We present 2D simulations of both beam-driven and laser-driven plasma wakefield accelerators, using the object-oriented particle-in-cell code XOOPIC, which is time explicit, fully electromagnetic, and capable of running on massively parallel supercomputers. Simulations of laser-driven wakefields with low $\backslash (\sim {10}^{16}\mathrm{W}/{\mathrm{cm}}^2\backslash )$ and high $\backslash (\sim {10}^{18}\mathrm{W}/{\mathrm{cm}}^2\backslash )$ peak intensity laser pulses are conducted in slab geometry, showing agreement with theory and fluid simulations. Simulations of the E-157 beam wakefield experiment at the Stanford Linear Accelerator Center, in which a 30 GeV electron beam passes through 1 m of preionized lithium plasma, are conducted in cylindrical geometry, obtaining good agreement with previous work. We briefly describe some of the more significant modifications to XOOPIC required by this work, and summarize the issues relevant to modeling relativistic electron-neutral collisions in a particle-in-cell code.

Detailed experimental results of staging two laser-driven, relativistic electron accelerators are presented. During the experiment called STELLA (staged electron laser acceleration), an inverse free-electron laser (IFEL) is used to modulate the electron energy, thereby, causing $\sim 3\mathrm{fs}$ microbunches to form separated by the laser wavelength at $10.6\mu \mathrm{m}$ (equivalent to a 35 fs period). A second IFEL accelerates the electrons depending upon the phase of the microbunches entering the second IFEL with respect to the laser beam driving the second IFEL. The data presented includes electron energy spectra as a function of the phase delay and laser power driving the first IFEL. Also shown is a comparison with the computer model, which includes space charge and misalignment effects.

This paper provides a systematic derivation of a guiding-center kinetic model that describes intense beam propagation through a periodic focusing lattice with axial periodicity length $S$, valid for sufficiently small phase advance (say, $\sigma <60\mathrm{}°$). The analysis assumes a thin $(a,b\ll S)$ axially continuous beam, or very long charge bunch, propagating in the $z$ direction through a periodic focusing lattice with transverse focusing coefficients ${\kappa }_x(s+S)={\kappa }_x\left(s\right)$ and ${\kappa }_y(s+S)={\kappa }_y\left(s\right)$, where $S=\mathrm{const}$ is the lattice period. By averaging over the (fast) oscillations occurring on the length scale of a lattice period $S$, the analysis leads to smooth-focusing Vlasov-Maxwell equations that describe the slow evolution of the guiding-center distribution function ${\overline{f}}_b(\overline{x},\overline{y},{\overline{x}}^{\prime },{\overline{y}}^{\prime },s)$ and (normalized) self-field potential $\overline{\psi }(\overline{x},\overline{y},s)$ in the four-dimensional transverse phase space $(\overline{x},\overline{y},{\overline{x}}^{\prime },{\overline{y}}^{\prime })$. In the resulting kinetic equation for ${\overline{f}}_b(\overline{x},\overline{y},{\overline{x}}^{\prime },{\overline{y}}^{\prime },s)$, the average effects of the applied focusing field are incorporated in constant focusing coefficients ${\kappa }_{x\mathrm{sf}}>0\mathrm{}$ and ${\kappa }_{y\mathrm{sf}}>0\mathrm{}$, and the model is readily accessible to direct analytical investigation. Similar smooth-focusing Vlasov-Maxwell descriptions are widely used in the accelerator physics literature, often without a systematic justification, and the present analysis is intended to place these models on a rigorous, yet physically intuitive, foundation.

We studied the electrostatic field due to a charged-particle beam with uniform particle density propagating inside an rf-shielding cage (rf cage) constructed from evenly spaced conducting wires. The beam and the rf cage are surrounded by a ceramic beam pipe positioned inside a conducting pipe concentric with the beam and the rf cage. The space-charge impedances in the long wavelength regime are investigated by considering the electrostatic fields due to the longitudinal and transverse perturbations on the density of the charged-particle beam. Shielding effects due to the rf cage are discussed and simple formulas are derived for estimating the space-charge impedances. Numerical examples are given for illustration. Comparisons between analytical estimates and the results produced by the field-solver computer program MAFIA show good agreement.

This paper outlines a formalism for the description of the linear transverse dynamics of charged particles in an axisymmetric ionization cooling channel. The particle trajectories in the absence of Coulomb scattering are described in terms of lattice functions à la Courant and Snyder, which depend only on the electric and magnetic fields in the channel. The process of multiple Coulomb scattering, which introduces stochastic terms into the particle equations of motion, is treated (in Gaussian approximation) by obtaining the distribution function in phase space as a solution of a Fokker-Planck equation. The distribution function is then used to obtain moment equations for the transverse variables and for combinations of variables such as the emittance and angular momentum. The distribution function is also used to obtain an expression for the peak four-dimensional phase space density and for the fraction of the beam that is within a certain area in phase space. The special case of a periodic channel is then considered and expressions for the asymptotic rms emittance and peak phase space density are obtained. Finally, the application of the general formalism to a numerical example, based on the reported design of a cooling channel for a neutrino source, is considered, and comparisons are made with numerical simulations of that channel.

