Nike KrF Facility Tour HAPL Meeting 31 October 2007 •NRL program became interested in KrF in mid 1980’s •KrF program begun in 1987 •Nike competed in 1995 •Up to 5 kJ obtained from main amplifier ( ~60% more with modern diode) •About 600 shots per year for target experiments with ~ 1.5-3 kJ on target •Complements Electra as half-full scale scale KrF reactor beamline
KrF lasers for inertial fusion energy PHYSICS Outstanding uniformity: reduces seed for hydro instabilities Shortest wavelength (248 nm) higher absorption, rocket efficiency minimizes risk from laser plasma instability Straight-forward "zooming“ increases absorption & pellet gain NRL ICF physics program is focused on target designs that benefit with KrF • Conventional direct drive • Shock ignited direct drive ( may reduce laser energy and increase gain) • Impact Fast Ignition
We match the electron-beam-pumped amplifier time scale to few ns target time scale via angular multiplexing LONG PULSE AMPLIFIER (~ 100's nsec) Demultiplexer Last Pulse Array (mirrors) Multiplexer Array e s l u (beam splitters) P t s r i F FRONT END ( few nsec FWHM) Target Only three pulses shown for clarity Adapted from Rosocha et al, Fusion Technology, May 1987 page 497
A KrF laser train uses Induced Spatial Incoherence (ISI) to produce very uniform target illumination The laser profile at the aperture is imaged through the amplifiers onto the target Object Amplifier 1 Amplifier 2 Spatially aperture (at FT plane) (at FT plane) incoherent Target 3 THz KrF source Intensity profile at aperture Intensity profile at target averaged averaged instantaneous instantaneous One can easily achieve focal zooming by passing different temporal portions of the pulse through different apertures Laser beam high F# optics Laser spot size follows imploding pellet
Nike laser Chain Illuminated aperture imaged onto target Nike laser provides highly uniform target illumination (best by far in the business) Laser profile in target chamber
60-cm aperture amplifier
Nike “propagation” Bay Final turning mirrors and target Optics for angularly chamber optics multiplexed beams
Nike target chamber Cyro targets Main Array Backlighter array Optical and x-ray diagnostics
We use Nike is to study laser-accelerated planar targets 1.86 keV imaging QUARTZ BACKLIGHTER MAIN LASER BEAMS CRYSTAL LASER BEAMS RIPPLED TARGET BACKLIGHTER TARGET Si 0 to 100 km/sec in <4 ns Sample RT Data Sample RT Data Time 2D IMAGE STREAK CAMERA Y. Aglitskiy, et al. , Phys. Rev. Letters, 86, 265001 (2001)
Initial Nike laser-plasma experiments show no evidence for parametric instability @ 2-3x10 15 W/cm 2 12 overlapped 300 ps Nike “backlighter” beams Cryo D 2 and plastic foam targets
Two Tour Groups: A-M with Victor Serlin + Y. Chan + Jim Weaver (start with target area) N-Z with David Kehne + Max Karasik + S. Obenschain (start with laser) NRL should be providing bus service (1/4 mile walk)
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