Coherent radiation from a chain of charged particles on a circular orbit around a dielectric ball

TL;DR

This paper studies how a chain of relativistic charged particles rotating around a dielectric sphere can produce highly coherent electromagnetic radiation, with intensity enhancements under specific conditions and potential applications in GHz/THz frequencies.

Contribution

It demonstrates the conditions for coherent radiation emission from a rotating charge chain around a dielectric sphere, including effects of particle distribution and dielectric properties.

Findings

Radiation intensity peaks at certain rotation frequencies.

Coherence persists despite up to 10% particle position shifts.

Emission occurs in GHz/THz frequency ranges with high power.

Abstract

We investigate the electromagnetic radiation from a chain of relativistic charged particles uniformly rotating along equatorial orbit around a dielectric ball. For weak absorption of radiation in the ball material, at certain rotation frequency the radiation intensity becomes significantly higher than the corresponding value for a chain of charges rotating in free space or in a transparent medium with the same dielectric constant as that for the ball material. In the case of an equidistant distribution of charged particles along the orbit we determine the values of parameters of the problem for which the charges in the chain emit coherently. It is shown that the radiation intensity on a given harmonic increases in proportion to the square of the number of emitting charges. We also show that the relative shifts in the particles locations up to 10\% do not destroy the coherence properties of the radiation. It is demonstrated that the coherence effects may also dominate in the radiation intensity for chains with non-equidistant distributions of particles. The numerical results obtained for different dielectric balls have revealed the emitted radiation to be in the GHz/THz frequency ranges. The high-power radiation of the chain propagates in the angular range with respect to the rotation plane determined by the Cherenkov condition for the velocity of the chain projection onto the ball surface.