- Email: [email protected]
A simple, effective method of constructing insensitive regions in proportional and drift chambers
N U C L E A R I N S T R U M E N T S AND METHODS
156 ( 1 9 7 8 )
215-218 ; ©
N O R T H - H O L L A N D PUBLISHING CO.
A SIMPLE, EFFECTIVE METHOD OF CONSTRUCTING INSENSITIVE REGIONS IN PROPORTIONAL AND DRIFT CHAMBERS M. EDWARDS
Rutherlbrd Laboratory, Chilton, Didcot, Oxon, England
A simple, effective method of constructing insensitive regions in proportional and drift chambers is described. Such regions are needed when, as in the case of the chambers for the European Muon Collaboration, an intense beam passes through the chamber. The method described has the advantage that the region can be relatively easily moved. Results are presented showing the effectiveness of the insensitive region and the sharpness of the transition from live to dead regions.
1. Introduction The apparatus of the European Muon Collaboration 1) is shown in fig. 1, and contains many planes of proportional and drift chambers. Many of these chambers have the intense muon beam passing through them. The intensity of the muon beam is expected to reach 108 muons/pulse, each pulse is just under 1 s duration. In order to detect muon scattered through small angles, down to 0.5 °, it was decided not to build chambers with a physical hole in them, but to develop devices to make the chambers insensitive in the area through which the beam passed. Several techniques to achieve this are possible2), this paper describes the method used for the chambers PI, P2, P3, W6 and W7 in fig. 1, constructed at the Rutherford Laboratory. 2. Construction 2.1. PROPORTIONAL CHAMBERS The muon beam passing through the proportional chambers inside the forward spectrometer magnet, is expected to be between 100 and 120 mm in diameter. The size of the insensitive region was, therefore, chosen to be somewhat less than 120 mm diameter. The insensitive region is of very simple construction consisting o f ' b o x e s ' . Each 'box' consists of two circular pieces of 0.1 mm thick Kapton film held apart by a cylinder formed from similar film. A 'box' is shown in fig. 2. The holes in the Kapton cylinder are to allow free passage of gas through the volume of the 'box', obviating any possibility of the 'box' outgassing over a long period. The thickness of the 'box' is made equal to
the half gap of the chamber with a tolerance of _+0.05 mm. As the chamber is assembled one 'box' is inserted between each plane of wires. The 'boxes' are held in position by 3 spots of epoxy resin on the high-voltage wires. They are not glued to the signal wires. 2.2. DRIFT CHAMBERS
The insensitive regions for the drift chambers W6 and W7 a) are similar in construction, but are made rectangular not circular. The long dimension is made equal to the corresponding dimension of the insensitive areas required. The width is made 8 mm less than the distance between the potential and anode wires, since it was found experimentally that if the edge of the 'box' was less than 1 mm from the anode wire, that length of the anode wire near the 'box' was insensitive to particles on both sides. Hence the 'boxes' were inserted in the drift chamber to be at least 2 mm from the anode wire which was required to be sensitive on one side (see fig. 3). The thickness is made equal to the distance between the wire plane and the cathode plane. The muon beam passing through the drift chambers W6 and W7 is expected to be between 150 and 180 mm diameter. Since the distance between the potential wire and anode wire of these drift chambers is 60 mm, it was decided to construct insensitive regions 180 mm square. These regions are built up from six 'boxes' of 180 mm by 58 ram, three mounted on each cathode plane. The arrangement of mounting on the cathode plane is shown in fig. 3, with a similar set of three 'boxes' mounted on the facing cathode plane. Ill.
P L A N A R DRIFT CHAMBERS
216
M. EDWARDS
÷ g:
,':ii!i
i[i;I Ill II
T ._[
=; ;
Fig. 2. Box for proportional c h a m b e r s . PmENT~AL ANODE POTENT~At ANODE W~RE WfRE W~RE W~RE Z i, "~1 ~=====~
%
Fig. 3. Box for drift c h a m b e r s .
iL' ' Im~
3. Performance
Z
,\
-t
O
"6 ¢-, O
The first production model of both a W 6 drift chamber and a proportional chamber were tested in a high intensity extracted proton beam from the C E R N PS. The extracted proton beam, s o m e 101° protons per pulse, was attenuated by approximately 30 cm o f lead and then passed d o w n a relatively short beam line to the experimental area. D u e to shortness o f this beam line the proton beam in the area was accompanied by a large halo o f total intensity comparable to the beam. Fig. 4 s h o w s the arrangeDRIFT CHAMBER 3500x4200
/
e-
PROPORTIONAL CHAMBER
.o
i
+
i
1000 x 2024
iI !!
