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Impact of Nonlocal Electron Heat Transport on the High Temperature Plasmas of LHD

Impact of Nonlocal Electron Heat Transport on the High Temperature Plasmas of LHD. N. Tamura , S. Inagaki, T. Tokuzawa, K. Tanaka, C. Michael, T. Shimozuma,S. Kubo, K. Ida, K. Itoh, D. Kalinina, S. Sudo, Y. Nagayama, K. Kawahata, A. Komori and LHD team

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Impact of Nonlocal Electron Heat Transport on the High Temperature Plasmas of LHD

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  1. Impact of Nonlocal Electron Heat Transport on the High Temperature Plasmas of LHD N. Tamura, S. Inagaki, T. Tokuzawa, K. Tanaka, C. Michael,T. Shimozuma,S. Kubo, K. Ida, K. Itoh, D. Kalinina, S. Sudo,Y. Nagayama, K. Kawahata, A. Komori and LHD team NIFS, National Institutes of Natural Sciences, JAPAN 21st IAEA Fusion Energy Conference Chengdu, China 16-21 October 2006

  2. Recently observedin LHD Phase inversion ofcold pulse polarity Full understanding of electron heat transport is necessaryfor achieving a good predictive capability • Electron heat transport can be explained only by local transport? • local transport assumption:qe(r1) = f(ÑTe(r1), Te(r1), Ñne(r1), ne(r1), …) • Experiments on toroidal plasmas shows nonlocality qe(r1) = f(ÑTe(r1), ÑTe(r1-dr), ÑTe(r1+dr), …, Te(r1), Te(r1-dr), …)in electron heat transport Fast plasma response(non-diffusive, ballistic) Phase inversion ofcold pulse polarity Profile resilience • Possible theoretical interpretation is “nonlocality” in turbulence (e.g. turbulence spreading) • Observations in LHD heliotron give new insight into nonlocal transport • Because LHD has • different magnetic configuration (normally negative magnetic shear) • no tokamak-like stiffness in Te profile N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  3. Edge cooling experiment of LHD showsa significant rise of core Te • No change in low-m MHD modes • No density peaking like PEP, RI-mode • Electron heating dominates (Te/Ti > 1) • Difference between Te measured and that simulated based on simple diffusion model is • pronounced in the core (r < 0.6) • little at the edge (r > 0.6) Significant rise of core Te in response to edge cooling in LHD N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  4. Characteristics of Nonlocal Te rise in LHD plasmas1) Condition for nonlocal Te rise • In the LHD, the nonlocal Te rise observed in various plasmas: • ECH plasma (i.e. net-current free plasma) • Toroidal plasma current and high-energy ion are not a factor • NBI plasma (still Te/Ti > 1) • High-energy electron is also not a factor • Inverse relationship between increment of core Te due to nonlocal effect and ne observed • Same as in tokamaks • In LHD, no differences among heating methods(but always electron heating) N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  5. Larger dTe/dt Te rise delayed Stronger edge cooling ne increases simultaneity Characteristics of Nonlocal Te rise in LHD plasmas2) Variety of time response N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  6. Characteristics of Nonlocal Te rise in LHD plasmas3) Dependence of delay time • Favorable condition for delay of nonlocal Te rise • Higher collisionality nb* in the core • Shorter Te gradient scale length at the edge N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  7. nonlocal local nonlocal Transient response analysis reveals complex relationshipbetween heat flux and Te gradient • Heat flux perturbation • Reduction of dqe/ne is not accompanied by changes in local ÑTe • Evidence against “standard transport theory” (local & diffusive) • Turn-back of dqe/ne is also independent of local ÑTe N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  8. Reduction of normalized heat flux due to nonlocal effect takes place in a wider region • Region where reduction of dqe/ne prominently appear is far from rapidly cooled region and strongly heated region N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  9. nonlocal nonlocal local Short-range Short-range Short-range ratio Long-range Long-range Long-range How can we understand nonlocal Te rise in LHD? • Clue from LHD experiment • Nonlocality in e-transport revealed by edge cooling • Transitions between “nonlocal” and “local” in e-transport also revealed • On a basis of radial correlation • Physical mechanism of long-range correlation is unclear • It should