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Final Optics Protection in Laser Inertial Fusion with Cryogenic Liquid Droplets.

DE200415006438

Publication Date	2000
Personal Author	Moir, R. W.
Page Count	28
Abstract	A burst of x rays and vaporized debris from high yield targets can damage the final optics in laser inertial fusion energy (IFE) power plants and in laboratory experimental facilities such as the National Ignition Facility (NIF) or Laser MegaJoule (LMJ). Noble gases such as Xe or Kr have been proposed to protect final optics from target-produced x rays and debris. Some problems with the use of such ambient gas fills are the large amount of gas involved, heat transfer to a cryogenic target, potential resonant reradiation of x rays absorbed, and a nonuniform index of refraction due to turbulence interfering with the focusing of laser light. Also the fast igniter laser intensity may be too great for propagation through an ambient gas. We propose to provide the gas in the form of many small closely spaced liquid droplets injected in front of the optics. In the case of NIF, the droplets would be injected only when needed just before a high yield shot. The laser light that is absorbed will cause evaporation of the liquid and spreading of this gas. The liquid droplets intercept only(approx)5% of the laser light allowing(approx)95% to pass through to the target. The light absorbed in the NIF example (assumed to be 50% of the intercepted light, whose intensity is 3.6 x 10(sup 9) W/cm(sup 2)) would cause the xenon droplets to evaporate and spread uniformly such that the x rays from 10 eV to 2 keV are appreciably attenuated when they arrive 40 to 70 ns later at the optical surface. X rays above 3 keV and below 10 eV are not attenuated very much but their intensities are rapidly falling off in this range anyway.
Keywords	Optics protection Cryogenics Evaporation Focusing Heat transfer Lasers Nozzles Optics Power plants Rare gases Refractive indexes Silicon Targets Thermonuclear reactors Vapor pressure Xenon Laser initial fusion Cryogenic liquid droplets National ignition facility
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Lawrence Livermore National Lab., CA.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200414

Final Optics Protection in Laser Inertial Fusion with Cryogenic Liquid Droplets.

Final Optics Protection in Laser Inertial Fusion with Cryogenic Liquid Droplets.
DE200415006438

Publication Date	2000
Personal Author	Moir, R. W.
Page Count	28
Abstract	A burst of x rays and vaporized debris from high yield targets can damage the final optics in laser inertial fusion energy (IFE) power plants and in laboratory experimental facilities such as the National Ignition Facility (NIF) or Laser MegaJoule (LMJ). Noble gases such as Xe or Kr have been proposed to protect final optics from target-produced x rays and debris. Some problems with the use of such ambient gas fills are the large amount of gas involved, heat transfer to a cryogenic target, potential resonant reradiation of x rays absorbed, and a nonuniform index of refraction due to turbulence interfering with the focusing of laser light. Also the fast igniter laser intensity may be too great for propagation through an ambient gas. We propose to provide the gas in the form of many small closely spaced liquid droplets injected in front of the optics. In the case of NIF, the droplets would be injected only when needed just before a high yield shot. The laser light that is absorbed will cause evaporation of the liquid and spreading of this gas. The liquid droplets intercept only(approx)5% of the laser light allowing(approx)95% to pass through to the target. The light absorbed in the NIF example (assumed to be 50% of the intercepted light, whose intensity is 3.6 x 10(sup 9) W/cm(sup 2)) would cause the xenon droplets to evaporate and spread uniformly such that the x rays from 10 eV to 2 keV are appreciably attenuated when they arrive 40 to 70 ns later at the optical surface. X rays above 3 keV and below 10 eV are not attenuated very much but their intensities are rapidly falling off in this range anyway.
Keywords	Optics protection Cryogenics Evaporation Focusing Heat transfer Lasers Nozzles Optics Power plants Rare gases Refractive indexes Silicon Targets Thermonuclear reactors Vapor pressure Xenon Laser initial fusion Cryogenic liquid droplets National ignition facility
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Lawrence Livermore National Lab., CA.; Department of Energy, Washington, DC.
Supplemental Notes	Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200414