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The HEPD detector on board CSES satellite: in-flight performance
Available online at www.sciencedirect.com
Nuclear and Particle Physics Proceedings 306–308 (2019) 92–97 www.elsevier.com/locate/nppp
The HEPD detector on board CSES satellite: in-flight performance Valentina Scottia,b , Giuseppe Osteriab , for CSES-Limadou Collaboration a Universit` a
di Napoli “Federico II” sezione di Napoli
b INFN
Abstract In this paper we will present a description of the High Energy Particle Detector (HEPD) onboard the China Seismo Electromagnetic Satellite (CSES) and its (preliminary) performance in flight. CSES mission aims at monitoring electromagnetic field, plasma and particles perturbations of atmosphere and inner Van Allen belts caused by solar and terrestrial phenomena and to the study of the low energy component of the cosmic rays. The satellite was launched from the Jiuquan Satellite Launch Center located in west of inner Mongolia on February 2nd , 2018 and is now orbiting in nominal condition. It hosts several instruments onboard: two magnetometers, an electrical field detector, a plasma analyser, a Langmuir probe and two particle detectors. The high energy particle detector (HEPD), designed and built by the Italian Limadou collaboration, is able to separate electrons and protons and identify nuclei up to Iron. HEPD provides good energy resolution and high angular resolution for electrons (3-100 MeV) and proton (30-200 MeV). The instrument consists of: 2 planes of double-side silicon microstrip sensors placed on the top of the instrument (direction of particle); 2 two layers of plastic scintillators (trigger) and a calorimeter (constituted by other 16 scintillators and a layer of LYSO sensors). A scintillator veto system completes the instrument. The commissioning of the HEPD and the other instruments on board was successfully completed in July 2018. Keywords: Instrumentation for Astroparticle Experiments, Satellite experiment
1. CSES Mission CSES (China Seismo-Electromagnetic Satellite) is a scientific mission dedicated to monitoring electromagnetic, plasma and particles perturbations of atmosphere, ionosphere, magnetosphere and Van Allen belts induced by natural sources and anthropocentric emitters and to study their correlations with the occurrence of seismic events. The CSES mission is part of a collaboration program between the China National Space Administration (CNSA) and the Italian Space Agency (ASI). The project is developed by China Earthquake Administration (CEA) and Italian National Institute for Nuclear Physics (INFN), together with several Chinese and Italian Universities and research Institutes. https://doi.org/10.1016/j.nuclphysbps.2019.07.014 2405-6014/© 2019 Elsevier B.V. All rights reserved.
CSES-1 is the first satellite of a space monitoring system proposed in order to investigate the topside ionosphere - with the most advanced techniques and equipment - and designed in order to gather world-wide data of the near-Earth electromagnetic environment. The observations will contribute to provide an observations sharing service for international cooperation and the scientific community. The first satellite was launched in February 2018 with an expected lifetime of 5 years. The satellite is on a Sun-synchronous orbit with 97.4◦ inclination, a height of about 507 km and an ascending node of 14:00 local time. The satellite is a 3-axis attitude stabilized satellite based on CAST2000 platform, with a total mass of 730 kg , and a peak power consumption of 900 W. The scientific payloads hosted onboard are a search-
V. Scotti, G. Osteria / Nuclear and Particle Physics Proceedings 306–308 (2019) 92–97
Measurements Electrical and magnetic fields and their perturbations in ionosphere Disturbance of plasma in ionosphere Flux and energy spectrum of the particles in the radiation belts Profile of electronic content
93
Instruments Search Coil Magnetometer (SCM) Fluxgate magnetometer Electrical Field Detector (EFD) Plasma analizer (PAP) Langmuir probe (LAP) High Energy Particle Package (HEPP) High Energy Particle Detector (HEPD) GPS occultation receiver (GNSS-RO) Tri-frequency transmitter (TBB)
Table 1: HEPD main technical characteristics.
Figure 1: An overview of the China Seismo-Electromagnetic Satellite.
