Particle Storage Rings Research Articles

Studies of the spin coherence time of protons at COSY

The search for the Electric Dipole Moments (EDM) of charged particles in storage rings necessitates polarized beams with long Spin Coherence Time (SCT) of the circulating beam. The SCT is the time during which the RMS spread of the orientation of spins of all particles in the bunch reaches one radian. A long SCT is needed to observe the coherent effect of a polarization build-up induced by the EDM. For deuterons the SCT of 1000 s has been achieved at the COoler SYnchrotron COSY (Jülich, Germany). Accomplishing such long SCT for protons is far more challenging due to their higher anomalous magnetic moment, but essential for the planned EDM experiments. It has been shown that for protons the SCT is strongly influenced by nearby intrinsic and integer spin resonances. The strengths of the latter have been calculated for a typical optics setting of COSY and the overall influence on the SCT was predicted. In addition, the efficiency of proton spin flipping with an RF solenoid from initially vertical direction into the ring plane is also investigated.

One-Step PRC Surface Pretreatment for Plating Onto Al Alloys

Faraday will describe our recent work on the development of a one-step electrochemical surface preparation process to prepare aluminum alloys for direct electrodeposition. Coating on aluminum commonly requires extensive surface pretreatment processes prior to deposition, owing to aluminum’s reactive nature and affinity for oxygen, leading to the formation of an oxide film that negatively affects coating adhesion to the substrate. Therefore, preparing the surface is critical to remove any oils or dirt attached to the surface and to remove the native oxide film to increase coating adhesion. Conventionally these issues are addressed by a continuous sequence of twelve (12) pretreatment process steps to prepare the surface for deposition. Such an extensive number of processing steps requires significant capital investment for a new vendor, increases the probability of errors during the process, is time consuming (lower industrial throughput that ties up equipment), and requires large volumes of hazardous chemicals (Hydrofluoric Acid) that are environmentally unfavorable and introduce cost and safety concerns. Therefore, alternative techniques that do not require such extensive pretreatment processing with similar or better performance to conventional methods are desired.Faraday has recently developed a simple environmentally benign pretreatment process utilizing our pulse reverse electrofinishing approach that can dramatically reduce the number of procedures and complexities required to prepare the surface for the direct deposition onto Al alloys. A specific application of interest that requires low-cost, simple fabrication technology for the deposition of wear, erosion, corrosion fatigue resistant coatings onto Al is Neutrino Focusing Horns. Neutrino Focusing Horns, required for research on particle accelerators and storage rings, are commonly made of aluminum. These horns must withstand repetitive thermal and magnetic loadings over millions of pulses in a radiation and corrosive environment and the thickness of the inner conductor is minimized to reduce absorption and scattering of secondary particles in the conductor material. Therefore, protection of the focusing horns from erosion, corrosion and fatigue is of critical importance to assure long time reliability. The most successful coating thus far has been an electroless nickel coating with conventional 12 step pretreatment method. The application of this coating, however, is challenging due to the large size of the horn (4 m x 1 m x 1 m), and industrialization is challenging due to the low part volumes, high capitalization and large number of process steps.This presentation will focus pulse/pulse reverse surface preparation processes being developed by Faraday Technology. It will explore surface pretreatment procedures to simultaneously prepare various Al surfaces such as Al 6061, Al 4043, Al 1100, and Al 5086 and subsequent direct deposition of ZnNi, NiP, or Ni coatings. These coating have since been characterized and compared to baseline electroless NiP coatings for their functional properties. The results of these characterization studies will be discussed in detail.

