Fusion's middle way

摘要

Fusion devices take hot fuel (an ionized gas, or plasma) and squeeze its particles together long enough for nuclei to fuse. Big mainstream projects do that by means of extremely high densities or long confinement times. Smaller private pioneers hope that avoiding such extremes will yield smaller, simpler, cheaper fusion machines. Two promising approaches: Magnetized target fusion (MTF) devices first confine the plasma with a magnetic field (as in magnetic fusion) and then crush it (as in inertial fusion). The crushing increases density and temperature and boosts the magnetic field, lengthening confinement time. Most MTF schemes create "compact toroids," or smoke rings of plasma. Electric currents in the plasma create magnetic fields that confine it for a few microseconds while "plasma guns" fire it into a crushing device.