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	314: Optimization of castellation for a new W-divertor of ITER: studies of shaped castellation in DIII-D
Name:	Dmitry Rudakov rudakov@fusion.gat.com	Affiliation:	University of California, San Diego
Research Area:	Plasma-material Interface	Presentation time:	Not requested
Co-Author(s):	A. Litnovsky (FZJ), M. Hellwig (FZJ), V. Philipps (FZJ), C.P.C. Wong (GA), R. Boivin(GA), N. Brooks (GA), J. Watkins (SNL), P. Stangeby (Univ. of Toronto), A.Mclean (GA), Y. Krasikov (FZJ), J. Boedo (UCSD), R. Moyer (UCSD), D. Matveev (FZJ), M. Komm (IPP Prague), G. De Temmerman (DIFFER), R. Pitts (ITER), M. van den Berg (DIFFER)	ITPA Joint Experiment :	Yes
Description:	The aim of this experiment is to evaluate the efficiency of deposition mitigation in the shaped castellation proposed for a new tungsten divertor of ITER. Castellation cells having roof-like shape with rounded edges will be used in this experiment. Shaping of castellation cells should provide significant difficulties for impurities and fuel particles to penetrate and accumulate inside the gaps whereas rounded edges should increase the necessary plasma-wetted area of the castellation around the gaps. Metallic plates below the castellation should provide the information on deposition at the bottom of the gaps.	ITER IO Urgent Research Task :	Yes
Experimental Approach/Plan:	Impurity deposition and undesirable fuel accumulation in the gaps of castellated structures represent known safety issue for ITER. Recent studies revealed significant deposition at the bottom of the gaps which is yet to be understood and reliably modeled. Shaping of castellated structures is the most direct way for reduction of the impurity deposition and fuel accumulation in the gaps of castellation. Experiments in TEXTOR and DIII-D have proven the expected advantages of shaped castellation. It is planned to elaborate these experiments by making the long-term piggyback exposure using DiMES system. A conventional (rectangular) and new shaped tungsten castellation will be exposed simultaneously to allow for a direct comparison. To obtain the representative deposition patterns in the gaps a piggyback one-week exposure preferably in LSN configuration, is requested for the castellation. The metal plates installed below the castellation will be used to collect the deposited material at the bottom of the castellation. The gaps and instrumented plates will be analyzed at FZJ.
Background:	The castellated armor of the first wall and divertor in ITER will be used to maintain the durability of the machine under the thermal excursions during plasma operation and to alleviate the forces caused by induced currents. However, the impurity deposition and fuel accumulation in the gaps of castellated structures represent safety issue for ITER operation. Past and present research demonstrated that the fuel inventory in the gaps of castellated structures is significant and there are essential difficulties in fuel removal. Mitigation of the fuel accumulation in the gaps by the gap shaping and study of material migration towards the bottom of gaps are among key topics of a task DSOL 27 of the IEA-ITPA Joint Experiments Program. Within this task the comparative modeling studies of conventional and shaped castellation were made. In particular, the PIC code SPICE2 results predict a full suppression of the ion flux in the gaps of shaped castellation accompanied with a drastic decrease of impurity deposition as modeled with Monte-Carlo 3D GAPS code. To validate these results experimentally dedicated multi-machine investigations are ongoing on several tokamaks worldwide. The same design of a castellation will be used in DIII-D, ASDEX-Upgrade, EAST, KSTAR, LHD and TEXTOR. Flexible design allows for a direct comparison of conventional and optimized shaping within the same experiment along with an easy access to the bottom of the gaps. An essential advantage of this experiment is that the exposure of castellated samples will be performed at shallow angle with respect to magnetic field, similarly as expected in ITER. Another advantage of this experiment is the possibility of a direct comparison with experimental results from the other major tokamaks involved in multi-machine studies.
Resource Requirements:	One week piggyback exposure using DiMES manipulator system, preferably LSN operation, NBI-heated ELMy H-mode.
Diagnostic Requirements:	DiMES TV, floor Langmuir probes, in particular the probe at the DiMES radial location, MDS chord looking at DiMES.
Analysis Requirements:
Other Requirements: