Propagation of Fast Electron Current Driven By Biased Electrodes in C-2W

TAE Technologies’ current experimental device, C-2W (also called “Norm”), generates and sustains a high-temperature field-reversed configuration (FRC) plasma through a combination of neutral beams, edge-biasing electrodes, and a real-time plasma control system [1]. Electron heating and the emergence of a suprathermal tail in the X-ray energy spectrum have been observed in the central confinement vessel (CV) when voltages are applied to electrodes on either end of the device. It is hypothesized that the observed electron heating and suprathermal X-rays originate from a stream of fast electrons accelerated by the biased-electrodes toward the CV. To investigate the propagation of these fast electrons and their interaction with the bulk plasma, a beryllium-filtered, cerium-doped lutetium-yttrium oxyorthosilicate scintillator has been installed in a fueling region between the CV and the electrodes to detect X-rays emitted by these fast electrons. The design of this diagnostic is described here. Measurements from this diagnostic system show that emission of 500 -- 1000 eV X-rays increases significantly after FRC formation. Concurrently, electron density rises within the CV, more currents flow through the biased electrodes, and fluctuations in electrode voltage intensify. These observations suggest that the FRC provide a low-impedance path for fast electron current to propagate from the biased electrodes into the central plasma.

[1] T. Roche et al. Generation of field-reversed configurations via neutral beam injection. Nat. Commun. 16, 3487 (2025).