Artaud, J.

Bourdelle, C.

Citrin, J.

Crombe, K.

Hobirk, J.

Hogeweij, G.

Imbeaux, F.

Joffrin, E.

Koechl, F.

Schneider, M.

Stober, J.

English

MPG.PuRe

Predictive transport analysis of JET and AUG hybrid scenariosJ. Citrin1, J. Hobirk2, M. Schneider3, J.F. Artaud3, C. Bourdelle3, K. Crombe4, G.M.D. Hogeweij1,F. Imbeaux3, E. Joffrin5, F. Koechl6, J. Stober2, the AUG team,JET-EFDA contributors∗, and the ITM-TF ITER Scenario Modelling group1 FOM Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, Nieuwegein, The Netherlands2 MPI für Plasmaphysik, EURATOM Assoc., Boltzmannstr. 2, 85748 Garching, Germany3 CEA, IRFM, F-13108 Saint Paul Lez Durance, France4 Department of Applied Physics, Ghent University, Rozier 44, 9000 Ghent, Belgium5 JET-EFDA-CSU, Culham Science Centre, Abingdon, OX14 3DB, UK6 Association EURATOM-ÖAW/ATI, Atominstitut, TU Wien, 1020 Vienna, AustriaIntroductionHybrid scenarios in present machines are characterized by improved confinement comparedto the IPB98(y,2) empirical scaling law expectations. A number of possibilities explainingthis improvement have been proposed: reduction in deleterious MHD, pedestal confinementimprovement, rotational shear turbulence suppression, increased turbulent thresholds due to q-profile shaping, and stiffness reduction at low magnetic shear [1, 2, 3]. This work concentrateson isolating the impact of increased s/q at outer radii (where s is the magnetic shear) on coreconfinement inlow-triangularity JET and ASDEX Upgrade (AUG) experiments. This is carriedout by predictive heat and particle transport modelling using the integrated modelling codeCRONOS [4] coupled to the GLF23 turbulent transport model [5]. This work aims to validaterecent predictions of the ITER hybrid scenario also employing CRONOS/GLF23, where a highlevel of confinement and resultant fusion power sensitivityto the s/q profile was found [6].Experimental dischargesFor both machines, discharge pairs were analyzed displaying similar pedestal confinementyet significant differences in core confinement. A variationn q-profile was experimentallyachieved in each pair, via the ’current-overshoot’ method for the JET case (79626/79630, withBT = 2T , Ip = 1.7MA and βN(Wth) = 1.9/2.1, βN(Wdia) = 2.6/2.8) [7, 1], and by varyingthe auxiliary heating timing in the AUG case (20993/20995, with BT = 2.4T , Ip = 1MA, andβN(Wth) = 1.6/1.9,βN(Wdia) = 1.9/2.3) [8]. Temporal evolution of the total plasma current,heating powers and confinement factors (H98≡ τth/IPB98(y,2)) can be seen in figure 1. Thes/q and rotation profiles used throughout this analysis can be seen in figure 2. For the JETpair, the interpretative q-profiles were used since the transient effect of the current overshootmay in certain cases be within the error bars of the MSE measurments. For the AUG pair,the measured q-profiles were used since the interpretative q-profiles failed to reproduce themeasured relaxed q-profiles within experimental error, andMHD activity may be redistributingthe current, clamping the q-profile to 1. The rotation profiles for the JET case are similar. Forthe AUG case, the 20993 (lower confinement) case has a significantly flatter rotation profile inthe low magnetic shear region x<0.4. Finally, all discharges are devoid of NTMs in the temporalperiods studied, apart from AUG 20993, which has a 3/2 NTM in the vicinity of x = 0.5.Modelling tools and techniquesThe core of CRONOS is a 1.5D transport solver, whereby 1D current diffusion, particle andenergy equations are solved up to the separatrix, self consiste tly with 2D magnetic equilibrium.*See the Appendix of F. Romanelli et al., Proceedings of the 23rd IAEA Fusion Energy Conference 2010, Daejeon, Korea38th EPS Conference on Plasma Physics (2011) P1.1333 5 7 900.511.52t [s]I p [MA] / P [107 W] / H98  Ip 30Ip 26Ptot 30Ptot 26H98 30H98 261 2 3 4 5 600.511.5t [s]I p [MW] / P [107 W] / H98  Ip 93Ip 95Ptot 93Ptot 95H98 93H98 95Figure 1: Evolution ofIp[MA], Ptot [107W ] andH98 for the JET (left panel)and the AUG (l panel) pairsThe NBI heat and current sourcesare calculated by NEMO/SPOT[9, 10]. In all simulations,GLF23 is employed within theregion x=0-0.83, where x is thenormalized toroidal flux coor-dinate. For each discharge, com-parison simulations were car-ried out substituting the q-profileinput with the q-profile fromthe other member of each pair. In such a manner GLF23 predictsthe confinement differencesolely due to the q-profile. Further linear threshold analysis examining the effect of s/q is alsocarried out with the quasilinear gyrokinetic transport model QuaLiKiz [11].0 0.2 0.4 0.6 0.800.20.40.60.811.21.4xs/q  s/q JET30s/q JET26s/q AUG93s/q AUG950 0.2 0.4 0.6 0.8 1050100150xv tor [krad/s]  vtor JET30vtor JET26vtor AUG93vtor AUG95Figure 2: s/q (left) and rotation (right) profiles for all analysed dischargesResultsFigure 3 shows theTi pre-dictions for JET 79630. Thesesimulations includeheat trans-port only, and runs were car-ried out both with and withoutExB suppression. 