Metal foil infrared bolometer for measurement of toroidal radiation asymmetry during plasma disruption mitigation experiments in ADITYA-U tokamak

A metal foil infrared (IR) bolometer has been developed and installed at multiple toroidal locations in the ADITYA-U tokamak to study toroidal radiation asymmetry during plasma disruption mitigation scenarios. The diagnostic uses a graphite-blackened platinum foil as a broadband absorber, with thermal emission detected by a 3-5 μm IR photodetector. The system design is optimized for ADITYA-U, considering the physics study requirements and the machine's port availability. Calibration against a blackbody source provides a model relating detector voltage to temperature, and calibration of the foil's thermal parameters is also performed, from which the incident radiation power on the foil is retrieved to estimate radiation power loss from the sampled volume. The nonlinearities in the calibration parameters (K and τc) have been addressed and accounted for in the power retrieval. The transient behavior of the bolometer foil at the initial laser onset and cutoff time has been adequately described, and a mathematical approach is used to suppress the transient effect in power retrieval. Thermal time constant, noise-equivalent power, and signal-to-noise ratio have been evaluated, demonstrating that the bolometer can reliably measure toroidal radiation asymmetry under ADITYA-U plasma conditions.