Pure Electron Plasma Research Articles

Resistive-Wall Destabilization of Diocotron Waves

The growth of the negative-energy $l=1$ diocotron wave has been studied on a column of pure electron plasma. An external $\mathrm{RC}$ circuit connecting sectors of the bounding wall is used to induce growth of the wave, which is otherwise essentially neutrally stable. Such a circuit also causes small shifts in the real part of the wave frequency. The experimentally measured growth rates and frequency shifts are in close agreement with the predictions of theory over a wide range of experimental parameters.

Experiments With Pure Electron Plasmas

Pure electron plasmas are one of the simplest systems on which plasma wave and transport effects can be studied. Two recent experiments on this system are discussed. The loss of electrons due to anomalous transport has been measured over a six order of magnitude variation in containment time. The containment time scales approximately as [magnetic field/plasma length]2. The growth of the l = 1 diocotron wave due to resistance between sections of the bounding wall has been observed. The measured growth rates agree with theory.

Physics of Non-Neutral Plasma

The theoretical basis for magnetic confinement is examined. Recent progress on confinement of pure electron plasma is magnetic mirrors and simple torodial configurations is described. Non-neutral configurations involving electrons and ions in mirror geometry are investigated. A basic experiment on mirror stability is proposed.

Effect of magnetic field errors on low-frequency waves in a pure electron plasma

It is demonstrated how static magnetic field errors can resonantly drive low-frequency electrostatic waves in a pure electron plasma column. The driving mechanism is identified as a charge bunching that results from the field error. It is found that the wave amplitude increases linearly with time.

Cooling of a pure electron plasma by cyclotron radiation

It has been suggested that a magnetically confined pure electron plasma might be cooled to the liquid and crystal states. Here, cyclotron radiation is considered as a possible cooling mechanism. The plasma and some cooled resisting medium are assumed to reside inside a conducting cavity. When the cyclotron motion of the electrons resonantly drives a cavity mode which is damped by the cooled medium, energy is transferred from the electrons to the medium. Attention is focused on the case where all of the electrons experience a sharp (i.e., high-Q) resonance with a single cavity mode. An interesting result is that the rate of energy loss per electron can exceed, by a factor of Q, the radiation rate for an electron executing cyclotron motion in unbounded space. The maximum value of Q is limited by cyclotron damping of the mode on the plasma itself and can be large for a non-neutral plasma at a density well below the Brillouin limit (i.e., for ωp<<Ω, where ωp is the plasma frequency and Ω is the cyclotron frequency).

Long-Time Containment of a Pure Electron Plasma

A pure electron plasma has been confined in cylindrical geometry for many minutes. Confinement scalings with background pressure and magnetic field show that the maximum confinement times, while long, are 100-5000 times shorter than the limit set by electron-neutral collisions.

Waves and transport in the pure electron plasma

Investigations of low frequency waves and transport in a plasma consisting almost purely of electrons are presented here. This plasma is trapped in a cylindrical system with radial confinement supplied by a strong axial magnetic field and axial confinement supplied by electrostatic fields. Very long containment times are possible. Classical transport due to electron-neutral collisions has been investigated and good agreement with the theory of Douglas and O’Neil is obtained. Externally launched diocotron waves are investigated. The modal frequencies agree well with linear theory, but the damping is governed by nonlinear effects. Experimental scaling laws for the damping rates are given. Measurements of spatial transport due to these modes are also presented. A signature of this process is that the transport is strongly localized spatially.

Velocity Autocorrelation Function in a Strongly Coupled, Magnetized, Pure Electron Plasma

The Alder-Wainwright effect for the velocity autocorrelation function is small and difficult to observe in a system of neutral particles but is more prominent in a strongly coupled plasma. The pure electron plasma recently produced by Malmberg and deGrassie provides an opportunity to observe the Alder-Wainwright effect experimentally. We speculate on the behavior of the velocity autocorrelation function for this system.

Finite length thermal equilibria of a pure electron plasma column

The electrons of a pure electron plasma may be in thermal equilibrium with each other and still be confined by static magnetic and electric fields. Since the electrons make a significant contribution to the electric field, only certain density profiles are consistent with Poisson’s equation. The class of such distributions for a finite length cylindrical column is investigated. In the limit where the Debye length is small compared with the dimensions of the column, the density is essentially constant out to some surface of revolution and then falls off abruptly. The falloff in density is a universal function when measured along the local normal to the surface of revolution and scaled in terms of the Debye length. The solution for the shape of the surface of revolution is simplified by passage to the limit of zero Debye length.

Transport to thermal equilibrium of a pure electron plasma

The transport of a pure electron plasma column across an axial magnetic field is considered, the transport being due to binary electron–electron collisions. The Boltzmann equation is expanded in inverse powers of the magnetic field, with the radial electric field and density gradient ordered self-consistently. The first nonvanishing terms in the particle flux involve the third derivative of the density and the second derivative of the electric field. An H theorem is used to show that this flux drives the plasma to a confined thermal equilibrium density profile. The electrons can come to thermal equilibrium with each other and still be confined magnetically, since the total canonical angular momentum is conserved. The final equilibrium can be predicted from the initial total number of particles, angular momentum, and energy. The approach to equilibrium is shown in a numerical example.

Pure Electron Plasma, Liquid, and Crystal

We speculate on the possibility of liquefying and crystallizing a magnetically confined pure electron plasma.

Wave-Induced Transport in the Pure Electron Plasma

The pure electron plasma is an excellent system in which to study transport across a strong magnetic field. We describe the basic experimental arrangement and report on measurements of transport due to an externally launched diocotron mode.

Excitation of Pure Electron Plasma Waves by Modulated Electron Beams

A new type of exciter consisting of electron beams for launching electron plasma waves is investigated experimentally and theoretically. When fast electron sheet beams, modulated at a prescribed frequency, are injected into plasmas, electron plasma waves are found to be excited nearly perpendicularly to the electron beams. Compared with a mesh excitation, we found that the beam excitation has several merits: it hardly excites ballistic modes, the direct coupling due to an electrostatic induction with another probe is small, and it can even be used in a very hot plasma.