Summary of CDBM joint experiment session

1. Summary of CDBM joint experiment session 12th ITPA CDBM Lausanne D C McDonald Structure of talk: • CDB-2: Confinement scaling in ELMy H-modes – b degradation • CDB-4: Confinement scaling in ELMy H-modes – n* scans at n/nG • CDB-6: Improving condition of global DBs – low A • CDB-8: r* scaling on ITER relevant path at low and high b • CDB-9: Density profiles at low collisionality • CDB-10?: Variation of low density PL-H with Bt and Ip D. C. McDonald, Summary of Joint Experiments Session, Lausanne, 10th May 2007

2. CDB-2 Beta dependence of energy confinement • Previous results have shown a range of Beta scalings from negligible to a strong degradation • Several candidates for differences, including: upper triangularity, fuelling rates, rotation • 2007 • DIII-D and AUG performed combined Beta scan at matched shape and parameters. • Preliminary results: some profiles not well matched; indication of beta degradation on both machines • JET performed beta scaling in Hybrid-like scenario. • Preliminary results show strong beta degradation. • Future work: • Analyse existing experiments • Study all scans to understand variation in scalings • Further experiments to determine parameter that determines beta scaling D. C. McDonald, Summary of Joint Experiments Session, Lausanne, 10th May 2007

3. CDB-4 Dependence of confinement on nu* and fGDL • No progress • JET nu* scan and C-Mod point show nu* dominates • NF paper being updated following strong referee comments • nu* scan on C-Mod required to complete experiment. awaiting C-Mod cryopump to enable access to low nu* D. C. McDonald, Summary of Joint Experiments Session, Lausanne, 10th May 2007

4. CDB-6 Improving condition of DB: low aspect ratio • MAST • New facility capability is JET PINI neutral beam. Objective is to extend quasi-stationary ELMy H-modes in power and current • Data release expected in next year. • NSTX • Additional ~100 obs. from 2006 run provided after Chengdu meeting • Similar conditions to data from 2005 experimental run (ELMy, ELM-free H-modes) • NSTX confinement trends different from those at higher aspect ratio • tE ~ BT0.6-0.9 Ip0.4 • Li wall evaporation provided possible new confinement mode. 40% improvement D. C. McDonald, Summary of Joint Experiments Session, Lausanne, 10th May 2007

5. CDB-8 rho* scaling at high and low beta • No progress • JET and C-Mod performed test shots in late 2006 • JET could match ITER nu*, but C-Mod density was too high. • Awaiting C-Mod cryopump, when better density control should enable C-Mod to run ITER-like nu* D. C. McDonald, Summary of Joint Experiments Session, Lausanne, 10th May 2007

6. CDB-9 density peaking at low collisionality example scaling ne2/ne = 1.350.015 –(0.120.01)lnneff +(1.170.01)G* – (4.30.8)b ITER: 1.45 • C-Mod data at low neff added to existing JET-AUG dataset • neff most important parameter in scalings. All fits including neff predict peaked profile for ITER ne2/ne >1.4 • Coefficient for G* gives c/D~1.5 • JET/AUG study suggests that ITER will have ne2/ne >1.4 • Future: • effect of strong e heating through addition of TCV, JT-60U data. • H & L-mode scalings, T/T D. C. McDonald, Summary of Joint Experiments Session, Lausanne, 10th May 2007

7. CDB-10 Variation of low density PL-H with Bt and Ip • Low density limit for PL-H observed in several experiments, but mechanism and scaling of this limit not clear • Has been identified as a potential issue for ITER • Proposed experiments will perform multi-machine L-H threshold density scans to study physics and parametric dependency of threshold. • Future: • Formal agreement; J. Snipes spokesperson • C-Mod, JET, AUG, DIII-D and TCV all to propose experiments D. C. McDonald, Summary of Joint Experiments Session, Lausanne, 10th May 2007