The heat is directly induced into the magnetron coil, if this is the EM drive I know of https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster

I have a theory that impulse is caused by nano-chaotic electron motion. This device demonstrates this could be correct. Assuming it is the same device. Recently also they discovered that electrostatic repulsion devices, based on capacitance, that previously had been developed to create impulse by repelling argon atoms or similar, could produce a usable amount of impulse without any gas at all. If it is an EM drive it also includes a resonant cavity, and I believe that the secret to making this device work is tuning the resonance to cause maximum nonlinearity and amplify frequency components beyond the frequency of cosmic rays. Which is why I think a tesla coil should be the emitter, not a magnetron.