Researchers have developed a forward-modeling tool for Absolute eXtended UltraViolet (AXUV) diode cameras on the ASDEX Upgrade (AUG) tokamak, according to a new preprint. The synthetic diagnostic, built within the Cherab-Raysect optical modeling framework, aims to validate simulations of mitigated plasma disruptions and enhance the interpretation of experimental data. The tool specifically models the response of four AXUV cameras located in two poloidal cross-sections of the device, providing a crucial link between theoretical plasma radiation models and actual hardware measurements during fast transient events like shattered pellet injection (SPI). Source: arXiv plasm-ph

AXUV diodes are essential for studying rapid plasma dynamics due to their high temporal resolution, which is on the order of microseconds. This is a significant advantage over traditional foil bolometers, whose response time is typically in the millisecond range. This speed makes AXUV diagnostics particularly suitable for observing the radiation localization and total radiated power during SPI events, which provides insight into the deposition of pellet material. However, the diodes exhibit non-uniform spectral responsivity and are subject to degradation, creating large systematic uncertainties in absolute power measurements, especially when plasma spectra are evolving rapidly. Source: arXiv plasm-ph

AXUV diodes are essential for studying rapid plasma dynamics due to their high temporal resolution, which is on the order of microseconds.

The new synthetic diagnostic directly addresses the challenge of interpreting AXUV data from complex experiments, such as SPI using mixed Neon and Deuterium (Ne/D2) pellets. In these scenarios, the plasma's composition and temperature change quickly, altering the emission spectrum. The forward-modeling tool simulates the expected signal from the AXUV cameras by integrating the predicted plasma emissivity with the known geometry and spectral sensitivity of the diagnostic hardware. This allows for a more direct and quantitative comparison between experimental results from the ASDEX Upgrade and complex magnetohydrodynamic simulations of the disruption mitigation process. Source: arXiv plasm-ph

By accurately modeling the instrument's behavior, the tool helps disentangle true plasma phenomena from measurement artifacts. This capability is critical for validating the physics models used to predict the effectiveness of disruption mitigation systems, which are a mandatory component for large-scale devices like ITER. Improved validation of SPI simulations will increase confidence in predictive modeling for next-generation fusion reactors, ensuring that these crucial safety systems perform as designed. The framework's application to existing tokamak experiments provides a testbed for refining both the diagnostic interpretation and the underlying plasma physics codes. Source: arXiv plasm-ph