A numerical model of the Jet poloidal circuit

The electrical circuit controlling the JET poloidal field system has been modelled numerically to enable modifications and enhancements to be analysed prior to installation. The model has been tested against a number of typical JET pulses with good agreement. A major enhancement of the system has been the current modulation circuit that causes different currents to flow in two parts of the JET primary magnetizing windings. The extra electromotive force obtained from this configuration allows plasma currents up to 7 MA to be sustained with material limiters. Magnetic separatrix limited plasmas with currents up to 5 MA are now also possible. The numerical model has been used to evaluate machine performance in these situations and to indicate where nominal thermal limits on coils would have been reached. A system to recover from a disruption using a series of fast rises has been analysed. It is intended that the model should become part of a larger system designed to help in the organisation of pulse schedules