The Gyrotron at 60: Historical Overview

Gyro-oscillators (gyrotrons) and gyro-amplifiers are fast-wave vacuum-electronic sources of coherent electromagnetic (EM) waves, known as electron cyclotron masers (ECMs). The operation of ECMs is based on the cyclotron-maser instability, which originates from the relativistic dependence of the electron cyclotron frequency on the electron energy. The free energy for generation of EM waves is the energy of electron gyration in an external magnetic field which defines the operating frequency. Therefore, in contrast to slow-wave devices, oversized interaction structures can be employed. Due to possibilities of using various methods of mode selection (electrodynamical and electronic), gyrotrons can operate in very high-order modes. Since the use of large, oversized cavities and waveguides reduces the role of Ohmic wall losses and breakdown limitations, gyrotrons are capable of producing very high-power millimeter (mm), sub-mm and THz waves. The possible applications of gyro-devices span a wide range of technologies. MW-class gyrotrons are used for electron cyclotron heating, non-inductive electron cyclotron current drive (ECH&CD: 14-170 GHz), plasma generation and diagnostics (Collective Thomson Scattering (CTS) and heat-pulse propagation studies) in magnetic-confinement nuclear fusion plasma devices. ... mehrOther applications are in EC resonance sources of highly ionized ions, submillimeter-wave and THz spectroscopy, materials processing and plasma chemistry. Gyro-amplifiers are being used in high-resolution radar ranging and imaging in atmospheric and planetary science. The first gyrotron was invented and designed at IAP-Gorky, USSR (now IAP-Nizhny Novgorod, Russia) and tested in September 1964 (10 GHz, 6 W). The present historical contribution shortly summarizes the developments during the past 60 years, the present state-of-the-art and future prospects. Ref. [1] gives a detailed overview of the history of gyrotrons up to 2014.