- Email: [email protected]
The ATLAS Semiconductor Tracker system test results
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
The ATLAS Semiconductor Tracker system test results P. Ferrari CERN-PH, 1211 Geneve 23, Switzerland On behalf of the ATLAS SCT Collaboration Available online 11 June 2004
Abstract Results are presented of tests with a prototype of a partial sector of the ATLAS SCT barrel and end-cap. This setup simulates the geometry and the electrical configuration of the final SCT detector in all its details of mounting, cooling, supply and shielding. An overview of the performances of the system and its components is presented in this paper. r 2004 Elsevier B.V. All rights reserved. PACS: 29.40.Gx Keywords: Tracking; Silicon strip
1. Introduction The ATLAS Semiconductor Tracker (SCT) consists of four nested cylindrical barrel sectors centred around the interaction point and nine disks in each of the two endcaps covering the forward region up to a pseudorapidity Z of 2.5, where Z ¼ ln tanðy=2Þ: The barrel layers and endcap disks will accommodate 4088 SCT modules consisting of single sided p-in-n silicon microstrip detectors. Each SCT module [1,2] is made of two planes of silicon micro-strips glued back to back at a small stereo angle of 40 mrad in order to provide bidimensional track reconstruction. Each plane of the barrels sensors consists of two 6 6 cm2 wafers for a total active strip length of about E-mail address: [email protected] (P. Ferrari).
12 cm: The end-cap sensors have three different radial geometries depending on their mounting position on the disks: inner, middle or outer. The sensors are glued on a highly thermally conductive baseboard. The modules are read out via 12 ASICS [3] mounted on a copper/kapton hybrid. The chips provide high-gain ð50 mV=fCÞ; fastshaping (20 ns peaking time) binary read out of 128 channels using radiation-hard technology. All channels read out by a chip have a common discrimination threshold, but channel specific variations can be compensated with a 4-bit trim DAC. The hit pattern is transferred to a binary pipeline that is 132 cells deep. To validate the electrical and noise performance of the detector, a system test for the barrel and the end-cap has been set up at CERN with the aim of running as many modules as possible in a configuration as close as possible to the one of the final ATLAS SCT.
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.05.044
ARTICLE IN PRESS P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
2. The system test setup The powering of the modules goes through three patch panels: 30 m long conventional cables connect prototype custom made low and highvoltage power supplies to Patch Panel 3 (PP3). Each low-voltage power supply card not only supplies analog and digital voltages to the detectors, but also reads out the NTC thermistor mounted on each side of the module. Before irradiation each module dissipates 5:6 W at 0 C [4], out of which 5.4 and 0:2 W are dissipated by the hybrid and the strips, respectively. After 10 years of operation at the LHC the modules will dissipate up to 10 W; out of which 7.5 and 2:5 W are dissipated by the chip and by the strips, respectively. Heat is dissipated through the baseboards which are clamped on aluminium cooling pipes in which an ethanol–water mixture is pumped. The temperature of this fluid is controlled by a commercial chiller. The high-voltage power supply powers 4 channels and provides maximum output voltage of 500 V: Final-design versions of these cards have been also tested at the barrel system test fulfilling the specifications [5]. The second section of the powering layout is not the final one since PP3 is directly connected to a second patch panel (PP2); 4 m long 100 mmaluminium-on-kapton power tapes connect to the next patch panel (PP1). To minimise the material in the SCT tracking volume the innermost section consists of 1:5 m long 50 mm-aluminium-on-kapton tapes (LMT). The LMT cables have a 0:05 4:5 mm2 cross-section and a 0:275 O=m resistance. Data and commands are transferred as optical signals through 25 m long optical fibres. Two chips are used to convert optical signals into electrical signals and vice versa, which are, respectively: the Digital Optical Receiver Integrated Circuit (DORIC) and the VCSEL Driver Chip (VDC) ASICS [6], where VECSEL stands for Vertical Cavity Surface Emitting Laser diode. The final readout system will be based on Read-Out Drivers (ROD) [7], but for the system test readout a custom set of VME modules has been adopted. A Data Acquisition software package based on ROOT [8] is running on a PC interfaced to the VME crate via a
39
National Instruments PC-VME interface. A CLOck And Control module (CLOAC) and a SLOw control Generator (SLOG) provide the 40 MHz-clock, trigger and commands, a MUltichannel Semiconductor Tracker Abcd Readout Device (MUSTARD) decodes the data received from the modules and an OPTo-electrical InterFace (OPTIF) acts as optical data receiver and transforms the clock and commands electronic signals into optical signals. A Detector Control System DCS is checking the humidity and the temperature of the cooling pipes.
