Helium I line intensity ratios in a plasma for the diagnostics of fusion edge plasmas

Abstract

Helium I line intensity ratios obtained by a collisional radiative model, including new recommended excitation rate coefficients and the effects of hot electrons, enable us to measure electron density (ne) and temperature (Te) in high density plasma. Measured ne and Te using 492.2 nm (4 1D→2 1P)/471.3 nm (4 3S→2 3P), 504.8 nm (4 1S→2 1P)/471.3 nm, and 492.2 nm/504.8 nm line intensity ratios are in good agreement with the Langmuir probe results in the helium discharge plasma in the NAGDIS-I linear device (Nagoya University Divertor Simulator) for ne and Te regions of 1011–4×1012 cm−3 and 5–20 eV. Hot electrons in the plasma are important for the He I line emissions when Te is below the excitation energy ≊20 eV. A resonance scattering effect included in the calculation accounts for the experimental result of the enhanced 501.6 nm (3 1P→2 1S) line emission.

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

“…137-142. For helium, similar work has been done on linear devices [143][144][145][146][147][148] and tokamaks. 66,149 To obtain a rough estimate of the importance of radiation trapping for GPI, one can evaluate the line center absorption coefficient for the Doppler broadened j → k transition [e.g.,…”

Simultaneous estimation of plasma parameters from spectroscopic data of neutral helium using least square fitting of CR-model

“…The light emitted during the discharge is transmitted by an optical fiber and fed to the visible monochromator (wavelength resolution *2.5 Å ) fitted with a charge coupled device (CCD) camera-based acquisition system to record the visible emission lines. ) line is affected by resonance scattering [27], we have worked with 9 lines out of these 10 observed lines. In fact, this effect has not been considered in the CR-model calculations of the ADAS code [26].…”

“…However, the line-ratio method is constrained by the fact that identified line-ratios must be sensitive either to electron density or to electron temperature for estimation of one plasma parameter at a time. Also, we have to identify suitable spectral line pairs to be used, which should follow either ionizing or recombining plasma conditions [25]. In this work, an effort has been made to develop a spectroscopic method which works on least square fitting of the absolute intensities of the observed visible neutral helium spectral lines from a PPD source and the CR-model-based estimated intensities using atomic data and analysis structure (ADAS) code [26] to find out the basic plasma parameters simultaneously from a large number of visible spectral lines.…”

Fluctuating Helium Emission in Optically Thick Divertor Plasmas

“…Since emission spectroscopic methods are non-interfering measurements the analysis of the helium emission has widely been applied for the determination of plasma parameters [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. However, the application of spectroscopic methods to fluctuating plasmas requests a high time resolution (µsec).…”