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Experimental Studies of ELMy H-mode on HL-2A Tokamak

Experimental Studies of ELMy H-mode on HL-2A Tokamak. Y. Huang J.Q.Dong, L.W.Yan, X.T.Ding X.R.Duan, HL-2A team Southwestern Institute of Physics P.O.Box 432 Chengdu , 610041 , P.R.China. International West Lake Symposium on Fusion Plasma Physics May 27, 2011 at Zhejiang University.

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Experimental Studies of ELMy H-mode on HL-2A Tokamak

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  1. Experimental Studies of ELMy H-mode on HL-2A Tokamak Y. Huang J.Q.Dong, L.W.Yan, X.T.Ding X.R.Duan, HL-2A team Southwestern Institute of Physics P.O.Box 432 Chengdu, 610041, P.R.China International West Lake Symposium on Fusion Plasma Physics May 27, 2011 at Zhejiang University

  2. Outline • Introduction of HL-2A Divertor Tokamak • Heating system,fuelling system • Experimental results of ELMy H-mode • Summary

  3. Introduction : ECRH2 NBI LHCD ECRH1 HL-2A Divertor Tokamak • R: 1.65 m • a: 0.40 m • Configuration: • Limiter, LSN divertor • BT:2.7 T • Ip:450 kA • ne:~ 6.0 x 1019 m-3 • Te:~ 5.0 keV • Ti:~ 2.8 keV • P.d.: ~4.3 seconds Auxiliary heating systems: ECRH/ECCD: 3 MW (60.5 MW/68 GHz/1 s) modulated: 10~50 Hz; 10~100 % NBI: 1 MW/45 keV/2 s LHCD: 1 MW (2 0.5 MW/2.45 GHz/1 s) Fueling systems N.Gas puffing(LFS, HFS, divertor)Extruded PI(40 pellets/shot, LFS, HFS)SMBI (LFS, HFS, H2/D2, He/Ne/Ar) LFS: f =10~60 Hz, time width>0.5ms Gas pressure: 0.3-3.0 MPa HFS: f = 1-5 Hz, 0.2-1.0 MPa

  4. Heating: 1# 6# 2# 4# 3# 5# The 68GHz ECRH System • 6 gyrotrons (4/68GHz/500kW/1sand2/68GHz/500kW/1.5 s ) • ECW injected from low field side, O-mode, 2nd harmonic X-mode, from 2 ports • Gyrotrons from GYCOM/Russia • outpower Modulation: frequency is 10~50 Hz; duty cycle is 10~100 %

  5. Heating: • antenna 1# for four wave beams • A fixed focusing mirror； • antenna 2# for two wave beams • Steerable • Remote controllable On-axis & off-axis heating Current drive ECW launcher Port: 350mm in diameter Injection angle of antenna 2#: 00-300 tor. and pol. Beam radius: 37mm in the center of plasma

  6. Heating: The NBI System Particle energy: ~ 35KeV Deuterium atom, 4 ion sources Injection angle : 580 toroidally. NBI power achieved: ~ 800kW

  7. Requirements: to reduce PLH threshold D2 as working gas; LSN divertor configuration; Ion magnetic gradient drift towards the lower X-point To have a good wall condition: 1: the surface of the shielding plates of MP1 and MP2 has been covered with carbon fibre composite(CFC), which can protect the first wall, and effectively avoid the splash of heavy metal impurity.

  8. Requirements: GDC and Siliconization D2 glow discharge cleaning is applied to remove impurities from the wall, and helium GDC for removing residual H2/D2 Siliconization by DC glow discharge with a gas mixture of 90% He + 10% SiD4 titanium gettering in the divertor region After siliconization, the impurity fluxes released from the first wall were reduced, especially the oxygen and high Z impurities; The total radiated power was decreased much. Main parameters: Ip=310 kA , Bt=2.35 T ne=1.35×1013 cm-3

  9. Discharge control Requirements: • Horizontal displacement presets to be 1 cm inwards, during NBI heating • Divertor configuration within 20 ms; to reduce impurity and radiation level; • configuration analyses/reconstruction The plasma surface interaction is usually strong in HL-2A due to the thin throats( <2 cm) between the dome and the buffer plates. careful analyses on the MHD equilibrium were performed with the EFIT code before the experiment was conducted, and configuration reconstruction is routinely performed to monitor the variation of the separatrix.

