Analysis procedure for calculation of electron energy distribution functions from incoherent Thomson scattering spectra

Abstract

Incoherent Thomson scattering (ITS) provides a nonintrusive diagnostic for the determination of one-dimensional (1D) electron velocity distribution in plasmas. When the ITS spectrum is Gaussian its interpretation as a three-dimensional (3D) Maxwellian velocity distribution is straightforward. For more complex ITS line shapes derivation of the corresponding 3D velocity distribution and electron energy probability distribution function is more difficult. This article reviews current techniques and proposes an approach to making the transformation between a 1D velocity distribution and the corresponding 3D energy distribution. Previous approaches have either transformed the ITS spectra directly from a 1D distribution to a 3D or fitted two Gaussians assuming a Maxwellian or bi-Maxwellian distribution. Here, the measured ITS spectrum transformed into a 1D velocity distribution and the probability of finding a particle with speed within 0 and given value v is calculated. The differentiation of this probability function is shown to be the normalized electron velocity distribution function.

Measurements of Electron Energy Probability Functions in inductively coupled plasma with laser Thomson scattering

“…Starting from the first measurement in Electron Cyclotron Resonance (ECR) plasma of low temperature plasma sources performed by M. Bowden, et al [3], many studies on the sources of Inductively Coupled Plasma (ICP) [4], Capacitively Coupled Plasma (CCP) [5], Magnetized Inductively Coupled Plasma (MICP) [6] and others [7][8][9] have been performed for measurements of EEPFs. Those results normally showed a typical maxwellian distribution [3,4,[6][7][8][9] or a bimaxwellian distribution [4,5,10] in high pressure or low pressure respectively, and its transition via pressure change, which is consistent with the result of probe EEPFs diagnostics [11]. Some of the researches have been performed to compare the LTS result with the Single Langmuir Probe (SLP) result [11,12,[12][13][14], and a research of more reliable LTS EEPFs diagnostics including a comparative result with SLP EEPFs is still needed not only to establish the reliable LTS EEPF diagnostic but also to support the uncertainty and accuracy for the SLP.…”

Analysis of uncertainty of electron density and temperature using laser Thomson scattering in helicon plasmas

“…[1][2][3][4][5][6][7][8] Among the diagnostic methods, the laser Thomson scattering (TS) method is believed to be a promising diagnostic method as a standard of the low temperature plasma metrology, because its basic measurement principle is very simple and it is not affected by the noises from plasma source (RF noise, magnetic field noise, and so on). 1,9,10) Although the laser Thomson Scattering method has been known for its high measurement accuracy, [11][12][13][14][15][16][17][18][19] there can be also large uncertainty in plasma parameter measurements depending on the input quantities in the measurement model such as a scattering signal or a stray light signal. Therefore, analysis of uncertainty for the input quantities and ultimately the measurand is needed.…”