DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
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Title	42: Compatibility of High Performance Plasmas With a Puff-and-Pump Radiating Divertor
Name:	Thomas Petrie petrie@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Steady State Heating and Current Drive	Presentation time:	Not requested
Co-Author(s):	C. Holcomb	ITPA Joint Experiment :	No
Description:	This study will combine all essential elements for making the first real test of the puff-and-pump concept applied to high performance DIII-D plasmas. Neon is injected into the private flux region (PFR)of the lower divertor. Deuterium plasma flow toward the lower divertor target on the low field side is enhanced by a combination of deuterium gas injected upstream of the divertor target and active cryo-pumping at the target. Previous puff-and-pump experiments with standard ELMing H-mode plasmas have shown that biasing the plasma magnetic balance toward the lower divertor (e.g., dRsep = -0.5 cm)and directing the gradB drift toward the upper divertor yield the best chance of optimizing the stability and transport benefits of (near) DN operation while maintaining plasmas relatively clean of impurity accumulation with low peak heat flux.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	The base plasmas are near-DN high performance H-mode plasmas that can be reliably maintained for at least two seconds flattop. The lower divertor cryo-pump is maintained at liquid helium temperature. The gradB ion drift direction is toward the upper divertor, and dRsep can range from -0.3 to -0.5 cm. "High performance" refers to betaN > 3, H89p ~ 2.5, and qmin >1.5. This experiment can best be done as follows: * First establish the sensitivity of the high performance plasma to deuterium gas injection. Scan the deuterium gas puff rate to establish the operational limit as to how much D2 the plasma can accommodate before there is appreciable degradation in AT properties. * Scan of the neon injection rate at the "best" D2 injection rate established above. Understanding the sensitivity of high performance DIII-D plasmas embedded in a "radiating divertor" environment is paramount. Important measurables from this experiment are changes in energy confinement, stored energy, and qmin. Other important measurables include changes in the radiated power distribution and heat flux, changes in the density and temperature at the divertor targets, and the accumulation of neon in the core plasma.
Background:	Several years of study here at DIII-D and other tokamak facilities have demonstrated the viability of a puff-and-pump radiating divertor in reducing power loading at the divertor targets while at the same time preserving high energy confinement and betaN in the core. However, for high performance plasmas, the cooling of the divertor and SOL by radiative means can lead to excessive cooling of the pedestal plasma and marked degradation of favorable plasma pedestal and core properties. Previous attempts using "radiaing mantle" approaches were successful in knocking down the peak heat flux by ~50% without serious degradation of core plasma properties. However, in this experiment, we believe that divertor heat flux can be reduced much further without seriously impinging on plasma performance. This is done using a combination of impurity (neon) injection plus D2 injected from a non-divertor (upstream) location. Experiments with puff-and-pump radiating divertor conducted here at DIII-D (2006-2010)on standard H-mode plasmas indicate that this approach can be extended to high performance discharges with a reasonably good chance of success.
Resource Requirements:	This experiment can use dedicated time (2-4 shots) at the end of the day in which SS Heating and Current Drive experiments were featured. We basically followed this prescription in the 2012 campaign. Cumulatively, ~0.5 day is needed for this experiment.
Diagnostic Requirements:	Standard core plasma diagnostics, plus these divertor diagnostics: Asdex gauge in all three baffles,lower divertor IR camera, bolometer, lower divertor and centerpost Langmuir probes, filterscopes, core SPRED, and lower divertor tangential visible TV.
Analysis Requirements:	SOLPS/UEDGE, and ONETWO
Other Requirements:	--