- Email: [email protected]
Construction of monitored drift tube chambers for ATLAS end-cap muon spectrometer at IHEP (Protvino)
Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
Construction of monitored drift tube chambers for ATLAS end-cap muon spectrometer at IHEP (Protvino) J. Bensingera, N. Bojkob, A. Borisovb, R. Fakhroutdinovb,*, S. Goryatchevb, V. Goryatchevb, V. Gushchinb, K. Hashemia, A. Kojineb, A. Kononovb, A. Larionovb, E. Paramoshkinab, A. Pilaevb, N. Skvorodnevb, A. Tchougouevb, H. Wellensteina a b
Department of Physics, Brandeis University, 415 South Street, Waltham, MA 02254, USA Institute for High Energy Physics, Pobeda Str. 1, 142281 Protvino, Moscow Region, Russia
Abstract Trapezoidal-shaped Monitored Drift Tube (MDT) chambers will be used in end-caps of ATLAS muon spectrometer. Design and construction technology of such chambers in IHEP (Protvino) is presented. X-ray tomography results confirm desirable 20 mm precision of wire location in the chamber. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.g Keywords: Drift tube; Muon chamber; ATLAS Muon Spectrometer
1. Introduction The ATLAS muon spectrometer [1] is designed to provide muon momentum resolution of DpT =pT ¼ 2–10% for transverse momenta from 6 GeV to 1 TeV over a pseudo-rapidity range of jZjp2:7: This requires very accurate track sagitta measurement with three layers of muon chambers in a super-conducting air-core toroid magnet and high-precision optical monitoring systems to correct for chamber misalignment. IHEP (Protvino) is responsible for construction of 60,000 drift tubes and their assembly into 192 chambers for whole *Corresponding author. E-mail address: [email protected] (R. Fakhroutdinov).
(Fig. 1) outer ring layers of the end-cap of the spectrometer. These layers are located at both sides from the ATLAS interaction point at distance 21:5 m: Each 23:7 m ring consists of 16 sectors composed of long (EOL) and short (EOS) chambers. The Monitored Drift Tube (MDT) is basic element of the chamber. The drift tube is made of thin-walled ð0:4 mmÞ aluminium pipe with 30 mm outer diameter and 50 mm central anode wire stretched between two end-plugs, which have precise outer reference surface for tube positioning. The drift tube works at 3 bar gas1 pressure to provide a single tube resolution about of 80 mm (RMS) at low gas gain 2 104 to minimize aging 1 Several gas mixtures were considered, now baseline one is Ar–CO2 (93–7).
0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 2 ) 0 1 5 3 5 - 8
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
481
sector A05
EO L4 EO L3 L2
EOL2 EOL1 E O
L5
or
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07
L6
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EOL6
EOL4
A
EOL2
EOL1 EO L1
EOL3
L1
or
ct se
EOL6
sector A09
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EO
EO L2 EO L EO 3 EO L4 EO L5 L6
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EOL1
EOL3
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se EOL5
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EO L1 1 EO EOL1 EO L2 EO L 3 EOL2 EO L4 EOL3 EO L5 se L EOL4 ct 6 or EOL5 A
15
se
EOL6
sector A13 23660
Fig. 2. Schematic view of chamber.
Fig. 1. Outer ring (A) of ATLAS end-cap spectrometer.
effects. Sense wire have to be positioned with an accuracy of 10 mm (rms) in the tube and 20 mm (rms) in the chamber. There is separate presentation at this conference devoted to the drift tube assembly [2]. The chambers (see Fig. 2) are constructed from 6 layers of drift tubes: 48 tubes per layer in EOL3EOL6, EOS4-EOS6 chambers and 56 tubes/layer for others. The chambers are built in a staircase trapezoidal shape with 8 tubes per step. The chambers come in two general types: long (EOL) with a corner angle 761 and short (EOS) with a corner angle 81:51: Height2 of the chamber is 0:35 m; length varies from 1.3 to 6:3 m: The drift tubes are arranged in two multi-layers (ML) of three layers each. Multi-layers (labelled 2 and 5 in Fig. 2) are glued to both sides of a rigid support structure (‘‘spacer frame’’). The structural components of the spacer are three cross-plates (3) connected by two long beams (7). MLs are glued to cross-plates made of 6 mm aluminium plate. Outer cross-plates have thin flexible parts with reduced thickness ð0:5 mmÞ thus allowing axial expansion of tubes with respect to the spacer frame 2
Dimension orthogonal to tube plane.
