Visualising the electron density structure of blobs and studying its possible effect on neutral turbulence

摘要: The electron density n e of turbulent coherent structures (blobs) has been measured at the edge plasma TJ-II stellarator using helium line ratio technique. A spectroscopic high-speed camera set-up allowed 2D imaging with spatial resolutions a few millimetres and exposure times down to 15 µs. have compared raw emission structures, which in principle should be similar due expected relation between both, although generally positive (negative) correspond blobs (holes), we see that shape is different some cases there even no correspondence all. possible explanation could neutral distribution, relates intensity e, varies on same spatio-temporal scale as turbulence. This would case if local variations holes regulated through ionisation, making it also within our experimental frequency ( 1 cm). To study this point simulate neutrals simple transport model reconstruct corresponding profiles experimentally obtained T radial profiles. We do for two cases: one where distribution stationary another atoms respond blob get locally depleted ionisation. Comparing simulated looking characteristic ionisation find clear indications fact slow thermal react fluctuations 10–100 kHz range, becoming turbulent.