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Characterization Update

Characterization Update. Slade J. Jokela. XPS Status. The hemispherical analyzer contains a 16 channel anode underneath a commercial MCP chevron pair. One channel (#9, near center) is completely dead

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Characterization Update

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  1. Characterization Update Slade J. Jokela

  2. XPS Status • The hemispherical analyzer contains a 16 channel anode underneath a commercial MCP chevron pair. • One channel (#9, near center) is completely dead • This channel was initially experiencing a very low count rate, but completely died after I removed the MCP module to examine it and after I checked the external amplifier, discriminator, counter circuits. • Other channels increased after the above examination and subsequent bake out of chamber and hemispherical analyzer.

  3. Troubleshooting • Amplifier Circuits • Three options: • Tie all 16 anodes together and run them back through all 16 amplifier circuits to see if they all give close to the same count rate • Set up a pulser to test each amplifier circuit • A little more difficult than it sounds as I need to protect the electronics from overvoltage (voltage divider or proper capacitor in series). • Ship the electronics back to the UK for testing at seller’s facility (PSP Vacuum).

  4. Troubleshooting • MCP Module • These MCPs were originally installed in 2000. They could stand to be replaced, but it’s not common for them to suddenly drop in count rate simply due to ageing. • Disassembly of MCP module risks shattering these MCPs, so I can’t check out the 2nd MCP or the anodes. • Resistance across each MCP is roughly 12 MOhm when tested in air. (didn’t check under vacuum yet). • Testing the electronics should be sufficient. If the problem isn’t there, then it’s here.

  5. SEY Progress • Identified reason for difficulty controlling beam current • 21 eV period • To understand where this comes from, I need to discuss my system setup

  6. Controlling Electron Beam Current Added recently for increased voltage resolution

  7. LV1 Addition • It was thought that the ripple was a result of poor voltage resolution on the Emission Grid (HV2) voltage source. • Partially true. I won’t be able to obtain very low beam current without a high resolution, high voltage source(es) • Real problem is the +/- 10V PCI reference card

  8. PCI Reference Card Test • Each arrow is 0.21V apart (21eV when applied to the HV1 source)

  9. Solution • Convert set voltage to nearest binary value • (-10 to +10 V range using 16 bits) • Measure voltage at each point • More accurate • I’ll do whichever one doesn’t require a complete rewrite of the Labview program, leaning towards a more accurate measurement.

  10. Some Recent(ish) Results

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