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

HL-2A 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 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 (H 2 /D 2 ): 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

HL-2A Transport study spontaneous particle transport barrier spontaneous particle transport barrier Non-local transport Non-local transport Zonal flow & turbulence Low frequency zonal flow Low frequency zonal flow GAM density fluctuationGAM density fluctuation Two regime fluctuations Two regime fluctuations MHD activities with ECRH Summary Content of the talk 3D GAM ( ), K.J.Zhao PRL 2006

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

HL-2A Analytical model [ S.P.Eury Phys.Plasma 2005] Density Modulation Analysis for pITB f 0 =9.6 Hz, r dep =25.4 cm Domain I: D 1 =0.1 m 2 /s, V 1 =1.0m/s Domain II: D 2 =0.06m 2 /s, V 2 =-2.7m/s Domain III: D 3 =0.5 m 2 /s, V 3 =6.0m/s V is negative (outward) if ne < n c V is positive (inward) if ne > n c V remains negative inside barrier D is rather well-like than step-like [D.R.Ernst Phys.Plasma 2005] Physics issues: pITB creation mechanism: TEM/ITG transition ? pITB location: rational flux surface? pITB critical density: TEM stabilization? ne modulation by SMBI frequency: 9.6 Hz pulse duration: 6 ms gas pressure: 1.3 MPa r ~ 25.4 cm phase sensitive to the diffusivity amplitude very sensitive to the convection IIIIII

HL-2A Transport study spontaneous particle transport barrier spontaneous particle transport barrier Non-local transport Non-local transport Zonal flow & turbulence Low frequency zonal flow Low frequency zonal flow GAM density fluctuation GAM density fluctuation Two regime fluctuations Two regime fluctuations MHD activities with ECRH Summary Content of the talk 3D GAM ( ), K.J.Zhao PRL 2006

HL-2A Non-local transport triggered by SMBI Bt = 2.36 T, Ip = 300 kA, P ECRH = 800 kW ne = 1.36 non-local effect depends on: core r electron density SMBI gas pressure … #8363 #6351

HL-2A Te (a.u.) 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 Non-local transport triggered by SMBI #8364 FFT of Te perturbation by modulated SMBI 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  e HP deduced from FFT 2-3 m 2 /s Physics issues: mechanism for non-local transport Location of the reversion Critical density

HL-2A Transport spontaneous particle transport barrier spontaneous particle transport barrier Non-local transport Non-local transport Zonal flow & turbulence Low frequency zonal flow Low frequency zonal flow GAM density fluctuation GAM density fluctuation Two regime fluctuations Two regime fluctuations MHD activities with ECRH Summary Content of the talk 3D GAM ( ), K.J.Zhao PRL 2006

HL-2A Transport spontaneous particle transport barrier spontaneous particle transport barrier Non-local transport Non-local transport Zonal flow & turbulence Low frequency zonal flow Low frequency zonal flow GAM density fluctuation GAM density fluctuation Two regime fluctuations Two regime fluctuations MHD activities with ECRH Summary Content of the talk 3D GAM ( ), K.J.Zhao PRL 2006

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

HL-2A Mechanism for GAM density fluctuation generation squared auto-bicoherencesummed bicoherence Physics issues: Radial structure GAM density fluctuation: m=1 vs m=-1 Effects on transport and confinement Mechanism for the turbulence

HL-2A Transport spontaneous particle transport barrier spontaneous particle transport barrier Non-local transport Non-local transport Zonal flow & turbulence Low frequency zonal flow Low frequency zonal flow GAM density fluctuation GAM density fluctuation Two regime fluctuations Two regime fluctuations MHD activities with ECRH Summary Content of the talk 3D GAM ( ), K.J.Zhao PRL 2006

HL-2A floating potential fluctuation spectra The distinct dispersion relation for the LFF and HFAT The lifetime of the LFF ( kHz) ~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]

HL-2A Physics issues: Identification of the LFFs and the HFAT Interactions & energy flows Effects on transport and confinement Nonlinear Coupling The squared auto-bicoherence about f=f 1 ±|f 2 | =20- 40kHz, f 1 =20-40kHz, and f 2 = ±20-40kHz is higher than the rest, indicating that the LFF are possibly generated by nonlinear three wave coupling A. Bt=2.4T, Ip=300kA, ne=2.5×10 13 cm 3, B. Bt=2.2T, Ip=200kA, ne=1×10 13 cm -3, C. Bt=1.4T, Ip=180kA, Ne=2.5×10 13 cm -3 The distinct dispersion relations were shown in the LFF and HFAT region in all case. bispectrum analysis

HL-2A Transport spontaneous particle transport barrier spontaneous particle transport barrier Non-local transport Non-local transport Zonal flow & turbulence Low frequency zonal flowLow frequency zonal flow GAM density fluctuationGAM density fluctuation Two regime fluctuations Two regime fluctuations MHD activities with ECRH Summary Content of the talk

HL-2A 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. Destabilization of internal kink mode

HL-2A The instability is excited by ECRH deposited at both the HFS and LFS. The mode occurs along with the increase of the keV energetic electrons, Destabilization of internal kink mode Physics issues: Driving force for the mode: trapped vs. passing energetic electrons Effects on confinement

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

HL-2A Off-axis heating with lower frequency modulation(10kHz) was applied. Appropriate deposition of the ECRH power is critical. Successive ECRH pulses for sustaining MHD-free phase and extending confinement improvement 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. – – near the q=2 surface – – 3cm away from q=2 surface Physics issues: The mechanism for the suppression of the island: simulation needed ECRH modulation effects: simulation needed

HL-2A Transport spontaneous particle transport barrier spontaneous particle transport barrier Non-local transport Non-local transport Zonal flow & turbulence GAM density fluctuationGAM density fluctuation Two regime fluctuation Two regime fluctuation MHD activities with ECRH Summary Content of the talk

HL-2A 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

HL-2A Thank you for your attention!