ENERGY FLOW IN ZETA DISCHARGE

The Zeta discharge in the low density regime is characterized by strong turbulence, rapid loss of plasma, a resistance much larger than that predicted from the electron temperature, and a high ion temperature. A model for the energy flow in this regime is proposed, based on the convective transport of the plasma to the walls. This model leads to coupled equations for the ion and electron temperatures and for the turbulent energy. From these equations, and from their integrated forms which govern the energy balance of the discharge as a whole, predictions of the ion and electron temperatures are obtained which are in gross disagreement with observation. It is shown that agreement can be obtained by introducing an additional energy loss process, thermal conduction along the lines of force which are assumed to follow a random path to the wall. Two other possible energy loss mechanisms are considered and shown to be inadequate alone, although some contribution from either in conjunction with thermal conduction cannot be ruled out.