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Title	50: Improved Heat Load Reduction Using Long Outer Divertor Leg Geometry During Puff and Pump Operation
Name:	Thomas Petrie petrie@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Divertor & SOL Physics	Presentation time:	Requested
Co-Author(s):	--	ITPA Joint Experiment :	No
Description:	This experiment is the logical extension to our puff-and-pump studies and, separately, our divertor shaping studies. It is designed to provide a clear assessment of possible advantages provided by increasing the poloidal length (or parallel SOL connection length) of the outer divertor leg. Based on 1-D two-point modeling: ntar is proportional to [Lpar]^6/7 [nsep]^3 and Ttar is proportional to 1/{[Lpar]^4/7 [nsep]^2}, where nsep is the midplane separatrix density and Lpar is the parallel SOL connection length between Xpoint and target. These scalings suggest that conditions conducive to a radiative divertor solution can be achieved at low nsep by increasing Lpar. Our data from the 2011 and 2012 campaigns are consistent with the above Lpar scalings. In this experiment, we test whether this line of thinking can be successfully coupled to puff-and-pump operation. We compare the performance of the core and divertor plasmas in these long-legged outer divertor configurations with much shorter-legged ("standard") outer divertor plasmas, under radiating divertor, puff-and-pump conditions.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Our base case is a high X-point plasma shape (poloidal outer leg length ~75 cm), modelled on LSN shot 149603: Ip = 0.8 MA,Bt = 2.0 T, Pinj = 5 MW. Rtar = 1.32 m, if only the present lower divertor view by the IR is available; Rtar =1.35 m, if the new periscope IR camera system is available. For this experiment the gradB drift direction is toward the upper divertor. Deuterium gas puffing is done from either gasA (or GasD, if necessary), while neon is injected into the private flux region of the lower divertor. For steady trace neon injection, three steady values of D2 puffing are used: 0, 50, 100 tl/s. Then, for steady D2 injection during the shot (best D2 puffing rate from above), use two values neon injection at perturbing levels---these levels generate radiating divertor conditions. This process is repeated for the low-xpoint configuration (poloidal outer divertor length ~20 cm). Measurables include heat flux, density and temperature at the outer divertor target via IR camera and Langmuir probes. Behavior of upstream separatrix and pedestal density and temperature, and impurity neon accumulation and energy confinement in the main plasma are measured by Thomson scatter, CER, SPRED, and magnetics.
Background:	From 2003-2006 the focus was on active particle exhaust (and the conditions needed to optimize pumping). From 2006-2010, the focus was on radiating divertor physics (and the conditions needed to optimize radiating divertor operation). And from 2011-2012, the focus was on how divertor shaping affects the divertor and upstream plasma conditions in the SOL (and how these divertor shaping changes might be set up to optimize heat load reduction). This experiment brings all three of these facets together. Based on our understanding of the past decade of divertor activity in these areas, one expects that the high X-point, "isolated" divertor to generate more radiated power outside the main plasma, lower peak heat flux at the outer divertor target, and a much "cleaner" core plasma with better performance measurables, as when compared with more standard, lower X-point configurations.
Resource Requirements:	0.5-1.0 day of experimental time and minimum of 5 co-sources.
Diagnostic Requirements:	Divertor IR camera, floor Langmuir probes, bolometer, Thomson scattering, core SPRED, lower divertor tangential camera
Analysis Requirements:	SOLPS and ONETWO
Other Requirements:	--