Four-channel spectral system for SUBMM-wave radiometry of hot plasma

In this report we describe a radiometric system for registering submillimeter wave radiation in the frequency range 260- 400 GHz. The system incorporates calibrated fast Schottky- detectors and enables to perform simultaneous registration of radiation in four different spectral subbands with typical bandwidth 30 GHz. Subband separation is realized by means of two quasi-optical band-pass filters standing in a transmission line of the system. Each filter is a multilayer interference structure consisting of specially designed thin anisotropic 2D resonant metal meshes separated by polypropylene films 150 microns thick. Anisotropy of resonant meshes comprising a single filter provides ~ 60 GHz frequency shift of transmittance maxima for mutually orthogonal polarizations of the incident radiation. It enables to use only two filters for realizing a four-channel spectral system that reduces costs of its production. The system described in the report is being prepared as passive diagnostics of submm-wave emission from hot (T~ 1 keV) and dense (n~ 5ldr10¹⁴cm^-3) plasma in the GOL-3 multimirror open trap heated by a relativistic electron beam (REB). Due to a high level of Longmuir turbulence, pumped by two-stream instability of REB, submm-wave emission is expected as a result of nonlinear fusion of two Longmuir waves into the electromagnetic one. Radiometric measurements of such emission provide important information on dynamics and parameters of turbulent plasma.