coil magnetometer [1], an electric field detector [2], a high precision magnetometer [3], a GNSS Occultation receiver, a plasma analyzer, a Langmuir probe, an energetic particle detector [4] [8], and a three-frequency beacon. A schematic view of the satellite is showed in Figure 1, while the main purposes of every instrument are summarized in table 1. There are two different orbital working zones: • payload operating zone: instruments will collect measurements (latitude range of ±65◦ ); • platform adjustment zone: all detectors are switched off, in order to perform the activities of the satellite attitude and orbit control system. 2. The High Energy Particle Detector The High-Energy Particle Detector (HEPD) of the CSES satellite, described in this paper, has been designed for investigating seismo-induced particles perturbations. The particles trapped in the geomagnetic field lines of the Van Allen belts execute gyro-motion, bouncing and longitudinal drift according with their adiabatic invariants. The trapped particles are sensitive to both solar terrestrial interactions and the internal electromagnetic emissions from the geomagnetic cavity. These effects constitute a background in studying possible elec-
tromagnetic perturbations induced by lithospheric processes. Even though with extremely less efficacious effects, also the seismo-electromagnetic fluctuations occurring in space are capable to generate local perturbations of the inner Van Allen belt. Anomalous sharp increases of electron and proton counting rates (from a few MeV to several tens and hundreds of MeV) have been detected mostly below the inner Van Allen radiation belt, near the South Atlantic anomaly (SAA), at altitudes of about 400 –1200 km, by several space experiments. The existence of a temporal correlation between these anomalous fluctuations, called particle bursts (PBs), and the occurrence of earthquakes of medium and strong magnitude have been suggested by several authors [5] and confirmed by data obtained on board of METEOR3A and AUREOL-3 satellites [6] [7]. By measuring energy spectrum, direction and composition of particle fluxes, HEPD will study the stability of the inner Van Allen belts and particles precipitation trying to carefully discriminate anomalous events possibly induced by seismic events from the natural background, caused by geomagnetic, tropospheric and anthropogenic electromagnetic emissions. Another very important scientific objective of the HEPD is the study of the solar-terrestrial environment, as Coronal Mass Ejections (CMEs), Solar Energetic Particle (SEP) events and low-energy cosmic rays. The CSES mission will monitor the solar impulsive activity and the cosmic ray solar modulation by detecting proton and electron fluxes from a few MeV to hundreds MeV. These measurements will provide an extension down to
V. Scotti, G. Osteria / Nuclear and Particle Physics Proceedings 306–308 (2019) 92–97
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Parameter Energy Range
Figure 2: A schematic view of the High-Energy Particle Detector.
Angular resolution Energy resolution Particle identification Free field of view Pointing Operative temperature Mass Power Consumption Mechanical dimensions
Value Electrons: 3-100 MeV Protons: 30-200 MeV < 8◦ 5 MeV < 10% 5 MeV > 90% ≥ 70◦ Zenith -10◦ +45◦ 45 kg ∼27 W 530 × 382 × 404 mm3
Table 2: HEPD main technical characteristics.
very low energy of the range of the particle spectra obtained in the current 24th solar cycle by PAMELA and AMS experiments. Moreover, fluxes of light nuclei up to hundreds MeV/n will be provided. 3. The instrument The High-Energy Particle Detector is designed to detect electrons in the energy range between 3 and 100 MeV, protons between 30 and 200 MeV and light nuclei. The detector is made up of several sub-detectors arranged as shown in Fig.2: • Tracker: two planes of double-side silicon microstrip detectors are placed on the top of the detector in order to track the direction of the incident particle limiting the effect of Coulomb multiple scattering on the direction measurement; • Trigger: a layer of thin plastic scintillator, placed 10 mm below the tracker, divided into six segments (200 × 30 × 5 mm3 each) along the y direction; • Calorimeter: a tower of 16 layers of 1 cm thick plastic scintillator planes followed by a 3x3 matrix of an inorganic scintillator LYSO. • Veto system, consisting of 5 plastic scintillator counters, four lateral and one at the bottom of the instrument. All the scintillators (plastic and inorganic) are read out by photomultiplier tubes (PMT R9880-210 from Hamamatsu). The Electronics Subsystem [9] of the HEPD can be schematized into three blocks: Silicon detector, Scintillator detectors (trigger, energy and veto detectors), Global control and data managing. Each detector block includes power chain for bias distribution and a data
Figure 3: The launch of CSES from the Jiuquan Satellite Launch Center, China, in the Gobi desert (Inner Mongolia) .
acquisition processing chain. The main Power Supply provides the low voltages to the detector electronics and the high bias voltages for PMTs and silicon modules. The HEPD has mechanical dimensions of 530×382× 404 mm3 , a mass of 45 kg and a power consumption of about 27 W in its default flight configuration. Rejection of particles hitting the lateral or bottom veto planes is performed online or offline by using different trigger commands. An electron/proton separation for fully contained events greater than 90% is achieved by the ΔEvsEtot method, where ΔE is obtained by the two layers of the silicon tracker, while Etot is measured by the calorimeter. Some of the main parameters of HEPD are summarized in table 2. Following the standard procedures for space applications, four models of HEPD have been built and fully integrated in the clean rooms at the INFN laboratories of Roma Tor Vergata in Rome (Italy). The electrical model (EM), the structural and thermal model (STM), the qualification model (QM), and, finally, the flight model (FM). Every model went under several tests, the most significant are described in the following section. The final configuration of the HEPD FM installed on CSES is shown in Figure 6.
