Gun Arc at 30 kV

• On Thursday 12/6/12 low-level radiation group requested SEM be operated at max voltage and current.
• I set the beam voltage to 30 kV. The system had not be operated above 10 kV for some time. Just as the voltage reached 30 kV I heard the "snap" of an arc. The gun went off, there were no error messages.
• I had trouble restarting the gun, I got "EHT Vac not ready" (see previous notes). Raising pressure, restarting PC no help. After putting electronics to standby and back to run, EHT Vac was good, gun started.
• Emission current almost doubled, from ~ 107 uA to ~ 170 uA. I was afraid filament had been damaged during arc, however the same feature was centered in the field of view, and it was possible to get similar image quality. 
• Robert Ribay from Zeiss happened to be working on the Supra, he looked at the image quality, did a quick alignment, and did not see serious problems.