TJ-II:Plasma Wall Interaction

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To condition the wall of the TJ-II vacuum vessel, a number of techniques is used, such as a baking system. [1]

Glow Discharge Cleaning

Glow discharge cleaning is routinely used at TJ-II. [2] [3]

Limiters

TJ-II is fitted with two mobile limiters. Nevertheless, the main interaction between the plasma and the wall occurs at the central "groove". [4]

Wall conditioning

TJ-II retractable Lithium evaporation oven in action

Careful control of wall conditions is essential for successful operation. [5]

The walls can be coated by various materials, using a set of 4 evaporation ovens: two fixed and two mounted on retractable manipulators. In the course of time, TJ-II has been operated with the following types of wall:

TJ-II was the first stellarator to be operated with Lithium-coated walls. The lithium coating has led to much improved density control.

References

  1. R. Carrasco, Hybrid baking system for the vacuum vessel of the Spanish stellarator TJ-II, Proc. 18th Symposium on Fusion Engineering (1999) 231-234
  2. D. Tafalla and F.L. Tabarés, Wall conditioning and density control in the TJ-II stellarator, Journal of Nuclear Materials 290-293 (2001) 1195-1198
  3. D. Tafalla and F.L. Tabarés, Wall conditioning of TJ-II stellarator by glow discharge, Vacuum 64, Issues 3-4 (2002) 411-415
  4. J. Botija et al, Vacuum vessel, wall protection, pumping system and poloidal limiters of the Spanish stellarator TJ-II, 15th IEEE/NPSS Symposium on Fusion Engineering, Vol. 1 (1993) 529-532
  5. F.L. Tabarés et al, Density control and plasma edge characterisation of ECRH heated plasmas in the TJ-II stellarator, Journal of Nuclear Materials 290-293 (2001) 748-752
  6. F.L. Tabarés et al, Plasma–wall interaction in the Spanish stellarator TJ-II Diagnostics and first results, Journal of Nuclear Materials 266-269 (1999) 1273-1278
  7. F.L. Tabarés et al, Edge characteristics and global confinement of electron cyclotron resonance heated plasmas in the TJ-II Stellarator, Plasma Phys. Control. Fusion 43 (2001) 1023-1037
  8. D. Tafalla and F.L. Tabarés, First boronization of the TJ-II stellarator, Vacuum 67, Issues 3-4 (2002) 393-397
  9. F.L. Tabarés at al, Plasma performance and confinement in the TJ-II stellarator with lithium-coated walls, Plasma Phys. Control. Fusion 50 (2008) 124051
  10. J. Sánchez et al, Impact of lithium-coated walls on plasma performance in the TJ-II stellarator, Journal of Nuclear Materials 390-391 (2009) 852-857
  11. J. Sánchez et al, Confinement transitions in TJ-II under Li-coated wall conditions, Nucl. Fusion 49 (2009) 104018
  12. F.L. Tabarés, M. Ochando, D. Tafalla, F. Medina, K. McCarthy, J.M. Fontdecaba, M. Liniers, J. Guasp, E. Ascasíbar, T. Estrada, I. Pastor, TJ-II Team, Energy and Particle Balance Studies Under Full Boron and Lithium-Coated Walls in TJ-II, Contrib. Plasma Phys. 50, 6-7 (2010) 610–615