Electron cyclotron resonance (ECR) plasmas: A topical review through representative results obtained over the last 60 years

The present review is devoted to the electron cyclotron resonance (ECR) plasmas. Considering that the electromagnetic wave absorption using the ECR concept has been employed since the 1960s, it becomes obvious that the coverage of the field of the ECR plasma physics, engineering, applications, and prospectives in its entirety would be a utopia in the context of a single report. Thus, the backbone of this work is a meaningful categorization of the wide applications of the ECR plasmas (Secs. III, V, and VI), by citing representative publications. The applications mainly refer to surface processes (etching, deposition, nano-construction, functionalization, cleaning, etc.), biotechnology, thrusters, and ion sources. The text also focuses on the details of different ECR setup designs, as they are tailored for specific projects. At the same time, physical parameters and the pros and cons of the ECR discharges are evaluated. This approach leads to a brief but telling compilation of the state of the art of the ECR-driven plasmas over the last 60 years (mainly 1960–2023) as well as of their prospective aspects. An introductory discussion on the ECR plasma history (Sec. I) and on the fundamental principles of the ECR heating, multipolar confinement, technical aspects, practical setups, and features of ECR plasmas (Sec. II) is given at the early beginning of this work, facilitating, thus, the consideration of the topics that follow. Special attention is paid to the distributed or modular ECR plasmas (Sec. IV) since they may mirror the road map for engineering the future ECR plasma systems. The review is throughout supported by future-proof classic and up-to-date bibliographies to encourage further reading and to fill any information gap that inevitably appears in the present work. It is underlined that the main claims or conclusions of most of the cited works are here reproduced intentionally. In other words, it is the pretension of the present article to become a quick, but pithy, guide on the ECR plasmas and on the results achieved over the last 60 years, for potential readers of different disciplines and various backgrounds. Finally, Sec. VII recaps the present perspective on the ECR plasmas, and it points to the ECR plasma prospectives.