HL-2A Southwestern Institute of Physics 1/15 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,, P.R.China P.O.Box 432 Chengdu, , P.R.China International West Lake Symposium on Fusion Plasma Physics May 27, 2011 at Zhejiang University

HL-2A Southwestern Institute of Physics 2/15 Introduction of HL-2A Divertor Tokamak Heating system,fuelling system Experimental results of ELMy H-mode Summary Outline

HL-2A Southwestern Institute of Physics 3/15 R:1.65 m a:0.40 m Configuration: Limiter, LSN divertor B T :2.7 T I p :450 kA n e :~ 6.0 x m -3 T e :~ 5.0 keV T i :~ 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: MPa HFS: f = 1-5 Hz, MPa NBI LHCD ECRH 2 ECRH 1 Introduction : HL-2A Divertor Tokamak

HL-2A Southwestern Institute of Physics 4/15 The 68GHz ECRH System 5# 3# 4# 6# 2# 1#  6 gyrotrons (4/68GHz/500kW/1s and 2/68GHz/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 % Heating:

HL-2A Southwestern Institute of Physics 5/15 On-axis & off-axis heating Current drive Heating: ECW launcher antenna 2# for two wave beams Steerable Remote controllable antenna 1# for four wave beams A fixed focusing mirror ； Port : 350mm in diameter Injection angle of antenna 2#: tor. and pol. Beam radius : 37mm in the center of plasma

HL-2A Southwestern Institute of Physics 6/15 The NBI System Heating: Particle energy : ~ 35KeV Deuterium atom, 4 ion sources Injection angle : 58 0 toroidally. NBI power achieved: ~ 800kW

HL-2A Southwestern Institute of Physics 7/15 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. Requirements: to reduce P LH threshold D2 as working gas; LSN divertor configuration; Ion magnetic gradient drift towards the lower X-point

HL-2A Southwestern Institute of Physics 8/15 Main parameters: Ip=310 kA, B t =2.35 T n e =1.35×10 13 cm -3 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. 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 Requirements:

HL-2A Southwestern Institute of Physics 9/15 Discharge control  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 Requirements: 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.

HL-2A Southwestern Institute of Physics 10/15 First H-mode operation is achieved in 2009 spring experiments NBI and 2 nd X-mode ECRH at Bt~1.3T the cutoff of ECW at n e > 2.2  m -3 The discharge enters L- mode phase after P ECRH =0.6 MW at t = 260 ms with obvious density pumping out L-H transition occurs after P NBI =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 Results:

HL-2A Southwestern Institute of Physics 11/15 Results: NBI and O-mode ECRH at Bt~2.4T Realized in 2011 spring the cutoff of ECW at n e > 4.3  m -3 Density feedback Plasma parameters are higher than those of NBI and 2 nd X-mode ECRH at Bt~1.3T

HL-2A Southwestern Institute of Physics 12/15 Two H-mode phases induced by the SMBI fueling The ELMs appear at 640 ms with n e =1.8  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 n e >2.2  m -3. The stored energy, the density and radiation power rise again after the SMBI fuelling is added again at t = 770 ms with n e =1.5  m -3. The process is repeated by using SMBI fuelling. The clear ELM appears at 793 ms with a density ~1.7  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. Results:

HL-2A Southwestern Institute of Physics 13/15 About Type-III ELMs ~1m s ~3ms in this shot, ELM frequency decreases with heating power increasing  Type III ELMs Results: 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 ms. The periods should rely on edge plasma pressure and density profiles even if the heating power and line-averaged density are fixed. Power step rise

HL-2A Southwestern Institute of Physics 14/15  P sep =P aux +P ohm -P rad -dW/dt  ELM frequency: Hz  ELM frequency increases with P sep increasing, that Type-I ELM ΔW=2-4J  ELMs crash modulate the electron density and Ip  ELMs cause the energe loss 6-12% of stored energy About Type-I ELMs(large ELMs) Data in 2010 spring experiments