Experimental demonstration of optical stochastic cooling

Particle accelerators and storage rings have been transformative instruments of discovery, and, for many applications, innovations in particle-beam cooling have been a principal driver of that success1. Stochastic cooling (SC), one of the most important conceptual and technological advances in this area2–6, cools a beam through granular sampling and correction of its phase-space structure, thus bearing resemblance to a ‘Maxwell’s demon’. The extension of SC from the microwave regime up to optical frequencies and bandwidths has long been pursued, as it could increase the achievable cooling rates by three to four orders of magnitude and provide a powerful tool for future accelerators. First proposed nearly 30 years ago, optical stochastic cooling (OSC) replaces the conventional microwave elements of SC with optical-frequency analogues and is, in principle, compatible with any species of charged-particle beam7,8. Here we describe a demonstration of OSC in a proof-of-principle experiment at the Fermi National Accelerator Laboratory’s Integrable Optics Test Accelerator9,10. The experiment used 100-MeV electrons and a non-amplified configuration of OSC with a radiation wavelength of 950 nm, and achieved strong, simultaneous cooling of the beam in all degrees of freedom. This realization of SC at optical frequencies serves as a foundation for more advanced experiments with high-gain optical amplification, and advances opportunities for future operational OSC systems with potential benefit to a broad user community in the accelerator-based sciences.

Development of a multi-channel power supply for silicon photomultipliers reading out inorganic scintillators

The motivation of the current R&D project is based upon the requirements of the JEDI international collaboration11http://collaborations.fz-juelich.de/ikp/jedi/. aiming to measure Electric Dipole Moments (EDMs) of charged particles in storage rings. One of the most important elements of such an experiment will be a specially designed polarimeter with the detection system based on a modular inorganic scintillator (LYSO crystal) calorimeter. The calorimeter modules are read out by Silicon Photo Multipliers (SiPMs). This paper describes the development of a multi-channel power supply for the polarimeter modules, providing very stable and clean bias voltages for SiPMs. In order to ensure the best possible performance of SiPMs in conjunction with the crystal-based calorimeter modules and to guarantee the required level of calorimeter stability, several quality requirements have to be met by the power supply. Additionally, it is required to provide features including remote control via the network, ramping of the output voltage, measuring and sending the information about its output voltages and currents, etc. The obtained results demonstrate that the goals for the JEDI polarimeter are met. The developed hardware will be useful in other fields of fundamental and applied research, medical diagnostic techniques and industry, where SiPMs are used.

Sub-THz Waveguide Spectroscopy of Coating Materials for Particle Accelerators

The electromagnetic characterisation of different materials for the inner wall coating of beam pipes is a long-standing problem in accelerator physics, regardless the purpose they are used for, since their presence may affect in an unpredictable way the beam coupling impedance and therefore the machine performance. Moreover, in particle accelerators and storage rings of new generation very short bunches might be required, extending far in frequency the exploration of the beam spectrum and rendering therefore more and more important to assess the coating material response up to hundreds of GHz. This paper describes a time domain method based on THz waveguide spectroscopy to infer the coating properties at very high frequencies. The technique has been tested on Non Evaporable Getter thick films deposited by DC magnetron sputtering on copper plates.

Computation and consequences of high order amplitude- and parameter-dependent tune shifts in storage rings for high precision measurements

Nonlinear effects of the various electric field and magnetic field components of storage rings to confine the particles and bend their trajectory can cause substantial amplitude-dependent tune shifts within the beam. Furthermore, tune shifts are often sensitive to variations of system parameters, e.g. total particle momentum offsets [Formula: see text]. Such amplitude- and parameter-dependent tune shifts influence the dynamics and stability of a beam in particle storage rings. Thus, it is critical for high precision measurements to analyze and understand these influences. On this basis, we present normal form methods for the calculation of high order amplitude and system parameter dependencies of the horizontal and vertical tunes in storage rings using the differential algebra (DA) framework within COSY INFINITY. A storage ring is simulated using COSY INFINITY to generate a DA Poincaré return map describing the transverse phase space behavior after each revolution in the storage ring. The map is expanded around the parameter-dependent closed orbit of the system before transforming the resulting map into normal form coordinates to extract the high order tune dependencies on the phase space amplitude and variation in the system parameters. As a specific example, a storage ring similar to the Storage Ring of the Muon [Formula: see text]-2 Experiment at Fermilab (E989) is investigated.

