First results with amplitude modulation reflectometry on the PBX‐M tokamak

Electron density profile measurements have been obtained on PBX‐M by amplitude modulation reflectometry. With this technique, the measurement of the time delay is obtained from the phase delay of the modulating envelope (200 MHz in PBX‐M). The system operates with the extraordinary mode, in the range 32–50 GHz. Under these conditions the density profile of PBX‐M can be probed from the scrape‐off layer up to typically r/a=0.7. With a final bandwidth of 40 kHz, the reflectometer is able to obtain the edge profile in 1 ms. The profiles obtained are relatively noise free and in good agreement with Thomson scattering measurements. Perturbations due to the strong‐edge turbulence are kept to a minimum, and no software filtering or other signal processing was necessary to extract the time delay information from the raw data. Profiles have been measured for ohmic and Neutron Beam Injection heated discharges.