Journal of Fusion Energy

, Volume 28, Issue 2, pp 140–143 | Cite as

The Formation of a Tokamak-like Plasma in Initial Experiments Using an Outboard Plasma Gun Current Source

  • D. J. Battaglia
  • M. W. Bongard
  • R. J. Fonck
  • A. J. Redd
  • A. C. Sontag
Original Paper


Solenoid-free tokamak startup via point-source DC helicity injection is demonstrated on the Pegasus Toroidal Experiment using a high current density, low impurity plasma gun mounted near the outboard midplane. A threshold in the vacuum vertical magnetic field strength that allows the injected current filament to relax into a tokamak-like topology is observed. A simple 2-D model of the vacuum magnetic field suggests this threshold is the maximum field strength that allows a toroidally connected field null to form. Discharges with I p ≈ 17 kA are produced using less than 2 kA of injected current and no inductive drive. The tokamak-like discharges exhibit current decay times about five times longer than the injected current decay, expansion of the plasma into the vacuum region and a significant increase in the line-integrated density.


DC helicity injection Solenoid-free startup Plasma guns 



The authors thank E. Hinson, J. Cole, A. Robinson, and A. Wiersma for their assistance with Pegasus operations and G. Winz, B. Lewicki, B. Kujak-Ford for the design and construction of the outboard plasma gun system. This work supported by US DOE Grant DE-FG02-96ER54375.


  1. 1.
    Y.-K. Peng et al., Plasma Phys. Control. Fusion 47, 263 (2005)CrossRefGoogle Scholar
  2. 2.
    J.B. Taylor, Rev. Mod. Phys. 58, 741 (1986)CrossRefADSGoogle Scholar
  3. 3.
    M. Berger et al., Plasma Phys. Control. Fusion 41, 167 (1999)CrossRefADSGoogle Scholar
  4. 4.
    R. Raman et al., Nucl. Fusion 45, 15 (2005)CrossRefADSGoogle Scholar
  5. 5.
    R. Raman et al., Phys. Rev. Lett. 90, 075005 (2003)CrossRefADSGoogle Scholar
  6. 6.
    M. Ono et al., Phys. Rev. Lett. 59, 2165 (1987)CrossRefADSGoogle Scholar
  7. 7.
    D.S. Darrow et al., Phys. Fluids B 2, 1415 (1990)CrossRefADSGoogle Scholar
  8. 8.
    G. Fiskel et al., Plasma Sources Sci. Technol. 5, 78 (1996)CrossRefADSGoogle Scholar
  9. 9.
    D. Den Hartog et al., Plasma Sources Sci. Technol. 6, 492 (1997)CrossRefADSGoogle Scholar
  10. 10.
    G.D. Garstka et al., Phys. Plasmas 10, 1705 (2003)CrossRefADSGoogle Scholar
  11. 11.
    N.W. Eidietis et al., J. Fusion Energy 26, 43 (2007)CrossRefGoogle Scholar
  12. 12.
    A.J. Redd et al., will be published in this issue (2008)Google Scholar
  13. 13.
    C.R. Sovinec et al., Phys. Rev. Lett. 94, (2005)Google Scholar
  14. 14.
    N.W. Eidietis, Ph.D. Dissertation (University of Wisconsin – Madison, 2007)Google Scholar
  15. 15.
    I.H. Hutchinson, Principles of Plasma Diagnostics, 2nd edn. (Cambridge University Press, Cambridge, UK, 2002)Google Scholar

Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  • D. J. Battaglia
    • 1
  • M. W. Bongard
    • 1
  • R. J. Fonck
    • 1
  • A. J. Redd
    • 1
  • A. C. Sontag
    • 1
  1. 1.Department of Engineering PhysicsUniversity of Wisconsin – MadisonMadisonUSA

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