79630 simu-lations with the substituted q-profile from 79626 (the improvedconfinement case) are also shown.The inclusion of ExB suppression leads to overprediction ofTi. This overprediction is alsoseen in JETTO [12] simulations of the same discharge, displayed in the same figure. However,independently of the degree of prescribed ExB suppression,the q-profile substitution leads to a0 0.2 0.4 0.6 0.8 1024681012xT i [keV]  EXP 30EXP 26CRONOS wo/ExB q30CRONOS wo/ExB q26JETTO wo/ExB q300 0.2 0.4 0.6 0.8 10246810121416xT i [keV]  EXP 30EXP 26CRONOS w/ExB q30CRONOS w/ExB q26JETTO w/ExB q30Figure 3: Heat transport only GLF23 predictions for ion tempratures inJET 79630, excluding ExB suppression (left panel) and including ExBsuppression (right panel), and with the substituted q-profile from 79626degree ofTi increase compara-ble to the experimentally ob-served difference. A more quan-titative analysis of these dif-ferences, and of all subsequentsimulations discussed below, canbe found in table 1. This pat-tern is replicated in the AUGsimulations, displayed in fig-ure 4 for a heat transport sim-ulation of shot 20995. In theAUG case the degree ofTi overprediction is more severe. However, regardless of the ExBsuppression assumption, the q-profile substitution leads to a Ti difference consistent with38th EPS Conference on Plasma Physics (2011) P1.133observations.0 0.2 0.4 0.6 0.8 10246810xT i [keV]  EXP 93EXP 95CRO wo/ExB q95CRO wo/ExB q93CRO w/ExB q95CRO w/ExB q93Figure 4: Heat transport only GLF23predictions for ion temperatures in AUG20995In figure 5, the results ofcombined heat and particletransport simulations for JET 79630 are shown. The patternremains similar to the heat transport only cases, althoughthe primary effect on confinement improvement followingthe q-profile substitution is now in the particle channel. Thereduction of theTi gradient increase in comparison to theheat transport only case, is due to positive correlation inGLF23 between density gradients and transport, interpretedas the destabilization of TEM modes. Similar results areshown for AUG 20995 in figure 6. For the AUG case,the degree of improved particle transport is consistent with observation, although whenExB suppression is included thene profiles are significantly overpredicted. In table 1 thesimulation results are summarized in terms of the predictedore thermal energy content:Wcore =∫ xped0 (Pth(x)−Pth(xped))Jdx, wherexped is taken at the GLF23 operational zone boundary at0 0.2 0.4 0.6 0.8 1024681012xTi [keV]  EXP 30EXP 26CRO wo/ExB q30CRO wo/ExB q26CRO w/ExB q30CRO w/ExB q260 0.2 0.4 0.6 0.8 101234567xTe [keV]  EXP 30EXP 26CRO wo/ExB q30CRO wo/ExB q26CRO w/ExB q30CRO w/ExB q260 0.2 0.4 0.6 0.8 10123456xne [1019 m−3]  EXP 30EXP 26CRO wo/ExB q30CRO wo/ExB q26CRO w/ExB q30CRO w/ExB q26Figure 5: Heat and particle transport GLF23 predictions ofTi (left panel),Te(center panel), andne (right panel) for JET 79630x=0.83, and J the Jacobiancorresponding to the volumeelement. The table summa-rizes - according to GLF23- the extent of the s/q effectalone in explaining the coreconfinementdifferences be-tween each pair, both in-cluding and excluding ExBshear stabilization. Finally, additional analysis was carried out for the JET case with QuaLiKiz,where we assess the sensitivity of the instability linear thres olds to the q-profile, atx = 0.65.The experimentalR/LTi is 5.9±0.5 and 6.3±0.3 for 79630 and 79626 respectively, calculated0 0.2 0.4 0.6 0.8 10123456xTi [keV]  EXP 93EXP 95CRO wo/ExB q95CRO wo/ExB q93CRO w/ExB q95CRO w/ExB q930 0.2 0.4 0.6 0.8 10123456xTe [keV]  EXP 93EXP 95CRO wo/ExB q95CRO wo/ExB q93CRO w/ExB q95CRO w/ExB q930 0.2 0.4 0.6 0.8 10246810xne [1019 m−3]  EXP 93EXP 95CRO wo/ExB q95CRO wo/ExB q93CRO w/ExB q95CRO w/ExB q93Figure 6: Heat and particle transport GLF23 predictions ofTi (left panel),Te(center panel), andne (right