Long Pulse ICRF and ECH Experiment in LHD

Transcription

1 Long Pulse ICRF and ECH Experiment in LHD T. Seki, T. Mutoh, R, Kumazawa, K. Saito, Y. Nakamura, M. Sakamoto 1, T. Watanabe, S. Kubo, T. Shimozuma, Y. Yoshimura, H. Igami, K. Ohkubo, Y. Takeiri, Y. Oka, K. Tsumori, M. Osakabe, K. Ikeda, K. Nagaoka, O. Kaneko, J. Miyazawa, S. Morita, K. Narihara, M. Shoji, S. Masuzaki, M. Goto, T. Morisaki, B.J. Peterson, K. Sato, T. Tokuzawa, N. Ashikawa, K. Nishimura, H. Funaba, H. Chikaraishi, N. Takeuchi 2, T. Notake 2, H. Ogawa 3, Y. Torii 4, F. Shimpo, G, Nomura, M. Yokota, C. Takahashi, A. Kato, Y. Takase 5, H. Kasahara 5, M. Ichimura 6, H. Higaki 6, Y.P. Zhao 7, J.G. Kwak 8, H. Yamada, K. Kawahata, N. Ohyabu, K. Ida, Y. Nagayama, N. Noda, T. Watari, A. Komori, S. Sudo, O. Motojima and LHD Experimental Group National Institute for Fusion Science, Toki , Japan 1 Kyushu University, Kasuga , Japan 2 Nagoya University, Faculty of Engineering, Nagoya , Japan 3 Graduate University for Advanced Studies, Hayama , Japan 4 Kyoto University, Institute of Advanced Energy, Uji , Japan 5 University of Tokyo, Tokyo, Japan 6 University of Tsukuba, Tsukuba, Japan 7 Institute of Plasma Physics, Academia Sinica, Hefei 2331, P.R. China 8 Korea Atomic Energy Research Institute, Daejeon 35-6, Korea Rep. KPS Meeting October 21-22, 25 Chonbuk University

2 Outline Introduction of LHD Long pulse ICRF experiment ICRF system Improvement for experiment Experimental results Long pulse ECH experiment ECH system Improvement for experiment Experimental results Summary

3 External diameter 13.5 m Plasma major radius 3.9 m Plasma minor radius.6 m Plasma volume 3 m 3 Magnetic field 3 T Total weight 1,5 t ECH 84,168 GHz NBI Large Helical Device (LHD) ICRF 25-5 MHz Plasma vacuum vessel NBI Local Island Divertor (LID) World largest NBI superconducting coil system Magnetic energy 1 GJ Cryogenic mass (-269 degree C) 85 t Tolerance < 2mm LHD Device and Experimental Hall NBI ICRF 25-5 MHz

4 % < > [%] LHD plasma performance has been progressing steadily LHD(NIFS) CHS(NIFS) W7AS(IPP,FRG) ATF(ORNL,USA) HeliotronE(Kyoto U.) year Temperature [kev] m T e () T i () t pulse '98 '99 ' '1 '2 '3 ' Experimental Campaign Discharge duration [min.] Achieved major parameters Pressure : 4.3 % Temperature T e () : 1 kev, T i () : 13.5 kev Density n e : m -3 Triple fusion product nt E T i : m -3 skev Discharge duration 65 min. by ECH (11kW) and 31 min. by ICH (68kW)

5 Purpose of long pulse experiment in LHD To demonstrate capability of steady state operation in Heliotron configuration which needs no toroidal current. Basic research relating to steady state plasma such as PFC, divertor physics, particle control

6 LHD Specifications -Major radius 3.4 ~ 4.1 m -Minor radius ~.63 m (at R ax =3.6m) -Plasma Volume ~ 3 m 3 (at R ax =3.6m) -Magnetic field 2.98 T (at R ax =3.5m) Heating power -ECH (84 /168 GHz) 2. MW.2MW/CW -N-NBI (<17keV, H ) 13. MW.2 MW/ 2 min -ICRF ( 25-1MHz) 2.7 MW 1-2 MW/ CW Cross-section of LHD and heating power available Divertor Leg Cryostat vessel Vacuum Chamber Plasma Poloidal coils Helical coils Total Weight 1,5ton World Largest Superconducting Device

7 ICRF long pulse experiment

8 ICRF antenna Loop antenna for fast wave launch -U, L antenna Three pairs are installed from upper and lower vertical vacuum port. -Fast wave is excited at outboard of torus and higher magnetic field side. -Front surface of antenna fits to last closed flux surface. -Antenna size length : 6cm width : 46cm strap width : 3cm -All components are cooled by water. -Antenna is movable by 15cm in radial direction.