3. Set of measurements This paper summarises the results of the following set of measurements: *
*
Three point gain calibration scan: 3 different charges (1.5, 2 and 2:5 fC) are injected at the preamplifier input individually for each detector strip. The choice of the injected charges is determined by the necessity to have a quick evaluation of the gain in the region between the operational discrimination threshold ðQTH ¼ 1 fCÞ and the typical signal charge ðQSIGNAL B3:3 fCÞ: The response to the calibration charge is obtained by scanning the discriminator threshold, resulting in an occupancy ‘‘s-curve’’ histogram for each channel. A complementary error function is fitted to this histogram, yielding the median 50% point efficiency and the noise from the Gaussian spread. The gain of the detectors amplification chain can be obtained as a linear fit of the mean results of the three fits. The Equivalent Noise Charge (ENC) can be extracted from the ratio of the noise and the gain. Noise occupancy: is obtained as a function of the threshold charge from calibrations scans. A linear fit to the ln(Occupancy) is performed in order to determine the ENC. In fact for a threshold charge QTH bQNOISE the following Q2
relation holds: ln(Occupancy) B 12 Q2 TH ; see NOISE Ref. [9]. Deviations from the linear behaviour would indicate noise pick-up.
ARTICLE IN PRESS 40 *
P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
Common mode noise measurement: the mean and the variance of the hits on a large number of events are related assuming a random noise source in the noise occupancy measurement. Deviations from the random noise behaviour are indicating the presence of common mode noise [9].
4. The barrel system test The barrel system test consists of a prototype sector built to hold up to 48 modules. Four harnesses are mounted on it, three on one side and one on the other. Therefore a full row of 12 modules could be mounted on the sector like in the final ATLAS detector, see Fig. 1a. Nonirradiated detectors are fully depleted at 50 V and have been
Fig. 2. Noise measurements in ENC with a row of 12 modules on the sector. Comparisons are shown between noise measured (a) in a noise occupancy scan and in a calibration scan (b) in a calibration scan and in individual measurements on the electrical bench. Modules are indicated by their serial number and the ordering on the plot refers to the actual mounting position on the sector. Each entry on the plot represents the average noise per chip.
Fig. 1. (a) Photograph of the barrel system test showing a configuration with one row completely equipped with modules. (b) The end-cap system test with 6 modules mounted on the sector.
