Average Power Free Electron Lasers Research Articles

Design study of an improved laser wire system for electron beam measurement

The laser wire (LW) method has been demonstrated to be an effective non-interceptive technique for measuring transverse profile and emittance of electron beams in colliders, storage rings and dumping rings. In this paper, we present an improved design of high repetition LW system for high average power free electron lasers (HAP FELs) and energy recovery linacs (ERLs). This improved LW utilizes the excess power of the photocathode drive laser, thus making itself much cheaper and simpler. The system main parameters are optimized with numerical calculations and Monte Carlo simulations, indicating that resolutions would be better than 100 μm and scanning time less than 1 minute. Status of the experiment preparation is also presented.

High average power free-electron lasers

Ever since the first free-electron laser (FEL) was both con- ceived and demonstrated in the 1970s at Stanford, it has attracted much attention as a promising foundation for a high average power light source. Since its light is produced from free electrons, an FEL can be designed to lase at virtually any wavelength. Furthermore, since its light is generated from a relativistic beam that is continually replenished, its gain medium cannot be damaged by any conventional means. Accord- ingly, as there have been several ambitious attempts to design and construct high average power FELs over the past several decades, we chronicle some of these efforts. Additionally, we provide an overview of FEL technology and theory, discuss some of the obstacles that remain in the construction of a high-power FEL, and provide a road map toward a megawatt-class device. © 2012 Society of Photo-Optical Instrumentation Engineers

Wall-Plug Efficiency and Beam Dynamics in Free-Electron Lasers Using Energy Recovery Linacs

In a high average power free-electron laser (FEL) the wall-plug efficiency is of critical importance in determining the size, complexity, and cost of the overall system. The wall-plug efficiency for the FEL oscillator and amplifier (uniform and tapered wiggler) is strongly dependent on the energy recovery process. A theoretical model for electron beam dynamics in the energy recovery linac is derived and applied to the acceleration and deceleration of nano-Coulomb electron bunches for a tapered FEL amplifier. For the tapered amplifier, the spent electron beam exiting the wiggler consists of trapped and untrapped electrons. Decelerating these two populations using different phases of the radio-frequency wave in the recovery process enhances wall-plug efficiency. For the parameters considered here, the wall-plug efficiency for the tapered amplifier can be ~10% using this approach.

A CW normal-conductive RF gun for free electron laser and energy recovery linac applications

Currently proposed energy recovery linac and high average power free electron laser projects require electron beam sources that can generate up to ∼ 1 nC bunch charges with less than 1 mm mrad normalized emittance at high repetition rates (greater than ∼ 1 MHz ). Proposed sources are based around either high voltage DC or microwave RF guns, each with its particular set of technological limits and system complications. We propose an approach for a gun fully based on mature RF and mechanical technology that greatly diminishes many of such complications. The concepts for such a source as well as the present RF and mechanical design are described. Simulations that demonstrate the beam quality preservation and transport capability of an injector scheme based on such a gun are also presented.

Review of various approaches to address high currents in SRF electron linacs

The combination of high-brightness electron sources and high-current SRF Energy Recovery Linacs (ERL) leads to a new emerging technology: high-power, high-brightness electron beams. This technology enables extremely high average power free-electron lasers, a new generation of extreme brightness light sources, electron coolers of high-energy hadron storage rings, polarized electron–hadron colliders of very high luminosity, compact Thomson scattering X-ray sources, terahertz radiation generators and much more. What is typical for many of these applications is the need for very high current, defined here as over 100 mA average current, and high brightness, which is charge dependent, but needs to be in the emittance range of between submicron up to perhaps 50 μm, usually the lower – the better. Suffice it to say that while there are a number of projects aiming at this level of performance, none is anywhere near it. This work will review the problems associated with the achievement of such performance and the various approaches taken in a number of laboratories around the world to address the issues.