to avoid chamber bending due to a temperature gradient between MLs. Long beams are made of 3 mm aluminium plate and they do not touch the tubes. The spacer need to be constructed to a moderate mechanical accuracy of 70:5 mm; precise positioning of the drift tubes is provided by the assembly procedure. The spacer also carries four mounting blocks needed for connection of the chamber to end-cap rail structure and in-plane optical system to monitor mechanical deformation of the chamber. There are four RASNIK3 [3] rays. Each ray is CCD (1) which views the coded mask (6) through the lens providing a possibility to monitor the chamber deformations with accuracy of 1 mm:There are 2 CCDs, 2 masks and 4 lenses in chamber. Four platforms (4) are glued onto top of the chamber. Additional CCD cameras and masks will be placed on them to see corresponding masks and cameras on adjacent chamber and on alignment bar, providing global alignment in the spectrometer. The alignment system for end-caps of the ATLAS muon spectrometer is developed by Brandeis University [4].
3 RASNIK is alignment monitoring system, developed at NIKHEF.
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J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
Gas manifolds and Faraday-cages with electronics will be placed at the chamber ends. Temperature sensors are distributed on the chamber.
2. Chamber assembly The extreme mechanical precision demanded by the ATLAS muon spectrometer requires great efforts to build very stable and precise facilities and tooling for the chamber construction. The chambers are assembled on a very stable and flat surface (granite table 6:6 2:3 0:6 m3 ) in a temperature ð70:51CÞ and humidity (40–60%) controlled room. The chambers are built by first placing tubes on precise combs (Fig. 3) which are aluminium beams with row of groves to position the tubes. The grooves are made of steel balls (diameter 16:0030:001 mm) glued into the beams through precisely machined template with holes. There were only 3 types of templates which allowed us to replicate all needed combs. The wire
position is defined by balls which touch the end plug outer reference surface. During gluing a layer the tubes are attracted to the balls via vacuum suction cups row of which is fixed onto each comb. The combs are aligned vertically and horizontally with 10 mm precision by using special tools, which is based on principles described in Ref. [4]. After tubes are positioned on the combs, they are glued together with Araldite 2011 delivered by a glue machine (Fig. 4) which carries a gluedispenser over the tube layer. The glue-dispenser pumps premixed epoxy into nozzles (1 or 3 in dependence of glued layer) which put strips of glue onto tube where their circumferences come in touch. The glue-dispenser sits on the bridge which rides on the rails attached to the comb ends. The machine is driven from switchboard panel (black box in Fig. 4). After start the machine is moved automatically, at each end of tube the gluedispenser jumps to the next tube. Gluing of 4 m long 48 tubes layer takes 30 min: As soon as the first layer of tubes is wet by glue, three auxiliary
Fig. 3. View of two combs, ‘‘angle’’ and ‘‘straight’’.
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
483
Fig. 4. Glue machine view.
