SIEMENS

Nuclear fusion is pure solar energy. Deep within a star, the atomic nuclei of light elements fuse, generating vast amounts of energy in the process. For a long time now, scientists have wanted to use such fusion power here on earth, because it promises to provide us with a virtually inexhaustible source of clean energy. The raw materials (water and lithium) for fusion power are available in practically unlimited amounts. Fusion energy does not emit CO₂ into the atmosphere and - unlike nuclear fission plants, which split heavy atomic nuclei - fusion does not produce highly radioactive waste that remains hazardous for thousands of years. The interior walls of a fusion reactor become only slightly radioactive after being bombarded by fast particles. After about 100 years, the radiation level declines to such an extent that all of the material can either be recycled or disposed of.

All fusion power plant concepts are based on fusing the hydrogen isotopes deuterium and tritium. The tritium, a rare substance, is produced by bombarding widely available lithium with fast neutrons that are created during the fusion reactions. Deuterium is produced from water. The plan is not without its problems, however. Because atomic nuclei have a positive charge and repel one another, they have to collide with one another very quickly for fusion to take place.

The difficulty is to heat a gas to a temperature of more than 100 million degrees Celsius and to keep the resulting hot plasma compacted long enough. Whereas researchers in the 1970s were still optimistic about the prospects of fusion power, they eventually realized that the plasma is extremely unstable and reacts negatively to even minimal disruptions. According to Prof. Günther Hasinger, Director of the Max Planck Institute for Plasma Physics (IPP) in Garching near Munich, Germany, this problem has now been overcome. "Plasma physics has come a long way in the past few decades through bigger experiments, for one thing, but also because supercomputers can simulate plasma processes," he says. "I think most of the difficulties have been solved and the focus is now on creating optimal reactor designs and operating scenarios."

The goal is to have two large-scale facilities generate more energy than is fed into them (see box). If the reactors are a success, these experiments will lead to the construction of commercial supower plants by 2050. Is this too late to help reduce global CO₂ emissions? Hasinger doesn’t think so. "The transformation of our energy generation systems will be one of the biggest tasks of the century," he says. "All the scenarios for the development of energy consumption, the availability of fossil fuels, and the necessary reduction of harmful greenhouse gas emissions show that far greater efforts will be required in the second half of the century than in the period up to 2050. If we manage to exploit fusion power by mid-century, it will come at just the right time to make a big difference."

Hot Synergies. Because fusion power involves technologies from a broad spectrum of fields, industrial companies are monitoring associated research efforts with great interest. One of these efforts is the search for suitable materials for the fusion reactor wall. Although a magnetic field keeps the hot plasma at a safe distance, the "cooler" outer areas of the plasma are channeled toward the reactor floor in order to clean it. Researchers estimate that certain plasma states could cause the temperature of the wall interior to rise to over 2,000 degrees Celsius, which few substances are capable of withstanding. In addition, the huge amount of heat generated by the deceleration of neutrons from a fusion reaction must not impair the mechanical stability of the reactor shell.

Siemens’ Energy Sector is looking for heatresistant materials for its turbine blades, which are covered with ceramic insulation material that allows them to operate reliably even at 1,300 degrees Celsius. Although such blades are far from reaching their melting point at that temperature, their rapid rotation causes centrifugal forces to affect them as heat levels rise.