Parallel Structure of Edge Turbulence S. Zweben, J. Terry, O. Grulke, D. Stotler, E. Marmar, M. Greenwald, J. Myra, D. D’Ippolito, 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

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)

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)