operated at 100 V in the tests described in the following. Noise measurements from a 3 point gain and noise occupancy scans give compatible results within 100-200 ENC, see Fig. 2a. The differences in the results are determined by the diversity of the two methods. Good agreement is also found when comparing the results obtained on the sector with individual results on the electrical bench, see Fig. 2b. Larger noise on the sector would have indicated the presence of noise pick-up or cross-talk between modules overlapping along the z direction or between the left and the right harnesses, which are floating with respect to each other. In Fig. 2a and b the modules are operated at 15 C ambient temperature (warm
ARTICLE IN PRESS P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
running), while the final operational temperature at LHC will be around—7 C (cold running). The modules noise when running cold is well within the specifications, i.e. below 1500 ENC. The noise increases with temperature by 6 ENC= C: These measurements have been repeated with 16 modules mounted on the 3 left harnesses to check the behaviour of the sector when modules are overlapping both in the z and in the azimuthal direction. The results are in good agreement with the ones obtained on the electrical bench. The common mode noise is found to be always lower than 150 ENC but in most cases compatible with zero within the statistical error of the measurement, therefore the contribution of common mode noise can be considered small. Different grounding configurations have been studied for the barrel system test. The configurations [10] giving the best results are discussed in the following. One of the goals of the grounding schemes is to avoid capacitive effects between the highly conductive baseboard and the cooling pipes that would result in unwanted noise in the front end electronics. The main characteristics of the grounding schemes are summarised below: Scheme A: DC connection between module ground and cooling pipe. The cooling pipes are electrically connected in the sector centre. In fact, as for the harnesses, each cooling pipe serves only one half of the sector. Scheme B: cooling pipes are not electrically connected in the sector centre. Shunt shields are used. The shunt shields are copper on kapton pads placed between the cooling pipe and the baseboard and connected to the module reference ground, such that variations of the potential on the cooling pipe would induce variations on the shunt shield potential only. To verify the performances of different grounding schemes a sinusoidal noise current at different frequencies, ranging from 2 to 35 MHz; has been injected into the system. The current has been injected via a magnetic field generated by a ferrite and a coil into different components of the system: (1) in an individual conventional cable, (2) in a bundle of 6 tape pairs between PP2 and PP1 and (3) in the cooling pipes and in the thermal shield surrounding the sector. The noise pick-up is
41
Fig. 3. (a) Noise pick-up of a row of 12 barrel modules indicated by their serial number, when injecting a 10 MHz noise in a conventional cable in scheme A (dark grey/red) and in scheme B (lighter grey/green). Each histogram entry represents the noise in one chip. (b) Noise occupancy measured at a threshold of 1 fC averaged over more than 100 individual measurements, the four modules on the right having been irradiated. Each entry in the plot represents the average occupancy per chip.
obtained from single calibration scans at a threshold of 2 fC as the difference in noise with respect to no injection. For all injection modes the maximum pick-up is for 10 MHz noise. The performance of grounding scheme A is worse,
ARTICLE IN PRESS 42
P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
equivalent and better than scheme B for injection of type 1, 2, 3, respectively, see Fig. 3. The two grounding schemes seem therefore to be equivalent, but more information on this subject is expected from a revised system test with grounding and shielding closer to that planned for the final SCT. Four irradiated modules have been mounted on the sector and tested. The full modules have been irradiated with 3 1014 24 GeV protons=cm2 ; corresponding to 1.5 times the LHC dose, and annealed for 7 days at 25 C: The modules have been operated at 103 C and at 350 V depletion voltage, being fully depleted. Typical values of the bias current are about 2:5 mA: The noise occupancy at 1 fC threshold has to be lower than 5 104 as for the specifications: while unirradiated modules are well below this limit, irradiated modules have higher noise, see Fig. 3. This behaviour has been already observed during the individual tests of those modules. The common mode noise measurement yields negligible pick-up for the irradiated modules too.
Scheme A: the module ground is DC connected to the cooling block but not to the copper enclosure (shield). Scheme B: the module ground is shorted to the shield at the first Patch Panel. The shunt shields are used, as described in Section 2. Scheme C: The module ground is shorted to the shield and DC connected to the cooling block. A sinusoidal noise current has been injected into the LMTs: the response to the noise injection depends on the mounting position of the module. The modules which are mounted nearer to the
5. The end-cap system test The end-cap system test is mounted on a carbon fibre sector that corresponds to one-fourth of a disk and can hold up to 13 outer, 10 middle and 10 inner modules. The sector is supported by an aluminium frame contained in a copper enclosure that is representative of the thermal shield. Fig. 1b shows the forward system test with 6 modules mounted on the sector. The noise performance of the modules is well within the specifications, i.e. lower than 1500 electrons. Noise occupancy measurements obtained with up to 6 modules mounted on the sector are in good agreement with the individual results on the electric bench. The grounding and shielding scheme used for the forward system test is also based on [10]. Shunts shield protect the signal ground from variations in the potential of the cooling blocks on which the modules are mounted and are integrated in the design of the K5 forward modules used in the tests described below. Three different grounding and shielding schemes have been selected as the ones with best performances:
Fig. 4. Noise pick-up in ENC for each chip of three outer modules mounted on the end-cap system test. (a) Shows the noise pick-up when sinusoidal noise at 10 MHz frequency has been injected with grounding scheme A (light grey/red) and in scheme B (black); (b) noise pick-up in scheme C for injected noise at several frequencies between 2 and 35 MHz: the maximum pick-up noise is at 10 MHz: Each entry in the plot represents the noise in one chip.
