Cold-Plasma Effects in Finite-Length Plasmas

Criteria are derived for the relative cold-plasma density necessary to stabilize the grad B drift waves in finite-length energetic plasmas separated from grounded conducting end plates by a cold plasma. For a dense (ω2pi≫ω2ci) hot-electron plasma in which the electron precession frequency, ωge≪ωci, the ion gyrofrequency, it is found that (Ncold/Nhot)critical ∼ 2l2(ωge/ωci)(LhLc/2R2p)m/M, where k⊥ = l/Rp. If lωge ∼ ωci, the corresponding criterion is very roughly given by (Ncold/Nhot)critical∼(l2/δ)(LhLc/2Rp2)(m/M),where 0 < δ = 1 − (lωge/ωci) < 1. For hot-ion plasmas, a two-dimensional stability diagram is given which predicts a high-density stable regime for small ratios of Ncold/Nhot. A tentative comparison with thresholds observed in several experiments is made.