Global modelling of impurities in JET belt limiter discharges

The rate of production of impurities by physical sputtering is discussed in terms of a self-consistent zero-dimensional model based on energy balance. The importance of the effective self-sputter yield is emphasised and the effect of the uncertainty in this parameter is examined. The model is used to calculate how the plasma edge temperature, impurity influx, impurity concentration and total radiation depend on plasma average density and total input power. These results are compared with experimental results obtained using graphite and beryllium limiters in JET.