Trouble Making a Penning Ion Source

[sam2212]

Hi
I built penning ions source , works fine on lower vacuum, my issue is in high vacuum 1x10-4 or more, the plasma ignites in the supplied tube to the penning source not inside the chamber. Tried to isolate the gas supply with ceramic inlet, ( feedthrough metal metal => teflon tube=>ceramic =>chamber). Didn't work still plasma in the teflon, tried to ground the inlet and remove the ground still the same. My setup for the ion source:
Anode 5kv
Cathode 4.3kv
Extraction -300v
Gas H 0.5 sccm
Diameter of the feedthrough and teflon 2mm ID.
Any ideas?
Thanks for the help

 

[Astronuc]

the plasma ignites

The hydrogen gas is igniting (as in combustion) or arcing? If the former, it would seem one has an air (oxygen) leak, or free F through decomposition of teflon. H + F = HF is a fairly energetic reaction.

Is the Penning source a negative H^- ion supply?

 

[sam2212]

Not igniting as explosion. Like plasma. This happens in the tube. It's high vacuum no gases there. The plasma should happen inside the chamber not in the tube