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Design of Coaxial Helicity Injection on SUNIST

SUNIST. Design of Coaxial Helicity Injection on SUNIST. Li ZENG Department of Engineering Physics, Tsinghua University Cl01@mails.tsinghua.edu.cn Supervised by Professor Yexi HE. SUNIST. Outline. Configuration of SUNIST (Sino UNIted Spherical Tokamak )

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Design of Coaxial Helicity Injection on SUNIST

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  1. SUNIST Design of Coaxial Helicity Injection on SUNIST Li ZENG Department of Engineering Physics, Tsinghua University Cl01@mails.tsinghua.edu.cn Supervised by Professor Yexi HE

  2. SUNIST Outline Configuration of SUNIST (Sino UNIted Spherical Tokamak ) • Some important issues of CHI system design • Coaxial helicity injector on SUNIST • Conclusion

  3. SUNIST 1 Configuration of SUNIST • Main parameters: R~ 30 cm, r~ 23cm, natural elongation ~ 1.6， B0~ 0.15T, Ip~ 50kA • Main aims： basic characters of plasmas at low-aspect ratio; non-inductive heating and current startup • Recent experiment plan： routine ohmic inductive discharge

  4. SUNIST 2 Some issues of CHI system design2.1 Theory (I) • Magnetic helicity ： A measurement of the topological properties of the configuration ；more fundament than any specific geometrical property. • Definition: K=∫v A • B dv Where B =  A

  5. SUNIST 2 Some issues of CHI system design2.1 Theory (II) • Helicity in open and multiply connected volumes: relative helicity ：

  6. SUNIST 2 Some issues of CHI system design2.1 Theory (III) • In order to conserve the helicity in the volume, external helicity must be compensate the helicity dissipation. • The rate of helicity injection in open and multiply connected volumes:

  7. SUNIST 2 Some issues of CHI system design2.2 Conditions of injection effectively • Hypothesis: helicity balance and enery conservation; • Condtions（shown on right）

  8. SUNIST Some issues of CHI system design2.3 Typical CHI system in STs • Components of CHI system： bias field coil; insulated gaps； injector； absorber； DC power supply； fast valves； control system

  9. SUNIST 3 Coaxial helicity injector on SUNIST3.1 Impedance model of injector • Hypothesis: ideal conducting wall, force-free conduction, helicty balance • Mode:

  10. SUNIST 3 Coaxial helicity injector on SUNIST3.2 Supported experiment of impedance mode

  11. SUNIST 3 Coaxial helicity injector on SUNIST3.3 Impedance calculations • Range of parameters: resistivity Magnetic energy：4-12 kJ • Suitable impedance; 50-100 m ohm

  12. SUNIST 3 Coaxial helicity injector on SUNIST3.4 Injector on SUNIST • Injector flux:1.2 mWb; • Electrode material : spray-coat plasma-facing surfaces with a thin layer of tungsten. • Electrode distance:4 cm • electrodes:cone-shaped • Intrinsic impedance：50-100 m ohm； • Peaked current:>10 kA; • Threshold current of formation closed lines: ? kA

  13. SUNIST 3 Coaxial helicity injector on SUNIST3.3 Others • Rebuild of central conductor • Pre-ionization ? • Fast puff valves

  14. SUNIST 4 Conclusion • Impedance model of coaxial helicity injector： • Injector on SUNIST: • ECR pre-ionization assisted CHI non-inductive plasma initiation：

  15. SUNIST References • [1] Sykes A, High beta produced by neutral beam injection in the START (Small Tight Aspect Ratio Tokamak) spherical tokamak , Physics of Plasmas 4, 1997:1665-1671 • [2] Sykes A, Overview of recent spherical tokamak results, Plasma physics and controlled fusion 43, 2001: A127-A139 • [3] Akers RJ, Ahn JW, Appel LC, et al., H-mode access and performance in the Mega-Amp Spherical Tokamak, Physics of plasmas 9, 2002: 3919-3929 • [4] Gates DA., Bell MG. et al. Recent Progress on the National Spherical Torus Experiment (NSTX), 29th EPS Conference on Plasma Physics and Controlled. Fusion, Montreux, ECA Vol. 26B, 2001 • [5] Jarboe TR, Gu P, Izzo VA et al., Current drive experiments in the HIT-II spherical tokamak, Nuclear fusion 41, 2001:679-685 • [6] Taylor JB, Relaxation and magnetic reconnection in plasmas, Reviews of modern physics 58, 1986:741-763 • [7] McCollam KJ, Jarboe JR, Magnetic relaxation in coaxial helicity injection, Plamsa physics and controlled fusion 44, 2002:493-516 • [8] Cheng Zhang, Deng Zhou, Sizheng Zhu, Analysis of plasma current profile driven by coaxial helicity injection in a low aspect ratio tokamak, Nuclear fusion 41, 2001:1567-1573 • [9] Mitchell A Berger, Introduction to magnetic helciity,Plasma physics and controlled fusion 41, 2001:B167-B175

  16. SUNIST Thanks!

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