Evaluation of Monte Carlo tools for high energy atmospheric physics

Abstract

Abstract. The emerging field of high energy atmospheric physics (HEAP) includes terrestrial gamma-ray flashes, electron–positron beams and gamma-ray glows from thunderstorms. Similar emissions of high energy particles occur in pulsed high voltage discharges. Understanding these phenomena requires appropriate models for the interaction of electrons, positrons and photons of up to 40 MeV energy with atmospheric air. In this paper, we benchmark the performance of the Monte Carlo codes Geant4, EGS5 and FLUKA developed in other fields of physics and of the custom-made codes GRRR and MC-PEPTITA against each other within the parameter regime relevant for high energy atmospheric physics. We focus on basic tests, namely on the evolution of monoenergetic and directed beams of electrons, positrons and photons with kinetic energies between 100 keV and 40 MeV through homogeneous air in the absence of electric and magnetic fields, using a low energy cutoff of 50 keV. We discuss important differences between the results of the different codes and provide plausible explanations. We also test the computational performance of the codes. The Supplement contains all results, providing a first benchmark for present and future custom-made codes that are more flexible in including electrodynamic interactions.

TGF Afterglows: A New Radiation Mechanism From Thunderstorms

“…The loss due to the production of neutrons, that is, the photonuclear reaction k ph-nuc = c ph-nuc n air ≈ 8 × 10 2 s −1 , can be neglected in equation (2) as k ph-absorp ≫ k ph-nuc . In Figure 2 one sees that the photon number N (t) (displayed as diamonds) first increases, as the TGF beam creates also secondary photons, which are counted in the simulation, but equation (2) approximates only the number of high-energy photons (with energies say ≳1 MeV), see further discussion by Rutjes et al (2016).…”

“…Here we present two simulations made with the general purpose Monte Carlo code FLUKA [www.fluka.org] (Böhlen et al, 2014;Ferrari et al, 2005), which performs very well in the energy regime relevant for TGFs (Rutjes et al, 2016), and which has state-of-the-art neutron transport and interactions (Böhlen et al, 2014). We simulate in air (78.085% N 2 , 20.95% O 2 , and 0.965% Ar) with the altitude-dependent density profile given by the "U.S. Standard Atmosphere (1976)" (by the U.S. Committee on Extension to the Standard Atmosphere).…”

“…with the photon absorption rate k ph-absorb = c ≈ 2 × 10 5 s −1 at STP, (where is the photon attenuation coefficient; for a discussion see Rutjes et al, 2016). The loss due to the production of neutrons, that is, the photonuclear reaction k ph-nuc = c ph-nuc n air ≈ 8 × 10 2 s −1 , can be neglected in equation (2) as k ph-absorp ≫ k ph-nuc .…”

Gamma Ray Glow Observations at 20‐km Altitude

“…It is used to simulate particle propagation through matter (Agostinelli et al, 2003;Allison et al, 2006) with or without electromagnetic fields. The ability of Geant4 to accurately simulate particle propagation, acceleration, and all multiplication mechanisms in the context of thunderstorms and high-energy atmospheric radiation was extensively tested by Skeltved et al (2014), Rutjes et al (2016), and Sarria et al (2018).…”

Cold Electron Runaway Below the Friction Curve

“…For example, a relativistic electron (with energy much above 1 MeV) on its path through matter loses energy mostly by creating many low-energy particles while it essentially keeps its original direction; so it effectively loses energy continuously and experiences some friction force, known as continuous slowing down approximation (CSDA), and it can be clearly distinguished by its high energy from the many liberated electrons in the electron volt regime. As discussed by Rutjes et al (2016), this approximation is improved in some high-energy codes by including the generation of all secondary particles below an energy threshold cut into an effective friction force acting in the primary particle, while collisions where the primary particle loses more energy are treated explicitly and stochastically. In nuclear physics where one is interested in the thickness of some material needed to shield some particle radiation, the friction on the energetic particle is also called the stopping power of the material it penetrates.…”