ARTICLE IN PRESS P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
LMT tapes (see module in the centre of Fig. 4) suffer of larger pick-up. As can be seen in Fig. 4a scheme A performs slightly better than scheme B, but the best results are obtained with scheme C shown in Fig. 4b.
6. Conclusions Results of the tests done on the SCT forward and barrel system test are demonstrating that the noise performances of the system are well within specifications, negligible common mode noise is found, no cross-talk and low noise pick-up are observed. The system test measurements are also determinant for the choice of the final grounding and shielding to be adopted in ATLAS.
43
References [1] Y. Unno, Nucl. Instr. and Meth. A 453 (2000) 109. [2] T. Kondo, Nucl. Instr. and Meth. A 485 (2002) 27. [3] W. Dabrowski, et al., The ACBD Binary readout chip for silicon strip detectors in the ATLAS Silicon Tracker, CERN/LHCC/98-36, 175. [4] H. Pernegger, et al., ATL-IS-ES-0042. [5] J. Bohm, et al., ATL-IS-ES-0088. [6] D.J. white, et al., Nucl. Instr. and Meth. A 457 (2001) 369. [7] ATLAS Collaboration, ATLAS Technical Design Report—Inner Detector, CERN/LHCC/97-16 and CERN/ LHCC/97-17 (1997). [8] http://root.cern.ch/. [9] L. Feld, et al., Nucl. Instr. and Meth. A 487 (2002) 557. [10] N. Spencer, ATLAS SCT/Pixel grounding and shielding note, ATL-IC-EN-0004; N.A. Smith, et al., Grounding and shielding for the SCT end-cap, ATL-IS-ER-0019.
Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
The ATLAS Semiconductor Tracker system test results P. Ferrari CERN-PH, 1211 Geneve 23, Switzerland On behalf of the ATLAS SCT Collaboration Available online 11 June 2004
Abstract Results are presented of tests with a prototype of a partial sector of the ATLAS SCT barrel and end-cap. This setup simulates the geometry and the electrical configuration of the final SCT detector in all its details of mounting, cooling, supply and shielding. An overview of the performances of the system and its components is presented in this paper. r 2004 Elsevier B.V. All rights reserved. PACS: 29.40.Gx Keywords: Tracking; Silicon strip
1. Introduction The ATLAS Semiconductor Tracker (SCT) consists of four nested cylindrical barrel sectors centred around the interaction point and nine disks in each of the two endcaps covering the forward region up to a pseudorapidity Z of 2.5, where Z ¼ ln tanðy=2Þ: The barrel layers and endcap disks will accommodate 4088 SCT modules consisting of single sided p-in-n silicon microstrip detectors. Each SCT module [1,2] is made of two planes of silicon micro-strips glued back to back at a small stereo angle of 40 mrad in order to provide bidimensional track reconstruction. Each plane of the barrels sensors consists of two 6 6 cm2 wafers for a total active strip length of about E-mail address: [email protected] (P. Ferrari).
12 cm: The end-cap sensors have three different radial geometries depending on their mounting position on the disks: inner, middle or outer. The sensors are glued on a highly thermally conductive baseboard. The modules are read out via 12 ASICS [3] mounted on a copper/kapton hybrid. The chips provide high-gain ð50 mV=fCÞ; fastshaping (20 ns peaking time) binary read out of 128 channels using radiation-hard technology. All channels read out by a chip have a common discrimination threshold, but channel specific variations can be compensated with a 4-bit trim DAC. The hit pattern is transferred to a binary pipeline that is 132 cells deep. To validate the electrical and noise performance of the detector, a system test for the barrel and the end-cap has been set up at CERN with the aim of running as many modules as possible in a configuration as close as possible to the one of the final ATLAS SCT.
