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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:

  • Metal wall [6] [7]
  • Boron-coated wall [8] (starting 2002)
  • Lithium-coated wall [9] [10] [11](starting 2007)

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
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