First-wall conditioning for enhanced confinement discharges and the DT experiments in TFTR

Conference · Tue Nov 01 04:00:00 EST 1988

OSTI ID:6584928

Dylla, H F; Ulrickson, M; Bell, M G; Owens, D K; Buchenauer, D; Budny, R V; Hill, K W; Kilpatrick, S J; Manos, D M; LaMarche, P H

The conditioning techniques applied to the TFTR first-wall configuration that will be in place for the DT experiments in 1990--1991 are reviewed. Of primary interest is the helium conditioning procedure that was developed to control hydrogenic recycling from the graphite, inner-wall bumper limiter. Operation of TFTR over the plasma density range for gas-fueled ohmic plasmas, /bar n//sub e/ = (2 /minus/ 5) /times/ 10/sup 19/ m/sup /minus/3/, typically results in hydrogenic recycling coefficients near unity. The use of the helium conditioning procedure produced recycling coefficients as low as 0.5, and decreased the minimum ohmic plasma density to /bar n//sub e/ = 0.5 /times/ 10/sup 19/ m/sup /minus/3/ at I/sub p/ = 0.8 MA. Low density ohmic target plasmas with low recycling conditions are prerequisite conditions for the enhanced confinement (e.g., ''supershot''), neutral-beam-heated discharges observed in TFTR during 1986-1987, which is the primary mode being considered for study in the DT experiments. The recycling changes induced by the helium conditioning procedure are believed to be the result of a plasma pumping effect in the graphite induced by He and C ion desorption of hydrogenic species from the near-surface (< 20 nm) layer of the limiter. The capacity of the conditioned limiter to pump gas-fueled, and neutral-beam-fueled discharges is compared. The helium conditioning technique is also beneficial for isotopic exchange and for minimizing the in-vessel tritium inventory. 31 refs., 7 figs., 2 tabs.

• Research Organization: Princeton Univ., NJ (USA). Plasma Physics Lab.
• DOE Contract Number: AC02-76CH03073
• OSTI ID: 6584928
• Report Number(s): PPPL-2570; CONF-880512-17; ON: DE89004631
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
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CARBON
CONFINEMENT
CONFINEMENT TIME
DEGASSING
ELEMENTAL MINERALS
ELEMENTS
FIRST WALL
GRAPHITE
IMPURITIES
LIMITERS
MINERALS
NONMETALS
PELLET INJECTION
PLASMA CONFINEMENT
PLASMA DENSITY
TFTR TOKAMAK
THERMONUCLEAR REACTOR WALLS
THERMONUCLEAR REACTORS
TOKAMAK TYPE REACTORS