Dynamics of Electron-Rich Plasmas in the CNT Stellarator

Abstract

Pure electron plasmas and electron plasmas with a finite ion fraction have been studied in the Columbia Nonneutral Torus (CNT) since the end of 2004. Results from the first three years of operation are summarized. Stable, small Debye length pure electron plasmas are routinely created, and have confinement times up to 20 msec. The confinement is limited by radial transport caused by internal rods, as well as electron-neutral collisions. The neutral driven transport rate is indicative of poor particle orbits in CNT, despite the strong radial electric field. Numerical simulations shed light on this issue, demonstrating the detrimental effects of variations in the electrostatic potential on a magnetic surface. With the installation of a magnetic surface conforming electrostatic boundary and the transition to external diagnostics, significantly longer confinement times should be possible. Also presented are observations of sudden confinement jumps that have a hysteretic behavior, and observations of an ion driven instability.

Confinement jumps in a non-neutral plasma

“…12, and the main results from nonneutral plasma experiments so far are summarized in Ref. 13. The experiments presented here are quite similar to those described in Refs.…”

Plans for the creation and studies of electron–positron plasmas in a stellarator

“…We therefore summarize the most important results here. Most of these results have already appeared in the peer reviewed literature [11,14,24,42,43]. The CNT stellarator experiment received funding in 2002 and went into operation in 2004.…”

First experimental studies of the physics of plasmas of arbitrary degree of neutrality

“…Confinement of pure electron plasmas (η ≈ 1) is enhanced by the strong radial electric field created by the large space charge. These plasmas are stable, quiescent, and have been extensively studied in CNT [13,15].…”