9 Layout of ICRF antenna - six antennas for steady-state ICRF heating U&L antenna to #1, 2 RF transmitter water cooled F.S. 4.5 U&L antenna (spare) not connected to RF transmitter F.S. cooled by Cu heat conduct 7.5 U&L antenna To #6A, 6B RF transmitter F.S. cooled by Cu heat conduct

10 ICRF transmitters Dummy load test at MHz -Four transmitters are connected to antennas. #1: 4CM2,5KG.55MW/1hr 38.47MHz #2: 4CM2,5KG.54MW/1hr #6A: TH525A.52MW/.5hr.23MW/1hr 38.47MHz 28.4MHz 38.47MHz #6B: TH525A.49MW/.5hr.24MW/1hr 28.4MHz 38.47MHz

11 ICRF heating mode - He plasma with minority H ions - n H /n e =1%, n e =1.x1 19 m -3 - B=2.75T, R axis =3.6m - Frequency: 38.47MHz - Ion cyclotron resonance of H ions: Saddle point of magnetic configuration Ion Cyclotron Resonance Two-ion Hybrid Resonance R Cut off - Minority ion heating Good heating efficiency in the short pulse experiment L Cut off ICRF Antenna

12 Uncontrollable electron density increase B=2.75T, R ax =3.6m, He(H)plasma n e (x1 19 m -3 ) P rad (kw) T e, T i (kev) P RF (kw) He puff rate(pa m 3 /sec) T i (ArXVII) T e P f P r Time(sec) P n n e n e =5~6x1 18 m -3 Out-gassing from graphite of divertor plates? or antenna side protectors? T e ~T i ~2keV P ICRF ~5kW After 1sec P rad ~1kW to Pressure (x1-4 Pa) T div ( o C) (2-Iport) 25kW with density Increase => P rad /P rf =5% H (a.u.) Increase in H after 1 sec Temp. divertor plate: 4 o C

13 High performance divertor plates are developed Structure and heat flow path in divertor plate A) Standard MADP type B) High performance type C) Standing SBLDP (17 pcs in LHD) (2 pcs in LHD) / / SUS Divertor plates were replaced partially by the supreme one, c).

14 Hot spot was observed at antenna One candidate of source of outgas IR camera Shot 5292 time:1sec - Hot spot was seen on top of side protector. - Not seen in vacuum RF injection (without plasma). - Temperature of Faraday shield was kept low.

15 Optimization of antenna position - Temperature increase at 7.5U antenna P ICRF =25kW Pulse length: 4.5sec n e =.9x1 19 m -3 B=2.789T R ax =3.55m Temperature increment [ o C] T R p [cm] ( : distance between Faraday shield and last closed flux surface) - Antenna position was set to 13 cm. - Temperature rise was reduced extremely. - Loading resistance is still Plasma Loading Resistance [ ]

16 Real time control of impedance matching - Manual frequency control - Interlock level: P ref /P fw ~2% Reflected RF Power Fraction(%) df/f~.1% => P ref /P fw <1% Lreflection.freq.qdc 3 Interlock level 2 wo freq. control f= f=38.44mhz with freq. control time(s) Frequency control was done manually from 38.47MHz to 38.44MHz. Transmitter could not work below 38.44MHz with same output tuning condition. Reflected power increased again after this control.

17 Real time control of impedance matching - Liquid stub tuner - automatic feedback liquid surface control in every 7 sec => P ref /P fw < 4% Reflected RF power fraction(%) Liquid surface level: h liq =52cm at t=s ich52857we-35uf&r Plasma collapse Two stubs of triple stub tuner were controlled automatically by try and error method. Control was continued automatically until reflected power fraction decreased under 4%. It took long time to reduce the reflection time(sec)

18 ICRF Power [kw] n e [1 19 m -3 ] T e [kev] (R=3.524m) Effect of magnetic axis swing on divertor temperature Fixed magnetic axis R axis =3.55m ICRF Power [kw] n e [1 19 m -3 ] T e [kev] Magnetic axis swing R axis = m (R=3.618m) T div [ o C] 4 3 3I-U Div 2 # Time [sec] 4 5 -Divertor temperature at inboard side increased quickly. - Heat load on divertor plate was scattered and temperature rise is reduced. T div [ o C] R axis [m] Div # 1 3I-U 4.5U-I Div # Time [sec]

19 -Duration time: 31min 45sec (195sec) -Heating power: P tot =.68MW P ICH =.52MW P ECH =.1MW P NBI =.6MW (averaged on duration time) -Injected heating energy: W h =1.29GJ (ICRF: 1GJ) -Magnetic axis swing: R ax = 3.67m - 3.7m (18.5rounds) n e ~.8x1 19 m -3 T i ~2keV Longest plasma discharge Power [kw] [1 19 m -3 ] n e T i, T e [kev] T div [ o C] P ICRF P ECH 3 T i 2 1 T e (ECE:R=3.466m) 2 T div (4.5U-I) n e Gas Puff G R ax Shot P NBI T div (3I-U) Time [s] No serious increase of electron density. G [Pa m 3 /s] Rax [m]

20 Temperature of divertor plate after longest plasma discharge 31 min. 1.3 GJ Axis swing: m Thermo Couples embedded divertor plate positions antenna -Divertor temperature remains tolerable level.

