NONSTATIONARY GENERATION OF ELECTROMAGNETIC RADIATION IN NONEQUILIBRIUM MIRROR-CONFINED PLASMA

We demonstrate the use of a laboratory setup based on a magnetic mirror trap with plasma sustained by a gyrotron radiation under the electron cyclotron resonance conditions aimed at identifying the role of the background plasma as a trigger of the electron cyclotron instability. New regime of instability has been revealed during the plasma decay after the gyrotron switch-off when the plasma density becomes low enough, so that the electron plasma frequency is much less than the electron gyrofrequency. At this stage, we observe the excitation of electromagnetic waves which propagate nearly perpendicular to the magnetic field and cause precipitation of energetic electrons to the trap ends. The instability is detected as series of quasi-periodic broadband pulses of electromagnetic radiation (25...27 GHz frequency, typical pulse duration of 1...10 microseconds) and related precipitation of energetic (>10 keV) electrons. These emissions of the fast electrons can be attributed to the development of the kinetic instability of the extraordinary wave propagating quasiperpendicular to the magnetic field near the fundamental cyclotron harmonic.