High-resolution Thomson scattering system on the COMPASS tokamak: Evaluation of plasma parameters and error analysis

Abstract

The electron density and temperature profiles measured by the Thomson scattering diagnostic on the COMPASS tokamak are used for estimation of electron kinetic energy, energy confinement time, and effective charge number Z(eff). Data are compared with the line-integrated electron density measured by a microwave interferometer in an ohmically heated plasma with a circular cross section. An error analysis of both electron temperature and density are performed by two methods-a constant chi-square boundaries method and a Monte Carlo simulation, determining asymmetrical error bars for the electron temperature.

Bi-Maxwellian electron energy distribution function in the vicinity of the last closed flux surface in fusion plasma

“…The source was estimated after fitting the experimental density profile with ad hoc transport coefficients with fixed e T and i T profiles, and considering a typical particle confinement time τ p = 30 ms. As an output result we obtained a value for energy confinement time τ Ε = 3.4 ms. It is in agreement with the value between 3 ms and 4 ms evaluated in [30]. It is clearly seen that the region in the vicinity of the LCFS where the EEDF is bi-Maxwellian corresponds to the source of electrons.…”

“…The spatial resolution is about 5 mm. Detailed information about the accuracy of the TS data can be found in [30]. Although the two profiles are complementary, it is seen that the TS temperature measured in the proximity of the LCFS location is close to the temperature of the low-energy electron fraction and differ by about a factor of two from the high energy electron fraction temperature.…”

Analysis method for Thomson scattering diagnostics in GAMMA 10/PDX

“…Thomson scattering (TS) diagnostics is one of the most useful methods for measuring electron temperature, T e , and density, n e , in fusion plasmas. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] For the tandem mirror GAMMA 10/PDX, we developed TS diagnostics for T e and n e measurements for single laser and plasma shots. 6 The value of n e (∼2 × 10 18 m −3 ) in the GAMMA 10/PDX plasma is typically lower than that in other fusion plasmas.…”

“…1,2,4 Some TS systems use high-speed analog-todigital converters or oscilloscopes to obtain the raw signal waveforms. [6][7][8][9][10][11] The output signals of the polychromators in a TS system are normally fitted to a Gaussian function in order to obtain the single-pass TS signal intensities. [7][8][9][10][11] TS data processing methods for raw TS signals with high-timeresolution data acquisition systems have been developed for electron temperature and density measurements, e.g., Monte-Carlo simulation for analyzing TS signals, 12 maximumlikelihood fitting method for TS fitting data, 13 and non-Gaussian pulse shape fitting method.…”

Electron temperature and density measurement by Thomson scattering with a high repetition rate laser of 20 kHz on LHD

“…For magnetically confined fusion devices, electron temperature ( T e ) and electron density ( n e ) are fundamental parameters of plasmas. Thomson scattering diagnostics is a widely adopted measurement method of T e and n e in fusion plasma devices [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] because of the reliability of the results and no perturbation for the plasma. Since the cross-section of Thomson scattering, σ T , is almost 6.65 × 10 −29 m 2 , pulsed lasers with an energy of a few joules are usually used for this measurement.…”