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Jerry Hughes C-Mod Ideas Forum December 15, 2006

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Presentation on theme: "Jerry Hughes C-Mod Ideas Forum December 15, 2006"— Presentation transcript:

1 Jerry Hughes C-Mod Ideas Forum December 15, 2006
H-mode density control and edge pedestal profile response to cryopumping Jerry Hughes C-Mod Ideas Forum December 15, 2006

2 Motivation: Global H-Mode density connected to pedestal fueling
H-mode density control on C-Mod has been fairly poor with gas puffing only High SOL neutral opacity Pedestal self-screening Apparent critical gradient physics nPED~IP, increases weakly with L-mode target density A number of proposed experiments call for lower edge collisionality, using cryopumping as a knob Low L-mode starting densities may preclude H-mode formation (see Snipes’s low-n limit idea) Can we form H-mode at normal densities, then “pump down” pedestal and core? OR, does plasma transport physics continue to clamp density? Goals of proposal Develop ability to operate in H-mode with strong pumping Evaluate response of edge profiles, core fueling Develop operational recipes for “dialing up” edge collisionality ne,PED~IP C-Mod Ideas Forum: 13—15 Dec 2006 J.W. Hughes, “H-mode density control . . .” (H-mode Baseline TF) Slide 2 of 3

3 Experimental work Establish pumping control methods (SSEP controls, optimal magnetic geometry) Get all practical measurements working (TS, probes, CXRS, neutral emission) Obtain H-mode in pumped and non-pumped discharges Compare L-H threshold power, profiles, flows Assess impact on obtained pedestal and confinement Increase pumping rate after H-mode formation; examine pedestal response and core pump-out rate Repeat at different values of IP , varying “strength” of ETB 2 days of run time (for the blue bullets) could help answer some open questions in pedestal physics related to fueling Relative contributions to neutral screening from SOL and pedestal Roles of critical gradients and neutral transport in determining pedestal profiles at low density Processes clamping the density pedestal: Can we substantially regulate the value nPED/nG with large pumping? Sample profiles from H-mode gas puffing experiments: unpuffed and puffed C-Mod Ideas Forum: 13—15 Dec 2006 J.W. Hughes, “H-mode density control . . .” (H-mode Baseline TF) Slide 3 of 3


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