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NBI Modulation Experiments to Study Momentum Transport on JET + Status of TC-15

NBI Modulation Experiments to Study Momentum Transport on JET + Status of TC-15. Tuomas Tala, Association Euratom-Tekes, VTT, Finland. JET-EFDA Culham Science Centre Abingdon, UK Transport and Confinement ITPA Meeting, 31 March - 2 April 2009. Scientific Team.

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NBI Modulation Experiments to Study Momentum Transport on JET + Status of TC-15

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  1. NBI Modulation Experiments to Study Momentum Transport on JET + Status of TC-15 Tuomas Tala,Association Euratom-Tekes, VTT, Finland JET-EFDA Culham Science Centre Abingdon, UK Transport and Confinement ITPA Meeting, 31 March - 2 April 2009

  2. Scientific Team T. Tala1,J. Ferreira2, P. Mantica3, D. Strintzi4, G. Tardini5, K.-D. Zastrow6, M. Brix6, G. Corrigan6, C. Giroud6, L. Hackett6I. Jenkins6, T. Johnson7, J. Lönnroth8, V. Naulin9, V. Parail6, A.G. Peeters10, A. Salmi8, M. Tsalas4, T. Versloot11, P.C. de Vries6 and JET-EFDA contributors* And data from J. Rice and M. Yoshida for TC-15 JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom 1Association EURATOM-Tekes, VTT, P.O. Box 1000, FIN-02044 VTT, Finland 2Associação EURATOM/IST, Centro de Fusão Nuclear, 1049-001 Lisbon, Portugal 3Istituto di Fisica del Plasma CNR-EURATOM, via Cozzi 53, 20125 Milano, Italy 4National Technical University of Athens, Euratom Association, Athens, Greece 5Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, Garching, Germany 6EURATOM/UKAEA Fusion Association, Culham Science Centre, United Kingdom 7Association Euratom-VR, KTH, Stockholm, Sweden 8Association EURATOM-Tekes, TKK, P.O. Box 2200, FIN-02150 TKK, Finland 9Association Euratom-Risø DTU, Denmark 10Center for Fusion, Space and Astrophysics, Department of Physics, Univ. of Warwick, United Kingdom 11FOM Instituut for Plasmafysica Rijnhuizen, Association EURATOM-FOM, The Netherlands *See Appendix of F. Romanelli et al., paper OV/1-2, IAEA 2009, Geneva

  3. Outline • Summary and status of the NBI modulation experiments on JET • Dependence of the momentum pinch on q-profile and density gradient length R/Ln and comparison with linear Gyro-Kinetic simulations with GKW • NBI modulation experiments in plasmas with toroidal magnetic field ripple • Status of TC-15 Joint ITPA Experiment: Dependence of Momentum and Particle Pinch on Collisionality

  4. Summary of NBI Modulation Sessions on JET • NBI modulation without ripple: • Non-compensated modulation: 10+4 good physics pulses • Compensated modulation: 2+2 good physics pulses • NBI modulation with using toroidal magnetic field ripple: • Non-compensated modulation: 4+2 good physics pulses • Compensated modulation: 1+2 good physics pulses Non-compensated Compensated Tangential NBI Normal NBI PNBI PNBI Time Time

  5. Determination of the Momentum Diffusivity and Pinch • Step 1: Determination χi and χ,eff • Calculate χi • Step 2: Determination of Pr or χ = Prχi • Fix Prby fitting the modelled phase profile with the experimental one, as phase almost independent of vpinch • Choose Pr profile reproducing best the experimental phase • Step 3: Determination of vpinch • Vary vpinch profile to fit both the amplitude of ω and the steady-state profile of ω Exp. amplitude Aω Exp. phase ω Sim. amplitude Aω Sim. phase ω 1st harmonic 2nd harmonic -vpinch (m/s) T. Tala et al., PRL 102, 075001 (2009)

  6. Outline • Summary and status of the NBI modulation experiments on JET • Dependence of the momentum pinch on q-profile and density gradient length R/Ln and comparison with linear Gyro-Kinetic simulations with GKW • NBI modulation experiments in plasmas with toroidal magnetic field ripple • Status of TC-15 Joint ITPA Experiment: Dependence of Momentum and Particle Pinch on Collisionality