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Figure 5: HEPD calibration plot as function of energy (preliminary). Figure 4: Energy loss by 30 MeV electrons within the upper segment of the HEPD calorimeter. The second and third peaks are produced by the pile-up of 2 or 3 simultaneous electrons.
4. Pre-flight operations A full GEANT4 simulation of the whole apparatus was performed, accounting for detector response to all particles and reproducing readout electronics and trigger conditions. Simulations were developed in order to have Monte Carlo output and real data in the same format. The same software is used to reconstruct the event in both cases, allowing a fair comparison of reconstructed parameters and Monte Carlo truth. In Spring 2016, after the integration of the HEPD in Roma Tor Vergata, the test and qualification campaign of the HEPD QM started. The procedure included vibration test, to simulate launch and flight conditions, and thermal and vacuum test at SERMS laboratory to simulate space environment. These qualification tests were carried on at SERMS laboratory in Terni (PG). Calibrations of the QM and FM were then performed by electron and proton beams. Electron tests took place at the Beam Test Facility (BTF) at the INFN Frascati National Laboratories. The parameters of the BTF were optimized to obtain beam bunches of low multiplicity electrons, for different energies: 30 MeV, 45 MeV, 60 MeV, 90 MeV and 120 MeV. Data collected were transmitted to the EGSE module that was controlled remotely from the control room, so emulating the satellite orbiting conditions. QM and FM were calibrated at different incident angles and positions. The total energy loss in the calorimeter for 30 MeV electrons is shown in Fig. 4. One, two or three electrons hitting the instrument in a single beam bunch are clearly visible. The proton test was performed on the FM at the Proton Therapy Center in Trento (Italy), where a cyclotron produces protons at energies ranging between 70 and
Figure 6: The HEPD mounted on the CSES satellite.
230 MeV. Energies below 70 MeV were obtained by using a degrader along the beam line. The detector was irradiated with protons at different energies between 37 and 228 MeV. The plot in Figure 5 summarizes the (preliminary) results of the calibration of the detector performed on ground by test beams and atmospheric muons. The flight model was shipped to China in December 2016. In January 2017, the functionality of the instrument was successfully tested standalone with its EGSE; then it was installed on the CSES satellite (Figure 6 ). Vibration, thermal-vacuum, magnetic cleanliness and aging tests were accomplished during 2017. In December 2017, HEPD has been transferred to the Jiuquan Satellite Launch Center, China, in the Gobi desert (Inner Mongolia) from where it has been launched, by a Long March 2D rocket, on the February 2nd, 2018. A picture of the launch is shown in Figure 3.
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5. In-flight operation After the launch, the apparatus underwent the commissioning phase. On the 6th February 2018, the HEPD health check procedure was successfully run. The day after HEPD was tested in the framework of the satellite platform verification. The payload operated along 3 orbits. During the commissioning phase (February-July 2018), the HEPD has been tested in different configurations in order to:
with beam test data confirms that the region between 2000 and 4000 ADC counts is mainly associated to a proton contribution.
• study the trigger rates along the orbit in different trigger configurations; • study to define the optimal trigger thresholds in flight; • perform an in-flight calibration to be compared with beam test results. The CPU software is capable to identify the position of CSES with respect to the Earth by using GPS broadcast data sent from the satellite every second, properly configure the detector and apply a scheduled sequence of operations. These procedures include, for instance, dedicated calibration runs performed in the equatorial region. During a calibration run, triggers are generated by the trigger board in order to estimate the pedestals in the signal of each photo-multiplier tube and silicon channel. Since the beginning of May 2018 an encrypted data transfer from China (CEA-ICS) to Italy (ASI-SSDC) has been working. The data retrieval, processing and storage in Italy has been implemented in a two nodes infrastructure with a shared file system providing high availability and high resilience of the storage. A processing pipeline has been developed as several layers of software with an interface to a processing database and to the storage of the infrastructure. The HEPD status is monitored in quasi-real time by quicklook software to get immediate information (strips and PMTs ADC counts, rate and orbital zones, trigger rate, etc).
Figure 7: ADC counts (proportional to energy release) on a channel of the second plane of the energy sub-detector. The two arrows indicate the MIP and the proton peaks.
