Electra is an electron beam pumped laser being developed at the Naval Research Laboratory as an inertial
confinement fusion (ICF) driver. Two opposing 500 kV, 100 kA electron beams pump the main amplifier, which
achieves energies of 730 J over a 100 ns pulse at 248 nm when run in an oscillator configuration. KrF lasers have been
shown to have intrinsic efficiencies of greater than 12% and, based on that, wall plug efficiencies of >7% are projected
for an IFE system based on our established improvements in laser physics and pulsed power technologies. The Electra
main amp has run at rep-rates of 1 Hz, 2.5 Hz, and 5 Hz in runs exceeding 10,000 shots.
This paper will present an overview of the Electra accomplishments and highlight recent research, including
integrating Electra's amplifiers into a durable full laser system, interferometric measurements of the near field spatial
distortions in the amplifiers and their effect on the far field profile, and spatially and temporally resolved temperature
measurements of the electron beam transmission foil.
The first results are reported from a repetitively pulsed, electron-beam-pumped angularly multiplexed krypton fluoride (KrF) laser system. This laser system, called Electra, was constructed at the U.S. Naval Research Laboratory. The technologies developed on Electra are scalable to a full-size fusion power plant beam line and should meet the inertial fusion energy (IFE) requirements for durability, efficiency, and cost. As in a full-size fusion power plant beam line, Electra is a multistage laser system that consists of a commercial discharge laser, a 175-keV electron-beam-pumped (40-ns flat-top) preamplifier, and a 500-keV (100-ns flat-top) main amplifier. Angular multiplexing is used in the optical layout to provide pulse length control and to maximize laser extraction from the amplifiers. The laser system initially demonstrated 452 J in a single shot and 1.585 kJ total energy in a one-second, 5-Hz burst. The preamplifier alone produces a 25-J KrF output with two angularly multiplexed beams. Extraction volumes were calculated for both a single-pass and a double-pass angularly multiplexed amplifier. A standard ray trace must be used to calculate the extraction volumes for the double-pass amplifier with focusing elements.
Electra is a repetitively pulsed, electron beam pumped Krypton Fluoride (KrF) laser at the Naval Research Laboratory that is developing the technologies that can meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. The technologies developed on Electra should be directly scalable to a full size fusion power plant beam line. As in a full size fusion power plant beam line, Electra is a multistage laser amplifier system which, consists of a commercial discharge laser (LPX 305i, Lambda Physik), 175 keV electron beam pumped (40 ns flat-top) preamplifier,
and 530 keV (100 ns flat-top) main amplifier. Angular multiplexing is used in the optical layout to provide pulse length control and to maximize laser extraction from the amplifiers. Single shot yield of 452 J has been extracted from the initial shots of the Electra laser system using a relatively low energy preamplifier laser beam. In rep-rate burst of 5 Hz for durations of one second a total energy of 1.585 kJ (average 317 J/pulse) has been attained. Total energy of 2.5 kJ has been attained over a two second period. For comparison, the main amplifier of Electra in oscillator mode has demonstrated at 2.5 Hz rep-rate average laser yield of 270 J over a 2 hour period.
Electra is a repetitively pulsed, electron beam pumped Krypton Fluoride (KrF) laser at the Naval Research Laboratory
that is developing the technologies that can meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency,
and cost. Electra in oscillator mode has demonstrated single shot and rep-rate laser energies exceeding 700 J with 100 ns
pulsewidth at 248 nm. Continuous operation of the KrF laser has lasted for more than 2.5 hours without failure at 1 Hz
and 2.5 Hz. The measured intensity and energy per shot is reproducible in rep-rate runs of 1 Hz, 2.5 Hz and 5 Hz for
greater than thousand shot durations. The KrF intrinsic efficiency is predicted to be 12% with measurements and
modeling (Orestes Code). In addition we have compared Orestes with initial results of 23 J for the Electra Pre-Amplifier.
The positive agreement between Orestes and our results lead allow us to predict that large KrF laser systems will meet
the efficiency requirements for inertial fusion energy driver. The focal profile measurements show for single shot
conditions recovery in less than 200 ms, the time needed for 5 Hz operation. Rep-rate focal profile measurements at 1 Hz
show reproducibility in spatial extent and energy.
Electra is a repetitively pulsed, electron beam pumped Krypton Fluoride (KrF) laser at the Naval Research Laboratory that is developing technologies to meet the Inertial Fusion Energy (IFE) requirements for durability, efficiency, and cost. Electra has demonstrated single shot and rep-rate laser energies as an oscillator exceeding 700 J with 100 ns pulsewidth at 248 nm. Peak output of 731 J laser energy in single shot operation demonstrates a total pulse intrinsic efficiency of 8.3%, and an intrinsic efficiency during the flat-top region of 9.6%. Improvements in the window transmissivity from the present 93% to excimer grade fused silica with anti-reflection coatings on both sides could provide up to 17% enhancement of the output intensity, and likewise for the efficiency. The Electra KrF gain measured in 4 positions of the laser aperture in an amplifier configuration demonstrates near field uniformity. In addition, the amplifier and oscillator results are qualitatively consistent in the pressure dependence on KrF yield. A quantitative Rigrod analysis and comparison is provided at the peak oscillator yield conditions for both, oscillator and amplifier, configurations. Continuous operation of the KrF laser at 300 J has lasted for 2.5 hours without failure at 1 Hz. Successful operation at 5 Hz with 400 J per pulse output has occurred in bursts of 100 seconds. In all of these runs the laser pulse waveform is extremely consistent from the first shot to the last.