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Instabilities in the Long Pulse Discharges on the HT-7
X.Gao andX.Gao and HT-7 Team HT-7 TeamInstitute of Plasma Physics, Chinese Academy of Sciences, Institute of Plasma Physics, Chinese Academy of Sciences,
P.O.Box 1126, Hefei, Anhui 230031, P.R.ChinaP.O.Box 1126, Hefei, Anhui 230031, P.R.China(e-mail: [email protected])(e-mail: [email protected])
4th General Scientific Assembly of Asia Plasma & Fusion Association On 4th General Scientific Assembly of Asia Plasma & Fusion Association On
New Development of Plasma Physics and Fusion Technology, Hangzhou, China, Oct. 13-16, 2003New Development of Plasma Physics and Fusion Technology, Hangzhou, China, Oct. 13-16, 2003
HT-7
ASIPP
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Abstract
• In the HT-7 superconducting tokamak, long-pulse discharge can be generated by synergy of high power LHCD (300-600 kW, 2.45 GHz) and high power IBW (200-350kW, 27 MHz) heating;
• MHD behaviors and thermal instabilities which limited the high performance operation was studied in detail;
• For lower performance (Ip = 60 kA, Te(0) = 0.5-1 keV, <ne> = 0.5-1xE19 m-3) operation, more than 60 s of long pulse plasma was obtained by the LHCD (< 200 kW) in the HT-7 tokamak.
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HT-7 Superconducting TokamakHT-7 Superconducting Tokamak
R = 1.22m, a = 0.27m
Ip = 100~250 kA (250)
BT = 1~2.5T(2.5)
ne = 1~8x1013cm-3 (6.5)
Te = 1~5 KeV (4)
Ti = 0.2~1.5K eV (1.5)
ICRF:
f = 15~30MHz, P=0.3MW(0.35)
f = 30~110MHz, P = 1.5MW
LHCD:
f = 2.45GHz, P = 1.2MW(0.8)
Fuelling:
Pellet injector
Supersonic beam injection
Main Goal: Advanced Steady state operation and related physics
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Candidates for long pulse operation in the HT-7
• (1) Low hybrid current drive (LHCD)• LHW: 100 ~ 800 kW, the current drive efficiency: 0.5-0.8E19 A/m2W
• Vloop = 0, <ne> = 0.8E19/m3, Ip > 100 kA @ 140 kW, t > 10 s
• Thermal instabilities: impurity, outgassing, and uncontrolled density
• (2) Full non-inductive current drive by synergy of LHW and IBW heating (LHCD + bootstrap current)
• ITB-like Ti, Te, ne profiles, high beta plasma N = 2 ~ 3, IBS/Ip up to 38%
• Thermal instabilities
• MHD instabilities: sawtooth, mode locking, collapse and disruption
• Reference:[1]X.Gao et al., “Study of LHW and IBW Synergy Experiment on the HT-7 Superconducting Tokamak”, 1
8th IAEA Fusion Energy Conference (Sorrento, Italy, 4-10 October 2000), IAEA-CN-77/EXP4/12.
[2]B.Wan et al., “Investigation of the Synergy of IBW and LHCD for Integrated High Performance in the HT-7 Tokamak”, 19th IAEA Fusion Energy Conference (Lyon, France, 14-19 October 2002), IAEA-CN-94/EX/P3-20.
