Analyses of Transport and Stability in Tokamaks with Hollow Current Profile

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1. Improvement of Transport ModelThe effect of plasma rotation was introduced into the turbulent transport model of the current-diffusive ballooning mode. Transport simulations using this new model successfully reproduced the formation of internal transport barriers with delayed transition, as was observed in experiments, We have also carried out transport simulations including particle transport in order to describe the formation of internal transport barrier with a hollow current profile. Time evolution of density, temperature and safety factor is in good agreement with experimental observation.2. Analysis of Electron Cyclotron Current Drive with Parallel ProcessingIn order to simulate the time evolution of tokamak plasmas with less computation time and more memory size, we have developed a parallel computation code which runs on a computer cluster composed of 8 computers connected with high-speed network. Especially the electron cyclotron current drive code (TASK/EC) was parallelize … More d and employed to study the current drive required for maintaining the hollow current profile. The code includes the analyses of MHD equilibrium, wave propagation and velocity distribution. Off-axis current drive is effective to sustain the hollow current profile and the current drive efficiency was evaluated. In the analysis of electron velocity distribution, the computation time with 8 processors was reduced to less than 1/5 of that with single processor.3. Stability Analysis of Alfven EigenmodeLinear stability of Alfven eigenmodes in a tokamak with a hollow current profile was studied by the use of three-dimensional full wave code (TASK/WM). It was found that, in addition to the toroidicity-induced Alfven eigenmode, the global Alfven eigenmode has also a significant role in a reversed magnetic shear configuration. The eigen frequency is sensitive to the detail of the current profile. This code was also parallelized for a distributed-memory computer cluster. Considerable reduction of computation time and enlargement of memory space were achieved. Less