Collective effects, such as the microwave instability, influence the longitudinal dynamics of an electron beam in a storage ring. In a storage ring free electron laser (FEL) they can compete with the induced beam heating and thus be treated as a further concomitant perturbing source of the beam dynamics. Bunch length and energy spread measurements, carried out at the Super-ACO storage ring, can be correctly interpreted according to a broad-band impedance model. Quantitative estimations of the relative role that is played by the microwave instability and the laser heating in shaping the beam longitudinal dynamics have been obtained by the analysis of the equilibrium laser power. It has been performed in terms of either a theoretical limit, implemented with the measured beam longitudinal characteristics, or the numerical results obtained by a macroparticle tracking code, which includes the laser pulse propagation. Such an analysis, carried out for different operating points of the Super-ACO storage ring FEL, indicates that the laser heating counteracts the microwave instability.

A tall, dielectric-lined rectangular wakefield microstructure is analyzed as a possible element of an advanced linear wakefield accelerator. This accelerator would be driven by a train of fs electron microbunches that would be chopped out of a longer bunch using a powerful ${\mathrm{CO}}_2$ laser and then formed into a train of rectangular-profile bunches using a quadrupole. The bunches set up a periodic wakefield in the microstructure that can be built up to $400–600\mathrm{MV}/\mathrm{m}$, for example, using a train of ten 3-fs 1-pC bunches. Two major issues are examined. First, interference is studied using the particle-in-cell code KARAT between transition radiation and Cerenkov wakefield radiation, both set up by the passage of a charge bunch through a dielectric structure of finite length. Of significance is the difference in propagation speeds of transition radiation and Cerenkov radiation (which travels almost at the vacuum light speed $c$) and the magnitude of the respective fields. Second, stability is examined for drive and accelerated bunches using computations of test particle orbits in the longitudinal and transverse wakefields excited by the drive bunches. It is found that nearly all test electrons in the drive bunches are confined within the structure for a travel distance of 30 cm or more, while test electrons located in an accelerated bunch can have stable motion over greater than 30 cm without passing through the structure walls.

We develop a new method to simulate coherent synchrotron radiation numerically. It is based on the mesh calculation of the electromagnetic field in the frequency domain. We make an approximation in the Maxwell equation which allows a mesh size much larger than the relevant wavelength so that the computing time is tolerable. Using the equation, we can perform a mesh calculation of coherent synchrotron radiation in transient states with shielding effects by the vacuum chamber. The simulation results obtained by this method are compared with analytic solutions. Though, for the comparison with theories, we adopt simplifications such as longitudinal Gaussian distribution, zero-width transverse distribution, horizontal uniform bend, and a vacuum chamber with rectangular cross section, the method is applicable to general cases.

A spin matching method to cure intrinsic coupled spin resonances in the AGS is proposed and explored using an extension of the existing DEPOL program algorithm. The extension of DEPOL to handle linear coupling in the polarized beam acceleration is documented. Data collected from recent polarized proton experiments in the AGS are compared with the predictions derived from the extended DEPOL program.

This paper employs a one-dimensional kinetic model to investigate the nonlinear longitudinal dynamics of a long coasting beam propagating through a perfectly conducting circular pipe with radius $r_w$. The average axial electric field is expressed as $⟨E_z^s⟩=-e_b{g}_0\partial {\lambda }_b/\partial z-e_b{g}_2{r}_w^2{\partial }^3{\lambda }_b/\partial z^3$, where $g_0$ and $g_2$ are constant geometric factors, and ${\lambda }_b(z,t)=\int d{p}_z{F}_b(z,p_z,t)$ is the line density. Assuming a waterbag distribution for the longitudinal distribution function $F_b(z,p_z,t)$, it is shown that weakly nonlinear disturbances moving near the sound speed evolve according to the Korteweg–deVries equation.

