Operation of two grating polychromators on TFTR and new observations of magnetohydrodynamic phenomena

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Abstract
A second grating polychromator instrument has been installed recently on the Tokamak Fusion Test Reactor device. Both this new instrument and the original one, at a different toroidal location, measure electron cyclotron emission from which electron temperature fluctuations and profiles can be obtained. This combination of instruments is designed to provide crucial information on both the poloidal and toroidal structure of magnetohydrodynamic phenomena internal to the TFTR plasma. These instruments are designed to operate within the high neutron flux environment of deuterium‐tritium operation in TFTR. Already, this combination of instruments has proven extremely valuable in identifying toroidally nonaxisymmetric phenomena. In addition to toroidal mode numbers, these instruments have yielded valuable new information on the evolution of the structure of the temperature profile during both high‐density and high‐beta disruptions, and the precursors to these disruptions. In the high‐density case, the fast growing (m,n)=(1,1) structure of a cold bubble is verified conclusively. In the high‐beta case, a ballooning type of precursor, toroidally and poloidally localized, appears to play an important role in the disruption. Also, this combination of instruments has provided positive verification of the existence of locked and stationary modes, and the temporal evolution of these modes.

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