DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
Print this page

Print this page
Title	59: Effect of Changing the Grad-B Drift Direction on Snowflake Divertor Behavior, Including Detachment
Name:	Thomas Petrie petrie@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Divertor & SOL Physics	Presentation time:	Not requested
Co-Author(s):	S.L. Allen and V.A. Soukhanosvskii	ITPA Joint Experiment :	No
Description:	This experiment explores the role that particle drifts play in determining the plasma properties of the Snowflake divertor. Here, the focus is the direction of the ion grad-B drift direction, which previous studies on standard DIII-D divertors have shown to play a major part in determining important divertor properties, such as detachment, heat flux distribution, particle exhaust, and injected impurity behavior. In this experiment, we compare Snowflakes having identical shape but with their ion grad-B drift direction opposite each other. We examine the Snowflake (minus) in ion both grad-B drift directions at 3 densities. In each case, neon is injected into the private flux region at trace levels. Beam power is fixed at 6 MW.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Start with the ion grad-B drift direction toward the main divertor. On the first shot, start with standard lower SN divertor with trace neon injection into the PFR but without D2 injection; after equilibration of neon in core, then switch to SF(-)later in the shot. Next, program standard SN for the entire shot; density to increase during the shot so that density reaches 80% of the Greenwald limit by the end of the current flattop; no neon is injected on this shot. Choose three density levels that characterize (or span) this density range; at each density (maintained with feedback control), start with standard SN and inject a steady stream of neon into the private flux region at a trace level; as neon equilibrates in the main plasma, change to Snowflake(-). At higher density, equilibration time for the standard SN divertor might be too long, so a separate shot focusing on the SF(-) phase may be necessary. This part of the experiment should require only 7-8 good shots. On the second day of this experiment when the ion grad-B drift direction is reversed, repeat the process established on Day #1. If possible, match the fixed density levels established on day #1. Measurables include density and temperature at the divertor targets, as well as heat flux profiles (with IR camera) and imaging of the lower divertor in CIII/Dalpha light using the lower divertor tangential camera. In addition to upstream density and temperature (TS), we will determine the amount of neon in the core plasma (CER and SPRED).
Background:	The Snowflake divertor configuration is based on the creation of a second-order null point via bringing together two first order null-points of a standard divertor. The result of this is an extended region of reduced magnetic field, with favorable consequences for plasma stability, transport, and heat flux reduction. The latter was clearly demonstrated on DIII-D during the last campaign. However, virtually nothing is known about the divertor properties of a Snowflake plasma having its ion grad-B drift directed away from the main divertor. Detailed studies with standard divertor configurations on DIII-D have shown that some divertor and core plasma properties improve when the ion grad-B drift is directed away from the main divertor, among them control over particle exhaust, reduced impurity accumulation in the main plasma, and a wider density operating range. In this experiment, we expect to find out if these favorable divertor and core properties in standard divertors with ion grad-B away from the divertor carry over to Snowflake. We also expect to have a detailed characterization of the divertor plasma of Snowflakes with opposite ion grad-B drift directions.
Resource Requirements:	0.3 day in "forward" BT and 0.3 day in "reverse" Bt, for a total of 0.6 day. Six co-beam sources, lower divertor cryo-pump at liquid helium temperature.
Diagnostic Requirements:	Core Thomson scattering, CER, Langmuir probes, IR camera, bolometer, Asdex gauge in the lower divertor pumping plenum, core SPRED, tangential lower divertor visible-light camera.
Analysis Requirements:	SOLPS/UEDGE, ONETWO
Other Requirements:	--