  10. Results: First H-mode operation is achieved in 2009 spring experiments • NBI and 2nd X-mode ECRH at Bt~1.3T • the cutoff of ECW at ne> 2.21019 m-3 • The discharge enters L-mode phase after PECRH=0.6 MW at t = 260 ms with obvious density pumping out • L-H transition occurs after PNBI=0.7 MW soon near t = 350 ms • The H-mode easily appears after power reaches its threshold • H-mode sustains 550ms until auxiliary heating power ended

  11. Results: • NBI and O-mode ECRH at Bt~2.4T • Realized in 2011 spring • the cutoff of ECW at ne> 4.31019 m-3 • Density feedback • Plasma parameters are higher than those of NBI and 2nd X-mode ECRH at Bt~1.3T

  12. Results: Two H-mode phases induced by the SMBI fueling • The ELMs appear at 640 ms with ne=1.81019 m-3, rising for 30 ms. • The ELMs are sustained for 100 ms and then disappear after the SMBI is turned off and due to the cutoff of ECRH power at ne>2.21019 m-3. • The stored energy, the density and radiation power rise again after the SMBI fuelling is added again at t = 770 ms with ne=1.51019 m-3. • The process is repeated by using SMBI fuelling. The clear ELM appears at 793 ms with a density ~1.71019 m-3 and disappears at 851 ms, 8 ms after the NBI heating is turned off. • The overall discharge exhibits a series of L-H-L-H-L transitions induced with SMBI fueling.

  13. Results: ~3ms ~1ms About Type-III ELMs Power step rise • The time intervals of ELMs tend to increase with total heating power, thus ELM frequency decreases correspondingly, Type III ELMs. • The periods are irregular in the range of 0.6-3.4 ms. • The periods should rely on edge plasma pressure and density profiles even if the heating power and line-averaged density are fixed. in this shot, ELM frequency decreases with heating power increasing • Type III ELMs

  14. Data in 2010 spring experiments About Type-I ELMs(large ELMs) • ELMs crash modulate the electron density and Ip • ELMs cause the energe loss 6-12% of stored energy ΔW=2-4J • Psep=Paux+Pohm-Prad-dW/dt • ELM frequency:100-400Hz • ELM frequency increases with Psep increasing, that Type-I ELM

  15. Some large ELMs have periods of 10-30 ms with energy loss more than 10 % large ELMs have obvious perturbation to plasma current, Te and ne at plasma edge as well Results: r/a~0.6 r/a~0.6 r/a~0.8 r/a~0.8 Comparison of Type-I &Type-III ELMs

  16. Density pedestal width Type-I(large) ELMy H-mode MW reflectometry and Langmuir probes for pedestal width Pedestal density is 1.25×1019 m-3 with nped/ne = 0.6 Density pedestal width is about 2.8 cm Results: r/a~0.6 r/a~0.8 Density pedestal width is about 3 cm

  17. Characteristics of ELMy H-mode Results: No large difference in PLH with ECH About PLH power PLH-ASDEX is about twice as the prediction of the scaling law;the HL-2A H-mode runs at low density,so needs more power, and ECRH is different from NBI at low density;discharge conditions be optimized

  18. Results: dwell time of L-H mode transitionwith total heating power • There is a dwell time between additional heating and the L-H transition • The dwell time tends to drop with power rising • The time is about 200 ms for low power discharge and only needs 20 ms for higher one • Powerful heating can decrease the dwell time • The dwell time also depends on plasma density after heating power is fixed

  19. Results: delay time of H-L transitionversus total heating power • No clear power dependence is observed to the delay time. • The transient transition to L-mode is observed in wide range of heating power. • Typical delay time is 10-30 ms, which is the same order as energy confinement time.

  20. Results: Energy confinement time versus plasma current • The confinement time is close to linear increase with plasma current, consistent with theoretic prediction. • Most H-mode discharges are conducted at Ip = 160 kA for the last campaign. • The confinement time should change with density and heating power even if the current remains invariant.

