Jiaqi Dong Southwestern Institute of Physics & Institute for Fusion Theory and Simulation, ZJU

1. Physics Issues in HL-2A Tokamak Experiments Jiaqi Dong Southwestern Institute of Physics & Institute for Fusion Theory and Simulation, ZJU International West Lake Workshop on Fusion Theory and Simulation Dec. 25-27, 2008, Hangzhou, China

2. HL-2A tokamak-present status • R: 1.65 m • a: 0.40 m • Bt: 1.2~2.7 T • Configuration: • Limiter, LSN divertor • Ip:450 kA • ne:~ 8.0 x 1019 m-3 • Te:~ 5.0 keV • Ti:~ 1.5 keV Auxiliary heating: ECRH/ECCD: 2 MW (4/68 GHz/500 kW/1 s) modulation: 10~30 Hz; 10~100 % NBI (tangential): 1.5 MW LHCD: 1 MW (2/2.45 GHz/500 kW/1 s) Fueling system (H2/D2): Gas puffing (LFS, HFS, divertor) Pellet injection (LFS, HFS) SMBI(LFS,HFS) LFS: f =1~60 Hz, pulse duration > 0.5 ms, gas pressure < 3 MPa

3. Content of the talk • Transport study • spontaneous particle transport barrier • Non-local transport • Zonal flow & turbulence • Low frequency zonal flow • GAM density fluctuation • Two regime fluctuations • MHD activities with ECRH • Summary 3D GAM ( ), K.J.Zhao PRL 2006

4. pITB pITB MHD without obvious change After SMBI pulse 2-D density gradient Spontaneous particle transport barrier perfectly reproducible phenomena if ne > nc turbulent poloidal rotation velocity due to steepness of ne/ne After SMBI #7557 pITB critical density: nc ~ 2.21019m-3 density gradient: -ne/ne=1/Ln change of density gradient: Ln~10cm inside barrier, Ln~50cmfor r=20-28 cm Ln~25cmfor r=30-36 cm barrier is well-like

5. r ~ 25.4 cm Density Modulation Analysis for pITB ne modulation by SMBI frequency: 9.6 Hz pulse duration: 6 ms gas pressure: 1.3 MPa Analytical model [S.P.Eury Phys.Plasma 2005] I II III f0=9.6 Hz, rdep=25.4 cm Domain I: D1=0.1 m2/s, V1=1.0m/s Domain II: D2=0.06m2/s,V2=-2.7m/s Domain III: D3=0.5 m2/s, V3=6.0m/s V is negative (outward) if ne < nc V is positive (inward) if ne > nc V remains negative inside barrier D is rather well-like than step-like • Physics issues: • pITB creation mechanism: TEM/ITG transition? • pITBlocation: rational flux surface? • pITB critical density: TEM stabilization? • phase sensitive to the diffusivity • amplitude very sensitive to the convection [D.R.Ernst Phys.Plasma 2005]

6. Content of the talk • Transport study • spontaneous particle transport barrier • Non-local transport • Zonal flow & turbulence • Low frequency zonal flow • GAM density fluctuation • Two regime fluctuations • MHD activities with ECRH • Summary 3D GAM ( ), K.J.Zhao PRL 2006

7. Non-local transport triggered by SMBI Bt = 2.36 T, Ip = 300 kA, PECRH = 800 kW #6351 #8363 core non-local effect depends on: electron density SMBI gas pressure … r ne = 1.36

8. Te (a.u.) Non-local transport triggered by SMBI characteristics of non-local transport phenomenon: The core temperature rises up to 25%. The duration of the process ~ 30 ms, may be prolonged by changing the period of modulated SMBI. Both the bolometer radiation and the Hα emission decrease when the core Te increases, accompanying with the increase of the storage energy. The non-local effect is enhanced by ECRH FFT of Te perturbation by modulated SMBI #8364 • A strong decrease in amplitude & a clear phase jump at the reverse position • Possible two perturbation sources in the regions outside and inside the inversion radius • eHP deduced from FFT 2-3 m2/s • Physics issues: • mechanismfor non-local transport • Location of the reversion • Critical density

9. Content of the talk • Transport • spontaneous particle transport barrier • Non-local transport • Zonal flow & turbulence • Low frequency zonal flow • GAM density fluctuation • Two regime fluctuations • MHD activities with ECRH • Summary 3D GAM ( ), K.J.Zhao PRL 2006

10. Content of the talk • Transport • spontaneous particle transport barrier • Non-local transport • Zonal flow & turbulence • Low frequency zonal flow • GAM density fluctuation • Two regime fluctuations • MHD activities with ECRH • Summary 3D GAM ( ), K.J.Zhao PRL 2006

