SUNIST 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 (o), (fax) SUNIST United Laboratory Department of Engineering Physics, Tsinghua University, Beijing , P.R.China *Institute of Physics, Chinese Academy of Science, Beijing , P.R.China The 3 rd IAEA TCM on Spherical Torus and the 11 th 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: and ), and International Atomic Energy Agency (Research contract No /R0).

OUTLINE UNIST SUNIST SUNIST spherical tokamak Preliminary result Remained questions

SUNIST United Laboratory UNIST SUNIST 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 , P.R.China, (lab), (fax), Yang, Xuanzong Institute of Physics, Chinese Academy of Science, Beijing , P.R.China (office), Wang, Long Institute of Physics, Chinese Academy of Science, Beijing , P.R.China (office), Feng, Chunhua Institute of Physics, Chinese Academy of Science, Beijing , P.R.China (office), Gao, Zhe Department of Engineering Physics, Tsinghua University, Beijing , P.R.China, (lab), (fax), Wang, Wenhao Department of Engineering Physics, Tsinghua University, Beijing , P.R.China, (lab), (fax), Xie, Lifeng Department of Engineering Physics, Tsinghua University, Beijing , P.R.China, (lab), (fax), SUNIST spherical tokamak

SUNIST SUNIST main parameters: major radiusR0.3 m minor radiusa0.23 m Aspect ratio A ~ 1.3 elongationκ ~ 1.6 toroidal field （ R 0 ） B T 0.15T plasma current I P 0.05 MA flux (double swing)ΔΦ0.06 Vs SUNIST spherical tokamak

SUNIST spherical tokamak magnets and power supply UNIST SUNIST coilturn L(  H)R(m  ) I D (kA)V C (V)Capacitor(mF) TF (1280) HF /1280 EF /1201(2)/476(18.8) Vacuum vessel and BV magnet assembling toroidal magnet pre-assembling Cross section and designed magnetic surface SUNIST spherical tokamak

SUNIST spherical tokamak vacuum and vacuum vessel SUNIST main parameters – vacuum vessel: outer diameter1.2m inner diameter0.13m height1.2m volume~ 1m 3 surface area~ 2.3m 2 vacuum pumps: TMP (1000l//s) Sputtering Ti pump (200l/s) wall conditioning: baking: PTC （ Curie point C) glowing discharge, siliconization background pressure: ~ 6×10 -5 P a leaking rate on cross seal: ≯ 2×10 -7 P a m 3 /s SUNIST spherical tokamak

SUNIST spherical tokamak diagnostics and data acquisition SUNIST 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 I si, Φ, and V toroidal Data acquisition : 48 channel ADC: 32ch new, 16ch used in CT-6B SUNIST spherical tokamak

SUNIST Typical Discharge SUNIST spherical tokamak

OUTLINE UNIST SUNIST SUNIST spherical tokamak Preliminary result Remained questions

SUNIST Typical discharge of ECR startup Preliminary result Microwave: P out < 100kW, t pulse ~ 30 ms, f = 2.45 GHz background pressure ~ 1  Pascal hydrogen pressure ~ 1  Pascal during discharge

SUNIST Discharge with a group of plasma current peaks Preliminary result

SUNIST Dependence of plasma current on vertical field Preliminary result

SUNIST Electrode arrangement Preliminary result

SUNIST Typical discharge with electrode assistance Preliminary result

SUNIST Plasma current counteracted by electrode current Preliminary result

SUNIST One special discharge with electrode assistance Preliminary result

SUNIST 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 I P on vertical field is consistent with the toroidal plasma current by vertical field drift effect in ECR plasma. I P could increase above 10% (Fig. 7) in co-direction, I P 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.

OUTLINE UNIST SUNIST SUNIST spherical tokamak Preliminary result Remained questions

SUNIST 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.

SUNIST 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 I i-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.

SUNIST Remained questions In preliminary experiments, the background pressure of vacuum vessel increased from less than 1  Pascal up to a balanced value, ~ 3  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.

SUNIST SUNIST- Sino UNIted Spherical Tokamak Preliminary experiment of plasma current startup by ECR wave on SUNIST spherical tokamak THANKS The 3 rd IAEA TCM on Spherical Torus and the 11 th STW, St. Petersburg

SUNIST about central solenoid - Is it impossible to keep? A questions hard modesave 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