Alessandro Sotgiu on Behalf of the CSES-Limadou Collaboration
The High-Energy Particle Detector capabilities in the measurement of proton and electron fluxes along
the China Seismo-Electromagnetic Satellite orbits
INFN – Section of Rome Tor Vergata and
University of Rome Tor Vergata (Department of Physics)
CSES-01 Mission
CSES-01 (China Seismo-Electromagnetic Satellite) is the first of a series of scientific space missions dedicated to monitoring electromagnetic fields, plasma, and particle perturbations in LEO regions (~500 km altitude).
The mission aims to study a possible correlation between these perturbations and the occurrence of seismic events.
CSES-01 is equipped with 9 instruments, among them the Italian High-Energy Particle Detector (HEPD-01).
The Satellite (CSES-01)
CAST-2000 is the platform baseline.
– Earth oriented 3-axis stabilization system, with orbit maneuver ability.
– X-Band Data Transmission,120Mbps.
– USB TT&C System.
– Peak Power Consumption: ~900W.
Launched on 2018-02-02
CSES-Limadou Collaboration
Limadou refers to the Italian contribution to the mission that includes the realization of High-Energy Particle Detector (HEPD) and the participation in the realization of the Electric Field Detector (EFD)
Several Italian institutes and universities involved:
➢ Italian Space Agency (ASI)
➢ INFN - Roma “Tor Vergata”, Bologna, Perugia, LNF, Naples, TIFPA
➢ University of Rome “Tor Vergata”
➢ University of Trento
➢ National Institute for Astrophysics - Institute for Space Astrophysics and Planetology (INAF-IAPS)
➢ UniNettuno University
➢ Istituto Nazionale di Geofisica e Vulcanologia (INGV)
The High-Energy Particle Detector
HEPD-01 is devoted to the measurements of electrons (3-100 MeV) and protons (30-200 MeV) fluxes and their variations.
The detector is composed of :
➢ the tracker system - made of two layers of double-sided silicon strip sensors - for the reconstruction of the incoming particle direction
➢ the trigger plane - made of a segmented layer of 6 plastic scintillator bars - for the generation of the trigger pulse
➢ the calorimeter - made of a plastic scintillator tower (16 planes) plus a final layer of LYSO inorganic crystals - for the measurement of the energy deposition
➢ the veto system - made of 5 plastic scintillator planes - for the rejection of particles not fully contained inside the calorimeter
Geant4 Simulation CAD
P. Picozza et al. “Scientific Goals and In-orbit Performance of the High- energy Particle Detector on Board the CSES”. In: The Astrophysical
Journal Supplement Series 243.1 (July 2019)
Proton Analysis
https://www.swpc.noaa.gov/products/solar-cycle-progression
You are here!
✔ Possibility to extend PAMELA
results for galactic protons at lower energies
✔ Study of the proton population inside the SAA
✔ New flux measurements of cycle 25 for modulated particles (at low energy)
✔ Possibility to study more transient events (SEPs, storms etc.), since we are moving towards the
maximum of the 25th cycle
Galactic Cosmic Rays - Analysis (1/3)
Particles are selected when they hit T & P1 & P2 (the trigger plane and the first two planes of the plastic scintillator tower).
Further selections are then applied to clean the proton sample and to select galactic particles:
✔ the containment in the calorimeter → for the correct energy reconstruction
✔ a trigger multiplicity cut → for the rejection of multi-particle events;
✔ plane continuity → for the rejection of interacting events
✔ proton selection → to separate protons from electrons and heavier nuclei
✔ a LYSO multiplicity cut → for the rejection of possible electromagnetic showers
Two curves define the p+ band for the selection of proton particles → good
separation with > 90% efficiency
Selection cut efficiency evaluated with MC simulations after a proper tuning of the MC
software with test beam data
Galactic Cosmic Rays - Analysis (2/3)
✔ A static cutoff map is used to select galactic protons
✔ The map is obtained during a quit period of 2018, at an altitude of ~500 km, considering the magnetic field from the IGRF-12 and Tsyganenko-89 models, and for particles coming from all directions allowed by the HEPD’s field-of-view
✔ HEPD is switched off at + 65° but considering its large field-of-view is capable to collect galactic protons for a fair amount of time per days
✔ The live time is accumulated only in the above-cutoff regions
Galactic Cosmic Rays - Analysis (3/3)
Bayesian approach is used to take into account passive structures of HEPD and unfold the final spectrum
Contamination of the flux sample due to high-energy electrons is below 10% above 50 MeV∼
Unfolding procedure and the intrinsic difference between MC and flight data are considered as systematic uncertainties
Total geometrical acceptance of HEPD for Z=1 particles as a function of the energy.
It is evaluated using a MC simulation of
isotropically generated (0 ◦ < θ <90 ◦ and 0 ◦ < φ
< 180 ◦ ) protons with primary energy ranging from 1 MeV to 10 GeV
Galactic Cosmic Rays - Results
S. Bartocci et al. “Galactic Cosmic-Ray Hydrogen Spectra in the 40-250 MeV Range Measured by the High-energy Particle Detector (HEPD) on board the CSES-01 Satellite between 2018 and 2020” In The Astrophysical Journal (September 2020)
Galactic Cosmic Rays - Results
[*] M.J. Boschini et al. “Propagation of cosmic rays in heliosphere: The HelMod model”. In: Advances in Space Research 62.10 (2018).
