Energy selectivity in electron absorptive heating methods: does the angular momentum trap matter? An experimental investigation

Comparison between the Maxwell demon and a planar electrode has been revisited with an in-depth analysis of whether the angular momentum trap of the Maxwell demon indeed provides better energy selectivity than a small planar electrode that absorbs electrons indiscriminately. The evolutions of the EEDF under the influence of these heating techniques is directly analyzed, as well as the resultant plasma parameters. Experimental results show that the Maxwell demon indeed provides better energy selectivity as shown by its better retention of hot electrons than an indiscriminative absorption surface, which in turn results in smaller disturbance to the plasma potential a smaller reduction of the plasma density in the heating process. Experimental result also shows no electron heating when the demon is replaced by an ion-sheath forming large electrode, this is consistent with Mackenzie's original results (MacKenzie et al 1971 App. Phys. Lett. 18 529). While it is possible to obtain the exact same plasma parameters replacing the Maxwell demon with a suitably sized planar plate and additional plasma parameters control, for experiments sensitive to the exact processes from which plasma parameters are formed, one should not overlook the physical differences of these heating methods.