Methane Screening on C-MOD EDA ELM-mitigated Plasmas Jim Strachan, PPPL Nov. 30, 2004 Goal: compare impurity behavior in ELM mitigated plasmas – ergodic fields on DIII-D, pacing pellets on AUG, and EDA on C-MOD (AUG XP already accepted for spring 05) Propose: measure carbon screening on ELM mitigated plasmas and contrast the effect of ELM mitigation on the screening. Analyze with EDGE2D applied to the 3 machines, allowing projection to JET and ITER. Previous C-MOD methane screening (McCracken NF, also Granetz JNM) did not measure in EDA regime.

As for JET: Inject Methane for 3 E and Compare VB Zeff to Similar Injection of D2, With Equal D Injection Rate D2 El inj rate CD4 For same nC/ne: C-MOD injects 0.7 x JET, or 1021 CD4/s ne Zeff Zeff JET sample results from forward vs reverse fields

Experiment: only a few discharges to inject methane, measure SOL, and establish EDA, probably want to compare to H-Mode without EDA Some Issues: 1.What are best SOL measurements to constrain EDGE2D? (SOL flow?) 2. What is the best equilibrium (and fields) to both achieve EDA and to compare to AUG and DIII-D operated in their ELM mitigated regimes? 3. EDGE2D grid needs to be single null and wide enough to encompass all of the carbon ionization (5 cm at OMP for JET, 5 eV at grid edge). OK? 4. I am resurrecting A. Loarte’s EDGE2D runs for C-MOD (91018 and 91122 from Sept 22, 1996). With these, I can mock up the experiment, and will have a better idea about how it will look. What does the C-MOD group think about 91018 and 91122, and the relation to EDA operation? 5. As our ideas develop, then we might want to add in a scan (power is SOL temperature and carbon mobility; density is carbon ionization distance from LCFS; B/I is SOL connection length to the divertor; confinement is carbon diffusivity; or possibly a parameter which relates to EDA effectiveness,) 6. Bruce Lipschultz is worried about whether enough methane can be injected on C-MOD.