ECE diagnostic for ATF

Electron cyclotron emission (ECE) from the Advanced Toroidal Facility (ATF) torsatron will allow measurement of plasma electron temperature. For low-field operation (0.95 T) the second harmonic is cut off at a relatively low density; therefore, third-harmonic emission from 67 to 83 GHz is used to yield central electron temperatures. At high-field operation (1.9 T) second-harmonic emission from 82 to 114 GHz is optically thick and can provide T/sub e/(r) information. A vertical view of the saddle-point geometry of the ATF mod B spatial contours provides a line of sight along which the mod B contours are symmetric with respect to flux surfaces. A single horn--lens viewing beam system with a vertical view is designed to cover the entire 67--114-GHz range, providing a spot size on the order of 6 cm. Radiation will be delivered to one of three waveguide mixers by C-band waveguide. Each of the three mixers covers a 16-GHz segment of the emission spectrum, downconverting it to the 2--18-GHz intermediate-frequency band, where it is processed by a 16-channel array of bandpass filters, providing 1-GHz frequency resolution