By Andrei Seryi
CRC Press
Particle accelerators have led to remarkable discoveries and enabled scientists to develop and test the Standard Model of particle physics. On a different scale, accelerators have many applications in technology, materials science, biology, medicine (including cancer therapy), fusion research, and industry. These machines are used to accelerate electrons, positrons or ions to energies in the range of 10 s of MeV to 10 s of GeV. Electron beams are employed in generating intense X-rays in either synchrotrons or free-electron lasers, such as the Linear Collider Light Source at Stanford or the XFEL in Hamburg, for a range of applications.
Particle accelerators developed over the last century are now approaching the energy frontier. Today, at the terascale, the machines needed are extremely large and costly. The size of a conventional accelerator is determined by the technology used and final energy required. In conventional accelerators, radiofrequency microwave cavities support the electric fields responsible for accelerating charged particles. Plasma-based particle accelerators, driven by either lasers or particle beams, are showing great promise as future replacements, primarily due to the extremely large accelerating electric fields they can support, leading to the possibility of compact structures. These fields are supported by the collective motion of plasma electrons, forming a space-charge disturbance moving at a speed slightly below the speed of light in a vacuum. This method is commonly known as plasma wakefield particle acceleration.
Plasma-based accelerators are the brainchild of the late John Dawson and colleagues at the University of California, Los Angeles, and is a topic that is being investigated worldwide with a great deal of success. In the 1980s, John David Lawson asked: “Will they be a serious competitor and displace the conventional ‘dinosaur’ variety?” This is still a valid question, with plasma accelerators already producing bright X-ray sources through betatron radiation at the lower energy scale, and there are plans to create electron beams that are good enough to drive free-electron lasers and future colliders. The topic and application of these plasma accelerators have seen rapid progress worldwide in the last few years, with the result that research is no longer limited to plasma physicists, but is now seeing accelerator and radiation experts involved in developing the subject.
The book fills a void in the understanding of accelerator physics, radiation physics and plasma accelerators. It is intended to unify the three areas and does an excellent job. It also introduces the reader to the theory of inventive problem solving (TRIZ), proposed by Genrikh Altshuller in the mid 20th century to aid in the development of successful patents. It is argued that plasma accelerators fall into the prescription of TRIZ, however, it could also be argued that knowledge, imagination, creativity and time were all that was needed. The concept of TRIZ is outlined, and it is shown how it can be adopted for scientific and engineering problems.
The book is well organised. First, the fundamental concepts of particle motion in EM fields, common to accelerators and plasmas, are presented. Then, in chapter 3, the basics of synchrotron radiation are introduced. They are discussed again in chapter 7, with a potted history of synchrotrons together with Thomson and Compton scattering. It would make sense to have the history of synchrotrons in the earlier chapter.
The main topic of the book, namely the synergy between accelerators, lasers and plasma, is covered in chapter 4, where a comparison between particle-beam bunch compression and laser-pulse compression is made. Lasers have the additional advantage of being amplified through a non-linear medium amplification using chirped-pulse amplification (CPA). This method, together with optical parametric amplification, can push the laser pulses to even higher intensities.
The basics of plasma accelerators are covered in chapter 6, where simple models of these accelerators are described, including laser- and beam-driven wakefield accelerators. However, only the lepton wakefield drivers, not the proton one used for the AWAKE project at CERN, are discussed. This chapter also describes general laser plasma processes, such as laser ionisation, with an update on the progress in developing laser peak intensity. The application of plasma accelerators as a driver of free-electron lasers is covered in chapter 8, describing the principles in simple terms, with handy formulae that can be easily used. Proton and ion acceleration are covered in chapter 9, where the reader is introduced to Bragg scattering, the DNA response to radiation and proton-therapy devices, ending with a description of different plasma-acceleration schemes for protons and ions. The basic principles of the laser acceleration of protons and ions by sheaths, radiation pressure and shock waves are briefly covered. The penultimate chapter discusses beam and pulse manipulation, bringing together a fairly comprehensive but brief introduction to some of the issues regarding beam quality: beam stability, cooling and phase transfer, among others. Finally, chapter 11 looks at inventions and innovations in science, describing how using TRIZ could help. There is also a discussion on bridging the gap between initial scientific ideas and experimental verification to commercial applications, the so-called “Valley of Death”, something that is not discussed in textbooks but is now more relevant than ever.
This book is, to my knowledge, the first to bridge the three disciplines of accelerators, lasers and plasmas. It fills a gap in the market and helps in developing a better understanding of the concepts used in the quest to build compact accelerators. It is an inspiring read that is suitable for both undergraduate and graduate students, as well as researchers in the field of plasma accelerators. The book concentrates on the principles, rather than being heavy on the mathematics, and I like the fact that the pages have wide margins to take notes.
