Gracefully lighting and keeping a plasma

[Gunnar Mein]

We have learned how to ignite a plasma in the 30-40 micron region with a relatively low voltage (say 1000 V). We are struggling with how to get to low pressure / high voltage from here. Keeping our turbo pump (Varian V70) from just going full bore is an artform, and once we start to lower the inflowing stream on the needle valve, the pump just insists on going all the way. We are pretty sure that going to 5 microns and then building up voltage, and then starting the gas stream (still working with air here) is not the way to go (walked down that path and cried and opened our hearts and wallets). So how does one get to plasma at higher voltages?

I have been looking through the FAQs for most of the evening, but would appreciate a pointer.

[Joe Gayo]

Do you have a gate valve between the TMP and the main chamber? A manual gate valve will help you throttle the pumping speed by reducing the input conductance.

Are you sure you have negative DC voltage? I noticed the diode orientation on the multiplier board and if I'm interpreting the board correctly, they are oriented correctly but are you sure they haven't failed shorted? AC will have a lower breakdown voltage.

Last, using hydrogen/deuterium will increase the breakdown voltage substantially. However, make sure to address the previous items first.

[Gunnar Mein]

We don't have a gate valve there - were never able to find one we could afford. No worries about the diodes - they were marked incorrectly on the board, but if you look at the ones actually in place, you will find those are correct.