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

Preliminary experiment of current startup by ECR wave on SUNIST spherical

HE Yexi, ZHANG Liang, *FENG Chunhua, FU Hongjun, GAO Zhe, TAN Yi, WANG Wenhao, *WANG Long, *YANG Xuanzong, XIE Lifeng [email protected], 86-10-62791874 (o), 86-10-62782658 (fax) SUNIST United Laboratory Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China *Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China

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

SUNIST- Sino UNIted UNISTSUNISTUNISTSUNIST

OUTLINE

SUNIST spherical tokamak

Preliminary result

Remained questions UNISTSUNISTUNISTSUNIST SUNIST spherical tokamak

SUNIST United Laboratory

SUNIST United Laboratory founded in 2004, consists of Department of Engineering Physics, Tsinghus University (DEP) ; Institute of Physics, Chinese Academy of Science (IOP) and keeping very close collaboration with Southwestern Institute of Physics (SWIP) and Institute of Plasma Physics, Chinese Academy of Science (IPPAS). Members of SUNIST Laboratory He, Yexi Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86-10- 62791874(lab), 86-10-62782658(fax), [email protected] (e-mail) Yang, Xuanzong Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China 86-10- 82649132(office), [email protected] (e-mail) Wang, Long Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China 86-10- 82649137(office), [email protected] (e-mail) Feng, Chunhua Institute of Physics, Chinese Academy of Science, Beijing 100080, P.R.China 86-10- 82649132(office), [email protected] (e-mail) Gao, Zhe Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86-10- 62776446(lab), 86-10-62782658(fax), [email protected] (e-mail) Wang, Wenhao Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86-10-62776446(lab), 86-10-62782658(fax), [email protected] (e-mail) Xie, Lifeng Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86- 10-62776446(lab), 86-10-62782658(fax), [email protected] (e-mail) SUNISTSUNIST SUNIST spherical tokamak

SUNIST spherical tokamak

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 UNISTSUNIST UNISTSUNIST SUNIST spherical tokamak

SUNIST spherical tokamak magnets and power supply

Vacuum vessel and BV magnet assembling toroidal magnet pre-assembling

Cross section and designed magnetic surface

coil turn L(μH) R(mΩ) 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) SUNISTSUNIST SUNIST spherical tokamak

SUNIST spherical tokamak vacuum and vacuum vessel

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

-5 background pressure: ~ 6×10 Pa -7 3 leaking rate on cross seal: ≯2×10 Pam /s SUNISTSUNIST SUNIST spherical tokamak

SUNIST spherical tokamak diagnostics and data acquisition Diagnostics electromagnetic 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 SUNISTSUNIST SUNIST spherical tokamak

Typical Discharge UNISTSUNISTUNISTSUNIST

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SUNIST spherical tokamak Preliminary result Remained questions SUNISTSUNIST Preliminary result

Typical discharge of ECR startup

Microwave: Pout < 100kW, t pulse ~ 30 ms, f = 2.45 GHz background pressure ~ 1×10-4 Pascal hydrogen pressure ~ 1×10-2 Pascal during discharge SUNISTSUNIST Preliminary result

Discharge with a group of plasma current peaks SUNISTSUNIST Preliminary result

Dependence of plasma current on vertical field SUNISTSUNIST Preliminary result

Electrode arrangement SUNISTSUNIST Preliminary result

Typical discharge with electrode assistance SUNISTSUNIST Preliminary result

Plasma current counteracted by electrode current SUNISTSUNIST Preliminary result

One special discharge with electrode assistance SUNISTSUNIST Preliminary result

Performances of preliminary ECR current startup

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. UNISTSUNISTUNISTSUNIST

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SUNIST spherical tokamak Preliminary result Remained questions SUNISTSUNIST 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. SUNISTSUNIST 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. SUNISTSUNIST Remained questions

Remained questions

In preliminary experiments, the background pressure of vacuum vessel increased from less than 1×10-4 Pascal up to a balanced value, ~ 3×10-4 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. rd th SUNISTSUNIST The 3 IAEA TCM on Spherical Torus and the 11 STW, St. Petersburg

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

THANKS

SUNIST- Sino UNIted Spherical Tokamak SUNISTSUNIST A questions

about central solenoid - Is it impossible to keep?

hard mode save mode

too high J CS,then stress,thermal load in high Φ problem moderate J CS, just operating very short time

operation mode

conclusion Impossible to keep ?