Energetic electron detection by a time-sampled Langmuir probe in a helicon plasma source

Summary form only given, as follows. In an RF plasma, ordinary time-average Langmuir probe traces can be distorted by RF perturbations. Experimentally we found that the effect of RF perturbations on the probe traces becomes secondary or ignorable if the plasma density is high enough. In these small RF perturbation situations, we have detected energetic electrons with energies ranging from 20 eV to 120 eV, and these data are consistent with wavelength data. However, when an RF filter system, which filters out 13.56 MHz and 27.12 MHz harmonics, is used in the probe circuit, the energetic electron information disappears from probe traces. The hot electron information may be filtered out by the filter because the hot electrons observed by a Langmuir probe are time dependent (at the RF frequencies). To be certain that the data we detected are not due to RF perturbations, we need to eliminate the effects of RF perturbations without using a RF filter system. A method to do this is to graph the probe I-V characteristics by sampling the probe output RF signal at fixed times under different probe bias voltages. Energetic electrons with energies ranging from 20 eV to 30 eV have been detected by this time-sampled technique. Comparison between hot electron energies observed from time-average and time-sampled probe traces shows good agreement.