Performance of an Advanced Repetitively Pulsed Electron Beam Pumped KrF Laser Driver

Electa is a repetitively pulsed, electron beam pumped krypton fluoride (KrF) gas laser that is a step in developing the technologies that meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, repetition rate, and cost. The technologies to be developed in the Electa system are to be directly scalable to a full size fusion power plant beam line. We have fielded an advanced pulsed power driver for the KrF preamplifier in the Electa system which serves two roles: it completes the laser system and serves as a demonstrator for the advanced pulsed power topology that can meet the IFE requirements. The initial system employs a gas switched Marx with improved reliability and maintenance schedule. The Marx will later be retrofitted (circa 2006) with advanced solid state switches, presently under development in the Electa program. The output of the pulsed power driver, delivered to counter-streaming electron beam diodes, is 20/40/30 ns (t_rise/flattop/t_fall), 150-175 kV, and 60-80 kA per side with a 1.1 ohm nominal impedance. The pulser operates in single-shot, burst, and continuous modes at up to 5 Hz, with 1 ns (1 sigma) or less absolute timing jitter. A single pulsed power driver is coupled to the opposing electron guns via four liquid-filled TTI's (transit time isolators). These TTI's are necessarily compound (oil/water/oil) in order to balance their electrical lengths against unequal mechanical lengths. The Marx is gas-insulated and charges a 1.1-ohm water PFL in less than 100 ns. An output magnetic switch with a saturated inductance of less than 14 nH using Metglasreg cores discharges the pulse forming line (PFL) into the four parallel compound TTI's. A set of four (2 each side) inverted Z-stack bushings provide the interface between the TTI's and the vacuum chambers and diodes. The pulsed power driver design for this preamplifier has been described previously.