  7. Dependence of the Pinch on q-profile and Density Gradient Length R/Ln1/2 • 4 discharges chosen for accurate comparison • Plasmas very similar, similar Bt, heating power, temperatures, edge conditions • q-profile (plasma current) and R/Ln (density) scans performed among the 4 shots , R/Ln-scan q-scan 66128, original reference 73701, reference 73702, low q pulse 73709, low R/Ln

  8. Dependence of the Pinch on q-profile and Density Gradient Length R/Ln2/2 66128, original reference 73701, reference 73702, low q pulse 73709, low R/Ln Preliminary

  9. Comparison of the Pinch and Pr with Linear Gyro-Kinetic GKW Simulations 1/4 Pulse number 66128, old reference Experiment x GKW simulation

  10. Comparison of the Pinch and Pr with Linear Gyro-Kinetic GKW Simulations 2/4 Pulse number 73701, reference pulse Experiment x GKW simulation

  11. Comparison of the Pinch and Pr with Linear Gyro-Kinetic GKW Simulations 3/4 Pulse number 73702, low q pulse Experiment x GKW simulation

  12. Comparison of the Pinch and Pr with Linear Gyro-Kinetic GKW Simulations 4/4 Pulse number 73709, low R/Ln pulse Experiment x GKW simulation Preliminary

  13. Outline • Summary and status of the NBI modulation experiments on JET • Dependence of the momentum pinch on q-profile and density gradient length R/Ln and comparison with linear Gyro-Kinetic simulations with GKW • NBI modulation experiments in plasmas with toroidal magnetic field ripple • Status of TC-15 Joint ITPA Experiment: Dependence of Momentum and Particle Pinch on Collisionality

  14. Use of Magnetic Field to Perturb/Modulate Rotation at the Edge Comparison of ASCOT and PENCIL torque density profiles with 1.5% ripple • NBI torque source very different at large magnetic field ripple • The torque density profile peaks towards the edge at 1.5% ripple • Can be used to induce a rotation perturbation at the edge (this technique used in JT-60U) • On JET, due to beam geometry, its use is complicated due to non-edge localised source

  15. The Amplitude and Phase of the Rotation Very Different in Plasmas with Magnetic Ripple 1/2 non-ripple shot, normal PINIs modulated, PNBI=5MW Modulation in non-ripple plasma, normal PINIs #77089 1.5% ripple, tangential PINIs modulated, PNBI=5MW 1.5% ripple, normal PINIs modulated, PNBI=5MW 1st harmonic A 2nd harmonic  1st harmonic  steady-state ω 1.5% ripple, normal PINIs modulated PNBI=5MW, + 2MW of ICRH 2nd harmonic A

  16. The Amplitude and Phase of the Rotation Very Different in Plasmas with Magnetic Ripple 2/2 Modulation of normal PINIs at 1.5% ripple, 77090 Modulation of tangential PINIs at 1.5% ripple, #77091 2nd harmonic  1st harmonic A 1st harmonic A 1st harmonic  2nd harmonic  1st harmonic  2nd harmonic A 2nd harmonic A

  17. Comparison of TRANSP and ASCOT Torque in non-ripple Plasma Phase (torque, degrees) Amplitude (torque, N/m2) Agreement is good, the shift of the peak JxB torque amplitude due to equilibrium, ASCOT uses EFIT, TRANSP its own internal equilibrium

  18. Outline • Summary and status of the NBI modulation experiments on JET • Dependence of the momentum pinch on q-profile and density gradient length R/Ln and comparison with linear Gyro-Kinetic simulations with GKW • NBI modulation experiments in plasmas with toroidal magnetic field ripple • Status of TC-15 Joint ITPA Experiment: Dependence of Momentum and Particle Pinch on Collisionality

  19. Status of TC-15 Joint Experiment: Dependence of Momentum and Particle Pinch on Collisionality XXX No progress (to my knowledge)XXX Some data exist, but not directly linked to this Joint Experiment XXX Experiment planned XXX Experiment done Colour codes:

