We have augmented the code POSINST to include solenoid fields and used it to simulate the buildup of electron cloud due in the PEP-II positron ring. We find that the distribution of electrons is strongly affected by the resonances associated with the cyclotron period and bunch spacing. In addition, we discover a threshold beyond which the electron density grows exponentially until it reaches the space charge limit. The threshold does not depend on the bunch spacing but does depend on the positron bunch population.

This work is a three-dimensional stability study based on the modal analysis for a continuous beam with an axisymmetric Kapchinskij-Vladimirskij (KV) distribution. The analysis is carried out self-consistently within the context of linearized Vlasov-Maxwell equations and electrostatic approximation. The emphasis is on investigating the coupling between longitudinal and transverse perturbations in the high-intensity region. The interaction between the transverse modes supported by the KV distribution and the “usual transverse modes” is examined. We found two classes of “coupling modes” that would not exist if longitudinal and transverse perturbations are treated separately. We also found that some transverse modes can interact among themselves through longitudinal perturbation to cause instability. The effects of wall impedance on beam stability is also studied and numerical examples are presented.

The transverse evolution of the envelope of an intense, unbunched ion beam in a linear transport channel can be modeled for the approximation of linear self-fields by the Kapchinskij-Vladimirskij (KV) envelope equations. Here we employ the KV envelope equations to analyze the linear stability properties of so-called mismatch perturbations about the matched (i.e., periodic) beam envelope in continuous focusing, periodic solenoidal, and periodic quadrupole transport lattices for a coasting beam. The formulation is analyzed and explicit self-consistent KV distributions are derived for an elliptical beam envelope in a periodic solenoidal transport channel. This derivation extends previous work to identify emittance measures and Larmor-frame transformations to allow application of standard form envelope equations to solenoidal focusing channels. Perturbed envelope equations are derived that include driving sources of mismatch excitation resulting from focusing errors, particle loss, and beam emittance growth. These equations are solved analytically for continuous focusing and demonstrate a factor of 2 increase in maximum mismatch excursions resulting from sudden driving perturbations relative to adiabatic driving perturbations. Numerical and analytical studies are carried out to explore properties of normal mode envelope oscillations without driving excitations in periodic solenoidal and quadrupole focusing lattices. Previous work on this topic by Struckmeier and Reiser [Part. Accel. 14, 227 (1984)] is extended and clarified. Regions of parametric instability are mapped, new classes of envelope instabilities are found, parametric sensitivities are explored, general limits and mode invariants are derived, and analytically accessible limits are checked. Important, and previously unexplored, launching conditions are described for pure envelope modes in periodic quadrupole focusing channels.

When an electron beam collides with a high-intensity laser beam, the spectrum of the nonlinear Thomson scattering in the backward direction shows strong oscillations like those in the spectrum of an optical klystron. Laser gain on the backward Thomson scattering is estimated using the Madey theorem, and the results suggest that Thomson-backscatter free-electron lasers are possible at wavelengths extending to the far uv using a terawatt laser beam from a chirped-pulse amplifier and a high-brightness electron beam from a needle cathode.

Recently a novel approach has been proposed for performing multiturn extraction from a circular machine. Such a technique consists of splitting the beam by means of stable islands created in transverse phase space by magnetic elements creating nonlinear fields, such as sextupoles and octupoles. Provided a slow time variation of the linear tune is applied, adiabatic with respect to the betatron motion, the islands can be moved in phase space and eventually charged particles may be trapped inside the stable structures. This generates a certain number of well-separated beamlets. Originally, this principle was successfully tested using a fourth-order resonance. In this paper the approach is generalized by considering other types of resonances as well as the possibility of performing multiple multiturn extractions. The results of numerical simulations are presented and described in detail. Of course, by time reversal, the proposed approach could be used also for multiturn injection.

An alternative layout of the TESLA linear collider (Technical Design Report, DESY Report No. 2001-011, 2001), based on weakly coupled multicell superconducting structures (superstructures), significantly reduces the investment cost due to a simplification in the rf system of the main accelerator. In January 1999, preparation of the beam test of the superstructure began in order to prove the feasibility of this layout. Progress in the preparation was reported frequently in Proceedings of TESLA Collaboration Meetings. Last year, two superstructures were installed in the Tesla Test Facility linac at DESY to experimentally verify methods to balance the accelerating gradient in a weakly coupled system, the stability of the energy gain for the entire train of bunches in macropulses, and the damping of higher order modes. We present results of the first cold and beam test of these two Nb prototypes.

When accelerating gold ions in the Relativistic Heavy Ion Collider (RHIC) the transition energy must be crossed. For this purpose, RHIC uses a set of correction quadrupoles and special power supplies which can reverse polarity in less than 40 ms. These quadrupoles are used to produce dispersion bumps which increase the transition energy as the beam approaches transition. The change of polarity will then jump the transition energy across the beam energy. This paper describes the commissioning of the RHIC first-order matched transition crossing system.

