Effects of helium ash on fusion reactor operation and analogies with fission reactors

It is well known from early reactor physics textbooks that fission products , especially xenon 135, have an important impact on fission reactor operati on. An excess reactivity must be provided to compensate the reactivity loss due to this highly absorbing isotope and power oscillations must be suppre ssed by the control system. In the actual paper it is shown that in a magne tically confined fusion reactor the helium emerging from deuterium-tritium reactions will have an impact on reactor operation. It is necessary to prov ide additional auxiliary heating Furthermore it is shown that under certain circumstances in the initial phase of the plasma discharge oscillations of power and temperature are possible. Such oscillations have to be suppresse d by a control system. The analogies in fission and fusion systems with res pect to reaction products are discussed.