Reviews of Accelerator Science and Technology

The following sections are included:

• Editorial Preface
• Contents

The success of the first few years of LHC operations at CERN, and the expectation of more to come as the LHC's performance improves, are already leading to discussions of what should be next for both proton–proton and electron–positron colliders. In this discussion I see too much theoretical desperation caused by the so-far-unsuccessful hunt for what is beyond the Standard Model, and too little of the necessary interaction of the accelerator, experimenter, and theory communities necessary for a scientific and engineering success. Here, I give my impressions of the problem, its possible solution, and what is needed to have both a scientifically productive and financially viable future.

In the last five decades, proton–proton and proton–antiproton colliders have been the most powerful tools for high energy physics investigations. They have also deeply catalyzed innovation in accelerator physics and technology. Among the large number of proposed colliders, only four have really succeeded in becoming operational: the ISR, the SppbarS, the Tevatron and the LHC. Another hadron collider, RHIC, originally conceived for ion–ion collisions, has also been operated part-time with polarized protons. Although a vast literature documenting them is available, this paper is intended to provide a quick synthesis of their main features and key performance.

This article describes the fundamental limitations on the performance of electron–positron circular colliders. After introducing the subject from its end use parameter, the luminosity, we discuss in detail the various accelerator physics limitations and the evolution of several ingenious frontier ideas to ever increase the luminosity of these colliders.

High energy ion colliders are large research tools in nuclear physics for studying the quark–gluon–plasma (QGP). The collision energy and high luminosity are important design and operational considerations. The experiments also expect flexibility with frequent changes in the collision energy, detector fields, and ion species. Ion species range from protons, including polarized protons in RHIC, to heavy nuclei like gold, lead, and uranium. Asymmetric collision combinations (such as protons against heavy ions) are also essential. For the creation, acceleration, and storage of bright intense ion beams, limits are set by space charge, charge change, and intrabeam scattering effects, as well as beam losses due to a variety of other phenomena. Currently, there are two operating ion colliders: the Relativistic Heavy Ion Collider (RHIC) at BNL and the Large Hadron Collider (LHC) at CERN.

The physics motivation, accelerator science, plans for future facilities and major accelerator systems of electron–ion colliders are presented. The science enabled by these machines motivates the machine design with high luminosity and flexibility, and thus leads to new challenges in accelerator science. Innovative solutions, developed in order to achieve the objectives set for these machines, are described. Major accelerator systems and accelerator physics issues are also described, and references are provided for readers interested in greater detail.

An overview of linear collider programs is given. The history and technical challenges are described and the pioneering electron–positron linear collider, the SLC, is first introduced. For future energy frontier linear collider projects, the International Linear Collider (ILC) and the Compact Linear Collider (CLIC) are introduced and their technical features are discussed. The ILC is based on superconducting RF technology and the CLIC is based on two-beam acceleration technology. The ILC collaboration completed the Technical Design Report in 2013, and has come to the stage of “Design to Reality.” The CLIC collaboration published the Conceptual Design Report in 2012, and the key technology demonstration is in progress. The prospects for further advanced acceleration technology are briefly discussed for possible long-term future linear colliders.

After an introduction, the projected performances are presented for muon colliders with a range of energies from 126 GeV (the Higgs mass) to 6 TeV. Estimates of potential wall power consumption are also given. It is noted that a merit factor, the number of simultaneously operated detectors times the luminosity divided by the power consumption, rises rapidly above 1.5 TeV. At 6 TeV it is projected to be almost two orders of magnitude higher than that for an e⁺e⁻ linear collider. The reason for this is discussed. The physics potential of these machines is then outlined, including the 126 GeV collider's unique ability to measure the Higgs width, and the potential for a high energy machine's study of any structure seen in a hadron collider. The design and simulations of the different components are then reviewed, followed by a discussion of the supporting experiments and technology R&D.

The idea of converting an electron linear collider into a photon–photon collider through the addition of high power lasers was put forward in the early 1980s. Progress in the field of high average power, short pulse lasers has brought the state of the art within striking range of what would be required to realize a photon collider. In parallel, the necessary modifications to the detector and accelerator to enable a photon collider have been laid out. The basic concept of the photon collider, the requirements for the laser, and the detector and accelerator impact are reviewed in this article.

I review some accelerator physics topics for circular as well as linear colliders, considering both lepton and hadron beams.

For several decades already, particle colliders have been essential tools for particle physics. From the very beginning, such accelerators have been among the most complicated scientific instruments ever built, including a number of innovative technological developments. Examples are ultrahigh vacuum systems, magnets with a very high magnetic field, and equipment for sub-ns synchronization and sub-mm precision alignment of equipment inside multi-km underground tunnels. Some key technologies are related to the focusing of the beam down to a scale of sub-μm at the collision point to obtain high luminosity. This review provides an overview of collision concepts and technologies for circular particle colliders, starting from the first ideas. In particular, it discusses such novel schemes and related technologies as crab waist collision and round beam collision.

This article describes the distinguished career of Andrew M. Sessler, the visionary former director of the Lawrence Berkeley National Laboratory (LBNL), one of the most influential accelerator physicists, and a strong, dedicated human-rights activist. Andy died on 17 April 2014 from cancer at age 85. He grew up in New York City, and attended Harvard (BA in Mathematics, 1949) and then Columbia (PhD in Physics, 1953.) After an NSF postdoc at Cornell with Hans Bethe and a stint on the faculty at the Ohio State University in 1954–59, he joined the Lawrence Radiation Laboratory (now LBNL) in 1959, and spent the remainder of his career there. Although Andy left his mark on several areas of physics, including nuclear structure theory, elementary-particle physics, and many-body problems, his lasting and most important contributions came from his efforts in accelerator physics and engineering, to which he devoted most of his life's work. In collaboration with his colleagues of the legendary Midwestern Universities Research Association, he developed theories for the RF acceleration process and the collective instability phenomena, helping to realize the colliding-beam accelerators with which most of the high-energy-physics discoveries of the last few decades have been made. His work in connection with the free-electron-laser (FEL) amplifier for high-power microwave generation constructed at the Lawrence Livermore National Laboratory anticipated the optical-guiding and the self-amplified spontaneous-emission principles, upon which the success of the X-ray FELs as the fourth-generation light sources is based. Throughout his career Andy made major contributions to issues related to the impact of science and technology on society. He helped usher in a new era of research on energy efficiency and sustainable-energy technology and was instrumental in building the research agendas in those areas for the Atomic Energy Commission (AEC) and later the Department of Energy. With a lifelong interest in promoting the human rights of scientists, Andy was instrumental in initiating the American Physical Society's Committee on International Freedom of Scientists and in raising funds to endow the APS Andrei Sakharov Prize. He and Moishe Pripstein cofounded Scientists for Sakharov, Orlov, and Sharansky; the group's protests along with those of other groups led to the release of the three Soviet dissidents. More importantly, Andy's voice and example became a major force in helping call the world's attention to the plight of scientists trapped in places where their human rights and their ability to do science were severely compromised. Andy received many honors, including the AEC's Ernest Orlando Lawrence Award in 1970, the APS's Dwight Nicholson Medal in 1994, and the Enrico Fermi Award from the US Department of Energy in 2014.