Southwestern Institute of Physics, Chengdu, China

1. The Second A3 Foresight Workshop on Spherical Torus Experimental Progress on HL-2A HL-2A Team (Presented by Longwen Yan) Southwestern Institute of Physics, Chengdu, China

2. Outline • HL-2A tokamak • Diagnostic development • Confinement improvement and transport • Energetic physics and MHD activity • Turbulence and zonal flows • Summary

3. HL-2A tokamak • R: 1.65 m • a: 0.40 m • Bt: 2.7 T • Ip:450 kA • ne:~ 6.0 x 1019 m-3 • Te:~ 5.0 keV • Ti:~ 2.8 keV Auxiliary heating systems ECRH/ECCD: 3 MW: 60.5 MW/68 GHz/1 s 2 MW: 21 MW/140 GHz/3 s Modulated f=10~30 Hz; Amp. 10~100% NBI: 3 MW/55 kV/2 s (5 MW/80keV) LHCD: 2 0.5 MW/2.45GHz (2 MW/3.7GHz) Fuelled system (H2/D2): Gas puffing(LFS, HFS, divertor) Extruded PI (40 pellets/LFS, HFS) SMBI (LFS, HFS) LFS: f =10~60 Hz, pulse>0.5ms Gas pressure: 0.3-3.0 MPa HFS: f = 1-5 Hz, 0.2-1.0 MPa

4. Outline • HL-2A tokamak • Diagnostic development • Confinement improvement and transport • Energetic physics and MHD activity • Turbulence and zonal flows • Summary

5. Comparison of MSE spectral broadening Simulation parameters • Beam dissipation d≈1.0° • Lenssize=37mm • Energy dissipation dv=2% Fitted functions • I0 is intensity of central wavelength • 0 is Stark splitting at central wavelength and σ is spectral width Jiang N. et al 2013, CPL30, 065201

6. Profiles of magnetic field pitch angle Radial profiles of magnetic field pitch angles slightly increase with time, indicating current profiles to be peaking gradually

7. FILD diagnostics successful on HL-2A Current flattop during NBI Plasma disruption with NBI • Flattop phase: Fast ion loss energy 40-50 keV and pitch angle 630. • Disruption phase: Fast ion loss energy and pitch angle change with magnetic perturbation rather largely. Shot 22614 Bt=1.34 T Frame f=500 fps Probe at R=2.13 m

8. Pedestal structure evolution during ELM Pedestal structure during an ELM measured by a new microwave reflectometry with high spatiotemporal resolutions

9. Outline • HL-2A tokamak • Diagnostic development • Confinement improvement and transport • Energetic physics and MHD activity • Turbulence and zonal flows • Summary

10. Basis of confinement and transport • Particle ITB observed in HL-2A for the first time(Xiao W. W. 2010, PRL. 104 215001) • NLT effect induced by SMBI fuelling and ECRH switching off (Sun H.J.et al. 2010, PPCF 52 045003; Sun H.J. et al. 2012 NF 51, 113010) • Turbulence and ELM characteristics (Duan X.R. 2010, NF 50, 095011; Yan L.W. 2011, NF 51 094016) • ELM mitigation by SMBI/CJI fuelling succeeded on HL-2A for the first time, and confirmed by KSTAR and EAST (Xiao W. W. et al. 2012 NF52, 114027 ) • Duan X.R., NF 49 (2009) 104012 • Xiao W. W. 2010, PRL. 104 215001 • Zhong W.L., PoP 17, (2010)112307 • Liu Yi, PRE, 84 (2011) 016403 • Huang Y., NF 52 (2012)114008

11. ELM mitigated by SMBI successfully (a) Pedestal density gradient drops after SMBI fuelleing, indicating particle confiement degeneration ne=1.8~2.3×1019m-3 Paux=0.9-1.4 MW Xiao W. W. et al. 2012 NF52, 114027

12. ELM mitigated by CJI better Cluster jet injection (CJI）mitigates ELM instability with better effect than SMBI Duan X. R. 2013, NF53, 104009

13. L-I-H transition by sawtooth crashes • L-H transition may be triggered by sawtooth crashes • Plasma density and energy increase with time • The frequency of I-phase oscillations decrease from 2.2kHz, 1.9kHz to 1.4 kHz. • The I-H transition successfully after the fourth sawtooth crash Liu C. H. et al. EPS2013, P5.157 Zhao K. J. et al. NF 53 (2013) 123015

14. ELM-free H-mode with EHO-like • EHO-like mode leads to density rate dropping and turbulent particle flux rising in SOL • This mode located near r/a=0.94) with f=5-10 kHz and mode number m/n=3/1 • The EHO appears on D and SXR emission Zhong W. L. 2013, NF53, 083030

15. Strong particle convection after SMBI • The density at outer channels (Z = -17.5, 24.5 cm) drop after a few milliseconds fuelled by SMBI • The density at central region (Z = ±3.5 cm) sustains about 30 ms to be dropping • The density gradually peaks after SMBI (h). • The results indicate that strongly inward convection exists after SMBI Yu D. L. 2012, NF 52, 082001

16. Impurity transport in Ohmic and ECRH (b) • There is a good agreement between the simulation (lines) and the experiments (symbols) results with diffusion D = 0.6 m2/s and inner convection V(a) = -1 m/s in Ohmic plasma • The strong decrease of the CV intensity compared with CIV in ECRH can only be reproduced with outer convection V(a) = 7 m/s Cui Z. Y. et al 2013, NF 53, 093001

