Parallel Structure of Edge Turbulence

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Parallel Structure of Edge Turbulence S. Zweben,
J. Terry, O. Grulke, D. Stotler, E. Marmar, M.
Greenwald, J. Myra, D. DIppolito, M.
Umansky C-Mod Ideas Forum 12/2-3/04
Goal Determine whether edge turbulence has
any visible structure along the B field line
Method Use a side view of plasma with PSI-4
or PSI-5 cameras (not the normal GPI view) Run
time Can piggy back initially, perhaps on
pellet view
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Previous Results
Side view of toroidal vs. poloidal structure
of edge turbulence in C-Mod seems to have
parallel structure, as if emission were not
constant along a field line (as is expected)
20 cm
Could be a cause of partial decorrelation
found between GPI and probe along field lines
(Grulke)
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Possible C-Mod Experiments

• Put PSI-4 or -5 camera(s) at existing side
  views of C-Mod,
• probaby using a coherent fiber bundle
• Passively view the parallel structure vs.
  q(a), collisionality,
• RF power, spectral line (D, He, Ne ?), etc.
• Assuming this is real, try to identify
  cause
• nonlinear ion acoustic wave (Cs 10-20 cm /
  4 µsec) ?
• fast variations in local ion source (fed by
  turbulence) ?
• ionization instability (striations from
  radiation cooling) ?
• Try to perturb the plasma elsewhere along the
  field line
• and measure parallel propagation (e.g. with gas
• puff, pellet, LH, probe, RF or AE antenna, etc)