Electra: A Repetitively Pulsed, Electron Beam Pumped KrF Laser to Develop the Technologies for Fusion Energy

The Electra Krypton Fluoride (KrF) Laser program is developing the science and technology needed for inertial fusion energy (IFE). The Electra main amplifier is pumped by two 500 kV, 100 kA, 140 nsec, electron beams. The pulsed power system can run continuously at 5 Hz for 100,000 shots . Electra has produced 700 J of laser energy per pulse in 1 Hz and 5 Hz bursts, and 300 Joules for 10,000 shots at 1 Hz (about 2.8 hrs). Recent advances include: a) a new "ceramic honeycomb cathode" that improves the e-beam rise time and uniformity, b) experiments and supporting simulations to efficiently pass the e-beam the vacuum window (hibachi foil) and into the laser gas, and c) first e-beam tests of the smaller "Pre- Amplifier" Laser (175 kV, 85 kA, 40 nsec) that will provide the laser input to the main amplifier. Electra is close to meeting its goals: We have demonstrated a new laser gated and pumped thyristor which will be the basis for a durable and efficient pulsed power system. The front end will demonstrate this architecture. The overall laser efficiency (wall plug to light on target) is predicted to be > 7%, based on advances in the individual components. The major remaining challenge is to realize a long lived hibachi foil at the higher (5 Hz) rep rate. We believe this to be an issue of thermal management, and several methods of cooling the foil are under evaluation.