Gyeongbok Jo 1, Jongdae Sohn 2, KyeongWook Min 2, Yu Yi 1, Suk-bin Kang 2 1 Chungnam National University 2 Korea Advanced Institute of Science and Technology

Introduction NEXTSAT-1 Space Storm ISSS High Energy Particle Detector Detection Method SSD Signal Process Design Mechanical design Summary Content

NEXTSat-1 : Next Generation Small Satellite -1 Launch : 2017 Mission period : 2years Purpose : Verification of space core technology and science mission Orbit : Sun-synchronous polar orbit, 700km Payloads For verification of Space core technology NISS : Near-Infrared Imaging Spectrometer for Star History Formation ISSS : Instruments for the Study of Space Storm (a) NEXTSat-1 (b) NISS (c) ISSS

Space storm : Abrupt reduction of geomagnetic fields Cause of occurrence : Changes in solar activity( CMEs, Solar Flare ) High speed solar winds generated by CIR passing through the magnetosphere Phenomenon: Increases in radiation belt particles Increases in auroras Changes in the ionosphere, the circulation of neutral wind, density variation. Influence : Communication disruption Hazard for spacecraft & astronaut

ISSS : Instruments for the Study of Space Storm Purpose : Observe the radiation storm and ionosphere storm, Comprising Instruments Instruments for radiation storm MEPD : Medium Energy Particle Detector HEPD : High Energy Particle Detector Instruments for Ionosphere storm LP : Langmuir Probe RPA : Retarding Potential Analyzer IDM : Ion Drift Meter (a) HEPD (b) MEPD(c) LP (d) RPA (e) IDM

(b) Flux density of particles in the vicinity of the Earth between the Sun and the Earth (Schimmerling & Curtis 1978) (a) Satellite observing radiation belt (white line : magnetic field line, Inner blue region : inner Van Allen belt, outer blue region : outer Van Allen belt.) (sohn et al. 2012)

Signal from SSD : ~ mV charge signal Classification process CSA : Charge Signal Amplifier Amplifies the magnitude of the charge signal from SSD PSA : Pulse Shaping Amplifier Transform the shape of the charge signal to pulse signal of Gaussian shape Discriminator : Determining the validity of the signal PDSH : Peak Detection Sampling and Hold Catch the signal’s maximum value, and hold ADC : Analog to Digital Converter Compare peak and LUT, determine particle’s energy (a) CSA & PSA output(b) PDSH output

(a) Parameter of a cylindrical geometry (b) HEPD telescope cross- sectional diagram (c) HEPD Mechanical Structure 3-D Model

Sensor Thickness LET is according to the species of incident particles, energy and material properties, thickness. To check LET change perform the simulation using Geant4. As a result, we determined that use 1.0mm SSD two pieces. To shield from low energy particle, placed 0.05mm aluminum foil (a) Electron’s LET change according to sensor thickness(b) Protron’s LET change according to sensor thickness

(a) Placement of entire HEPD sensor Detection Channel To determine channel, performed Geant4 simulation for entire HEPD sensor. Result ~150 keV electrons and ~ 2MeV Protons are blocked On the sensor, electrons are detected up to 2 MeV protons are detected up to 20 MeV Electron channel : 50 keV ~ 2 MeV / 30ch Proton channel : 2 MeV ~ 20 MeV / 10ch (b) Electron’s LET change about entire HEPD(c) Protron’s LET change about entire HEPD

HEPD is one of the equipments comprising ISSS onboard the NEXTSat-1 Main target is high energy electron and proton’s flux, streaming into the Earth radiation belt during the event of a space radiation storm In order to design HEPD, calculated geometrical factor and using this value, determined HEPD’s mechanical design To select sensor, performed simulation by Geant4, we determined that use 1.0mm SSD 2pieces, and 0.05mm aluminum for shield from low energy particle To determine detection channel, performed simulation for entire HEPD sensor, as a result, selected channel as follow electron : 50 keV ~ 2 MeV / 30ch proton : 2 MeV ~ 20 MeV / 10ch