JET 2006-7 dimensionless confinement scaling studies

1. JET 2006-7 dimensionless confinement scaling studies D C McDonald, L Laborde, C Giroud, I Nunes, J Ongena, D Howell, C Perez Von Thun, M Brix, K Jakubowska, A Fonseca, J Hobirk, H Leggate, I Voitsekhovitch, P Mantica, J G Cordey E Joffrin, C Petty, Yong-Su Na, B Alper, E de la Luna, N Hawkes, J Hobirk, S Jachmich, R Koslowski, T Loarer, M Valisa, V Zoita Structure of talk: • Collisionality studies • Beta studies • Modelling All data analysis should be treated as preliminary D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

2. previous nu* scans on different machines a • Range of n* scans performed on different machines show different scalings • Seems to be a trend towards a weaker n* dependence at lowest n* • Consistent with a change in the dominant transport mechanism with changing n* • JET experiment aims for a wide scan to low n* a D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

3. Match: global parameters #69744 highest n* #68455 high n* #68461 mid n* #68449 low n* PNBI (MW) nedl (1019m-3) Te/B2 (eV T-2) q95 Da (1016 ph cm-2s-1sr-1) D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

4. Match: local parameters #69744 highest n* #68455: high n* #68461: mid n* #68449: low n* • Averaged data from... • Old shots 57-58s, except for CX data on low n* which is taken at 59.3s • New shot: 59-60s • 3 point n* scan with good matches in r*, bth, q, Ti/Te • no NTMs, no MARFEs, no locked modes. Some ST. D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

5. Density peaking: as expected low n* is more peaked 68449 59-60s 68455 59-60s ne (1019m-3) low n* high n* Te (keV) In dimensionless n*-scan, ne=const and n*~1/T2. Thus n* is perfectly correlated with normalised particle flux GT/Q ~ T ~ 1/n*1/2. Therefore from NBIH n*-scans it is difficult to separate dependence of peaking on particle flux from that on n*. Seems that one has to be concerned about the change of normalised density gradient  =LT/Ln = f(GT/Q, n*, …) and whether x =0 in BtE~n*xnx. D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

6. Global energy confinement scaling Degradation of confinement B tE [Ts] n*(x=0.5) • Errors estimated from previous studies are 10.4% for n*, 8.3% for BtE • Normalised tE falls by factor 3 as n* increase by factor 8 • Fall in tE with n* counter to IPB98(y,2) • Significant “knee” in n* dependence • Gas fuelling rises with n*, but JET/C-Mod studies suggest this is not a factor D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

7. b scan in hybrid-like scenario • b scan experiments on JET (2003): negligible effect of b on ELMy H-modes confinement. In contradiction to IPB98(y,2) scaling. => Confinement time at b > 2 could be higher than expected, leading to improved fusion performance in ITER. • Hybrid regime offers access to high b plasmas. • JET experiment: perform scan in b in a hybrid-like scenario at constant r*, n* => Ip  B n  B4 T  B2 D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

8. Comparison of hybrid and H-mode discharge • Good MHD stability at q95=2.7 • Standard type I ELMs • H98≈ 1 • n/nG≈ 0.85 • H89xN/q952 =0.72 • Sawtoothing discharge • The baseline and hybrid scenario converge to identical plasma parameters !! • So, the new experiment can be viewed as a b scan in a new region of parameter space D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

9. Shape match 68686 bN th=1.4 68695 bN th=1.7 68590 bN th=2.0 • Good match in high triangularity, d=0.45, HT3 shape • b variation means that match at top and core is not perfect D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

10. Parameter match 68590 Ip=1.40 MA B0=1.69 T bN th=2.0 68595 Ip=1.28 MA B0=1.60 T bN th=1.7 68686 Ip=1.22 MA B0=1.52 T bN th=1.4 D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

11. Dependence of confinement on b • Three point scan in Hybrid achieved with good matches in r*, n*, q, Ti/Te, …. • Normalised tE falls by 35% as b rises by 40% • Fall in tE with b in line with IPB98(y,2) and in contradiction to H-mode b scan results BtE  1/bN H98=0.99 H98=0.98 H98=0.94 NB: errors are correlated D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

12. Dependence of core and edge confinement on b • Fall in confinement seen in both core and edge. • Edge behaviour appears inconsistent with a simple MHD stability model. • Change in edge behaviour may be due to increased q-shear or d in these discharges. NB: errors are correlated D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

13. Differences between beta scans • Why does the 2006 scan give different results to the 2003 scans? key parameters for the scans are listed below • Strong edge effect suggests that influence of edge q-profile or shape may be the critical difference D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

14. Hybrid confinement trend with beta • Scans agreement with HIPB98(y,2) scaling is consistent with trend in wider JET Hybrid DB JET Hybrids 2003-7 D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

15. H-mode confinement trend with beta JET H-modes 1994-2001 • 2003 scans disagreement with HIPB98(y,2) scaling is consistent with trend in wider JET H-mode DB D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

16. Variation of shape in hybrid data • Weak indication that beta dependence may vary with triangularity • Confused by the fact that 2006-7 work has focused on high triangularity which is correlated with high beta operation JET Hybrids 2003-7 D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

17. Hybrid confinement trend with fuelling • 2006-7 studies have also been performed with increased fuelling • signs that confinement degrades with fuelling JET Hybrids 2003-7 D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

18. Modelling of scans Te Ti Transp GLF23 prediction using Transp density and power deposition profiles 68686 GLF23 prediction using modified inputs to match 68595 prediction • Laurent Laborde has modelled these scans using GLF23 and MMM • early results shown for the beta scan with GLF23 modelling. a effects, b effects on linear ITG/TEM modes, and EM flutter included. 68595 68590 D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

19. Observed and predicted confinement scalings BtE b a a = - 5.1 a = - 1.5 a = - 0.1 Transp GLF23 prediction using Transp density and power deposition profiles GLF23 prediction using modified inputs to match 68595 prediction • “idealised” modelled scan has negligible beta scaling. • a scan with the same mismatches as in the experiment shows a strong degradation D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007

20. ELM behaviour 68686 bN th=1.4 1015 68695 bN th=1.7 1016 68590 bN th=2.0 1016 t (s) • ELM behaviour changes. Rise in fELM associated with fall in confinement. D. C. McDonald et al, JET 2006-7 dimensionless confinement scaling studies, Lausanne, 7th May 2007