Reviews of Accelerator Science and Technology

Particle accelerators and their detectors are the world’s most powerful microscopes. They enable us to inspect the constituents of matter at attometer scales, study matter under unusual conditions, and concentrate extraordinary amounts of energy into tiny volumes to create new forms of matter and initiate new phenomena. The progress of particle physics and of accelerator science and technology go hand in hand. I look to the past, present, and future, raising questions that we would like to answer about nature along the way.

Here, we consider the future of accelerators in nuclear physics. First, we look at the future of unstable beams toward a broader region of nuclei. Second, we review the possibilities in generating new forms of nuclear matter with heavy-ion beams. Third, we discuss the efforts to produce stronger powered proton beams for generating secondary particles, including neutrinos, kaons, muons, and anti-protons. Fourth, we discuss the possible electron–ion scatterings including their colliders. Other subjects such as hadron spectroscopy are not covered.

Accelerator-based X-ray sources have contributed uniquely to the physical, engineering and life sciences. There has been a constant development of the sources themselves as well as of the necessary X-ray optics and detectors. These advances have combined to push X-ray science to the forefront in structural studies, achieving atomic resolution for complex protein molecules, to meV scale dynamics addressing problems ranging from geoscience to high-temperature superconductors, and to spatial resolutions approaching 10nm for elemental mapping as well as three-dimensional structures. Here we discuss accelerator-based photon science in the frame of imaging and highlight the importance of optics, detectors and computation/data science as well as the source technology. We look to a bright future for X-ray systems, integrating all components from accelerator sources to digital image production algorithms, and highlight aspects that make them unique scientific tools.

Particle therapy is the expanding radiotherapy treatment option of choice for cancer. Its cost, however, is currently hindering its worldwide expansion. Also, the ideal application of particle therapy is restricted by a series of unsolved technical challenges. Both the cost and technical limitations are directly traceable to dependence on legacy accelerators and their associated treatment possibilities. This chapter is written to address these needs. Firstly, a technical overview is presented of photon and particle therapy for cancer tumours. Secondly, the underlying limitations of the existing legacy systems are identified, especially those related to accelerators, and suggestions are made for current and future developments to address these shortcomings. The legacy systems referred to here are of the slow scanning variety using large, circular accelerators.

This paper also attempts to make a scientific comparison of the various types of accelerators currently used or being developed for particle therapy.

The following procedure is pursued to perform a comparison between various types of accelerators:

• ⁽¹⁾The parameters which are pertinent to particle therapy accelerators (‘specified parameters’) are identified from clinical efficiency and overall cost considerations.
• ⁽²⁾The range and values of ‘specified parameters’ associated with each type of particle therapy accelerator are identified.
• ⁽³⁾A comparison is made on the best match between the various types of accelerators for each of the ‘specified parameters,’ i.e., the best in class accelerator, when compared to each criterion.
• ⁽⁴⁾Based on this match, an overall conclusion is made on the type of accelerator which best fits the needs for particle therapy.

This section updates Volume 4 of the Reviews of Accelerator Science and Technology titled “Accelerator Applications in Industry and the Environment,” published in 2011 [A. W. Chao and W. Chou (eds.), Reviews of Accelerator Science and Technology, Accelerator Applications in Industry and the Environment, Vol. 4 (World Scientific, 2011)]. We also include the new material available about this field following the publication of “The Beam Business: Accelerators in Industry” in 2011 [R. W. Hamm and M. E. Hamm, Physics Today 46–51 (June 2011)] and “Industrial Accelerators and Their Applications” in 2012 [R. W. Hamm and M. E. Hamm, Industrial Accelerators and Their Applications (World Scientific, 2012)], both written and co-edited by one of us (RWH). We start with some general trends in industrial accelerator developments and applications and then move on to bringing the up-to-date developments in each article of Volume 4. In this regard, we owe a debt of gratitude to many of the authors of sections of RAST-$4$ , and they are gratefully acknowledged in each of their individual update submissions.

Based on their great economic value, many current uses and state of the technology, the future of accelerators in medicine, industry, homeland security and research is assured for a long time to come. We review some of the areas in which R&D could have an important impact in the future and mention a few examples.

Part I of this article provides a status update on the ongoing projects for both high-beta and low-beta applications. Some of these projects are already under production, others are perfecting prototypes and future plans. We first cover the funded projects and continue with the planned projects. The update naturally captures the state-of-the-art for superconducting RF (SRF) performance for applications in progress. Part II goes on to present a vision for future prospects for performance progress in the field, along with some advice about the likely fruitful R&D paths to follow. In general, the R&D paths chosen for discussion will benefit most SRF-based accelerators.

Superconducting Magnets for High Energy Physics Accelerators are entering a new era. The successful operation of the LHC in the last decade has marked the summit of the Nb-Ti technology exploitation initiated by the Tevatron. Now, after two decades of development, Nb₃Sn technology for accelerators is becoming mature and the construction of the high luminosity LHC (HL-LHC) magnets will be the most tangible sign of the new phase, with magnets that will operate well beyond the symbolic threshold of 10 T. In addition, 30 years after its discovery, the high temperature superconductors (HTSs) for accelerator magnets are under development and test, to understand if these materials can enable the 20 T range for next accelerator/colliders foreseen after 2030. The paper reviews the main issues and the criticalities of the magnets’ development for the next future project, HL-LHC, and gives the prospect for the design and technological effort that is underway in magnet technology for the energy Frontier (FCC/HE-LHC).

