Experimental Evidence of Inward Momentum Pinch on JET and Comparison with Theory

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1 Experimental Evidence of Inward Momentum Pinch on JET and Comparison with Theory Tuomas Tala, Association Euratom-Tekes, VTT, Finland JET-EFDA Culham Science Centre Abingdon, UK 22nd IAEA Fusion Energy Conference Geneva October 2008 Tuomas Tala 1/16

2 Scientific Team T. Tala1,J. Ferreira2, P. Mantica3, A.G. Peeters4, G. Tardini5, P.C. de Vries6, K.-D. Zastrow6, M. Brix6, G. Corrigan6, C. Giroud6, I. Jenkins6, V. Naulin7, A. Salmi8, D. Strintzi9, T. Versloot10 and JET-EFDA contributors* JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom 1 Association EURATOM-Tekes, VTT, P.O. Box 1000, FIN VTT, Finland 2 Associação EURATOM/IST, Centro de Fusão Nuclear, Lisbon, Portugal 3 Istituto di Fisica del Plasma CNR-EURATOM, via Cozzi 53, Milano, Italy 4 Center for Fusion, Space and Astrophysics, Department of Physics, Univ. of Warwick, United Kingdom 5 Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, Garching, Germany 6 EURATOM/UKAEA Fusion Association, Culham Science Centre, United Kingdom 7 Association Euratom-Risø DTU, Denmark 8 Association EURATOM-Tekes, TKK, P.O. Box 2200, FIN TKK, Finland 9 National Technical University of Athens, Euratom Association, Athens, Greece 10 FOM Instituut for Plasmafysica Rijnhuizen, Association EURATOM-FOM, The Netherlands *See Appendix of F. Romanelli et al., paper OV/1-2, this conference Association EuratomTekes Tuomas Tala 2/16

3 Why Is There No Reliable Prediction for Toroidal Rotation Velocity Profile in ITER? Momentum transport much less studied than heat and particle transport 1) Sources of rotation: NBI torque source well established 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 1) Edge rotation: Similar problem as predicting the temperature profile the pedestal value must be known in order to predict the core toroidal rotation profile 1) Transport: The magnitude of diffusive and convective (pinch) terms not studied in detail Tuomas Tala 3/16

4 Outline Comparison of core momentum and ion heat transport using the JET rotation database NBI modulation experiments to study both diffusive and convective terms of toroidal momentum transport Detailed description of the perturbative momentum transport analysis method including the torque calculation Experimental results and comparison with gyro-kinetic simulations Consequences of the JET results for ITER Tuomas Tala 4/16

5 Γ φ ~ χ φ ( vφ n) + v pinch vφ n = χ φ,eff ( vφ n) Discrepancy in the Ratio of Effective Momentum and Ion Heat Diffusivity between JET Database and Theory φ Coupling of momentum and ion heat transport (characterised by the Prandtl number Pr= χφ/χi): JET rotation database covering over 600 shots: Early ITG fluid theory χφ/χi=1 N. Mattor & P. Diamond, Phys. Fluids 1988 Recent gyro-kinetic simulations χφ/χi 0.8 A. Peeters, PoP 2005 Effective Prandtl number, Pr,eff= χφ,eff/χi,eff from JET rotation database significantly smaller qi Γφ Γφ = momentum flux χ i,eff = χ φ,eff = n Ti qi = ion heat flux mnvφ Γ φ ~ χ φ ( vφ n) + v pinch vφ n = χ φ,eff ( vφ n) Small effective Prandtl number Pr,eff could be due Torque sources other than NBI in the momentum P. de Vries et al., NF 2008 Tuomas Tala 5/16

6 Intrinsic Rotation Much Smaller than Rotation in NBI Heated Plasmas JET pulses no , and In NBI driven JET discharges (cobeams), ωφ in the plasma centre is typically krad/s, an order of magnitude larger than ωφ from intrinsic rotation 12 MW NBI (high torque input) Intrinsic rotation cannot explain the small Pr,eff 0.2 or χφ,eff found on JET momentum database 6MW ICRH, no NBI torque Torque source from intrinsic rotation neglected as the NBI is by far the dominant torque source 2 MW LHCD, no NBI torque L.-G. Eriksson et al., RF Topical Conference 2007 M.F.F. Nave et al., EPS 2007 Tuomas Tala 6/16

7 NBI Modulation Experiments on JET 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 Modulation amplitudes: ωφ ~ 45% Ti and Te ~ 1% ne ~ negligible Tuomas Tala 7/16

8 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 Amplitude of torque 1st harmonic Phase of torque 1st harmonic Torque has been calculated with NUBEAM Monte-Carlo code in TRANSP using particles to minimise the noise J B torque dominates in the core region 2nd harmonic As modulated torque is not radially localised, determination of diffusivity and pinch is difficult directly from data modelling needed No Alfven Eigenmodes or any other MHD activity observed Tuomas Tala 8/16

