Active microwave pulse compressor using an electron-beam triggered switch.

A high-power active microwave pulse compressor is described that operates by modulating the quality factor of an energy storage cavity by means of mode conversion controlled by a triggered electron-beam discharge across a switch cavity. This Letter describes the principle of operation, the design of the switch cavity, the configuration used for the tests, and the experimental results. The pulse compressor produced output pulses with 140-165 MW peak power, record peak power gains of 16∶1-20∶1, and FWHM pulse duration of 16-20 ns at a frequency of 11.43 GHz.

Asymmetric bimodal accelerator cavity for raising rf breakdown thresholds.

We consider an axisymmetric microwave cavity for an accelerator structure whose eigenfrequency for its second lowest TM-like axisymmetric mode is twice that of the lowest such mode, and for which the fields are asymmetric along its axis. In this cavity, the peak amplitude of the rf electric field that points into either longitudinal face can be smaller than the peak field which points out. Computations show that a structure using such cavities might support an accelerating gradient about 47% greater than that for a structure using similar single-mode cavities, without an increase in breakdown probability.

Observation of stimulated emission at high gyroharmonics: basis for a synchrotron resonance maser.

First experimental observations are reported on stimulated coherent synchrotron radiation from highly relativistic electrons in a strong magnetic field. The experiment employed a quasioptical millimeter-wave resonator and a 6-MeV electron beam gyrating in a field of up to 25 kG. Coherent radiation at 54 GHz, corresponding to the 11th gyroharmonic, was observed and characterized. These observations demonstrate the possibility of a synchrotron resonance maser.

Energy-gain measurements from a microwave inverse free-electron-laser accelerator.

Experiments are reported on inverse free-electron-laser acceleration, including for the first time observations of the energy change as a function of relative injection phase of the electron bunches. The microwave accelerating structure consists of a uniform circular waveguide with a helical wiggler and an axial magnetic field. Acceleration of the entire beam by 6% is seen for 6 MeV electron bunches at optimum relative phase. Experimental results compare favorably, for accelerating phases, with predictions of a three-dimensional simulation that includes large-orbit effects.

Laser-driven electron cyclotron autoresonance accelerator with production of an optically chopped electron beam.

Analysis is presented of the gyroresonant acceleration of electrons in a vacuum using a focused laser. Continuous and equal acceleration is shown for electrons injected at all optical phases over an interaction length of tens of centimeters. Beam stalling is avoided as beam energy increases. Acceleration from 50 to 178 MeV is predicted for a 4 TW, 10.6-microm laser focused to a waist radius of 1.0 mm; these parameters correspond to a planned experiment. A beam stop with an off-axis hole after acceleration is shown to create a train of optically chopped bunches with 3-fs bunch lengths and a 35-fs period.