We investigate the validity of the Vlasov-Poisson equations for calculating properties of systems of $N$ charged particles governed by time-independent Hamiltonians. Through numerical experiments we verify that there is a smooth convergence toward a continuum limit as $N\to \infty$ and the particle charge $q\to 0$ such that the system charge $Q=qN$ remains fixed. However, in real systems $N$ and $q$ are always finite, and the assumption of the continuum limit must be questioned. We demonstrate that Langevin simulations can be used to assess the importance of discreteness effects, i.e., granularity, in systems for which the physical particle number $\mathcal{N}$ is too large to enable orbit integrations based on direct summation of interparticle forces. We then consider a beam bunch in thermal equilibrium and apply Langevin techniques to assess whether the continuum limit can be safely applied to this system. In the process we show, especially for systems supporting a sizable population of chaotic orbits that roam globally through phase space, that for the continuum limit to be valid, $\mathcal{N}$ must sometimes be surprisingly large. Otherwise the influence of granularity on particle orbits cannot be ignored.

Extraordinarily high fields generated by focused lasers are envisioned to accelerate particles to high energies. In this paper, we develop a new method to calculate laser acceleration in vacuum based on the energy exchange arising from the interference of the laser field with the radiation field of the particle. We apply this method to a simple accelerating structure, a perfectly conducting screen with a round hole, and show how to optimize the energy gain with respect to the hole radius, laser angle, and spot size, as well as the transverse profile of the laser. Limitations and energy scaling of this acceleration method are also discussed.

Proof-of-principle experiments on the induction synchrotron concept are scheduled using the KEK 12-GeV proton synchrotron, in which rf bunches and a superbunch will be accelerated with a long step voltage generated in the induction accelerating gaps. An unavoidable droop in the induction voltage gives an additional focusing or defocusing force in the longitudinal direction. It largely deforms the barrier bucket confining the superbunch, leading to a nonuniform particle distribution. The effects are serious in an induction synchrotron with a transition energy. Longitudinal emittance blowup beyond the transition energy is not acceptable. The necessity of compensating for the droop is discussed.

Plasma density transition trapping is a recently proposed self-injection scheme for plasma wakefield accelerators. This technique uses a sharp downward plasma density transition to trap and accelerate background plasma electrons in a plasma wakefield. This paper examines the quality of electron beams captured using this scheme in terms of emittance, energy spread, and brightness. Two-dimensional particle-in-cell simulations show that these parameters can be optimized by manipulating the plasma density profile. We also develop, and support with simulations, a set of scaling laws that predicts how the brightness of transition trapping beams scales with the plasma density of the system. These scaling laws indicate that transition trapping can produce beams with brightness $\ge 5\times {10}^{14}\mathrm{A}/(\mathrm{mrad}{)}^2$. A proof-of-principle transition trapping experiment is planned for the near future. The proposed experiment is described in detail.

Coupling impedance values of accelerator components can be obtained from standard bench measurements based on the coaxial wire method. Longitudinal impedance is obtained with one wire and the transverse impedance with a twin wire inserted into the “device under test.” The coupling impedance follows from the interpretation of the scattering coefficients from a network analyzer. In this paper, models and formulas applicable to the interpretation of the data are collected and reviewed. The paper is focused on lumped and distributed kicker magnets, for which a simulated measurement is numerically analyzed with the results graphically presented. This study suggests that the application of the standard lumped formula or the simple log formula for distributed impedances is appropriate.

We propose using an optical parametric amplifier, with a $\sim 12\mu \mathrm{m}$ wavelength, for optical-stochastic cooling of ${}^{79}\mathrm{Au}$ ions in the Relativistic Heavy Ion Collider. While the bandwidth of this amplifier is comparable to that of a Ti:sapphire laser, it has a higher average output power. Its wavelength is longer than that of the laser amplifiers previously considered for such an application. This longer wavelength permits a longer undulator period and higher magnetic field, thereby generating a larger signal from the pickup undulator and ensuring a more efficient interaction in the kicker undulator, both being essential elements in cooling moderately relativistic ions. The transition to a longer wavelength also relaxes the requirements for stability of the path length during ion-beam transport between pickup and kicker undulators.

In 1998 Bulanov et al. [Phys. Rev. E 58, R5257 (1998)] proposed a novel scheme for the production of high-quality electron beams in laser wakefield acceleration in which a controlled longitudinal nonlinear wave breaking is induced by a tailored electron density profile. This proposal was supported by both analytical and numerical results in a spatially one-dimensional configuration. In this paper we present results of a particle-in-cell simulation, two-dimensional in space and three-dimensional in the fields, of the interaction of an ultraintense laser pulse with a preformed plasma where the electron density decreases steeply from a first to a second plateau. We show that in our regime two-dimensional effects play a relevant role, allowing the production of well collimated, short and almost monochromatic electron beam. Remarkably low values of transverse and longitudinal normalized beam emittance ${ϵ}_{\mathrm{rms}}^{\mathrm{tr}}=9\times {10}^{-2}\mathrm{mm}\mathrm{mrad}$ and ${ϵ}_{\mathrm{rms}}^{\mathrm{lon}}=2\mathrm{mm}\mathrm{keV}$ are obtained.

