Effect of Finite Larmor Radius on the Cosmic Ray Penetration into an Interplanetary Magnetic Flux Rope

TL;DR

This paper investigates how finite Larmor radius effects and magnetic field irregularities influence cosmic ray penetration into interplanetary magnetic flux ropes, combining analytical solutions and numerical simulations.

Contribution

It provides new analytical and numerical insights into cosmic ray behavior inside flux ropes considering finite Larmor radius effects and magnetic irregularities.

Findings

Cosmic ray density distribution differs significantly from guiding center approximation.

Finite Larmor radius and magnetic irregularities greatly affect cosmic ray penetration.

Simulation results highlight the importance of small-scale magnetic field irregularities.

Abstract

We discuss a mechanism for cosmic ray penetration into an interplanetary magnetic flux rope, particularly the effect of the finite Larmor radius and magnetic field irregularities. First, we derive analytical solutions for cosmic ray behavior inside a magnetic flux rope, on the basis of the Newton-Lorentz equation of a particle, to investigate how cosmic rays penetrate magnetic flux ropes under an assumption of there being no scattering by small-scale magnetic field irregularities. Next, we perform a numerical simulation of a cosmic ray penetration into an interplanetary magnetic flux rope by adding small-scale magnetic field irregularities. This simulation shows that a cosmic ray density distribution is greatly different from that deduced from a guiding center approximation because of the effect of the finite Larmor radius and magnetic field irregularities for the case of a moderate to large Larmor radius compared to the flux rope radius.