Recent Experiment Results during electron cyclotron heating on HL-2A

17th IAEA Technical Meeting on Research Using Small Fusion Devices Recent Experiment Results during electron cyclotron heating on HL-2A Y.B.Dong, Y.Liu, H.J.Sun, W. Chen, W.W.Xiao, J. Zhou, W. Deng, L.H.Yao, B.B.Feng, J.Rao , Q.W.Yang , X.T.Ding , Yong Liu , and C.H.Pan E-mail of main author: caroldyb@swip.ac.cn Southwestern Institute of Physics (SWIP), Chengdu, China

Outline • ECRH experiment on HL-2A • Experiment results on HL-2A • Confinement enhancement by SMBI during ECRH • Non-local transport phenomena induced by SMBI • Reduced core transport after ECRH switch-off • Sawtooth behaviour during ECRH • Exiting of the m=1/n=1 mode during ECRH • Future plan in ECRH/CD experimenton HL-2A

HL-2A Tokamak • Main parameters of HL-2A • Major radius: 1.65 m • Minor radius: 0.40 m • Toroidal field: 2.8 T-3.5T • Plasma current: 480 kA • Magnetic flux: 5.0 Vs • Discharge duration:1.5 sec. • Plasma density: 4.2 x 1019 m-3 • Electron temperature: 5.0k eV • Ion temperature: 600 eV • Physics issues on HL-2A • Transport: thermal transport, particle transport, impurity transport, … • SOL and divertor: • Edge and pedestal physics: • MHD and disruptions: NTM, ELMs, TAEs, … • Turbulence: Zonal Flows • Confinement and advanced scenarios: H-mode, …

1.5MW/50keV/2sNBI system SMBIPellet Injection ECE CXRS 2*500kW /1s /68GHz ECRH/ECCD 8-Channel HCN interferometer MW reflectometer Thomson Scattering VUV spectrometer Bolometer & Soft X ray arrays SDD soft X ray spectrum 2*500kW /1S /2.45GHz LHCD system Fast scan probes Neutral Particle Analyzer 2*500kW/1s /68GHz ECRH/ECCD Other Diagnostics, … … Layout of HL-2A Tokamak

ECRH systerm • The fundamental O-mode EC wave with the wide steering angles in poloidal (~25º) and toroidal (~25º) directions • The ECW launched from 2 equatorial ports, 4 gyrotrons • The maximum power is 2 MW (1.7 MW in experiments) Transmission line corrugated waveguide, miterbends, DC breaks; Launcher focusing mirrors, steering mirrors;

ECRH Radiation increasing r/a = 0 H alpha inceasing Density pump-off r/a = 0.4 Radiation increasing ECH experiments Te increasing

Target plate Separatrix Hα Array 1 LN2 output SMB Valve H2 inlet LN2 inlet Turbo Pump CCD Camera Hα Array 2 Lower divertor SMBI on HL-2A • The SMBI with clusters may be of benefit for deeper fuelling Stair-shaped density increments • Arrangement for SMBI in the HL-2A • Gas pressure: 1 M Pa to 3 M Pa • Pulse duration of Jet : 2 ms • Pulse interval: 50 ms to 100 ms The plasma density increases after MBI, while a temperature drop was observed in the central ECE channel.

During ECRH a series pulse SMBI fueling, the plasma storage energy WE, Beta_p, line averaged density ne and “fusion neutron” account increase, the plasma confinement was improved. spring Laval nozzle valve piston neutron account outlet inlet Confinement enhancement by SMBI during ECRH SMB Injector A new pneumatic supersonic molecular beam injector is developing to realize the SMBI from HFS, which will be beneficial to deeper injection and higher fuelling efficiency. Gas pressure of D2: 2.0 MPa Pulse number: 10, later 5 pulses during ECRH Pulse duration: 0.3 ms Pulse interval: 50 ms ECRH Power: 1034 kW ECRH duration: from 800 ms to 1200 ms

Outline • ECRH experiment on HL-2A • Experiment results on HL-2A • Confinement enhancement by SMBI during ECRH • Non-local transport phenomena induced by SMBI • Reduced core transport after ECRH switch-off • Sawtooth behaviour during ECRH • Exiting of the m=1/n=1 mode during ECRH • Future plan in ECRH/CD experiment on HL-2A

q=2 q=2 Non-local transport phenomena induced by SMBI high field side (PECRH = 800 kW, TSMBI = 810 ms) • Ha and radiation losses drop（Enhanced energy confinement） After the injection of SMB, outside r~20cm the plasma is cooled while the core Te increase. A steep Te profile in the plasma core is sustained for about 40ms. Meanwhile the radiation of bolometer and Ha decrease. 15