Measured trigger rate presents an important background contribution due to fragmentation products, off acceptance and re-entrant particles. Figure 8 shows a raw trigger rate map. This map uses data collected from May, 14th up to June, 11th, with HEPD has been operating in a continuous data acquisition mode and in the same stable configuration. This allowed to have a first clean sample of data for analysis purposes (28 days of data-taking and 49 GB of stored raw data). The configuration selected for the generation of the trigger is the coincidence of the trigger plane T and the first three planes of the calorimeter P1, P2 and P3. In Figure 9 it is shown the trend of the trigger rate as a function of the on-board time. The peaks in red refer to the passages over the South Atlantic Anomaly (SAA),
6. In fligh performance: first results A first data analysis has been carried out to compare flight data to ground acquired data: beam test and atmospheric muon data. A comparison with atmospheric muon data confirms (figure 7) that pedestals, as well as the MIP peak, are in the same position, confirming that the behavior of the detector is not changed after the launch. A comparison
Figure 8: Raw trigger rate map.
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• Improved trigger logic and pre-scaling needed • A larger amount of acquired data (mass memory on board for buffering and increased data budget • Improved operating modes
Figure 9: Trigger rate as a function of the on-board time. Different rates on the South Atlantic Anomaly (SAA) and on the poles (NP, SP) are clearly visible.
where the proton belt is nearer the Earths surface due to tilted magnetic axis and the presence of trapped particle population overcomes the other particles by several orders of magnitude. On the other hand, the polar regions (marked as NP and SP in the plot) show lower rates compared to the SAA region, but higher than the equatorial portion of the Earth (marked as EQ) because at higher latitudes the geomagnetic cutoff becomes smaller allowing low energy galactic particles (absent at lower latitudes) to be detected. Particle identification analysis is still ongoing. Background contribution has to be accounted to obtain a proper separation between particle species. Preliminary results show that particle identification is compatible with expectations from simulation, in which no satellite background is accounted for. 7. Conclusions and perspectives The HEPD detector has been designed, built and fully tested for measuring electrons in the energy range between 3 and 100 MeV, protons between 30 and 200 MeV and light nuclei up to oxygen. The wide energetic range allows studying several phenomena beyond the seismo-associated ones, such as those related to magnetospheric currents, dynamics of radiation belts and cosmic rays flux. During the foreseen five years of the mission, a large part of the 24th solar cycle will be monitored. While the HEPD of the CSES-1 mission is successfully acquiring data, design and development of an improved detector for the CSES-2 mission are ongoing. The CSES-2 satellite will be launched in 3 years. The full operational requirement poses some constraints on HEPD-02 design: • Higher trigger rate at polar regions
The new design will have a lot of improvements with minor changes with respect to the first design (identical box dimensions and mechanical interfaces) and budgets. A new trigger system has already been designed, along with a calorimeter and veto shielding upgrade. To improve trigger efficiency a new system with crossed layers of 2 mm thick segmented counters read by lightguides has been designed. Acknowledgments This work was supported by the Italian Space Agency in the framework of the Accordo Attuativo n. 2016-16-H0 Progetto Limadou Fase E/Scienza (CUP F12F1600011005). References [1] Cao J B, Zeng L, Zan F, et al. The electromagnetic wave experiment for CSES mission: Search coil magnetometer. Sci China Tech Sci, 2018, 61:653-658, https://doi.org/10.1007/s11431-0189241-7 [2] L. Alfonsi et al. The HEPD particle detector and the EFD electric field detector for the CSES satellite. Radiation Physics and Chemistry, 2017, 137: 187-192, https://doi.org/10.1016/j.radphyschem.2016.12.022 [3] Cheng B, Zhou B, et al. High precision magnetometer for geomagnetic exploration onboard of the China SeismoElectromagnetic Satellite. Sci China Tech Sci, 2018, 61:659-668, https://doi.org/10.1007/s11431-018-9247-6 [4] Ambrosi G, Bartocci S, Basara L, et al. The HEPD particle detector of the CSES satellite mission for investigating seismoassociated perturbations of the Van Allen belts. Sci China Tech Sci, 2018, 61: 643-652, https://doi.org/10.1007/s11431-0189234-9 [5] Galper A M, Koldashov S V, Voronov S A. High energy particle flux variations as earthquake predictors. Adv Space Res, 1995, 15: 131-134, https://doi.org/10.1016/0273-1177(95)00085-S [6] Galperin Yu I, Gladyshev V A, Jordjio N V, et al. Precipitation of high-energy captured particles in the magnetosphere above epicenter of an incipient earthquake. Cosmic Res, 1992, 30: 89-106 [7] Pustovetov V P, Malyshev A V. Spatial-temporal correlation of the earthquakes and variations of high-energy particle flux in the inner radiation belt. Cosmic Res, 1993, 31: 84-87 [8] Scotti V, Osteria G. The high energy particle detector onboard the CSES satellite, https://doi.org/10.1109/NSSMIC.2016.8069878 [9] Scotti V, Osteria G. The electronics of the HEPD of the CSES experiment, Nuclear and Particle Physics Proceedings, 291-293: 118-121 https://doi.org/10.1016/j.nuclphysbps.2017.06.024
