Design of a Diamond-Based In-Vessel Soft X-Ray Camera for the SPARC Tokamak*

The in-vessel silicon diode arrays that are used for soft x-ray (SXR) detection in many tokamaks are sensitive to neutron damage, making them unsuitable for burning plasma devices like SPARC. In such a device, the silicon diodes would need to be placed far from the plasma—limiting their field of view—or an alternative detector could be used. One promising detector is chemical vapor deposition (CVD) single crystal diamond, which has been demonstrated to have excellent tolerance against 14 MeV neutrons. Thus far, these CVD diamonds have only been used in the form of single detectors. Presented here is the design of a camera made from an array of these diamonds. SPARC will employ several of these cameras in a single poloidal plane and their overlapping fields of view will enable tomographic inversion of the emissivity profile. The high temperature, high neutron flux, and disruption g-forces that will be experienced in SPARC present a unique design challenge that is addressed using both simulation and physical experiment. Simulations are performed to determine the optimal placement of the cameras, as well as their sensitivity to spatial misalignment and spectral miscalibration. Experiments are performed to calibrate the detectors for response time, spectral calibration, and spatial alignment.

Funded by Commonwealth Fusion Systems