Compact high‐field toroids: a shortcut to ignition?

The achievement of thermonuclear ignition in a deuterium–tritium plasma will require a temperature well in excess of 4 keV (50 million kelvin), and a confinement parameter $nτ$ (particle $density×confinement$ time) greater than $1014 sec/cm3.$ This important goal is being pursued primarily by designing and building ever larger tokamaks. But despite the size and cost of the large tokamaks now under construction in this country (Princeton's TFTR), Europe (JET), Japan (JT‐60) and Russia (T‐15), it is not expected that this generation of machines will achieve a self‐sustaining plasma burn. To that end, still larger tokamaks, costing a billion dollars or more, are now in the planning stage.