Millisecond Confinement and Observation of the m=1 Diocotron Mode in a Toroidal Electron Plasma

摘要

Electron plasmas with density in excess of 10~6 cm~(-3) are trapped for about 1 ms in a purely toroidal magnetic field (B_o = 200G, R_o = 43cm, a = 4.5cm). The trap is a partial torus, or curved Penning-Malmberg trap. The measured confinement time is an order of magnitude longer than previously published results in the same device, and is substantially longer than the confinement measured in all previous electron plasma experiments with purely toroidal magnetic fields. The confinement time exceeds all characteristic single particle drift timescales and implies the existence of an equilibrium in which the space charge generated E x B drift acts as an effective rotational transform. Confinement appears to be limited by the growth of a m=1 diocotron-like mode, observed with wall patch probes and a phosphor screen imaging detector. The mode grows to large amplitude whereupon electrons are lost to material surfaces.