RF compensated probes for high-density discharges

A Langmuir probe for the study of high-density RF discharges has been developed and tested in a helicon discharge in which the RF potential (approximate to 100V) is much larger than the electron temperature (approximate to 4eV) Carbon probe tips are used to minimize erosion by ion sputtering. Miniature chokes located close to the probe tip present RF impedances of 150 k Omega at the operating frequency of 27.12 MHz and 300 k Omega at the first harmonic at 54.24 MHz. It is further necessary to drive the probe tip to follow the RF fluctuations by coupling it to a larger floating electrode. We have been able to measure T(e) values as low as 3.4 eV in argon plasmas of 10(13) cm(-3) density; these temperatures are 1.6 eV lower than ones measured by probes with chokes alone, and 2.3 eV lower than measured by uncompensated probes.