Quality%20tests%20on%20LNF%20chambers

1
Quality tests on LNF chambers

• We present a summary of the quality tests
  performed on the
• M3R3 chambers built in LNF.
• The tests are
• gas leakage
• dark current
• gain uniformity (with radioactive source)

C. Forti, E.Dane, D. Pinci, A. Sarti
2
Wire pads in hospital
During the source test, half of the M3R3
chambers had wire pads drawing current.
We have set up a system for simultaneous
conditioning of 6 chambers. The chambers are
flown in parallel with a premixed bottle of the
standard mixture (20 CF4). The flow rate is one
volume every1-3 hrs. The goal is to perform a
complete conditioning of all chambers produced,
in particular to recover all pads in hospital.
Up to now, we have conditioned 5 chambers (over
56 produced). We require 0 nA _at_ 2.8 kV but try to
push up to 2.85 kV, so that during the source
test _at_ 2.75 kV we have no risk of discharges.
All wire pads in hospital (drawing current) in
the 5 chambers have been recovered. This confirms
that the presence of the hospitals was due
essentially to the fact that we pushed the
chambers up to 2.75 kV too early (in order to
perform the source test).
3
Chamber uniformity and HV equalization
The usual requirement is 95 of the gap area in
the range G0/1.25 lt G lt G01.25
Since the current measured with the radioactive
source is proportional to the gas gain and known
that for DV105 Volt the gain doubles, the
requirement above translates in a 34 Volt
window, but we know that the plateau width
is 170 V both in M1 and M2-M5 regions.

• The requirement above is appropriate to
  guarantee that all
• detectors are in the range imposed by the minimum
  efficiency
• and the maximum cluster size ?
• Do we need to set a different HV to each gap ?

I will show a preliminary analysis on 36 LNF
chambers to provide an answer to these questions.
C. Forti, D. Pinci LHCb Muon Roma I - 27-jul-04
4
Method for uniformity studies
For each chamber we have
For each gap we have the current in 48x3 cells
The gap uniformity is given by the current range
of 95 of the cells lt I gt/F lt I(95) lt lt I gtF
(where ltIgt is the average current in the
gap) From F we find a voltage range DV where DV
(lnF/ln2)105
5
Uniformity inside each bigap
2/72 bigaps of 2 ch. with DV gt 50 V
10/72 bigaps of 7 ch. with DV gt 34 V
DV gt 50 V 2 chambers over 36 DV gt 40 V 4
chambers over 36 DV gt 34 V 7 chambers over 36
6
New criteria for chamber classification
After the measurement of a set of chambers, we
know the average current in gaps and bigaps. For
example, after measuring 36 chambers in LNF with
a radioactive source, we have lt I(gap) gt215 nA
and lt I(bigap) gt 430 nA.
First, we define some requirements on the average
currents (or gains) A. For each gap i of a
chamber, the average current I(i) must satisfy lt
I(gap) gt/2 lt I(i) lt lt I(gap) gt2 (equivalent to
105 V range)   For each bigap j of a chamber,
the average current I(j) must satisfy B. lt
I(bigap) gt/1.5 lt I(i) lt lt I(bigap) gt1.5
(equivalent to 60 V range) These criteria can
be important in case it will not be possible to
set a different HV value to each gap.
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New criteria for chamber classification (II)
Then, we define some requirements on the gain
spread C1. in both double gaps - F1.3 (or
DV40 V) over at least 95 of the chamber area. -
Flt1.5 (or DVlt60 V) over 100 of the chamber
area. C2. the chamber fails test C1 but, in both
double gaps - F1.5 (or DV60 V) over at least
95 of the chamber area - Flt1.7 (or DVlt80 V) over
100 of the chamber area.   C3. If the chamber
fails test C2 but, in both double gaps - F1.7
(or DV80 V) over at least 95 of the chamber area
a. The chamber is GOOD if it satisfies
requirements A, B, C1   b. The chamber is
accepted as a SPARE if it satisfies
requirements A, B, C2.   c. The chamber is
accepted as a RESERVE if it satisfies A, B, C3
requirements. These chambers can be used in case
of unforeseen problems.
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Summary of results
56 M3R3 chambers built on 3-sept-04
Gas leak requirement DPlt2 mbar/h 44 ch.
measured / 2 with DPgt5 mbar/h / 2 with DP2.3-3.5
mbar/hr We believe gt2 chambers can be recovered
?2 rejected/44 built
Hospitals over 44 chambers switched on - 21
without hospitals since beginning - 5 have been
conditioned and are OK - 4 are under
conditioning 14 will be conditioned
Gain uniformity testover 40 chambers
measured 33 GOOD / 7 SPARE ?the requirement C1.
in both double gaps - F1.3 (or DV40 V) over at
least 95 of the chamber area. ? - Flt1.5 (or
DVlt60 V) over 100 of the chamber area. is too
severe
9
Spare transparencies follow
10
Gas leakage scheme of the system

