The ORNL fast-wave ICRF antenna for Alcator C-MOD

A fast-wave ICRF (ion cyclotron range of frequencies) antenna being designed for Alcator C-MOD is described. The antenna is in many respects prototypical of the baseline launcher design for the Compact Ignition Tokamak (CIT). The C-MOD launcher has a single current strap, with a strap and cavity geometry very similar to one quadrant of the CIT launcher (which has four straps in a 2×2 configuration). The antenna fits entirely within an 8-in-wide by 25-in-long port and is radially movable over a distance of 15 cm. It will operate at a frequency of 80 MHz for pulse lengths up to 1 s, at a maximum power level of 2 MW, corresponding to a power flux of >1.5 kW/cm². The antenna is an end-fed, double-loop configuration in which the current strap is grounded in the middle to provide mechanical support. The design includes a disruption-support system that accommodates thermal expansion of the antenna box while supporting large disruption loads. It also includes a matching system consisting of an external resonant loop with two shunt capacitors serving as tuning/matching elements