have characteristics as follows: • Response delayed with higher nb* & shorter Te gradient scale length • Radial extent close to a N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  10. Summary • Nonlocal Te rise invoked by edge cooling observed in low density and high temperature plasmas of LHD as well as tokamaks • New aspects of nonlocal Te rise from LHD • Observation in net-current free plasma • Time response of nonlocal Te rise is variable • Time response of core Te rise is quicken by larger edge perturbation (larger Te gradient scale length?) • Delay of nonlocal Te rise increased with… • increase in collisionality in the core • decrease in Te gradient scale length at the edge • Transient response analysis suggests • complex relationship between flux and gradient • transitions between “nonlocal” and “local” N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  11. END N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  12. No relationship between density fluctuations andnonlocal Te rise is observed in LHD N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  13. No relationship between density fluctuations andnonlocal Te rise observed in LHD • No significant change in core density fluctuation (measured by X-mode Reflectometer) observed after the onset of core Te rise N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  14. Comparison with a linear gyro-kinetic calculation N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  15. Comparison with a linear gyro-kinetic calculation • To esimate growth rate gITG and real frequency wr(ITG) of ITG/TEM modes, GOBLIN (GyrOkinetic Ballooning LINnear equation solver)code used • Comparison is done for two time slices1.38s (Before TESPEL injection)1.40s (Just before nonlocal Te rise) • Profiles of ne, Te, Ti as input parameters • ne: increase outside r ~ 0.6 • Te: almost not changed • Ti: Profile shape of Ti is assumed to be same as that of Te (only Ti0 is measured) • In the code, collisionless approximation is used • Stabilization of TEM modes due to the increase of collisionality* cannot be expressed by the GOBLIN code*F. Ryter et al., PRL 95, 085001(2005) N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  16. kri is fixed at 0.5 Linear gyro-kinetic calculation shows TEM turbulencedominant at the periphery of the plasma with nonlocal Te rise • Calculation results • ITG/TEM is unstableoutside r ~ 0.2 • TEM-driven component dominant outside r ~ 0.5 • Experimental results • Maximum change of normalizedheat flux takes place aroundr ~ 0.4 N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  17. Characteristics ofe-transport in LHDw/o nonlocal Te rise N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  18. A gyro-Bohm like dependence can explain low-power NBIheated plasmas in LHD • Critical gradient scale length is unclear • A gyro-Bohm like dependence of ce on Te observed • ctrcPB observed ce weakly depends on ÑTe N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  19. Difference between Nonlocal Te rise & CERC N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  20. Nonlocal Te rise in CERC plasma • Feature of CERC • Strongly peaked Te profile • Associated withEr bifurcation • Antithetical feature ofnonlocal Te rise • Heat flux jump takes placein a wider region of plasma • NOT associated withEr bifurcation Nonlocal Te rise and CERC coexist N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  21. Transient response analysis forstronger edge cooling N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  22. Larger dTe/dt Stronger edge cooling Heat flux jump rate increased Transient response analysis suggests heat flux jump rateincreased with stronger edge cooling N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  23. Experimentally observed Interaction betweenthe core and the edge N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

  24. Transient response analysis indicates existence ofinteraction between the core and the edge • dqe/ne with r > 0.4 decreases prior to reduction of that with r < 0.4 (A) • Termination of decrease in dqe/ne seems to propagate from core to edge (B) • Decrease in dqe/ne with r > 0.2 seems to be overshot, and goes back to a metastable level • Turn-back of dqe/ne to pre-injection level is started almost simultaneously, seems to propagate from edge to core (C) N. Tamura, FEC2006, EX/5-6, Oct. 19, 2006

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