Particle acceleration by stimulated emission of radiation: Theory and experiment

Abstract

The interaction of electromagnetic radiation with free electrons in the presence of an active medium has some appealing outcomes. Among them is particle acceleration by stimulated emission of radiation (PASER). In its framework, energy stored in an active medium (microscopic cavities) is transferred directly to an e -beam passing through. We have developed a two-dimensional analytic model for the evaluation of the energy exchange occurring as a train of electron microbunches traverses a dilute resonant medium. Efficient interaction occurs at resonance-namely, when the frequency of the train matches the resonance frequency of the medium. It is shown that the energy exchange is gamma independent for relativistic energies and it drops dramatically with an increase of the beam's radius. Based on this model, we have evaluated the relative change in the kinetic energy of a 0.1-nC 45-MeV macrobunch traversing an excited CO2 gas mixture-the former being modulated at the CO2 laser wavelength. Good agreement is found between the theoretical predictions and the results of the PASER experiment performed recently at Brookhaven National Laboratory.

PASER – particle acceleration by stimulated emission of radiation: theory, experiment, and future applications

“…However, if the electromagnetic wake-field attached to this moving electron encounters a medium with different characteristics from the vacuum, the electron will experience the field scattered by the medium. To understand the essence of the PASER from this perspective, let us briefly consider the interaction of a moving electron with three different media [50]. Each medium is characterized by its complex frequency-dependent relative dielectric coefficient ε r (ω).…”

“…In order to overcome this difficulty, it was suggested to inject a train of microbunches rather than a single macrobunch, with periodicity identical to the resonance wavelength of the medium. In other words, the resonance wavelength matches the spacing between any two adjacent microbunches [50]. Accordingly, the projection of the train's spectrum on the resonance frequency of the medium becomes dominant, facilitating efficient energy transfer.…”

“…We may expect a non-zero net acceleration only if the number of atoms in the excited state is larger than those in the lower state, i.e., the population is inverted. From the previous description, it is obvious that the acceleration force is a result of stimulated radiation, and accordingly the acronym PASER stands for particle acceleration by stimulated emission of radiation [43][44][45][46][47][48][49][50]. Considering the 200 keV electron's kinetic energy gain, as demonstrated by Banna et al [49,50], and since each CO 2 molecule stores about 0.1eV, such an electron undergoes about two-million coherent collisions of the second kind.…”

“…Optical acceleration benefits from significantly more energetic photons and virtually eliminates the breakdown limitations associated with the current microwave cavities. In all optical acceleration schemes with the exception of the PASER [43][44][45][46][47][48][49][50], the energy is stored in an active medium, being ultimately converted into a laser pulse that, in turn, facilitates the acceleration according to the specific laserelectron interaction mechanism. The query to be scrutinized in this review is whether energy stored in microscopic cavities such as molecules may be directly utilized for electron acceleration.…”

Electron bunching in a Penning trap and accelerating process for CO 2 gas mixture active medium

“…In the proof-of-principle PASER experiment [3] which gave the first experimental result about PASER. The bunch equipment consists of existing accelerator, wiggler, and high power laser, which are very complex and expensive.…”