Development of a compact fiber interferometer on HFRC

A compact fiber interferometer system was developed on the HUST Field Reversed Configuration(HFRC) for plasma electron density measurement. The system adopts a Mach-Zehnder configuration with a 1550 nm continuous-wave laser as the light source, the system incorporates seven probe chords arranged within the θ-pinch coils of the HFRC’s plasma formation region. A 40-MHz acousto-optic modulator is adopted for heterodyne detection. Its main body is enclosed in a six-millimeter-thick aluminum shielding box, with 1550 nm-optimized single-mode fibers and high-precision fiber couplers (1525–1575 nm working bandwidth, greater than 90% coupling efficiency, single-mode compatibility) mounted on a quartz tube, occupying less than 0.5 square meters for compactness and portability. HFRC experiments demonstrate that it captures plasma dynamics: poloidal density follows coil current trends, axial channels track density decay from 1.577 × 1021 m-2 to 6.485 × 1020 m-2 and migration velocity reduction. The phase resolution of the interferometers is within 0.044 rad.