While testing out the new vacuum chamber I figured out that in contrast to the smaller vacuum chamber I could not reach the needed vacuum level to ignite the arc with 780VDC from the voltage doubler.
So I tried out whether it would be possible to melt the metal powder with a ZVS driver driven flyback transformer and in contrast to the single MOSFET flyback driver that I tried out before the ZVS driver could deliver enough power to melt the metal powder by its own.
Using the ZVS flyback would have the advantages, that it can melt the powder by its own so that the welder circuit would no longer be needed (only the flyback transformer, ZVS driver and a relay/mosfet), that it creates less EMI than the ignition coil arc starter and that it can ignite the arc by its own.
In term of the vacuum, I think it would be the best to keep it just low enough that the chamber stays sealed to keep everything simple. Doing so could make it possible to use just mechanical seals to bring the motion inside the chamber or even use stepper motors inside.