Characterization of the temperature of free electrons diffusing from a magnetically expanding current-free double layer plasma

Electron temperature is characterized in a low-pressure argon plasma diffusing from a magnetically expanding radiofrequency plasma containing a current-free double layer (DL) over the argon gas pressure of 0.3-3 mTorr. The measured electron energy probability function (EEPF) is Maxwellian at the downstream side of the DL, while the upstream EEPF shows a depleted tail corresponding to free electrons, which can overcome the potential drop of the DL and diffuse into the downstream side. The free electrons relating to the amplitude of the DL electrically neutralize a supersonic ion beam accelerated by the DL. The electron temperature measured at the downstream plasma is found to be in good agreement with that of the free electrons in the upstream source tube and agrees with the numerical result given from low-pressure diffusion theory.