Summary of experimental progress and suggestions for future work (H mode confinement)

Publisher Website
Google Scholar
Abstract
Since the last H-mode workshop in 1991, there has been significant progress in a number of areas. In addition to H-modes in tokamaks, H-mode has been achieved in a current-free stellarator, a heliotron/torsatron with some net toroidal current and in a linear, tandem mirror. Because H-mode has been seen in a variety of magnetic confinement devices and has been produced by a variety of methods, a universal explanation is needed for the H-mode confinement improvement. The hypothesis of turbulence stabilization by sheared E*B flow has this universality. New diagnostics have confirmed the structure of Er at the plasma edge in tokamaks and have lead to direct determination of the reduction in turbulence-driven transport in the H-mode. Improved measurements of the edge rotation and pressure gradients in tokamaks have lead to better understanding of the physics of the Er formation and to tighter tests of L to H transition theories. Significant improvements in core confinement have also been seen in several tokamaks; the data here indicate that sheared E*B flow may be playing a role in the core confinement improvement. Power balance studies of the change in core thermal diffusivity after the L to H transition have raised fundamental questions about the relationship between heat flux and the temperature gradient. Finally, helium transport studies have shown that helium transport is quite similar to deuterium transport indicating that helium ash removal in a reactor operating in ELMing H-mode should be feasible.