17. Outline • HL-2A tokamak • Diagnostic development • Confinement improvement and transport • Energetic physics and MHD activity • Turbulence and zonal flows • Summary

18. Basis of Energetic Physics • Beta-induced Alfven eigenmode (e-BAE) by energetic electrons was identified for the first time • Multiple BAE modes are investigated • Ion and electron fishbones were confirmed • The frequency jump of e-fishbone was found uring ECRH. • Long-lived runaway electron beam was observed during major disruptions (Zhang Y.P., PoP 19 (2012) 032510) • The fast ion slowing-down time is in agreement with classical theoretical prediction (Zhang Y.P., PoP 19 (2012) 112504) Chen W., NF 49 (2009) 075022 Chen W., NF 50 (2010) 084008 Chen W., PRL 105 (2010)18500 Chen W., NF 51 (2011) 063010

19. Splitting Alfvén-acoustic mode Tearing mode Beta-induced Alfvén acoustic eigenmode Shot 10391 • Ip = 170 kA • Bt = 1.4T, • qa 4.0, • Te  1.0 keV • Ti  0.8 keV • PNBI =0.6 MW • BAAE with f = 15-40 kHz identified by frequency up-chirping, consistent with the solution for Alfvén-acoustic continuum • A clear spectrum splitting is first observed on BAAE Liu Yi, et al 2012, NF 52 074008

20. Frequency jump of e-fishbone mode Electron fishbone frequency jump was observed in the low density ECRH plasma, where the trapped particles are dominant. Ip=155-160 kA ne=0.3~0.7×1019m-3 BT=1.2-1.22 T ECRH deposited inside q=1 surface • Both low and high frequency branches are observed • The high frequency branch could be observed only if PECRH > 0.8 MW • Frequency jump gap increases with the ECRH power • Low & high frequency modes are m/n = 1/1 and 2/2 Yu L. M., et al NF53, 053002

21. Low-frequency multimode coexistance m/n = 4/2, 5/2, 3/1, 6/2, 4/1 • Low frequency multiple Alfven modes coexist during high power ECRH. • Mode frequencies decrease with ne and slightly increase with Te, finally overlap with each other. Ip= 155-160 kA Bt = 1.2-1.4 T ne < 1.4 × 1013cm-3 PECRH > 0.6 MW Ding X. T. et al 2013 NF 53 043015

22. Long lived mode & its control LLM observed during NBI with weakly reversed or broad low magnetic shear LLM suppressed by ECRH or SMBI • LLM degrades plasma confinement and enhances fast ion loss • LLM oscillation in LFS is stronger than that in HFS Deng W. et al. 2014, NF 54 013010

23. Outline • HL-2A tokamak • Diagnostic development • Confinement improvement and transport • Energetic physics and MHD activity • Turbulence and zonal flows • Summary

24. Basis of edge turbulence and ZFs • The toroidal symmetries of GAM and LFZF were confirmed on HL-2A for the first time • Turbulence nonlinear energy transfer was identified for the first time • Two types of LCO were founded • Three dimensional structure of filamentary plasma was studied • Zhao K.J., PRL 96 (2006) 255004 • Yan L.W., NF 47 (2007) 1673 • Zhao K.J., PoP 14 (2007)122301 • Lan T., PoP 15 (2008) 056105 • Zhao K.J., NF 49 (2009) 085027 • Cheng J., NF 49 (2009) 085030 • Liu A.D., PRL103 (2009) 095002 • Zhao K.J., PPCF 52 (2010)124008

25. Nonlinear energy transfer • Turbulent kinetic energy was transferred into LFZFs and GAMs • the energy transferred into LFZFs increases with heating power • Turbulence drives low frequency sheared flows Nonlinear energy transfer rate XuM. et al. 2012 PRL 108, 245001

26. Two types of I-phase trajectory • Trajectories of the system in phase space of normalized radial electric field Erand RMS of the density envelope (20-100 kHz) measured at Δr = −5 mm for discharge with L-I-H transition (a) and L-I-L transition (b). Cheng J. et al. 2013 PRL. 110 265002

27. Filament generation near the inner LCFS Dependent on the significant parallel correlation -6s -4s -8s Ip = 160-170 kA Bt =1.8-1.9 T ne= 1.8-2.5×1013cm-3 q95= 4.5-5.5 r/a = 0.96-1 0s -2s 2s Spatiotemporal evolution of E×B shearing rate • Eddy amplitude increases firstly, it is stretched and split into two islands by strong E×B flow, finally plasma filaments are ejected into SOL • The flow shearing time at filamentary birth position is identified to be close to the filament generation time (~4 s ) Cheng J. et al 2013 NF53, 093008

28. Summary • MSE, FILD, and MWR with high resolutions succeeded • ELM frequency rises to a factor of 2-3.5 but its amplitude drops 38% by using SMBI/CJI mitigation. • CJI is more efficient than SMBI for the ELM mitigation • L-I-H transition can be induced by sawtooth crashes • ELM-free H-mode observed with m/n=3/1 EHO mode of 5-8 kHz • The SMBI fuelling efficiency is enhanced by strong convection • The strong decrease of the CV intensity compared with CIV in ECRH needs a outer convection velocity of 7 m/s • Frequency jump of e-fishbone and LF multimode coexistence • Long lived modes have been controlled by ECRH and SMBI • Turbulent energy transferred into ZFs＆GAMby nonlinear process • Normalized Er ~ 1 is critical to trigger L-I-H transition • Plasma filament just generated at the inner LCFS

29. Thank you for your attention !