Nuclear and Particle Physics Proceedings 306–308 (2019) 92–97 www.elsevier.com/locate/nppp
The HEPD detector on board CSES satellite: in-flight performance Valentina Scottia,b , Giuseppe Osteriab , for CSES-Limadou Collaboration a Universit` a
di Napoli “Federico II” sezione di Napoli
b INFN
Abstract In this paper we will present a description of the High Energy Particle Detector (HEPD) onboard the China Seismo Electromagnetic Satellite (CSES) and its (preliminary) performance in flight. CSES mission aims at monitoring electromagnetic field, plasma and particles perturbations of atmosphere and inner Van Allen belts caused by solar and terrestrial phenomena and to the study of the low energy component of the cosmic rays. The satellite was launched from the Jiuquan Satellite Launch Center located in west of inner Mongolia on February 2nd , 2018 and is now orbiting in nominal condition. It hosts several instruments onboard: two magnetometers, an electrical field detector, a plasma analyser, a Langmuir probe and two particle detectors. The high energy particle detector (HEPD), designed and built by the Italian Limadou collaboration, is able to separate electrons and protons and identify nuclei up to Iron. HEPD provides good energy resolution and high angular resolution for electrons (3-100 MeV) and proton (30-200 MeV). The instrument consists of: 2 planes of double-side silicon microstrip sensors placed on the top of the instrument (direction of particle); 2 two layers of plastic scintillators (trigger) and a calorimeter (constituted by other 16 scintillators and a layer of LYSO sensors). A scintillator veto system completes the instrument. The commissioning of the HEPD and the other instruments on board was successfully completed in July 2018. Keywords: Instrumentation for Astroparticle Experiments, Satellite experiment
1. CSES Mission CSES (China Seismo-Electromagnetic Satellite) is a scientific mission dedicated to monitoring electromagnetic, plasma and particles perturbations of atmosphere, ionosphere, magnetosphere and Van Allen belts induced by natural sources and anthropocentric emitters and to study their correlations with the occurrence of seismic events. The CSES mission is part of a collaboration program between the China National Space Administration (CNSA) and the Italian Space Agency (ASI). The project is developed by China Earthquake Administration (CEA) and Italian National Institute for Nuclear Physics (INFN), together with several Chinese and Italian Universities and research Institutes. https://doi.org/10.1016/j.nuclphysbps.2019.07.014 2405-6014/© 2019 Elsevier B.V. All rights reserved.
CSES-1 is the first satellite of a space monitoring system proposed in order to investigate the topside ionosphere - with the most advanced techniques and equipment - and designed in order to gather world-wide data of the near-Earth electromagnetic environment. The observations will contribute to provide an observations sharing service for international cooperation and the scientific community. The first satellite was launched in February 2018 with an expected lifetime of 5 years. The satellite is on a Sun-synchronous orbit with 97.4◦ inclination, a height of about 507 km and an ascending node of 14:00 local time. The satellite is a 3-axis attitude stabilized satellite based on CAST2000 platform, with a total mass of 730 kg , and a peak power consumption of 900 W. The scientific payloads hosted onboard are a search-
V. Scotti, G. Osteria / Nuclear and Particle Physics Proceedings 306–308 (2019) 92–97
Measurements Electrical and magnetic fields and their perturbations in ionosphere Disturbance of plasma in ionosphere Flux and energy spectrum of the particles in the radiation belts Profile of electronic content
93
Instruments Search Coil Magnetometer (SCM) Fluxgate magnetometer Electrical Field Detector (EFD) Plasma analizer (PAP) Langmuir probe (LAP) High Energy Particle Package (HEPP) High Energy Particle Detector (HEPD) GPS occultation receiver (GNSS-RO) Tri-frequency transmitter (TBB)
Table 1: HEPD main technical characteristics.
Figure 1: An overview of the China Seismo-Electromagnetic Satellite.