  20. He Gas Puff Modulation on JT-60U The difference between Deuterium and Helium D and v? H. Takenaga, Nucl. Fusion 39, 1917 (1999)

  21. Momentum Pinch Versus Collisionality on JT-60U Database Plot of momentum pinch versus collisionality Ip~0.9 MA, BT~3.8 T, ~0.3, q95~8.2, ne~1.6x1019 m-3, N~0.34, *~0.04, ne* is the effective electron collision frequency normalized to the bounce frequency. Ip~1.5 MA, BT~3.8 T, ~0.3, q95~4.2, ne~1.6-2.5x1019 m-3, N~0.26-1.07, *~0.04-0.05, Yoshida M. et al 2007 Nucl. Fusion 47 856

  22. Comparison of Toroidal Velocity and Electron Density Profiles in C-Mod J. Rice

  23. Collisionality Dependence of Momentum and Particle Pinch in GK Simulations • ITG (Waltz standard case with R/Ln = 2) • Particle flux changes sign with collisionality, but momentum pinch does not Weaker dependence on collisionality • For particle pinch, the perturbation in the trapped region is important while for the momentum pinch, it is the symmetry in the low field side. This is not affected by collisions. • Other parameters to be scanned in TC-15 (R/Ln, q and s)? Effective particle diffusivity Momentum Pinch Number A.G. Peeters, Self consistent mode structure, submitted PoP

  24. Conclusions • NBI modulation experiments shown to be a very good tool to study momentum transport and torque sources on JET • Significant inward momentum pinch vpinch -20m/s found on JET, decrease of vpinch with R/Ln observed. Experiments show a pinch number 2-3 larger than GKW simulations. • Reasons for the discrepancy between GKW and experiments could be: GKW includes only Coriolis pinch (ExB pinch term missing), non-linear simulations would be different from linear ones, some torque source is modulated in the experiments and not taken into account in the experimental analysis. • Values of Pr=0.6–1.2 found in JET experiments, consistent with theory and gyro-kinetic calculations. • NBI modulation data with magnetic field ripple to be analysed • TC-15 Joint Experiment is now under planning stage on DIII-D, JET and NSTX.

  25. Does vpinch Affect the Prediction of Toroidal Rotation Profile in ITER? Ti (and χi) from GLF23 • ITER scenario 2 (baseline scenario) • Plasma profiles from ITER Scenario 2 • Torque profiles from ASCOT orbit-following Monte-Carlo code, 1MeV NBI • χifrom GLF23 transport model • Predictive simulations with JETTO codefor toroidal rotation ω • Assuming similar plasma parameters and pinch number Rvpinch/χ in ITER as in JET vpinch,ITER  RJET/RITERχ,ITER/χ,JET vpinch,JET 1/6  vpinch,JET Torque from ASCOT vpinch -7m/s Pr=0.3, vpinch= 0  vpinch,JET0 Pr=0.9, vpinch= 1/8vpinch,JET-2m/s Pr=0.9, vpinch= 1/4vpinch,JET-5m/s Pr=0.9, vpinch= 1/3vpinch,JET-7m/s vpinch -5m/s vpinch -2m/s vpinch 0 Note: Not the ‘final’ ITER simulation, considers only NBI driven rotation

  26. Similar vpinch and Pr Profiles Confirmed in Plasma with Slightly Different Profiles Exp. amplitude Aω Exp. phase ω Sim. amplitude Aω Sim. phase ω Frame (a): Aω Aω Pr=0.25, vpinch=0 shown in blue in frames (c) and (d) ω ω Frame (b): Pr~1, vpinch~ -20m/sshown in black in frames (c) and (d) T. Tala et al., submitted to PRL

