Power law fitting of the ion saturation current and the three-temperature Maxwellian EEDF in a multi-dipole confined hot cathode discharge: an experimental revisitation

Langmuir probe diagnostic in a multi-dipole confined hot cathode discharge has been revisited with an improved sheath expansion model with fitted expansion parameters. The results show a three-temperature Maxwellian EEDF composition also observed in previous studies using a very similar system. The dependence on neutral pressure and discharge current of each electron species are consistent with known physical processes in a multi-dipole confined hot cathode discharge. This shows that the employment of the new ion saturation fitting method does not eliminate the contribution of the high energy degraded primaries to the Langmuir probe I-V trace, as sheath expansion and high energy electron current contributes differently on an I-V trace. The result remains supportive to the existence of a very hot (T (dp) > 15 eV) degraded primary electron species separate from the typical hot electron (T (hot) similar to 3 eV) species. Thus it is recommended to sweep the Langmuir probe beyond the bias voltage of the hot cathode, whenever possible, in order to properly resolve the contribution to the I-V trace of the degraded primaries.