Dark Matter Particle Explorer:The First Chinese Cosmic Ray and Hard γ-ray Detector in Space

The Dark Matter Particle Explorer (DAMPE) mission is one of the five scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Science (CAS) approved in 2011. The main scientific objective of DAMPE is to detect electrons and photons in the range of 5GeV-10TeV with unprecedented energy resolution (1.5% at 100GeV) in order to identify possible Dark Matter (DM) signatures. It will also measure the flux of nuclei up to above 500TeV with excellent energy resolution (40% at 800GeV), which will bring new insights to the origin and propagation high energy cosmic rays. With its excellent photon detection capability, the DAMPE mission is well placed for new discoveries in high energy-ray astronomy as well.      

以载荷为中心的暗物质探测卫星机电热一体化设计

暗物质粒子探测卫星是中国第一颗空间高能探测卫星,用于实现5GeV~10TeV大动态范围高能宇宙线（电子、正电子、伽马射线等）能谱测量.卫星有效载荷包括BGO量能器、硅阵列探测器、塑闪阵列探测器和中子探测器,是目前中国发射的载荷比最大的卫星.本文介绍了卫星相关技术方案,包括技术指标、轨道方案、工作模式及系统组成等,突出了其以载荷为中心的机电热一体化设计特点.      

暗物质粒子探测卫星BGO量能器热控设计与验证

暗物质粒子探测卫星是2015年12月发射的中国自主设计建造的空间天文实验卫星,主要包括塑闪阵列探测器、硅阵列探测器、BGO量能器与中子探测器四个探测器.BGO量能器是暗物质粒子探测卫星的核心探测器,主要任务是精密测量高能宇宙线粒子的能量,并通过比较簇射沉积能量的空间分布,进行粒子种类鉴别.本文结合BGO量能器工作原理,分析了BGO量能器热控设计需求与约束,进行了单机热控设计.根据热控设计方案,进行有限元仿真分析,开展了单机飞行件的真空热平衡试验.分析与试验结果表明,热控设计方案合理有效,能够满足需求.      

Cosmic-ray electron spectrum above 100 GeV from PPB-BETS experiment in Antarctica

Cosmic-ray electrons have been observed in the energy region from 10 GeV to 1 TeV with the PPB-BETS by a long duration balloon flight using a Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an average altitude of 35 km in January 2004. The PPB-BETS detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. In the study of cosmic-ray electrons, there have been some suggestions that high-energy electrons above 100 GeV are a powerful probe to identify nearby cosmic-ray sources and search for particle dark matter. In this paper, we present the energy spectrum of cosmic-ray electrons in the energy range from 100 GeV to 1 TeV at the top of atmosphere, and compare our spectrum with the results from other experiments.     

Progress and Prospects of the Strategic Priority Program on Space Science

In May 2018, the second phase of the Strategic Priority Program on Space Science (SPP II) was officially approved by the Chinese Academy of Sciences, in view of the significant scientific achievements of the first phase of the Strategic Priority Program on Space Science (SPP I) which includes 4 space science missions:the Dark Matter Particle Explorer (DAMPE), ShiJian-10 (SJ-10), Quantum Experiments at Space Scale (QUESS) and Hard X-ray Modulation Telescope (HXMT). Aiming to address fundamental scientific questions, SPP II focuses on two major themes:How the universe and life originate and evolve and What is the relationship between the solar system and human beings. In areas that Chinese scientists have advantages, new space science missions including Graviational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM), the Advanced space-based Solar Observatory (ASO-S), the Einstein Probe (EP), and Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) have been approved in the framework of SPP II. This paper presents the research highlights of the SPP I, introduces the recent progress of SPP II, and puts forward the prospects for future development.      

High-energy cosmic-ray electrons in the Galaxy

The intensity of cosmic-ray electrons is only ∼1% of the protons at 10 GeV, and decreases very rapidly with energy to be ∼0.1% of protons at 1 TeV. Nevertheless, electrons in cosmic-rays have unique features, complementary to all other cosmic-ray nucleonic components, because they enable us to find the origins of cosmic-rays and the properties of their propagation mechanisms in the Galaxy. High-energy electrons lose energy by synchrotron and inverse Compton processes during the propagation in the Galaxy. Since the energy loss rate by these processes is proportional to the square of energy, TeV electrons accelerated in the sources at distances larger than ∼1 kpc, or ages greater than a few 10⁵ yr, cannot reach the solar system. This suggests that some nearby sources leave unique signatures in the form of identifiable structures in the energy spectrum of TeV electrons, and show increases of the flux towards the sources. In this paper, I review the past observations of high-energy cosmic-ray electrons and discuss their astrophysical significance.     

