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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: xgao@ipp.ac.cn)(e-mail: xgao@ipp.ac.cn)

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.