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.05.044
ARTICLE IN PRESS P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
2. The system test setup The powering of the modules goes through three patch panels: 30 m long conventional cables connect prototype custom made low and highvoltage power supplies to Patch Panel 3 (PP3). Each low-voltage power supply card not only supplies analog and digital voltages to the detectors, but also reads out the NTC thermistor mounted on each side of the module. Before irradiation each module dissipates 5:6 W at 0 C [4], out of which 5.4 and 0:2 W are dissipated by the hybrid and the strips, respectively. After 10 years of operation at the LHC the modules will dissipate up to 10 W; out of which 7.5 and 2:5 W are dissipated by the chip and by the strips, respectively. Heat is dissipated through the baseboards which are clamped on aluminium cooling pipes in which an ethanol–water mixture is pumped. The temperature of this fluid is controlled by a commercial chiller. The high-voltage power supply powers 4 channels and provides maximum output voltage of 500 V: Final-design versions of these cards have been also tested at the barrel system test fulfilling the specifications [5]. The second section of the powering layout is not the final one since PP3 is directly connected to a second patch panel (PP2); 4 m long 100 mmaluminium-on-kapton power tapes connect to the next patch panel (PP1). To minimise the material in the SCT tracking volume the innermost section consists of 1:5 m long 50 mm-aluminium-on-kapton tapes (LMT). The LMT cables have a 0:05 4:5 mm2 cross-section and a 0:275 O=m resistance. Data and commands are transferred as optical signals through 25 m long optical fibres. Two chips are used to convert optical signals into electrical signals and vice versa, which are, respectively: the Digital Optical Receiver Integrated Circuit (DORIC) and the VCSEL Driver Chip (VDC) ASICS [6], where VECSEL stands for Vertical Cavity Surface Emitting Laser diode. The final readout system will be based on Read-Out Drivers (ROD) [7], but for the system test readout a custom set of VME modules has been adopted. A Data Acquisition software package based on ROOT [8] is running on a PC interfaced to the VME crate via a
39
National Instruments PC-VME interface. A CLOck And Control module (CLOAC) and a SLOw control Generator (SLOG) provide the 40 MHz-clock, trigger and commands, a MUltichannel Semiconductor Tracker Abcd Readout Device (MUSTARD) decodes the data received from the modules and an OPTo-electrical InterFace (OPTIF) acts as optical data receiver and transforms the clock and commands electronic signals into optical signals. A Detector Control System DCS is checking the humidity and the temperature of the cooling pipes.
3. Set of measurements This paper summarises the results of the following set of measurements: *
*
Three point gain calibration scan: 3 different charges (1.5, 2 and 2:5 fC) are injected at the preamplifier input individually for each detector strip. The choice of the injected charges is determined by the necessity to have a quick evaluation of the gain in the region between the operational discrimination threshold ðQTH ¼ 1 fCÞ and the typical signal charge ðQSIGNAL B3:3 fCÞ: The response to the calibration charge is obtained by scanning the discriminator threshold, resulting in an occupancy ‘‘s-curve’’ histogram for each channel. A complementary error function is fitted to this histogram, yielding the median 50% point efficiency and the noise from the Gaussian spread. The gain of the detectors amplification chain can be obtained as a linear fit of the mean results of the three fits. The Equivalent Noise Charge (ENC) can be extracted from the ratio of the noise and the gain. Noise occupancy: is obtained as a function of the threshold charge from calibrations scans. A linear fit to the ln(Occupancy) is performed in order to determine the ENC. In fact for a threshold charge QTH bQNOISE the following Q2
relation holds: ln(Occupancy) B 12 Q2 TH ; see NOISE Ref. [9]. Deviations from the linear behaviour would indicate noise pick-up.
ARTICLE IN PRESS 40 *
P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
Common mode noise measurement: the mean and the variance of the hits on a large number of events are related assuming a random noise source in the noise occupancy measurement. Deviations from the random noise behaviour are indicating the presence of common mode noise [9].
