ICRF Heating

Peaked density profiles may not only improve confinement properties, but also give the additional benefits of increased fusion production and ignition margin in BPX, as shown in Fig. 8.1. The ability to control density profiles in the core and scrape-off regions is governed by a number of both physics and operational considerations that make it difficult to specify optimized fueling systems. For this reason, the fueling systems for BPX are designed to maximize flexibility, allowing operation to determine optimal scenarios. After listing some of the issues impacting fueling assessments, we present the latest information on pellet ablation and penetration and then give example fueling scenarios. Some degree of external control over the density profile in the core can be achieved through pellet injection, but recycle and other plasma edge physics limit the degree of control that is possible. Passive pumping and fueling by the walls, limiters, and other structures (collectively called fuel recycle) is a function of the temperature of the surface, incident particle energy, and history of the fluence.’ In H-mode operation, diffusive losses are sharply reduced at the separatrix, and the lower scrape-off density allows better penetration of neu-