Stable confinement of toroidal electron plasma in an internal conductor device Prototype-Ring Trap

Abstract

A pure electron plasma has been produced in an internal conductor device Prototype-Ring Trap (Proto-RT). The temporal evolution of the electron plasma was investigated by the measurement of electrostatic fluctuations. Stable confinement was realized when the potential profile adjusted to match the magnetic surfaces. The confinement time varies as a function of the magnetic field strength and the neutral gas pressure, and is comparable to the diffusion time of electrons determined by the classical collisions with neutral gas. Although the addition of a toroidal magnetic field stabilized the electrostatic fluctuation of the plasma, the effects of the magnetic shear shortened the stable confinement time, possibly because of the obstacles of coil support structures.

Ion accumulation in an electron plasma confined on magnetic surfaces

“…This method is directly applicable to the pure electron plasma experiments in Proto-RT, 8,15 which also have insulated rods in the plasma. In the pure electron plasma experiments in the Compact Helical System ͑CHS͒ stellarator, 13,16,17 electrons are injected from the outside, but diagnostic rods that are usually used inside the plasma 18 provide a mechanism for ion loss and therefore the ion rate balance is also analogous to that in CNT.…”

Confinement of electron plasma by levitating dipole magnet

“…1͒. In investigating the internal potential structures of electron plasma in Proto-RT, 20,21 we found that the confinement properties were drastically improved when the shapes of potential contours were adjusted to those of the magnetic surfaces by negatively biasing the case of the dipole field coil. We have started studies on toroidal non-neutral plasma in a dipole magnetic field.…”

“…17 Proto-RT [19][20][21] was a prototype magnetospheric device with a dipole field coil that was mechanically supported in the chamber. 1͒.…”

Diagnosing pure-electron plasmas with internal particle flux probes

“…In those experiments, the confinement time is typically measured through the decay rate of image charge on a capacitive probe placed outside the plasma. [9][10][11]21 The emitter filament is mounted near the end of a hollow 0.5 in. diameter ceramic rod.…”