4. The barrel system test The barrel system test consists of a prototype sector built to hold up to 48 modules. Four harnesses are mounted on it, three on one side and one on the other. Therefore a full row of 12 modules could be mounted on the sector like in the final ATLAS detector, see Fig. 1a. Nonirradiated detectors are fully depleted at 50 V and have been
Fig. 2. Noise measurements in ENC with a row of 12 modules on the sector. Comparisons are shown between noise measured (a) in a noise occupancy scan and in a calibration scan (b) in a calibration scan and in individual measurements on the electrical bench. Modules are indicated by their serial number and the ordering on the plot refers to the actual mounting position on the sector. Each entry on the plot represents the average noise per chip.
Fig. 1. (a) Photograph of the barrel system test showing a configuration with one row completely equipped with modules. (b) The end-cap system test with 6 modules mounted on the sector.
operated at 100 V in the tests described in the following. Noise measurements from a 3 point gain and noise occupancy scans give compatible results within 100-200 ENC, see Fig. 2a. The differences in the results are determined by the diversity of the two methods. Good agreement is also found when comparing the results obtained on the sector with individual results on the electrical bench, see Fig. 2b. Larger noise on the sector would have indicated the presence of noise pick-up or cross-talk between modules overlapping along the z direction or between the left and the right harnesses, which are floating with respect to each other. In Fig. 2a and b the modules are operated at 15 C ambient temperature (warm
ARTICLE IN PRESS P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
running), while the final operational temperature at LHC will be around—7 C (cold running). The modules noise when running cold is well within the specifications, i.e. below 1500 ENC. The noise increases with temperature by 6 ENC= C: These measurements have been repeated with 16 modules mounted on the 3 left harnesses to check the behaviour of the sector when modules are overlapping both in the z and in the azimuthal direction. The results are in good agreement with the ones obtained on the electrical bench. The common mode noise is found to be always lower than 150 ENC but in most cases compatible with zero within the statistical error of the measurement, therefore the contribution of common mode noise can be considered small. Different grounding configurations have been studied for the barrel system test. The configurations [10] giving the best results are discussed in the following. One of the goals of the grounding schemes is to avoid capacitive effects between the highly conductive baseboard and the cooling pipes that would result in unwanted noise in the front end electronics. The main characteristics of the grounding schemes are summarised below: Scheme A: DC connection between module ground and cooling pipe. The cooling pipes are electrically connected in the sector centre. In fact, as for the harnesses, each cooling pipe serves only one half of the sector. Scheme B: cooling pipes are not electrically connected in the sector centre. Shunt shields are used. The shunt shields are copper on kapton pads placed between the cooling pipe and the baseboard and connected to the module reference ground, such that variations of the potential on the cooling pipe would induce variations on the shunt shield potential only. To verify the performances of different grounding schemes a sinusoidal noise current at different frequencies, ranging from 2 to 35 MHz; has been injected into the system. The current has been injected via a magnetic field generated by a ferrite and a coil into different components of the system: (1) in an individual conventional cable, (2) in a bundle of 6 tape pairs between PP2 and PP1 and (3) in the cooling pipes and in the thermal shield surrounding the sector. The noise pick-up is
41
Fig. 3. (a) Noise pick-up of a row of 12 barrel modules indicated by their serial number, when injecting a 10 MHz noise in a conventional cable in scheme A (dark grey/red) and in scheme B (lighter grey/green). Each histogram entry represents the noise in one chip. (b) Noise occupancy measured at a threshold of 1 fC averaged over more than 100 individual measurements, the four modules on the right having been irradiated. Each entry in the plot represents the average occupancy per chip.