E
g
CA= RxR
.A: 0 CB'~"
Cc = 4 x 4
Co = 10 "lO
#
m
.......... i
r,,
Fig. 4. A r r a n g e m e n t in the test beam.
Y
CONSTRUCTING
INSENSITIVE
ment used in the area. CA and CB are two small scintillation counters (8 x 8 and 3 x 2 mm 2) mounted on a common remotely controlled two dimensional scanning table. Cc and CD are another pair of small counters ( 4 x 4 and 10x 10 mm 2) mounted on a second common scanning table. A coincidence between at least one counter on each scanning table was used to define a track through the system, and trigger the read-out system. With the proton beam passing through the centre of the insensitive region in the proportional and drift chambers the halo was used to check the sharpness of the edge of the insensitive region. The trigger counters were positioned above the insensitive region and, using the halo of the beam, the efficiency of the planes was measured as they were scanned down into the insensitive region. EDGE OF BOX
100~
o
~"
60
217
REGIONS
The resultant efficiency/position plot for the proportional chambers is shown in fig. 5. The pair of counters used were the 8 x 8 and 1 0 x l 0 m m 2 counters CA and Co. As can be seen, the drop in efficiency is very sharp. The counters CA and CD were not aligned vertically with the direction of the beam halo, thus effectively defining a rectangular area of the chamber 4 mm high by 8 mm wide. The exact profile of the area so defined was measured using histograms of the hits per wire in the proportional chamber. The result of unfolding this profile from the data of fig. 5 was that the efficiency drops from 90% to 10% in approximately 1 mm. Due to shortage of beam time, and to difficulties arising from the high flux of particles through the drift chamber, the testing of the insensitive region in the drift chamber was restricted to checks that detailed results obtained with a small prototype chamber were valid for the large production chamber. This small chamber was scanned across an electron beam from NINA at Daresbury. The beam was defined by a very thin (2 mm wide) counter. The chamber contained two orthogonal planes each equipped with a single 120x60 mm 2 'box', positioned as shown in fig. 6. The chamber
Z
EDGE OF BOX
u 4G
>. 80 CENTRE OF CHAMBER
20
4O 20 2~
'
~o
'
340
POSITION
38o
3OO
4~o
340 POSITION turn
mm
Fig. 5. Proportional chamber efficiency vs position. POTENTIAL WIRE
_
BOXES _ k , . . .
1017
,f
E[~-~ OF BOX
EDGE OF BOX
ANODE WIRE I POTENTIAL WIRE
b
ANODE WIRE 2 POTENTIAL WIRE
..r.
ANODE WIRE 3
uJ ~
m
~
m
_
m
2~o
~o
'
~o
POSITION
Fig. 6. Position o f insensitive regions irl" prototype drift chamber.
'
~o
'
41o
mm
Fig. 7. (a) Drift chamber efficiency vs position for anode wire 6. (b) Drift chamber efficiency vs position for anode wire 2. Ill.
PLANAR
DRIFT
CHAMBERS
218
M. EDWARDS
was moved across the beam and the efficiency of each plane measured. The results of this scan are shown in figs. 7a and 7b. As can be seen the efficiency drops off rapidly, and, if the direction of electron drift is away from the 'box' (fig. 7a), the position of the fall in efficiency is as expected. If, however, the direction of drift is along the edge of the 'box' (fig. 7b), then the effective width is greater than the actual width of the 'box'. In this case, the actual width varies with distance from the anode wire, being almost the actual width at the anode wire, and 12-13 mm greater at the potential wire. 4. Conclusion A method has been described by which well defined areas of proportional and drift chambers may be made insensitive. The insensitive regions are of simple construction and easy to install in a chamber, resulting in the possibility of changing their size and/or position relatively quickly.
The efficiency in the insensitive region is difficult to measure precisely, due to the high statistics required, but is considerably less than 10 -3 . The transition from full efficiency to essentially zero efficiency is extremely sharp. I would like to thank Dr. E. Gabathuler, Dr. P. R. Norton and those members of the European Muon Collaboration who helped in the running of the tests on the PS at CERN. I would also like to acknowledge those members of the Rutherford Laboratory and the Physics Department of the University of Lancaster who constructed the proportional and drift chambers.
References 1) The European Muon Collaboration, CERN/SPSC/74-78. 2) R. R. Crittenden and J. C. Krider, Nucl. Instr. and Meth. 128 (1965) 599; U. Hahn et al., these Proceedings. 3) K. Connell et al., Nucl. Instr. and Meth. 144 (1977) 453.
