Singular Azimuthally Propagating Electromagnetic Fields

TL;DR

This paper investigates azimuthally propagating electromagnetic fields in cylindrical cavities, revealing singularities at the center that can still have finite energy and may influence phenomena like lightning or cosmic jets.

Contribution

It introduces the concept of singular electromagnetic solutions in cylindrical cavities and discusses their experimental observation and potential physical implications.

Findings

Singular solutions exist with finite energy in cylindrical cavities.

These solutions can be experimentally excited using metallic wedges.

Potential implications for lightning initiation and cosmic phenomena.

Abstract

We study the characteristics of azimuthally propagating electromagnetic fields in a cylindrical cavity. It is found that under certain conditions, the transverse components of the electromagnetic field are singular at the center of the cavity but the corresponding electromagnetic field remains of finite energy. The solutions are arranged in branches each of which starts from a root of $J_1(x)=0$ for the TE modes and a root of $J_0(x)=0$ for the TM modes. The lowest (dominant) branch starts from a resonance that corresponds to the solution $x=0$ of $J_1(x)=0$. Its energy has a logarithmic singularity in a lossless structure. The singular solutions with finite energy can be observed experimentally by forcing them to resonate in a cavity with inserted metallic wedges. They can also be excited by transient sources. The singular electromagnetic field of these waves is strong enough to ionize the air. Whether these transient singular fields can initiate lightning, a phenomenon that is still not understood, is a very interesting question. It is also worth investigating whether the lowest resonance is excited in violently energetic cosmological phenomena such as cosmic jets.