PPAC in a ZDC

1. PPAC in a ZDC E. Norbeck University of Iowa Ed Norbeck U. of Iowa

2. What is a PPAC? (Parallel Plate Avalanche Counter) • Two flat, conductingplates with a little gas between them • Simple, low cost device • Can be radiation hard • Unaffected by heat, light • No electronics or photodetectors attached Ed Norbeck U. of Iowa

3. One plate can be divided into pixels to provide position resolution. We have studied a small PPAC as a single pixel of a detector for electromagnetic showers. Outline of talk • PPAC design for ZDC • Results from small PPAC • Use of PPACs in calorimeters Ed Norbeck U. of Iowa

4. Individual PPACs for ZDC Individual PPACscan be replaced if necessary Rigid coax and gas lines extend to top of TAN No organic materials in high-radiation region Beam In Ed Norbeck U. of Iowa

5. PPAC Array for ZDC EM Front-end Coax and gas lines extend out of radiation area No organic materials in high-radiation region Gives excellent position and time resolution. Beam In Ed Norbeck U. of Iowa

6. Single Pixel PPAC For Test With High-Energy Electrons • 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 Ed Norbeck U. of Iowa

7. Detail of gap and guard ring Ed Norbeck U. of Iowa

8. Test at home with a 7 mCi 137Cs source at the side of the detector Get up to 20 mV signals directly into 50 W coax Ed Norbeck U. of Iowa

9. Signal into coax with no amplifier Signal observed directly with fast scope Ed Norbeck U. of Iowa

10. We did not havehigh-energy electrons so we made them in situ from protons interacting near the front end of our tantalum cylinder. The showers had amplitudes as much as 40 mV Ed Norbeck U. of Iowa

11. -30 mV 1.62 ns FWHM Signal shape from shower This signal is so fast that one third of its amplitude is lost in 60 feet of standard RG58 coax. Ed Norbeck U. of Iowa

12. Typical Calorimeter Beam In The green is solid metal (W). Detectors that sample the showerare shown in blue. Ed Norbeck U. of Iowa

13. For electromagnetic showers in a high Z material the final deposition of most of the energy is by low energy electrons. If the plates of a PPAC are made of the same high Z material, the PPAC will provide a faithful sample of the energy deposition in the absorber. This does not work for thicker detectors because the lower energy electrons stop in the surface of the detector. The sampling fraction in a PPAC is small. The fractional error from sampling fluctuations is proportional to E-½. Fluctuations are not a problem if the showers have a large enough energy. Ed Norbeck U. of Iowa

14. High-energy showers with double PPAC (Shower passes through both PPACs) • Test with EM showers using 80 ps bunches of 7 GeV positrons from the Advanced Photon Source, at Argonne National Laboratory • Each bunch contained 3.6 x 1010 positrons • The showers were made by the beam halo striking the beam pipe. The energy was a small fraction of the 2 x 1020 eV in the bunch • This is still a very large energy! Ed Norbeck U. of Iowa

15. Double PPAC for testing energy resolution Ed Norbeck U. of Iowa

16. Energy Resolution Data of PPAC Test at ANL Ratio Efront to Eback is constant to within ± 2% Ed Norbeck U. of Iowa

17. CONCLUSIONS • Can connect PPACs directly into 50 W coax • Can test with g source on side PPACs for a calorimeter • Can be made radiation hard. • Can provide position information. • Have good energy resolution for high energy showers. • Have sub nanosecond time resolution. Ed Norbeck U. of Iowa

18. Ed Norbeck U. of Iowa