General description of electromagnetic radiation processes based on instantaneous charge acceleration in “endpoints”

Abstract

We present a new methodology for calculating the electromagnetic radiation from accelerated charged particles. Our formulation -the 'endpoint formulation' -combines numerous results developed in the literature in relation to radiation arising from particle acceleration using a complete, and completely general, treatment. We do this by describing particle motion via a series of discrete, instantaneous acceleration events, or 'endpoints', with each such event being treated as a source of emission. This method implicitly allows for particle creation/destruction, and is suited to direct numerical implementation in either the time-or frequency-domains. In this paper, we demonstrate the complete generality of our method for calculating the radiated field from charged particle acceleration, and show how it reduces to the classical named radiation processes such as synchrotron, Tamm's description of Vavilov-Cherenkov, and transition radiation under appropriate limits. Using this formulation, we are immediately able to answer outstanding questions regarding the phenomenology of radio emission from ultra-high-energy particle interactions in both the Earth's atmosphere and the Moon. In particular, our formulation makes it apparent that the dominant emission component of the Askaryan Effect (coherent radio-wave radiation from high-energy particle cascades in dense media) comes from coherent 'bremsstrahlung' from particle acceleration, rather than coherent Vavilov-Cherenkov radiation.

Interpretation of the cosmic-ray air shower signal in Askaryan radio detectors

“…The obtained fields agree well with the microscopic calculations presented in [8][9][10][11], and references therein. The coherent transition radiation obtained within this formalism can be understood as the emission just above the air-ice boundary at t r − , and the emission just below the boundary at t r + .…”

Probing the radio emission from air showers with polarization measurements

“…The shower front, where both the induced transverse current and the charge excess reside, moves through the air with nearly the velocity of light. Because air has a refractive index which differs from unity, Cherenkov-like time compression occurs [15,16], which affects both the radiation induced by the transverse current as well as by the charge excess. The polarization of the emitted radiation differs for current-induced and charge-induced radiation, but its direction for each of these individual components does not depend on the Cherenkov-like time compression caused by the refractive index of air.…”

Modelling of radio emission in the SLAC T-510 Experiment using microscopic Geant4 simulations

“…In addition to the fact that both simulation tools are based on different hadronic and electromagnetic interaction codes to handle particle interaction, they also use different models to calculate the radio emission by the simulated particle showers. The "endpoint" formalism [3][4] applied in CoREAS [5] based on CORSIKA and the "ZHS" formalism [6] applied in ZHAireS [7] based on AIRES. The two formalisms calculate the electric field of the moving charged particles in the shower.…”