Non-local transport phenomena The non-local effect appears after the injection of the latter two SMBs during ECRH and OH, while the first one doesn’t induce such an effect. The effect always occurs with low density and the density limit is larger during ECRH. • Happened in low density range（ne~1-2x1013cm-3） • Located between q=1 and q=2 surface • Central temperature increase of 200ev • Duration of the process is longer: the effect lasts about 5ms in RTP, it is about 40ms in HL-2A • Radiation of bolometer and Ha decrease in HL-2A, there is no sign of the decrease in RTP

Off-axis ECRH Delayed Te decrease Power deposition location Te increase Reduced core transport after ECRH switch-off Steep SX profile The central Isx remains constant for some times after ECRH switch off, while the off-axis Isx decrease, ▽Te increase and the transport coefficients reduce. 23

Larger sawtooth Possible explanation: ne increase slightly Reduced core transport after ECRH switch-off Nearly unchanged Te0 Steep SX profile Off-axis ECRH switch-off leads to current density redistribution and transiently low shear, causing a local confinement improvement.

normal (b) off-axis ECH (PECH=340kW) (a) on-axis ECH ( PECH=450kW); larger smaller giant double saturated hill humpback Sawtooth behaviour during ECRH • The auxiliary heating power is up to 2MW in the ECRH experiment of HL-2A tokamak. • on-axis ECH (with a more peaked profile) • off-axis ECH (with flat profile, no “hot ears”) A sawtooth tends to saturate or decrease in its ramp phase, and the sawtooth shape is usually changed, leading to formation of a saturated sawtooth, a compound sawtooth, a humpback or a hill. 20

SVD m=1 island SVD m=1island Non-standard sawtooth during ECRH • Double Sawtooth • Compound(saturated+double)Sawtooth 21

Possible explanation: Non-standard sawtooth during ECRH hills humpback The Te growth in both case corresponds to some temporary improvement of the global confinement • Heating effect during crash or reconnection 22

Stabilization of sawtooth activity–giant sawtooth The most significant response to a change in the heating location is the rapid change in sawtooth shape and period as the heating location crosses the inversion surface. Large sawtooth: PECRH=1393kW, Bt=2.24T, r’=-14cm, Ne=2.4×1019m-3, rq=1=12cm(obtained from SVD)，deposion location is just outside the q=1 surface. q=1 surface axis Ne=2.0×1019m-3, Pecrh=1100kW, rq=1 = 11cm, The maximum sawtooth period is obtained for power deposition close to the HFS q=1 surface, located at 9.8cm. The sawtooth periods are smaller near the axis. 25

Crash Fishbone like instabilities • 20 • 15 • 10 • f（kHz） • 5 • 705 • 710 • 715 • 720 • 725 • 730 • 700 • wavelet spectrum • 0.5 • 0.4 Fast particle driven instabilities: Fishbones Low field side deposition PECRH =650kW m=1/n=1 “fishbone like instaility” exited with • Electron density < 3x1013cm-3 • Power of ECRH < 900kW • Both high field side and low field side deposition High field side deposition PECRH=280kW

30 – 60 keV 10 –30 keV Normalized precession velocity of circulating electrons Destabilizing effect of suprathermal electrons Increase of hard X ray during ECRH • Electron fishbone excited by the barely trapped electrons(Procession reversal ) (Ding X.T,Liu Yi,Nuclear Fusion Vol.42,No5(2002)491) • Electron fishbone excited by the circulating electrons Z.T.Wang,Nuclear Fusion47 32

Future plan in ECRH/CD experiment on HL-2A Future plan in ECRH/CD experimenton HL-2A • Confinement enhancement with ECRH ( H-mode ) • Transport study with ECRH • ITB formation; • Non-local transport phenomena • Electron heat transport and ECRH modulation experiments • MHD study with ECRH/CD • Correlation between MHD activities and ITB emergence • Control of NTM mode by controlling of sawtooth period • Exiting of the e-fishbone during ECRH 46

Thank you for attention!

Recent Experiment Results during electron cyclotron heating on HL-2A