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Limitation of long pulse discharges during LHCD
• Heat exhaust and particle control
• High performance PFCs
• Plasma Control
• LHW system
• Edge physics
impurityimpurity outgassingoutgassing
uncontrolled Neuncontrolled Ne
Thermal Thermal instabilitiesinstabilities
MoIMoI
LimiterLimiter
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Ip = 104kA, Ne0 = 1.2x1019m-3, PLHCD=140kW, BT=2.0T
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Long pulse operation (>1 min) by LHCD
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Progress of Long Pulse Operation in the HT-7 Superconducting Tokamak
Long pulse operation in the HT-7 tokamak
0102030405060708090100
1994 1996 1998 2000 2002 2004
Year
Puls
e le
ngth
(s)
Di schargeMax- l ength
1994:First plasma1996:Development ofplasma control anddiagnostics system1998:Feedback controlfor plasma current,displacement and density1999:RF wall condition2000:Upgrade dataacquisition & diagnostics2001:Ferritic steel toreduce ripple loss; NewLHCD antenna system2002:Water coolingpoloidal and belt graphitelimiters
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Comparison between LHCD and IBW+LHW
• Ip = 150 kA, Bt = 2T, N|| = 2.35
• LHW: near on-axis current drive in target plasma
• IBW: 30MHz, on-axis heating
• Broadened HXR profile
• Increased driven efficiency
• Improved particle and energy confinement
• Peak position of HXR ~ first maximum of IBW n||
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ITB by synergy of IBW and LHCD
• Ip = 200 kA, Bt = 2T, N|| = 2.35
• LHW: near on-axis current drive in target plasma
• IBW: 27MHz, off-axis heating ~ 0.5a
• Similar profiles as in IBW heating
• Strong gradient in pressure ~0.5a
• Improved particle and energy confinement
ITB
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H89*N > 3, Te(0) > 3keV by high power
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80% non-inductive current by IBW+LHWIp = 120 kA, Bt = 1.8 T, Vloop = 0.25 V, Te(0) = 2.2keV, ne(0) = 2xE19 /m3
H89*N > 2 for ~ 200E and fLHCD+fBS = 80%
fBS = 38%
fLHCD = 42%
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Collapse during IBW + LHCD
• Ip = 150 kA
• Bt = 1.8 T
• <ne>=1.5E19/m3
Collapse
• LHW: 200 kW
• IBW: 200 kW
(30MHz)
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Sawtooth instability during IBW + LHCD
• Ip = 200 kA
• Bt = 1.8 T
• <ne> = 1.8-3.2
xE19 /m3
• LHW: 540 kW
• IBW: 230 kW
(27MHz)
Sawtooth
oscillations
Proposal of sawtooth suppression by ECRH: D.Zhou at this meeting
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m=2 mode locking during IBW + LHCD
• Ip = 120 kA
• Bt = 1.7 T
• <ne>=1.2E19/m3
Mode locking
• LHW: 465 kW
• IBW: 220 kW
(27 MHz)
MHD suppression by modulated LHW: J.S.Mao at this meeting
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0.0 0.2 0.4 0.6 0.8 1.00.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
we(KJ)
time
59017
LHCDIBW
MHD behaviors in high beta plasmas (IBW+LHW)
Ip=125kA, ne=1.4x1013cm-3, Bt=1.75T, LHW=290KW, IBW=200KW (27MHz):Larger sawtooth m=2 mode disruption
Collapse
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Full non-inductive CD by IBW + LHCD
• Ip = 120 kA, Bt = 1.6 T, Vloop ~ 0 V
• ne(0)=1.5xE19 /m3, Te(0)=2.3 keV
• fLHCD = 73%, fBS = 27%
• LHW: 500 kW
• IBW: 200 kW(27MHz), near-axis heating @ high field r/a = -0.2
• Sawtooth free
• Improved confinement
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Conclusion
• Progress of long pulse operation is summarized for HT-7 tokamak. Candidates for advanced steady state operation is discussed;
• In the HT-7 superconducting tokamak, long-pulse discharge can be generated by synergy of high power LHCD (300-600 kW, 2.45 GHz) and high power IBW (200-350kW, 27 MHz) heating;
• MHD behaviors and thermal instabilities which limited the high performance operation was studied;
• For lower performance (Ip = 60 kA, Te(0) = 0.5-1 keV, <ne> = 0.5-1xE19 m-3) operation, more than 60 s of long pulse plasma was obtained by the LHCD (< 200 kW) in the HT-7 tokamak.
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Acknowledgement
• This work has been supported by the National Nature Science Foundation of China, contract number: 10005010.
• This work was also supported partly by JSPS-CAS Core-University Program on Plasma and Nuclear Fusion in 2003.
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