aluminium strips which are mechanically attached to a stiff-back frame are glued on top of the layer by epoxy glue DP460. After curing of glue the layer is lifted from the jig using the stiff-back. When the next tube layer is put on the combs and covered by the glue the stiff-back with previously glued layer is returned on the table again. The upper tube layer at the moment is held by the stiffback and positioned by lowering the stiff-back on sphere-block towers which provide precise transverse and vertical displacements between tube layers. The displacements are monitored by RASNIK based system. Fig. 5 shows view of combs on the table: rails for the glue machine are seen at both sides of combs; one sphere block is seen in the foreground; the stiff-back with already glued two layers is at the top. Separate stiff-back frames is used for each ML. The stiff-back is constructed from three arched girders made of welded aluminium which are connected by demountable partitions. Length of the partitions is adjusted in accordance to one of the chamber to be
assembled, so after each 16 chamber series the stiff-backs are re-assembled. When three tube layers of the second4 ML are glued, their stiff-back is removed and the spacer frame assembled outside of the clean area using flat surface of large cast iron table is glued (DP460) onto the top of the ML. The top of the spacer is covered by the same glue and the first stiff-back brings the first ML onto the spacer. After hardening of the glue the aluminium strips are de-attached from first stiff-back. The stiff-back is removed and praxial alignment platforms [4] are glued on top of the chamber. Finally, after hardening of the platform glue the chamber is removed from the table and, using small handcarts, transported to storage area (see Fig. 6 where two chambers—one on the carts and one on the temporal support—are shown.)
4 Here the first and the second mean production consequence of MLs.
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J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
Fig. 5. Jig layout view. Two already glued layers are hanged up by the stiff-back.
Fig. 6. Two chambers at temporal supports and at hand-carts.
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
40
485
Stiff-back 1 pos.1
EOL3 Corner 2 wrt. average
Stiff-back 1 pos.2 Stiff-back 1 pos.3
30
Stiff-back 1 pos.4 Stiff-back 2 pos.1
20
Stiff-back 2 pos.2 Stiff-back 2 pos.3
Y,µm
10 0 -10 -20 -30 -40 -40
-30
-20
-10
0
10
20
30
40
Z,µm Fig. 7. Stiff-back monitor of corner 2, EOL3 chambers.
Minimal time interval needed to cure the glue is 10 h that limits chamber production rate: 5 working days per chamber for two-shifts work. The combs grove pitch was verified once by measurements of the templates at 3D numerical control machine. The pitch is 30:037 mm with standard deviation 3 mm: Planarity of the grooves was checked during Module Zero (M0) chamber assembling, standard deviation of distances between top of end plug and the granite table surface is 5 mm (rms) including a spread of end plug outer reference surface diameter. Position of the side combs, which are most responsible for wire location, is monitored by CCD cameras. The CCD camera and masks are attached to the comb (Fig. 3), corresponding lens is attached to the table. For each chamber type its own set of combs is arranged on the table with comb separation 0:5 m: The sphere blocks were surveyed with 5 mm accuracy. Positions of the stiff-back on the sphereblocks is controlled by RASNIK-based systems.
Each corner of the stiff-back is equipped by RASNIKs mask which is viewed by CCD camera mounted on a tower attached to the table. Example of the monitor data is shown in Fig. 7, where scatter plot of RASNIK readings is presented for 16 EOL3 series chambers; standard deviations (vertical and horizontal) are below 8 mm: Finished chamber is subjected to control its mechanical precision. Distance between ML and relative shift of layers are checked for all chambers. For instance, for EOL3 series chambers ML separation is 199:96070:007 ðrmsÞ mm; while design value is 199:9670:01 mm: There is a decision of the ATLAS Muon collaboration that 10% of chambers should be certified by X-ray tomography at CERN [5]. We have finished already full set (16 chambers) of EOL3 type. Two chambers from this series were scanned at X-ray tomograph at CERN. Both have passed successfully through the tests. Results for M0 chamber are given in Ref. [6]. Fig. 8 presents example of wire coordinates distributions with
486
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486 Z-dist. wrt. nominal. Scan EOL_2001_01_p1_r0_106
Y-dist. wrt. nominal. Scan EOL_2001_01_p1_r0_106
h1 h1 Nent Nent==286 286 Mean Mean ==0.03353 0.03353 RMS RMS ==13.47 13.47
14
h2 h2 Nent Nent==286 286 Mean ==-0.02546 -0.02546 Mean RMS RMS ==10.58 10.58
16 14
12
12 10 10 8 8 6
6
4
4
2
2
0 -100 -80 -60 -40 -20
0
20
40
60
80
100
0 -100 -80 -60 -40 -20
Y-Ynom,µm
0
20
40
60
80
100
Z-Znom,µm
Fig. 8. Y - and Z-distribution of wire positions with respect to nominal grid.
respect to nominal grid as it was measured for M0 EOL3 chamber. Standard deviation of measured wire positions is within of 12–21 mm with respect to grid with nominal parameters.