HL-2A Southwestern Institute of Physics 15/15 Some large ELMs have periods of ms with energy loss more than 10 % large ELMs have obvious perturbation to plasma current, Te and ne at plasma edge as well Results: Comparison of Type-I &Type-III ELMs r/a~0.6 r/a~0.8 r/a~0.6 r/a~0.8

HL-2A Southwestern Institute of Physics 16/15 Density pedestal width Type-I(large) ELMy H-mode MW reflectometry and Langmuir probes for pedestal width Pedestal density is 1.25×10 19 m -3 with n ped /n e = 0.6 Density pedestal width is about 2.8 cm Results: Density pedestal width is about 3 cm r/a~0.6 r/a~0.8

HL-2A Southwestern Institute of Physics 17/15 Characteristics of ELMy H-mode Results: About P LH power No large difference in P LH with ECH P LH-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

HL-2A Southwestern Institute of Physics 18/15 dwell time of L-H mode transition with 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 Results:

HL-2A Southwestern Institute of Physics 19/15 delay time of H-L transition versus 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 ms, which is the same order as energy confinement time. Results:

HL-2A Southwestern Institute of Physics 20/15 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. Results:

HL-2A Southwestern Institute of Physics 21/15 Energy confinement time with 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  m −3 limited by the second harmonic X-mode ECRH, which in turn limits the density to be smaller than 1.7  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 Results:

HL-2A Southwestern Institute of Physics 22/15 Energy confinement time with 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 Results:

HL-2A Southwestern Institute of Physics 23/15 H-factor of energy confinement time with P tot at I p =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. Results:

HL-2A Southwestern Institute of Physics 24/15 Plasma stored energy with P tot at I p ~160 kA The stored energy is close to linear increase with total heating power. It is increased to ~28 kJ at P tot = 1.5 MW from ~13 kJ at P tot = 0.8 MW. The basic reason is that plasma temperature is always rising with the heating power though particle confinement is probably degenerated. Results:

HL-2A Southwestern Institute of Physics 25/15 SMBI (He gas) mitigation PI monitor D 2 -pellet injection SMBI/PI effect on ELMs Prof. Yao talked this mourning Results:

HL-2A Southwestern Institute of Physics 26/15 Precursors of type-I ELMs (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) The Spectrogram of the ELM precursors from magnetic probe (LFS) and soft-X ray (edge channel). The divertor D α indicates the onset of ELM. (a) (b) (c) Results:

HL-2A Southwestern Institute of Physics 27/15 q a effect on ELMs  in this shot, Ip increased → qa decreased  qa decreasing→ ELMy ampilitude decreasing, ELMy frequency decreasing  Ip, Bt scanning → qa changing(shot by shot)  ELMs frequency is proportional to qa  On JET for type I ELMs, q95↑→ELMy frequency↑, amplitute↓ Results:

HL-2A Southwestern Institute of Physics 28/15 ELMs if He is puffed from divertor (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) (a) (b) (c) Results: r/a~0.6 r/a~0.8  in experiments of target detachment, He  Type-I ELMs may be easily excited if gas is puffed from divertor chamber

HL-2A Southwestern Institute of Physics 29/15 r/a=0.8 r/a=0.06 r/a=0.75 r/a=0 Quiescent H-mode? Carbon impurity Horizontal displaceme nt ELM-free H-mode Results: H-factor Energy confinement time

HL-2A Southwestern Institute of Physics 30/15 Edge Harmonic Oscillation (EHO) m/n=3/1 Mirnov Coil EHO? m/n=3/1 EHO? m/n=2/1 m/n=3/2 NTM Soft X-ray ECE m/n=2/1 Results:

HL-2A Southwestern Institute of Physics 31/15 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 ms, which tends to decrease with power increasing. Typical delay time of H-L transition is comparable with the energy confinement time, such as 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

HL-2A Southwestern Institute of Physics 32/15 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 state ELM-free H-mode/QH-mode exploration Construction of the new device: HL-2M

HL-2A Southwestern Institute of Physics 33/15 Thanks for you attention !