X-ray and particle diagnostics of a high-density plasma by laser implosion (invited)
Review of Scientific Instruments 61:10 (1990) 3235-3240
Abstract:
A series of laser fusion implosion experiments of plastic hollow shell targets was performed by using the Gekko XII glass laser in order to achieve the required fuel areal density for ignition. Introducing random phase plates to improve illumination uniformity, high-density compression of more than 600 times deuterium liquid density has been achieved. The implosion dynamics and symmetry were observed with a spatially resolved x-ray streak camera and an x-ray multiframing camera. The three-dimensional emission profile of the laser-heated plasma was reconstructed from the x-ray images by use of computed tomography and was compared with the laser illumination profiles. The areal density of the imploded core was measured by the neutron activation of a silicon tracer, the secondary reaction method, and the knock-on proton method. Although the measured density and areal density were consistent with those from 1-D hydrodynamic simulation, experimental neutron yields were significantly lower than those predicted by the simulation for convergence ratios larger than 20. This suggests that better implosion uniformity is required to create a hot spark.High power laser development and experimental applications to x-ray lasers, and short pulse energy transport
Laser And particle Beams 8:1-2 (1990) 19-25
Abstract:
University research in the UK with high power lasers is carried out at the SERC’s Central Laser Facility with a multiterawatt neodymium glass laser, VULCAN, and a developmental KrF laser, SPRITE. These systems are briefly described together with the design of a new KrF laser to supersede VULCAN. The new laser design, SUPERSPRITE, is based on optical and raman multiplexing which is being developed with the present SPRITE system. The Specification of SUPERSPRITE is For 3.5 kj in 1 ns and a peak power of 300 TW in short pulses. The new technology is seen as highly cost effective in relation to neodymium glass lasers. A Resumé of the development of XUV lasers in the UK in collaboration with laboratories overseas is given. The work is based on laser action through recombination in highly ionized ions and recent progress includes collaborative experiments on the GEKKO XII facility in japan which have demonstrated laser action at the shortest wavelength to date at 45 Å in Mg XII. The physics of energy transport in short pulses is fundamental to the extrapolation of recombination lasers to shorter wavelengths and is being studied from a more basic standpoint using both the VULCAN and SPRITE facilities. Some details of this work are given. © 1990, Cambridge University Press. All rights reserved.Measurement of the mass ablation rate for 0.53 μm random phased laser irradiation of spherical targets
(1989) 143
Abstract:
The mass ablation rate has been measured using the 12-beam GEKKO XII glass laser. An X-ray pinhole camera coupled to a streak camera was used to provide both spatial and temporal history of the emission from buried maker layers. The camera was filtered by 0.75 μm of Al to enhance the image of the cool, denser plasma near the ablation front. The targets (diameter approximately 500 μm) were both polymer shells and solid polymer pellets and were overcoated with up to four maker layers sandwiched between CH ablator layers. Laser energies of up to 8 kJ in 1.7 ns were incident on the targets, with absorbed irradiances of up to 4.0 × 1014 W-cm-2. Good agreement has been found between the experiment and a one-dimensional hydrodynamic code in which the heat flow is obtained from the Fokker-Planck equation. The mass data were consistent with the temporal behavior of spectral line emissions observed by a streaked crystal spectrograph. The introduction of random phase plates had no significant influence on the mass ablation rate for imploding targets. The results indicate that a highly uniform drive pressure has been achieved for the GEKKO XII laser.Twenty-fold increase in thermonuclear reaction yield in laser driven compression
Optics Communications 71:3-4 (1989) 184-188
Abstract:
The production of large yields of thermonuclear neutrons in 12 beam laser driven implosion of deuterium filled glass microballoons of very high aspect ratio has been studied. It has been found that significantly enhanced yield is obtained when the target irradiation is symmetrical but locally concentrated. A simple model satisfactorily describes a wide range of experimental results. © 1989.Production of hot near-solid-density plasma by electron energy transport in a laser-produced plasma
Physical Review A 40:5 (1989) 2857-2859