Observation of improved confinement at the center of a FT-2 tokamak plasma with rapid current rise and lower-hybrid heating

The problem of optimizing the conditions for central lower-hybrid heating has stimulated experiments with improved confinement at the center of the discharge in analogy to discharges with an inverted shear of the q profile. To this end, a current pulse rising rapidly from 22 to 30 kA over 0.5 ms was used in the FT-2 tokamak during lower-hybrid heating. In these experiments a substantial increase in the lifetime of the energy in the ionic component was observed. A decrease of the fluxes of high-energy charge-exchange atoms and a suppression of the microoscillations of the plasma determined in the central regions of the discharge are observed. These and other data were used together with the computer simulation to clarify the mechanism leading to the improvement of energy and particle confinement at the center of the discharge. The influence of variations in both the q profile and the electric fields, which accompanied the rapid current rise, on the transport processes is studied.

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