Influence of a fast electron component on the plasma sheath structure at the inside of the tunnel probe

The possible influence of a small population of suprathermal electrons on the tunnel probe, a new kind of Langmuir probe for fast DC measurements of ion flux and electron temperature in the tokamak scrape-off layer, has been investigated by numerical simulations. It was found that suprathermal electrons can influence the ion current distribution over the inner plasma collecting surfaces of the tunnel probe, and thus influence tunnel probe Te measurements. The ion current distribution depends on the structure of the Debye and the magnetic sheath inside the tunnel probe. Therefore, we make here a first attempt at investigating the influence of suprathermal electrons on the scaling of those sheaths. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)