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Modelling of JET, Tore Supra and Asdex Upgrade current ramp-up experiments

Modelling of JET, Tore Supra and Asdex Upgrade current ramp-up experiments. F. Imbeaux, F. Köchl, D. Hogeweij, J. Citrin, J. Hobirk, X. Litaudon, V. Basiuk, J. Fereira, J. Lönnroth, V. Parail, G. Pereverzev, Y. Peysson, G. Saibene, M. Schneider, G. Sips, G. Tardini, I. Voitsekhovitch

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Modelling of JET, Tore Supra and Asdex Upgrade current ramp-up experiments

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  1. Modelling of JET, Tore Supra and Asdex Upgrade current ramp-up experiments F. Imbeaux, F. Köchl, D. Hogeweij, J. Citrin, J. Hobirk, X. Litaudon, V. Basiuk, J. Fereira, J. Lönnroth, V. Parail, G. Pereverzev, Y. Peysson, G. Saibene, M. Schneider, G. Sips, G. Tardini, I. Voitsekhovitch On behalf of : JET-EFDA contributors, Tore Supra workprogram, AUG workprogram, ITER Scenario Modelling group (ITM-TF)

  2. Introduction • Aim of the working group : model current ramp-up (and ramp-down) in ITER • Implications on PF systems, H&CD methods for current profile shaping, flux consumption • Main issue is the heat transport model  try to validate a model against present experiments • Validation criterion : li and Vloop (0D), Te profile, q-profile, test against several JET experiments (ohmic, NBI, LHCD, ICRH) • A few shots from other experiments : Tore Supra, ASDEX Upgrade • Only energy transport and current diffusion are modelled, density and Zeff prescribed from experiment) • L mode plasmas 2

  3. What has been done • JETTO, CRONOS, ASTRA have been used, not distinguished in the following • We checked that for the same model, results are independent of the transport code • Li prediction and Flux consumption are strongly dependent on the Te prediction in the outer half of the plasma  the challenge is to predict Te up to r = 1 in L mode • Models that fail inside r = 0.5 may still be acceptable for predicting li, Vloop • Tried a variety of transport models • Scaling-based (prescribed radial shape, renormalised to scalings of global energy content HH-98 = 0.4 or HL-97 = 0.6) • Empirical Bohm/gyro-Bohm (L-mode version, ITB shear function off) • GLF23 (either up to r = 1; or r = 0.8 with large cedge = 8 m2/s) • Empirical Coppi-Tang model : could not understand / agree with US colleagues what to use (doubts about the definition of the model) 3

  4. Further details • Te, Ti, current transport predicted • Vtor not taken into account (usually Vtor, Ti not measured since no NBI) • Boundary Te (r = 1) taken from experiment (guessed from ECE) • Ne profile taken from experiment (JET : inversion of interferometer : NFT2 PPF) • Flat Zeff assumed, <Zeff> taken from experiment (Bremsstrahlung) • Recent reprocessing of KS3 means we have to redo a number of simulations (+20 to + 40 % increase in Zeff). Conclusions on Vloop may be affected, but likely not on the transport model Te profile trends. • Prescribed plasma boundary from experiment (EFIT) 4

  5. Present database • Current ramp-up : 5

  6. JET 72818 (ohmic) • Li reproduced within Dli = 0.1 • B/gB is the most accurate on li, not necessarily on Te • GLF23 needs patch at the edge otherwise strong error in li • GLF23 with patch is quite accurate on Te inside r = 0.7 6

  7. JET 72823 (2 MW LHCD) • Li reproduced within Dli = 0.1 (problem during the first 500 ms – too much LH current predicted) • B/gB is the most accurate on li, scaling-based better on Te • GLF23 needs patch at the edge otherwise strong error in li • GLF23 with patch : too flat Te, it is a miracle that it produces so good li 7

  8. JET 72823 (2 MW LHCD) • NBI blips during ramp-up allowed some MSE and Ti measurements • Scaling-based on one hand, B/gB and GLF23 on the other, seem to provide a sort of enveloppe to the experimental data • ! Large fluctuations of Ti measurements on this shot 8

  9. JET 71827 (ohmic) • Li reproduced within Dli = 0.1 • B/gB and GLF23 accurate in Te and li, scaling-based better tend to overestimate Te in the core • Coppi-Tang much too peaked and overestimated on Te. 9

  10. JET 71827 (ohmic) • Later time • All models slightly overestimate Te inside mid-radius, little impact on li • NB : average sawteeth effect taken into account in the simulation 10

  11. Tore Supra 40676 (ECCD) TORE SUPRA • Li reproduced within Dli = 0.1 • Co-ECCD at r = 0.3 during the Ip ramp • GLF23 gives an excellent prediction of li, though works badly on the electron temperature • NB : average sawteeth effect taken into account in the simulation 11

  12. Tore Supra 40676 (ECCD) TORE SUPRA • Li reproduced within Dli = 0.1 • Co-ECCD at r = 0.3 during the Ip ramp • GLF23 gives an excellent prediction of li, though works badly on the electron temperature • NB : average sawteeth effect taken into account in the simulation 12

  13. ITER projections, Ip flattop = 15 MA (ohmic) • Ip = 15 MA ramped-up in 100 s • Prescribed plasma boundary • « Ordering » of models in Te prediction is the same as on the JET experiments (scaling-based slightly more optimistic), deviations somewhat larger • All « relevant » models give the same li within Dli = 0.1 • Small differences in target q-profile (Dq <= 0.1 outside of q = 1) 13

  14. ITER projections (20 MW ECRH mid-radius) • Larger differences in Te due to strong and localised heating • All « relevant » models give the same li within Dli = 0.1 • Some differences in target q0, from flat to slightly reversed, target q above 1 everywhere 14

  15. Conclusions : present experiments • A selection of 4 models has been made, matching present JET experiments in terms of li dynamics (within Dli = 0.15) for various heating schemes • Same degree of agreement found for a few other discharges from Tore Supra and Asdex Upgrade • These models are empirical  • What happens outside r = 0.8 has a strong weight on li • GLF23 needed patch recipe outside r = 0.8 • Need to understand : • The « edge barrier » produced by GLF23 when applied up to r = 1 • Why H97 = 0.6 seems the best scaling for ohmic and L-mode during the ramp-up phase 15

  16. Conclusions : ITER projections • Same models applied to ITER current ramp-up (ohmic, ECRH) • Behavior of models and discrepancies between them similar as when applied to JET cases • Range of li prediction remains within Dli = 0.1 between models • Do not believe this is the absolute prediction of li ! • Sensitivity analysis to be carried out on the following parameters : • Zeff, density profile peaking, initial equilibrium conditions, boundary Te conditions • Dependence on plasma boundary shape should also be considered, likely not in self-consistent simulations for the coming conferences • EPS paper (D. Hogeweij), IAEA/ITPA paper (F. Imbeaux) 16

  17. Details on scaling-based model • Scaling-based : ohmic and L-mode rampup energy content well represented by either • H mode scaling with H98 = 0.4 • L mode scaling with H97 = 0.6 • ci = ce, renormalised so that • Fixed c(r) shape : power balance chi’s during ramp-up tend to be rather flat, then strong increase towards the plasma edge : c(r,t) = A(t)(1+6 r2 + 80 r20) 17

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