Colliding Beam Accelerator Research Articles

Misconceptions about Calorimetry

In the past 50 years, calorimeters have become the most important detectors in many particle physics experiments, especially experiments in colliding-beam accelerators at the energy frontier. In this paper, we describe and discuss a number of common misconceptions about these detectors, as well as the consequences of these misconceptions. We hope that it may serve as a useful source of information for young colleagues who want to familiarize themselves with these tricky instruments.

J/ψ and Ψ Polarization in Hadronic Production Processes

Both charm and bottom quarks form nonrelativistic bound states analogous to positronium. The J/ψ and ψ(2S) charmonium states and the first three Ψ(nS) bottomonium states, all spin-triplet S-wave quarkonium states below open heavy-flavor thresholds, have relatively large branching ratios to e−e+ or μ−μ+ pairs. In hadron collisions, experiments measuring lepton pairs can determine polarization by using angular correlation techniques. The polarization, in turn, can be related theoretically to the production mechanism for the bound state. This review summarizes experimental studies with proton beams at fixed-target and colliding-beam accelerators, covering a center-of-mass energy range from 39 to 7,000 GeV for nucleon and antiproton targets. Analyses using various polarization frames and spin-quantization axes are described and results compared. A pattern emerges that connects experimental results over the whole energy span. The theoretical implications of the pattern are presented, and a set of new measurements is proposed.

Andy Sessler: The Full Life of an Accelerator Physicist

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.

Physics with the L3 Detector

LEP is the largest accelerator under construction today. It is very likely to be the highest energy facility built for elementary particle physics research in this century. Initially, LEP is scheduled to be ready for experiment by 1988, starting at c.m.s. energy \(\sqrt{S}\) = 100 GeV and gradually reaching \(\sqrt{S}\) ≈ 180 GeV, above the W+W- pair threshold. By the mid-1900s, the existing LEP may be filled with superconducting magnets to provide a 5 TeV p + 5 TeV p colliding beam accelerator. The large circumference (27 km) of LEP makes it relatively easy both to increase the energy of the e+e-accelerator and to convert it to other types of colliders.

From Factory to Farm: Dissemination of Computing in High-Energy Physics

Computing in high-energy physics relied on large computers and dedicated central facilities in the 1960s and 1970s. With the advent of colliding-beam accelerators, minicomputers, and microcomputers in the 1980s, physicists elaborated a new decentralized model of computing in high-energy physics. They restored control to and autonomy of their analysis of physics data, while simultaneously replacing large computers with farms, or clusters of microprocessors custom-built for their tasks. This new division of labor has become dominant in scientific collaborations in other fields and is presented here in the context of the culture of the Fermi National Accelerator Laboratory, which was a crucible for the creative efforts required to disseminate computing power to users. Fermilab, the last National Accelerator Laboratory, came on line as federal expenditures for high-energy physics ebbed in the 1970s and 1980s.

Computational characteristics of a neutron source based on the CERN colliding-beams accelerator

The computational characteristics of a pulsed source of thermal neutrons, which can be implented on the basis of the collidng-beams accelerator under construction at CERN, are presented. The calculations were performed at the All-Russia Reserach Institute of Experimental Physics (Sarov) using two Monte Carlo programs: the GEANT-3 program developed at CERN and our own program S-95. The neutron source is assumed to be a cylindrical tungsten target with an internal neutron moderator made of zirconium hydride bombarded by protons from a colliding-beam accelerator. The maximum power of the source is estimated on the basis of the results of calculations of the dynamical stresses in tungsten. To decrease the negative impact of mechanical stresses, recommendations are formulated dividing the target efficiently into individual elements.

