Microwave backend for density profile plasma reflectometry at SPARC

Commonwealth Fusion Systems plans to install a reflectometry diagnostic in the SPARC tokamak to measure the outboard midplane radial plasma density profile [1, 2]. The reflectometry system will comprise four microwave bands from 18-90 GHz and work in O-mode and X-mode using the left-hand cutoff. The system will cover a density range of ~3x10¹⁸m^-3 to ~4x10²⁰m^-3 at a magnetic field of 12.2T on-axis. Due to limited port space, the four microwave bands will be combined in pairs, sharing the transmission line and antennas. Band combination will require quasi-optical combination and splitting units, taking inspiration from current multi-band transmission systems like in JET [3]. Band combination will require comprehensive frequency planning and system prototyping. The backend electronics must provide reliability and flexibility for the operation across all microwave bands and propagation modes while focusing on minimizing costs. The current system plan consists of four transmitter units (one per band) and eight receivers (one per band and mode) with heterodyne detection and state-of-the-art plasma reflectometry architectures. At this conference, we will present the backend design of the edge scanning reflectometry diagnostic, focusing on the microwave generation, detection, and band combination.