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.

Beam instability excited by space charge effect is investigated by particle simulations during final beam bunching in heavy ion inertial fusion. The beam current is continuously increased along the beam transport line with longitudinal bunch compression. A transverse particle-in-cell simulation is carried out with a simple model of beam current increase. The multiparticle simulation shows emittance growth accompanied by the restructuring of charge distribution in the interior of the beam. An analytical stability criterion for the high-current beam transport predicts the growth of density fluctuation by the space charge effect. Although results indicate that an abrupt emittance growth is induced by the space charge oscillation at critical tune depression in the final buncher, the increase of emittance can be estimated as high as 23% at the worst case during the bunching process.

In this paper, we report on the halo formation and emittance growth driven by a parametric resonance during beam-beam collisions with optically mismatched injection. In the regime of the weak-strong beam-beam interaction, if two beams have the same machine tunes, on-axis head-on collisions between a mismatched strong beam and a weak beam will not cause the formation of halo. However, if the two beams collide with an initial offset, the beam-beam force from the mismatched strong beam can cause halo formation and emittance growth in the weak beam. Meanwhile, if two beams have different machine tunes, for opposite charged colliding beams, when the machine tune of the weak beam is smaller than that of the strong beam, there is emittance growth in the weak beam. When the machine tune of the weak beam is larger than that of the strong beam, there is little emittance growth. In the regime of the strong-strong beam-beam interaction, halo is formed in both beams even when the two beams collide head-on on the axis with equal machine tunes. This puts a strong requirement for a good beam match during the injection to colliders in order to avoid emittance growth if there are no other mechanisms after the injection to decohere the mismatched envelope oscillation.

The cumulative beam breakup problem excited by the resistive-wall wake is formulated. An approximate analytic method of finding the asymptotic behavior for the transverse bunch displacement is developed and solved. Comparison between the asymptotic analytical expression and the direct numerical solution is presented. Good agreement is found. The criterion of using the asymptotic analytical expression is discussed.

Several modern applications of radiation processing require compact and self-contained electron accelerators. To match these requirements, a 5 MeV, 1 kW electron linac has been developed at the Dipartimento di Fisica (Università di Messina) and will be described in this paper. This standing wave accelerator, driven by a 3 GHz, 2.5 MW magnetron generator, has an autofocusing structure and will be used to study several applications of radiation processing.

The charge-exchange method is now one of the main techniques for ion injection into accelerators and storage rings. The disadvantages of conventional methods, based on the atom or ion stripping in a material target, are emittance growth, energy straggling, and production of ions in many charge states. Recently suggested stripping methods based on direct photoionization require employment of hard-UV lasers, which still do not exist and must obviously be very bulky and expensive. An alternative method, suggested for injection of proton beams, employs excitation of the atom to $3p$ intermediate state with subsequent Lorentz ionization in a magnetic field gradient. This technique applies rigid requirements to laser characteristic and is not free of growing of the beam divergence. In this paper a variant of the stripping technique based on the resonantly enhanced two-photon ionization (RETPI) is considered. The technique allows ionization of singly charged ions of the elements from helium to bismuth. A variant of the technique can be used for proton injection. RETPI can be applied for both ion injection and stacking, as well as for diagnostics of ion beam characteristics on the orbit. Stripping efficiency can be about 100% for the singly charged ions having the singlet ground state and decreases for the other ions. Special methods for “cleaning” unwanted atomic states in such ions, that can provide high stripping efficiency, are discussed. Excimer lasers with very moderate parameters can be employed for implementation of this technique for almost all elements. Numerical examples show that for most of the singly charged ions and for hydrogen atom necessary laser-beam energy density is merely $0.5–8\mathrm{J}/{\mathrm{cm}}^2$ for a 1 m interaction region, and is 10 times higher for several light ions.

Pulse compression systems for future linear colliders, such as NLC and JLC, involve hundreds of kilometers of waveguide runs. These waveguides are highly overmoded to reduce the rf losses. In this paper we present a novel idea for utilizing these waveguides several times by using different modes. This idea is suitable for reflective delay lines. All the modes being used have low-loss characteristics. We describe mechanically simple mode transducers that switch the propagation mode from one configuration to another with no observable dispersion. We apply this technique to a resonant delay line pulse compression system. We also present experimental results that verify these theoretical developments.