156 ( 1 9 7 8 )
215-218 ; ©
N O R T H - H O L L A N D PUBLISHING CO.
A SIMPLE, EFFECTIVE METHOD OF CONSTRUCTING INSENSITIVE REGIONS IN PROPORTIONAL AND DRIFT CHAMBERS M. EDWARDS
Rutherlbrd Laboratory, Chilton, Didcot, Oxon, England
A simple, effective method of constructing insensitive regions in proportional and drift chambers is described. Such regions are needed when, as in the case of the chambers for the European Muon Collaboration, an intense beam passes through the chamber. The method described has the advantage that the region can be relatively easily moved. Results are presented showing the effectiveness of the insensitive region and the sharpness of the transition from live to dead regions.
1. Introduction The apparatus of the European Muon Collaboration 1) is shown in fig. 1, and contains many planes of proportional and drift chambers. Many of these chambers have the intense muon beam passing through them. The intensity of the muon beam is expected to reach 108 muons/pulse, each pulse is just under 1 s duration. In order to detect muon scattered through small angles, down to 0.5 °, it was decided not to build chambers with a physical hole in them, but to develop devices to make the chambers insensitive in the area through which the beam passed. Several techniques to achieve this are possible2), this paper describes the method used for the chambers PI, P2, P3, W6 and W7 in fig. 1, constructed at the Rutherford Laboratory. 2. Construction 2.1. PROPORTIONAL CHAMBERS The muon beam passing through the proportional chambers inside the forward spectrometer magnet, is expected to be between 100 and 120 mm in diameter. The size of the insensitive region was, therefore, chosen to be somewhat less than 120 mm diameter. The insensitive region is of very simple construction consisting o f ' b o x e s ' . Each 'box' consists of two circular pieces of 0.1 mm thick Kapton film held apart by a cylinder formed from similar film. A 'box' is shown in fig. 2. The holes in the Kapton cylinder are to allow free passage of gas through the volume of the 'box', obviating any possibility of the 'box' outgassing over a long period. The thickness of the 'box' is made equal to
the half gap of the chamber with a tolerance of _+0.05 mm. As the chamber is assembled one 'box' is inserted between each plane of wires. The 'boxes' are held in position by 3 spots of epoxy resin on the high-voltage wires. They are not glued to the signal wires. 2.2. DRIFT CHAMBERS
The insensitive regions for the drift chambers W6 and W7 a) are similar in construction, but are made rectangular not circular. The long dimension is made equal to the corresponding dimension of the insensitive areas required. The width is made 8 mm less than the distance between the potential and anode wires, since it was found experimentally that if the edge of the 'box' was less than 1 mm from the anode wire, that length of the anode wire near the 'box' was insensitive to particles on both sides. Hence the 'boxes' were inserted in the drift chamber to be at least 2 mm from the anode wire which was required to be sensitive on one side (see fig. 3). The thickness is made equal to the distance between the wire plane and the cathode plane. The muon beam passing through the drift chambers W6 and W7 is expected to be between 150 and 180 mm diameter. Since the distance between the potential wire and anode wire of these drift chambers is 60 mm, it was decided to construct insensitive regions 180 mm square. These regions are built up from six 'boxes' of 180 mm by 58 ram, three mounted on each cathode plane. The arrangement of mounting on the cathode plane is shown in fig. 3, with a similar set of three 'boxes' mounted on the facing cathode plane. Ill.
P L A N A R DRIFT CHAMBERS
216
M. EDWARDS
÷ g:
,':ii!i
i[i;I Ill II
T ._[
=; ;
Fig. 2. Box for proportional c h a m b e r s . PmENT~AL ANODE POTENT~At ANODE W~RE WfRE W~RE W~RE Z i, "~1 ~=====~
%
Fig. 3. Box for drift c h a m b e r s .
iL' ' Im~
3. Performance
Z
,\
-t
O
"6 ¢-, O
The first production model of both a W 6 drift chamber and a proportional chamber were tested in a high intensity extracted proton beam from the C E R N PS. The extracted proton beam, s o m e 101° protons per pulse, was attenuated by approximately 30 cm o f lead and then passed d o w n a relatively short beam line to the experimental area. D u e to shortness o f this beam line the proton beam in the area was accompanied by a large halo o f total intensity comparable to the beam. Fig. 4 s h o w s the arrangeDRIFT CHAMBER 3500x4200
/
e-
PROPORTIONAL CHAMBER
.o
i
+
i
1000 x 2024
iI !!
