2017 US/EU Transport Task Force Workshop April 26 th 2017 Williamsburg, VA

Transcription

1 Pablo Rodriguez-Fernandez 1, A. E. White 1, N. M. Cao 1, A. J. Creely 1, M. J. Greenwald 1, N. T. Howard 1, A. E. Hubbard 1, J. W. Hughes 1, J. H. Irby 1, C. C. Petty 2, J. E. Rice 1 1 Plasma Science and Fusion Center (MIT), Cambridge MA 2 General Atomics, San Diego CA 2017 US/EU Transport Task Force Workshop April 26 th 2017 Williamsburg, VA Work supported by US DoE under grants DE-FC02-99ER54512 (C-Mod) and DE- FC02-04ER54698 (DIII-D) and La Caixa Fellowship

2 Perturbative transport studies the response of the plasma to intentional or spontaneous perturbations Relationship between transport fluxes and gradients during transient perturbations Physics of pulse propagation. Perturbative experiments are useful to isolate different effects and identify contributions to transport. c pert Exp = 4.0 m 2 s pert c GYRO = 0.4m 2 s χ e PB = 1 n e Q e T e χ e inc = 1 n e Q e T e Turbulent transport models should Ion Heat Flux- Matched Simulation be able to reproduce perturbative measurements Validation Courtesy of A.J. Creely 1

3 Cold-pulse injections via laser blow-off can be used for impurity and heat transport studies Impurities can be injected using laser blow-off (LBO). Enhanced radiation causes drop in edge temperature Cold pulse. Cold pulse propagates inwardly from edge to core. Impurity and heat transport phenomena can be tested. Core Edge 2

4 Heat-pulse injections via partial sawtooth and modulated ECH are also used to probe transient heat transport Partial sawtooth heat pulses are used in Alcator C-Mod and ASDEX-U to measure χ HP e. (see talk: A.J. Creely, Thursday 4.50pm) Extended-Time-to-Peak method [Tubbing NF 1987]: χ e HP = 4.2 a cv HP α Propagation of ECH heat pulses is used in DIII-D to measure χ e HP. Gentle s ODE method: Creely NF 2016 χ e HP 2 T e + V e HP T e + 1 τ HP + i 3 2 ω T e + ξhp n e = ሚ S e n e DeBoo APS

5 Alcator C-Mod Experiments 4

6 At low density, edge cold-pulse injections trigger fast reversed-polarity responses in the core. Expected cold-pulse propagation is observed at high-density. At low density, core T e rapidly rises after edge cold-pulse injection. Past work referred to these phenomena as non-local transport events. C-Mod TEXT Core Edge Gentle PoP

7 Past work on C-Mod and recent results from KSTAR suggest correlation with intrinsic rotation [Rice 2013; Gao 2014] In C-Mod, Non-local transport (1) and Intrinsic Rotation (2) abruptly change at the same value of n e LOC SOC [Shi 2016] In KSTAR, correlation is also present with addition of ECH. (1) (1) (2) (2) Rice NF 2013 Gao NF

8 Recent C-Mod work demonstrates that correlation is not universal Not present at high current Absence of T e inversion with reversed rotation at low/medium I p. New parameterization reveals that T e inversions persist passed the reversal density at 1.1 MA. 7

9 Also: Absence of temperature inversions is observed with co-current rotation in ICRF plasmas on C-Mod Absence of T e inversions with peaked co-current rotation with ICRF. Contrasts work with ECH plasmas in KSTAR [Shi 2016], where rotation is counter-current when T e inversions disappear. Courtesy of N.M. Cao P ICH = 1. 2MW 8

