Two-chord interferometry using a pin switch for plasma density measurement

Microwave interferometry is a useful diagnostic for measuring the line-integrated density of plasmas. To obtain a detailed switch, we have successfully measured profile of the electron density, multi chord interferometry is indispensable. Using a pin the density along two chords by alternating the beam with a time interval of 2 its for each chord. This method is very cost advantageous, because it requires only one set of sources and detection components. The system has been applied to Tokyo Spherical Tokamak-2 (TST-2) to measure two vertical chords at different major radii. It is shown that from the densities measured along the two chords, profile changes can be deduced.