Design and Operation of 96 GHz and 40 GHz Interferometers for Density Measurement in a Large Scale Laboratory Plasma

Summary form only given. The design construction and operation of two quadrature homodyne millimeter wave interferometers, one operating at 96 GHz and the second operating at 40 GHz, are described. Together with electrostatic probes, these interferometers will provide absolute electron density measurements at two axial locations in the Helcat (helicon-cathode) plasma device. Helcat is a four meter long magnetized plasma device with a thermionic cathode source at one end and a RF helicon source at the other. Plasma densities with both sources range from 10¹²-10¹⁴/cc, often with significant axial density gradients. The two interferometer frequencies are optimized for operation at the high and low density ends of the device respectively. The circuit, optical and mechanical design as well as initial measurements will be presented.