Passive Superconducting Flux Conservers for Rotating-Magnetic-Field-Driven Field-Reversed Configurations

Abstract

The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RM F o ) current drive and plasma heating system to form and sustain high-β plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RM F o from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (τ f c ) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with τ f c > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 10 3 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.

Inductive probe measurements in a rotating magnetic field thruster

“…This would also have the benefit of moving the separatrix radius inward, potentially solving the problem of the separatrix intersecting the thruster walls. FRC compression using flux conservers is a standard practice in the fusion community, and indeed flux conserver conductivity is a key figure of merit in that field [28]. With this being said, we anticipate structure field amplification to be a suboptimal method of increasing performance.…”

A direct fusion drive for rocket propulsion

“…The FCs in the PFRC-2 employ high-temperature superconducting materials set in a liquid nitrogen cooled copper mandrel. For a full discussion on the design, construction, and testing of the PFRC-2's FCs, see [39].…”