Speaker
Description
There is renewed interest in using the sub-divertor for diagnosis of the fusion plasma burn process, as this region of the reactor chamber would not require access via the main chamber wall and T-breeding blanket [1]. In the referenced study, it was shown that it would be feasible to control the DT burn by feedback from $^3$He concentration measurement in the sub-divertor, assuming the reactor is using the same $^3$He ICRH heating scheme as used in JET DTE2.
The present study is looking at the viability of sensing plasma surface interaction phenomena that could link to the sub-divertor via enhanced emission of fuel or impurity gases, or molecular compounds thereof. Specifically, cases from two long-pulse devices, WEST and W7-X are explored, in which the mass 3 (amu = 3) reading from a sub-divertor mass spectrometer is correlated to PSI phenomena in the main chamber. In the case of WEST, a rise in mass-3 is correlated to formation of HD at heated plasma surfaces, contribution for more HD molecular radical presence in the mass spectrometer than what might naturally form in the analyzer [2]. In the case of W7-X, where deuterium is not yet deployed, a rise in mass-3 is interpreted as due to formation of H$_3$ under certain PSI conditions, and H$_3$ molecular emission from the island divertor region is being explored via IR spectroscopy to validate this correlation. [3, 4]
The present contribution will include first outcomes from a modeling exploration for the case of WEST, deploying an advanced modeling framework- STRIPE -recently developed to analyze material erosion and the global transport of eroded impurities originating from radio-frequency (RF) antenna structures in full 3D linear and toroidal geometries [5,6]. The aim for this work is to determine the likelihood of HD formed in enhance PSI can reach at least the divertor pumping gap.
*Work supported, in part, by U.S. Department of Energy under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.
References
[1] C.C. Klepper et al., 2025 Nucl. Fusion 65 086015; DOI: 10.1088/1741-4326/ade9dc
[2] G. Schlisio et al., "A novel fast mass spectrometer for fusion applications - in preparation", and related contribution #147 this Conference.
[3] E.A. Hodille et al., 2025 Nucl. Mater. Energy 45 101999, DOI: 10.1016/j.nme.2025.101999
[3] E. Gauthier, EPS 1995.
[4] A. Kumar et al 2025 Nucl. Fusion 65 076039; DOI: 10.1088/1741-4326/ade455
[5] A. Kumar et al 2025 EPJ Web. Conf. (accepted for publication)