In a recent Brief Comment, the results of an experiment to measure the refraction of a particle beam were reported [P. Muggli et al., Nature 411, 43 (2001)]. The refraction takes place at a passive interface between a plasma and a gas. Here the full paper on which that Comment is based is presented. A theoretical model extends the results presented previously [T. Katsouleas et al., Nucl. Instrum. Methods Phys. Res., Sect. A 455, 161 (2000)]. The effective Snell's law is shown to be nonlinear, and the transients at the head of the beam are described. 3D particle-in-cell simulations are performed for parameters corresponding to the experiment. Additionally, the experiment to measure the refraction and internal reflection at the Stanford Linear Accelerator Center is described.

Detailed experimental studies of the first operation of an $X$-band (8.547 GHz) rf photoinjector are reported. The rf characteristics of the device are first described, as well as the tuning technique used to ensure operation of the $1\frac{1}{2}$-cell rf gun in the balanced $\pi$-mode. The characterization of the photoelectron beam produced by the rf gun includes: measurements of the bunch charge as a function of the laser injection phase, yielding information about the quantum efficiency of the Cu photocathode ( $2\times {10}^{-5\mathrm{}}$ for a surface field of $100\mathrm{MV}/\mathrm{m}$); measurements of the beam energy (1.5–2 MeV) and relative energy spread ( $\Delta \gamma /{\gamma }_0=1.8\mathrm{}\pm 0.2\%$) using a magnetic spectrometer; measurements of the beam 90% normalized emittance, which is found to be ${\varepsilon }_n=1.65\mathrm{}\pi \mathrm{mm}\mathrm{mrad}$ for a charge of 25 pC; and measurements of the bunch duration ( $<2\mathrm{}\mathrm{ps}$). Coherent synchrotron radiation experiments at Ku-band and Ka-band confirm the extremely short duration of the photoelectron bunch and a peak power scaling quadratically with the bunch charge.

The fields produced by a long beam with a given transverse charge distribution in a homogeneous vacuum chamber are studied. Signals induced by a displaced finite-size beam on electrodes of a beam position monitor (BPM) are calculated and compared to those produced by a pencil beam. The nonlinearities and corrections to BPM signals due to a finite transverse beam size are calculated for an arbitrary chamber cross section. Simple analytical expressions are given for a few particular transverse distributions of the beam current in a circular or rectangular chamber. Of particular interest is a general proof that in an arbitrary homogeneous chamber the beam-size corrections vanish for any axisymmetric beam current distribution.

We report on electron beam quality measurement results from the Massachusetts Institute of Technology 17 GHz RF gun experiment. The 1.5 cell RF gun uses a solenoid for emittance compensation. It has produced bunch charges up to 0.1 nC with beam energies up to 1 MeV. The normalized rms emittance of the beam after 35 cm of transport from the gun has been measured by a slit technique to be $3\pi \mathrm{mm}\mathrm{mrad}$ for a 50 pC bunch. This agrees well with PARMELA simulations at these beam energies. At the exit of the electron gun, we estimate the emittance to be about $1\pi \mathrm{mm}\mathrm{mrad}$, which corresponds to a beam brightness of about $80\mathrm{A}/(\pi \mathrm{mm}\mathrm{mrad}{)}^2$. Improved beam quality should be possible with a higher energy output electron beam from the gun.

A method for finding four-dimensional symplectic maps with an enlarged nearly integrable region is described. The method relies on solving for parameter values at which the linear stability factors of the fixed points (periodic orbits) of the map have the values corresponding to integer island tunes. This method is applied to accelerator lattices in order to increase dynamic aperture. The result shows a significant increase of the dynamic aperture after correction.

Space charge presents a fundamental limitation to high intensity circular accelerators. Its effects are especially important in the latest designs for high-intensity proton rings, which require beam losses much smaller than presently achieved in existing facilities. It is therefore necessary to understand the major space-charge effects which could lead to emittance growth and associated beam loss. In this paper, we explore the excitation of high-order collective beam modes and associated instabilities driven by space-charge coupling resonances. Such studies help us to understand energy exchange and emittance growth driven by space-charge coupling. They also have direct application to the choice of a good working point in a high-intensity machine. The studies are performed using an earlier version of the Spallation Neutron Source lattice, which was used as a generic example of a circular machine. In this way, we explore the nature of the observed space-charge coupling effect and its applicability to high-intensity rings in general.

In electron accelerator facilities, radio frequencies for a linac accelerator and a circular accelerator including a booster synchrotron ring and a storage ring are completely different. In order to improve the beam transmission efficiency from a linac to a circular accelerator, and to make the beam intensity constant, both rf's are generally synchronized. This method is well known and uses a common subharmonic frequency of around 10 MHz. The rf's used are generated by using a frequency multiplier from the common frequency, and they are continuously generated. We paid attention to the fact that the electron beam from a linac accelerator is always pulsed, and the rf of the linac requires only a moment during beam emission and acceleration. Taking this fact into account, we invented a new synchronization method for the rf's of both the linac and the circular accelerators. The new method is explained by describing a concrete example at the synchrotron radiation facility, SPring-8 (Super Photon ring 8 GeV). A 2856 MHz rf for the linac is generated by 508.58 MHz rf of the storage ring for a short duration of about $290\mu \mathrm{s}$. Thus, the phase difference between the two rf's is automatically fixed. This method can be applied to any combination of arbitrary different rf's.

