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A set of multichord, absolutely calibrated viewing arrays has been used to measure the distributions of H/D and C+2 emissions. A total of 227 chordal views are available, with the chords separated at the plasma by ∼1 cm typically. The chord brightness profiles have been combined and inverted (without recourse to symmetry assumptions) to yield local volume emission rates. Because of the thickness of the superstructure surrounding Alcator C-Mod, the views are from points re-entrant to the vacuum vessel. All but one of the arrays employ 64-channel, linear diode arrays, which are read out serially, thus requiring only one digitizer channel per array. Variable frame rates (∼1 Hz to ∼3.5 kHz) result in an extremely large dynamic range for these detectors. A 35-channel diode array which is read out in parallel and can track fast events like ELMs or pellets is also in use.
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Terry et al. (1995) studied this question.
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