The high energy cosmic-radiation detection (HERD) facility onboard China's Space Station

Abstract

The High Energy cosmic-Radiation Detection (HERD) facility is one of several\nspace astronomy payloads of the cosmic lighthouse program onboard China's Space\nStation, which is planned for operation starting around 2020 for about 10\nyears. The main scientific objectives of HERD are indirect dark matter search,\nprecise cosmic ray spectrum and composition measurements up to the knee energy,\nand high energy gamma-ray monitoring and survey. HERD is composed of a 3-D\ncubic calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) from\nfive sides except the bottom. CALO is made of about 10$^4$ cubes of LYSO\ncrystals, corresponding to about 55 radiation lengths and 3 nuclear interaction\nlengths, respectively. The top STK microstrips of seven X-Y layers are\nsandwiched with tungsten converters to make precise directional measurements of\nincoming electrons and gamma-rays. In the baseline design, each of the four\nside SKTs is made of only three layers microstrips. All STKs will also be used\nfor measuring the charge and incoming directions of cosmic rays, as well as\nidentifying back scattered tracks. With this design, HERD can achieve the\nfollowing performance: energy resolution of 1\\% for electrons and gamma-rays\nbeyond 100 GeV, 20\\% for protons from 100 GeV to 1 PeV; electron/proton\nseparation power better than $10^{-5}$; effective geometrical factors of $>$3\n${\\rm m}^{2}{\\rm sr}$ for electron and diffuse gamma-rays, $>$2 $ {\\rm\nm}^{2}{\\rm sr}$ for cosmic ray nuclei. R\\&D is under way for reading out the\nLYSO signals with optical fiber coupled to image intensified CCD and the\nprototype of one layer of CALO.\n