Optimizing Cherenkov photons generation and propagation in CORSIKA for CTA Monte-Carlo simulations

TL;DR

This paper presents code optimization techniques for CORSIKA simulations to improve efficiency and portability, crucial for supporting CTA's extensive Monte Carlo simulations in gamma-ray astronomy.

Contribution

The paper introduces multiple code transformations that enable automatic vectorization and enhance hardware portability of CORSIKA simulations.

Findings

Significant reduction in CPU time for simulations

Enhanced code portability across hardware architectures

Facilitated automatic vectorization by compilers

Abstract

COsmic Ray SImulations for KAscade) is a program for detailed simulation of extensive air showers initiated by high energy cosmic ray particles in the atmosphere, and is used today by almost all the major instruments that aim at measuring primary and secondary cosmic rays on the ground. The Cherenkov Telescope Array (CTA), currently under construction, is the next-generation instrument in the field of very-high-energy gamma-ray astronomy. Detailed CORSIKA Monte Carlo simulations will be regularly performed in parallel to CTA operations to estimate the instrument response functions, necessary to extract the physical properties of the cosmic sources from the measurements during data analysis. The estimated CPU time associated with these simulations is very high, of the order of 200 million HS06 hours per year. Code optimization becomes a necessity towards fast productions and limited costs. We propose in this paper multiple code transformations that aim to facilitate automatic vectorization done by the compiler, ensuring minimal external libraries requirement and high hardware portability.