Relativistic Electronics For The Twenty-first century

During the last three decades, startling advances have been made in the capabilities of high power microwave generators by exploiting relativistic effects. The gyrotron, which produces coherent radiation near the electron cyclotron frequency, is based on the relativistic energy dependence of electron mass; gyrotron oscillators are producing hundreds of kilowatts of average power at wavelengths of a few mm, many orders of magnitude above the average power capabilities of nonrelativistic microwave tubes. The Free Electron Laser (FEL) which achieves unusually high frequency operation by utilizing a relativistic Doppler shift effect, has extended the operation of vacuum electronic coherent e.m. generators to the submillimeter, the infrared, the visible and the UV regions of the spectrum. The physical principles of these devices are very different from the principles of non-relativistic conventional microwave tubes, and this leads to some surprises in their operating characteristics which will be described.