Status of the TPG

1. Status of the TPG E.Radicioni MICE coll. Meeting - RAL, 27-29 Oct. 2004

2. Outline • Recall of the main characteristics • Construction and operation • First of the detector behavior • Design aspects • Electronics • Field-cage • Gas • Background E.Radicioni

3. The TPG is a cylindrical TPC equipped with GEM amplification and a special high-resolution pad-plane • TPCs with GEMs are actively studied by several groups around the world in view of the linear collider experiments. • The novelty of the TPG consists in the pad-plane, where projective readout promises high granularity with a reduced number of channels • Dedicated design choices for MICE were • the dimensions (100cm length, 30cm diameter) to fit into the tracker magnet • The gas (He) chosen because of its low conversion probability E.Radicioni

4. B E Construction solenoid GEM stage drift volume field cage read-out plane E.Radicioni

5. The GEM foil • Triple-layer structure • Each layer divided in 8 regions, independently powered • Max amplification depends on gas and HV. With good gas it can be as high as 106.\ E.Radicioni

6. The hexaboard • ~710000 hexagonal pads • size: 300 mm • pitch: 500 mm • grouped into strips along 3 coordinates at 120 degrees (u, v, w) running at different depths E.Radicioni

7. Strips and pads E.Radicioni

8. 300 mm 500 mm E.Radicioni

9. Spot the error … and correct it! E.Radicioni

10. Hexaboard quality, from this: E.Radicioni

11. … to this: E.Radicioni

12. Support structures • outer metal ring • o-rings for gas tightness • stiffener plate • GEMs support rings • guard ring 5 4 2 3 1 E.Radicioni

13. E.Radicioni

14. Assembling the detector E.Radicioni

15. E.Radicioni

16. E.Radicioni

17. The dream team at work E.Radicioni

18. Last computations and timing checks … E.Radicioni

19. ... what is this detector trying to tell us ??? E.Radicioni

20. 55Fe source calibration • Absolute energy, equalization • Preamp gain calibration is not included yet • First indications are • Despite the lack of gain equalization, the energy resolution is already quite good • The plots are very sensitive to the cuts on cluster size, as expected from a properly working detector E.Radicioni

21. 55Fe source • “beam profile” • Unconnected strips • Ill electronic channels • Dead • Noisy E.Radicioni

22. Capability of seeing detector structures • 55Fe source illuminates the center of the pad plane • Large lines: spacer grid in between the GEMs: 2mm large • Thin lines: non-working electronics channels E.Radicioni

23. 55Fe source All clusters ≥2 strips ≥3 strips E.Radicioni

24. U,V vs. W correlations • out-of-line events are due to lack of gain calibration • Correlation is important: it can be exploited as an additional tool for getting rid of fake combinations • In addition to the use of the 3rd projection • Compass is able to reject (almost all) fakes by this technique TPG COMPASS E.Radicioni

25. Low energy tracks • 500 samples @10MHz • Ar/CO2 90/10, 10cm/s  total 50cm drift path • e- from Sr source • B=0.07T (1/10 nominal) • Color code gives charge amplitude E.Radicioni

26. 2 MeV/c electron in B=0.07T • Transverse diffusion spreads the charge E.Radicioni

27. Intrinsic resolution • 55Fe X-ray conversion position can be determined by 2 projections, then cross-checked with the 3rd one. • The intrinsic resolution is VERY promising • This has been obtained with a 3cm drift cell. • Actual resolution over longer drift depends on gas properties. U+V vs. W resolution ~40µm E.Radicioni

28. Design improvements • Electronics • Ingredients for good resolution • Gas choice • Discussion on overall parameters • A compact emittometer, alias TPG ? E.Radicioni

29. Electronics • New electronics from ALICE • Higher integration • Total (including DAQ) 10 CHF / channel • Digitization is close to detector (less noise) • Data get out from the detector on a few optical fibers (elegant, simple) • Large range of possible sampling frequencies up to 40 MHz. E.Radicioni

30. 4cards 16 ch ALTRO EVOLUTION 4 PQFP 100 8 SSOP 28 24 mm 135 mm 20 mm Integrated ADCs 1998 CHANNELS / CHIP: 1 POWER / CH: 120mW PRICE / CH: 50CHF 1999 CHANNELS / CHIP: 4 POWER / CH: 80mW PRICE / CH: 8CHF 2001 CHANNELS / CHIP: 1 POWER / CH: 16mW PRICE / CH: 5CHF

31. BC II BC I TCF Digital Conditioning of the TPC Signal EV 1 EV 2 EV 1 EV 2 EV 3 EV 3 ADC EV 1 EV 1 EV 2 EV 2 EV 3 EV 3

32. Momentum resolution • Position resolution is driven by • Readout pitch (fixed) • Diffusion in gas • Ionization and gain • Gas choice is a key point: we should look for larger gain and ionization and smaller diffusions. • Momentum resolution is driven by • Position resolution • Number of available points • From the simple Glukstern formula: 50 points give dp/p resolution factor only 1.5 better than 20 points. • If more distant points are affected by more diffusion, we should really consider limiting the number of points and the drift length. E.Radicioni

33. Gas choice E.Radicioni

34. Shorter field-cage? E.Radicioni

35. Tracks and Background in the short TPG • Intrinsic occupancy limit of the detector: N.strips/cluster size  ~ 200 • By exploiting correlations (a-la-compass) one could maybe do better • 1 muon per s  6 tracks in one “image” • Number of background tracks (normalized per MHz imput photons) ~ 0.013 MHz-1 • Quoting Rikard’s computations: 22MHz of photons entering the tracker volume in the upstream spectrometer  if this rate is OK there will not be any trouble. • Photon conversion in the HV membrane could account to the same number as conversions in gas  not much of a difference. E.Radicioni

36. Conclusions • The TPG detector is operational in the HARP test-bed • Placed an order for 2000 channels of the new electronics • First results indicate performances at the expected level or better • Several design parameters can be reviewed • Better gas choice  better resolution • Shorter detector  less material, straightforward construction, compact, could stay in shorter solenoid. • Faster drift time  less X-ray background • Better resolution • More results from beam tests in the near future E.Radicioni