One way of mitigating runaway damage of the plasma-facing components in a tokamak
fusion reactor is by limiting the runaway electron energy under a few MeV, while not
necessarily reducing the runaway current appreciably. Here, we describe a physics
mechanism by which such momentum space engineering of the runaway distribution can be
facilitated by externally injected high-frequency electromagnetic waves such as whistler
waves. The drastic impact that wave-induced scattering can have on the runaway energy …