Multichannel HCN laser interferometer for electron density measurements of the JIPP T-IIU tokamak

A six-channel HCN laser interferometer system has been developed for the measurement of the electron density profile in the JIPP T-IIU tokamak. The fringe shift of the probe beam is directly read out using a reference beam, the frequency of which is Doppler shifted by 50 kHz with a rotating grating. The optical configuration is of the Michelson interferometer type, of which reflecting mirrors are directly attached on the wall of the vacuum vessel. An effective area of the optical window is only φ40 mm. This optical configuration enables us to make the electron density profile measurements by the multichannel laser interferometer with a single small optical window.