COOLING NUCLEAR FUSION
In theory, nuclear fusion is a virtually inexhaustible source of energy. The prototype of a fusion reactor that will deliver more energy than it consumes is under construction in Cadarache, in the south of France. The centerpiece of the plant is an ultra-high vacuum chamber in which strong magnetic fields will heat up a plasma consisting of hydrogen nuclei to over 100 million degrees Celsius. The vacuum pumps that can be used to evacuate the chamber are tested with gaseous helium. For this purpose, the temperature of the gas must be maintained precisely between minus 193 and minus 173 degrees Celsius. The helium is cooled with liquid nitrogen in a special heat exchanger from Messer. Controlling the pressure permits very accurate gas temperature adjustment, thereby enabling precise cooling regulation.