Repetitively pulsed, high energy KrF lasers for inertial fusion energy

Abstract

Krypton fluoride (KrF) lasers produce highly uniform beams at 248 nm, allow the capability of ‘zooming’ the spot size to follow an imploding pellet, naturally assume a modular architecture and have been developed into a pulsed-power-based industrial technology that readily scales to a fusion power plant sized system. There are two main challenges for the fusion power plant application: to develop a system with an overall efficiency of greater than 6% (based on target gains of 100) and to achieve a durability of greater than 3 × 108 shots (two years at 5 Hz). These two issues are being addressed with the Electra (700 J, 5 Hz) and Nike (3000 J, single shot) KrF lasers at the Naval Research Laboratory. Based on recent advances in pulsed power, electron beam generation and transport, hibachi (foil support structure) design and KrF physics, wall plug efficiencies of greater than 7% should be achievable. Moreover, recent experiments show that it may be possible to realize long lived electron beam diodes using ceramic honeycomb cathodes and anode foils that are convectively cooled by periodically deflecting the laser gas. This paper is a summary of the progress in the development of the critical KrF technologies for laser fusion energy.

Electron-beam accelerator for pumping of a Xe2 lamp

“…Two powerful KrF lasers, Electra and Nike were developed for inertial fusion energy research at the United States Naval Research Laboratory. Electra is a high average power laser, which employs two counter-propagating electron beams for pumping of a laser cell, each beam of a 500 KeV, 100 kA, 150 ns, and area 30 × 100 cm 2 at repetition rate of 5 Hz (Sethian et al, 2000;Myers et al, 2004). The Nike laser amplifier produces opposing 750 kV, 500 kA, 240 ns, 60 × 200 cm 2 electron beams (Sethian et al, 1997;Karasik et al, 2010).…”

Zooming in on Laser-Driven Fusion

“…Potential schemes to implement zooming of the focal spot on target involve modifications to the spatial coherence of the laser that cause broadening in the beam's far field [19]. The most practical method for implementing zooming on modern laser systems (e.g., OMEGA and National Ignition Facility) appears to be time-dependent phase conversion.…”

Low jitter, high voltage, repetitive laser triggered gas switches

“…The system, which is capable operating continuously for several hours at repetition rates of up to 5 pulses per second (pps), was designed to drive electron beam producing diodes for a KrF laser. [30][31][32][33][34][35][36][37][38][39] For this application it is desired, that for tens of thousands of continuous shots, the switch misfire rate is reduced to a statistical anomaly and that switch jitter does not exceed ±10 ns for 99.9% of the shots (i.e., 99.9% of the data values are within a ±3.3 sigma standard deviation). While these specifications have been easily achieved with a 275 kV solid state pulser [40], detailed analyses of laser triggered SF 6 spark gaps for long continuous switch operation have not been previously published.…”