A FIR grating polychromator using conical diffraction as a diagnostic tool for ECE plasma measurements
article
A new 6(12) grating polychromator based on the principle of conical diffraction has been designed for the millimetre wavelength range. The application will be the study of electron cyclotron emission spectra of large tokamaks. The conical diffraction principle has two relevant advantages, namely a wavelength-independent efficiency and a very large wavelength range, accessible by one grating, 85-425GH2. The experimental dispersion and imaging characteristics are shown. The resolution of the instrument is shown to depend linearly on 1, which combined with the typical l/R dependence of the tokamak magnetic field gives almost constant spatial resolution in the line of sight. The spectral range of the instrument (4,i. : 0.33 mm independent of grating angle) results in a spatial coverage of the plasma in second harmonic radiation of Ld ld : 0.03 Aoe, where d is the diameter of the plasma, Bo the magnetic field on axis and e the inverse aspect ratio, Rla. The radiation is detected by cryogenically-cooled InSb, with ryl ps temporal resolution. The theoretical efficiency is given.
TNO Identifier
246512
Source
Infrared Physics, 24(6), pp. 511-525.
Publisher
Pergamon Press
Collation
15 p.
Pages
511-525
Files
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