AVS 46th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS-TuA

Paper PS-TuA3
Thomson Scattering with Gated Intensified CCD Detectors for Diagnostic of rf Discharge Plasmas

Tuesday, October 26, 1999, 2:40 pm, Room 609

Session: Plasma Diagnostics II
Presenter: S.A. Moshkalyov, Queen's University of Belfast, Northern Ireland, UK
Authors: S.A. Moshkalyov, Queen's University of Belfast, Northern Ireland, UK
T. Morrow, Queen's University of Belfast, Northern Ireland, UK
C. Thompson, Queen's University of Belfast, Northern Ireland, UK
W. Graham, Queen's University of Belfast, Northern Ireland, UK
Correspondent: Click to Email
Thomson scattering (TS) with high-repetition rate lasers has been recently introduced as a diagnostic of electron parameters (electron density and electron energy distribution function, EEDF) in low-temperature gas discharge plasmas. This method has some distinct advantages over other techniques (like electric probes) which are commonly used to measure electron parameters in gas discharges. This technique is non-intrusive, and the interpretation of data is straightforward. However, due to the small cross-section of light scattering by free electrons, TS signals are extremely low (~ 20-30 photoelectrons/pulse for an electron density of 10@super 11@ cm@super -3@). To improve signal-to-noise ratios, measurements are typically made by accumulating the signals over ~10@super 3@ laser pulses. In most TS experiments, single-channel photomultiplier tubes are used for the light detection. A further step in the diagnostic development is the use of multichannel detectors such as gated intensified CCD's which record the entire TS spectrum and thus reduce considerably the time needed for measurements of the electron parameters. In our experiments, TS system with 10 Hz YAG laser (0.5 J at 532 nm) and a low-noise ICCD detector is used for diagnostics of an inductively coupled RF discharge plasma in a GEC reference cell. Experiments were carried out in Ar plasma for low pressures (25-250 mTorr) and relatively low powers (30-70 W). Experiments have shown that high accuracy of EEDF measurements in an extended range of electron energies (up to 12-15 eV) can be achieved by accumulating TS signals in 500-2500 pulses, with overall measurement time as small as 2-10 minutes. For high argon pressures EEDF has shown to be close to Maxwellian, while for low pressures strong deviation from Maxwellian distribution has been observed. The study of the effect of other gases admixtures to Ar is now on the way.