Fokker-Planck calculations of hot-electron formation by electron cyclotron resonance heating in the TMX-Upgrade tandem mirror

The paper studies cold plasma trapping and heating of hot electrons in mirror geometry using a time-dependent, bounce-averaged Fokker-Planck code with quasi-linear diffusion due to RF heating at fundamental and second harmonic frequencies. With the restriction k || = 0, the code models the beam-controlled heating (spatially restricted electric fields) that will be used to create thermal barriers in the TMX-Upgrade tandem-mirror experiment. By spatially localizing the microwave beams, which are strongly absorbed in a single pass, the mean hot-electron energy may be controlled. Heating is away from the midplane to control anisotropy (P ⊥ /P || ). For a given magnetic field geometry and cold-plasma source temperature T s , the parameters of the hot electrons scale with the quantity χ ≡ 2 /n s ω, where is the electric field, n s is the cold-plasma density, and ω is the frequency.