TRANSPORT CODE STUDIES OF ELECTRON CYCLOTRON HEATING EXPERIMENTS ON TFR
Transport code simulations are presented for the Electron Cyclotron Heating (ECH) experiments performed on TFR. The simulations cover both the bulk heating and the MHD mode control experiments. For each of three experimentally identified plasma regimes a scaling of the anomalous electron heat conductivity is identified that yields satisfactory fits for the global plasma characteristics and profiles. For the so-called High- Current and Iron-Dominated regimes the corresponding scalings "Xe"simT"rm e""0.5" also yields a satisfactory description with ECH. This was not the case for the Low-Current regime which showed an exceptionally high ohmic confinement and a strong degradation of confinement for ECH. Instead, good simulations of the ECH phases of Low-Current discharges were obtained with the scaling for the High-Current regime. Shifting the electron cyclotron resonance off-axis led to a gradual decrease of confinement in the simulations. This is in contrast with the experimental findings which showed a strong reduction of confinement already when the resonance was displaced by more than pm 5 cm. This discrepancy can be explained by increased radial transport caused by the destabilization of the m=2, n=1 tearing mode as a consequence of the broader profiles that are generated by off-axis heating. Furthermore, simulations of the mode control experiments were performed using the quasi-linear theory for tearing modes. Starting from an ohmic target plasma which was unstable to the m=2, n=1 tearing mode, the evolution of the m=2, n=1 magnetic island during a 100 ms ECH pulse was calculated for various positions of the electron cyclotron resonance and levels of injected power. The best results, i.e. a complete suppression of the island, are obtained for heating almost exactly on the q=2 surface. In contrast to experimental results, the suppression of the island is found to be only temporary. It is concluded that the suppression of the MHD activity obtained in the experiment cannot be explained by profile tailoring alone.
Bibliographic Reference: REPORT FOM-87-175, 1987, AVAILABILITY: FOM-INSTITUUT VOOR PLASMAFYSIKA, RIJNHUIZEN, NL
Record Number: 1989126071900 / Last updated on: 1989-05-01
Available languages: en