Effect of reflections on 2D tomographic reconstructions of filtered cameras and on interpreting spectroscopic measurements in the JET ITER-like wall divertor

Abstract

Considering reflections from metallic wall surfaces in generation of tomographic reconstructions of the tangentially viewing, visible-range spectroscopic divertor cameras in JET has been observed to yield enhanced spatial accuracy and significant reduction of emission artifacts in experimentally resolved 2D line emission distributions. Neglection of reflections in the tomography process was found to lead to overestimation of the emission near the wall surfaces by up to a factor of 4, as well as to formation of bright emission artifacts between the main emission regions and the wall surfaces, comprising locally up to 50% of the emission. Mimicking divertor spectroscopy measurements by integrating the tomographic reconstructions along vertical lines-of-sight implies that reflections comprise 15%-25% of the observed line-integrated emission peaks. The spatial differences in the reflection contribution between the different lines-of-sight are less pronounced than in the 2D reconstructions due to the dominance of the brightest emission regions through which the spectroscopic lines-of-sight pass. However, postprocessing EDGE2D-EIRENE simulations using the CHERAB code and synthetic spectroscopy suggests a decrease of the spectroscopically inferred divertor electron temperature by up to 75%, when redistribution of the observed light due to reflections is considered.

ELM and inter-ELM tungsten erosion sources in high-power, JET ITER-like wall H-mode plasmas

“…The total intensity of 400.9 nm W I emission predicted by ERO2.0 (Fig. 3) at the LFS target is consistent with 2D poloidal tomographic reconstructions [18] of measurements (Fig. 4) using a tangentiallyviewing wavelength-filtered divertor endoscope camera [19].…”

Experimental distinction of the molecularly induced Balmer emission contribution and its application for inferring molecular divertor density with 2D filtered camera measurements during detachment in JET L-mode plasmas

“…ASDEX Upgrade [17], MAST Upgrade [18], JET [19,20] and TCV [21] for using tomographic reconstructions of the deuterium Balmer line emission for inferring estimates of divertor plasma conditions, such as electron temperature, T e , and density, n e , atomic deuterium density, n at , ionization rate, S ion , and recombination rate, S rec , directly based on the emission data. These methods complement the established lineintegrated spectroscopic measurements of T e [22,23], n e [24][25][26] and S ion/rec [23,27,28], offering improved localization, as well as decreased potential for misinterpretations due to line-integration effects [19,23] and reflections from metallic wall surfaces [6,29].…”

Inference of molecular divertor density from filtered camera analysis of molecularly induced Balmer line emission during detachment in JET L-mode plasmas

“…Methodology for generating 2D estimates of the electron density, n e , electron temperature, T e , and atomic density, n at , in the JET divertor volume was introduced in [4,5], based on intensity ratios of reflection-corrected tomographic reconstructions [9][10][11][12] of divertor camera images of the Balmer D 𝛼 , D 𝛾 and D 𝜀 emissions. The estimates are provided as results of a Markov chain Monte Carlo [13,14] optimization model with the help of atomic data of the ADAS database [15] and constraints from line-integrated spectroscopic measurements of the divertor n e and T e [16][17][18].…”