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FPT Discussions on Current Research Topics Z. Lin University of California, Irvine, California 92697, USA

FPT Discussions on Current Research Topics Z. Lin University of California, Irvine, California 92697, USA. Outline. Electron transport Momentum transport GAM Finite- b effects Coupling between turbulence and energetic particles. Transport: eddy mixing or wave-particle decorrelation? .

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FPT Discussions on Current Research Topics Z. Lin University of California, Irvine, California 92697, USA

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  1. FPT Discussions on Current Research Topics Z. Lin University of California, Irvine, California 92697, USA

  2. Outline • Electron transport • Momentum transport • GAM • Finite-b effects • Coupling between turbulence and energetic particles

  3. Transport: eddy mixing or wave-particle decorrelation? • Case studies of electron heat transport mechanism in tokamak • Comparative studies of CTEM, ITG, & ETG • GTC simulations: while saturation can be understood in context of fluid processes, kinetic processes related to instability drive often responsible for transport

  4. Transport driven by local fluctuation intensity • Effective wave-particle decorrelation time twp=4ce/3dvr2 ~ 4.2LT/ve • twp << 1/g ~ 33: linear time scale not important to transport • Wave-particle correlation length dvrtwp << streamer length • Electron radial excursion diffusive:streamer length does not determine transport directly • From linear to nonlinear, ce/dvr2decreases by a factor of ~5 • Nonlinear loss of wave-particle correlation ce ce/dvr2 r/re time (LT/ve)

  5. Kinetic & fluid time scales in ETG turbulence tauto >> 1/g >>twp ~ 1/Dk||ve Wave-particle decorrelation of parallel resonance d(w-k||v||) dominates Quasilinear calculation of ce agrees well with simulation Saturation: wave-wave coupling determines fluctuation intensity Transport: wave-particle decorrelation determines transport level

  6. Effects of kinetic electrons on ITG mode • ITG mode dominates when hi=3.1 • Trapped electrons typically interact non-resonantly with ITG mode • Trapped electrons increase ITG growth rate • High kqmodes are CTEM g (vi / Ln) wr (vi / Ln) kinetic electron kinetic electron adiabatic electron adiabatic electron kqri kqri

  7. ITG turbulence drive small electron heat transport • Convergence using 10 and 40 particles per cell • No coherent ITG-electron interaction in linear phase • Ion transport: resonant; proportional to intensity [Lin & Hahm, PoP2004] • Electron transport: non-resonant • ITG mode scattering off trapped electrons? • Relation to energetic particle transport by microturbulence? c / (df)2 heat flux ion ion electron electron

  8. CTEM linear dispersion • CTEM mode dominates when hi=1 • Driven by electron precessional resonance • Modestly ballooning

  9. Nonlinear saturation • Nonlinear convergence using 20-800 particle per cell • Short wavelength modes kqri >0.4 dominate at initial saturation • Initial saturation caused by small scale zonal flows krri~1 • The 2nd burst not deterministic; driven by kqri<0.4 time (1/g)

  10. Nonlinear bursting • Nonlinear loss of CTEM-electron correlation • Zonal flow the agent? • Burst caused by nonlinear growth • Electron heat transport mechanism: precessional resonance de-tuning? • n-spectral width; Radial diffusion • Nonlinear burst suggestive of avalanche?

  11. Nonlinear bursting • Burst originates at r=0.5a, outward propagation faster than inward • Inward spreading ballistic with a speed close to drift velocity • Relation to EPM avalanche [Zonca, Briguglio, Vlad, etal, PPCF2006]? Ion transport Electron transport ci ce r/ri r/ri time (1/g) time (1/g)

  12. Geodesic Acoustic Modes & Zonal Flow • GAM linear physics: short wavelength, collisionless & collisional damping • Nonlinear excitation: turbulence & zonal flows • Effects on turbulence: active or passive? • Role of quasimodes? • Acoustic eigenmode? Higher frequency harmonics? • EM: roles of low-order rational surfaces in driving ZF & GAM?

  13. GTC electromagnetic simulation • Demonstrate finite-b stabilization of ITG and excitation of KBM/AITG • Demonstrate Alfven wave propagation in tokamak, continuum damping, and existence of toroidal frequency gap • Truly global geometry allowing all n-modes • Recover MHD dispersion relation of Alfven wave in tokamak; Allow E|| • [Nishimura, Lin, and Wang, PoP2007] ce (vere2/LT) time (LT/ve)

  14. Turbulent transport & energetic particle physics • Coupling of TT & EP in ITER: turbulence in the presence of energetic particles; Many interacting EP modes lead to EP turbulence • Kinetic effects of thermal ions: damping of TAE; coupling between Alfvenic and acoustic branches, e.g., GBAAE • Cross-gap coupling between Alfvenic and acoustic modes • Cross-scale coupling between TT & EP, e.g., coherent structures (zonal flows/fields), structure corrugation & dynamic modulation

  15. Fundamental constituents

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