Indirectly driven targets for ignition
Both Los Alamos and Lawrence Livermore Laboratories have studied capsule and laser driven target designs for the National Ignition Facility. The current hohlraum design is a 2.76mm radius, 9.5mm long gold cylinder with 1.39mm radius laser entrance holes covered by 1{mu}m thick plastic foils. Laser beams strike the inside cylinder wall from two separate cones with a peak power less than 400 TW. The problem with a pressure pulse caused by wall plasma stagnating on axis has been overcome by filling the hohlraum with gas. Currently this is equi-molar hydrogen-helium gas at 0.83 mg/cc density. One capsule uses a 160 {mu}m plastic ablator doped with oxygen and bromine surrounding an 80 {mu}m thick DT ice layer with an inner radius of 0.87 mm. Los Alamos integrated calculations of the hohlraum and this capsule using 1.4 MJ of laser energy achieve yields of 4.9 MJ using LTE atomic physics, and 3.5 MJ with non-LTE. This confirms Livermore calculations of ignition. For radiation driven implosions, a beryllium ablator offers a viable alternative to plastic. It is strong enough to contain high DT pressures. Copper, soluble at required levels, is an excellent dopant to add opacity. A beryllium capsule with a 155 {mu}m thick ablator doped with 0.9 atom % copper, and the same inner dimensions as the plastic capsule, placed in a similar hohlraum , yields 6.9 MJ with LTE. Although these calculations show the designs are sensitive, they add to the confidence that NIF can achieve ignition. Using their best integrated calculations which are not yet fully optimized, they confirm Livermore calculations of ignition with a plastic capsule, and have added an alternate capsule design with a beryllium ablator.
- Research Organization:
- Los Alamos National Lab., NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-36; W-7405-ENG-48
- OSTI ID:
- 10116836
- Report Number(s):
- LA-UR--94-3115; CONF-9409226--4; ON: DE95006451
- Country of Publication:
- United States
- Language:
- English
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