Online storage ring optimization using dimension-reduction and genetic algorithms

Particle storage rings are a rich application domain for online optimization algorithms. The Cornell Electron Storage Ring (CESR) has hundreds of independently powered magnets, making it a high-dimensional test-problem for algorithmic tuning. We investigate algorithms that restrict the search space to a small number of linear combinations of parameters ("knobs") which contain most of the effect on our chosen objective (the vertical emittance), thus enabling efficient tuning. We report experimental tests at CESR that use dimension-reduction techniques to transform an 81-dimensional space to an 8-dimensional one which may be efficiently minimized using one-dimensional parameter scans. We also report an experimental test of a multi-objective genetic algorithm using these knobs that results in emittance improvements comparable to state-of-the-art algorithms, but with increased control over orbit errors.

Electrostatic deflector studies using small-scale prototype electrodes.

The search for electric dipole moments of particles in storage rings requires the development of dedicated electrostatic deflector elements. The JEDI prototype-ring design consists of more than 50 electric deflectors of 1 m length with 60 mm spacing between the plates with electric fields of 10 MV m-1. This paper presents studies of scaled-down uncoated prototype electrodes with 10 mm radius made of stainless steel. The electric field at electrode gap distances from 1 mm to 0.05 mm increased from 15 to 90 MV m-1. In future investigations, we will study different materials and coatings at similar electrode spacings. Preparations are also underway to study large deflector elements.

Recent progress of the JEDI collaboration

This article describes two different methods to measure the electric dipole moment (EDM) of charged particles in storage rings. The frozen spin concept relies on a large fraction (possibly 100%) of the bending field to be electric while an rf Wien filter method can also be used in purely magnetic rings albeit at lower sensitivity. In recent years the JEDI collaboration has developed several important techniques that are applicable for both methods and major milestones are presented here.

Field Quality From Tolerance Analyses In Eight-Piece Quadrupole Magnet

Quadrupole magnets are used extensively in particle accelerators, synchrotrons, and storage rings all over the world. Excellent field quality is needed in these magnets, which requires machining the magnet parts to high precision. An eight-piece quadrupole design and assembly method is developed that produces the desired magnetic field quality by accurately positioning the pole tips. In this magnet design, all the parts need to be machined only within standard machining tolerances. This paper presents the magnetic and mechanical tolerance analyses of this quadrupole design. We performed mechanical tolerance stack-up analyses using the Teamcenter Variation Analysis software to evaluate the relationship of part-level machining tolerances to final magnet assembly errors. We then performed finite element analyses using OPERA to estimate the effect of assembly errors on magnetic field quality; and in turn to set the acceptable machining tolerances for parts to achieve the desired magnetic performance. We conclude from our tolerance analyses that a 0.025-mm symmetry in pole tip gaps and pole tip diagonal gaps can be achieved with 0.050-mm standard machining tolerances, resulting in improved field quality. The analysis results are compared to the magnetic measurements in an R&D eight-piece quadrupole magnet.

Novel technique for injecting and extracting beams in a circular hadron accelerator without using septum magnets

With a few exceptions, all on-axis injection and extraction schemes implemented in circular particle accelerators, synchrotrons, and storage rings, make use of magnetic and electrostatic septa with systems of slow-pulsing dipoles acting on tens of thousands of turns and fast-pulsing dipoles on just a few. The dipoles create a closed orbit deformation around the septa, usually referred to as an orbit bump. A new approach is presented which obviates the need for the septum deflectors. Fast-pulsing elements are still required, but their strength can be minimized by choosing appropriate local accelerator optics. This technique should increase the beam clearance and reduce the usually high radiation levels found around the septa and also reduce the machine impedance introduced by the fast-pulsing dipoles. The basis of the technique is the creation of stable islands around stable fixed points in horizontal phase space. The trajectories of these islands may then be adjusted to match the position and angle of the incoming or outgoing beam.

