- Email: [email protected]
Construction and performance of the AMS-02 transition radiation detector for the International Space Station
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 563 (2006) 343–345 www.elsevier.com/locate/nima
Construction and performance of the AMS-02 transition radiation detector for the International Space Station Francesca R. Spada Universita` di Roma ‘‘La Sapienza’’ and INFN, Italy Available online 22 March 2006
Abstract AMS-02 (Alpha Magnetic Spectrometer) will fly during three years on the International Space Station performing spectroscopy of cosmic particles, allowing the direct search of antimatter and the indirect search of dark matter. Annihilation of supersymmetric dark matter candidates could produce an excess in the 10–300 GeV region of the positron spectrum. An overall 106 separation factor for positrons from the more abundant protons is required to detect the signal. A Transition Radiation Detector (TRD) has been designed to achieve these physics goal. r 2006 Elsevier B.V. All rights reserved. PACS: 93.35.+d; 29.40.Cs Keywords: Cosmic rays; Dark matter; Transition radiation
1. Introduction The AMS-02 (Alpha Magnetic Spectrometer) will operate on the International Space Station performing spectroscopy of cosmic rays, directly searching for antimatter (i.e., antihelium nuclei) and indirectly searching for dark matter, trying to identify the products of the annihilation of candidates such as neutralinos. A relativistic (g1000 or greater) charged particle crossing the interface between two media with different dielectric constants has a probability of the order of 1% to emit a photon in the soft X-ray region [1]. The energy of the emitted photon depends from the particle’s mass and momentum, thus allowing for particle discrimination at very high energies where e.g. Cherenkov detectors are no longer useful. The annihilation of a neutralino of a few hundred GeV mass could produce an excess in the 10–300 GeV region of the cosmic rays positron spectrum. With the joint use of a Transition Radiation Detector (TRD) and of an electromagnetic calorimeter, providing an overall 106 rejection factor for protons, AMS can detect a positron with a 90% efficiency (in the energy range under Tel.: +39 06 49694212; fax: +39 06 4957697.
E-mail address: [email protected]. 0168-9002/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2006.02.184
study, protons are about 104 times more abundant than positrons in ordinary cosmic rays). 2. The TRD layout The probability of transition radiation emission increases with the number of boundaries that the particle has to cross, but a compromise with the correspondent photon absorption increase must be found. In the TRD of AMS-02 the radiator is a fleece of 10 mm thick propylene fibers (LRP 375 BK), with a density of 0.06 g/cm3 [2]. The photon emission probability thus increases to 50%, and the X-rays can be collected, together with the ionization, in proportional straw tubes of 6 mm diameter filled with a Xe:CO2 [80:20] gas mixture. The tubes provide large nuclear measurements, fast drift of ionization electrons with no collection losses, high gain in the amplification region around the sense wire. The overall detector consists of 328 modules of 16 tubes each, interleaved with the radiator. To minimize the absorption, the carbon stiffeners and the support structures are as thin as possible compatibly with the mechanical stability of the module, that has to withstand the launch vibrations [3]. The detector has also to match weight requirements: this is why even though the
ARTICLE IN PRESS F.R. Spada / Nuclear Instruments and Methods in Physics Research A 563 (2006) 343–345
344
proton–positron separation capability increases with the number of radiator–detector layers, this has been limited to 20. The layers are arranged into an octagonal structure made of aluminum honeycomb walls and carbon fiber skins and bulkheads. The modules have different sizes, the shortest one being 0:8 m and the longest one 2 m. The upper and lower four layers lay parallel to the magnetic field, while the 12 central ones are orthogonal to it, to increase the tracking capability in the bending plane. The tube walls are made of a double layer kapton–aluminum foil of 72 mm thickness. The gas is distributed through polycarbonate end-pieces, which also center the Cu–Te crimp plugs holding the 30 mm gold-plated tungsten wire, which is tensioned with 1 N. Each of the 5248 straws is individually tested for gas tightness.
