Computer Tomography on Divertor Impurity Monitor for ITER with Minimizing Errors in a Logarithmic Scale

Abstract

The computer tomography for divertor impurity monitor, which measures plasma emissions in the divertor region, for ITER has been conducted using a ray-tracing technique. We have attempted four different solution methods for the inversion problem and compared the results. The solution methods which minimize errors in logarithmic scale had better performance than the methods which minimize errors in linear scale. This is likely due to the fact that the values in the emission profile vary in a wide range of orders of magnitude. The accuracy of the reconstruction has been investigated by changing discharge conditions and the number of field-of-views used. The deterioration in accuracy was most noticeable when the emission profile was reconstructed using only two field-of-views. In addition, the accuracy deteriorated, making the estimation more challenging, under discharge conditions with low emission intensity because of the wider range of emission intensity under such conditions.

Assessing global beryllium erosion via tomographic reconstruction of 3D beryllium emission profiles in ITER

“…The presence of stray light in the measured intensities is the reason why the tomography must be performed to assess Be influx, which could otherwise be estimated directly using the S/XB method [19]. Ray-tracing-aided tomography has been used for some time in fusion devices to mitigate the impact of stray light on optical diagnostics [20][21][22][23][24][25][26]. The performance of the method for the optical diagnostics of ITER was first demonstrated in [24], where the stray light was successfully filtered out in synthetic DIM signals.…”

“…The performance of the method for the optical diagnostics of ITER was first demonstrated in [24], where the stray light was successfully filtered out in synthetic DIM signals. Further analysis for DIM, namely, estimation of the accuracy of reconstruction of the H α emissivity profile in the divertor was carried out in [25]. While in [26], the method was applied to a combination of HA&VS, WAVS and DIM detectors, and the dependence of the accuracy of reconstruction of the H α emissivity profile in the entire SOL region on the edge plasma conditions and the uncertainty of the FW reflective properties was obtained.…”

“…While in [26], the method was applied to a combination of HA&VS, WAVS and DIM detectors, and the dependence of the accuracy of reconstruction of the H α emissivity profile in the entire SOL region on the edge plasma conditions and the uncertainty of the FW reflective properties was obtained. In [20][21][22][23][24][25][26] the problem was formulated and solved for axially symmetric (2D) emissivity profiles (H α radiation in [20][21][22][24][25][26] and unfiltered visible light in [23]). However the Be emissivity profiles are essentially 3D, although they show a certain periodicity in the toroidal direction due to the periodicity in the geometry and arrangement of the FW panels.…”