The Electra KrF Laser System

Electra is an electron beam pumped KrF laser system at the Naval Research Laboratory used to advance the technology towards a KrF laser driver for inertial fusion energy. Electra consists of two e-beam pumped amplifiers and one commercial discharge laser. The main amplifier includes two identical pulsed power systems, each with a capacitor bank, a 12:1 step-up transformer, parallel pulse forming lines, and laser triggered output switches. Each system generates a 500 kV, 110 kA, 140 ns electron beam that pumps the laser gas from two sides. Depending on the cathode and hibachi (laser gas/vacuum interface structure) configuration, the laser output energy ranges from of 200 to 700 J per shot. Operating as a laser oscillator, the main amplifier has run at repetition rates of up to 5 Hz, and has operated at 2.5 Hz for 25,000 continuous shots. The pre-amplifier pulsed power system utilizes a fast 10-stage Marx, pulse forming lines, and a magnetic switch. The system powers two diodes, which each operate at 175 kV, 70 kA, and 50 ns. Initial pre-amplifier laser experiments with a first generation cathode and hibachi, and with the 1 J discharge laser serving as the seed oscillator, produced an output energy of 20 J. Our planned improvements to both the cathode and hibachi should lead to an increase in laser energy of greater than 30 J per shot. This paper will present results of the overall laser system and discuss the performance of the pulsed power systems, the laser triggered output switches, cathode development, vacuum diode effects, laser system durability, and thermal management of the pulsed power components, hibachi, and the laser gas during long rep rates.