The ground-based large-area wide-angle γ-ray and cosmic-ray experiment HiSCORE

The question of the origin of cosmic rays and other questions of astroparticle and particle physics can be addressed with indirect air-shower observations above 10 TeV primary energy. We propose to explore the cosmic ray and γ-ray sky (accelerator sky) in the energy range from 10 TeV to 1 EeV with the new ground-based large-area wide angle (ΔΩ ∼ 0.85 sterad) air-shower detector HiSCORE (Hundred^∗i Square-km Cosmic ORigin Explorer). The HiSCORE detector is based on non-imaging air-shower Cherenkov light-front sampling using an array of light-collecting stations. A full detector simulation and basic reconstruction algorithms have been used to assess the performance of HiSCORE. First prototype studies for different hardware components of the detector array have been carried out. The resulting sensitivity of HiSCORE to γ-rays will be comparable to CTA at 50 TeV and will extend the sensitive energy range for γ-rays up to the PeV regime. HiSCORE will also be sensitive to charged cosmic rays between 100 TeV and 1 EeV.     

Direct measurement of the composition and spectra of cosmic rays above 1 TeV/amu from Jacee

Direct measurements on cosmic ray protons through iron above about 1 TeV/amu have been performed in a series of balloon-borne experiments with emulsion chambers. The measured energy spectra of protons and helium are power laws with exponents of 2.77 ± 0.09 and 2.72 ± 0.11 in the energy range 5 to 500 TeV and 2 to 50 TeV/amu, respectively. The proton spectrum shows no evidence of the steepening near 2 TeV which was reported by other experiments. Helium has a slightly higher intensity compared to extrapolations from lower energy measurements. The heavier elements, carbon to sulfur, show a small tendency for intensity enhancement in the relative abundance above 10 TeV/amu.     

Dark matter search with the CALET detector on-board ISS

The CALorimetric Electron Telescope, CALET, mission is proposed for the observation of high-energy electrons and gamma-rays at the Exposed Facility of the Japanese Experiment Module on the International Space Station. The CALET has a capability to observe the electrons (without separation between e⁺ and e⁻) in 1 GeV–10 TeV and the gamma-rays in 20 MeV–several TeV with a high-energy resolution of 2% at 100 GeV, a good angular resolution of 0.06 degree at 100 GeV, and a high proton-rejection power of nearly 10⁶. The CALET has a geometrical factor of 1 m²sr, and the observation period is expected for more than three years. The very precise measurement of electrons enables us to detect a distinctive feature in the energy spectrum caused from WIMP dark matter in the Galactic halo. The excellent energy resolution of CALET, which is much better than GLAST or air Cherenkov telescopes over 10 GeV, enables us to detect gamma-ray lines in the sub-TeV region from WIMP dark matter annihilations. The CALET has, therefore, a unique capability to search for WIMP dark matter by the hybrid observations of electrons and gamma-rays.     

Experimental verification of particle distributions in proton-induced cascades.

Predictions of shielding requirements, levels of induced radioactivity and of radiation damage around high-energy accelerators require accurate simulation of the physics of proton-induced cascades from energies above the TeV to energies below the eV region. Experimental studies of cascades using activation detector, dosimeter and counter techniques provide valuable data for validating simulation procedures and for extrapolating the required accelerator design parameters directly. Such studies include the yields of low-energy secondary neutrons in proton-nucleus interactions, the spatial distribution of hadrons, low-energy neutrons and energy deposition close to the core of proton cascades and measurements at large lateral depths in shields. This paper describes some of these measurement and compares them with the predictions made by Monte-Carlo simulations.     

