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

Abstract

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 smallsized 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.

NICHE detector and operations

“…A Winston cone of opening half-angle 45 • is attached above PMT to collect more inclined lights. We found the most of rays with θ = 43 • can not be seen by PMT according to the result of ray-tracing simulation for a NICHE detector using ROBAST [7] (see Fig. 3).…”

The status and performance of Cosmic Ray Air Fluorescence Fresnel lens Telescope (CRAFFT) for the next generation UHECR observatory

“…To establish detector configuration optimization, detection efficiency, and analysis method we have developed a detector simulation. Ray-trace simulation was developed based on ROBAST [14]. The spot of the CRAFFT detector has a unique structure as shown in Fig.…”

Detection of ultra-high energy cosmic ray air showers by Cosmic Ray Air Fluorescence Fresnel lens Telescope for next generation

“…The actual detector configuration of CRAFFT is considered in the ray tracing simulation as shown in Fig. 10 using ROBAST [13]. Left of Fig.…”