Application of far-infrared, integrated detector arrays to chord-averaged plasma measurements (invited)

The recent development of linear, monolithic microbolometer detector arrays for the far infrared has led to the construction of active imaging diagnostics for tokamak plasmas. Detector arrays have an advantage over discrete detectors in that the cost per detector is significantly reduced since many detectors are fabricated simultaneously. Also, the plasma can be probed with a higher spatial resolution than conventional discrete-beam systems because of the higher channel density. Another advantage is provided by the increased channel number which is important to chord-averaged measurements since it allows an increase in the accuracy of the calculation of Abel inversions of the measured line density profile which are used to reconstruct the actual electron density distribution. The usefulness of this technique has been demonstrated on the UCLA Microtor tokamak (a = 11 cm, B/sub T/ = 20 kG, I = 70 kA, n/sub e/ = 5 x 1013 cm-3) in which a 20-channel heterodyned interferometer at wavelengths of 800 and 1000 μm has been used to study the behavior of the plasma profile. Line density profiles during the startup phase of the tokamak discharge have been obtained, as well as sawtooth fluctuation profiles. The imaging technique can also be applied to Faraday rotation measurements of the poloidal magnetic field in the tokamak. A 20-channel polarimeter has been developed that operates simultaneously with the multichannel interferometer