O-mode Reflectometer

The 3ch O-mode reflectometer is designed for density fluctuation measurement. The targets of the reflectometer system are the change of fluctuation level, correlation and position of the cutoff layer, during formation of the transport barrier, H-L and L-H transition, ELM and MARFE activities.

[Diagnostic Method]
The O-mode reflectometer is configured as a heterodyne system having two separate sources. The probe beams from oscillators are launched to the plasma through the corrugated waveguide, which is shared between X-mode and O-mode reflectometer. Two IF (Intermediate Frequency) signals with the frequency of 140 MHz are produced, one comes from plasma and the other is used as a reference. The quadrature-type phase detection system provides sin- and cosine-components of reflected signal in each channel. Therefore, we can analyze both of the phase and amplitude of reflected signals.

The measured position (cutoff position) in O-mode propagation depends only on the electron density. To cover target plasma region, 3 frequencies in Q-band are chosen.

- Cutoff density : 1.4x1019m-3 (34GHz), 1.4-2.0x1019m-3 (34-40GHz), 2.8-3.1x1019m-3 (48-50GHz)
- Time resolution : 1 micro sec (Typical)
- Toroidal position : P-5 section, midplane port (Z=0.1m)

N Oyama and K Shinohara, Rev. Sci. Instrum. 73, 1169 (2002)