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Summary of efforts to find a way to do combined field and photo emission experiments

Summary of efforts to find a way to do combined field and photo emission experiments . b ↔ next E b correlation.

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Summary of efforts to find a way to do combined field and photo emission experiments

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  1. Summary of efforts to find a way to do combined field and photo emission experiments

  2. b↔ next Eb correlation One of the biggest annoyances in experimental breakdown work is that we have to put a fudge factor of 30-100 in field emission measurements. We need to correct by such large factors consistently in dc and rf and for all materials we have ever measured. Conditioning seems to be achieved through reducing this factor and breakdown rate occurs because it increases. So it’s pretty important. rf

  3. However high  features are rarely, if ever, observed independently of field emission. Specifically the expected field enhancements on samples are not predicted from, say, electron microscope images.  is usually ascribed to a geometrical field enhancement - a tip. But it just doesn’t feel right to me.  = 30! The other term in the Fowler-Nordheim equation that could be varying locally to produce the equivalent effect on field emission is , the work function. We know that local work function changes occur due to foreign atoms (cesiated cathodes) and dislocations (etch pits).

  4. Fowler-Nordheim equation Can we do experiments to distinguish Efrom ?

  5. One way that we should be able to distinguish this is to measure field and photo emission on the same surface. My sincere thanks to Wei Gai of Argonne for pointing this out to me. Simplistic view: field emission depends on both Eand  while photo emission depends only on  . More subtle view: Presence of E actually changes the work function,

  6. How do we do the measurement? Field emission – like usual Photo emission – ideal would be a tunable laser with an energy range of say 1 to 5 eV. You could then plot total emission area with work function below that value as a function of work function. Where can we do such an experiment? rf photo injector – Wei has actually taken some data at Tsinghua University and has see photo-emission from copper using a 3.1 eV laser (private communication). The work function of copper is 4.5 eV so sorry Einstein. Unfortunately the corresponding field emission data was not usable. He hopes to continue measuring again in a few months. dc system – PSI has a 500 kV dc system with windows to shine in laser, plus assorted laser systems. They also have a emission imaging capability so we could see if the field and photo emission came from the same place. They have expressed some interest but nothing has taken off yet.

  7. Questions Do these measurements make sense? Can you make predictions/estimates for experimental results from your simulations? Can we do something cleverer than the equivalent of a tunable laser? We’ll probably not have more than a couple of wavelengths available for any experiment. Should we work on copper, our standard, or is there something with more complementary information?

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