Research on Advanced Tokamaks using Dynamic Ergodic Divertorp

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(1)Improvement of Tokamak Operation for DED ExperimentsAn ohmic coil power supply has been built by combining an IGBT inverter power supply and a capacitor bank. Low q and disruptive discharges can be obtained reproducibly. Radial array magnetic proves have been installed to measure the penetration of the externally applied rotating helical magnetic field and the internal magnetic field during disruptions. The dynamic response of the tokamak plasma against the externally applied rotating helical magnetic field has been studied in detail. A 200 MHz lower hybrid wave heating system has been prepared to improve the rotation drive by DED. Now the antenna coupling and electron heating characteristics are studied.(2)Suppression of Island Growth by Plasma Current ModulationThe toroidal plasma current is modulated quickly to change the local q value and the effects of the plasma current modulation on the magnetic island formation were studied. When the external helical magnetic field is applie … More d, the plasma current modulation strongly suppresses the magnetic perturbation induced by the externally applied helical magnetic field. It is shown that a fast scan of the magnetic resonance surface can suppress the magnetic island growth. But spontaneously excited magnetic perturbations and islands in low q discharges(q〜3) were not suppressed significantly.(3)Dynamics of the Internal Magnetic Structure during Major DisruptionDynamic behavior of the internal magnetic filed during disruptions induced by tearing modes has been studied using an internal magnetic prove array. It is shown clearly that a very rapid drop (〜10μs << current diffusion time) of the poloidal magnetic field at an inner layer has been observed at just start of current quench, resulting a flattening of the current density profile. The internal magnetic field starts to increase slowly after the ringing oscillation (200kHz) of poloidal magnetic field following a sudden drop again. Now detail measurements of the internal magnetic structure have been carried out. Less