a gas composition analyzer and calibration tubes that monitor the detector performance; the manifolds that distribute the gas mixture to the straw tubes, equipped with shut-off valves which can isolate any of the 41 TRD segments in case of leakage. A feed control between supply box and circulation box is activated by computer approximately once per day to create the gas mixture and transfer it to the TRD system. At all points of the gas system, the valves have a two-fold redundancy. The system is piped with 3 or 6 mm outer diameter of stainless steel tubes with welded joints. The gas mixture is circulated through these tubes in a continuous loop. The pumps circulate the gas in the TRD at a pressure of approximately of 1.4 bar, and about 7 l per day are transferred to the TRD from the supply box, and the composition is continuously monitored to ensure the stability of the gas gain. The TRD gas system is shown in Fig. 1.
3. The gas distribution system The xenon and CO2 used to form the gas mixture are kept in two tanks of 50 and 40 cm of diameter respectively, containing an initial amount of 46 l of xenon and 4 l of carbon dioxide at pressures of 107 and 65 bar, respectively. This guarantees three to five years of operation. The system is divided in three blocks: a supply box, where the gas containers and the mixing system are located, and where the Xe–CO2 mixture is prepared and stored in a 1 l volume vessel; a circulation box, containing circulation pumps,
4. The gas system electronics The gas circulation system includes a Monitoring and Control Computer (JMDC), and a Power Distribution Box (PDB), which distributes the power supply from the 120 VDC provided by the Space Station. A board, named USCM (U¨bergangstrahlung Control Module) is connected to the monitor and control computer and main
FROM GSE
TO GSE
BOX C
V8a
RV5 Burkert 6124
BOX S
F3a Va Marotta MV197
T Xe vessel 107 bar
F1a
V1a Marotta MV197
V10a Marotta MV197
Kulite 0-3000
P1b GP50 0-3000
P1d Kulite 0-3000
CO2 vessel 65 bar
F1b
V20b Marotta MV197 V10b Marotta MV197
Vb F3b
V3a V2a Marotta Marotta F2a MV197 MV197 30 cc 60 cc O1a
V20a Marotta MV197
P1c
P1a GP50 0-3000
T
V8b
V1b Marotta MV197
Rv3a
burst disc
21 bar Rv3b
P2a GP50 0-300 V4a O2a
V18a
Marotta MV197 V18b V4b O2b
T 15 cc
O1b V3b V2b 30 cc Marotta F2b Marotta MV197 MV197
RV4 P3 GP50 0-25
V6a Marotta MV100 V6b
P2c Kulite 0-300
D vessel
CP2
multichannel analyzer
T
spirometer
Burkert CP1 6124
P4 GP50 0-25
MANIFOLD SEGMENT Vim D Burkert 6124
P2b GP50 0-300
5.6 liters P im B Honeywell
Fig. 1. The AMS-02 TRD gas system.
Vim C Vim B Vim A Burkert TRD segment Burkert Burkert 6124 6124 6124
Pim A Honeywell
ARTICLE IN PRESS F.R. Spada / Nuclear Instruments and Methods in Physics Research A 563 (2006) 343–345
data acquisition via CAN-BUS, and to the gas system control electronics via a dedicated custom bus. Via the USCM operates the monitor program, which tests the status information of the gas system against pre-conditions and executes operational commands. Other dedicated boards provide an electronic interface between the USCM and the electromechanical gas system devices, controlling the operations that contribute to provide the correct gas mixture, to monitor pressure and filling status (supply box). This interface runs the pumps, open valves to refill the TRD and monitor the gas pressure (circulation box). In
345
case of power and communications failure, the electronics will shut down the gas system safely.
References [1] R. Battiston, Nucl. Phys. Proc. Suppl. 44 (1995) 274; J. Alcaraz, et al., Nuovo Cimenta A 112 (1999) 1325; W.J. Burger, Nucl. Phys. Proc. Suppl. 113 (2002) 139. [2] T. Siedenburg, et al., Nucl. Phys. Proc. Suppl. 113 (2002) 154. [3] O. Toker, et al., Nucl. Instr. and Meth. A 340 (1994) 572; B. Alpat, et al., Nucl. Instr. and Meth. A 446 (2000) 552.