Here we will derive the general theory of the beam-breakup instability in recirculating linear accelerators, in which the bunches do not have to be at the same rf phase during each recirculation turn. This is important for the description of energy recovery linacs where bunches are recirculated at a decelerating phase of the rf wave and for other recirculator arrangements where different rf phases are of an advantage. Furthermore it can be used for the analysis of phase errors of recirculated bunches. It is shown how the threshold current for a given linac can be computed and a remarkable agreement with tracking data is demonstrated. The general formulas are then analyzed for several analytically solvable cases, which show (a) why different higher order modes (HOMs) in one cavity do not couple so that the most dangerous modes can be considered individually; (b) how different HOM frequencies have to be in order to consider them separately; (c) that no optics can cause the HOMs of two cavities to cancel; (d) how an optics can avoid the addition of the instabilities of two cavities; and (e) how a HOM in a multiple-turn recirculator interferes with itself. Furthermore, a simple method to compute the orbit deviations produced by cavity misalignments has also been introduced. It is shown that the beam-breakup instability always occurs before the orbit excursion becomes very large.

In order to obtain high magnetic fields in a short period undulator, superconductive undulators have been actively investigated in recent years. In this paper, however, we propose a new approach, the cryogenic permanent magnet undulator (CPMU) design, using permanent magnets at the cryogenic temperature of liquid nitrogen or higher. This cryogenic scheme can be easily adapted to currently existing in-vacuum undulators and it improves the magnetic field performance by 30%–50%. Unlike superconductive undulators operating around the liquid helium temperature, there is no big technological difficulty such as the thermal budget problem. In addition, existing field correction techniques are applicable to the CPMUs. Since there is no quench in the CPMUs, the operation of the CPMUs has the same reliability as conventional permanent magnet undulators.

Saturation of a high-gain harmonic-generation free-electron laser (HGHG-FEL) at 266 nm has been accomplished at the Brookhaven National Laboratory/Deep Ultra Violet Free Electron Laser Facility (BNL/DUV-FEL) by seeding with an 800 nm Ti:sapphire laser. We describe the diagnostics used to characterize the electron beam and the FEL output. Analytic and simulation calculations of the HGHG output are presented and compared with the experimental data. We also discuss the chirped pulse amplification of a frequency chirped seed by an energy chirped electron beam. The third harmonic at 88 nm accompanying the 266 nm fundamental has been used in an ion pair imaging experiment in chemistry, the first application of the BNL/DUV-FEL.

The aim of the CLIC Test Facility CTF3 at CERN is to demonstrate the feasibility of the key points of the two-beam acceleration based compact linear collider study. In particular, it addresses the efficient generation of a drive beam with the appropriate time structure of the electron bunches in order to produce high power rf pulses at a frequency of 30 GHz. This time structure requires a high bunch repetition frequency. It is obtained by successive injections of bunch trains into an isochronous ring using transversely deflecting rf structures. The major goal of the now completed first phase of the CTF3 was to achieve the bunch train combination at low charge. In this paper, we give a description of the project and summarize the experimental results, with a focus on the successful bunch frequency multiplication for various factors up to 5.

Stable, coherent, longitudinal oscillations have been observed in several accelerators. Within the context of perturbation theory, the beam parameters and machine impedance often suggest these oscillations should be Landau damped. When nonlinear effects are included, long-lived, stable oscillations become possible for low intensity beams. In this paper we report observations of stable humps in bunched beams and present a theoretical framework for their description. Implications for bunched beam stochastic cooling are considered.

Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Møller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of the relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the analyzing powers of Compton, Møller, and Mott scattering polarimeters has been made. Statistically significant disagreements among the values of the beam polarization calculated from the asymmetry measurements made with each polarimeter reveal either errors in the values of the analyzing power or failure to correctly include all systematic effects. The measurements reported here represent a first step toward understanding the systematic effects of these electron polarimeters. Such studies are necessary to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of the spin orientation exiting the injector that provides maximum longitudinal polarization in each experimental hall leads to an independent and very precise (better than ${10}^{\mathrm{-}\mathrm{4}}$) absolute measurement of the final electron beam energy.

