Electron Current Measurement of Helical Nonneutral Plasmas for Investigating Plasma Disruption Observed in CHS Experiments

Abstract

A nonneutral plasma confined on helical magnetic surfaces exhibits instability, although it is theoretically stable. In order to investigate the disruptive phenomenon in detail, electron particle flow into a probe tip is carefully measured inside the magnetic surfaces. Preliminary results indicate that the observed disruption is first to occur near the top of the plasma, and then, seems to propagate toward the center of the plasma.

Observations of an Ion-Driven Instability in Non-Neutral Plasmas Confined on Magnetic Surfaces

“…Although they are in a maximum energy state, Penning and pure-toroidal equilibria are stable in the absence of dissipation [11,12] and have excellent confinement properties due to angular momentum conservation [13]. Despite the stabilizing effect of magnetic surfaces, instabilities have now been observed in non-neutral plasmas confined in two stellarators, the Compact Helical System [14], and the Columbia Non-neutral Torus (CNT). In CNT, stable plasmas can be created at low neutral pressures [15], but the plasma is unstable when ion content is sufficiently high.…”