ATLAS MDT chamber construction activity in Protvino is supported by International Science and Technology Center in frame of ISTC project No. 1639. We are very thankful to the Center for that.
3. Conclusions
References
Mass production of ATLAS MDT outer ring end-cap chambers with rate 5 working days per chamber is in progress at IHEP (Protvino). Twenty-five chambers have been already glued. Two chambers out of EOL3 series (16 chambers) were certified by X-ray tomography which proved the specified 20 mm accuracy for a wire location within the chamber.
[1] ATLAS Muon Spectrometer Technical Design Report, CERN/LHCC/97-22, 31 May 1999. [2] A. Borisov, et al., ATLAS monitored drift tube assembly and test at IHEP (Protvino), Nucl. Instr. and Meth. A 494 (2002), these proceedings. [3] The muon alignment system Preliminary Design Review (7/ 03/2001), at URL http://atlasinfo.cern.ch/Atlas/GROUPS/ MUON/alignment/pdr/pdr doc.html [4] A. Borisov, et al., Simple control system of relative combs position on drift tube chamber assembling table, ATLAS Internal Note, ATL-MUON-98-219. [5] D. Drakoulakos, et al., The high-precision X-ray tomograph for quality control of the ATLAS MDT muon spectrometer, Preprint CERN, CERN-Open-97-023, July 1997. [6] R. Avramidou, et al., EOL3 M0 X-ray tomography test results, ATLAS Internal Note, ATL-COM-MUON-2001016.
Acknowledgements We are pleased to thank our colleagues from IHEP MDT group and ATLAS Muon management for fruitful collaboration.
Construction of monitored drift tube chambers for ATLAS end-cap muon spectrometer at IHEP (Protvino) J. Bensingera, N. Bojkob, A. Borisovb, R. Fakhroutdinovb,*, S. Goryatchevb, V. Goryatchevb, V. Gushchinb, K. Hashemia, A. Kojineb, A. Kononovb, A. Larionovb, E. Paramoshkinab, A. Pilaevb, N. Skvorodnevb, A. Tchougouevb, H. Wellensteina a b
Department of Physics, Brandeis University, 415 South Street, Waltham, MA 02254, USA Institute for High Energy Physics, Pobeda Str. 1, 142281 Protvino, Moscow Region, Russia
Abstract Trapezoidal-shaped Monitored Drift Tube (MDT) chambers will be used in end-caps of ATLAS muon spectrometer. Design and construction technology of such chambers in IHEP (Protvino) is presented. X-ray tomography results confirm desirable 20 mm precision of wire location in the chamber. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.g Keywords: Drift tube; Muon chamber; ATLAS Muon Spectrometer
1. Introduction The ATLAS muon spectrometer [1] is designed to provide muon momentum resolution of DpT =pT ¼ 2–10% for transverse momenta from 6 GeV to 1 TeV over a pseudo-rapidity range of jZjp2:7: This requires very accurate track sagitta measurement with three layers of muon chambers in a super-conducting air-core toroid magnet and high-precision optical monitoring systems to correct for chamber misalignment. IHEP (Protvino) is responsible for construction of 60,000 drift tubes and their assembly into 192 chambers for whole *Corresponding author. E-mail address: [email protected] (R. Fakhroutdinov).
(Fig. 1) outer ring layers of the end-cap of the spectrometer. These layers are located at both sides from the ATLAS interaction point at distance 21:5 m: Each 23:7 m ring consists of 16 sectors composed of long (EOL) and short (EOS) chambers. The Monitored Drift Tube (MDT) is basic element of the chamber. The drift tube is made of thin-walled ð0:4 mmÞ aluminium pipe with 30 mm outer diameter and 50 mm central anode wire stretched between two end-plugs, which have precise outer reference surface for tube positioning. The drift tube works at 3 bar gas1 pressure to provide a single tube resolution about of 80 mm (RMS) at low gas gain 2 104 to minimize aging 1 Several gas mixtures were considered, now baseline one is Ar–CO2 (93–7).
