Vacuum electronics at the dawn of the twenty-first century

TLDR

The Special Issue reviews the history, operating principles, and recent technological trends of vacuum electronic devices, highlighting the development and improvements of microwave power tubes over the past quarter century. The paper aims to introduce vacuum electronics and to describe the emergence of a new class of generators based on relativistic electron beams and fast-wave interactions such as gyrotrons and free‑electron lasers. The new generators employ relativistic electron beams interacting with fast waves, exemplified by gyrotrons and free‑electron lasers. Improvements in microwave power tubes have been substantial, driven by high‑power applications and advances in materials and computational science, and the new generators extend high‑power coherent radiation beyond the microwave range into millimeter‑wave, infrared, ultraviolet, and X‑ray frequencies.

Abstract

In this introduction to the Special Issue on vacuum electronics, the history, operating principles, and recent technological trends of vacuum electronic devices are reviewed. The development of microwave power tubes is described and improvements in these devices over the past quarter of a century are highlighted. These improvements have been substantial and have been driven by modern high-power applications and by advances in materials and computational science. The second part of this paper describes the advent of a new class of vacuum electronics generator as involving relativistic electron beams and interaction with fast waves (e.g., gyrotrons, free-electron lasers). These new types of generators are opening the electromagnetic spectrum beyond the microwave region (i.e., millimeter-wave, infrared, ultraviolet, and even X-ray) for applications of high-power, coherent generators of electromagnetic radiation.