The potential of muon beams for high energy physics applications is described along with the challenges of producing high quality muon beams. Two proposed approaches for delivering high intensity muon beams, a proton driver source and a positron driver source, are described and compared. The proton driver concepts are based on the studies from the Muon Accelerator Program (MAP). The MAP effort focused on a path to deliver muon-based facilities, ranging from neutrino factories to muon colliders, that could span research needs at both the intensity and energy frontiers. The Low EMittance Muon Accelerator (LEMMA) concept, which uses a positron-driven source, provides an attractive path to very high energy lepton colliders with improved particle backgrounds. The recent study of a 14-TeV muon collider in the LHC tunnel, which could leverage the existing CERN injectors and infrastructure and provide physics reach comparable to the 100TeV FCC-hh, at lower cost and with cleaner physics conditions, is also discussed. The present status of the design and R&D efforts towards each of these sources is described. A summary of important R&D required to establish a facility path for each concept is also presented.

Gamma–gamma colliders based on backward Compton scattering have been discussed mainly as an option for high energy electron–positron linear colliders, aiming to play a complementary role in energy frontier physics. The flexibility of gamma-ray beam by the Compton scheme, however, allows us to apply them to physics in a wide energy range, from MeV to TeV. In this paper, we review the future prospects of gamma–gamma colliders including recent discussions about Higgs boson factories and mid- and low-energy colliders as well as the option for electron–positron linear colliders.

With the advent of the Thin Film Compression, high energy single-cycled laser pulses have become an eminent path to the future of new high-field science. An existing CPA high power laser pulse such as a commercially available PW laser may be readily converted into a single-cycled laser pulse in the 10PW regime without losing much energy through the compression. We examine some of the scientific applications of this, such as laser ion accelerator called single-cycle laser acceleration (SCLA) and bow wake electron acceleration. Further, such a single-cycled laser pulse may be readily converted through relativistic compression into a single-cycled, X-ray laser pulse. We see that this is the quickest and very innovative way to ascend to the EW (exawatt) and zs (zeptosecond) science and technology. We suggest that such X-ray laser pulses have a broad and new horizon of applications. We have begun exploring the X-ray crystal (or nanostructured) wakefield accelerator and its broad and new applications into gamma rays. Here, we make a brief sketch of our survey of this vista of the new developments.

The present Fermilab proton Booster is an early example of a rapid-cycling synchrotron (RCS). Built in 1960s, it features a design in which the combined-function dipole magnets serve as vacuum chambers. Such a design is quite cost-effective, and it does not have the limitations associated with the eddy currents in a metallic vacuum chamber. However, an important drawback of that design is a high impedance, as seen by a beam, because of the magnet laminations. More recent RCS designs (e.g. J-PARC) employ large and complex ceramic vacuum chambers in order to mitigate the eddy-current effects and to shield the beam from the magnet laminations. Such a design, albeit very successful, is quite costly because it requires large-bore magnets and large-bore RF cavities. In this paper, we consider an RCS concept with a thin-wall metallic vacuum chamber as a compromise between the chamber-less Fermilab Booster design and the large-bore design with ceramic chambers.

Electrostatic accelerators have played a glorious role in physics, especially for low energy atomic and nuclear physics and electron microscopy. But circular accelerators have depended almost exclusively on the far greater bending force possible with static magnetic, rather than electric, fields. There is a potential exception to this magnetic bending monopoly for experimental high energy elementary particle physics — it is the possibility of measuring the electric dipole moments (EDMs) of charged elementary particles, such as proton, deuteron, or electron, using an electrostatic storage ring. Any such non-zero EDM would demonstrate violation of both parity (P) and time-reversal (T) invariance. One way of understanding the preponderance of matter over anti-matter in the present-day universe pre-supposes the existence of violations of P and T substantially greater than are allowed by the “standard model” of elementary particle physics. This provides the leading motivation for measuring EDMs. Currently, only upper limits are known for these EDMs. The very same smallness that makes it important to determine them makes their measurement difficult. Accepting as obvious the particle physics motivation, this paper concentrates on the accelerator physics of the (not very) high energy electrostatic accelerators needed for EDM measurements. Developments already completed are emphasized. Impressive advances have been made in the diagnostic tools, spin control and polarimetry that will make EDM measurement possible. Ring design for minimizing spin decoherence and limiting systematic EDM errors is presented. There have, however, been worrisome indications from low energy rings, concerning beam current limitations. A prototype ring design is proposed for investigating and addressing this concern.

In this paper we trace the origins of the International Committee for Future Accelerators (ICFA), and outline its structure and mandate, its activities and accomplishments. We also discuss ICFA’s anticipated activities related to the future directions of the field of particle physics.

Leon Max Lederman was a towering figure in the world of elementary particle physics in the second half of the 20th century. His experiments shaped our understanding of the world of particle physics. Included in the long list of his accolades was the 1988 Nobel Prize in Physics, which he shared with Melvin Schwartz and Jack Steinberger for the discovery that the muon neutrino is distinct from the electron neutrino. Among his many science leadership roles, he served for a decade as Director of Fermi National Accelerator Laboratory. Lederman was a spokesperson and champion for science and one of the most visible physicists of his generation. In his remarkable career Lederman journeyed from his youth in the Bronx, NY, to the directorship of Fermilab in Batavia, IL, to become an international proponent for physics beyond any one institution.

Burton Richter had an enormous impact on the field of accelerator science and technology. This paper recounts some of that impact through seven short essays from people who viewed his contributions to aspects of the field with topics ranging from colliding beam rings, linear colliders to Free Electron Lasers.