0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 2 ) 0 1 5 3 5 - 8
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
481
sector A05
EO L4 EO L3 L2
EOL2 EOL1 E O
L5
or
A
07
L6
EOL5
EOL6
EOL4
A
EOL2
EOL1 EO L1
EOL3
L1
or
ct se
EOL6
sector A09
EO
EO
EO L2 EO L EO 3 EO L4 EO L5 L6
EOL2
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11
03 A or
EOL4
ct
EO EO L6 EO L5 EO L4 EO L3 L2 EO L1
se EOL5
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ct
EOL5
EO L1 1 EO EOL1 EO L2 EO L 3 EOL2 EO L4 EOL3 EO L5 se L EOL4 ct 6 or EOL5 A
15
se
EOL6
sector A13 23660
Fig. 2. Schematic view of chamber.
Fig. 1. Outer ring (A) of ATLAS end-cap spectrometer.
effects. Sense wire have to be positioned with an accuracy of 10 mm (rms) in the tube and 20 mm (rms) in the chamber. There is separate presentation at this conference devoted to the drift tube assembly [2]. The chambers (see Fig. 2) are constructed from 6 layers of drift tubes: 48 tubes per layer in EOL3EOL6, EOS4-EOS6 chambers and 56 tubes/layer for others. The chambers are built in a staircase trapezoidal shape with 8 tubes per step. The chambers come in two general types: long (EOL) with a corner angle 761 and short (EOS) with a corner angle 81:51: Height2 of the chamber is 0:35 m; length varies from 1.3 to 6:3 m: The drift tubes are arranged in two multi-layers (ML) of three layers each. Multi-layers (labelled 2 and 5 in Fig. 2) are glued to both sides of a rigid support structure (‘‘spacer frame’’). The structural components of the spacer are three cross-plates (3) connected by two long beams (7). MLs are glued to cross-plates made of 6 mm aluminium plate. Outer cross-plates have thin flexible parts with reduced thickness ð0:5 mmÞ thus allowing axial expansion of tubes with respect to the spacer frame 2
Dimension orthogonal to tube plane.
to avoid chamber bending due to a temperature gradient between MLs. Long beams are made of 3 mm aluminium plate and they do not touch the tubes. The spacer need to be constructed to a moderate mechanical accuracy of 70:5 mm; precise positioning of the drift tubes is provided by the assembly procedure. The spacer also carries four mounting blocks needed for connection of the chamber to end-cap rail structure and in-plane optical system to monitor mechanical deformation of the chamber. There are four RASNIK3 [3] rays. Each ray is CCD (1) which views the coded mask (6) through the lens providing a possibility to monitor the chamber deformations with accuracy of 1 mm:There are 2 CCDs, 2 masks and 4 lenses in chamber. Four platforms (4) are glued onto top of the chamber. Additional CCD cameras and masks will be placed on them to see corresponding masks and cameras on adjacent chamber and on alignment bar, providing global alignment in the spectrometer. The alignment system for end-caps of the ATLAS muon spectrometer is developed by Brandeis University [4].
3 RASNIK is alignment monitoring system, developed at NIKHEF.
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J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
Gas manifolds and Faraday-cages with electronics will be placed at the chamber ends. Temperature sensors are distributed on the chamber.
