1. Status of test beam data analysis … with emphasis on resistive coating studies Progress and questions 1Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN

2. Chambers tested  P1:350 x 450 mm 2 standard, various strip pitches (reference chamber) – OK  P4:400 x 1400 mm 2 standard, 250 and 500 µm strip pitches, strips 400 and 1000 mm long (looks OK, data not yet analyzed)  S3: Standard 100 x 100 mm 2 ; 250 µm strip pitch  R3:as S3 + resistive paste on strips (150-200 µm, 10 MΩ), covered with metallic pads (1 x 0.15 mm 2 )  R4: as S3 + Kapton layer with strips on both sides – failed  R5:as S3 + resistive paste (1 mm, 5 kΩ) and metallic pads above strips  MM (S1) + GEM/MM as double-stage amplification (talk by VP) 2Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN

3. Test beam November 2009 P1 & R3 discharge studies HV and currents vs particle rates Chambers connected to ALTRO readout C PA = 100 pF/strip 3

4. HV/Current of P1 – 19 Nov 4 ≈ 3 hours HV mesh (V) Current mesh (µA)

5. HV/Current of P1 and R3 5 Current mesh (µA) HV mesh (V) Rate: 5–10 kHz/cm 2 P1 R3 ≈ 2.5 hours

6. HV/Current R3 – 20 Nov 6 HV mesh (V) Current mesh (µA) Rate: ≈ 10 kHz/cm 2 ≈20 kHz/cm 2 Rate: ≈ 25 kHz/cm 2 ≈ 2 hours

7. R3 ‘short’ 7

8. Local damage of resistive layer  Resistive layer is locally damaged, induced by some large charge (Resistive paste not very homogeneous, manually applied)  Regions with lower resistance (or some defects) are affected first.  Once the resistive layer is locally damaged, sparks with higher currents develop at the affected pad ➪ 1 st lesson: Resistive layer must be made more reliable 8 1mm x 0.15 mm pad Strip Muon Week, 11 Dec 2009Joerg Wotschack (CERN) PCB Mesh insulator Resistive paste 200 µm 128 µm

9. R3 performance 9 We observe  Nice signals  Noise is OK, not much different from std MM But  Many events with no or very small signals  Low efficiency  ???

10. Test of R3 in lab with 55 Fe source Same gas mixture (Ar:CO 2, 85:15) as in H6  Try to understand the behaviour of R3  Measured pulse spectra  72 strips connected together -> single preamplifier + Ortec amplifier  Coupling capacitor: C PA = 1.8 pF (!?)  ….. some surprises  Started with S3 (no resistive coating) Muon Week, 11 Dec 2009Joerg Wotschack (CERN)10

11. S3 (standard MM w/o resistive layer) Muon Week, 11 Dec 2009Joerg Wotschack (CERN)11 S3 Gain = 10 3 Gain = 10 4 σ =20% FWHM 55 Fe spectrum HV mesh = 535 V Ar:CO2 85:15

12. S3 + R3 ( 55 Fe source data) Muon Week, 11 Dec 2009Joerg Wotschack (CERN)12 S3 R3

13. Rate effect and local variations 13Muon Week, 11 Dec 2009Joerg Wotschack (CERN) R3 (h5) 1 2 3 5 4

14. Likely explanation  Bad contact b/w small pads and resistive paste => large resistance  Charge build-up on pad  Reduced potential b/w mesh and pad => Smaller amplification ➪ 2 nd lesson: pads must have a reliable contact with resistive layer 14 Mesh insulator 1mm x 0.15 mm pad Strip PCB Resistive paste Muon Week, 11 Dec 2009Joerg Wotschack (CERN)

15. S3 local response variations 15 1 2 3 5 4 Muon Week, 11 Dec 2009Joerg Wotschack (CERN)

16. The response of R3 vs S3 16 Gain = 10 4 Gain = 10 3 Muon Week, 11 Dec 2009Joerg Wotschack (CERN) Q(R3) ≈ 0.8 x Q(S3) S3 R3 (h5) R3 (h3)

17. Conclusions on R3  R3 seems to almost do what we want, as long as it did not break  Signal almost as large as with non-resistive S3  Low efficiency  Technical problems  Bad pad connections  Inhomogeneity in resistivity => burned pads Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN17

18. R5  Similar to R3 but with more robust resistive layer and different technique (Rui’s talk)  R ≈ 5 kΩ Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN18 PCB Resistive paste Insulator ≈ 50 µm 1mm x 0.15 mm pad Mesh

19. R5 spectra Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN19 Gain = 5000 10000 S3 (570 V)

20. R5: first observations  First measurements of R5 ( 55 Fe source)  Sparking starts at HV mesh ≈ 560 V  Large currents (several µA)  Large HV drop (100–200 V)  R5 signal ≈2 x S3 signal  For comparison: R3 signal ≈ 0.8 x S3 signal  Charge resolution much worse than for S3 (and R3); escape peak not well separated Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN20

21. Conclusions & plans  Main problem is the spark problem  Quite a bit of progress … but  R5 is not yet the final solution (more in Rui’s talk)  Need more and more systematic studies of different chambers  Measure capacitances  Use well defined readout electronics  Spice simulation of different schemes would help  Looking forward to R6 Meeting at CEA Saclay, 25 Jan 2010Jörg Wotschack, CERN21