ITPA Confinement Database and Modeling Proposals for Coordinated Research in 2004

1. ITPA Confinement Database and ModelingProposals for Coordinated Research in 2004 W.A. Houlberg (Chair), A. Polevoi (Co-chair) for the CDBM Topical Group 2nd IEA Large Tokamak Workshop on Implementation of the ITPA Coordinated Research Recommendations 23 November 2003 Naka, Japan

2. Proposals • 2003 results, 2-page summary reports submitted: • (CDB-2) Confinement scaling in ELMy H-modes: b degradation • (CDB-3a) Improving the condition of Global ELMy H-mode and Pedestal databases: Shaping/density limit • 2004 proposed: • Extension: • Confinement scaling in ELMy H-modes: b degradation • Modification: • Confinement scaling in ELMy H-modes: n* scans at fixed n/nG • New: • Effects of inside and vertical pellet launch: ELM behavior • Improving the condition of Global ELMy H-mode and Pedestal Databases: Low A • Ohmic identity experiments: Test of scaling with dimensionless parameters

3. (CDB-2) Confinement scaling in ELMy H-modes:b degradation • High Priority Issue: • Resolve difference between b scaling of global confinement databases and machine parameter scans • 2003 Results: • Joint experiments on DIII-D (C. Petty) and JET (G. Cordey) showed no degradation with b. • Though ELM behavior changed from type III to type I as b was increased it did not appear to affect scaling. • New semi-empirical scaling relations, derived from the confinement databases, that are gyroBohm-like and electrostatic predict that the fusion performance in ITER will optimize at high beta, yielding twice the fusion power as the nominal beta scenario at higher fusion gain.

4. (CDB-3a) Improving the condition of Global ELMy H-mode and Pedestal databases: Shaping/density limit • High Priority Issue: • Dependence of tE on shaping, vicinity of the Greenwald limit, and density peaking differs from tokamak to tokamak. To resolve difference, propose: a) gas scans with same configuration and q95 in each device for standard operational current; and b) two equivalent gas scans at same I, B, and P with extreme shaping and mild shaping in each machine. • 2003 Results: • AUG (F. Ryter, L. Horton) ran several series of H-mode discharges to document the core and pedestal properties in a wide range of density, triangularity and q95. About 60 discharges are currently being validated for the ITPA confinement and pedestal databases. • DIII-D (J. DeBoo, A. Mahdavi) had earlier showed that good confinement, H89p ~ 1.9-2.0 , can be obtained in high density discharges exceeding the Greenwald limit by a factor of 1.4-1.5. Discharges are in the global H-mode Database. • JET (G. Cordey, M. Valovic) earlier obtained similar results to DIII-D. 2003 experiments indicate that the density peaking increases at low collisionality. The origin of the peaking is being investigated.

5. Confinement scaling in ELMy H-modes:b degradation • High Priority Issue: • Resolve difference between b scaling of global confinement databases and machine parameter scans • 2003 Progress: • Joint experiments on DIII-D (C. Petty) and JET (G. Cordey) showed no degradation with b • 2004 Proposed Collaborations: • Scan with mainly RF, i.e. to vary Te/Ti for more ITER like conditions on AUG (F. Ryter) • Extend scan to b limit on JET (G. Cordey) • Other facilities?

6. Confinement scaling in ELMy H-modes:n* scans at fixed n/nG • High Priority Issue : • Determine whether n* or n/nG is the appropriate dimensionless parameter for global scaling • 2003 Progress: • JET and DIII-D completed initial comparisons indicating that n* is the appropriate dimensionless parameter. However, there is a large uncertainty in this observation. • 2004 Proposed Collaboration: • JET (G. Cordey) and C-Mod (J. Snipes) to maximize range in n*, and provide a basis for experiments to be considered by JT-60U (T. Takizuka) and DIID-D (C. Petty) at intermediate n*

7. Effects of inside and vertical pellet launch:ELM behavior • High Priority Issue: • Inside and/or vertical pellet launch has been shown to exhibit improved fueling efficiency over outside launch. Although there are various observations of impact on ELMs and other edge properties, these effects need to be quantified for testing models that extrapolate to burning plasma conditions. • 2003 Progress: • Began constructing pellet database using DIII-D data as a template (L. Baylor) • 2004 Proposed Collaboration: • Fueling and ELM mitigation • AUG (P. Lang), JET (G. Saibene, A. Loarte), DIII-D (L. Baylor)

8. Improving the condition of Global ELMy H-mode and Pedestal Databases: Low A • High Priority Issue : • Scaling of tE and pedestal characteristics are uncertain due to narrow range of A. Global ELMy confinement and pedestal data at low A is needed. • 2003 progress: • Initial data submitted to the Global Confinement and Threshold Databases by MAST and NSTX. • 2004 proposed collaboration: • The databases need to be better conditioned by extending to lower aspect ratios, but first some comparison experiments need to be made between NSTX and MAST to clarify differences between them due to single/double null, proximity to limiting surfaces. • Compare discharges with similar engineering parameters (e.g., R, A, Ip, Bt, Pheat, shape, etc) in both L-mode and H-mode on MAST (R. Akers, A. Kirk), and NSTX (S. Kaye, R. Maingi). Use center stack as limiter in L-mode. Tune H-mode carefully to ensure similar ELM behavior. Determine variation in both core and pedestal stored energies. Prepare for subsequent dimensionless variable scans to understand dependence of tE on b and r*.

9. Ohmic identity experiments:Test of scaling with dimensionless parameters • High Priority Issue : • Does the principle of characterizing confinement in terms of dimensionless parameters work under Ohmic conditions? • 2004 proposed collaboration (scheduled for 16-21 Jan 2004): • Match dimensionless parameters of AUG (F. Ryter), TS (F. Imbeaux), FTU (M. Romanelli), TCV (H. Weissen) Ohmic shots/sequences in JET (G. Cordey) to test scaling. Possibly include C-Mod? • Basically, each machine will bring its best Ohmic cases to JET and JET will try to match them.