Far‐infrared laser diagnostics on the HT‐6M tokamak

A multichannel far‐infrared (FIR) hydrogen cyanide (HCN) laser interferometer was developed to measure plasma electron density profile on the HT‐6M tokamak. The structure of the seven‐channel FIR laser interferometer is described. The laser source used in the interferometer was a continuous‐wave glow discharge HCN laser with a cavity length of 3.4 m and power output of about 100 mW at 337 μm. The detection sensitivity was 1/15 fringe with a temporal resolution of 0.1 ms. Experimental results were measured by the seven‐channel FIR HCN laser interferometer with edge Ohmic heating, a pumping limiter, and ion cyclotron resonant heating on the HT‐6M tokamak are reported.