coil magnetometer [1], an electric field detector [2], a high precision magnetometer [3], a GNSS Occultation receiver, a plasma analyzer, a Langmuir probe, an energetic particle detector [4] [8], and a three-frequency beacon. A schematic view of the satellite is showed in Figure 1, while the main purposes of every instrument are summarized in table 1. There are two different orbital working zones: • payload operating zone: instruments will collect measurements (latitude range of ±65◦ ); • platform adjustment zone: all detectors are switched off, in order to perform the activities of the satellite attitude and orbit control system. 2. The High Energy Particle Detector The High-Energy Particle Detector (HEPD) of the CSES satellite, described in this paper, has been designed for investigating seismo-induced particles perturbations. The particles trapped in the geomagnetic field lines of the Van Allen belts execute gyro-motion, bouncing and longitudinal drift according with their adiabatic invariants. The trapped particles are sensitive to both solar terrestrial interactions and the internal electromagnetic emissions from the geomagnetic cavity. These effects constitute a background in studying possible elec-
tromagnetic perturbations induced by lithospheric processes. Even though with extremely less efficacious effects, also the seismo-electromagnetic fluctuations occurring in space are capable to generate local perturbations of the inner Van Allen belt. Anomalous sharp increases of electron and proton counting rates (from a few MeV to several tens and hundreds of MeV) have been detected mostly below the inner Van Allen radiation belt, near the South Atlantic anomaly (SAA), at altitudes of about 400 –1200 km, by several space experiments. The existence of a temporal correlation between these anomalous fluctuations, called particle bursts (PBs), and the occurrence of earthquakes of medium and strong magnitude have been suggested by several authors [5] and confirmed by data obtained on board of METEOR3A and AUREOL-3 satellites [6] [7]. By measuring energy spectrum, direction and composition of particle fluxes, HEPD will study the stability of the inner Van Allen belts and particles precipitation trying to carefully discriminate anomalous events possibly induced by seismic events from the natural background, caused by geomagnetic, tropospheric and anthropogenic electromagnetic emissions. Another very important scientific objective of the HEPD is the study of the solar-terrestrial environment, as Coronal Mass Ejections (CMEs), Solar Energetic Particle (SEP) events and low-energy cosmic rays. The CSES mission will monitor the solar impulsive activity and the cosmic ray solar modulation by detecting proton and electron fluxes from a few MeV to hundreds MeV. These measurements will provide an extension down to
V. Scotti, G. Osteria / Nuclear and Particle Physics Proceedings 306–308 (2019) 92–97
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Parameter Energy Range
Figure 2: A schematic view of the High-Energy Particle Detector.
Angular resolution Energy resolution Particle identification Free field of view Pointing Operative temperature Mass Power Consumption Mechanical dimensions
Value Electrons: 3-100 MeV Protons: 30-200 MeV < 8◦ 5 MeV < 10% 5 MeV > 90% ≥ 70◦ Zenith -10◦ +45◦ 45 kg ∼27 W 530 × 382 × 404 mm3
Table 2: HEPD main technical characteristics.
very low energy of the range of the particle spectra obtained in the current 24th solar cycle by PAMELA and AMS experiments. Moreover, fluxes of light nuclei up to hundreds MeV/n will be provided. 3. The instrument The High-Energy Particle Detector is designed to detect electrons in the energy range between 3 and 100 MeV, protons between 30 and 200 MeV and light nuclei. The detector is made up of several sub-detectors arranged as shown in Fig.2: • Tracker: two planes of double-side silicon microstrip detectors are placed on the top of the detector in order to track the direction of the incident particle limiting the effect of Coulomb multiple scattering on the direction measurement; • Trigger: a layer of thin plastic scintillator, placed 10 mm below the tracker, divided into six segments (200 × 30 × 5 mm3 each) along the y direction; • Calorimeter: a tower of 16 layers of 1 cm thick plastic scintillator planes followed by a 3x3 matrix of an inorganic scintillator LYSO. • Veto system, consisting of 5 plastic scintillator counters, four lateral and one at the bottom of the instrument. All the scintillators (plastic and inorganic) are read out by photomultiplier tubes (PMT R9880-210 from Hamamatsu). The Electronics Subsystem [9] of the HEPD can be schematized into three blocks: Silicon detector, Scintillator detectors (trigger, energy and veto detectors), Global control and data managing. Each detector block includes power chain for bias distribution and a data
Figure 3: The launch of CSES from the Jiuquan Satellite Launch Center, China, in the Gobi desert (Inner Mongolia) .
acquisition processing chain. The main Power Supply provides the low voltages to the detector electronics and the high bias voltages for PMTs and silicon modules. The HEPD has mechanical dimensions of 530×382× 404 mm3 , a mass of 45 kg and a power consumption of about 27 W in its default flight configuration. Rejection of particles hitting the lateral or bottom veto planes is performed online or offline by using different trigger commands. An electron/proton separation for fully contained events greater than 90% is achieved by the ΔEvsEtot method, where ΔE is obtained by the two layers of the silicon tracker, while Etot is measured by the calorimeter. Some of the main parameters of HEPD are summarized in table 2. Following the standard procedures for space applications, four models of HEPD have been built and fully integrated in the clean rooms at the INFN laboratories of Roma Tor Vergata in Rome (Italy). The electrical model (EM), the structural and thermal model (STM), the qualification model (QM), and, finally, the flight model (FM). Every model went under several tests, the most significant are described in the following section. The final configuration of the HEPD FM installed on CSES is shown in Figure 6.
