Plasma Formation in a Tokamak

In fusion energy research the goal is to contain a hot plasma for a sufficiently long period of time so that the reacting species (deuterium and tritium nuclei) will release more energy in exothermic fusion reactions than is required to heat and contain the plasma. One of the promising concepts in magnetic fusion is the tokamak, a toroidal magnetic containment vessel first developed by Artsimovich (1972) and described in a recent survey article by Sheffield (1981). The magnetic field in a tokamak is composed of three parts: a strong toroidal magnetic field which is the main constraining field for particle motion, a poloidal field which is produced by a current in the plasma in the toroidal direction, and a vertical field to counteract the hoop force generated by the currents in the toroidal direction. The plasma current is driven by a transformer, and so the duration of a plasma discharge is limited by the volt-second capability of this transformer. One of the major problems in tokamak research is the impurities that are found in the hot plasma, causing a large radiative power loss and the development of possibly catastrophic instabilities.