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First Look at FLASH Thick Target Test Beam (Jan 2004) Results

This study examines the results of the FLASH thick target test beam, focusing on the background measurements and target variation. The study suggests that the background is mainly dominated by neutrons and the maximum background level is around 30-40 p.e. at 107 electrons per pulse. The study also compares the background levels in different optical channels and concludes that the background level remains consistent regardless of the operating voltage.

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First Look at FLASH Thick Target Test Beam (Jan 2004) Results

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  1. First Look at FLASH Thick Target Test Beam (Jan 2004) Results The Alumina Underground Jan. 13, 2004

  2. Target Setup • Alumnia bricks are 6”x4”x2” • Assume 3” of alumina ~ 1 r.l. • Picture shows ~14 r.l. of target

  3. Target Setup • Target thickness reduced by removing bricks from the updtream end of pile • Picture shows ~10 r.l. target

  4. Background Measurement • Background measured using 6 “blind” PMT • These are located behind at least 30 r.l. of lead shielding from target • 2” and 4” optical channels alternately tried • Signals seen in time with beam, but many late hits. • ADC results analyzed using standard calibration of PMT from Stan Thomas

  5. Background at 2000V, 2” optical channel

  6. Background at 2000V, 2” optical channel

  7. Background at 2000V, 4” optical channel

  8. Background at 2000V, 4” optical channel

  9. Target variation • Worst case of background appears to be at 10 r.l. and only marginally (~10-15%) different from 14 r.l. • Average background level equivalent to ~30-40 p.e. at 107 e- per pulse and 10 r.l. • Decrease by ~30-40% from 10 r.l. to 6 r.l. • Minimal background at 2 r.l.

  10. Target variation (cont’d) • The variation of the background vs. target thickness is inconsistent with GEANT prediction for gamma background • + large number of late hits suggests we are probably dominated by neutrons • PMT4 calibration is probably off; the other 5 are quite consistent

  11. 2” and 4” optical channel comaprison

  12. 2” vs. 4” • Difference in background between 2” and 4” optical channel configuration is small (less than ~10-20%)

  13. Varying HV: 2000V vs. 1600V

  14. Varying HV: 2000V vs. 1200V

  15. HV variation • No Discernible HV variation in background level estimate…suggests that background is dominated by electrons from photo-cathode

  16. Conclusion • Background probably dominated by neutrons • Maximum background level is equivalent to ~30-40 p.e. at 107 electrons per pulse. • 2” and 4” optical channels give similar background levels • Equivalent background level does not change with HV between 1200-2000 V.

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