Among possible approaches to fusion energy, we regard the Proton Fast Ignition (PFI) as the most credible. PFI as an alternate route to ignition was triggered by the discovery of ultra-bright beams of protons produced by ultra-intense lasers.
Protons are advantageous to other ion species and electrons. Because of their highest ionic charge-to-mass ratio, they are accelerated most efficiently up to the highest energies. They can penetrate deep into a target to reach the high-density region, where the hot spot is to be formed. And they exhibit a characteristic maximum energy deposition at the end of their range, desirable to heat a localized volume. Thus, Focused Energy Inc. has chosen PFI for the primary pathway to fusion energy.
Narrowband x-ray imagers using spherically bent crystals have been implemented on all three laser facilities (MTW,
OMEGA EP, and OMEGA) at the University of Rochester’s Laboratory for Laser Energetics. These spherical crystal
imagers (SCI’s) use a 150-μm-thick, 25.4-mm-diam quartz crystal cut either along the 2131 plane to reflect the Cu
Kα line at ∼8 keV with a Bragg angle of 88.7° or along the 1011 plane to reflect the Si Heα line at ∼1.865 keV with a Bragg angle of 83.9°. The SCI systems can be set up to either image the self-emission of a laser-heated target or to
backlight a high-energy-density plasma object.
Multi-shot damage tests were performed of gold coated mirrors in the femtosecond and in the nanosecond laser pulse regime. Sputtered gold films from different suppliers of various thicknesses were investigated. Considerable differences in the optical quality and the damage threshold are reported. The best films withstand a maximum fluence of 0.7 J/cm2 for 50-fs Ti:sapphire laser irradiation (804 nm) and 7 J/cm2 for 8-ns Nd:YAG irradiation (1064 nm). For gold films with poor optical quality a permanent surface modification one order of magnitude below the damage threshold was observed.
X-ray K- and L-shell emission from aluminum and carbon plasmas produced by subpicosecond UV-laser pulses has been investigated using various spectrographs. The spectra have been measured as a function of laser intensity in the range from 1014 W/cm2 to 1018 W/cm2. A computer simulation including reabsorption of the resonance lines has been performed and the observed and calculated spectra compared. Plasma parameters have been deduced by line emission and continuous emission observations. It has been found that for high laser intensities the resonance line emission and that from the satellites comes from the overdense region. A scaling of the electron temperature with the irradiance has been obtained. From the x-ray spectra measured at different laser intensities, the thresholds for the formation of hydrogen-like and helium-like ions in aluminum and carbon plasmas have been determined.
The experimental application of a scheme for travelling-wave excitation along a line focus to x-ray laser development is reported. The scheme utilizes an appropriately stepped prism or mirror inserted into the beam ahead of the focussing optics. It can be used for pulsed excitation down to about 1 ps. X- ray emission travelling with the velocity of light along a line focus is observed in an experiment using 500 fs to 1 ps KrF laser pulses.
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