Hot fusion research reaches a milestone.

Hot fusion research reaches a milestone

Though generating power from atomic fusion remains many, many moons away, physicists have reached a milestone in this effort to harness the energy source of the stars. Last week, two independent groups of researchers reported that deuterium atoms fusing within experimental reactors can now return enough of the reaction-priming power pumped into them to warrant their labs proceeding with the next step towards taming star-power.

That step would involve substituting a "higher-octane" blend of deuterium and radioactive tritium atoms for the all-deuterium fusion fuel now used in these reactors. Physicist Dale M. Meade of the Tokamak fusion Test Reactor (TFTR) at Princeton University and Paul-Henri Rebut, director of the Joint European Torus (JET) in England, say that deuterium-tritium fuel would give back more than half the power consumed in initiating fusion reactions. They announced their findings at an International Atomic Energy Agency fusion conference in Crystal city, Va.

Presently, JET and TFTR operate by heating atoms of deuterium (a heavy isotope of hydrogen) to many millions of degrees, while using strong magnetic fields to compress the resulting plasma of free electrons and nuclei to enormous densities within a hollow, doughnut-shaped vacuum vessel. Rebut and Meade report that fusion bursts within JET and TFTR can now produce a few thousandths of the power consumed to heat the deuterium plasma.

By itself, thaths a losing balance. But when the physicists project power outputs from deuterium-tritium plasmas -- which yield about 300 times the power of all-deuterium plasmas -- the balance presumably would reach about 60% in TFTR and 80% in JET. Tritium is a radioactive hydrogen isotope.

Scientists call the ratio of fusion-power output to heating-power input the "Q-value," and have generally agreed that the time to switch fusion fuels is when all-deuterium fusion power reaches a point that corresponds to projected deuterium-tritium Q-values above 0.5. These calculations ignore power used for non-heating roles.

For practical fusion power, a reactor would have to perform at a Q-value of 25 to 30, or it would have to host self-sustaining fusion reactions, which require no further power input once ignited. But first things first. Provided funds and necessary equipment come through, TFTR could gets its first deuterium-tritium fuel by 1993 or 1994, and JET probably by 1995.