Joule heating of the ITER TF cold structure: Effects of vertical control coil currents and ELMS

摘要

The toroidal field coil and support structures for ITER are maintained at cryogenic temperatures. The time-varying currents in the poloidal field coil system will induce eddy currents in these structures. The associated Joule dissipation will cause local heating and require heat removal which will show up as a load on the cryogenic system. Studies of Joule heating of the ITER TF cold structure (TFCS) due to the currents in the poloidal field coil system are presented. The two regimes considered in this study are the plasma vertical stability control and the Edge Loss Mode (ELM) events. The 3-D, thin-shell, eddy current program, EDDYCUFF was used to analyze the eddy currents and Joule losses in the cold structure. The current versus time scenarios were defined. Four control coil options were studied. All schemes use coils external to the TF cold structure. Analyses of power depositions during the plasma vertical stability control were performed for each of the four options. For each of these options three different recovery times were assumed. The times were 3, 1, and 1/3 seconds. Sets of four sequential ELMs, as well as isolated ELMs have been studied for various sets of active PF coils. The results showed that the lowest average power dissipation in the TF cold structure occurs when a subset of PF2 and PF7 are active, and all the other PF coils are passive. The general conclusion is that to minimize power dissipation in the TF cold structure it is preferable that only coils PF2 and PF7 are active. The other coils (PF3-PF6) should be passive and driven by a condition of constant flux. It is recommended in particular, that coils PF3 and PF5 be allowed to change currents to conserve flux, since they provide the maximum shielding of the TFCS from the fields caused by the active coils.