panel) for AUG 20995with respect to a radial co-ordinate defined as(Rin −Rout)/2, whereRin,out are theradii to the high field andlow field side flux surfaceson the midplane. If we takeRout as the radial coordinate,the gradients rise to 7.5±0.6 and 8.1±0.4. QuaLiKizpredictsR/LTi = 7.32 for 79630, andR/LTi = 8.08 for the same input apart from the substitutionof the 79626 q-profile and magnetic shear values. The experimental R/Ln(e,i) values were2.6/2.9, andR/LTe was kept at the observed ratio toR/LTi throughout theR/LT scan.38th EPS Conference on Plasma Physics (2011) P1.133Table 1: Core thermal energy following GLF23 predictions for JET and AUG hybrids. Units are [MJ].EXP Heat transport Heat and particleno ExB with ExB no ExB with ExB79630 (q30) 1.67 1.71 2.37 1.71 2.6879626 (q26) 1.97 1.9 2.62 1.83 3.03Ratio 1.17 1.11 1.11 1.07 1.13EXP Heat transport Heat and particleno ExB with ExB no ExB with ExB20995 (q95) 0.33 0.36 0.48 0.34 0.4720995 (q93) 0.22 0.3 0.43 0.29 0.41Ratio 1.5 1.2 1.12 1.17 1.15Discussion and conclusionsA significant proportion of improved confinement in the JET and AUG hybrid scenariosanalysed here is due to improved q-profile shaping in the highmagnetic shear region, atx >0.4, according to GLF23. A proportion of∼ 60/30% of the observed improvement in corethermal energy content within each JET/AUG pair respectively, is predicted through q-profilesubstitution alone (when averaging the ratios in the bottomline of table 1). In the heat transportsimulations, differences inR/LTi are in the JET case only observed in the high shear region(x>0.4) and are correlated with differences in s/q. In the AUG case, theR/LTi differences occurboth in the low and high magnetic shear regions within x=0.3-0.6. TheR/LTi difference in thehigh shear region is correlated with a difference in s/q. However, the difference in the low shearregion cannot be explained by s/q effects. Due to the difference in rotational shear for x<0.4between the two discharges in the AUG case, it may be possiblethat reduced stiffness in thelow shear region (not predicted by the stiff GLF23) may account for a further proportion ofcore confinement difference, as also observed in JET [3]. It is also possible that the 3/2 NTMobserved in AUG 20093 is partially responsible for the apparent overprediction of the coreconfinement by GLF23, even when not including ExB shear suppression, and can thus explaina proportion of the core energy content difference between th pair. Including rotation in GLF23leads to core energy content overprediction for all discharges, although it is not possible to verifywhether this is due to the GLF23 ExB shearing model or to an intrinsic overprediction of theturbulent thresholds. Nevertheless, confinement improvement due to s/q is independent of therotation assumption. The degree of improvement in the ITG/TEM linear thresholds in the JETpair is also well predicted by QuaLiKiz through the s/q effect. The overlap of the experimentalerror bars onR/LTi is however a caveat in such analysis.AcknowledgementsThis work, supported by the European Communities under the contract of Association betweenEURATOM/FOM and EURATOM/CEA, was carried out within the framework of the European FusionProgramme with financial support from NWO. The views and opini ns expressed herein do notnecessarily reflect those of the European Commission. This work is supported by NWO-RFBR Centre-of-Excellence on Fusion Physics and Technology (Grant nr. 047 018.002).References[1] E. Joffrin et al., in Fusion Energy 2010 (Proc. 23rd Int. Conf. Daejeon, 2010)(Vienna: IAEA).[2] C.F. Maggiet al., Nucl Fusion50 (2010) 025023.[3] P. Manticaet al., this conference.[4] J.F. Artaudet al., Nucl Fusion50 (2010) 043001.[5] J.E. Kinseyet al. Phys. Plasmas12 (2005) 052503.[6] J. Citrin et al., Nucl. Fusion50 9 (2010) 115007.[7] J. Hobirket al., submitted to Plasma Phys. Control. Fusion[8] J. Stoberet al., Nucl. Fusion47 7 (2007) 728.[9] M. Schneideret al., Nucl. Fusion49 7 (2009) 125005.[10] M. Schneideret al., Nucl Fusion51 (2011) 063019[11] C. Bourdelleet al., Phys. Plasmas47 14 (2007) 112501.[12] G. Cenacchihet al., ENEA RT/TIB/88/5 (1988).38th EPS Conference on Plasma Physics (2011) P1.133

Predictive transport analysis of JET and AUG hybrid scenarios

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Predictive transport analysis of JET and AUG hybrid scenarios

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