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Abstract:
NRL is investigating the physics issues involved in the direct illumination approach to laser fusion. Millimeter diameter planar targets are ablatively accelerated to speeds and conditions near those required of fusion pellet shells using 3-5 ns, 1.05 micrometer light from the PHAROS II laser. At 5 x 10 to the 13th power W/sq cm targets were accelerated to 160 km/sec with a velocity uniformity of + or - 7% through twenty times the initial target thickness and while remaining cool (<10 eV). A joint NRL-LLNL experiment on SHIVA extended these results to beyond 10 to the 14th power W/sq cm, the uniformity of acceleration of dense mm-diameter targets improved to better than + or - 3.5% and the interaction physics remained benign. Also, absorption was above 65% and fast electrons were a minor energy channel. Thus, the moderate- irradiance direct-illumination approach appears to be an attractive option for laser fusion. To further verify this conjecture, particular attention is paid to the factors affecting the uniformity of acceleration or targets such as laser beam and target uniformity requirements, and various hydrodynamic mechanisms such as Rayleigh-Taylor and Kelvin-Helmholtz instabilities. The study of the behavior of laser-plasma interactions is also extended into regimes closer to those expected to be encountered in reactor sized pellets. Large plasmas with long scalelengths are generated using two-pulse methods; backscatter, fast electron production, etc. are observed as the laser intensity is increased beyond 10 to the 14th power W/sq cm. New diagnostic techniques are also discussed for measurements of plasma properties. (Author)
| Description: |
Memorandum rept. |
| Pages: |
20 |
| Report Date: |
30 AUG 1982 |
| Report Number: |
A080911 |
Report Unavailable |
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