Confinement of Energetic Plasma in Magnetic Mirrors in the Model C Stellarator

Ion cyclotron waves are set up in a toroidal plasma (previously formed by Ohmic heating) contained in the Model C stellarator, and absorbed at local minima in the confining magnetic field. The plasma (1012−1013 cm−3) confined in these magnetic mirrors under certain conditions has little interaction with the main body of the plasma; the perpendicular ion temperature can reach several keV, while the electrons remain at less than 100 eV. We can thus reach a regime not yet available to other mirror confinement experiments. The observed cooling of the plasma in the mirrors agrees with the calculated ion-ion and ion-electron loss processes and charge exchange. At the highest temperatures and lowest densities, the confinement time in the mirrors is limited to ∼ 1 msec, most likely by charge exchange with a steady influx of neutral hydrogen. We find no evidence for any anomalous particle- or energy-loss process, although several instabilities are predicted by theory to occur.