A novel pellet acceleration concept using millimetre microwaves from MW gyrotron sources is presented that could pave the way for high-speed >3 km s−1 inner-wall pellet injection on ITER-class tokamaks. In the proposed concept, the high gas pressure is created by vapourization of a composite 'pusher' medium attached behind the deuterium–tritium (DT) fuel pellet. The pusher medium consists of small micron-sized conducting particles, e.g. Li embedded homogeneously in a D2 ice slug, thus facilitating microwave energy absorption by dissipation of eddy currents flowing within the conducting particles only. Gyrotron power Pgyr can be absorbed continuously in the pusher gas, and therefore the high gas pressure can be sustained behind the pellet while it is being accelerated down the waveguide/launch tube. A scaling law is derived which predicts that a pellet of mass Mp accelerated over a distance L reaches a velocity vp ≅ (PgyrL/Mp)1/3, with a hydrodynamic efficiency of 45%.