Ten-channel grating polychromator for electron cyclotron emission plasma diagnostics

A grating polychromator for electron cyclotron temperature diagnostic experiments is described. Two aluminum gratings are used to allow the instrument to operate for tokamak magnetic fields between 16–25 kG, i.e., for second harmonic electron cyclotron emission frequencies ranging between 90–140 GHz. The instrument utilizes an array of ten cryogenically cooled InSb hot electron bolometers to collect radiation at the focal surface of the spectrometer covering a fractional plasma radial distance of ΔR/R0∼0.3–0.4, where R0 is the major radius of the plasma. The resolving power of the spectrometer has been measured to be ℛ=ν/δν≊50. This instrument thus provides high spatial (3 cm) and temporal resolution (∼1 μs) and large spatial coverage. The detector cryostat has measured cryogen hold times of ≥24 h (liquid nitrogen) and ≊9 days (liquid helium) providing ease of operation during long plasma runs.