Heating and current drive actuators study for FNSF in the ion cyclotron and lower hybrid range of frequency

Abstract

This paper addresses considerations for the radio frequency (RF) heating and current drive actuators on the Fusion Nuclear Science Facility (FNSF), focusing on the Lower Hybrid Range of Frequency (LHRF) and Ion Cyclotron Range of Frequency (ICRF). FNSF will require long (∼months), steady-state pulses to fulfill its mission of high neutron fluence operation for the qualification of fusion nuclear technologies prototypical for a power plant. RF actuators are uniquely capable of sustaining the plasma without requiring large line-of-sight penetrations through the breeding blanket, which mitigates the impact on tritium breeding and neutron shielding. The technology for generation and transmission of RF waves in the LHRF and ICRF are fully mature, however the lifetime of plasma-facing antenna components in the reactor environment remains a significant technology gap. Moving the location of RF actuators from the low field side (LFS) to the high field side (HFS) of the tokamak reduces fluxes of turbulent plasma and energetic particles to the antenna. Compact HFS antenna designs are able to fit within the blanket sectors with minimal impact on overall dimensions. Material choices for antenna structures represent a significant challenge. Existing materials are unable to simultaneously meet the requirements for high conductivity, high strength, high temperature, and low activation. Pathways forward with respect to materials development are identified.