Description
We introduce an AXUV forward modelling tool to aid the interpretation of phenomena from experiments on ASDEX Upgrade (AUG) and support validation of plasma modelling. AXUV diodes detect electromagnetic radiation across a wide spectral range, albeit with a non-uniform spectral responsivity. This diagnostic has significantly higher time resolution (~μs) than foil bolometers (~ms) and is suitable for examining fast phenomena such as shattered pellet injection (SPI). Potential applications of the AXUV diagnostics include providing data on the radiation localization and radiated power during SPI, as these parameters carry information about pellet material deposition. The synthetic diagnostic models 4 AXUV cameras out of 14 on the AUG tokamak [1,2].
Due to the characteristics and inevitable degradation of AXUV diodes [1], absolute power measurements are subject to large systematic uncertainties, especially in dynamic scenarios with a spectrum that varies over time, of which neon-doped SPI is a prime example. This motivated the development of a synthetic diagnostic for the AUG AXUV system in Cherab [3], for two pairs of poloidally displaced cameras ~110 degrees away toroidally, creating an opportunity to examine toroidal asymmetries. The synthetic diagnostic provides a means to advance our understanding of the underlying physics during SPI and of how the diodes measure radiation in these circumstances. The details of the synthetic diagnostics are presented, with applications to AUG SPI simulations performed in JOREK [4]. The synthetic signals based on these simulations are also compared to actual measurements performed during the 2022 SPI campaign. Main features, like the velocity of the radiation front, show good agreement between the synthetic and the experimental signals.
References:
[1] M. Bernert et al 2014 Rev. Sci. Instrum. 85 033503, doi:10.1063/1.4867662
[2] P. Heinrich et al 2025 Nucl. Fusion 65 056036, doi:10.1088/1741-4326/adcbc0
[3] M. Carr et al 2017 in proceedings of the 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland (UK)
[4] W. Tang et al 2025 Nucl. Fusion 65 116003, doi:10.1088/1741-4326/adfce6