Fringe electric fields of flat and cylindrical deflectors in electrostatic charged particle storage rings

(Received 10 September 2013; revised manuscript received 13 June 2014; published 18 July 2014) Analytic expressions for the potentials and fields offlat and cylindrical plates, including the fringe fields, are given. The present analysis extends and simplifies the current expression for the fields of flat plates and develops expressions for the fringe fields of cylindrical plates in terms of polar coordinates. The development of a FORTRAN program to output the field strength at a given location within the Proton Electric Dipole Moment (Proton EDM) ring is then described. Fourth-order Runge-Kutta integration is used to investigate the effect of fringe fields on particle and spin dynamics with precision tracking in the proposed Proton EDM experiment.

Electric dipole moments: Flavor-diagonal CP violation

Abstract Searches for permanent electric dipole moments of particles, nuclei, atoms and molecules offer an extraordinary discovery potential to new mechanisms of CP violation beyond those incorporated in the standard electroweak model. The electric dipole moments induced by speculative scenarios, on different physical systems, require a complementary approach to pave the way to the fundamental CP-violating mechanisms. New avenues presently being explored in order to improve the experimental sensitivities include projects that consider the trapping of neutral particles, the confinement of charged particles in storage rings as well as the use of radioactive nuclei.

New generation electron-positron factories

In 2010 we celebrated 50 years since commissioning of the first particle storage ring ADA in Frascati (Italy) that also became the first electron-positron collider in 1964. After that date the particle colliders have increased their intensity, luminosity and energy by several orders of magnitude. Namely, because of the high stored beam currents and high rate of useful physics events (luminosity) the modern electron-positron colliders are called "factories". However, the fundamental physics has required luminosities by 1-2 orders of magnitudes higher with respect to those presently achieved. This task can be accomplished by designing a new generation of factories exploiting the potential of a new collision scheme based on the Crab Waist (CW) collision concept recently proposed and successfully tested at Frascati. In this paper we discuss the performance and limitations of the present generation electron-positron factories and give a brief overview of new ideas and collision schemes proposed for further collider luminosity increase. In more detail we describe the CW collision concept and the results of the crab waist collision tests in DAFNE, the Italian PHi-factory. Finally, we briefly describe most advanced projects of the next generation factories based on the CW concept: SuperB in Italy, SuperKEKB in Japan and SuperC-Tau in Russia.

Self-stimulated emission of undulator radiation

We raise attention to the fact that a particle in a downstream undulator interacting with its own wavelet emitted from an upstream undulator can be as strong as its direct interaction with the frictional field of undulator itself. This phenomenon could be used for the enhancement of the signal from pickup undulators in optical stochastic cooling as well as to decrease of the damping time of particles in storage rings.

Storage modes in a low energy charged particle storage ring for atomic and molecular experiments

Specific storage modes have been identified and explored both experimentally and computationally for a new type of low energy charged particle storage ring for use in Atomic & Molecular Physics experiments [Tessier et al, Phys. Rev. Lett., 99, 253201, (2007)]. These modes offer the possibility of storing monoenergetic charged particle beams injected into the ring. Alternatively, some of the storage modes identified may be appropriate for energy filtering a stored charged particle beam within the ring. The ring is entirely electrostatic and has been shown experimentally to be capable of storing low energy electrons with storage lifetimes in the region 50 microseconds (∼150 orbits) that are vacuum pressure limited. The ring is constructed from two 180° hemispherical deflector analyzers which are interconnected by two identical cylindrical lens stacks. Each lens stack is primarily controlled by 3 voltages. The storage modes observed occur at specific combinations of these voltages and are consistent with a multiple orbit charged particle optics model of the apparatus explored using both a matrix approach and trajectory integration in a 3 dimensional electrostatic model.

