With the new modifications to the spellman supply, I can now run at up to 9mA grid current at up to 40kV. After pumping on a turbo station for about 14 hours, the fusor pressure is down to 3e-4 torr as measured on an ion gauge. Running the ion injectors at low power without any grid bias lowers the pressure to about 2.8e-4 torr, but then it will rise back up to 3e-4 when the ion sources are turned off, that seems to be the limit of my system due to gas permeation of the viton o-rings / out-gassing of internal plastic parts ant the low conduction rate of my vacuum system. I also suspect the boron nitride grid ceramic insulators on the grid are out-gassing when bombarded with plasma. During operation, the pressure will rise towards 1mTorr, but will pump down pretty fast after grid bias is turned off.
With the anode layer ion sources off, at 3e-4 torr, there is no measurable current draw from the grid at -40kv. The injectors will run perfectly at this pressure with enough plasma current to easily hit the 9mA limit of the spellman. The fusor maintains rock solid discharge stability with these sources on all the way down to the 3e-4torr minimum achieved pressure(for reference, there is no ballast inductor or resistor in series with the grid supply), by varying the ion source bias, the current into the grid may be controlled up to the 9mA max as limited by the power supply.
4e-4torr, 1ma, 40kv, 4 injectors on
5e-4torr, 1.3ma, 40kv, 4 injectors on
7e-4torr, 7ma, 40kv, 4 injectors on
Vacuum during operation