H-mode and recycling control in JFT-2M

Abstract The effects of plasma edge modification on confinement have been investigated on the JFT-2M tokamak since 1985. In the course of investigations, a new enhanced confinement regime, limiter H-mode, was discovered in 1986. This paper is a review of investigations into edge recycling control methods which extend the H-mode operational regime. In addition to Ti-gettering, the following methods have been shown to reduce edge neutral buildup, to extend the operational regime and to improve n τ of H-mode discharges: (1) optimization of the gas-puff programming (decreased or terminated at the start of auxiliary heating), (2) a toroidally distributed gas-puff system, (3) edge heating by ECH, and (4) particle removal with a pump limiter.