  27. Gyro-Kinetic Simulations Also Show Pr1 and Inward Momentum Pinch • Linear gyro-kinetic simulations with GKW code (A. Peeters et al., PRL 2007)versus JET experiment • The slope of the curves indicates the Prandtl number and the intersection of y-axis the Pinch number • Prandtl number Pr=χ/χi • GKW: Pr=0.6–1.2 • Experiment: Pr=0.5–1.2 • ‘Pinch’ number -Rvpinch/χ • GKW: -Rv/χ=2–4 • Experiment: -Rv/χ4–8 • Excellent agreement between gyro-kinetic calculation and experiment in Pr (including the radial variation) • Roughly a factor of 2 discrepancy in the Pinch number JET pulse no. 66128 GKW using parameters fromJET pulse no. 66128

  28. The Pinch Velocity Increases with Increasing Rotation (Mach Number) • JET Experiments: • Data from the JET momentum database using the JETTO interpretive transport code • GKW code: • Calculated using parameters from JET pulse no. 66128 Normalised toroidal velocity u=v/vth

  29. A Sizeable Inward Momentum Pinch Results from the Analysis • Pr  0.5–1 (radial variation) needed to reproduce the phase profile • Inward momentum pinch velocity up to vpinch~ 25 m/s needed to reproduce the amplitude and steady-state at Pr  0.5–1. Important aspects to be taken into account in the analysis: • Plasma movement due to modulation • Profiles mapped inside TRANSP onto a plasma movement independent co-ordinate • Modulation in Ti and Te, the amplitude being about 1 % • Studied in simulations using time-dependent χi • Owing to the small amplitude 1–2 % in χi,the impact on vpinch and Pr is insignificant

  30. Global Energy and Momentum Confinement Times Example from JET momentum database • Energy and momentum confinement times similar in many tokamaks E E=Wth/Pin =mnRω/SNBI • In this work, we concentrate on core momentum transport studies … while the global confinement includes significant contribution from the edge pedestal • While core momentum transport smaller than that of ion heat, the opposite observed in pedestal resulting in roughly equal global momentum and energy confinement times on JET

  31. Discrepancy in the Ratio of Effective Momentum and Ion Heat Diffusivity between JET Database and Theory  = momentum fluxqi= ion heat flux JET rotation database covering over 600 shots: • Coupling of momentum and ion heat transport(characterised by the Prandtl number Pr= χ/χi): • Early ITG fluid theory χ/χi=1 N. Mattor & P. Diamond, Phys. Fluids 1988 • Recent gyro-kinetic simulationsχ/χi0.8 A. Peeters, PoP 2005 • Effective Prandtl number, Pr,eff= χ,eff/χi,eff from JET rotation database significantly smaller • Small effective Prandtl number Pr,eff could be due • Torque sources other than NBI in the momentum flux  (now consists only of NBI torque) • Inward momentum pinch resulting in χ,eff < χ and Pr,eff < Pr P. de Vries et al., NF 2008

  32. Intrinsic Rotation Much Smaller than Rotation in NBI Heated Plasmas JET pulses no. 66128, 66302 and 66399 • In NBI driven JET discharges (co-beams), ω in the plasma centre is typically 50–150 krad/s, an order of magnitude larger than ω from intrinsic rotation • Intrinsic rotation cannot explain the small Pr,eff  0.2 or χ,eff found on JET momentum database • Torque source from intrinsic rotation neglected as the NBI is by far the dominant torque source 12 MW NBI (high torque input) 6MW ICRH, no NBI torque 2 MW LHCD, no NBI torque L.-G. Eriksson et al., RF Topical Conference 2007 M.F.F. Nave et al., EPS 2007

  33. Ion Heat Diffusivity Similar among All the 4 Discharges

  34. Why to Do Such a Complicated NBI Modulation Experiments? Momentum transport much less studied than heat and particle transport, no reliable predictions for ITER rotation exist. Momentum Transport: • The magnitude of diffusive and convective (pinch) terms not studied in detail Sources of rotation: • NBI torque source well established (without ripple) • Other torque sources less understood, such as the driving mechanism for intrinsic rotation, sources at the edge, for example torque originating from edge ion losses due to finite toroidal magnetic field ripple Edge rotation: • Similar problem as predicting the temperature profile – the pedestal value must be known in order to predict the core toroidal rotation profile

