High Recycling H-modes in Alcator C-Mod
Abstract
A new steady state H-mode regime has been found in Alcator C-Mod at high density ( bar ne = 2.2 - 4.5 x 10^20 m-3) and scrape off layer power (P_SOL/S > 0.18 MW/m^2) called a High Recycling H-mode (HRH-mode). These H-modes are characterized by a large increase in H_α emission up to or exceeding L-mode levels after the initial drop into H-mode. The H_α emission is strongly peaked on the inboard nose of the divertor and moves up toward the inner wall with increasing P_SOL. The emission levels off when the density reaches a steady state, which can be maintained for as long as the ICRF power is on. Small irregular ELMs may accompany the increased H_α emission though in many cases there is no evidence of discrete ELMs. Steady state HRH-modes with τE up to 2 x ITER89P were obtained after boronization. Unlike in ELM-free H-modes, no accumulation of impurities is found in HRH-modes due to reduced edge particle confinement and improved impurity screening. Such steady state HRH-modes may be preferable to detached operation in ITER if the divertor heat flux can be tolerated. Supported by U.S. DOE Contract No. DE-AC02-78ET51013
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- November 1996
- Bibcode:
- 1996APS..DPP..5F06S