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Figure 5: HEPD calibration plot as function of energy (preliminary). Figure 4: Energy loss by 30 MeV electrons within the upper segment of the HEPD calorimeter. The second and third peaks are produced by the pile-up of 2 or 3 simultaneous electrons.
4. Pre-flight operations A full GEANT4 simulation of the whole apparatus was performed, accounting for detector response to all particles and reproducing readout electronics and trigger conditions. Simulations were developed in order to have Monte Carlo output and real data in the same format. The same software is used to reconstruct the event in both cases, allowing a fair comparison of reconstructed parameters and Monte Carlo truth. In Spring 2016, after the integration of the HEPD in Roma Tor Vergata, the test and qualification campaign of the HEPD QM started. The procedure included vibration test, to simulate launch and flight conditions, and thermal and vacuum test at SERMS laboratory to simulate space environment. These qualification tests were carried on at SERMS laboratory in Terni (PG). Calibrations of the QM and FM were then performed by electron and proton beams. Electron tests took place at the Beam Test Facility (BTF) at the INFN Frascati National Laboratories. The parameters of the BTF were optimized to obtain beam bunches of low multiplicity electrons, for different energies: 30 MeV, 45 MeV, 60 MeV, 90 MeV and 120 MeV. Data collected were transmitted to the EGSE module that was controlled remotely from the control room, so emulating the satellite orbiting conditions. QM and FM were calibrated at different incident angles and positions. The total energy loss in the calorimeter for 30 MeV electrons is shown in Fig. 4. One, two or three electrons hitting the instrument in a single beam bunch are clearly visible. The proton test was performed on the FM at the Proton Therapy Center in Trento (Italy), where a cyclotron produces protons at energies ranging between 70 and
Figure 6: The HEPD mounted on the CSES satellite.
230 MeV. Energies below 70 MeV were obtained by using a degrader along the beam line. The detector was irradiated with protons at different energies between 37 and 228 MeV. The plot in Figure 5 summarizes the (preliminary) results of the calibration of the detector performed on ground by test beams and atmospheric muons. The flight model was shipped to China in December 2016. In January 2017, the functionality of the instrument was successfully tested standalone with its EGSE; then it was installed on the CSES satellite (Figure 6 ). Vibration, thermal-vacuum, magnetic cleanliness and aging tests were accomplished during 2017. In December 2017, HEPD has been transferred to the Jiuquan Satellite Launch Center, China, in the Gobi desert (Inner Mongolia) from where it has been launched, by a Long March 2D rocket, on the February 2nd, 2018. A picture of the launch is shown in Figure 3.
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5. In-flight operation After the launch, the apparatus underwent the commissioning phase. On the 6th February 2018, the HEPD health check procedure was successfully run. The day after HEPD was tested in the framework of the satellite platform verification. The payload operated along 3 orbits. During the commissioning phase (February-July 2018), the HEPD has been tested in different configurations in order to:
with beam test data confirms that the region between 2000 and 4000 ADC counts is mainly associated to a proton contribution.
• study the trigger rates along the orbit in different trigger configurations; • study to define the optimal trigger thresholds in flight; • perform an in-flight calibration to be compared with beam test results. The CPU software is capable to identify the position of CSES with respect to the Earth by using GPS broadcast data sent from the satellite every second, properly configure the detector and apply a scheduled sequence of operations. These procedures include, for instance, dedicated calibration runs performed in the equatorial region. During a calibration run, triggers are generated by the trigger board in order to estimate the pedestals in the signal of each photo-multiplier tube and silicon channel. Since the beginning of May 2018 an encrypted data transfer from China (CEA-ICS) to Italy (ASI-SSDC) has been working. The data retrieval, processing and storage in Italy has been implemented in a two nodes infrastructure with a shared file system providing high availability and high resilience of the storage. A processing pipeline has been developed as several layers of software with an interface to a processing database and to the storage of the infrastructure. The HEPD status is monitored in quasi-real time by quicklook software to get immediate information (strips and PMTs ADC counts, rate and orbital zones, trigger rate, etc).
Figure 7: ADC counts (proportional to energy release) on a channel of the second plane of the energy sub-detector. The two arrows indicate the MIP and the proton peaks.
