Relativistic electron beam-CO2 laser interaction Σ program

The authors present recent progress of the Σ Program at the ILE, Osaka University, which consists of the CO2 laser beatwave acceleration of the relativistic electron beam (REB) and the CO2 laser wiggler FEL. As for the beatwave acceleration, the oscillator in the LEKKO system injected with the 9.6-μm cw laser generates both the 10.6- and 9.6-μm lines, which are sliced to a 1-ns pulse width. Each line, after being preamplified separately, is again collinearly combined and transported to the final amplifier, whose output is 100 J/each line in the 300-ps rise and 700-ps fall. The beam diameter is 20 cm. The REB is generated by the Blumlein diode and transported through the 10-kG magnetic solenoid coil in milliseconds to the interaction region, where the current is 0.5 kA/50 ns. The interaction region is shown. The movable magnetic coil coaligns the REB to the laser axis. The time jitter between the REB and laser is --200 ns, which should be improved. Prior to the REB injection an electromagnetic switch admits the nitrogen gas or dry air to the interaction tube, which is preionized by the incident laser, providing a resonant density of 1017/cm3 at 1 Torr air