Development of copper beam ducts with antechambers for advanced high-current particle storage rings

There has been continuous progress at the High Energy Accelerator Research Organization (KEK) in R&D on vacuum beam ducts adaptable to future high-current particle storage rings. Here we proposed copper beam ducts with antechambers to deal with the severe issues attributed to the high beam currents. The proposed antechamber scheme can withstand intense synchrotron radiation (SR), provide a beam duct with low beam impedance, and effectively reduce the electron cloud effect (ECE) in positron/proton rings. Several trial models were manufactured by a pressing or cold-drawn method, and assembled with electron beam welding. Special vacuum components, such as connection flanges, distributed pumps, and gate valves, were customized for the beam ducts. TiN coating on the inner surface of the beam duct was also investigated as a mitigating measure for the ECE. Trial models of the copper beam ducts were installed into the KEK B-factory (KEKB), and their performances were evaluated using real positron and electron beams.

Large high-vacuum systems for CERN accelerators

CERN operated over the more than 50 years of its existence particle accelerators and storage rings ranging from a few tens of metre to 27 km, the size of its latest project, the Large Hadron Collider (LHC) which is under construction and will be started in 2008. The challenges began with the Intersection Storage Rings (ISR) in the seventies. With a beam pipe length of 2 × 1 km, this accelerator required innovative solutions like bake-out and glow discharge to achieve the required static vacuum level, fight against beam-induced pressure increases and cancel beam neutralisation by trapped electrons. The vacuum system of the Large Electron Positron (LEP) storage ring (in operation between 1989 and 2001) of a total length of 27 km had to cope with very high levels of synchrotron power. The beam vacuum system of LHC (2 × 27 km) integrates some parts at 1.9 K and others at room temperature and will also have to cope with dynamic effects. In addition to the beam vacuum system, LHC requires insulation vacuum for the superconducting magnets and the helium distribution line. Whereas the required pressure is not very low, the leak detection and localisation is significantly more demanding for the insulation vacuum than for the beam vacuum because of the large volumes and the thermal insulation.When the size of an accelerator grows, the difficulties are not only to get a clean and leak tight vacuum system, but also to be able to measure reliably pressure or gas composition over long distances. Furthermore, in the case of LHC the integration of the beam vacuum system was particularly difficult because of the complexity induced by a superconducting magnet scheme and the reduced space available for the beam pipes. Planning and logistics aspects during installation, including the usage of mobile pumping and diagnostic means, were much more difficult to manage in LHC than in previous projects.

Global analysis of all linear stable settings of a storage ring lattice

The traditional process of designing and tuning the magnetic lattice of a particle storage ring lattice to produce certain desired properties is not straightforward. Often solutions are found through trial and error and it is not clear that the solutions are close to optimal. This can be a very unsatisfying process. In this paper we take a step back and look at the general stability limits of the lattice. We employ a technique we call GLASS (GLobal scan of All Stable Settings) that allows us to rapidly scan and find all possible stable modes and then characterize their associated properties. In this paper we illustrate how the GLASS technique gives a global and comprehensive vision of the capabilities of the lattice. In a sense, GLASS functions as a lattice observatory clearly displaying all possibilities. The power of the GLASS technique is that it is fast and comprehensive. There is no fitting involved. It gives the lattice designer clear guidance as to where to look for interesting operational points. We demonstrate the technique by applying it to two existing storage ring lattices---the triple bend achromat of the Advanced Light Source and the double bend achromat of CAMD. We show that, using GLASS, we have uncovered many interesting and in some cases previously unknown stability regions.

ON THE RELATION BETWEEN UNRUH AND SOKOLOV–TERNOV EFFECTS

We show that the Sokolov–Ternov effect — the depolarization of particles in storage rings coming from synchrotron radiation due to spin flip transitions — is physically equivalent to the Unruh effect for circular acceleration if one uses a spin-1/2 particle as the Unruh–DeWitt detector. It is shown that for the electron, with gyromagnetic number g ≈ 2, the exponential contribution to the polarization, which usually characterizes the Unruh effect, is "hidden" in the standard Sokolov–Ternov effect making it hard to observe. Thus, our conclusions are different in detail from previous work.