ROBAST: Development of a ROOT-based ray-tracing library for cosmic-ray telescopes and its applications in the Cherenkov Telescope Array

Akira Okumura, Koji Noda, Cameron Rulten

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We have developed a non-sequential ray-tracing simulation library, ROOT-based simulator for ray tracing (ROBAST), which is aimed to be widely used in optical simulations of cosmic-ray (CR) and gamma-ray telescopes. The library is written in C++, and fully utilizes the geometry library of the ROOT framework. Despite the importance of optics simulations in CR experiments, no open-source software for ray-tracing simulations that can be widely used in the community has existed. To reduce the dispensable effort needed to develop multiple ray-tracing simulators by different research groups, we have successfully used ROBAST for many years to perform optics simulations for the Cherenkov Telescope Array (CTA). Among the six proposed telescope designs for CTA, ROBAST is currently used for three telescopes: a Schwarzschild-Couder (SC) medium-sized telescope, one of SC small-sized telescopes, and a large-sized telescope (LST). ROBAST is also used for the simulation and development of hexagonal light concentrators proposed for the LST focal plane. Making full use of the ROOT geometry library with additional ROBAST classes, we are able to build the complex optics geometries typically used in CR experiments and ground-based gamma-ray telescopes. We introduce ROBAST and its features developed for CR experiments, and show several successful applications for CTA.

Original languageEnglish (US)
Pages (from-to)38-47
Number of pages10
JournalAstroparticle Physics
StatePublished - Mar 2016

Bibliographical note

Funding Information:
We are grateful to Dr. Andrei Gheata, the principal developer of the ROOT geometry library. We could not have developed ROBAST without his help and support. Dr. Akito Kusaka helped A. O. develop C++ code and initiated the idea of ray-tracing simulations. We also thank a number of colleagues in the Ashra collaboration and the CTA Consortium, who worked on the telescope optics designs and helped us simulate the ROBAST applications. We gratefully acknowledge Dr. Konrad Bernlöhr, who wrote sim_telarray and kindly allowed us to use part of his code in ROBAST . This study was supported by JSPS KAKENHI Grant nos. 25610040 and 25707017. A. O. was supported by a Grant-in-Aid for JSPS Fellows.


  • Gamma-ray astronomy
  • Optical systems
  • Ray tracing
  • Software
  • The Cherenkov Telescope Array

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