Dimensionless pedestal identity plasmas on Alcator C-Mod C

Transcription

1 Dimensionless pedestal identity plasmas on Alcator C-Mod C and JET G P Maddison 1, A E Hubbard 2, J W Hughes 2, I M Nunes 3, M N A Beurskens 1, S K Erents 1, Pasqualotto 4, E Giovannozzi 5, A Alfier 4, M A H Kempenaars 1, B Alper 1, S D Pinches 1, J A Snipes 2, B LaBombard 2, and JET-EFDA contributors 1 EUATOM/UKAEA Fusion Association, Culham Science Centre, UK. 2 PSFC MIT, Massachusetts, USA. 3 Associação EUATOM-IST, CFN Lisbon, Portugal. 4 Consorzio FX, EUATOM-ENEA Association, Padova, Italy. 5 Associazione EUATOM-ENEA, ENEA Centro icerche Frascati, Italy. see appendix of M L Watkins et al, Fusion Energy (Proc 21st Int Conf Chengdu, 2006) IAEA Motivation Identity scheme and plasma regimes Analysis of pedestal widths and sources Conclusions Outline 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 1

2 When is (density) pedestal width related to edge sources? M Mahdavi et al PoP 10 (2003) 3984 A Kirk et al PPCF 46 (2004) A187 MAST ped ne decreasing with n ped e consistent with neutralparticle penetration model on DIII-D, MAST. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 2

3 When is (density) pedestal width related to edge sources? M Mahdavi et al PoP 10 (2003) 3984 A Kirk et al PPCF 46 (2004) A187 MAST ped ne decreasing with n ped e consistent with neutralparticle penetration model on DIII-D, MAST. Not seen in AUG, C-Mod. I Nunes et al NF 45 (2005) 1550 J Hughes et al PoP 9 (2002) 3019 C-Mod ecall if p ped is stability limited ped n can influence ped T too. AUG n f ( q 95 ) 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 3

4 Clarify role of sources by pedestal dimensionless identity tests Matching ρ ped, ν ped e, β ped in tokamaks, [2] in principle keeps edge plasma transport the same, so other influences are emphasized, notably sources (also f Gwd, P in / P thresh, ). 2 C-Mod JET ped q95 n n e e a [2] ν Zeff a e = 5/ 2 2 ped T n n e e [2] a ped e (10 19 m 3 ) ped n e T e Te a [2] β = 2 T ped ped e (ev) T a B 0 T e e [2] 5/ 4 ρ B0 a [2] = B a B 0 B 0 [2] a 0 (T) / 4 a B0 I p a [2] q 95 = I I p (MA) p I p [2] a 3/ 4 2 3/ 2 P a [2] P ~ a n e T e ~ P (MW) P [2] a 5/ 4 t B ce dt' ( tb ta ) a Parameters to realise pedestal identity τ = t A ( tb ta ) [2] a for size ratio a JET / a C-Mod 4.1 [2] 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 4

5 C-Mod SND equilibrium accurately reproduced on JET Field, current, medium shape (from EFIT) well matched but global β N higher on JET. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 5

6 ELM-free H-mode H on C-Mod, C stationary near-elm ELM-free state on JET Global quantities typically less well matched in best pedestal counterparts implying different H-mode regimes? JET state very steady without significant ELMs though radiation persistently high. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 6

7 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/ height b + h, width 2 d, position 0, inner linear slope m. For C-Mod, 3 neighbouring time-slices averaged in steadiest parts of H-mode phases. For JET, instrument resolution also modelled by convolution with top-hat function 1.5 cm wide however, effect not typically significant. Profiles averaged in 0.5 s window of new High-esolution Thomson Scattering system see poster GP A Alfier, Pasqualotto et al. Pedestal profiles interpolated with modified tanh function Pedestal profiles interpolated with modified tanh function J W Hughes et al PoP 9 (2002) 3019 ( ) [ ] ( ) ( ), 0 1, 0 0, where, 1 tanh > < = = d x d x x H d H d m d h b f

8 C-Mod pedestal heights spanned exhibit smaller change in widths ange in C-Mod pedestal pressures has smaller variation of widths with ped T ped n. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 8

9 JET power scan matches C-Mod C at upper end of density range, scaled density pedestal systematically wider on JET ange in C-Mod pedestal pressures has smaller variation of widths with ped T ped n. Pedestal identity conditions achieved where JET P F scan crosses upper end of data but scaled ped n consistently wider than C-Mod. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/2007 9

10 JET power scan matches C-Mod C at upper end of density range, scaled density pedestal systematically wider on JET ange in C-Mod pedestal pressures has smaller variation of widths with ped T ped n. Pedestal identity conditions achieved where JET P F scan crosses upper end of data but scaled ped n consistently wider than C-Mod. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/

11 Best matching pair show steeper pedestal for C-Mod C case Superimposing C-Mod, scaled JET profiles in normalised-flux space checks relative positions and widths by inspection. For matching heights, pedestal is steeper in C-Mod plasma. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/

12 Kinetic modelling of ionisation sources within C-Mod/JET pedestals C-Mod JET Penetration of ionisation sources into pedestals modelled with 1-D kinetic code KN1D, using ionisation / Penning gauges respectively for boundary conditions (p C-Mod D2 ~ 100 p JET D2 ). 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/

13 EDGE2D-NIMBUS for JET matched upstream and at target upstream divertor outboard target 2-D modelling fitted well to HTS upstream and outboard target probes in divertor. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/

14 Kinetic modelling of ionisation sources within C-Mod/JET pedestals C-Mod JET Penetration of ionisation sources into pedestals modelled with 1-D kinetic code KN1D. JET results supported by independent calculation with 2-D EDGE2D-NIMBUS (M-C) code. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/

15 Kinetic modelling of ionisation sources within C-Mod/JET pedestals suggests decay-lengths in proportion to their widths C-Mod JET Penetration of ionisation sources into pedestals modelled with 1-D kinetic code KN1D. JET results supported by independent calculation with 2-D EDGE2D-NIMBUS (M-C) code. Decay-lengths of ionisation sources are in almost exact proportion to pedestal thicknesses. 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/

16 Normalised KN1D results suggest slightly deeper sources on JET Normalising KN1D sources / radial co-ordinates shows marginally deeper penetration on JET. Does this contribute to its broader density pedestal? 49th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/

17 Conclusions Non-dimensional identity at the pedestal top has been achieved in H-modes at high field (7.9 T) on C-Mod and low field (1.4 T) on JET, encompassing a factor 4 in absolute size. Despite some global plasma differences, pedestal profiles are similar but not identical. In particular, density pedestal width is proportionally somewhat wider on JET. 1-D (2-D) kinetic modelling of edge sources indicates neutral particles may penetrate deeper into the JET pedestal, perhaps contributing to its broadening. esults are therefore consistent with an intermediate condition where both plasma transport and edge sources influence pedestal formation. A next question would clearly be how this interplay evolves for lower ν ped e, higher β ped. Work conducted under the European Fusion Development Agreement / funded jointly by the UK EPSC and by the EC under the Contract of Association between EUATOM and UKAEA / supported by US DOE award DE-FC02-99E th Annual Meeting of the Division of Plasma Physics, American Physical Society, Orlando, 12-16/11/