Off-resonance effects on electrons in mirror-contained plasmas

Resonant heating by microwave power has been used to produce high β plasmas with electron temperatures near 1 MeV. Typically plasmas are produced with ωpe∼ωce. Further experimental heating studies described here have shown that a large increase in stored plasma energy is produced by microwave power with a frequency higher than the cold-electron resonance frequency. This increase, caused by off-resonance heating, is attributed both to stochastic heating and to the control of an instability through changes in the electron distribution function. Alternatively, a decrease in the stored plasma energy is produced by microwave power at a frequency below the cold-electron resonance frequency. This effect is attributed in part to enhanced diffusion into the loss cone. However, a small fraction of the plasma is heated to high energies.