A very fast damping of beam envelope oscillation amplitudes was recently observed in simulations of high intensity beam transport, through periodic FODO cells, in mismatched conditions [V. Variale, Nuovo Cimento Soc. Ital. Fis. 112A, 1571–1582 (1999) and T. Clauser et al., in Proceedings of the Particle Accelerator Conference, New York, 1999 (IEEE, Piscataway, NJ, 1999), p. 1779]. A Landau damping mechanism was proposed at the origin of observed effect. In this paper, to further investigate the source of this fast damping, extensive simulations have been carried out. The results presented here support the interpretation of the mechanism at the origin of the fast damping as a Landau damping effect.

In this paper we study beam transport through a straight solenoidal channel using the single-particle and linear optics approach. We derive the single-particle invariants and show their use in an extended Courant-Snyder theory for a solenoidal coupled system. Matching between solenoidal channels and between solenoidal and quadrupolar channels is discussed. We give envelope solutions and illustrate them with some numerical examples.

A magnetic bunch compressor was designed and commissioned to provide higher peak current for the Advanced Photon Source's Low-Energy Undulator Test Line free-electron laser [S. V. Milton et al., Phys. Rev. Lett. 85, 988 (2000)]. Of great concern is limiting emittance growth due to coherent synchrotron radiation. Tolerances must also be carefully evaluated to find stable operating conditions and ensure that the system can meet operational goals. Automated matching and tolerance simulations allowed consideration of numerous configurations, pinpointing those with reduced error sensitivity. Simulations indicate significant emittance growth up to 600 A peak current, for which the normalized emittance will increase from 5 to about $8.5\mu \mathrm{m}$. The simulations also provide predictions of emittance variation with chicane parameters and precompressor linac phase, which we hope to verify experimentally.

We present a new technique to measure the synchronous phase shift in an electron storage ring. A digital sampling oscilloscope is used to observe the cavity and beam signals simultaneously, and the amplitude and relative phase are obtained from a Fourier transform of the time-domain data. This procedure gives 6 mdeg resolution and is largely insensitive to input signal amplitude variations. The measurement system was used to study the dependence of the synchronous phase shift on beam current, gap voltage, and beam energy in the Brazilian Synchrotron Light Source electron storage ring.

High intensity ion beam dynamics in an axisymmetric rf focusing acceleration structure is considered. New equations of particles motion in polyharmonic rf field are devised by means of smooth approximation. Analysis of these equations allows one to formulate the conditions of beam stability. A new approach to rf focusing acceleration channel parameters choice is suggested. The relationship between 4D phase space volume of the bunch and transmission is studied by means of Hamiltonian analysis. The influence of the space charge on rf focusing conditions, transmission, longitudinal and transverse emittances, and other acceleration system characteristics is investigated by computer simulation. The “superparticles” method is being applied. The efficiency of the approach is confirmed by numerical simulation.

A radio frequency system with a fourth-harmonic “Landau” cavity suppresses coupled-bunch instabilities and increases the beam lifetime of the Aladdin electron storage ring. When the storage ring is operated with a small momentum compaction, instabilities limit the utility of the Landau cavity. Analytical modeling of instability frequencies and growth rates, simulations, and experiments suggest that the observed instabilities result from coupling between dipole and quadrupole Robinson modes.

Coherent synchrotron radiation (CSR) is of great interest to those designing accelerators as drivers for free-electron lasers (FELs). Although experimental evidence is incomplete, CSR is predicted to have potentially severe effects on the emittance of high-brightness electron beams. The performance of an FEL depends critically on the emittance, current, and energy spread of the beam. Attempts to increase the current through magnetic bunch compression can lead to increased emittance and energy spread due to CSR in the dipoles of such a compressor. The code elegant was used for design and simulation of the bunch compressor [M. Borland et al., in Proceedings of the 2000 Linear Accelerator Conference, Monterey, CA (SLAC, Menlo Park, CA, 2001), p. 863] for the low-energy undulator test line (LEUTL) FEL [S. V. Milton et al., Phys. Rev. Let. 85, 988 (1999)] at the Advanced Photon Source (APS). In order to facilitate this design, a fast algorithm was developed based on the 1D formalism of Saldin and co-workers [E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov, Nucl. Instrum. Methods Phys. Res., Sect. A 398, 373 (1997)]. In addition, a method of including CSR effects in drift spaces following the chicane magnets was developed and implemented. The algorithm is fast enough to permit running hundreds of tolerance simulations including CSR for 50 000 particles. This article describes the details of the implementation and shows results for the APS bunch compressor.