Cherenkov radiation in the THz frequency range from a magnetized plasma

Abstract

Summary form only given. Large amplitude electrostatic (es) plasma wave are excited by laser beams or particle bunches in plasma accelerators. These es waves couple poorly to vacuum electromagnetic (em) waves, and are dissipated in the plasma. A fraction of the es plasma wave can be converted into an em wave by a applying a static magnetic field transverse to the propagation direction of the laser or particle bunch. The laser or particle bunch couples to the left branch of the extraordinary (XO) mode of the magnetized plasma. This process can be described as Cherenkov radiation by the laser pulse or particle bunch in the magnetized plasma. The radiation is emitted essentially in the forward direction, and in practical cases, at the plasma frequency. In the UCLA Neptune laboratory 30 GV es fields are generated through resonant excitation of the plasma wave using the beating of a two-frequency CO/sub 2/ laser beam in the plasma beatwave accelerator (PBWA). The plasma frequency is around 1 THz. We plan to apply a magnetic field in the 7 kG range transversely to the plasma, and to detect the short pulses of THz radiation. Analysis of the amplitude of the Cherenkov radiation emitted by the plasma will provide information about the plasma wave amplitude and lifetime. Analysis of the radiation frequency will provide information about the plasma density. This radiation will be used as an additional diagnostic for the PBWA experiment. The experimental results will be use to investigate the possibility of using this radiation scheme as a new high-power, short-pulse, THz radiation source. The experimental set-up, 2-d and 3-d PIC simulations and preliminary experimental results will be presented.