2. Chamber assembly The extreme mechanical precision demanded by the ATLAS muon spectrometer requires great efforts to build very stable and precise facilities and tooling for the chamber construction. The chambers are assembled on a very stable and flat surface (granite table 6:6 2:3 0:6 m3 ) in a temperature ð70:51CÞ and humidity (40–60%) controlled room. The chambers are built by first placing tubes on precise combs (Fig. 3) which are aluminium beams with row of groves to position the tubes. The grooves are made of steel balls (diameter 16:0030:001 mm) glued into the beams through precisely machined template with holes. There were only 3 types of templates which allowed us to replicate all needed combs. The wire
position is defined by balls which touch the end plug outer reference surface. During gluing a layer the tubes are attracted to the balls via vacuum suction cups row of which is fixed onto each comb. The combs are aligned vertically and horizontally with 10 mm precision by using special tools, which is based on principles described in Ref. [4]. After tubes are positioned on the combs, they are glued together with Araldite 2011 delivered by a glue machine (Fig. 4) which carries a gluedispenser over the tube layer. The glue-dispenser pumps premixed epoxy into nozzles (1 or 3 in dependence of glued layer) which put strips of glue onto tube where their circumferences come in touch. The glue-dispenser sits on the bridge which rides on the rails attached to the comb ends. The machine is driven from switchboard panel (black box in Fig. 4). After start the machine is moved automatically, at each end of tube the gluedispenser jumps to the next tube. Gluing of 4 m long 48 tubes layer takes 30 min: As soon as the first layer of tubes is wet by glue, three auxiliary
Fig. 3. View of two combs, ‘‘angle’’ and ‘‘straight’’.
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
483
Fig. 4. Glue machine view.
aluminium strips which are mechanically attached to a stiff-back frame are glued on top of the layer by epoxy glue DP460. After curing of glue the layer is lifted from the jig using the stiff-back. When the next tube layer is put on the combs and covered by the glue the stiff-back with previously glued layer is returned on the table again. The upper tube layer at the moment is held by the stiffback and positioned by lowering the stiff-back on sphere-block towers which provide precise transverse and vertical displacements between tube layers. The displacements are monitored by RASNIK based system. Fig. 5 shows view of combs on the table: rails for the glue machine are seen at both sides of combs; one sphere block is seen in the foreground; the stiff-back with already glued two layers is at the top. Separate stiff-back frames is used for each ML. The stiff-back is constructed from three arched girders made of welded aluminium which are connected by demountable partitions. Length of the partitions is adjusted in accordance to one of the chamber to be
assembled, so after each 16 chamber series the stiff-backs are re-assembled. When three tube layers of the second4 ML are glued, their stiff-back is removed and the spacer frame assembled outside of the clean area using flat surface of large cast iron table is glued (DP460) onto the top of the ML. The top of the spacer is covered by the same glue and the first stiff-back brings the first ML onto the spacer. After hardening of the glue the aluminium strips are de-attached from first stiff-back. The stiff-back is removed and praxial alignment platforms [4] are glued on top of the chamber. Finally, after hardening of the platform glue the chamber is removed from the table and, using small handcarts, transported to storage area (see Fig. 6 where two chambers—one on the carts and one on the temporal support—are shown.)
4 Here the first and the second mean production consequence of MLs.
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J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
Fig. 5. Jig layout view. Two already glued layers are hanged up by the stiff-back.
Fig. 6. Two chambers at temporal supports and at hand-carts.
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486
40
485
Stiff-back 1 pos.1
EOL3 Corner 2 wrt. average
Stiff-back 1 pos.2 Stiff-back 1 pos.3
30
Stiff-back 1 pos.4 Stiff-back 2 pos.1
20
Stiff-back 2 pos.2 Stiff-back 2 pos.3
Y,µm
10 0 -10 -20 -30 -40 -40
-30
-20
-10
0
10
20
30
40
Z,µm Fig. 7. Stiff-back monitor of corner 2, EOL3 chambers.
Minimal time interval needed to cure the glue is 10 h that limits chamber production rate: 5 working days per chamber for two-shifts work. The combs grove pitch was verified once by measurements of the templates at 3D numerical control machine. The pitch is 30:037 mm with standard deviation 3 mm: Planarity of the grooves was checked during Module Zero (M0) chamber assembling, standard deviation of distances between top of end plug and the granite table surface is 5 mm (rms) including a spread of end plug outer reference surface diameter. Position of the side combs, which are most responsible for wire location, is monitored by CCD cameras. The CCD camera and masks are attached to the comb (Fig. 3), corresponding lens is attached to the table. For each chamber type its own set of combs is arranged on the table with comb separation 0:5 m: The sphere blocks were surveyed with 5 mm accuracy. Positions of the stiff-back on the sphereblocks is controlled by RASNIK-based systems.