• Overpressure is applied to two chambers
• Isolated reference volume (for the absolute
  method)
• Sensor of external parameter (Temperature and
  Pressure)
• Difference of DP Sensor_1 and Sensor_2 by
  software
• Second sensor is used in order to check the ref.
  chamber

E.Dane Roma 1
11
Gas leakage measurement procedure

• Apply to the chambers (test and ref.) an
  overpressure of 5 mbar
• Measure the drop of reference chamber and
  chamber to test
• Test length 1 hour

Drop of chamber to test
Drop of reference chamber
External temp and pressure
Subtraction between test and reference
E.Dane Roma 1
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Picture of the system

• Chambers are put in a box in order to uniform the
  temperature
• The box is in the clean room

• In the clean room the temperature varies from 23
  C to 26 C

13
Reference Chamber

• Measure of the reference chamber at constant
  temperature (23.80.1C) use the bottle and is
  not sensitive to the external pressure

E.Dane Roma 1
14
Plateau width (M2-M5)
From testbeams plateau width170 V for bigaps
150 V for 4-gaps
Lower plateau limits 95 for bigap (2.53 kV) /
99 quadrigap (2.55 kV)
Upper limit cluster size in quadrigap lt 1.2 ? HV
lt2.7 kV (calculated from oct03 results on the
bigaps)
2.62 0.75 kV
99
Testbeam oct. 03 BIGAP
GIF july 04 4-GAP
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Plateau width (M1)
FROM OCT03 (BIGAP) Upper limit cluster size
1.2 in bigap HV2.82 kV
FROM GIF Lower plateau limit e99 in
double-monogap ? HV2.65 kV
Work point 2.72 kV Plateau width 170 V
GIF july 04 DOUBLE-MONOGAP
Testbeam oct. 03 BIGAP
16
Compensation ofthe effect of the bent panel
Several panels are bent at the center. This
effect cannot be recovered during
chamber assembly.
However, if the bent panel is a layer 2 or 4
(pad-pad panel) in our R3 chambers, the bigap
uniformity is still good.
Ex. Of chamber 27 the panel between C and D is
bent but the effect is not visible on the bigap
current.
17
Compensation of bent panel effect (ch.27)
95 of the area of the bigap is in a current
range equivalent to DV around the average
current of the bigap lt I gt.
Even with the bent panel the voltage range of
CD is very small DV 15.8 V
18
No-compensation ofbent panel effect
C
Ex. of chamber 31 here the dependences of the
current on the wire pad number are similar in
gaps C and D, so there is no compensation.
D
CD
19
No-compensation of bent panel effect (ch.31)
Even in this bad case, we have that 95 of the
CD area is within 33.8 Volt from the average
current. This is equivalent to the
requirement ltIgt/1.25 lt I(95) lt ltIgt1.25
20
Uniformity inside each gap
8/144 gaps of 7 ch. with DV gt 50 V
40/144 gaps with DV gt 34 V
50 Volt
34 Volt
The gap uniformity does not profit
of compensation effect it provides a pessimistic
result.
21
Compensation of 2 adj. Gaps (ch.7)
A
B
AB
22
Equalization of the average gap gain
For each gap we find the shift DV required to
align its own average current with the
average current of all the gaps together ltIgt215
nA
HV system with 3 HV HV0 , HV0 D D 29 V from
minimization
HV system with 5 HV HV0 , HV0 D, HV0 2D D
20 V from minimization
23
Equalization of the average gap gain
Without equalization all gaps at same HV
This is the voltage spread DV in each gap to
guarantee that 95 of the gap area is within
DV from the average of all the gap currents
ltIgt215 nA
It is evident that we must set the HV of each gap
to align its gain to the average gain.
24
Effect of equalization
Percentage of bigaps within a certain range from
the average current of all bigaps. HV systems
with 1,3,5 HV values hospital are compared.
150 V
25
Effect of equalization
Percentage of BAD bigaps out of a certain DV
range from the average current.
In first column only the effect of intrisic
uniformity of the bigap. In other columns the
range DV is defined around the average current of
all bigaps (i.e. from the HV working point). 1 HV
means that all gaps are set at the same HV (no
equalization)
Uniformity 1 HV 3 HV 5 HV
DV gt 34 13.9 43 26 21
DV gt 50 2.8 18 10 7
18 - 2.8 is the effect of the spread of the
average bigap currents (next slide).
The advantage of 5HV with respect to 3HV is poor
(few percent).
26
Effect of equalization spread of the ltIgtof the
bigaps
ltIgt 2 s
No equalization
Band ltIgt/1.25 lt I lt ltIgt1.25
Equalization with 3 HV
Equalization with 5 HV
27
Set of HV values including M1
Working point from testbeams for M1 HV2.72 kV /
M2-M52.62 kV
Set of HV values in a 3 HV equalization system
M1 2690 2720 2750
M2-M5 2590 2620 2650
In this configuration, 6 HV values hospital are
needed
Set of HV values in a 5 HV equalization system
(not needed)
M1 2680 2700 2720 2740 2760
M2-M5 2580 2600 2620 2640 2660