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Purity Monitors

Purity Monitors. By Patrick Swanson. Purpose. TPC is filled with liquid argon Needs to be pure If not, electrons will be eaten up by the other molecules. Use of photoelectric effect Depending on work function, photons kick out electrons. How it works. How it works.

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Purity Monitors

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  1. Purity Monitors By Patrick Swanson

  2. Purpose • TPC is filled with liquid argon • Needs to be pure • If not, electrons will be eaten up by the other molecules

  3. Use of photoelectric effect Depending on work function, photons kick out electrons How it works

  4. How it works • Light shined at a photocathode, starts to emit electrons • Potential difference applied across copper plates • Electrons emitted accelerated to anode and collected there

  5. How it works • Quantum efficiency of cathode must be measured so we know theoretical number of electrons emitted • Electrons drift to anode, current is measured

  6. How it works • Theoretical number of electrons emitted is known, compared to actual number received • If argon is impure, electrons will be eaten by molecules (e.g. water or oxygen) • Electrons absorbed will not get to anode • In TPC, no events would be recorded

  7. Why Argon? • Argon does not ionize or combine with other elements • Sending electrons through it doesn’t change any of its properties • Makes $en$e

  8. Light sources • Italian scientists (ICARUS) have performed a similar experiment • Fiber and flashlamp used as light source • We investigated a similar fiber

  9. The Fiber • Special quartz fiber used (others absorb UV wavelengths) • Fiber is brittle and may wear out, length may be a factor as well • Replacement in detector is difficult

  10. Different lengths of fiber tested Conclusion: more light absorbed by wire as length increases, or more light may escape Fiber tests

  11. Fiber tested in phototube, pulsed overnight Conclusion: Fiber does not wear out easily More fiber tests

  12. More fiber tests • Tested in phototube with filter (~255 nm), pulsed overnight • Conclusion: output voltage less than unfiltered, but still linear

  13. More fiber tests • Tested at cold temperature (in LN2)

  14. More fiber tests • Tested with filter in cold temperature • Conclusion: Filter makes big difference in output voltage, temperature does not

  15. Fiber test with gold cathode

  16. Conclusions on fiber • Fiber efficiency depends on length but not on temperature • Gives relatively small signal for the wavelengths we’re interested in

  17. Our Experiment • Is fiber or UV LED better? • Gold, gallium arsenide, silver, CsI, and niobium have all been used as cathodes • Many tests done with 255 nm and 355 nm LED’s, only the 255 is of interest since it is more energetic

  18. Thanks! • Thanks to Andrea Albert, Walter Jaskierny, Hans Jostlein, Jamie Molaro, Stephen Pordes, and Leonel Villanueva

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