NEXT (Numerical EXperiment of Tokamak) aims to explain complicated phenomena on plasmas, which possesses the two aspects of particles and fluids. Under the NEXT program, numerical computations have been in progress using a complex parallel computer with thousands of CPU.
In fusion plasmas, microscopic fluctuations cause plasma turbulence and then vortexes of the turbulence induce particle- and heat-losses. It was experimentally demonstrated that the hollow profile of plasma current produced an inner transport barrier to suppress the particle- and heat-losses inside the plasma and enhanced confinement properties of the plasma. A zonal flow was also observed at the inner transport barrier produced by the hollow profile of the plasma current. Theoretical studies recently suggested the possibility that the flow stabilized plasma turbulence. In the present work numerical computations have been performed on the inner transport barrier generated by plasma electrons in order to investigate processes of forming the zonal flow and stabilizing plasma turbulence.
Figure 3-9 shows the time history of the electrostatic potential numerically computed for a region of the transport barrier. Microscopic fluctuations coming from a gradient of electron temperature in an early period (a) combine and evolve to turbulence with vortexes, which increase the outward particle- and heat-losses (b). Then dominant parts of the fluctuations have structures with long wavelengths perpendicular to the losses, and lead to the formation of plasma flow in the poloidal direction (c). Finally the zonal plasma flow appearing in the poloidal direction stabilizes the turbulent vortexes (d). The present numerical computations can explain successfully processes of zonal plasma flow at the inner transport barrier stabilizing plasma turbulence and suppressing particle- and heat-losses. |