Quenched! The ISABELLE Saga, I

This is the second part of a two-part article about ISABELLE, a colliding-beam accelerator conceived in 1971, officially approved in 1978, partially constructed, and terminated in 1983. I cover here the period from ISABELLE’s groundbreaking in 1978 to its termination in 1983. I treat the problems with ISABELLE’s superconducting magnets, the steps by which the problems became clear within the laboratory and to the outside, the initial failure of the laboratory administration to take forceful steps, conflicts with Fermilab, the alternate magnet projects, the repeated missing of openings that eventually used up the window of opportunity. I cover Robert Palmer’s successful creation of an alternate magnet that used Brookhaven’s existing tooling and techniques and provided (too late) a technical solution to the project’s problems, and the name change to the Colliding Beam Accelerator (CBA). I also discuss the failure of the machine to hold the physics community’s interest, and the project’s termination.

RHIC cryogenics

An integrated helium cryogenic system was designed with the specific performance goal of cooling and refrigerating the cryogenic magnets to below their nominal operating temperature. These magnets make up the steering and focusing elements for the Relativistic Heavy Ion Collider (RHIC). In addition to meeting the accelerator demands, reliability, flexibility, safety, and ease of operation were key considerations during the design phase of the project. The refrigerator, with a capacity of 25 kW at about 4 K, was originally designed to match the load for the Colliding Beam Accelerator Project. The existing refrigerator, along with its complimentary warm compressor system was reconfigured slightly to meet the cooling process cycle design for RHIC. The original VAX based process control system was also adapted for RHIC, and later expanded upon to integrate a new programmable logic controller based ring resident control system, hence forming a common system to monitor and control all cryogenic components.

Excitation of accelerating plasma waves by counter-propagating laser beams

The conventional approach to exciting high phase velocity waves in plasmas is to employ a laser pulse moving in the direction of the desired particle acceleration. Photon downshifting then causes momentum transfer to the plasma and wave excitation. Novel approaches to plasma wake excitation, colliding-beam accelerator (CBA), which involve photon exchange between the long and short counter-propagating laser beams, are described. Depending on the frequency detuning Δω between beams and duration τL of the short pulse, there are two approaches to CBA. First approach assumes (τL≈2/ωp). Photons exchanged between the beams deposit their recoil momentum in the plasma driving the plasma wake. Frequency detuning between the beams determines the direction of the photon exchange, thereby controlling the phase of the plasma wake. This phase control can be used for reversing the slippage of the accelerated particles with respect to the wake. A variation on the same theme, super-beatwave accelerator, is also described. In the second approach, a short pulse with τL≫ωp−1 detuned by Δω∼2ωp from the counter-propagating beam is employed. While parametric excitation of plasma waves by the electromagnetic beatwave at 2ωp of two co-propagating lasers was first predicted by Rosenbluth and Liu [M. N. Rosenbluth and C. S. Liu, Phys. Rev. Lett. 29, 701 (1972)], it is demonstrated that the two excitation beams can be counter-propagating. The advantages of using this geometry (higher instability growth rate, insensitivity to plasma inhomogeneity) are explained, and supporting numerical simulations presented.

Ralph P. Shutt

Ralph P. Shutt

TESLA Project Status (Germany)

The current status of the TESLA colliding-beam linear accelerator project is reviewed. The design is being developed by specialists from 44 institutes and 10 countries. The technological design phase has now been completed. The design characteristics of the basic systems of the accelerator have been demonstrated successfully on the TTF test accelerator at DESY. A decision concerning the financing of the project is expected in the near future.

The design and construction of a double-sided silicon microvertex detector for the L3 experiment at CERN

A silicon microvertex detector (SMD) has been commissioned for the L3 experiment at the Large Electron-Positron colliding-beam accelerator (LEP) at CERN. The SMD is a 72,672 channel, two layer barrel tracker that is comprised of 96 ac-coupled, double-sided silicon detectors. Details of the design and construction are presented. >

Compensation of time-dependent persistent current effects in superconducting synchrotrons.

