Details

Autor(en) / Beteiligte

• Brunner, D.
• Umansky, M.V.
• LaBombard, B.
• Rognlien, T.D.

Titel

Divertor ‘death-ray’ explained: An artifact of a Langmuir probe operating at negative bias in a high-recycling divertor

Ist Teil von

• Journal of nuclear materials, 2013-07, Vol.438, p.S1196-S1199

Ort / Verlag

United States: Elsevier B.V

Erscheinungsjahr

2013

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The divertor ‘death-ray’, enhanced plasma pressure near the outer strike-point relative to ‘upstream’ values, was thought to correspond to axisymmetric increased divertor heat flux. Recent measurements on Alcator C-Mod show that the ‘death-ray’ is localized to biased Langmuir probes. Heat fluxes deduced from plasma-sheath theory and surface thermocouples agree in sheath-limited and moderate-recycling regimes. They diverge in high-recycling and detached regimes; surface thermocouples measure reduced heat flux while a ‘death-ray’ appears on Langmuir probes. The ‘death-ray’ is caused by the probe’s negative bias affecting the local flux tube. With the bias, electron heat flux to the probe surface is reduced. Thus, the local electron temperature is raised, enhancing neutral ionization and increasing the ion flux to the probe. The plasma fluid code UEDGE is used to simulate and reproduce many of the features of this integrated biased probe/divertor system.