Measuring gross beryllium erosion with visible cameras in JET

Abstract

Two visible cameras with the same wide-angle view have been used to study the gross beryllium (Be) erosion in JET. An absolutely calibrated spectroscopy system employed in the past for the same object was used to quantitatively infer the camera photon fluxes and also to validate the results. To extract the effective sputtering yield, a simplified method is applied from the quotient of the measured radiances of the D α and the Be II line at 527 nm. The obtained results are in reasonably good agreement with those already published. The main benefit of using cameras is that the global view of the plasma–wall interaction surfaces of the whole vessel is monitored, and the different sources and their wetted areas can be identified and quantified. In addition, the measurement of the particle flux distributions can be used for the validation of three-dimensional erosion-transport codes.

Measuring the isotope effect on the gross beryllium erosion in JET

“…The second are two wide-angle view visible cameras installed outside the JET biological shield that receive the image from an equatorial port after being transported along a path of more than 10 m. One is equipped with a filter centred at the Be II 527 nm line and the other is an unfiltered high-speed or fast camera but where the light was demonstrated to be clearly dominated by D α (H α ) atomic emission [22]. Both cameras were recently calibrated and the measurements at the same limiter location where the spectrometer looks at are in good agreement [21].…”

“…In most cases, the main uncertainty comes from the fact that the radiance is a line-integrated measurement along the plasma edge emission layer and therefore a mean S/XB must be estimated since generally the n e− , the T e− and the emission-radial profiles are unknown. Here, we take advantage of the fact that the ratio of the S/XB coefficients of the measured atomic lines, Be II at 527 nm and D α (H α ) or D γ (H γ ), have a relatively small dependence near the separatrix on n e and T e for the limiter plasmas analysed here and we fix this ratio to a constant equal to 1.8 [21]. When making this approximation we accept an error that is estimated to be <±50% as discussed in [21], not much larger than the one generally assumed for this kind of measurements.…”

“…Here, we take advantage of the fact that the ratio of the S/XB coefficients of the measured atomic lines, Be II at 527 nm and D α (H α ) or D γ (H γ ), have a relatively small dependence near the separatrix on n e and T e for the limiter plasmas analysed here and we fix this ratio to a constant equal to 1.8 [21]. When making this approximation we accept an error that is estimated to be <±50% as discussed in [21], not much larger than the one generally assumed for this kind of measurements. However, this error should be much smaller when comparing the relative values of the yields for H and D, since equivalent discharges, that should have similar edge plasma parameters, have been compared.…”

“…Finally the results are discussed in view of the bibliography mentioned before. For a more detailed description and discussion of the experimental aspects and the analysis methodology and further examples of Y eff estimations including a plasma with divertor configuration the reader is referred to [21].…”

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

“…The synthetic signals obtained with ray tracing can be used to estimate the accuracy of solving the inverse problem, namely, the problem of reconstructing the 3D Be emissivity profile in the SOL using images from HA&VS and WAVS filtered cameras and signals from DIM lines of sight (LoS). 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].…”