Hydrodynamics of plasma and shock waves generated by the high-power GARPUN KrF laser

Abstract

The electron-beam-pumped KrF laser installation GARPUN with a 100-J output energy and long 100-ns pulse duration has been used to investigate laser-target interactions in a broad range of laser intensities for small~150 mm! and largẽ ;1 cm! irradiated spots. For higher intensities~up to 5 ϫ 10 12 W0cm 2 !, a conical shock wave was generated in condensed matter by megabar pressure at the ablation front. It propagated with a supersonic velocity in a quasisteady manner together with a conical shock wave inside a target. Evaporated target material moving with a velocity of ;50 km0s formed an extended plasma corona of ;5 mm length with an electron temperature of ;100 eV. Emission spectra of plasma have been investigated in the extreme UV range 120-250 Å. For lower intensities~10 8 -10 9 W0cm 2 !, planar shock waves in normal density air were produced with initial velocities up to 4 km0s in the forward direction and 7 km0s in the opposite direction toward incident radiation. In rarefied air, the forward shock wave kept velocities constant whereas the backward ones were accelerated up to 30 km0s. Planar compression waves in transparent condensed matter were also demonstrated propagating with sonic velocity.

Deep Penetration of UV Radiation into PMMA and Electron Acceleration in Long Plasma Channels Produced by 100 ns KrF Laser Pulses

“…It should be noted that in these experiments, during an exposure to nanosecond laser pulses, the ablation front passed a distance in the condensed matter less than the size of the irradiated spot, i.e., the one-dimensional (1D) plane geometry of the ablation front propagation and the SW generated by it was realized. In our previous experiments with Al, Pb, graphite and polyethylene (C 2 H 4 ) n targets at GARPUN KrF laser [20][21][22], pressures consistent with the above scaling were measured in the intensity range of 5 × 10 11 -5 × 10 12 W/cm 2 for 100 ns pulses and a focal spot of ~150 µm. The largest pressure value at an intensity of 5 × 10 12 W/cm 2 reached 4 Mbar.…”

“…Distinct features of the high-energy UV light interaction with PMMA observed in our experiments are: (i) a conical SW evidencing a 2D hydrodynamic regime; and (ii) a thin capillary-like channel with a diameter of 30-40 µm extending deep into the target up to ~1 mm from the top of the ablative crater (Figure 1). The microscope images were obtained with sample illumination by an unpolarized incoherent light source and in a projection scheme in the polarized light of copper vapor laser [20][21][22]. The formation of the capillary channel is explained by the pre-focusing of incident radiation nearby the crater top due to specular reflection by the plasma density gradient near the conical surface and the self-focusing of radiation transmitted through plasma in the PMMA [27].…”

Planar shock waves in liquids produced by high-energy KrF laser: A technique for studying hydrodynamic instabilities

“…Planar SW with velocities as high as 30 km/s were initiated toward the laser beam by erosion plasma blow-off in rarefied air when 100-J, 100-ns KrF laser pulses irradiated solid targets (Zvorykin et al, , 2004a(Zvorykin et al, , 2004bLebo et al, , 2004Bakaev et al, 2005;Krasnyuk & Lebo, 2006). In a forward direction, the SW was pushed by thin polystyren (CH) films accelerated by free-expanding plasma up to velocities 3.5 km/s independently of the gas density.…”

“…By increasing a distance between resonator mirrors, an output beam was made slightly convergent. It had a reduced cross section of 10 Â 10 cm when arrived at two-component homogenizing system consisting of a prism raster 1 and a lens (Zvorykin et al, 2004a;Bakaev et al, 2005). By splitting an incident beam into 25 individual 2 Â 2-cm beamlets and overlapping them at a focal plane (raster effective focal length F eff ¼ 1000 mm) this raster provided non-uniformity less then a few percents across the square spot, which could be resized by adding a focusing lens with an appropriate focal 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).…”