Characteristics of Hot Electron Ring in a Simple Magnetic Mirror Field

Characteristics of a hot electron ring are studied in a simple magnetic mirror machine. Hot electron rings (n≈1010 cm-3, T≈100 keV) are most effectively generated under two conditions, when the magnetic field on the axis of the midplane is set near the fundamental, or the second harmonic electron cyclotron resonance to the applied microwave frequency (6.4 GHz). The density profile of the hot electrons is observed to take a so-called ring shape. The radial-cut view of the ring, however, indicates an M-shape density profile, and the density of hot electrons on the axis at the center and is about one-half of the peak ring density encircling the axis. The hot electron ring is susceptible to a few instabilities which can be artificially triggered. With the instability generated, the hot electron ring is observed to transform into a filled cylinder in a few microseconds and then disappears.