10 Summary of Alcator C-Mod results P. Rodriguez-Fernandez et al., On the correlation between nonlocal effects and intrinsic rotation reversals in Alcator C-Mod, Nuclear Fusion (accepted) Conclusions from this work: I p and P ICRF break universality of correlation between T e inversions and intrinsic rotation reversals. At high plasma current, temperature inversions persist at high density. Core heating independent of magnitude of edge perturbation. This study did not explain why the core T e increase appears, but it proves a de-coupling between the two momentum and heat transport effects. The Million Dollar Question : Can local turbulent transport model explain the fast T e inversions and the the trends with plasma parameters? 9

11 DIII-D Experiments 10

12 Incremental diffusivity and stiffness are measured in heat pulse experiments at DIII-D using modulated ECH Perturbed transport equation: D HP 2 T e + V HP T e + 1 τ HP + i 3 2 ω T e + ξhp S = ሚ e n e n e The real power balance diffusivity can be estimated and the pinch term contribution in steady state can be inferred: D PB = 1 T ed න HP d T T e V PB = Q e PB e 0 This method assumes: Q e = n e D e T e + n e V e T e n e T e + 1 T e න 0 T ed HP d T e D e = D e (ρ,t e, T e,n, n) V e = V e (ρ,t e,n, n) It neglects changes in transport due to perturbations in the ion channel. 11 Name/Conference/Date r/a DeBoo PoP 12

13 The role of the ion channel in the electron transient transport at DIII-D is studied Comparison of χ inc e from gyro simulations and experiments depend on our capability to isolate the effect of different turbulence drives. Transport coupling between ions and electrons is not negligible. Previous work (M. Gildner, C.C. Petty) showed that collisional coupling is not enough to explain T i exp Coupling through transport coefficients needed. r/a r/a 12 Name/Conference/Date Gildner 05

14 New laser blow-off system will be installed on DIII-D Can we predict the cold pulse behavior? T e inversion phenomenon has never been studied in DIII-D. Looking for evidence of non-local transport is of great interest for the development of predictive transport models. Local models suggest ion-electron transport coupling. New experiments can be designed with Non-local thresholds [Gao, NF 2014] DIII-D? cold and heat pulses in same plasma. Comprehensive multi-field, multi-scale fluctuation measurements are available. R maj [m] PhD Thesis: Bring elements together (new LBO / ECH) to determine if local models can reproduce the transient behavior. 13 Name/Conference/Date

15 Modeling 14

16 Integrated modeling tools can be used to study cold pulse and heat pulse propagation Machine Parameters and Experimental Data (Diagnostics) Transport Fluxes Diffusivities GYRO GENE TGLF TRANSP Not measured quantities: q(r), J(r) Validation: T i offset, Z eff, dilution But TRANSP can also be used to predict plasma evolution from first principles Virtual Tokamak: Geometry, Magnetics, Heating Systems, Gas injections Profiles, output, performance P-TRANSP Theory-based models: Heat/particle transport, pedestal, sawtooth Budny NF 2008 Xingqiu APS

17 Predict First approach will be used to design cold/heat pulse experiments with LBO in DIII-D A new laser blow-off system will be installed on DIII-D in 2017/8. Cold and heat pulses can be launched in the same plasma. High-resolution Ti profile and fluctuation measurements will enable the study of propagation physics. Validation of modeling techniques for cold and heat pulse propagation New LBO in DIII-D will allow the validation of these predictions P-TRANSP Extensive database of cold pulses has been built in Alcator C-Mod: Rice NF 2013 Gao NF 2014 Rodriguez-Fernandez NF 2017 Predictions of propagation of pulses in DIII-D will be made before LBO is available 16

18 Perturbative Transport - based validation tool will be used to find combination of parameters Goal: Find combination of plasma parameters (e.g. Τ a L T ) within error bars for desired transport state (e.g. Q e, χ e inc ). Initial plasma conditions and fixed parameters are provided to PTRANSP. Both input and output parameters can vary within experimental error bars. Machine learning methods speed up optimization. To be presented at IAEA-TM on Fusion Data Processing, Validation and Analysis (May 30 th June 2 nd, Cambridge MA) 17

19 References 18