Reviews of Accelerator Science and Technology

The 150 years since Maxwell's formulation of the field equations, Lorentz's formulation of his force law, and Einstein's formulation of special relativity have seen electrodynamics emerge as one of the most fundamental elements of scientific and technical progress in the 20th and 21st centuries. Beginning with the analysis and demonstration of Hertzian waves, these fundamental contributions have launched a series of recurring cycles of discovery and application, in which each new discovery has been exploited to support new applications, which in turn have facilitated additional new discoveries and so on, revolutionizing in the process major elements of our economy with yet more to come through the research now in progress. It is the purpose of this article to relate my recollections of the invention and development of the free electron laser (FEL) within the context of the pervasive influence of the science and technology of electrodynamics in the 20th century.

Accelerator-based light sources stimulated progress in photon science in a truly extraordinary manner. The spectral brightness of storage-ring-based facilities increased by three orders of magnitude every 10 years since the 1960s. The extreme peak brightness at single-pass free electron X-ray lasers with pulse durations variable between about 1 and 300 femtoseconds will allow transformative experiments in many areas of science. This article is an attempt to show how progress in accelerator science and technology stimulated advancement in photon science, by discussing a limited number of examples of work at third generation storage ring facilities and free electron lasers. Hopes for further improvements in specific beam properties are expressed.

This article reviews some fundamental concepts and presents several recent techniques used for calculation of radiation in various environments. They include properties of longitudinal and transverse formation lengths of radiation, usage of the parabolic equation and the Kirchhoff diffraction integral in radiation, coherent radiation and fluctuations in the beam, and the radiative reaction force resulting from coherent radiation.

This article outlines the development and evolution of storage ring light sources, focusing on the latest, third generation light sources. After making brief historical remarks, it describes the current status, the performance, and the technological advancements of third generation light sources. The future developments of the ultimate storage ring as the next generation light source are envisioned.

Free electron lasers (FELs) are lasers which utilize the phenomenon of stimulated undulator radiation. Contrary to most lasers, the motion of an electron in the FEL may be described by classical mechanics and classical electrodynamics. Therefore, FELs belong to the family of vacuum electronic devices, such as traveling wave tubes or klystrons. In this article, basics of the low-gain FEL physics are discussed and general considerations are clarified through some examples.

In the last couple of years, free electron lasers (FELs) have been a remarkable success as fourth generation light sources all over the world. Operating in the SASE mode, they produce laser-like radiation in a broad wavelength range. Especially in the soft and hard X-ray ranges, these light sources open unique and completely new fields in physics and allow a vast range of applications in most scientific fields. This article gives an overview of the principles of FELs and the SASE process, discusses technological challenges and solutions, and presents an outlook for future developments.

Energy recovery linacs (ERLs), which can generate an electron beam having a high average current and a small-emittance with the complete manipulation of electron beams in the transverse and the longitudinal phase space, are expected to realize future light sources for various photon energies from terahertz to x- and γ-rays. In this paper, we present an overview of the history, current status, and prospects of ERLs for light sources. Research activities on the critical components of the ERLs, such as electron guns and superconducting cavities, are also described.

When a relativistic electron beam interacts with a high-field laser beam, intense and highly collimated electromagnetic radiation will be generated through Compton scattering. Through relativistic upshifting and the relativistic Doppler effect, highly energetic polarized photons are radiated along the electron beam motion when the electrons interact with the laser light. For example, X-ray radiation can be obtained when optical lasers are scattered from electrons of tens-of-MeV beam energy. Because of the desirable properties of the radiation produced, many groups around the world have been designing, building, and utilizing Compton sources for a wide variety of purposes. In this review article, we discuss the generation and properties of the scattered radiation, the types of Compton source devices that have been constructed to date, and the prospects of radiation sources of this general type. Due to the possibilities of producing hard electromagnetic radiation in a device that is small compared to the alternative storage ring sources, it is foreseen that large numbers of such sources may be constructed in the future.

Infrared radiation from the near- to the far-infrared (terahertz) region of the electromagnetic spectrum is extensively used for many different purposes. Accelerator-based sources of infrared and terahertz radiation have become well-accepted research tools. This article introduces the physics processes underlying the generation of infrared radiation by different methods. Special emphasis is put on the interesting properties of coherent radiation, and the corresponding accelerator requirements are discussed. Finally, the various available accelerator-based sources are compared in view of different figures of merit.

We discuss recent results on soft and hard X-ray free electron lasers (FELs) and how they can be used to design and optimize the next generation of these sources of high brightness, coherent photons, with femtosecond pulse duration, or very narrow linewidth. In particular, we consider the experimental and theoretical progress in the electron beam generation and manipulation. These results, when combined with the successful development of powerful simulation codes, can be used to design optimized, high intensity sources of coherent photons, and to reduce their size and cost.

This article reviews insertion devices (IDs) — wigglers and undulators — both for synchrotron radiation production and for machine parameter control. As there are many types of wigglers and undulators and it is impossible to describe them all in detail, here we particularly emphasize the design, characteristics and tolerances of undulators for free electron lasers and damping wigglers for controlling beam damping parameters. The influence of periodic IDs on beam parameters in cyclic accelerators is described in brief. A profound description of different ID types can be found in [1].

Fourth generation light sources based on high gain free electron lasers require production, acceleration and transport up to the undulator entrance of high brightness (low emittance, high peak current) electron bunches. Wake field effects in accelerating sections and in magnetic bunch compressors typically contribute to emittance degradation, and hence the design of the injector and its operation constitute the leading edge for high quality beam production and for the success of the future light sources. RF and DC guns, cathode materials, laser pulse shaping and sub-picosecond synchronization systems are evolving toward a mature technology to produce high quality and stable beams. Nevertheless, reduction of thermal emittance, damping of emittance oscillations and bunch compression are still the main issues and challenges for injector designs. With the advent of energy recovery linacs, superconducting RF guns have been also considered in many new projects as a possible electron source operating in CW mode. An overview of recent advancements and future perspectives of high performance electron injectors are presented in this article.

A review of various methods for generation of ultrashort X-ray pulses using relativistic electron beam from conventional accelerators is presented. Both spontaneous and coherent emission of electrons are considered.

It is generally accepted that the birth of the Large Hadron Collider (LHC) was in the Lausanne Workshop in 1984 [1], where machine builders and experimentalists first got together to discuss the next big project for CERN. In reality, the seeds were sown much earlier, with the construction of the Intersecting Storage Rings at CERN, followed by the proton–antiproton colliders at CERN and at Fermilab. In this article I try to give a historical perspective on how the LHC came to be, as well as my own account of some of the political, technical and financial challenges that had to be met in order to make it a reality.

In this brief article I present my memories and impressions of academician G. I. Budker (1918–1977), the brilliant physicist and outstanding leader of scientific research.