Sustainment of FRC-equilibrium by use of a centre solenoid in TS-4

Abstract

This paper addresses a basic equilibrium/confinement question whether a field reversed configuration (FRC) with a balanced amount of magnetic and thermal energies is sustained solely by inductive magnetic flux (magnetic energy) injection of a centre solenoid coil. A new finding is that preferential injection of magnetic energy causes a significant increase in thermal energy of the FRC to maintain high-beta equilibrium. The FRC plasma is concluded to have the robustness needed to self-adjust the plasma heating power depending on the magnetic energy injection. In the flux ramped-up phase, i.e. in the phase where the applied inductive electric field did not penetrate into the core of the plasma, the J × B compression (pinch effect) was considered to be dominant for heating the FRC. On the other hand, after the applied inductive electric field penetrated into the core region the resistivity of the FRC increased up to 10–20 times larger than the classical spitzer resistivity. This anomalous heating was the most probable cause for sustainment of the high-beta FRC in this phase. A quasi-steady state of the high-beta (volume averaged beta ∼0.6–0.7) FRC for 0.15 ms (∼energy confinement time of conventional FRCs) was achieved by the use of the present low power centre solenoid current drive. This successful result leads us to the next stage steady sustainment experiment of an FRC by increased capacitor bank energy.

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

“…This mechanism is similar to ohmic current maintenance in tokamaks except for the fact the current flows perpendicular to magnetic field in FRC plasmas. Recent experiments in TS-4 have added to our knowledge of Ohmic-sustainment of an FRC [21]. These experiments showed the sustainment of an FRC configuration for > 300 µs, without the growth of destructive instability utilizing argon as the working gas.…”

“…This configuration utilizes a stabilizing shell and neutral beam injection with a practically broad velocity distribution [13]. Experimentally, slow formation of an FRC plasma by the merging of spheromak plasmas has been successfully demonstrated in a number of experiments: the TS-3/4 devices [14][15][16][17][18][19][20][21] at the University of Tokyo, the Swarthmore Spheromak Experiment [22] (SSX), and MRX [23,24] at Princeton Plasma Physics Laboratory (PPPL). Sustainment of an FRC plasma by an Ohmic solenoid has been demonstrated [15].…”

“…The MTF (magnetic target fusion) experiment at Los Alamos focuses on formation of FRC plasmas by traditional theta-pinch techniques, aimed at providing a high-density plasma target for further compression [36,37]. The SSX experiment at Swarthmore College [22] and the TS-3/4 experiments at the University of Tokyo [14][15][16][17][18][19][20][21] continue to focus on the innovative formation and stability of FRC plasmas with relatively small sizes and without a neutral beam injection system. Early versions of the SPIRIT concept has been previously discussed [38,39], though this paper represents a more mature version of the concept.…”

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

“…More recently, techniques have been proposed and/or utilized to sustain the plasma, including neutral beam injection ͑NBI͒ 8,9 and rotating magnetic fields ͑RMF͒ [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] in axially elongated prolate FRCs. For the more spherical oblate FRC, inductive sustainment [27][28][29] has been utilized with some success. The continued development of FRC sustainment schemes would help both the reactor prospects and the basic understanding of these configurations.…”

“…These experiments were continued in the larger TS-4 device, 28 where sustainment of a larger flux FRC ͑ t Ϸ 3 mWb͒ was demonstrated for Ͼ250 s in argon discharges. These experiments provided important evidence that FRC sustainment via inductive current drive was possible.…”