Measured trigger rate presents an important background contribution due to fragmentation products, off acceptance and re-entrant particles. Figure 8 shows a raw trigger rate map. This map uses data collected from May, 14th up to June, 11th, with HEPD has been operating in a continuous data acquisition mode and in the same stable configuration. This allowed to have a first clean sample of data for analysis purposes (28 days of data-taking and 49 GB of stored raw data). The configuration selected for the generation of the trigger is the coincidence of the trigger plane T and the first three planes of the calorimeter P1, P2 and P3. In Figure 9 it is shown the trend of the trigger rate as a function of the on-board time. The peaks in red refer to the passages over the South Atlantic Anomaly (SAA),
6. In fligh performance: first results A first data analysis has been carried out to compare flight data to ground acquired data: beam test and atmospheric muon data. A comparison with atmospheric muon data confirms (figure 7) that pedestals, as well as the MIP peak, are in the same position, confirming that the behavior of the detector is not changed after the launch. A comparison
Figure 8: Raw trigger rate map.
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• Improved trigger logic and pre-scaling needed • A larger amount of acquired data (mass memory on board for buffering and increased data budget • Improved operating modes
Figure 9: Trigger rate as a function of the on-board time. Different rates on the South Atlantic Anomaly (SAA) and on the poles (NP, SP) are clearly visible.
where the proton belt is nearer the Earths surface due to tilted magnetic axis and the presence of trapped particle population overcomes the other particles by several orders of magnitude. On the other hand, the polar regions (marked as NP and SP in the plot) show lower rates compared to the SAA region, but higher than the equatorial portion of the Earth (marked as EQ) because at higher latitudes the geomagnetic cutoff becomes smaller allowing low energy galactic particles (absent at lower latitudes) to be detected. Particle identification analysis is still ongoing. Background contribution has to be accounted to obtain a proper separation between particle species. Preliminary results show that particle identification is compatible with expectations from simulation, in which no satellite background is accounted for. 7. Conclusions and perspectives The HEPD detector has been designed, built and fully tested for measuring electrons in the energy range between 3 and 100 MeV, protons between 30 and 200 MeV and light nuclei up to oxygen. The wide energetic range allows studying several phenomena beyond the seismo-associated ones, such as those related to magnetospheric currents, dynamics of radiation belts and cosmic rays flux. During the foreseen five years of the mission, a large part of the 24th solar cycle will be monitored. While the HEPD of the CSES-1 mission is successfully acquiring data, design and development of an improved detector for the CSES-2 mission are ongoing. The CSES-2 satellite will be launched in 3 years. The full operational requirement poses some constraints on HEPD-02 design: • Higher trigger rate at polar regions
The new design will have a lot of improvements with minor changes with respect to the first design (identical box dimensions and mechanical interfaces) and budgets. A new trigger system has already been designed, along with a calorimeter and veto shielding upgrade. To improve trigger efficiency a new system with crossed layers of 2 mm thick segmented counters read by lightguides has been designed. Acknowledgments This work was supported by the Italian Space Agency in the framework of the Accordo Attuativo n. 2016-16-H0 Progetto Limadou Fase E/Scienza (CUP F12F1600011005). References [1] Cao J B, Zeng L, Zan F, et al. The electromagnetic wave experiment for CSES mission: Search coil magnetometer. Sci China Tech Sci, 2018, 61:653-658, https://doi.org/10.1007/s11431-0189241-7 [2] L. Alfonsi et al. The HEPD particle detector and the EFD electric field detector for the CSES satellite. Radiation Physics and Chemistry, 2017, 137: 187-192, https://doi.org/10.1016/j.radphyschem.2016.12.022 [3] Cheng B, Zhou B, et al. High precision magnetometer for geomagnetic exploration onboard of the China SeismoElectromagnetic Satellite. Sci China Tech Sci, 2018, 61:659-668, https://doi.org/10.1007/s11431-018-9247-6 [4] Ambrosi G, Bartocci S, Basara L, et al. The HEPD particle detector of the CSES satellite mission for investigating seismoassociated perturbations of the Van Allen belts. Sci China Tech Sci, 2018, 61: 643-652, https://doi.org/10.1007/s11431-0189234-9 [5] Galper A M, Koldashov S V, Voronov S A. High energy particle flux variations as earthquake predictors. Adv Space Res, 1995, 15: 131-134, https://doi.org/10.1016/0273-1177(95)00085-S [6] Galperin Yu I, Gladyshev V A, Jordjio N V, et al. Precipitation of high-energy captured particles in the magnetosphere above epicenter of an incipient earthquake. Cosmic Res, 1992, 30: 89-106 [7] Pustovetov V P, Malyshev A V. Spatial-temporal correlation of the earthquakes and variations of high-energy particle flux in the inner radiation belt. Cosmic Res, 1993, 31: 84-87 [8] Scotti V, Osteria G. The high energy particle detector onboard the CSES satellite, https://doi.org/10.1109/NSSMIC.2016.8069878 [9] Scotti V, Osteria G. The electronics of the HEPD of the CSES experiment, Nuclear and Particle Physics Proceedings, 291-293: 118-121 https://doi.org/10.1016/j.nuclphysbps.2017.06.024