Thermal Analysis of DIII-D Coils for Long Pulse Operation

DIII-D tokamak will be operated at higher magnetic flux and longer pulse lengths starting in 2006. Hence the water-cooled copper coils will be subjected to higher currents and longer pulse length. In order to insure that the coils do not overheat during such an operating condition, a systematic program of analysis and experiments is being implemented. F8A coil has been operated with limited I²t, due to its long cooling path and limited coolant flow rate. The geometry of this coil was modeled which accounted for the forced convective heat transfer to the coolant, conduction heat transfer between the windings, heat loss to the atmosphere and change in coolant temperature as a function of distance. The model was used to determine the flow rate required and time to cool down the coil for higher currents and longer pulse operation without exceeding the safe temperature limits