Description
The Modular Diagnostics Platform (MDP) [1] is a microwave-based, port-plug–integrated diagnostic system that consolidates a minimal yet sufficient set of fusion-plant-relevant measurements into a standardized and maintainable architecture. To support its development, prototype profile reflectometry (PR) and electron cyclotron emission (ECE) diagnostics are being developed and planned to be tested on existing research tokamaks. A key objectives are the test of a joint PR-ECE front-end transmitting line for the 40-110 GHz frequency range and flexible adaptation to different machine configurations, with design constraints driven primarily by variations in toroidal magnetic field and tokamak size. Accordingly, the diagnostics are specified to operate within ranges of Bt0=1.0–2.0 T and R0=0.8−1.7 m.
Profile reflectometry employs the ultrafast frequency-modulated continuous-wave (FMCW) technique for electron density profile determination, following an ITER-like multiband architecture. The system comprises several independently operated frequency bands covering the upper X-mode cutoff. Each band uses a voltage-controlled oscillator (VCO) operating in the K/Ka band, followed by frequency multipliers to reach probing frequencies in the 40–80 GHz range. The FMCW signal is split into reference and probing paths; the probing signal is transmitted to the plasma via corrugated waveguides and a broadband horn antenna. The reflected signal is routed back through the same transmission line using a directional coupler and mixed with the reference signal, producing an intermediate-frequency (IF) beat signal proportional to the group delay, from which the density profile is reconstructed.
The ECE diagnostic measures second-harmonic electron cyclotron emission in X-mode polarization using a heterodyne radiometer scheme. The system operates in the 60–110 GHz range and employs a tunable local oscillator operating at 60–90 GHz to down-convert the signal to a 2–20 GHz IF band. The IF signal is divided into multiple channels using fixed band-pass filters, each corresponding to a distinct radial location. Square-law Schottky diode detectors provide high temporal resolution, enabling measurements of fast temperature dynamics and MHD activity.
References:
[1] G. Subbotin et.al. Modular diagnostics platform – a microwave-based integrated measurement complex concept for magnetic confinement fusion power plants. EPS-2026, poster.