We report a measurement of the multidimensional phase-space density distribution of an electron bunch. The measurement combines the techniques of picosecond slice-emittance measurement and high-resolution tomographic measurement of transverse phase space. This technique should have a significant impact on the development of low emittance beams and their many applications, such as short-wavelength free-electron lasers and laser accelerators. A diagnostic that provides detailed information on the density distribution of the electron bunch in multidimensional phase space is an essential tool for obtaining a small emittance at a reasonable charge and for understanding the physics of emittance growth. We previously reported a measurement of the slice emittance of a picosecond electron beam [J. S. Fraser, R. L. Sheffield, and E. R. Gray, Nucl. Instrum. Methods Phys. Res., Sect. A 250, 71 (1986).]. The tomographic reconstruction of the phase space was suggested [X. Qiu, K. Batchelor, I. Ben-Zvi, and X. J. Wang, Phys. Rev. Lett. 76, 3723 (1996).] and implemented [C. B. McKee, P. G. O’Shea, and J. M. J. Madey, Nucl. Instrum. Methods Phys. Res., Sect. A 358, 264 (1995); I. Ben-Zvi, J. X. Qiu, and X. J. Wang, in Proceedings of the Particle Accelerator Conference, Vancouver, 1997 (IEEE, Piscataway, NJ, 1997).] using a single quadrupole scan. In the present work we expand the tomographic reconstruction work and combine it with the slice-emittance method. Our present tomographic work pays special attention to the accuracy of the phase-space reconstruction. We use a transport line with nine focusing magnets, and present an analysis and technique aimed at the control of the optical functions and phases. This high-precision phase-space tomography together with the ability to modify the radial charge distribution of the electron beam presents an opportunity to improve the emittance and apply nonlinear radial emittance corrections. Combining the slice emittance and tomography diagnostics leads to an unprecedented visualization of phase-space distributions in five-dimensional phase space and provides an opportunity to perform high-order emittance corrections.

We study the response of coasting beams in the presence of space charge to linear coupling as well as gradient errors, based on linearizing the self-consistent Vlasov-Poisson equation. We determine the coherent shift of the resonance conditions as well as the response on lattice errors in smooth approximation, but allowing for arbitrary tune and/or emittance ratios. A characteristic feature is cancellation between the external forces due to the lattice errors and the beam induced space-charge forces, if the resonance condition is satisfied for the (space-charge shifted) single-particle tunes. For the linear coupling mode and small tune split we also identify a parameter region, where spontaneous instability exists in addition to the resonance.

The TREDI Monte Carlo program is briefly described, devoting some emphasis to the Lienard-Wiechert potentials approach followed to account for self-field effects and the covariant technique devised to achieve regularization of electromagnetic fields. Some guidelines to the choice of the correct parameters to be used in the simulation are also sketched. The predictions obtained for the reference work point of the space-charge compensated SPARC photoinjector and a benchmark chicane designed to study coherent synchrotron radiation effects in a magnetic compressor are compared to those of other well-established simulation codes.

The combined effect of space charge and nonlinear resonance on beam loss and emittance was measured in a benchmarking experiment over a 1.2 s long flat bottom at 1.4 GeV kinetic energy in the presence of a single controllable octupole. By lowering the working point towards the resonance, a gradual transition from a loss-free core emittance blowup to a regime dominated by continuous loss was found. We compare the observation with 3D simulations based on a new analytical space charge model and obtain good agreement in the emittance blowup regime. Our explanation is in terms of the synchrotron oscillation, which causes a periodic tune modulation due to space charge, and leads to trapping and detrapping on the resonance islands. For working points very close to the resonance this induces a beam halo with large radius. The underlying dynamics is studied in detail, and it is claimed that the predicted halo in conjunction with a reduced dynamic aperture for the real machine lattice is the source of the loss observed in the experiment.

Superconducting cavities provide high accelerating gradient in linear accelerators. However, it is desirable to have a constant geometry of the accelerating cells in order to simplify manufacturing. Such geometry leads to a nonsynchronism. A separatrix formalism has been developed for a superconducting linear accelerator based on a model of stationary separatrixes overlapping, and an effective separatrix, moving together with a quasisynchronous particle. This formalism is applied to two cases: either the phase velocity changes from cavity to cavity, or the phase velocity is constant for cavities, belonging to one family. Solving Hamiltonian equations, it is shown qualitatively and quantitatively, how the quasisynchronous phase velocity has to be adjusted either by a stepped phase velocity or by a stepped rf phasing in order to minimize the effect of nonsynchronism in the first or the second case.