Particle Transport WG

1. Particle Transport WG Density Profiles at Low Collisionality Recent progress • Motivation • AUG-JET combined density profile database • Most relevant and significant variables governing density profile peaking • Including C-MOD data • Impact on fusion performance • Regressions and ITER extrapolations • Under investigation: • Density profiles under intense electron heating • Summary ITPA CDBM and Transport TG Lausanne 7-10.5.2007

2. 2006: Combined AUG & JET DB’s C. Angioni et al, PRL 90 (2003) 205003 H. Weisen et al, NF 45 (2005) L1-L4JETPEAK profile database neff@r=0.5 COMBINED DATABASE (2006) 277 JET H-modes, 343 AUG H-modes Reduced colinearities between physics variables

3. Dimensionless physics variables • Dimensionless NBI source term from diffusion-convection equation in steady state • Additional variables: NGR ,q95,Te(r=0.2)/Te, d, (R0) • Flux due to edge neutrals in core region poorly known, but typically one order of magnitude below NBI flux (Zabolotsky NF 2006, Valovic NF lett.). Not included here. • Ware pinch also unimportant

4. Strongest bivariate correlations • Wide variety of discharges conditions, with and without beam fuelling • Correlation of lnneff with NGR=ne/nGR is strong • Correlations of lnneff with G* and r* in combined database are weak 1 0.01 0.25 ITER 0.2 ITER 0 0 0.1 1 10 0.1 1 10 0.1 1 10 ITER

5. Bivariate correlations • Density peaking increases as neff drops, even in absence of NBI fuelling • Greenwald fraction nearly as correlated with density peaking as ln(neff) • Peaking in NBI-only discharges correlates with source parameter • Correlations with r*, q95,Te(0.2)/Te, dand wcetEare insignificant 2 2 2 0.52 ITER ITER ITER 1 1 1 0.1 1 10 0.2 1 0 0.3 neff

6. Multivariate regressions • Strong correlation between neff and NGR regress with only one and both, with and without device label R0 (details: see poster/paper IAEA EX/8-4 or C.Angioni et al, NF subm.) • Summary of multivariate study: • neff is the most relevant whenever included in a fit (mostly also most significant) • G* is relevant and significant whenever included • NGR, R0 and/or r* become significant and relevant only if neff is excluded • b may be significant or not depending on other variables. Small contribution. • q95,Te(r=0.2)/Te, d always insignificant and irrelevant

7. Multivariate regressions EXAMPLE • All fits including neff predict peaked profile for ITER ne2/ne >1.4 • All fits excluding neff predict flat profile for ITER ne2/ne ~1.2 • However theory (dimensionless scaling) and appearance of strong R0 dependence when neff omitted, suggest that it is wrong to exclude neff. • Coefficient for G* gives c/D~1.5 • JET/AUG study suggests that ITER will have ne2/ne >1.4 ne2/ne = 1.350.015 –(0.120.01)lnneff +(1.170.01)G* – (4.30.8)b ITER: 1.45

8. Other parameters (JET H-modes & hybrids) • No correlation of ne2/ne and Te2/Te(at odds with theory) • (Weak) dependences on Ti/Te , li under re-investigation including 2006-07 data. (M.Maslov PWG tomorrow) • Coefficient for source G* in fit for R/Ln at mid-radius provides experimental value for c/D~1.5 fnb=Pnbi/Ptot Rne/ne=0.970.34-(0.650.1)lnneff+(1.460.63)DG*/c +(0.650.4)Ti/Te ITER:Rne/ne2.6, ne2/ne 1.46

9. n/nG New C-MOD results at low neffconfirm NG not appropriate parameter M.Greenwald APS 07 • High ne~21020, some Vloop~0 • Combined JET –AUG – C-Mod database established • Preliminary analysis shows combined fits with neff represent C-MOD data better than those with NG and Rmag • Details in PWG tomorrow JET data from Weisen PPCF 2006 neff

10. New C-MOD results at low neffconsistent with JET-AUG • Preliminary analysis shows combined fits with neff represent C-MOD data better than those with NG. Details in PWG tomorrow with NG with neff

11. JT-60U: low fuelling, dominant electron heating • Data obtained in wide ranges of eff, Te/Ti and particle source in 2005-06. • Density peaking with low central fuelling and electron heating (EC+N-NB) is comparable to or even stronger than that with central fuelling and ion dominant heating (P-NB). • Peaking stronger than in JET,AUG, C-MOD. Why? • Details in PWG tomorrow

12. Purely electron heated H-modes with bN2 in TCV • Recent 1-1.5 MW ECRH-heated TCV H-modes at neff0.2 with Te/Ti 2 and bN 2 show large variability of density peaking factor. • Profiles may be flat or peaked irrespective of collisionality! • Strongly varying thermodiffusion (in/out) around ITG/TEM border? • Weak Te/Ti influence on JET suggests thermodiffusive density flattening not significant in ITER, which will be closer to equipartition. OH ECRH extra plot to come

13. Impurity transport Giroud IAEA FEC 2006 • Large experimental database with impurities from He to Ni on JET, still being analysed • With exceptions in core in some regimes, impurity densities typically less peaked than electron densities (good). • TCV in L-modes contrast with JET H-modes. • Transport coefficients are anomalous and Z-dependent • Impact of fuel density peaking on fusion power needs to take impurities into account. Dilution depends on nz(a), Dz(r), Vz(r). • More in PWG sessions Tuesday pm, Wednesday am

14. Summary Current results Areas in progress • Density peaking with strong electron heating (TCV, JT60-U) may deviate (+/-) from JET, AUG, CMOD • Lack of T/T, shear dependences in H-mode at odd with simple minded theory expectations • ‘Minor’ dependencies still under scrutiny • Differences between H and L-mode behaviour not understood • Impurity transport, especially He important for fusion power: • Both particle and impurity transport require systematic comparison with theoretical predictions • Collisionality main parameter for peaking in JET, AUG, CMOD, JT-60U • NBI source effect consistent with c/D~1.5 • Edge fuelling, Ware pinch not important in confinement zone • Impurity transport clearly anomalous in gradient zone and not simply related to electron or fuel transport