The study of high power electron beam transport for C-2W experiments

A high-power long pulse electron beam was created at TAE. The beam is designed to be installed in a diverter and injected axially into the C-2W FRC device^[1] for additional plasma heating^[2]. The beam currently operates at a test stand, and the research on beam injection through a strong magnetic field is carried out. The experimental setup consists of an electron source, a 2-meter long beamline with guiding coils, and a short solenoid with a magnetic field of 1 T. The electron source generates a 30 keV, 100 A electron beam up to 10 ms. The beam is transported in a guiding magnetic field and injected into the short solenoid replicating the magnetic conditions in the mirror region of C-2W. It was understood theoretically and demonstrated in the experiments that the injected beam current is limited primarily by the space charge rather than the initial pitch angle and the magnetic moment conservation. When the electron beam is installed on C-2W, the space charge will be partially compensated by the plasma. At the test stand, space charge compensation was achieved with the additional gas puff into the beamline, and the plasma discharge was ignited and sustained by the beam itself. The parameters of the beam and the plasma were monitored with an extensive set of diagnostics. This paper reports our findings on beam transport through a region with a strong magnetic field.

[1]  H. Gota et al., Nucl. Fusion 59, 112009 (2019).

[2]  Seidl, Miloš. Review of electron-beam heating of magnetic-mirror confined plasmas, with application to the Tandem Mirror Experiment. No. UCRL-52759. California Univ., Livermore (USA). Lawrence Livermore Lab., 1979.