The 3 rd IAEA TCM on Spherical Torus and the 11 th STW, St. Petersburg Preliminary experiment of plasma current startup by ECR wave on 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) 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 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). - Sino UNIted Spherical Tokamak
UNIST OUTLINE spherical tokamak Preliminary result Remained questions
UNIST spherical tokamak United Laboratory 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 Laboratory He, Yexi Department of Engineering Physics, Tsinghua University, Beijing 100084, P.R.China, 86-10- 62791874(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 86-10- 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- 82649137(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, 86-10-62776446(lab), 86-10-62782658(fax), xielf@mail.tsinghua.edu.cn (e-mail)
spherical tokamak spherical tokamak main parameters: major radius R 0.3m minor radius a 0.23m Aspect ratio A ~1.3 elongation κ ~1.6 toroidal field (R 0 ) B T 0.15T plasma current I P 0.05MA flux (double swing) ΔΦ 0.06Vs
UNIST spherical tokamak 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) I D (ka) V C (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)
spherical tokamak 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 m 3 surface area ~ 2.3 m 2 vacuum pumps: TMP (1000l//s) Sputtering Ti pump (200l/s) wall conditioning: baking: PTC(Curie point 160 0 C) glowing discharge, siliconization background pressure: ~ 6 10-5 P a leaking rate on cross seal: 2 10-7 P a m 3 /s
spherical tokamak 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 I si, Φ, and V toroidal Data acquisition: 48 channel ADC: 32ch new, 16ch used in CT-6B
spherical tokamak Typical Discharge
UNIST OUTLINE spherical tokamak Preliminary result Remained questions
Preliminary result Typical discharge of ECR startup Microwave: P out < 100kW, t pulse ~ 30 ms, f = 2.45 GHz background pressure ~ 1 10-4 Pascal hydrogen pressure ~ 1 10-2 Pascal during discharge
Preliminary result Discharge with a group of plasma current peaks
Preliminary result Dependence of plasma current on vertical field
Preliminary result Electrode arrangement
Preliminary result Typical discharge with electrode assistance
Preliminary result Plasma current counteracted by electrode current
Preliminary result One special discharge with electrode assistance
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 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 counterdirection with electrode discharge assistance. We obtained one special discharge that the currents of plasma and electrode are cutoff and extended to wave timescale.
UNIST OUTLINE spherical tokamak Preliminary result Remained questions
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.
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 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.
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.
The 3 rd IAEA TCM on Spherical Torus and the 11 th STW, St. Petersburg Preliminary experiment of plasma current startup by ECR wave on spherical tokamak THANKS - Sino UNIted Spherical Tokamak
A questions about central solenoid - Is it impossible to keep? hard mode save mode problem too high J CS,then stress,thermal load in high Φ neutron moderate J CS, just operating very short time operation mode conclusion Impossible to keep?