)] we noted some irregularities to the Nernst mechanism which obscure its operation. For example, by taking characteristic density and temperature length-scales ln and lT respectively, we observed that consistent analytical treatment of the instability requires kln,T ≫ 1, preventing the peak-growth limit k → 0. Furthermore, the Nernst term—which compresses magnetic field perturbations—does not couple to a corresponding term acting on thermal perturbations, and as such does not describe an unstable feedback mechanism. In this article we probe the origin of such ambiguities more formally, and in so doing argue (contrary to reports existing elsewhere in the literature) that the Nernst effect does not drive instability in un-magnetised conditions, at least not in the fashion typically cited.

We present a new model for the generation of thermoelectric currents during laser welding, taking into account sheath effects at both contact points as well as the potential drop within the quasi-neutral plasma generated by the laser. We show that the model is in good agreement with experimentally measured electric potential difference between the hot and the cold parts of the welded workpiece. In particular, all three elements of the model are needed to correctly reproduce the sign of the measured voltage difference. The mechanism proposed relies on the temperature dependence of the electron flux from the plasma to the workpiece and hence does not need thermoemission from the workpiece surface to explain the experimentally observed sign and magnitude of the potential drop.

We present a theoretical investigation on the propagation of surface waves on the magnetized degenerate electron plasma half-space with spin effects. Using magnetohydrodynamic model with quantum effects due to the Bohm potential, Fermi degenerate pressure and electron spin, the dispersion relations of surface plasmon polaritons (SPPs) are derived. The dispersion relation of electrostatic surface waves is also obtained by taking electrostatic limit.

Kinetic magnetohydrodynamics refers usually to the hybrid fluid and kinetic description of a zero-Larmor-radius collisionless plasma, originally formulated in the classic papers of Kruskal and Oberman (1958) (Kruskal, M. D. and Oberman, C. R. 1958 Phys. Fluids1, 275), Rosenbluth and Rostoker (1959) (Rosenbluth, M. N. and Rostoker, N. 1959 Phys. Fluids2, 23), and Kulsrud (1962) (Kulsrud, R. 1962 Phys. Fluids5, 192). Such a theory is revisited here, as a special limit of the more general description put forward in Ramos (2010, 2011) (Ramos, J. J. 2010 Phys. Plasmas, 17, 082502; Ramos, J. J. 2011 Phys. Plasmas, 18, 102506). The present approach has the advantage of fulfilling the quasineutrality condition and avoiding the redundancy between the fluid and kinetic parallel force balance conditions with a built-in, rigorous account of the parallel electric field, thus affording a clear-cut handling of these issues. At zero-frequency marginal stability, the Rosenbluth–Rostoker fluid closures for the parallel and perpendicular pressures are obtained, in a solution with vanishing parallel electric field and non-zero parallel fluid displacement that satisfies exactly the desired quasineutrality and parallel force balance.

Plasma instabilities play a important role in producing small-scale irregularities in the ionosphere. In particular, current-driven electrostatic ion-acoustic (CDEIA) instabilities contribute to high-latitude F-region electrodynamics. Ion temperature anisotropies with enhanced perpendicular temperature often exist in the high-latitude F-region. In addition to temperature anisotropies, ion velocity shears are observed near auroral arc edges, sometimes coexisting with thermal ion upflow processes and field-aligned currents (FAC). We investigated whether ion temperature anisotropy lowers the threshold conditions required for the onset of sheared CDEIA instabilities. We generalised a dispersion relation to include ion thermal anisotropy, finite Larmor radius corrections and collisions. We derived new fluid-like analytical expressions for the threshold conditions required for instability that depend explicitly on ion temperature anisotropy. We studied how the instability threshold conditions vary as a function of the wave vector direction in both fluid and kinetic regimes. We found that, despite the dampening effect of collisions on ion-acoustic waves, ion temperature anisotropy lowers in some cases the threshold drift requirements for a large range of oblique wave vector angles. More importantly, realistic ion temperature anisotropies contribute to reducing the instability threshold velocity shears that are associated with small drift thresholds, for modes propagating almost perpendicularly to the geomagnetic field. Small shear thresholds that seem to be sustainable in the ionospheric F-region are obtained for low-frequency waves. Such instabilities could play a role in the direct generation of field-aligned irregularities in the collisional F-region that could be observed with the Super Dual Auroral Radar Network (SuperDARN) array of high-frequency radars. These modes would be very sensitive to the radar probing direction since they are restricted to very narrow angular intervals. The ion temperature anisotropy is an important parameter that needs to be considered in the studies of sheared and collisional CDEIA waves and instabilities in the high-latitude F-region.

In this paper, we study the (3+1)-dimensional generalized Johnson model, which can be used to describe the dust-ion-acoustic waves in a cosmic unmagnetized dusty plasma, and its perturbed model, which can be found in an unmagnetized dusty plasma for the electron temperature below the Curie temperature. (I) For the original model: Bilinear form and soliton solutions are obtained. Amplitude of the one soliton reaches the maximum when the equilibrium electron (ne0) and ion (ni0) densities take certain values which correspond with ne0/ni0 = 2. Overtaking and head-on interactions between the two solitons are given. (II) For the perturbed model: Phase projections are given numerically. Via the spectral analysis, two kinds of chaotic motions, i.e., the weak and developed chaos, are investigated. Largest Lyapunov exponents and power spectra are investigated to corroborate that those motions are indeed chaotic. Dynamic behavior of such a perturbed model varying with the external perturbation is different when the nonlinear term changes. With the damped term considered, two kinds of periodic motions are studied, and spectra of those periodic motions are also given. Through the comparison between the chaotic motions and periodic ones, possible chaotic or periodic motions in the perturbed model can be predicted.

Large amplitude ion-acoustic double layer (IADL) is studied using Sagdeev's pseudo-potential technique in collisionless unmagnetized plasma comprising hot and cold Maxwellian population of electrons, warm adiabatic ions, and dust grains. Variation of both Mach number (M) and amplitude |φm| of large amplitude IADL with charge, concentration, and mass of heavily charged massive dust grains is investigated for both positive and negative dust in plasma. Our numerical analysis shows that system supports only rarefactive large amplitude IADL for the selected set of plasma parameters. Our investigations for both negative and positive dust grains reveal that ion temperature increases the mobility of ions, resulting in increase in the Mach number of IADL. The larger mobility of ions causes leakage of ions from localized region, resulting into decrease in the amplitude of IADL. Other parameters, e.g. temperature ratio of hot to cold electrons, charge, concentration, mass of heavily charged massive dust grains also play significant role in the properties and existence of double layers. Since it is well established that both positive and negative dust are found in space as well as laboratory plasma, and double layers have a tremendous role to play in astrophysics, we have included both positive and negative dust in our numerical analysis for the study of large amplitude IADL. Further data used for negative dust are close to experimentally observed data. Hence, it is anticipated that our parametric studies for heavily charged (both positive and negative) dust may be useful in understanding laboratory plasma experiments, identifying nonlinear structures in upper part of ionosphere and lower part of magnetosphere structures, and in theoretical research for the study of properties of nonlinear structures.