Inexpensive High Voltage Feedthrough
Inexpensive High Voltage Feedthrough
For those seeking an inexpensive high voltage feedthrough, the photos below show an example from a turbo pumped commercial instrument operating in the 10-7 torr range. The feedthroughs are "SKINTOP" brand Liquid-Tight Metallic Strain Relief Cable Glands tightened on RG217 coax. The strain reliefs are sold with NPT threads (among others). I haven't disassembled this one, so it may be sealed to the flange with something like TorrSeal. The RG217 is only rated for 7000 volts rms, but obviously handles much higher voltage DC. The application shown involves pulsed 30 kV DC, so the setup would likely handle significantly higher voltage continuous DC. On the inside, they extend the coax dielectric about three inches. The PE dielectric will likely not hold up long compared to alumina when exposed to plasma, but one could periodically cut off the end and extend new dielectric into the chamber. One could also put an alumina sleeve over the PE. The application shown is in a mass spectrometer. This approach is a much cheaper way to get high voltage into the chamber than using a standard conflat deramic feedthrough, if one could deal with the PE dielectric in a harsh environment.