Sensitive Ion Pump Current Monitoring using an InHouse

Sensitive Ion Pump Current Monitoring using an In-House Built Ion Pump Power Supply Notice: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC 05 -06 OR 23177. J. Hansknecht, P. Adderley, A. Comer, M. L. Stutzman ABSTRACT Nitrogen 1 E+06 Ion Pump current (n. A) ~10 -10 Torr Full Scale Ion Pump Current vs. Extractor Gauge Pressure 1 E+07 Hydrogen 2003 Hydrogen data 1 E+05 hydrogen, Be. Cu, 4 k. V Manufacturer Data 1 E+04 1 E+03 UHV supply current during RGA scan. Sawtooth period corresponds to RGA scan frequency. 1 E+02 1 E+01 1 E+00 Discharge event in beamline 1 E-01 1 E-12 1 E-11 1 E-10 1 E-09 1 E-08 1 E-07 1 E-06 1 E-05 1 E-04 Pressure (Torr) RGA on and scanning Pressure and Current vs. Voltage 3, 0 E-10 90 2, 5 E-10 75 2, 0 E-10 60 1, 5 E-10 45 1, 0 E-10 30 5, 0 E-11 15 0, 0 E+00 0 0 2000 4000 6000 Pump Voltage (V) 8000 Ion pump (n. A) Onset of field emission during HV processing Pressure (Torr) Current (10 -10 A) UHV supplies monitor ion pump current to 0. 1 n. A, corresponding to ~10 -11 Torr Supplies used on CEBAF injector baked beamline monitor vacuum activity associated with • Onset of field emission during gun high voltage processing • Viewer discharge events when running from unanodized photocathode with beam halo Provide additional laboratory diagnostic for pressure in UHV systems Voltage dependence Lowering voltage past threshold results in reduction in pumping, evidenced by higher extractor gauge pressure RGA off