THz Cerenkov radiation from a magnetized plasma

Abstract

Summary form only given. Electro-static (ES) waves with amplitudes between 1 and >100 GeV/m are routinely excited in plasma accelerators. However, the ES waves couples very weakly to vacuum modes and its energy is dissipated in the plasma. By applying a static magnetic field in the direction perpendicular to the ES wave propagation, a fraction of the ES wave is converted into electromagnetic (EM) radiation. The mode excited in the plasma is the lower branch of the magnetized plasma XO-mode. The plasma XO-mode can be viewed as the Cerenkov radiation emitted in the plasma by a particle bunch or by a laser (photon) pulse. The frequency of the EM radiation is close to the plasma frequency, and the radiation is emitted by the plasma predominantly in the forward direction (direction of propagation of the ES wave). The power of the EM radiation scales as the square of the strength of the applied magnetic field. The group velocity of the XO-mode is small (/spl Lt/c), and the radiation is expected to be emitted for the life time of the XO-mode in the decaying plasma. In the case of the UCLA-Neptune plasma beatwave accelerator (PBWA) experiment, the plasma wave is driven by a TW, two-frequency CO/sub 2/ laser pulse.