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

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 ( 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

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

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

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

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

R3 ‘short’ 7

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

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  ???

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

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

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

Rate effect and local variations 13Muon Week, 11 Dec 2009Joerg Wotschack (CERN) R3 (h5)

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)

S3 local response variations Muon Week, 11 Dec 2009Joerg Wotschack (CERN)

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)

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

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

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

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

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