Persistent currents in superconducting accelerator magnets are caused by the magnetization of the superconducting filaments in the field of the magnet itself. The magnetized filaments create additional field distortions which can have an important effect on beam dynamics. During the initial operation of the Tevatron as a colliding beam accelerator, the chromaticities at the injection energy were found to be time dependent, leading to instabilities and particle loss during injection and at the start of acceleration. Laboratory measurements on single Tevatron dipole magnets indicated that these effects were due to time-dependent persistent current phenomena. Using additional laboratory measurements and beam observations, we have developed a set of procedures to compensate the time-dependent chromaticities due to the persistent currents. The application of these procedures has eliminated all problems caused by time-dependent persistent current effects. We will discuss the general problem of persistent current distortions in superconducting accelerators, and, then, the laboratory measurements, the beam observations, and the successful implementation of the correction schemes. While these procedures have worked well, they have limitations which will be discussed, as well as possible future improvements and implications for future projects.

Design criteria for prompt radiation limits on the relativistic heavy ion collider site.

The Relativistic Heavy Ion Collider (RHIC) is a superconducting colliding beam accelerator facility that is currently under construction. Relatively small amounts of energy depositing in the coils of superconducting magnets can result in a "quench," the irreversible transition to the normal resistive state. The quench limit of superconducting magnets, therefore, constrains local beam loss throughout the injection, acceleration, and storage cycles to extremely low levels. From a practical standpoint, it follows that there is essentially no prompt radiation in most regions due to normal operations. The design of shielding is, therefore, principally driven by the consequences of a single pulse fault at full energy in one of the two storage rings. Since there are no regulatory requirements or guidance documents that prescribe radiological performance goals for this situation, the RHIC Project has proposed a scheme to classify the various areas of the RHIC complex based on Design Basis Accident faults. The criteria is then compared to existing regulatory requirements and guidance recommendations.

Pattern recognition at the Fermilab collider and Superconducting Supercollider.

In a colliding beam accelerator such as Fermilab or the Superconducting Supercollider (SSC) protons, or antiprotons, collide at a rate between 10(5) (Fermilab) and 10(8) (SSC) collisions per second. In real time experimentalists have to select those events which are candidates for exploring the limit of known phenomena at a much lower rate, 1-100 per second, for recording on permanent media. The rate of events from new physics sources is expected to be much lower, as low as a few per year. This is a severe problem in pattern recognition: with an input data stream of up to 10(15) potential bits per second in its images, we have to pick out those images that are potentially interesting in real time at a discrimination level of 1 part in 10(6), with a known efficiency. I will describe the overall filtering strategies and the custom hardware to do this event selection (a.k.a. pattern recognition).

Brookhaven Starts Building the Relativistic Heavy-Ion Collider

Brookhaven has finally been allowed to start building RHIC, the relativistic heavy-ion collider designed to occupy the 4-km-circumference tunnel left vacant eight years ago by the cancellation of the Colliding Beam Accelerator project. CBA, née Isabelle, was to have been a 200×200-GeV proton-proton collider, but construction never got beyond the civil engineering stage.

Improved beta detection efficiency with granular aluminum superconducting strips

Abstract Irradiation of granular aluminum (g-Al) superconducting strips by betas with energies in the minimum-ionizing range has demonstrated a high detection efficiency. An efficiency of almost 70% was found for 0.5 μm wide g-Al strips operating at a temperature of 1.4–1.7 K. This is a very encouraging result for this new concept of a high-resolution tracking detector, which could be used in future colliding-beam accelerators such as the proposed Superconducting Super Collider or other large hadron colliders. As was found earlier with X-ray irradiation, the experiments are accurately described by our thermal-propagation model.

