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SUNIST- Sino UNIted Spherical Tokamak

Preliminary experiment of plasma current startup by ECR wave on SUNIST spherical tokamak

HE Yexi, ZHANG Liang, *FENG Chunhua, FU Hongjun, GAO Zhe, TAN Yi, WANG Wenhao, *WANG Long, *YANG Xuanzong, XIE Lifeng

yexihe@mail.tsinghua.edu.cn, 86-10-62791874 (o), 86-10-62782658 (fax)

SUNIST United LaboratoryDepartment of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China

*Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China

The 3rd IAEA TCM on Spherical Torus and the 11th STW, St. Petersburg

This work was supported by JSPS-CAS Core-University Program on Plasma and Nuclear Fusion, the National Nature and Science Fund of China (Grant numbers: 10275041 and 10375089) , and International Atomic Energy Agency (Research contract No. 12935/R0) .

OUTLINE

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SUNIST spherical tokamak

Preliminary result

Remained questions

SUNIST United Laboratory

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SUNIST United Laboratory

founded in 2004, consists of Department of Engineering Physics, Tsinghus Unive

rsity (DEP) ; Institute of Physics, Chinese Academy of Science (IOP) and keeping

very close collaboration with Southwestern Institute of Physics (SWIP) and Instit

ute of Plasma Physics, Chinese Academy of Science (IPPAS).

Members of SUNIST LaboratoryHe, Yexi Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86-10-6

2791874(lab), 86-10-62782658(fax), yexihe@mail.tsinghua.edu.cn (e-mail)Yang, Xuanzong Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China 86-1

0-82649132(office), xzyang@aphy.iphy.ac.cn (e-mail)Wang, Long Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China 86-10-826

49137(office), wanglong@aphy.iphy.ac.cn (e-mail)Feng, Chunhua Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China 86-10-

82649132(office), chfeng@aphy.iphy.ac.cn (e-mail)Gao, Zhe Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86-10-

62776446(lab), 86-10-62782658(fax), gaozhe@mail.tsinghua.edu.cn (e-mail)Wang, Wenhao Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China,

86-10-62776446(lab), 86-10-62782658(fax), whwang@mail.tsinghua.edu.cn (e-mail)Xie, Lifeng Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86-1

0-62776446(lab), 86-10-62782658(fax), xielf@mail.tsinghua.edu.cn (e-mail)

SUNIST spherical tokamak

SUNIST spherical tokamak

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SUNIST main parameters:

major radius R 0.3m

minor radius a 0.23m

Aspect ratio A ~1.3

elongation κ ~1.6

toroidal field （ R0） BT 0.15T

plasma current IP 0.05MA

flux (double swing) ΔΦ 0.06Vs

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SUNIST spherical tokamak magnets and power supply

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coil turn L(H) R(m) ID(kA) VC(V) Capacitor(mF)

TF 24 508 4.72 9.4 200 2560(1280)

HF 236 519 17.8 13 3000 13.3/1280

EF 26 684 15 1.5 1200/120 1(2)/476(18.8)

Vacuum vessel and BV magnet assembling

toroidal magnet pre-assembling

Cross section and designed magnetic surface

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SUNIST spherical tokamak vacuum and vacuum vessel

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main parameters – vacuum vessel:outer diameter 1.2 m

inner diameter 0.13 m

height 1.2 m

volume ~ 1 m3

surface area ~ 2.3 m2

vacuum pumps: TMP (1000l//s)

Sputtering Ti pump (200l/s)

wall conditioning: baking: PTC（ Curie point 160 0C) glowing discharge,

siliconization

background pressure: ~ 6×10-5 Pa

leaking rate on cross seal: ≯?2×10-7 Pam3/s

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SUNIST spherical tokamak diagnostics and data acquisition

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Diagnosticselectromagnetic probes: 2 Rogowski probes, 9 flux loops (4 inside vessel)

15 2-D minor probes (13 in one poloidal cross section)

electrostatic probes: sets of movable 4 probes for Isi, Φ, and Vtoroidal

Data acquisition: 48 channel ADC: 32ch new, 16ch used in CT-6B

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Typical Discharge

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SUNIST spherical tokamak

Preliminary result

Remained questions

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Typical discharge of ECR startup

Preliminary result

Microwave: Pout < 100kW, t pulse ~ 30 ms, f = 2.45 GHz

background pressure ~ 110-4 Pascalhydrogen pressure ~ 110-2 Pascal during discharge

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Discharge with a group of plasma current peaks

Preliminary result

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Dependence of plasma current on vertical field

Preliminary result

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Electrode arrangement

Preliminary result

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Typical discharge with electrode assistance

Preliminary result

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Plasma current counteracted by electrode current

Preliminary result

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One special discharge with electrode assistance

Preliminary result

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Performances of preliminary ECR current startup

Preliminary result

Plasma current is just spikes ~ hundreds millisecond of bottom width

when the plasma existed during wave injecting from the lightening signal.

The dependence of driven IP on vertical field is consistent with

the toroidal plasma current by vertical field drift effect in ECR plasma.

IP could increase above 10% (Fig. 7) in co-direction,

IP would be counteracted more obviously (Fig.8), in counter-

direction with electrode discharge assistance.

We obtained one special discharge that the currents of plasma and

electrode are cutoff and extended to wave timescale.

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SUNIST spherical tokamak

Preliminary result

Remained questions

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Remained questions

Remained questions

This kind of plasma current spike is impossible

to develop to typical ST plasma current.

It is necessary to rearrange launch system of

microwave for better coupling to plasma.

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Remained questions

Remained questions

The discharge shown in Fig. 9 suggests that

there is a discharge regime with no limitations of

density cut off on ECR current startup and Ii-sat with

electrode discharge assistance.

The questions are why this regime exists and

how to find it for developing it from occasional event

to reproducible discharge.

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Remained questions

Remained questions

In preliminary experiments, the background

pressure of vacuum vessel increased from less

than 110-4 Pascal up to a balanced value, ~ 310-4

Pascal.

Driven plasma current decreased with the

increase of background pressure just like to scan

fuelling gas to higher pressure.

It is necessary to control wall condition for

further experiments.

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SUNIST- Sino UNIted Spherical Tokamak

Preliminary experiment of plasma current startup by ECR wave on SUNIST spherical tokamak

THANKS

The 3rd IAEA TCM on Spherical Torus and the 11th STW, St. Petersburg

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about central solenoid - Is it impossible to keep?

A questions

hard mode save mode

too high J CS,then stress,thermal load in high neutron

moderate J CS, just operating very short time

Impossible to keep ?

problem

operation mode

conclusion