Observations of tilt instabilities in field-reversed configurations of a confined plasma

Abstract

We report the first consistent observations of internal tilt instabilities in field-reversed configurations. Detailed comparisons with numerical calculations establish that data from an array of external magnetic probes are signatures of these destructive plasma instabilities. As suggested by finite-Larmor-radius theory, field-reversed configurations appear grossly stable when s/e [(average number of ion gyroradii)/(separatrix elongation)] is less than 0.2-0.3 and show MHD-like tilt instabilities when s/e-~\.

Formation and sustainment of field reversed configuration (FRC) plasmas by spheromak merging and neutral beam injection

“…The recent simulations demonstrate for variety of equilibria that the normalized tilt mode growth rate is a function only of the parameter S*/E [8]. This supports the empirical stability scaling obtained earlier with the parameter S*/E [5] shown in Eq. (1).…”

“…According to an empirical scaling relation [5] based on experimental data, a stability criterion of FRCs of various shape against global MHD modes is written as S*E< 3-4,…”

Studies of Global Stability of Fluid-reversed Configuration Plasmas using a Rigid Body Model

“…On the other hand, due to the lack of a center conductor and a con ning toroidal eld, FRC's are predicted to be unstable to many global magnetohydrodynamic MHD modes. However, FRC plasmas formed in -pinch devices exhibit remarkable global stability 1 with a few exceptions 2 . Much theoretical e ort has been made to reveal stabilizing mechanisms of the predicted instabilities tilt mode in particular, including e ects from plasma rotation 3 5 , t wo-uid 5 , ion nite Larmor radius FLR 6 10 , energetic ions 11;12 , and current pro le 13 15 .…”

A Self-Organized Plasma with Induction, Reconnection, and Injection Techniques: the SPIRIT Concept for Field Reversed Configuration Research

“…Significant progress in the theoretical understanding of FRC stability properties has been achieved in the past few years. According to an empirical scaling relation [40] based on experimental data for prolate FRCs, stability with respect to global MHD modes is achieved for S */E < 3-4, where E is the separatrix elongation, and the kinetic parameter S * = R s /λ i , is the ratio of the separatrix radius to the ion skin depth (S * is also approximately equal to s, the ratio of the separatrix radius to the ion gyroradius ρ i in the external magnetic 004-2 Table 1 Stability properties of prolate and oblate FRCs. field, since ρ i ∼ λ i for β ∼ 1). Several recent theoretical studies have considered the stabilizing effects of finite ion Larmor radius effects (ion FLR effects), the effects of the Hall term, and the effects of sheared ion flow on the n = 1 tilt mode in prolate FRC configurations [8-13, 27, 41-47].…”