Each corner of the stiff-back is equipped by RASNIKs mask which is viewed by CCD camera mounted on a tower attached to the table. Example of the monitor data is shown in Fig. 7, where scatter plot of RASNIK readings is presented for 16 EOL3 series chambers; standard deviations (vertical and horizontal) are below 8 mm: Finished chamber is subjected to control its mechanical precision. Distance between ML and relative shift of layers are checked for all chambers. For instance, for EOL3 series chambers ML separation is 199:96070:007 ðrmsÞ mm; while design value is 199:9670:01 mm: There is a decision of the ATLAS Muon collaboration that 10% of chambers should be certified by X-ray tomography at CERN [5]. We have finished already full set (16 chambers) of EOL3 type. Two chambers from this series were scanned at X-ray tomograph at CERN. Both have passed successfully through the tests. Results for M0 chamber are given in Ref. [6]. Fig. 8 presents example of wire coordinates distributions with
486
J. Bensinger et al. / Nuclear Instruments and Methods in Physics Research A 494 (2002) 480–486 Z-dist. wrt. nominal. Scan EOL_2001_01_p1_r0_106
Y-dist. wrt. nominal. Scan EOL_2001_01_p1_r0_106
h1 h1 Nent Nent==286 286 Mean Mean ==0.03353 0.03353 RMS RMS ==13.47 13.47
14
h2 h2 Nent Nent==286 286 Mean ==-0.02546 -0.02546 Mean RMS RMS ==10.58 10.58
16 14
12
12 10 10 8 8 6
6
4
4
2
2
0 -100 -80 -60 -40 -20
0
20
40
60
80
100
0 -100 -80 -60 -40 -20
Y-Ynom,µm
0
20
40
60
80
100
Z-Znom,µm
Fig. 8. Y - and Z-distribution of wire positions with respect to nominal grid.
respect to nominal grid as it was measured for M0 EOL3 chamber. Standard deviation of measured wire positions is within of 12–21 mm with respect to grid with nominal parameters.
ATLAS MDT chamber construction activity in Protvino is supported by International Science and Technology Center in frame of ISTC project No. 1639. We are very thankful to the Center for that.
3. Conclusions
References
Mass production of ATLAS MDT outer ring end-cap chambers with rate 5 working days per chamber is in progress at IHEP (Protvino). Twenty-five chambers have been already glued. Two chambers out of EOL3 series (16 chambers) were certified by X-ray tomography which proved the specified 20 mm accuracy for a wire location within the chamber.
[1] ATLAS Muon Spectrometer Technical Design Report, CERN/LHCC/97-22, 31 May 1999. [2] A. Borisov, et al., ATLAS monitored drift tube assembly and test at IHEP (Protvino), Nucl. Instr. and Meth. A 494 (2002), these proceedings. [3] The muon alignment system Preliminary Design Review (7/ 03/2001), at URL http://atlasinfo.cern.ch/Atlas/GROUPS/ MUON/alignment/pdr/pdr doc.html [4] A. Borisov, et al., Simple control system of relative combs position on drift tube chamber assembling table, ATLAS Internal Note, ATL-MUON-98-219. [5] D. Drakoulakos, et al., The high-precision X-ray tomograph for quality control of the ATLAS MDT muon spectrometer, Preprint CERN, CERN-Open-97-023, July 1997. [6] R. Avramidou, et al., EOL3 M0 X-ray tomography test results, ATLAS Internal Note, ATL-COM-MUON-2001016.
Acknowledgements We are pleased to thank our colleagues from IHEP MDT group and ATLAS Muon management for fruitful collaboration.