Grating filter for grating polychromator on measurement of electron temperature profile from second harmonic electron cyclotron emission

It is important for electron temperature measurement from second harmonic electron cyclotron emission (ECE) using a polychromator not to allow higher harmonic ECE to enter which would spoil the signals. The emission of frequencies equal to and higher than the fourth harmonic frequency at the edge of the low field side should be discarded. The emission of frequencies equal to and less than the third harmonic frequency at the edge of the low field side should not be discarded. The grating filters are designed according to the theory of the echelette grating and the reflectance of the grating filters are measured. By comparison between theory and measurement, the design principle of the grating filter is optimized. (author)