Theory of CARM devices: The free electron laser perspective

The cyclotron autoresonance maser (CARM) has been developed since the seventies of the last century. It grew in parallel with the undulator-based free electron laser theoretical and experimental efforts. Authoritative studies have pointed out the relevant analogies and distinctive features of these devices. The intrinsic efficiency, significantly larger for the first, is one of its characterizing features, which has generated considerable interest in its application as an external source for additional plasma heating in fusion research. The development of CARM theory has revealed how the electron beam qualities constitute a bottleneck, severely limiting overall performance. In this direction, significant efforts have focused on designing these devices and developing practical tools for their design. This article describes the development of a theoretical framework of the CARM theory, providing essential elements to guide the design of these devices.