Nuclear Instruments and Methods in Physics Research A 563 (2006) 343–345 www.elsevier.com/locate/nima
Construction and performance of the AMS-02 transition radiation detector for the International Space Station Francesca R. Spada Universita` di Roma ‘‘La Sapienza’’ and INFN, Italy Available online 22 March 2006
Abstract AMS-02 (Alpha Magnetic Spectrometer) will fly during three years on the International Space Station performing spectroscopy of cosmic particles, allowing the direct search of antimatter and the indirect search of dark matter. Annihilation of supersymmetric dark matter candidates could produce an excess in the 10–300 GeV region of the positron spectrum. An overall 106 separation factor for positrons from the more abundant protons is required to detect the signal. A Transition Radiation Detector (TRD) has been designed to achieve these physics goal. r 2006 Elsevier B.V. All rights reserved. PACS: 93.35.+d; 29.40.Cs Keywords: Cosmic rays; Dark matter; Transition radiation
1. Introduction The AMS-02 (Alpha Magnetic Spectrometer) will operate on the International Space Station performing spectroscopy of cosmic rays, directly searching for antimatter (i.e., antihelium nuclei) and indirectly searching for dark matter, trying to identify the products of the annihilation of candidates such as neutralinos. A relativistic (g1000 or greater) charged particle crossing the interface between two media with different dielectric constants has a probability of the order of 1% to emit a photon in the soft X-ray region [1]. The energy of the emitted photon depends from the particle’s mass and momentum, thus allowing for particle discrimination at very high energies where e.g. Cherenkov detectors are no longer useful. The annihilation of a neutralino of a few hundred GeV mass could produce an excess in the 10–300 GeV region of the cosmic rays positron spectrum. With the joint use of a Transition Radiation Detector (TRD) and of an electromagnetic calorimeter, providing an overall 106 rejection factor for protons, AMS can detect a positron with a 90% efficiency (in the energy range under Tel.: +39 06 49694212; fax: +39 06 4957697.
E-mail address: [email protected]. 0168-9002/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2006.02.184
study, protons are about 104 times more abundant than positrons in ordinary cosmic rays). 2. The TRD layout The probability of transition radiation emission increases with the number of boundaries that the particle has to cross, but a compromise with the correspondent photon absorption increase must be found. In the TRD of AMS-02 the radiator is a fleece of 10 mm thick propylene fibers (LRP 375 BK), with a density of 0.06 g/cm3 [2]. The photon emission probability thus increases to 50%, and the X-rays can be collected, together with the ionization, in proportional straw tubes of 6 mm diameter filled with a Xe:CO2 [80:20] gas mixture. The tubes provide large nuclear measurements, fast drift of ionization electrons with no collection losses, high gain in the amplification region around the sense wire. The overall detector consists of 328 modules of 16 tubes each, interleaved with the radiator. To minimize the absorption, the carbon stiffeners and the support structures are as thin as possible compatibly with the mechanical stability of the module, that has to withstand the launch vibrations [3]. The detector has also to match weight requirements: this is why even though the
ARTICLE IN PRESS F.R. Spada / Nuclear Instruments and Methods in Physics Research A 563 (2006) 343–345
344
proton–positron separation capability increases with the number of radiator–detector layers, this has been limited to 20. The layers are arranged into an octagonal structure made of aluminum honeycomb walls and carbon fiber skins and bulkheads. The modules have different sizes, the shortest one being 0:8 m and the longest one 2 m. The upper and lower four layers lay parallel to the magnetic field, while the 12 central ones are orthogonal to it, to increase the tracking capability in the bending plane. The tube walls are made of a double layer kapton–aluminum foil of 72 mm thickness. The gas is distributed through polycarbonate end-pieces, which also center the Cu–Te crimp plugs holding the 30 mm gold-plated tungsten wire, which is tensioned with 1 N. Each of the 5248 straws is individually tested for gas tightness.