11. GAM density fluctuation 1.33 m • m, n estimated with k and k, respectively. • mainly localize at m=0.51.2 and n= -0.010.02. m=1.2±0.4 /n=0.036±0.039. rake and 3-step LP arrays • The peak at frequency fGAM = 9.8 kHz not only in Is, but also in Vf, • Theoretical frequency is 9.0 kHz with fGAM~(2Te/ Mi)0.5/ (2R) [P.H.Diamond PPCF 2005] • FWHM of the GAM density fluctuation ~4 kHz  lifetime 250 s. • The phase shift between Is and Vf is ~0.45, consistent with the theoretical prediction (0.5 )

12. Mechanism for GAM density fluctuation generation squared auto-bicoherence summed bicoherence • Physics issues: • Radial structure • GAM density fluctuation: m=1 vs m=-1 • Effects on transport and confinement • Mechanismfor the turbulence

13. Content of the talk • Transport • spontaneous particle transport barrier • Non-local transport • Zonal flow & turbulence • Low frequency zonal flow • GAM density fluctuation • Two regime fluctuations • MHD activities with ECRH • Summary 3D GAM ( ), K.J.Zhao PRL 2006

14. floating potential fluctuation spectra • The distinct dispersion relation for the LFF and HFAT • The lifetime of the LFF ( 20-100kHz) ~25-50µs from FWHM of 20-40kHz • The poloidal and radial wave vectors 0.9cm-1 and 1.9cm-1 respectively. • Correlation length: poloidal ~6.5 cm, toroidal ~ 80 cm • Autocorrelation time of HFAT ~5µs , poloidal correlation length ~0.5 cm • [K.J. Zhao, PRL 2006, Phys.Plasmas 2007]

15. Nonlinear Coupling bispectrum analysis A. Bt=2.4T, Ip=300kA, ne=2.5×1013cm3, B. Bt=2.2T, Ip=200kA, ne=1×1013cm-3, C. Bt=1.4T, Ip=180kA, Ne=2.5×1013cm-3 The distinct dispersion relations were shown in the LFF and HFAT region in all case. • The squared auto-bicoherence about f=f1±|f2| =20-40kHz , f1=20-40kHz, and f2= ±20-40kHz is higher than the rest, indicating that the LFF are possibly generated by nonlinear three wave coupling • Physics issues: • Identification of the LFFs and the HFAT • Interactions & energy flows • Effects on transport and confinement

16. Content of the talk • Transport • spontaneous particle transport barrier • Non-local transport • Zonal flow & turbulence • Low frequency zonal flow • GAM density fluctuation • Two regime fluctuations • MHD activities with ECRH • Summary

17. Destabilization of internal kink mode The m = 1 modes poloidally rotate in the electron diamagnetic drift direction The mode frequency decreases slightly with the decreasing of the amplitude of the burst. The frequency of the mode is between 4 and 8 kHz.

18. Destabilization of internal kink mode • The instability is excited by ECRH deposited at both the HFS and LFS. • The mode occurs along with the increase of the 35-70 keV energetic electrons, • Physics issues: • Driving force for the mode: trapped vs. passing energetic electrons • Effects on confinement

19. ECRH 0.85 ECRH Z(m) 0 -0.85 1.05 1.7 R(m) Stabilization of Tearing mode with ECRH 2.35 • The stabilization of m=2/n=1 tearing mode has been realized with off-axis heating located around q=2 surface.

20. Successive ECRH pulses for sustaining MHD-free phase and extending confinement improvement • Off-axis heating with lower frequency modulation(10kHz) was applied. • Appropriate deposition of the ECRH power is critical. • The suppression event is characterized by a continuous rise in plasma density, central temperature and stored energy. • The additive effect of the delayed central temperature decrease after each ECRH pulse switch-off may play a role. • Physics issues: • The mechanism for the suppression of the island: simulation needed • ECRH modulation effects: simulation needed • near the q=2 surface • 3cm away from q=2 surface

21. Content of the talk • Transport • spontaneous particle transport barrier • Non-local transport • Zonal flow & turbulence • GAM density fluctuation • Two regime fluctuation • MHD activities with ECRH • Summary

22. Summary • The recent HL-2A experimental campaigns focused on studying and understanding the physics of transport, turbulence, MHD instabilities and energetic electron dynamics • Significant progress has been made • Quite a few physics issues are raised in the experiments • Theory and simulation support are urgently desirable

23. Thank you for your attention!