9 Determination of the Momentum Diffusivity and Pinch Simulate ωφ (using the time-dependent torque profiles from TRANSP) with JETTO transport code to fit the amplitude and phase of the modulated ωφ together with steadystate ωφ by trying different Pr profile and vpinch profile Step 1: Determination of χi and χφ,eff i Calculate χ (no evidence of ion heat pinch), Mantica EX/2-4, Ryter EX/P5-19 r,eff φ,eff i Calculate P = χ /χ 0.25 Tuomas Tala 9/16

10 Determination of the Momentum Diffusivity and Pinch Exp. amplitude Aωφ ωφ Sim. amplitude Aωφ ωφ Step 1: Determination χi and χφ,eff i Calculate χ Calculate P r,eff 1st harmonic φ,eff χ i,eff /χ 0.25 Step 2: Determination of Pr or χφ = Pr χi r Fix P by fitting the modelled phase profile with the experimental one,pinch as 2nd harmonic phase is almost independent of v r Try first P = 0.25 Tuomas Tala 10/16

11 Determination of the Momentum Diffusivity and Pinch Step 1: Determination χi and χφ,eff i ωφ Calculate χ φ,eff r,eff Calculate P Exp. amplitude Aωφ χ Sim. amplitude Aωφ ωφ i,eff /χ st harmonic Step 2: Determination of Pr or χφ = Pr χi r Fix P by fitting the modelled phase profile with the experimental one, as phase almost pinch independent of v 2nd harmonic r Try first P = 0.25 r Pr Choose P profile reproducing best the experimental phase Tuomas Tala 11/16

12 Determination of the Momentum Diffusivity and Pinch Step 1: Determination χi and χφ,eff Exp. amplitude Aωφ i ωφ Calculate χ φ,eff r,eff Calculate P χ ωφ i,eff /χ st harmonic Step 2: Determination of Pr or χφ = Pr χi Sim. amplitude Aωφ r Fix P by fitting the modelled phase profile with the experimental one, as phase almost pinch independent of v r 2nd harmonic Try first P = 0.25 r Choose P profile reproducing best the experimental phase -vpinch Step 3: Determination of vpinch φ pinch Vary v profile to fit both the amplitude of ω φ and the steady-state profile of ω Tuomas Tala 12/16

13 A Sizeable Inward Momentum Pinch Results from the Analysis Pr 0.51 (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 Profiles of vpinch and χφ similar (indication of a similar turbulent origin) T. Tala et al., submitted to PRL Tuomas Tala 13/16

14 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 P =χ /χ JET pulse no GKW using parameters from JET pulse no Tuomas Tala 14/16

15 Does vpinch Affect the Prediction of Toroidal Rotation Profile in ITER? ITER scenario 2 (baseline scenario) Plasma profiles from ITER Scenario 2 Torque profiles from ASCOT orbitfollowing Monte-Carlo code, 1MeV NBI Torque from ASCOT pinch χ from GLF23 transport model -2m/s v v 0 T (and χ ) from GLF23 Predictive simulations with JETTO code for toroidal rotation ωφ Note: Not the final ITER simulation, considers only NBI driven rotation Tuomas Tala 15/16

16 Conclusions Significant inward momentum pinch vpinch -20m/s found on JET Values of Pr=0.61 found in JET experiments, consistent with theory and gyro-kinetic calculations Large inward pinch also explains the low effective Pr,eff 0.2 found in the rotation database The parametric dependence (q, R/Ln, ωφ, ) of the inward pinch and Pr needs to be clarified before giving reliable ITER predictions as vpinch certainly plays an important role Other open issues remain in ITER ωφ predictions: Other torque sources must be taken into account in the prediction Are intrinsic and NBI rotations additive? What rotation pedestal can be expected? Tuomas Tala 16/16

17 The Diffusivity Is the Dominant Contributor to the Phase Profile Exp. amplitude Aωφ ωφ Sim. amplitude Aωφ ωφ Two simulations compared with same Pr,no pinch (dashed), large pinch (solid) Tuomas Tala 17/16

18 Similar vpinch and Pr Profiles Confirmed in Plasma with Slightly Different Profiles Exp. amplitude Aωφ Sim. amplitude Aωφ ωφ ωφ Frame (a): P =0.25, v =0 Aωφ Aωφ Frame (b): Pr~1, vpinch~ -20m/s shown in black in frames (c) and (d) T. Tala et al., submitted to PRL Tuomas Tala 18/16

19 The Pinch Velocity Increases with Increasing Rotation (Mach Number) JET Experiments: GKW code: Calculated using parameters from JET pulse no Data from the JET momentum database using the JETTO interpretive transport code Rv pinch 1 χ φ,eff = χ φ 1 + χ R / L φ u Normalised toroidal velocity u=vφ/vth Tuomas Tala 19/16

20 A Sizeable Inward Momentum Pinch Results from the Analysis Pr 0.51 (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 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 timedependent χi Owing to the small amplitude 12 % in χi, the impact on vpinch and Pr is insignificant Tuomas Tala 20/16

21 Global Energy and Momentum Confinement Times Energy and momentum confinement times similar in many tokamaks τφ τe Example from JET momentum database τe=wth/pin τφ=mnrωφ/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 timesfusion on JET Tuomas Tala 21/16 IAEA Energy Conference 2008, Geneva