a gas composition analyzer and calibration tubes that monitor the detector performance; the manifolds that distribute the gas mixture to the straw tubes, equipped with shut-off valves which can isolate any of the 41 TRD segments in case of leakage. A feed control between supply box and circulation box is activated by computer approximately once per day to create the gas mixture and transfer it to the TRD system. At all points of the gas system, the valves have a two-fold redundancy. The system is piped with 3 or 6 mm outer diameter of stainless steel tubes with welded joints. The gas mixture is circulated through these tubes in a continuous loop. The pumps circulate the gas in the TRD at a pressure of approximately of 1.4 bar, and about 7 l per day are transferred to the TRD from the supply box, and the composition is continuously monitored to ensure the stability of the gas gain. The TRD gas system is shown in Fig. 1.
3. The gas distribution system The xenon and CO2 used to form the gas mixture are kept in two tanks of 50 and 40 cm of diameter respectively, containing an initial amount of 46 l of xenon and 4 l of carbon dioxide at pressures of 107 and 65 bar, respectively. This guarantees three to five years of operation. The system is divided in three blocks: a supply box, where the gas containers and the mixing system are located, and where the Xe–CO2 mixture is prepared and stored in a 1 l volume vessel; a circulation box, containing circulation pumps,
4. The gas system electronics The gas circulation system includes a Monitoring and Control Computer (JMDC), and a Power Distribution Box (PDB), which distributes the power supply from the 120 VDC provided by the Space Station. A board, named USCM (U¨bergangstrahlung Control Module) is connected to the monitor and control computer and main
FROM GSE
TO GSE
BOX C
V8a
RV5 Burkert 6124
BOX S
F3a Va Marotta MV197
T Xe vessel 107 bar
F1a
V1a Marotta MV197
V10a Marotta MV197
Kulite 0-3000
P1b GP50 0-3000
P1d Kulite 0-3000
CO2 vessel 65 bar
F1b
V20b Marotta MV197 V10b Marotta MV197
Vb F3b
V3a V2a Marotta Marotta F2a MV197 MV197 30 cc 60 cc O1a
V20a Marotta MV197
P1c
P1a GP50 0-3000
T
V8b
V1b Marotta MV197
Rv3a
burst disc
21 bar Rv3b
P2a GP50 0-300 V4a O2a
V18a
Marotta MV197 V18b V4b O2b
T 15 cc
O1b V3b V2b 30 cc Marotta F2b Marotta MV197 MV197
RV4 P3 GP50 0-25
V6a Marotta MV100 V6b
P2c Kulite 0-300
D vessel
CP2
multichannel analyzer
T
spirometer
Burkert CP1 6124
P4 GP50 0-25
MANIFOLD SEGMENT Vim D Burkert 6124
P2b GP50 0-300
5.6 liters P im B Honeywell
Fig. 1. The AMS-02 TRD gas system.
Vim C Vim B Vim A Burkert TRD segment Burkert Burkert 6124 6124 6124
Pim A Honeywell
ARTICLE IN PRESS F.R. Spada / Nuclear Instruments and Methods in Physics Research A 563 (2006) 343–345
data acquisition via CAN-BUS, and to the gas system control electronics via a dedicated custom bus. Via the USCM operates the monitor program, which tests the status information of the gas system against pre-conditions and executes operational commands. Other dedicated boards provide an electronic interface between the USCM and the electromechanical gas system devices, controlling the operations that contribute to provide the correct gas mixture, to monitor pressure and filling status (supply box). This interface runs the pumps, open valves to refill the TRD and monitor the gas pressure (circulation box). In
345
case of power and communications failure, the electronics will shut down the gas system safely.
References [1] R. Battiston, Nucl. Phys. Proc. Suppl. 44 (1995) 274; J. Alcaraz, et al., Nuovo Cimenta A 112 (1999) 1325; W.J. Burger, Nucl. Phys. Proc. Suppl. 113 (2002) 139. [2] T. Siedenburg, et al., Nucl. Phys. Proc. Suppl. 113 (2002) 154. [3] O. Toker, et al., Nucl. Instr. and Meth. A 340 (1994) 572; B. Alpat, et al., Nucl. Instr. and Meth. A 446 (2000) 552.