Active feedback stabilization of multimode flute instability in a mirror trap

Abstract

The flute instability in a table-top mirror machine has been stabilized by a feedback system consisting of optical sensors, a digital signal processor and charge-injecting electrodes. The use of multiple sensors and actuators enable the feedback to simultaneously stabilize two modes of the fast-growing, slowly rotating flute instability.Step function response and magnetohydrodynamic spectroscopy indicate a smooth frequency response and an inherent delayed response of the plasma drift due to the sheath resistivity. The measured feedback power is very small relative to the heating power of the plasma.

Physics basis for the Wisconsin HTS Axisymmetric Mirror (WHAM)

“…2019), close fitting conducting shells (Kesner 1985; Beklemishev 2016; Kotelnikov et al. 2022) and feedback (Prater 1971; Be'ery, Seemann & Fisher 2014; Be'ery & Seemann 2015; Beklemishev 2017).…”

“…The strategy for WHAM will be to use the known physics of FLR and vortex stabilization first, and later to test other promising techniques that may extrapolate better to future fusion reactors. Many ideas have been suggested and demonstrated to work over the past 50 years, (summarized well by Ryutov et al 2011), including the use of good curvature (Mirnov & Ryutov 1979;Bagryansky et al 2011), cusp boundaries (Prater 1971;Ferron et al 1983;Kotelnikov et al 2019), ponderomotive effects (Ferron et al 1987), rotating magnetic fields (Seemann, Be'ery & Fisher 2018; Zhu et al 2019), close fitting conducting shells (Kesner 1985;Beklemishev 2016;Kotelnikov et al 2022) and feedback (Prater 1971;Be'ery, Seemann & Fisher 2014;Be'ery & Seemann 2015;Beklemishev 2017).…”

Prospects for a high-field, compact break-even axisymmetric mirror (BEAM) and applications

“…The total response time of the feedback system needs to be considerably shorter than the perturbation's growth time and rotation velocity for energy-efficient feedback stabilization. The feedback actuators can take the form of azimuthally segmented and biased end rings (Prater 1971; Kang, Lieberman & Sen 1988; Lieberman & Wong 2002; Be'ery, Seemann & Fisher 2014; Be'ery & Seemann 2015) or magnetic saddle coils on the perimeter of the plasma that can band the static mirror magnetic field (Kogan, Be'ery & Seemann 2016; Beklemishev 2017). A detailed design for a feedback-stabilized plasma with close-fitting conducting shells is underway to be tested on WHAM before being implemented on BEAM.…”

Microseconds-scale magnetic actuators system for plasma feedback stabilization

“…An ongoing research at the Rafael Plasma Lab (RPL) aims to control the flute instability in a linear mirror machine by active feedback [15,16]. A necessary step toward this goal is the development of an extremely fast, high power magnetic actuators system.…”