Novel scanning interferometer for two-dimensional plasma density measurements

A novel multichannel scanning interferometer designed for tomographically inferring contours of electron density in magnetically confined plasmas is described. The scanning element is a multisectored blazed rotating grating. The diffracted beam emerges at a different angle from each sector, giving rise to a fan array of discrete beams for each rotation of the grating. Signals from the probing chords are multiplexed in time enabling the use of a single detecting element for the extraction of many channels of line-integrated density information. An air-turbine-driven grating wheel assembly has been fabricated and initial tests performed. The proposed interferometer is to operate at 337 μm and will be installed on the H-1 helical axis stellarator currently under construction at the Australian National University.