21 Snap shots of plasma monitor in uncontrollable plasma termination 1641.s Normal s Spark near 7I port Fe influx? s T e dropped T e =.5keV s FeX max s CIII max s Just before ICRF turn-off s Just after ICRF turn-off n e (1 19 m -3 ), T eece (kev), FeX(a.u.), CIII(a.u.) 2 1 T eece P ICH n e FeX CIII 53775,ne,Te,FeX,CIII,PICH, time(s) -Spark was seen near 7I port. -Plasma was terminated by influx of metallic impurity. 1.5 PICH (MW)

22 Sparks in plasma with large high energy tail Si-FNA n e =.4*1 19 [m -3 ](#54274) n e =.8*1 19 [m -3 ](#54271) n e =1.3*1 19 [m -3 ](#54273) Frequent Sparks 7I port Counts No Sparks Energy [kev] -A lot of sparks were observed in a low density plasma with a large tail. -High energy tail may be one of causes of sparks. -High energy particles may collide with divertor plate or first wall directly or by charge exchange reaction. -Higher density operation is planned in future experiment.

23 ECH long pulse experiment

24 Introduction Former long pulse ECH discharges in helical system ATF(1992) 28GHz, 7kW, 4667s, 3x1 18 m -3 (low Te) LHD(2) 84GHz, 5kW, 12s (duty 95%), 3-5x1 17 m -3, 3eV LHD(24) 84GHz, 7kW, 756s, 2.4x1 17 m -3, 24eV

25 ECH system for LHD U-Antennas LHD Hall 168GHz 5 kw,1s Heating Equipment Room 84GHz 8kW,3 s 84GHz 2kW,1s L-Antennas O-Antennas 6-3.5inch non-evacuated waveguides 2-1.5L 31.75mm Evacuated waveguides 82.7 GHz 5kW,2s 8 set of gyrotrons, transmission lines, antennas are operated GHz(Toshiba), 2-84GHz CPD (GYCOM), GHz non CPD (GYCOM) 1-84GHz CPD (GYCOM) 2kW 1 s (diamond window) 2- evacuated 1.25 inch corrugated waveguide system. 6-non-evacuated 3.5 inch corrugated waveguide system. Total injection power to the LHD exceeds 2.1 MW at maximum in 6th cycle experimental campaign.

26 ECH waveguide antenna for CW Experiment Existing mirror antennas LHD 1.5L port New waveguide antenna Connected to 31.25mm evacuated waveguide line. Free from heat handling problem (without mirrors) Remotely switchable by corrugated waveguide switch. LHD and transmission line is separated by diamond window.

27 Former ECH long pulse experiment 756 sec discharge (shot #48821) R axis =3.5 m B = T P ECH,in = 72 kw (84GHz) n e,av = 2.4 x 1 17 m -3 T e,ece =24 ev repetitive gas puff 2ms/1Hz Manually switched not to cause radiation collapse Stopped by pressure rise of ECH transmission line

28 Pressure rise in MOU/waveguides Pressure (Torr.) threshold for interlock Gate valve is closed time (s) Pulse stopped due to increase of pressure in the waveguide. Out gassing from wall Poor conductivity in waveguide Initial and constant pressure rise may be due to increase of out gassing by temperature rise of waveguide wall. Latter half increase of pressure may be due to a leak at DC break (damaged).

29 Modification and Installation of 9-Pump out Tees Pump out Gap 1mm 9-pump out tees are manufactured and installed along transmission line for CW operation Smaller gap (1 mm) than old one Good evacuation efficiency

30 Improvement of evacuation system Pumping port for waveguide system is increased up to 9 along transmission line. Out gassing rate decreased due to efficient conditioning by increased pumping rate and enforced cooling. Maximum pressure decreased shot by shot.

31 ECH succeeded one hour plasma sustainment with 11 kw/65min injection B=1.48T, R ax =3.6m 2nd harmonic heating P in ~11 kw, 65 minutes T e >1.~1.5 kev n e >1.5x1 18 m -3 Gas feed controlled manually by mass flow controller Tried to increase density after 2s ECH terminated manually Due to the data acquisition setting

32 Temperature and pressure rise in transmission line Due to enforcement of cooling and pumping system, temperature and pressure rise almost saturated within safety level.

33 Development of long pulse experiment Injected energy [GJ] JT-6 (JAERI) Tore Supra (F) LHD LHD TRIAM-1M JET (EU) 1 Min HT-7 (China) 1 Hr (Kyushu) 1 Day Plasma duration time [sec] Highest injected heating energy was achieved. 1.3GJ : world record previous record : 1.7GJ (Tore Supra) Successful demonstration of potential of helical system towards steady state operation Achieved in divertor configuration -Divertor study for steady state operation Longer discharge with higher heating power is planned.

34 Summary Steady state operational region was much extended. -68kW / 195s, total input energy reached 1.3GJ. -11kW / 65min. by ECH Key factors for steady state operation -Suppression of local heat load on divertor plates by swing of magnetic axis position for ICRF heating. -Enforcement of cooling and pumping of transmission line for ECH. Next step -Longer pulse (>1hr.) by higher power (>1MW) for ICRF heating. Avoid influx of metallic impurity by high density discharge. -Higher power operation to achieve 1 19 m -3 for ECH.