Alternative Fuels for ICF Targets

The first observation of the beta-layering phenomenon showed that it was possible to fabricate inertial confinement fusion (ICF) targets having an outer ablating shell surrounding a symmetric solid layer of DT fusion fuel. The sensitivity of fusion yield to the internal DT ice roughness is a function of many factors, one of which is the relatively low density of solid DT (0.25 g/cm³), leading to a high Atwood number for the ablator/fuel interface. This is one of the issues that has led us to consider other DT-based fuels having higher densities than pure DT but still capable of being automatically redistributed into a uniform layer by beta-layering. The two principle conditions for beta-layering redistribution, self-heating and a moderately high vapor pressure, can be found in only a few other systems. But by concentrating on hydrides of elements in the second row of the periodic chart, we can find materials which should beta-layer and which might be good candidates for fusion fuel. We exclude lithium hydride and beryllium hydride, because these materials are solids at room temperature where an automatic redistribution technique such as beta-layering would not be necessary. Therefore we begin with boron and consider the following materials:

• diborane: B₂(DT)₃ (or B₂D₃T₃),
• methane: C(DT)₂ (or CD₂T₂),
• ammonia: N(DT)_3/2 (i.e., 0.5·NDT₂ + 0.5·ND₂T),
• water: DT0, and
• hydrofluoric acid: (DT)_1/2F (i.e., 0.5·kDF + 0.5·TF).