Density Regimes of Low-Aspect-Ratio RFP Plasmas in RELAX

The line-averaged electron density has been measured over a wide range of discharge conditions in a low-aspect-ratio reversed field pinch (RFP) machine RELAX. A 104 GHz heterodyne interferometer was mainly used throughout the experiments. The measured electron density ne varied from ∼0.3 × 1019 m−3 to ∼3 × 1019 m−3, depending upon the discharge conditions. A new 60 GHz homodyne interferometer, characterized by simplicity and low cost, has been developed for the density measurement particularly in low density regime. The results from the new homodyne interferometer have shown good agreement with those from the heterodyne system in low-density regime of ne up to ∼1019 m−3.