Saturation of the plasma-three-wave-mixing process

The saturation mechanism for the plasma three-wave-mixing process is thought to be caused by nonlinear parametric instabilities which limit EPW energy density. However, in this experiment the high electron-neutral collision frequency increases the instability threshold, thereby permitting larger EPW amplitudes. This is consistent with our observation that reducing the pressure results in lowering the output radiation power. Recent results obtained using an upgraded system are reported. A new probe array is used to investigate the beam and plasma wave characteristics at several positions along the beam path. New plasma-cathode e-beams, which provide up to 10 A/cm2 at 30 kV, are used to reach the three-wave-mixing beam-current saturation level