空间科学任务及其特点综述

人类进入太空以来已经发射了近1万个人造航天器,其中大约10%执行的是空间科学和探测任务.近年来中国经济快速发展,提供了更多的基础研究经费,经济转型也对创新驱动发展提出了更高需求,中国对空间科学的投入开始逐年增加.2015年以来先后成功发射了悟空号、实践十号、墨子号和慧眼号4颗科学卫星,天宫2号空间实验室也成功实施了一系列空间科学实验.重要科学发现和成果正在不断地产出.空间科学卫星任务（或称计划）与应用卫星从提出到评价都有很大不同,因此有必要对其所具有的特点进行分析,从而引导空间科学界从科学团队、技术团队到管理团队提高认识,确保未来的空间科学任务发挥最大效益,获得最大科学产出.      

Gamma ray astrophysics and signatures of axion-like particles

We propose that axion-like particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to effects in the spectra of high-energy gamma-ray sources detectable by satellite or ground-based telescopes. We discuss two kinds of signatures: (i) a peculiar spectral depletion due to gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the “Hillas criterion”, such as jets of active galactic nuclei or hot spots of radio galaxies; (ii) an appearance of otherwise invisible sources in the GeV or TeV sky due to back-conversion of an ALP flux (associated with gamma-ray emitters suffering some attenuation) in the magnetic field of the Milky Way. These two mechanisms might also provide an exotic way to avoid the exponential cutoff of very high energy gamma-rays expected due to the pair production onto the extragalactic background light.     

The energy spectra of protons and helium measured with the ATIC experiment

The Advanced Thin Ionization Calorimeter (ATIC) balloon experiment is designed to investigate the composition and energy spectra of cosmic rays at the highest energies currently accessible by direct measurements, i.e., the region up to 100 TeV. The instrument consists of a silicon matrix for charge measurement, a graphite target (0.75 nuclear interaction length) to induce hadronic interactions, three layers of scintillator strip hodoscopes for triggering and trajectory reconstruction, and a Bismuth Germanate (BGO) crystal calorimeter (18 radiation lengths) to measure particle energies. ATIC has had two successful Long Duration Balloon (LDB) flights from McMurdo, Antarctica: one from 12/28/00 to 01/13/01 and the other from 12/29/02 to 01/18/03. We present the energy spectra of protons and helium extracted from the first flight, over the energy range from 100 GeV to 100 TeV, and compare them with the results from other experiments at both the lower and higher energies. ATIC-1 results do not indicate significant differences in spectral shape between protons and helium over the investigated energy range.     

CREAM: 70 days of flight from 2 launches in Antarctica

The Cosmic-Ray Energetics And Mass balloon-borne experiment has been launched twice in Antarctica, first in December 2004 and again in December 2005. It circumnavigated the South Pole three times during the first flight, which set a flight duration record of 42 days. A cumulative duration of 70 days within 13 months was achieved when the second flight completed 28 days during two circumnavigations of the Pole on 13 January 2006. Both the science instrument and support systems functioned extremely well, and a total 117 GB of data including 67 million science events were collected during these two flights. Preliminary analysis indicates that the data extend well above 100 TeV and follow reasonable power laws. The payload recovered from the first flight has been refurbished for the third flight in 2007, whereas the payload from the second flight is being refurbished to be ready for the fourth flight in 2008. Each flight will extend the reach of precise cosmic-ray composition measurements to energies not previously possible.     

Multiple Coulomb scattering method to reconstruct low-energy gamma–ray direction in the GAMMA-400 space-based gamma–ray telescope

The GAMMA-400 currently developing space-based gamma-ray telescope is designed to measure the gamma-ray fluxes in the energy range from ～20?MeV to several TeV in the highly elliptic orbit (without shadowing the telescope by the Earth) continuously for a long time. The physical characteristics of the GAMMA-400 gamma-ray telescope, especially the angular and energy resolutions (at 100-GeV gamma rays they are ～0.01° and ～1%, respectively), allow us to consider this space-based experiment as the next step in the development of extraterrestrial high-energy gamma-ray astronomy. In this paper, a method to improve the reconstruction accuracy of incident angle for low-energy gamma rays in the GAMMA-400 space-based gamma-ray telescope is presented. The special analysis of topology of pair-conversion events in thin layers of converter was performed. Applying the energy dependence of multiple Coulomb scattering for pair components, it is possible to estimate the energies for each particle, and to use these energies as weight in the angle reconstruction procedure. To identify the unique track in each projection the imaginary curvature method is applied. It allows us to obtain significantly better angular resolution in comparison with other methods applied in current space-based experiments. When using this method for 50-MeV gamma rays the GAMMA-400 gamma-ray telescope angular resolution is about 4°.     