E
g
CA= RxR
.A: 0 CB'~"
Cc = 4 x 4
Co = 10 "lO
#
m
.......... i
r,,
Fig. 4. A r r a n g e m e n t in the test beam.
Y
CONSTRUCTING
INSENSITIVE
ment used in the area. CA and CB are two small scintillation counters (8 x 8 and 3 x 2 mm 2) mounted on a common remotely controlled two dimensional scanning table. Cc and CD are another pair of small counters ( 4 x 4 and 10x 10 mm 2) mounted on a second common scanning table. A coincidence between at least one counter on each scanning table was used to define a track through the system, and trigger the read-out system. With the proton beam passing through the centre of the insensitive region in the proportional and drift chambers the halo was used to check the sharpness of the edge of the insensitive region. The trigger counters were positioned above the insensitive region and, using the halo of the beam, the efficiency of the planes was measured as they were scanned down into the insensitive region. EDGE OF BOX
100~
o
~"
60
217
REGIONS
The resultant efficiency/position plot for the proportional chambers is shown in fig. 5. The pair of counters used were the 8 x 8 and 1 0 x l 0 m m 2 counters CA and Co. As can be seen, the drop in efficiency is very sharp. The counters CA and CD were not aligned vertically with the direction of the beam halo, thus effectively defining a rectangular area of the chamber 4 mm high by 8 mm wide. The exact profile of the area so defined was measured using histograms of the hits per wire in the proportional chamber. The result of unfolding this profile from the data of fig. 5 was that the efficiency drops from 90% to 10% in approximately 1 mm. Due to shortage of beam time, and to difficulties arising from the high flux of particles through the drift chamber, the testing of the insensitive region in the drift chamber was restricted to checks that detailed results obtained with a small prototype chamber were valid for the large production chamber. This small chamber was scanned across an electron beam from NINA at Daresbury. The beam was defined by a very thin (2 mm wide) counter. The chamber contained two orthogonal planes each equipped with a single 120x60 mm 2 'box', positioned as shown in fig. 6. The chamber
Z
EDGE OF BOX
u 4G
>. 80 CENTRE OF CHAMBER
20
4O 20 2~
'
~o
'
340
POSITION
38o
3OO
4~o
340 POSITION turn
mm
Fig. 5. Proportional chamber efficiency vs position. POTENTIAL WIRE
_
BOXES _ k , . . .
1017
,f
E[~-~ OF BOX
EDGE OF BOX
ANODE WIRE I POTENTIAL WIRE
b
ANODE WIRE 2 POTENTIAL WIRE
..r.
ANODE WIRE 3
uJ ~
m
~
m
_
m
2~o
~o
'
~o
POSITION
Fig. 6. Position o f insensitive regions irl" prototype drift chamber.
'
~o
'
41o
mm
Fig. 7. (a) Drift chamber efficiency vs position for anode wire 6. (b) Drift chamber efficiency vs position for anode wire 2. Ill.
PLANAR
DRIFT
CHAMBERS
218
M. EDWARDS
was moved across the beam and the efficiency of each plane measured. The results of this scan are shown in figs. 7a and 7b. As can be seen the efficiency drops off rapidly, and, if the direction of electron drift is away from the 'box' (fig. 7a), the position of the fall in efficiency is as expected. If, however, the direction of drift is along the edge of the 'box' (fig. 7b), then the effective width is greater than the actual width of the 'box'. In this case, the actual width varies with distance from the anode wire, being almost the actual width at the anode wire, and 12-13 mm greater at the potential wire. 4. Conclusion A method has been described by which well defined areas of proportional and drift chambers may be made insensitive. The insensitive regions are of simple construction and easy to install in a chamber, resulting in the possibility of changing their size and/or position relatively quickly.
The efficiency in the insensitive region is difficult to measure precisely, due to the high statistics required, but is considerably less than 10 -3 . The transition from full efficiency to essentially zero efficiency is extremely sharp. I would like to thank Dr. E. Gabathuler, Dr. P. R. Norton and those members of the European Muon Collaboration who helped in the running of the tests on the PS at CERN. I would also like to acknowledge those members of the Rutherford Laboratory and the Physics Department of the University of Lancaster who constructed the proportional and drift chambers.
References 1) The European Muon Collaboration, CERN/SPSC/74-78. 2) R. R. Crittenden and J. C. Krider, Nucl. Instr. and Meth. 128 (1965) 599; U. Hahn et al., these Proceedings. 3) K. Connell et al., Nucl. Instr. and Meth. 144 (1977) 453.