Thomson Scattering Density Calibration by Rayleigh and Rotational Raman Scattering on NSTX

Abstract

The multi-point Thomson scattering (MPTS) diagnostic measures the profiles of the electron temperature T e (R) and density n e (R) on the horizontal midplane of NSTX.Normal operation makes use of Rayleigh scattering in nitrogen or argon to derive the density profile. While the Rayleigh scattering n e (R) calibration has been validated by comparison with other density measurements and through its correlation with plasma phenomena, it does require dedicated detectors at the laser wavelength in this filter polychromator based diagnostic. The presence of dust and/or stray laser light precludes routine use of these dedicated spectral channels for Thomson scattering measurement.Hence it is of interest to investigate the use of Raman scattering in nitrogen for the purpose of density calibration, since it could free up detection equipment, which could then be used for the instrumentation of additional radial channels. In this paper the viewing optics "geometrical factor" profiles obtained from Rayleigh and Raman scattering are compared. While both techniques agree nominally, residual effects on the order of 10% remain and will be discussed. leblanc@pppl.gov* Contributed paper, published as part of the

The Thomson scattering system at Wendelstein 7-X

“…For the required Raman cross section we used the values published by B.P. LeBlanc 4 . In most cases the absolute values of TS density profiles agrees with line integrated measurements by a single channel interferometer (will be published later in RSI) within ±10 %.…”

Application of Thomson scattering to helicon plasma sources

“…Therefore, an absolute in situ calibration is needed for every plasma measurement. The rotational anti-Stokes lines of nitrogen are routinely used for the absolute calibration, this technique is commonly used for TS in large fusion devices (LeBlanc 2008;Scannell et al 2010). The anti-Stokes part of the nitrogen spectrum is composed of narrow lines, mostly located in the region of the spectrum covered by filters F1 and F2, as shown in figure 6(a).…”

“…The rotational anti-Stokes lines of nitrogen are routinely used for the absolute calibration, this technique is commonly used for TS in large fusion devices(LeBlanc 2008;Scannell et al 2010). The anti-Stokes part of the nitrogen spectrum is composed of narrow lines, mostly located in the region of the spectrum covered by filters F1 and F2, as shown (a) Location of the anti-Stokes Raman lines with respect to the filters' transmissivity (b) Raman calibration data obtained with filter 1 and filter 2, and linear fits of the experimental data.…”

Recent Improvements in Fast Wave Heating in NSTX

“…GENRAY predicts about 70-80% of the RF power is damped on electrons with the remaining power deposited on slowing NBI ions. A time-dependent analysis using the TRANSP plasma transport code and a non-self consistent TORIC RF package predicts the fraction of RF power deposited to slowing NBI ions decreases from 50% to 25% during the duration of the RF pulse [11]. A double-feed antenna upgrade installed for the 2009 run campaign should allow higher power coupling to H-mode plasmas and an ELM discrimination and/or resilience upgrade of the HHFW heating system is planned for 2010-11.…”