Collective microwave scattering diagnostic on the H-1 heliac

A multichannel microwave scattering diagnostic has been developed and insta lled on the H-1 heliac. The purpose of the new diagnostic is to study small -scale plasma fluctuations in H-1, which are believed to be responsible for the loss of particles and energy from the plasma. The diagnostic is a 132 GHz, four-channel superheterodyne system. The transmitter and receiver ante nnas (consisting of horns and focusing bispherical mirrors) are located ins ide the vacuum vessel of H-1. A radial resolution of Deltar/a similar to0.2 is achieved. The scattering volume is positioned in the density gradient r egion at r/a similar to0.6. At present, the system is aligned to measure fl uctuations in the poloidal wave number range from approximately 10 to 25 cm (-1). The use of the heterodyne detection system allows the fluctuation pro pagation direction to be determined. The low frequency bandwidth of the sys tem is 1 MHz. The instrument sensitivity is about P-s/P-i similar to 10(-6) . (C) 2001 American Institute of Physics.