obtained from single calibration scans at a threshold of 2 fC as the difference in noise with respect to no injection. For all injection modes the maximum pick-up is for 10 MHz noise. The performance of grounding scheme A is worse,
ARTICLE IN PRESS 42
P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
equivalent and better than scheme B for injection of type 1, 2, 3, respectively, see Fig. 3. The two grounding schemes seem therefore to be equivalent, but more information on this subject is expected from a revised system test with grounding and shielding closer to that planned for the final SCT. Four irradiated modules have been mounted on the sector and tested. The full modules have been irradiated with 3 1014 24 GeV protons=cm2 ; corresponding to 1.5 times the LHC dose, and annealed for 7 days at 25 C: The modules have been operated at 103 C and at 350 V depletion voltage, being fully depleted. Typical values of the bias current are about 2:5 mA: The noise occupancy at 1 fC threshold has to be lower than 5 104 as for the specifications: while unirradiated modules are well below this limit, irradiated modules have higher noise, see Fig. 3. This behaviour has been already observed during the individual tests of those modules. The common mode noise measurement yields negligible pick-up for the irradiated modules too.
Scheme A: the module ground is DC connected to the cooling block but not to the copper enclosure (shield). Scheme B: the module ground is shorted to the shield at the first Patch Panel. The shunt shields are used, as described in Section 2. Scheme C: The module ground is shorted to the shield and DC connected to the cooling block. A sinusoidal noise current has been injected into the LMTs: the response to the noise injection depends on the mounting position of the module. The modules which are mounted nearer to the
5. The end-cap system test The end-cap system test is mounted on a carbon fibre sector that corresponds to one-fourth of a disk and can hold up to 13 outer, 10 middle and 10 inner modules. The sector is supported by an aluminium frame contained in a copper enclosure that is representative of the thermal shield. Fig. 1b shows the forward system test with 6 modules mounted on the sector. The noise performance of the modules is well within the specifications, i.e. lower than 1500 electrons. Noise occupancy measurements obtained with up to 6 modules mounted on the sector are in good agreement with the individual results on the electric bench. The grounding and shielding scheme used for the forward system test is also based on [10]. Shunts shield protect the signal ground from variations in the potential of the cooling blocks on which the modules are mounted and are integrated in the design of the K5 forward modules used in the tests described below. Three different grounding and shielding schemes have been selected as the ones with best performances:
Fig. 4. Noise pick-up in ENC for each chip of three outer modules mounted on the end-cap system test. (a) Shows the noise pick-up when sinusoidal noise at 10 MHz frequency has been injected with grounding scheme A (light grey/red) and in scheme B (black); (b) noise pick-up in scheme C for injected noise at several frequencies between 2 and 35 MHz: the maximum pick-up noise is at 10 MHz: Each entry in the plot represents the noise in one chip.
ARTICLE IN PRESS P. Ferrari / Nuclear Instruments and Methods in Physics Research A 530 (2004) 38–43
LMT tapes (see module in the centre of Fig. 4) suffer of larger pick-up. As can be seen in Fig. 4a scheme A performs slightly better than scheme B, but the best results are obtained with scheme C shown in Fig. 4b.
6. Conclusions Results of the tests done on the SCT forward and barrel system test are demonstrating that the noise performances of the system are well within specifications, negligible common mode noise is found, no cross-talk and low noise pick-up are observed. The system test measurements are also determinant for the choice of the final grounding and shielding to be adopted in ATLAS.
43
References [1] Y. Unno, Nucl. Instr. and Meth. A 453 (2000) 109. [2] T. Kondo, Nucl. Instr. and Meth. A 485 (2002) 27. [3] W. Dabrowski, et al., The ACBD Binary readout chip for silicon strip detectors in the ATLAS Silicon Tracker, CERN/LHCC/98-36, 175. [4] H. Pernegger, et al., ATL-IS-ES-0042. [5] J. Bohm, et al., ATL-IS-ES-0088. [6] D.J. white, et al., Nucl. Instr. and Meth. A 457 (2001) 369. [7] ATLAS Collaboration, ATLAS Technical Design Report—Inner Detector, CERN/LHCC/97-16 and CERN/ LHCC/97-17 (1997). [8] http://root.cern.ch/. [9] L. Feld, et al., Nucl. Instr. and Meth. A 487 (2002) 557. [10] N. Spencer, ATLAS SCT/Pixel grounding and shielding note, ATL-IC-EN-0004; N.A. Smith, et al., Grounding and shielding for the SCT end-cap, ATL-IS-ER-0019.