We describe a mechanism using clearing electrodes and solenoids to remove the electron cloud in the Spallation Neutron Source’s accumulator ring. Simulation indicates that strong multipacting could happen at median clearing fields. A similar phenomenon was reported in an experimental study at Los Alamos Laboratory’s Proton Storage Ring. A weak solenoid is proven to be a good remedy for suppressing multipacting by confining electrons near the chamber wall’s surfaces. We investigated the clearing mechanism using both electrodes and solenoids.

In the soft x-ray region, the demand for helicity switching of circularly polarized undulator radiation is increasing to study circular dichroism. The asymmetric figure-8 undulator is an insertion device to provide circularly polarized radiation (CPR) and a simple method of helicity switching which has been proposed and built at SPring-8. Because of its complicated magnetic structure, it is important to optimize the magnetic parameters for more effective utilization of CPR. Using an analytical method, the relation between the magnetic parameters to maximize the degree of circular polarization is obtained. The impact of the finite emittance of electron beams on the polarization performance is also investigated numerically.

Crystalline undulators with periodically deformed crystallographic planes offer coherent electromagnetic fields on the order of 1000 T and provide undulator period $L$ in submillimeter range. We present an idea for creation of a crystalline undulator and report its realization. One face of a silicon crystal was given periodic microscratches (grooves) by means of a diamond blade, with a period ranging from 0.1 to 0.5 mm in different samples. The x-ray tests of the crystal deformation have shown that a sinusoidal-like shape of crystalline planes goes through the bulk of the crystals. This opens up the possibility for experiments with high-energy particles channeled in the crystalline undulator, a new compact source of radiation. The first experiments on photon emission in the crystal undulator are in preparation at IHEP (Protvino) with 2–15 GeV positrons and at LNF (Frascati) with 500–800 MeV positrons, aiming to produce undulator photons in the range of 50–500 keV. The results of Monte Carlo simulations for the planned experiments are presented as well.

We recently studied spin flipping of a $1.94\mathrm{GeV}/c$ vertically polarized proton beam at COSY in Jülich, Germany. We swept an rf-dipole’s frequency through an rf-induced spin resonance to flip the beam’s polarization direction. After determining the resonance’s frequency, we varied the dipole’s strength, frequency range, and frequency ramp time. At the rf-dipole’s maximum strength, and optimum frequency range and ramp time, we measured a spin-flip efficiency of $99.3\%\pm 0.1\%$. This result indicates that an rf dipole may allow efficient spin flipping in high energy proton rings.

This paper describes a self-consistent kinetic model for the longitudinal dynamics of a long, coasting beam propagating in straight (linear) geometry in the $z$ direction in the smooth-focusing approximation. Starting with the three-dimensional Vlasov-Maxwell equations, and integrating over the phase-space $({\mathbf{x}}_{\perp },{\mathbf{p}}_{\perp })$ transverse to beam propagation, a closed system of equations is obtained for the nonlinear evolution of the longitudinal distribution function $F_b(z,p_z,t)$ and average axial electric field $⟨E_z^s⟩(z,t)$. The primary assumptions in the present analysis are that the dependence on axial momentum $p_z$ of the distribution function $f_b(\mathbf{x},\mathbf{p},t)$ is factorable, and that the transverse beam dynamics remains relatively quiescent (absence of transverse instability or beam mismatch). The analysis is carried out correct to order $k_z^2{r}_w^2$ assuming slow axial spatial variations with $k_z^2{r}_w^2\ll 1$, where $k_z\sim \partial /\partial z$ is the inverse length scale of axial variation in the line density ${\lambda }_b(z,t)=\int d{p}_z{F}_b(z,p_z,t)$, and $r_w$ is the radius of the conducting wall (assumed perfectly conducting). A closed expression for the average longitudinal electric field $⟨E_z^s⟩(z,t)$ in terms of geometric factors, the line density ${\lambda }_b$, and its derivatives $\partial {\lambda }_b/\partial z,\dots$ is obtained for the class of bell-shaped density profiles $n_b(r,z,t)=({\lambda }_b/\pi r_b^2)f(r/r_b)$, where the shape function $f(r/r_b)$ has the form specified by $f(r/r_b)=(n+1)(1-r^2/r_b^2{)}^n$ for $0\le r<r_b$, and $f(r/r_b)=0$ for $r_b<r\le r_w$, where $n=0,1,2,\dots$. The general kinetic formalism developed here is valid for the entire range of beam intensities (proportional to ${\lambda }_b$) ranging from low-intensity, emittance-dominated beams, to very-high-intensity, low-emittance beams.