Abstract Details
| Name: Debangana Sarkar Affiliation: Bhabha Atomic Research Centre Conference ID: ASI2017_1286 Title : GPS based Event Time Stamp and Time Synchronization of various Subsystems of MACE gamma ray Telescope Authors and Co-Authors : D Sarkar, N Chouhan, A K Tickoo, R C Rannot Astrophysical Sciences Division Bhabha Atomic Research Centre, Mumbai 400085 debangana@barc.gov.in Abstract Type : Poster Abstract Category : Instrumentation and Techniques Abstract : MACE (Major Atmospheric Cerenkov Experiment) will be a low threshold energy gamma-ray telescope being setup at Hanle (32.7 N, 78.9 E, 4200 m asl) in Ladakh region of North India. It is based on the most successful and widely used Imaging Atmospheric Cherenkov Technique (IACT) to detect Very High Energy (VHE) gamma-rays. When operational, it will be the largest ground based gamma ray telescope in the northern hemisphere. Aims and objectives of the telescope are to study a variety of galactic and extra galactic potential VHE gamma-ray sources in the energy range of 20 GeV – 5 TeV. We record Cherenkov event data during observation of VHE gamma-ray sources during mostly moonless and cloudless nights. The Cherenkov event data from the imaging camera of the telescope requires GPS synchronized time to attach time stamp to acquired events, with an accuracy better than ±1µs. The telescope has various subsystems like Telescope drive Control Unit (TCU), Active Mirror Alignment System, Camera Electronics and Signal Processing System, Calibration System, Operator Console, Weather Monitoring System, Sky Monitoring System etc. These subsystems must be time synchronized with each other before the start of observation run as the individual subsystem executes the respective command sequence based on system time. Further, the analysis of VHE gamma-ray data from pulsars also demands high precision in the recorded event arrival times. Accordingly, we have designed a master clock based time synchronization approach for the telescope. Wherein it will use a Global Positioning System (GPS) based highly stable temperature controlled oscillator clock with an accuracy of ~30 nanoseconds to Universal Time Coordinated (UTC) and frequency better than 1x10-12 per seconds. TCU and Data concentrator (DC) responsible for event time stamp, the two most critical systems with respect to time synchronization receives date and time information in Inter-Range Instrumentation Group- B (IRIG-B) standard through dedicated link. IRIG-B time code decoder is implemented in onboard Field-Programmable Gate Array (FPGA) on the DC. The other subsystems present in system synchronize their system clock with the master clock using Network Time Protocol (NTP). In this paper we shall present a detailed architecture and implementation of the GPS based time synchronization system. |