Bayesian inference of particle source and sink in a closed-divertor using Balmer line spectroscopy

Abstract

A new analysis technique for Balmer line spectroscopy that enables recombination rate (particle sink) and ionization rate (particle source) inference in a closed divertor configuration is reported. Bayesian inference is employed to systematically utilize all available information from multiple Balmer lines and constrain parameter ranges by using prior knowledge about plasmas. While a closed-divertor facilitates detachment, neutral plugging typically leads to large spatial variations in plasma parameters. A forward model is developed to take into account non-uniformity in the plasma parameters and applied to test data generated by divertor plasma simulations. It is shown that the forward model robustly provides particle source and sink inference over a wide parameter range. In addition, the precision improves as more Balmer lines are resolved simultaneously. The new analysis technique is also applied to an L-mode ASDEX Upgrade plasma in the high-recycling regime. The inferred quantities and their profiles are consistent with the expectations of a high-recycling divertor plasma. The further insight into the detachment physics will be provided by using this new analysis technique.

Experimental investigation of L- and H-mode detachment via the divertor Thomson scattering at ASDEX Upgrade

“…The possibility to access to 2D n e and T e profiles of a large part of the divertor is a breakthrough for divertor studies at AUG. For example, the combination of the measurements shown in this work with the divertor spectroscopy will allow the assessment of the divertor neutral density and in turn of the plasma particle balance [42,43]. Furthermore, it provides an extremely valuable benchmark and input for any modeling activity.…”

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].…”

Assessment of filtered cameras for quantitative 2D analysis of divertor conditions during detachment in JET L-mode plasmas

“…Line-integrated spectroscopic measurements of the divertor n e and T e , based on the Stark broadening of the high-excitation Balmer lines of deuterium [2][3][4] and spectral features of the continuum emission [5,6], as well as various methodologies for inferring ionization and recombination rates from the Balmer emission spectra [6][7][8], have become standard passive methods for studying divertor conditions in different tokamaks, such as JET [2,4,6], ASDEX Upgrade [3,8,9] and TCV [7,10]. Such measurements provide critical reference data for post-processed divertor simulations but potentially misinterpret the local conditions at, e.g.…”