A Gyrotron-Powered Pellet Accelerator for Tokamak Fueling*

A novel pellet acceleration concept [1] using microwave power from MW gyrotron sources has been developed that could pave the way for high-speed $>$3 km/s inner-wall pellet injection on ITER-class tokamaks. The concept is based on the principal of a gun, where a high-pressure propellant gas drives the projectile down the barrel. In the proposed concept, the high gas pressure is created by evaporative explosion of a composite ``pusher'' medium attached behind the DT fuel pellet. The pusher consists of micron-sized conducting particles, (Li, Be, C) embedded uniformly in a D$_{2}$ ice slug with $<$5{\%} volume concentration, thus facilitating microwave energy absorption by dissipation of eddy currents flowing within the conducting particles only. Microwave power is delivered to the pusher along a waveguide, which also serves as the pellet launch tube. A scaling law predicts that a pellet of mass M accelerated over a distance $L$ reaches a velocity v $\cong $ (PL/M)$^{1/3}$, where P is the gyrotron power.$\backslash $pard[1] P. Parks {\&} F. Perkins, US patent application ``Microwave-Powered Pellet Accelerator,'' No. 11/256/662, October 21, 2005.