We study the dynamics of phase space holes in a non-collisional plasma by numerical integration of the one-dimensional Vlasov equation. The plasma is bounded and connected to vacuum by two interfaces, which gives rise to non-periodic boundary conditions. By choosing different initial conditions, we consider four different situations: development of a sinusoidal wave, two-stream instability, development of an ab initio Bernstein–Greene–Kruskal state and the expansion of a plasma into vacuum. For the latter situation ions move with a realistic mass of 1837 electron masses. The most prominent results of our investigation are: (a) a clockwise revolution of holes in phase space; (b) the appearance of stable oscillations of the total electron momentum, which, despite their striking linearity, cannot be related to electrostatic plasma oscillations. To the best of our knowledge none of these phenomena have been reported in kinetic simulations before: indeed we prove that the non-periodicity of the boundary conditions is an essential requirement for the sustainment of both hole revolution and momentum oscillations.

The sawtooth activity in an ohmically heated plasma on the HT-7 tokamak has been investigated experimentally using soft x-ray (SXR) diode arrays, magnetic probes and other diagnostics. Its behaviour and occurrence are correlated closely to the discharge conditions such as the electron density $N_{e}$, the electron temperature $T_{e}$, the safety factor $q_a$ on the plasma boundary and the wall condition, etc. Generally speaking, as $N_{e}$ increases, the sawtooth activity grows, becoming stronger with a longer period $T_{s}$, a larger inversion radius $r_{s}$ and a larger amplitude fluctuation $\Delta I_{sx}/\bar{I}_{sx}$ on the SXR radiation intensity signal, and evolve from a small to a moderate sawtooth, to a large or even a giant sawtooth. Sometimes, a double sawtooth and a monster sawtooth activity emerge without apparent deterioration of the plasma confinement and without major plasma disruption. During the events, abundant magnetohydrodynamic phenomena are observed, including a long partial sawtooth collapse. In this paper, the general sawtooth behaviour and the dependence of the occurrence of the sawtooth instability on the electron density $N_{e}$ and wall condition have been summarized. Experimental properties of two types of double sawtooth and monster sawtooth activities are also presented and discussed. The set up of the HT-7 tokamak and the main diagnostics available are also briefly described.

A plasma formed with a low field (1 V cm$^{-1}$) at low temperatures (e.g. $\approx{10}^3$ K) from atomic hydrogen generated at a tungsten filament and strontium which was vaporized by heating the metal. Strong extreme ultraviolet emission was observed, but not when sodium, magnesium or barium replaced strontium or with hydrogen or strontium alone. Characteristic emission was observed which supported a resonant energy-transfer mechanism. Significant Balmer $\alpha$ line broadening corresponding to an average hydrogen atom temperature of 23–45 eV was observed for glow discharges of strontium–hydrogen, helium–hydrogen, argon–hydrogen, strontium–helium–hydrogen and strontium–argon–hydrogen compared with $\approx$3 eV for pure hydrogen, krypton–hydrogen, xenon–hydrogen and magnesium–hydrogen. To achieve the same optically measured light output power, hydrogen–sodium, hydrogen–magnesium and hydrogen–barium mixtures required 4000, 7000 and 6500 times the power of the hydrogen–strontium mixture, respectively. A glow discharge plasma formed for hydrogen–strontium mixtures at an extremely low voltage of about 2 V compared with 250 V for hydrogen alone and sodium–hydrogen mixtures, and 140–150 V for hydrogen–magnesium and hydrogen–barium mixtures.

A generalized, but simplified, kinetic equation for the distribution $F$ of a dust component in a plasma is derived in the seven-dimensional phase space $({\bf{r}},{\bf{v}},Q)$, where $Q$ is the dust particle charge. The equation for $F({\bf{r}},{\bf{v}},Q,t)$ takes into account charging, charge spread, collisions and an electric field. The charge $Q$ is considered to vary continuously. From the equation we find an analytic solution for the evolution of dust in the seven-dimensional phase space that shows collisionless diffusion owing to the combined effects of charging, charge spread and a constant electric field. We also derive a ‘vector kinetic equation’ of dust and subsequently a set of macroscopic equations, and show that the equations lead to a generalized classical diffusion of dust particles owing to fields and non-uniformities, collisions and charging, including charge spread, and to plasma wave effects including damping caused by charging and charge spread in the collisionless case.