DIETZ@slb-test.CSNET ("Paul F. Dietz") (11/01/86)
Geoff, In regards to that Technology Review article about fusion: it was a critique of *magnetic confinement* fusion; specifically, tokamaks and magnetic mirrors. Inertial confinement fusion does not suffer from the same problems, since the first wall can be a liquid lithium alloy or ceramic pebble blanket, and the reaction vessel need not contain a high vacuum. Also, it's not clear if Lidsky's complaints apply to D-He3 reactors, since these can use direct conversion and avoid the major costs of steam turbines and generators. There's a form of fusion power that is possible today. It's possible to excavate large cavities in salt domes by circulating water. Fill the cavity with high pressure steam, add some impurities to make the steam cloudy, and detonate about 100 kilotons of bombs per day. That's about 5 gigawatts of heat, not counting heat from radioactive decay products. Fissile material for the bombs can be bred separately or in-situ by surrounding the bombs with breeding blankets. This scheme has obvious safety problems, but requires no new science. Small scale inertial fusion may be closer many think. Light ion beam fusion is close to the power levels needed for ignition (although delivering the beam to the target is more problematical). There's been a report that "hohlraum" targets (in which driver energy is converted to thermal x-rays which then drive the fuel element) have been tested by using thermal x-rays from underground bomb explosions. These two schemes can be combined by using multi-stage fuel elements. A small pellet with about a gigajoule of energy output is used to generate x-rays to detonate a 300 gigajoule (say) pellet. Detonate one every 5 minutes in a cavity to generate a gigawatt of heat. This scheme might make it practical to deliver the initial driver energy by means of disposable conductors. It might also make a reasonably low-tech "mini-Orion" engine for moving asteroids, if detonated behind a pusher plate. Where one draws the line between large fuel pellets and small hydrogen bombs is unclear; would such a rocket violate the Outer Space Treaty?