  21. Results: Energy confinement timewith plasma density at Ip=160 kA • Energy confinement time is close to linear increase with plasma density. • The maximum line-averaged density is 2.31019 m−3 limited by the second harmonic X-mode ECRH, which in turn limits the density to be smaller than 1.71019 m−3 before L-H transition. • Low density may increase L-H power threshold. • No contrast of confinement time for the same density range between the L-mode and H-mode

  22. Results: Energy confinement timewith total heating power at Ip=160 kA • The confinement time of H-mode clearly decreases with total heating power. • The scaling law of confinement time with total heating power has not been verified due to enough experimental data. • The L-mode confinement time tends to decrease with increase of the heating power, consistent with the prediction by the scaling law of ITER89-P

  23. Results: H-factor of energy confinement timewith Ptot at Ip=160 kA • The H-factor tends to decrease with total heating power. • It is changed from 1.5 at low heating power to 1.1 at higher one. • The L-mode confinement decreases with the heating power too. • The H-factor of L-mode is a little larger than unit at low heating power and lower than unit for higher one. • The H-mode clearly has higher confinement than the L-mode at the same heating power.

  24. Results: Plasma stored energy with Ptot at Ip~160 kA • The stored energy is close to linear increase with total heating power. • It is increased to ~28 kJ at Ptot = 1.5 MW from ~13 kJ at Ptot = 0.8 MW. • The basic reason is that plasma temperature is always rising with the heating power though particle confinement is probably degenerated.

  25. Results: PI monitor SMBI(He gas) mitigation SMBI/PI effect on ELMsProf. Yao talked this mourning D2-pellet injection

  26. Results: The Spectrogram of the ELM precursors from magnetic probe (LFS) and soft-X ray (edge channel). The divertor Dα indicates the onset of ELM. (a) (b) (c) (a) (a) (a) (a) (a) (a) (a) (a) (a) (b) (b) (b) (b) (b) (b) (b) (b) (b) (c) (c) (c) (c) (c) (c) (c) (c) (c) Precursors of type-I ELMs

  27. Results: qaeffect on ELMs • Ip, Bt scanning → qa changing(shot by shot) • ELMs frequency is proportional to qa • On JET for type I ELMs, q95↑→ELMy frequency↑, amplitute↓ • in this shot, Ip increased → qa decreased • qa decreasing→ ELMy ampilitude decreasing, ELMy frequency decreasing

  28. Results: r/a~0.6 r/a~0.8 (a) (a) (a) (a) (a) (a) (a) (a) (a) (b) (b) (b) (b) (b) (b) (b) (b) (b) (c) (c) (c) (c) (c) (c) (c) (c) (c) ELMs if He is puffed from divertor • in experiments of target detachment, He • Type-I ELMs may be easily excited if gas is puffed from divertor chamber

  29. Results: Quiescent H-mode? Energy confinement time Carbon impurity H-factor Horizontal displacement ELM-free H-mode r/a=0.8 r/a=0.06 r/a=0.75 r/a=0

  30. Results: Soft X-ray Mirnov Coil m/n=3/2 NTM m/n=3/1 m/n=3/1EHO? EHO? m/n=2/1 ECE m/n=2/1 Edge Harmonic Oscillation (EHO)

  31. Summary • ELMy H-modes have been achieved by combination of NBI and ECRH with 2nd harmonic X-mode at Bt~1.3T NBI and ECRH with O-mode at Bt~2.4T • The minimum power threshold is about 1.0 MW. • The energy loss is smaller than 3 % by a type-III ELM type-I ELMs result in more energy loss and obvious drop of Ip • There is a dwell time of L-H transition in 20-200 ms, which tends to decrease with power increasing. • Typical delay time of H-L transition is comparable with the energy confinement time, such as 10-30 ms. • The confinement time of H-mode discharges increases with Ip and density, but it decreases with total heating power. • ELM control/mitigation experiments by using SMBI/PI

  32. Plans in near future years • 1 MW ECRH at 140GHz • Another NBI beamline with 2MW power • LHCD • Wall conditioning by Lithium vaporization • L-H transition physics • Energetic particle phenomena and MHD in H-mode phase • L-H transition by sole Paux of NBI/ECRH/LHCD • Type-I ELM control/mitigation by SMBI, PI, RMP coil • Steady stateELM-free H-mode/QH-mode exploration • Construction of the new device: HL-2M

  33. Thanks for you attention !

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