DOI: https://doi.org/10.1016/j.asr.2017.04.017.
The heliospheric modulation model (HelMod) [*] is a 2D Monte Carlo model to simulate the solar modulation of galactic cosmic rays (GCRs)
It is capable of providing modulated spectra that agree within the experimental errors with those measured by AMS-01, BESS, PAMELA, and AMS-02 during the solar cycles 23 and 24
Galactic Cosmic Rays – Solar Modulation
PR EL IM IN AR Y
Solar Modulation is evident only in the lowest energy bins.
For energy higher than 50 MeV, it is almost absent.
First observations of Forbush decrease for
G3 storms
Protons inside the SAA (1/2)
Same proton selections as discussed for the GCRs analysis!
➢
A selection on both the magnetic field B<20500 nT and McIlwain parameter L-shell<1.3 (calculated using
IRBEM libraries) is performed to operatively define the SAA region
➢
Trapped electrons inside the SAA are mainly confined at energies lower than 8 MeV, thus not affecting the 40-250 MeV energy range for protons analyzed in this work
➢
Contamination from anti-protons is considered negligible
Flux estimation was performed using a multi-dimensional
matrices approach.
Protons inside the SAA (2/2)
The HEPD results are averaged over the period between August
2018 and December 2020 and compared with the predictions, for
the same
period, of the NASA AP9 (95% CL) empirical model.
These are the first results on SAA protons at Low-Earth Orbit during the minimum activity phase between the 24
thand the
25
thsolar cycle in the
energy range lower than 250
MeV.
Electron Analysis
Example of ~ 150 cosmic electron trajectories.
Particle energy greater than 15 MeV
✔ Electron analysis is more complicated, especially for the galactic population
✔ Due to the higher flux of galactic protons, particle separation is more important
✔ Due to a large number of secondary electrons, the static cutoff map cannot achieve a proper selection of the primary component
✔ We are currently working on the back-tracing of the electron trajectories in order to confirm the galactic origin of the particles
✔ We focused on re-entrant electrons!
✔ HEPD proved capable of measuring transient events (e.g. during storms)
F. Palma et al. “The August 2018 Geomagnetic Storm Observed by the High-Energy Particle Detector on Board the CSES-01 Satellite” in Applied Sciences (June 2021)
The August 2018 G3 storm
Re-entrant electrons
A trigger is generated when a particle hits T & P1 & P2 (the trigger plane and the first two planes of the plastic scintillator tower).
Further selections are then applied offline to clean the lepton sample and to select the re-entrant albedo component:
➢ the containment → needed for the reconstruction of the deposited energy. The bottom anti-coincidence is also used to remove splash albedo particles with an upward direction.
➢ a trigger multiplicity equals 1 → rejection of multi-particle events;
➢ plane continuity → a continuous release of signal inside the scintillator tower is requested;
➢ lepton selection → to separate electrons and positrons from protons, ionization energy losses inside each calorimeter plane are required to be compatible with the expectation for a singly charged minimum ionizing particle (MIP);
➢ 1.1 RE < L-shell < 1.2 RE and B > 23000 nT → selection of sub-cutoff particles outside of the SAA → live time accumulated considering the time spent in this region with the detector capable to acquire new events.
Re-entrant Selection
Lepton Selection
Re-entrant electrons - Results
The Geometrical Factor (~ 350 cm2sr @ peak) and the selection cut efficiencies have been evaluated with Monte Carlo (MC) simulations tuned with test beam data.
The contamination due to high-energy protons (E > ~500 MeV), contained inside the calorimeter because of inelastic interactions, has been estimated with MC simulations (< 5% in the whole energy range)
HEPD-01 data shown together with PAMELA measurements[1] (same geomagnetic selections applied) and with a theoretical model[2] used for the calculation of secondary electron and positron
fluxes at the top of atmosphere.
GF for fully-contained e
-[1] O. Adriani et al., Measurements of quasi‐trapped electron and positron fluxes with PAMELA [2] S. V. Koldashov et al., Electron and Positron Albedo Spectra with Energy more than 20 MeV.
Conclusions
➢
We measured the galactic hydrogen energy spectrum between 40 and 250 MeV with great accuracy, during the period from August 2018 to January 2020
➢
These have been the first results on galactic hydrogen obtained in such an energy range, at 1 au, since a series of balloon flights in the 1960s/1970s
➢
We reported the first analysis of proton fluxes in the SAA, as a function of energy, pitch angle, and L-shell
➢
For SEP events and solar modulation, the upcoming new solar maximum will allow us to make detailed measurements in the next 2 years
➢
Regarding electrons, we plan to finalize the re-entrant flux analysis and to carry on the analysis of galactic flux.
Transient effect already observed during storms
➢
Another mission (CSES-02) is in preparation, and it will include a new particle detector (HEPD-02) which is
expected to offer further insight into low-energy physics throughout the 25th solar cycle