PPAC

1. PPAC Jonathan Olson University of Iowa Thesis Defense 8 April 2005

2. What have we done? • Investigate PPACs for use as a high energy particle detector • It should be useful in a calorimeter looking for shower particles

3. Example of low-pressure PPAC(Parallel Plate Avalanche Counter) • Two flat plates • Separated by1 mm • Filled with 100 torr hydrocarbon • 1000 V between plates

4. Non-homogenous Sampling Calorimeter Absorber sandwiched detectors

5. How it works • Particle enters the calorimeter • Particle develops a shower in the absorber material • Shower particles ionize the active gas medium in the detector • Avalanche results from ionization • We collect the ionization charge and try to determine the energy of the initial particle

6. A Look at the Detectors • “Alpha” PPAC • Double PPAC • Pixel PPAC (aka Electron PPAC) • New Pixel PPAC (just built, not yet used)

7. Alpha PPAC • First detector built • intended to study gas mixtures

8. Double PPAC Intended to test energy and time resolution

9. Single Pixel PPAC • Gap 0.6 mm 950 V across gap • Cathode 7X0 = 29 mm of tantalum • Area of anode is 1.0 cm2 • Guard ring to simulate neighboring pixels • Gas is isobutane at 120 torr Detail of gap and guard ring

10. How we readout the signal

11. Signal Shape ions ~1 mV in 500 ns electrons 37 mV in 1.6 ns

12. - - + + + - + - + + + - + + - - + + + - + + + + - + + Motion of the charges Anode Cathode

13. Afterpulses Delayed photo-ionization, Photoelectric emission, Electron detachment

14. 20 torr ethane 550 V 0.6 mm gap

15. Electromagnetic Shower Test (APS at ANL) PPAC under beam line to beam dump

16. Conditions of the beam at APS • 7 GeV positrons • 76 ps bunches • 2 Hz bunches • 3.6 x 1010 positrons/bunch. • The entire beam bunch has an energy of 2.5 x 1020 eV, or 2.5 x 108 TeV !!! • Outer halo of the beam hit the beam pipe. • Wall acted as an absorber

17. Energy Resolution at APS Ratio Efront to Eback is constant to within ± 2%

18. Hadronic Shower Test (MTBF at FNAL)

19. Fermilab’s Accelerator Chain

20. MTBF with the Pixel PPAC Shower from protons interacting near the front end of our tantalum cylinder. The showers had amplitudes as much as 40 mV

21. MTBF with the Pixel PPAC ~1 mV in 500 ns 37 mV in 1.6 ns

22. Gamma Source

28. Gases that have been used • C4H10 • C2H6 • CH4 Alkanes work well as avalanche gases • C3F8 • CF4 • C4F8 Additional benefit with perfluoro-analog • Argon -CO2 Can be operated at 1 atm pressure and low voltage (~1 kV)

29. Why Fluorocarbons? • Have fast electron drift velocity to give even faster signal than C4H10 • Molecules have high cross-section • No Hydrogen – so even less likely to have Texas Tower effect • Shouldn’t polymerize or age • No health or fire hazard • Can be easily purified and reused

30. Radiation Resistant A PPAC can be entirely metal and ceramic so that it will not be damaged by radiation levels that would melt scintillators

31. Speed vs Size For high speed, the RC time constant must be kept small. Only PPACs of small area are fast, ~1 ns R = 50 Ω (coax cable). C is the capacity between the plates Small PPAC ~1 ns C = .885 pF for 1 mm gap and area of 1 cm2Larger PPAC with C = 168 pF for 2 mm gap and area of 1 cm2 rise time ~5 ns fall time ~7 ns

32. Ion and electron signals with 2 mm spacing 168 pF Ion collection time is three times as long with the 1 mm spacing. 6.2ns 1.3ms 1.6ms Amplified signal using gamma source.Positive overshoot is from amplifier.

33. Individual PPAC to replace Scintillators Beam In Coax and gas lines extend out of radiation area No organic materials in high-radiation region Beam In

34. - + PPAC Readout Summing amplifier can be used to add PPAC signals, increasing the effective size of PPAC (without increasing the time width of the signals)

35. CONCLUSIONS PPACs • Have good energy resolution. • Have sub nanosecond time resolution. • Can be made radiation hard. • Can provide position information by making into pixels.