Pulsed laser deposition with a high average power free electron laser: Benefits of subpicosecond pulses with high repetition rate

We have conducted experiments exploring pulsed laser deposition of thin films using the high average power Thomas Jefferson National Accelerator Facility Free Electron Laser. The combination of parameters of this laser, including subpicosecond pulses, high average power, high repetition rate, and tunability, makes it a unique tool for the study of the effects of laser characteristics on thin-film quality. When compared to ablation and deposition with an ultrafast, high energy per pulse, low repetition rate laser (amplified Ti:sapphire), we find that the lower energy per pulse with high repetition rate of the free electron laser leads to very different plasma emission and produces films with high quality with the potential of very high deposition rates. This is demonstrated in the optical spectroscopy of plasma emission from Ti and the growth of Ni80Fe20 thin films.

Research on DC-RF superconducting photocathode injector for high average power FELs

To obtain high average current electron beams for a high average power Free Electron Laser (FEL), a DC-RF superconducting injector is designed. It consists of a DC extraction gap, a 1+ 1 2 superconducting cavity and a coaxial input system. The DC gap, which takes the form of a Pierce configuration, is connected to the 1+ 1 2 superconducting cavity. The photocathode is attached to the negative electrode of the DC gap. The anode forms the bottom of the 1 2 cavity. Simulations are made to model the beam dynamics of the electron beams extracted by the DC gap and accelerated by the superconducting cavity. High quality electron beams with emittance lower than 3 π-mm-mrad can be obtained. The optimization of experiments with the DC gap, as well as the design of experiments with the coaxial coupler have all been completed. An optimized 1+ 1 2 superconducting cavity is in the process of being studied and manufactured.

The high average power free electron laser program

Abstract The potential advantages of the FEL for military applications (tunability, short-wavelength operation, efficiency, and high power) have been the goals of the Joint U.S. Army/SDIO, and Defense Research Project Agency (DARPA) programs since 1976. From the outset of the program, it was clear that funding constraints would mandate the development and demonstration of these attributes in separate but closely coupled subscale technology efforts prior to integration in a full scale weapons prototype. These efforts have so far successfully demonstrated the tunability, short wavelength generation, and high extraction efficiency of FELs. Among the most important attributes and technologies that have been developed to date are validated design codes, high quality electron beams for short wavelength operation, ring resonators, tapered wigglers, optical gain guiding, cryogenic accelerator components, energy recovery, and critical high average power components such as CW433 MHz klystrons, photoinjectors, and accelerating cavities. These technologies will be integrated into the 10 μm. 100 kW average power laser experiment (APLE), which will be built at the Boeing facility in Seattle, and which can be upgraded to operate at higher powers and shorter wavelengths. The accomplishments of the program will be described, and the paths to a high power, cryogenic FEL will be outlined.

Radio-frequency linac-driven free-electron laser configurations

Recent developments in accelerator technology and the optical guiding property of the free-electron laser (FEL) radiation indicate that rf linacs may be a strong contender for driving high average power FEL amplifiers. We discuss two rf linac-driven FEL configurations: the master oscillator power amplifier (MOPA) and the single-state power amplifier (SSPA). Our numerical results are obtained using the source-dependent expansion (SDE) method in the computer code shera. The SDE method and the code shera are discussed and illustrations of the MOPA and SSPA configurations presented.

Progress in accelerator technology for strategic defense

Progress in accelerator technology has made possible many applications in strategic defense. The feasibility of developing high brightness neutral particle beams has been demonstrated with a low energy pulsed test stand, and through individual component development. Free electron lasers (FELs) employing high peak power electron beams from induction linear accelerators are now a promising approach to ground based lasers. Advances in radio-frequency linear electron accelerators suggest applications for high average power free electron lasers for space or ground basing. The invention of laser guided electron beams using ion focusing has led to new recirculating accelerator concepts, beam transport with high efficiency, and novel applications for intense beams combining the best features of lasers and particle beams.