Power and particle balance studies using an instrumented limiter system on ATF

Power and particle balance studies on the Advanced Toroidal Facility (ATF) torsatron are carried out using a rail limiter system. Both top and bottom limiters are made of graphite tile arrays, and these tiles are instrumented with thermocouples and Langmuir probes for calorimetric and particle flux measurements. Initial experimental results indicate that the limiter power loss accounts for about 12% of the total and the radiation loss for about 30% of the total; the rest of the plasma heating power appears to be going to the vessel wall. The particle flux to the limiters is also about 18%. The fractions of power and particle flux to the limiters are relatively lower than in Tokamaks because of the low edge safety factor, q approximately 1 rather than q approximately 3 as in a typical Tokamak, at the natural boundary of the ATF plasma (which results from the magnetic stellarator configuration of this currentless device). Therefore, for limiters of the same size, these fractions are about a factor of q lower in ATF than in a comparable Tokamak device.