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

Abstract

A comprehensive research concept, known as SPIRIT, is described for the investigation of the formation, stability, and sustainment of oblate field reversed configurations (FRCs). This concept, whose name stands for Self-organized Plasma with Induction, Reconnection, and Injection Techniques (SPIRIT), allows for the study of FRC stability properties on time scales much longer than the energy confinement time. Counter-helicity merging of inductively formed spheromaks is utilized to form large-flux FRCs. These FRCs are sustained by neutral beam injection with the initial aid of compact ohmic solenoids. Stability to n = 1 tilt/shift modes is provided by plasma shaping and conducting shells. Stability to n ≥ 2 co-interchange modes is achieved by a distribution of highenergy non-thermal ions provided by the neutral beam. The combination of plasma shaping, conducting shells, current sustainment, and the non-thermal beam component are expected to lead to a configuration with stability to all global MHD modes, a regime recently discovered through hybrid-MHD simulation using the HYM code. An experimental test of the concept, utilizing the existing Magnetic Reconnection Experiment (MRX) facility, is described. Initial experiments in MRX have confirmed the viability of the SPIRIT concept, and calculations indicate that the confinement of high-energy ions in MRX should be sufficient to test the SPIRIT concept.

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

“…This section describes a promising FRC reactor program based on SPIRIT (Self-organized Plasmas by Induction, Reconnection and Injection Techniques) concept developed late 1990's at PPPL [22,23]. Three critical issues were discussed regarding plasma formation, sustainment of plasma with the use of plasma shaping, conducting shells, neutral beam injection (NBI) and a current transformer.…”

“…Three critical issues were discussed regarding plasma formation, sustainment of plasma with the use of plasma shaping, conducting shells, neutral beam injection (NBI) and a current transformer. In the SPIRIT program, compact toroid plasmas would be generated by the merging of co-and counter-helicity spheromaks produced by inductive discharges utilizing flux cores, and the plasmas would be sustained by the use of neutral beam injection (NBI) [23]. Plasma shaping, conducting shells, and the NBI would provide stabilization to MHD modes.…”

“…A key element of the SPIRIT program was NBI stabilization of the plasma via finite Larmor radius (FLR) effects [23]; the target plasma must have sufficient orbit confinement of these high energy particles for this scheme to be successful. In order to generate plasmas with proper flux levels and shaping for neutral beam injection, FRC plasmas would be generated by the counter-helicity merging of inductively formed spheromaks.…”

Inductive Sustainment of Oblate FRCs with the Assistance of Magnetic Diffusion, Shaping and Finite-Lamor Radius Stabilization

“…Indeed, sustainment by NBI has been proposed as part of the SPIRIT oblate FRC program. 47 However, the oblate shape allows for an addi-tional sustainment technique: inductive sustainment via a solenoid. Inductive sustainment of an FRC was first demonstrated in the TS-3 spheromak merging device, where a preliminary experiment demonstrated sustainment of small ͑trapped poloidal flux t Ͻ 0.7 mWb͒ FRCs for ϳ200 s.…”

“…It has been predicted that FLR stabilization will be more difficult in oblate FRCs 39 than their prolate cousins, but that stabilization by a beam of high-energy ions could lead to a macroscopically stable oblate FRC. 43,47 Hence, the experimental extension of FLR studies to the oblate regime is an important step.…”