Status of test beam data analysis

… with emphasis on resistive coating studies

Progress and questions

1Meeting at CEA Saclay, 25 Jan 2010 Jörg Wotschack, CERN

Chambers tested P1: 350 x 450 mm2 standard, various strip pitches (reference

chamber) – OK P4: 400 x 1400 mm2 standard, 250 and 500 µm strip pitches,

strips 400 and 1000 mm long (looks OK, data not yet analyzed) S3: Standard 100 x 100 mm2; 250 µm strip pitch R3: as S3 + resistive paste on strips (150-200 µm, 10 MΩ),

covered with metallic pads (1 x 0.15 mm2) 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 2010 Jörg Wotschack, CERN

Test beam November 2009

P1 & R3 discharge studiesHV and currents vs particle rates

Chambers connected to ALTRO readoutCPA = 100 pF/strip

3

HV/Current of P1 – 19 Nov

4

≈ 3 hours

HV

me

sh (

V)

Cur

rent

me

sh (

µA

)

HV/Current of P1 and R3

5

Cur

rent

me

sh (

µA

)

HV

me

sh (

V)

Rate: 5–10 kHz/cm2

P1 R3

≈ 2.5 hours

HV/Current R3 – 20 Nov

6

HV

me

sh (

V)

Cur

rent

me

sh (

µA

)

Rate: ≈ 10 kHz/cm2 ≈20 kHz/cm2 Rate: ≈ 25 kHz/cm2

???

≈ 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➪ 1st lesson: Resistive layer must be made more reliable

8

1mm

x 0

.15

mm

pad

Strip

Muon Week, 11 Dec 2009 Joerg Wotschack (CERN)

PCB

MeshinsulatorResistive 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 55Fe source

Same gas mixture (Ar:CO2, 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: CPA = 1.8 pF (!?) …..

some surprises Started with S3 (no resistive coating)Muon Week, 11 Dec 2009 Joerg Wotschack (CERN) 10

S3 (standard MM w/o resistive layer)

Muon Week, 11 Dec 2009 Joerg Wotschack (CERN) 11

S3

Gain = 103 Gain = 104

σ =20% FWHM

55Fe spectrum

HVmesh = 535 VAr:CO2 85:15

S3 + R3 (55Fe source data)

Muon Week, 11 Dec 2009 Joerg Wotschack (CERN) 12

S3

R3

Rate effect and local variations

13Muon Week, 11 Dec 2009 Joerg Wotschack (CERN)

R3 (h5)

1

2

3

54

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➪ 2nd 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 2009 Joerg Wotschack (CERN)

S3 local response variations

15

1

2

3

54

Muon Week, 11 Dec 2009 Joerg Wotschack (CERN)

The response of R3 vs S3

16

Gain = 104Gain = 103

Muon Week, 11 Dec 2009 Joerg 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 2010 Jörg Wotschack, CERN 17

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 2010 Jörg Wotschack, CERN 18

PCB

Resistive pasteInsulator

≈ 50 µm

1mm

x 0

.15

mm

pad

Mesh

R5 spectra

Meeting at CEA Saclay, 25 Jan 2010 Jörg Wotschack, CERN 19

Gain = 5000 10000

S3 (570 V)

R5: first observations

First measurements of R5 (55Fe source) Sparking starts at HVmesh ≈ 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 2010 Jörg Wotschack, CERN 20

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 2010 Jörg Wotschack, CERN 21