I measure the operating pressure with a wide range ion gauge that will go up to 50 microns and is calibrated for D2. It has fussy electronics, so the "head" stays in an anti static bag on a shelf until the end of a run. After I shut off the HV, I plug in the ion gauge electronics module and measure, after verifying that the reading from the convection gauge did not change after turning off the HV.
So equipped, here are the results of my 40 KV runs.
October 12, 2014
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Eg 40 KV
Ig 7 mA
Pressure 12.5 microns
Flow rate 4.0 sccm
40 bubbles over 5 mins at 20 cm distance
calculated isotropic neutron emission 569,000 n/s
I did not have time to do any more runs that day. I shut off the electrolyzer and closed the mass flow contoller , but left the vacuum system running holding the system at 3 x 10-6 torr so I would not have to go though baking out again when I had a chance to resume testing.
Oct 22, 2014
As long as the system is properly purged, after "walking it in" from standby I am now getting fairly consistent results. Here are my 1/2 meg plus results for today. Between each measurement, I kept the fusor "idling" at 35 KV and 3.0 sccm gas flow for 30 minutes while waiting for the bubble detector to reset.
Run #1
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Eg 40 KV
Ig 7 mA
Pressure 13.4 microns
Flow rate 3.7 sccm
36 bubbles over 5 mins at 20 cm distance
calculated isotropic neutron emission 517,000 n/s
Run #2
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Eg 40 KV
Ig 7 mA
Pressure 13.1 microns
Flow rate 3.8 sccm
37 bubbles over 5 mins at 20 cm distance
calculated isotropic neutron emission 526,000 n/s
Run #3
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Eg 40 KV
Ig 7 mA
Pressure 13.1 microns
Flow rate 5.0 sccm
42 bubbles over 5 mins at 20 cm distance
calculated isotropic neutron emission 577,000 n/s
That's about a 10% difference from best to worst of the three.