  35. NBI Modulation Experiments on JET,Non-ripple Plasmas • Steady-state analysis cannot separate diffusivity and pinch terms in the momentum flux, modulation of rotation needed • H-mode plasma at Ip=1.5MA, Bt=3.0T and low collisionality • Modulation measured with CX at 12 radial channels and time resolution of 10 ms • Typical modulation amplitudes: • ω~ 4–5% • Tiand Te ~ 1% • ne ~ negligible

  36. Calculation of the Torque Profiles • Two separate torque mechanisms: • instantaneous JB torque (red) due to beam ions injected into trapped orbits • collisional torque (blue) due to slowing down of beam ions on passing orbits • Torque has been calculated with NUBEAM Monte-Carlo code in TRANSP using 160 000 particles to minimise the noise • JB torque dominates in the core region • Accurate calculation of torque mandatory • As modulated torque is not radially localised, determination of diffusivity and pinch is difficult directly from data modelling needed Amplitude of torque Phase of torque 1st harmonic 1st harmonic 2nd harmonic No Alfven Eigenmodes or any other MHD activity observed

  37. Determination of the Momentum Diffusivity and Pinch • Simulate ω (using the time-dependent torque profiles from TRANSP) with JETTO transport code to fit the amplitude and phase of the modulated ω together with steady-state ω by trying different Pr profile andvpinch profile • Step 1: Determination of χi and χ,eff • Calculate χi(assuming no ion heat pinch) • Calculate Pr,eff = χ,eff/χi  0.25

  38. Determination of the Momentum Diffusivity and Pinch Exp. amplitude Aω Exp. phase ω Sim. amplitude Aω Sim. phase ω • Step 1: Determination χi and χ,eff • Calculate χi • Calculate Pr,eff  χ,eff/χi,eff  0.25 • Step 2: Determination of Pr or χ = Prχi • Fix Pr by fitting the modelled phase profile with the experimental one, as phase is almost independent of vpinch • Try first Pr = 0.25 1st harmonic 2nd harmonic

  39. A Sizeable Inward Momentum Pinch Results from the Analysis • Pr  0.5–1 (radial variation) needed to reproduce the phase profile • Inward momentum pinch velocity up to vpinch~ 25 m/s needed to reproduce the amplitude and steady-state at Pr  0.5–1. • Profiles of vpinch and χsimilar T. Tala et al., PRL 2009

  40. Summary of Data Analysis and Modelling Performed so Far Performed: • OFMC and SELFO/ASCOT analyses for safety assessment of fast particle ripple losses (only pulses with large ripple amplitude needed this) • Data validation of CXRS and MSE data, part of the shots has also HRTS data • FFT of the modulated rotation data • TRANSP performed for most of the shots without ripple for VERY accurate torque calculation • JETTO analysis to determine the pinch and diffusivity carried out for part of the discharges • Linear Gyro-kinetic calculation with GKW performed to compare the Coriolis pinch theory with experiments for part of the discharges • Comparison of Prandtl number between experiments, GKW and GS2 for some shots To be performed: • TRANSP torque for the rest of non-ripple pulses Jorge Ferreira’s talk • Comparison of TRANSP and ASCOT (JINTRAC) torque Antti Salmi’s talk • JINTRAC torque calculations for the ripple session • Linear GKW simulations taking into account the collisions Arthur Peeters’ talk • Non-linear GKW simulations for the pinch and diffusivity

  41. Determination of the Momentum Diffusivity and Pinch • Step 1: Determination χi and χ,eff • Calculate χi • Step 2: Determination of Pr or χ = Prχi • Fix Prby fitting the modelled phase profile with the experimental one, as phase almost independent of vpinch • Choose Pr profile reproducing best the experimental phase Exp. amplitude Aω Exp. phase ω Sim. amplitude Aω Sim. phase ω 1st harmonic 2nd harmonic Pr

  42. The Diffusivity Is the Dominant Contributor to the Phase Profile Exp. amplitude Aω Exp. phase ω Sim. amplitude Aω Sim. phase ω Two simulations compared with same Pr,no pinch (dashed), large pinch (solid)

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