Experiments on the Injection and Containment of Electron Clouds in a Toroidal Apparatus

Abstract

Injection and containment of unneutralized clouds of electrons has been accomplished with an azimuthally symmetric, toroidal, magnetic field. The confining magnetic field is produced within a conducting toroidal chamber. The induction of this magnetic field has been used to inject the electron cloud (inductive charging). Average electron densities of 4 × 109 cm−3 and peak electrostatic well depths of ≈ 400 kV have been achieved. Semiempirical correlations are given which show the inductive charging scheme to be governed by an electron energy restriction and finally limited by the occurrence of anomalous crossed field beam noise. Stable equilibria, without the necessity of a rotational transform have been observed for times in excess of 60 μsec. Correlation of the containment time observations with the predictions of a theoretical model for an ion-diocotron wave instability shows that the containment time is governed by the rate of ionization of the residual neutral gas (p > 10−7 Torr) in the apparatus. The correlation of theory and experiment appear to confirm the theoretical prediction that a significant degree of charge neutralization (in the range of 10-20%) can be stably contained. Interpretation of these results suggests that significant improvement in both electron cloud density and containment time should be possible.

Electron plasma confinement in a partially toroidal trap

“…Under certain restrictions, the equilibria are also expected to be stable [5,6,7]. Experiments confirm the existence of equilibria [8,9,10,11], but to date, no experiment has tested the theory closely.…”

“…Controlled injection of charge into the toroidal field is a significant initial hurdle to successful trapping of a nonneutral plasma. Past experimenters focused significant effort toward solving this problem [8,9,10,11], but none of them achieved the kind of reproducible initial charge distributions routinely obtained in cylindrical traps. The present experiment provides controlled charge injection by limiting the confinement region to a 'C'-shaped segment of the torus.…”

Experimental Studies of Helical Nonneutral Plasmas with a Helical Magnetic Axis

“…Experiments on nonneutral plasmas have been conducted on various machines such as the Penning trap [1], the Paul trap [2], and toroidal devices [3]. Recently, toroidal nonneutral plasmas confined on helical magnetic surfaces (HMSes) have been conducted [4,5].…”

Measurement of the Density Profile of a Toroidal Non-neutral Plasma with a Wall-Probe Array

“…A pure electron plasma can be confined in RT-1; the density is of the order of 10 11 m −3 , and the confinement time is longer than 400 s [3]. A toroidal system [4][5][6][7][8][9][10][11][12][13][14] has merits in trapping various kinds of charged particles including antimatters [15][16][17][18]. In our previous experiment on the Proto-RT device [6][7][8], we measured the internal electric potential by inserting probes and showed that an appropriate control of the potential of the internal ring produces closed equi-potential surfaces aligned with the magnetic surfaces, achieving good confinement.…”

“…In this study, multiple wall probes [4] were used for perturbation-free diagnostics of radial electric field strength and spatial profiles of the plasma, as well as electrostatic fluctuation measurements in RT-1. To minimize electrostatic perturbations, image currents were measured using current amplifiers, where there were no voltage differences between the walls and the chamber.…”