The general transfer matrix of the superimposed solenoid magnet linear fringe field is given in this paper. It is an exact analytic matrix. The symplectic condition for the arbitrary shape solenoid will be discussed also.

A detailed statistical analysis of beam position monitors (BPM) performance at RHIC is a critical factor in improving regular operations and future runs. Robust identification of malfunctioning BPMs plays an important role in any orbit or turn-by-turn analysis. Singular value decomposition and Fourier transform methods, which have evolved as powerful numerical techniques in signal processing, will aid in such identification from BPM data. This is the first attempt at RHIC to use a large set of data to statistically enhance the capability of these two techniques and determine BPM performance. A comparison from run 2003 data shows striking agreement between the two methods and hence can be used to improve BPM functioning at RHIC and possibly other accelerators.

The usual formulas for the resistive-wall wake field are derived considering ultrarelativistic beams, traveling at the speed of light. This simplifies the calculation, and it leads to a cancellation between electric and magnetic fields. However, for proton beams below 10 GeV and for many heavy-ion beams, the velocities may significantly differ from the speed of light. In this paper, we compute the longitudinal and transverse wake fields for velocities smaller than $c$ and examine under which conditions nonrelativistic effects become important. We illustrate our results by a few examples.

Both theoretical models and beam observations of negative mass instability fall short of a full description of the dynamics and the dynamical effects. Clarification by numerical modeling is now practicable because of the recent proliferation of so-called computing farms. The results of modeling reported in this paper disagree with some predictions based on a long-standing linear perturbation calculation. Validity checks on the macroparticle model are described.

Key issues in heavy-ion beam (HIB) inertial confinement fusion (ICF) include an accelerator design for an intense HIB, an efficient HIB transport, a HIB-target interaction, a reactor design, and so on. In this paper, three-dimensional computer simulations are performed for a HIB irradiation onto a direct-driven spherical fuel pellet in HIB-ICF in order to clarify dependence of multi-HIB illumination nonuniformity on parameter values of HIB illumination. For various beam parameters and reactor chamber radii we investigate the energy deposition nonuniformity using 12, 20, 32, 60, 92, and 120-beam irradiation systems. In this study, the effects of HIB temperature, HIB illumination systems, HIB emittance, and pellet temperature on the HIB illumination nonuniformity are also evaluated. In addition, the nonuniformity growth due to a little pellet displacement from a reactor chamber center is investigated. The calculation results demonstrate that we can realize a rather low nonuniform energy deposition, for example, less than 2.0 % even for a 32-beam irradiation system.

In this paper we study the impact of the rf deflectors beam loading on the transverse beam dynamics of the CTF3 combiner ring. A general expression for the single-passage wake field is obtained. Different approximated formulas are derived applying linearization of the rf deflector dispersion curve either on a limited or an unlimited frequency range. A dedicated tracking code has been written to study the multibunch multiturn effects on the transverse beam dynamics. The numerical simulations reveal that the beam emittance growth due to the wake field in the rf deflectors is a small fraction of the design emittance if the trains are injected perfectly on axis. Nevertheless in case of injection errors the final emittance growth strongly depends on the betatron phase advance between the rf deflectors. If the finite bunch length is included in the tracking code, the scenario for the central part of the bunches does not change. However, for some particular injection errors, the tails of the bunches can increase the total transverse bunch emittances.

The Tevatron in Run II is operating with three trains of 12 bunches each. Long-range beam-beam interactions have been significant sources of beam loss and lifetime limitations of antiprotons. The dynamics due to the long-range beam-beam interactions depends on several beam parameters such as tunes, coupling, chromaticities, beam separations, intensities, and emittances. We have developed analytical tools to calculate, for example, amplitude dependent tune shifts and chromaticities, beam-beam induced coupling, and resonance driving terms. We report on these calculations and estimates of dynamic aperture and diffusion coefficients with long-term tracking. These theoretical results are compared with observations and used to predict performance at design values of beam parameters.