Transport of electron beams and stability of optical windows in high-power e-beam-pumped krypton fluoride lasers

Abstract

Two of the key issues of a krypton fluoride (KrF) laser driver for inertial fusion energy are the development of long life, high transparency pressure foils (to isolate vacuum in the electron beam diode from a working gas in the laser chamber), and the development of durable, stable, optical windows. Both of these problems have been studied on the single-pulse e-beam-pumped KrF laser installation GARPUN. We have measured the transport of electron beams (300 keV, 50 kA, 100 ns, 10 × 100 cm) through aluminum-beryllium and titanium foils and compared them with Monte Carlo numerical calculations. It was shown that 50-μm thickness Al-Be and 20-μm Ti foils had equal transmittance. However, in contrast to Ti foil, whose surface was strongly etched by fluorine, no surface modification nor fatal damages were observed for Al-Be foils after ∼1000 laser shots and protracted fluorine exposure. We also measured the 8% reduction in the transmission of CaF2 windows under irradiation by scattered electrons when they were set at 8.5 cm apart from the e-beam-pumped region. However an applied magnetic field of ∼0.1 T significantly reduced electron scattering both across and along the laser cell at typical pumping conditions with 1.5 atm pressure working gas. Thus the e-beam-induced absorption of laser radiation in optical windows might be fully eliminated in an e-beam-pumping scheme with magnetic field guiding.

Fluorescence and transient absorption spectra of excimer laser mixtures

“…Experiments are performed at Berdysh laser module [6], which is pumped by 80x1200-mm cross-section e-beam of 50-A/cm 2 peak current, 70-ns pulse duration, and ~250-350 keV average electron energy. Specific pumping power is of ~0.6-0.8 MW/cm 3 Fluorescence and absorption spectra are registered at pressures from 0.2 to 2.5 atm in the spectral range from 190 to 510 nm with the broadband spectrometer equipped with CCD-array.…”

Fluorescence and transient absorption spectra of Ar/Kr/F 2 mixtures excited by e-beam

“…Experiments were performed at "Berdysh" preamplifier module of GARPUN KrF laser facility [12]. A gas mixture Ar/Kr/F 2 = 0.3/8.9/91.8% at total pressure up to p = 1.8 atm was filling the laser chamber of 10*10 cm 2 cross-section and I I I I I I I I of 170-cm length.…”

GARPUN-MTW: A hybrid Ti:Sapphire/KrF laser facility for simultaneous amplification of subpicosecond/nanosecond pulses relevant to fast-ignition ICF concept

“…laser-plasma interaction during the past two decades at 0.1-10.0 kJ-class single-shot KrF facilities AURORA (Los Alamos National Laboratory; LANL) (Rosocha et al, 1986(Rosocha et al, , 1987Harris et al, 1993), NIKE Naval Research Laboratory (NRL) (Obenschain et al, 1996;Pawley et al, 1997Pawley et al, , 1999Aglitskiy et al, 2002), SPRITE (RAL) National Institute of Advanced Industrial Science and Technology (Shaw et al, 1993(Shaw et al, , 1999Divall et al, 1996), ASHURA National Institute of Advanced Industrial Science and Technology (AIS & T) (Owadano et al, 1989(Owadano et al, , 1993(Owadano et al, , 1999(Owadano et al, , 2001 and GARPUN Lebedev Physical Institute (LPI) (Basov et al, 1993;Zvorykin & Lebo, 1999;Zvorykin et al, 2001Zvorykin et al, , 2004Zvorykin et al, , 2006aWang et al, 2002), and especially at rep-rate Electra laser (NRL) (Sethian et al, 1998Wolford et al, 2006) have proved that e-beam-pumped KrF laser might be the best challenge for direct-drive ICF power plant. To satisfy physical and economical requirements, they should be scaled to output energies of 30-60 kJ per one module, operating all together with the total laser energy of $2 MJ at rep-rate of 5 Hz and overall system efficiency of 7.5% (Svyatoslavsky et al, 1992;Von Rosenberg, 1992;McGeoch et al, 1997;Sethian et al, 2003).…”