Expanding shells of young pulsars as sources of high-energy neutrinos

The initial power outputs P_o of pulsars are not yet well known, but these seem to follow approximately a distribution law N(> P_o) ∝ P_o⁻ⁿ where 0.5 ≤ n ≤ 1.0. It seems likely that P_o ≥ 10³⁸ ergs/sec. With these assumptions, we estimate that the DUMAND detector can record ≥ 10³ high-energy (> 4 TeV) neutrino events in a four-month period per Galactic supernova; (in our Galaxy, these are estimated to occur at the rate of about 8 per century.) Neutrinos from supernova shells in the Virgo supercluster would be marginally detectable (one very bright supernova per decade at about 20 Mpc) if N(> P_o) ∝ P_o^−0.5, but undetectable if N(> P_o) ∝ P_o⁻¹. The diffuse flux summed over distant extragalactic supernovae is likely to be well below the detection threshold.     

高能激光光束质量的测量

高能激光广泛应用于科研、工业和军事等领域,其光束质量的精确计量对激光器性能的评价及化学和固体激光武器系统的作战效能的评估至关重要。提出一种高能强激光光束质量测量装置,能实时观察光束强度分布变化,通过数据处理系统可获得光束直径、束散角、光束指向稳定性及M2因子等光束质量参数,最后分析和讨论了各测量参数的测量不确定度。     

Flux upper limits of diffuse TeV gamma rays from the Galactic plane using the effective area of the Tibet-II and -III arrays

We obtained new upper limits on the diffuse gamma rays from the inner Galactic (IG) and outer Galactic (OG) planes in 3–10 TeV region, using the Tibet air shower data and new Monte Carlo simulation results. A difference of the effective area of the air-shower array for observing gamma rays and cosmic rays was carefully taken into account in this analysis, resulting in that the flux upper limits of the diffuse TeV gamma rays were reduced by factors of 4.0–3.7 for 3–10 TeV than those in our previous results (Amenomori, M., Ayabe, S., Cui, S.W., et al. Observation of multi-TeV diffuse gamma rays from the Galactic plane with the Tibet air shower array. Astrophys. J. 580, 887–895, 2002.). This new result suggests that the inverse power index of the energy spectrum of source electrons responsible for generating diffuse TeV gamma rays through inverse Compton effect should be steeper than 2.2 and 2.1 for IG and OG planes, respectively, with 99%C.L.     

Progress of Strategic Priority Program on Space Science

The most important all-round progress in China's Space Science in recent years is the official go-ahead of Strategic Priority Program(SPP) on Space Science in 2011,which marks China's space science has entered a new stage.SPP on Space Science includes 4 satellites(DAMPE,SJ-10,QUESS and HXMT),the Intensive Study of Future Space Science Missions,and the Advanced Research of Space Science Missions and Payloads.It is expected that the innovative breakthroughs will be achieved,and the great leaps of related high-technology will be driven through both independent space science missions and international cooperation.The implementation of the SPP on Space Science will enable the rapid development of China's space science endeavor,and contribute to the progress of human civilization.     

Centaurus A: Multiwavelength observations of the nearest active galaxy from radio to gamma-rays

Centaurus A (Cen A, NGC 5128) is the nearest active galaxy and, notably, the viewing angle with respect to the jet axis is very large (> 70°). A first contemporaneous OSSE, COMPTEL, and EGRET spectrum obtained in October 1991 covers an energy range from 50 keV up to 1 GeV. This γ-ray broad-band spectrum was taken when Cen A was in an intermediate emission state as defined by the BATSE X-ray light-curve. The first simultaneous multiwavelength spectrum from radio to γ-rays was measured in July 1995 when Cen A was in a low emission state (the prevailing state for the last 7 years). The different spatial and temporal resolution in the different frequency regimes produces problems in the construction and interpretation of the multiwavelength spectra. These are addressed in this paper. The detection of emission > 1 MeV makes the inclusion of such high-energy emission into models for the spectral energy distribution mandatory.