Studies of the LBL CMOS integrated amplifier/discriminator for randomly timed inputs from fixed target experiments

A group at Lawrence Berkeley Laboratory (LBL) has reported an elegant CMOS VLSI circuit for amplifying, discriminating, and encoding the signals from highly segmented charge-output devices, e.g. silicon strip detectors or pad readout structures in gaseous detectors. The design exploits switched-capacitor circuits and the well-known time structure of data acquisition in colliding-beam accelerators to cancel leakage effects and switching noise. For random inputs, these methods are not directly applicable. However, the high speed of the reset switches makes possible a mode of operation for fixed target experiments that uses fast resets to erase unwanted data from random triggers. Data acquisition in this mode has been performed. Details of operation and measurements of noise and rate capability are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ACCELERATOR PHYSICS ISSUES AT THE SSC

The proposed Superconducting Super Collider (SSC) is a high-luminosity proton-proton colliding-beam accelerator, unique in the world, providing access to particle collision energies at least an order of magnitude greater than are available at existing facilities. The design of the SSC has been previously described in the Conceptual Design Report.1 Although not the final SSC design, this paper updates the previous design to include the changes due to the change in cell phase advance from 60 to 90 degrees, and particularly emphasizes the underlying accelerator physics issues which are involved in the SSC. A brief history of the SSC program is given followed by detailed design considerations.

Niobium demand and superconductor applications: An overview

Niobium applications in applied superconductivity are described under six major categories following an examination of supply and demand to the turn of the century. The demand is relatively small. Somewhere between 500 and 1000 tonnes of niobium are expected to be used in superconducting devices to be produced over the next ten years; the large range in demand being due to the uncertainty about whether or not the latest proposals to build new particle physics colliders will be approved. The impact of possible space programs has not been considered. The quantity of niobium contained in the primary ore needed for alloy and compound production will be about double this amount, to compensate for losses incurred during the various stages of production to final product. By comparison, world-wide steel industry demands for niobium are around 15 000 tonnes per year. Thus the world superconductor industry is very small. Fears that there may be a shortage of niobium for superconducting applications are unfounded. A major world supplier of ferro-niobium and niobium oxide is Companhia Brasileira de Metalurgia e Mineracao (CBMM) of Brazil and most of the raw material used in the practical superconducting alloys comes from this source. Reserves in the CBMM mine alone are adequate to supply projected world needs for all purposes for at least 500 years. Other world sources of niobium exist and some are being worked, but they contain lower concentrations of niobium in the ore than those in the CBMM mine and therefore they cost more to extract. In spite of the importance of niobium in technology it is not a strategic mineral because of its world-wide abundance and the availability of substitutes for its major applications. A new development in superconductivity has been the discovery of the ceramic oxide superconductors in the last two years with critical temperatures close to 100 K, offering the possibility of cheaper and simpler liquid nitrogen cooling, as opposed to liquid helium cooling, for some future superconducting applications. Near-term applications in simple electronic devices are expected but for present day and projected applications, niobium-based alloys and compounds are likely to be the workhorses of superconductivity for the remainder of this century. The major commercial superconductor application, to date, is that for whole-body magnetic imaging as a tool in medical diagnostics. These units began to reach the market-place in 1982 and over one thousand are now in use world-wide. A further recent development is the use of superconducting r.f. cavities using high purity niobium sheet. Machines using these devices will need over 30% of the total niobium demand for applied superconductivity over the next five or six years. A potential demand is that for new colliding beam accelerators proposed for particle physics and nuclear physics research. If they are built, about 600 tonnes of niobium will be needed for these machines. Requirements for energy industry technologies and transportation, so high about 15 years ago, are likely to be dismally low for the next 20 years or so. Other commercial uses for superconducting magnets at present are those for gyrotrons, magnetic separators and research and development activities. In addition to machines for physics research, smaller accelerators with superconducting magnets are under development for use in medical and industrial applications and for the production of high intensity X-ray light sources. The energy related applications are not yet commercial but the required superconducting magnet technology has been developed over the last 25 years. Applications include magnetic fusion, superconducting generators, magnetohydrodynamic power generation, superconducting power transmission and energy storage, current limiters and superconducting transformers. Successful high-speed land transportation systems based on superconducting magnet levitation have been demonstrated, as have superconducting ship drives. A wide range of superconducting instrumentation is in everyday use and the possibilities for superconducting computers continue to be studied. The status of these various technologies is discussed in the following paragraphs.