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.

The high brightness electron beam required by a short wavelength self-amplified spontaneous emission free-electron laser (FEL) may be reached only with an accurate design of the beam dynamics from the generation in the rf injector up to the undulator. The beam dynamics is affected by strong self-consistent effects at injection, in the compression stage, and during the FEL process. The support of numerical simulations is extensively used in the predictions of the beam behavior in these nonlinear dynamical conditions. I present a review of available simulation techniques, currently exploited in the design of short wavelength free-electron lasers.

Theoretical and experimental work has been carried out to study the longitudinal space-charge effects in a retarding field energy analyzer. A one-dimensional, steady state model for both a monoenergetic beam and a thermal beam has been developed for this purpose. Potential improvements of using two-dimensional and time-dependent solutions are also briefly discussed. The study shows that, if the current density inside the device is higher than a critical value, the longitudinal space-charge effect and the formation of a potential minimum similar to the virtual cathode formation in an electron gun will distort the measured energy spectrum. The measured FWHM and the rms energy spread will be affected. The measured mean energy will also be shifted toward the low-energy side. By using a two-dimensional correction, the theoretical model also qualitatively explains the appearance of a visible tail at the high-energy side of the spectrum, as observed in experiments. According to the theory, to avoid this measurement distortion due to the longitudinal space charge, care has to be taken to limit the current density inside the device.

Frequency map analysis [J. Laskar, Icarus 88, 266 (1990)] is used here to analyze the transverse dynamics of four third generation synchrotron light sources: the ALS, the ESRF, the SOLEIL project, and Super-ACO. Time variations of the betatron tunes give additional information for the global dynamics of the beam. The main resonances are revealed; a one-to-one correspondence between the configuration space and the frequency space can be performed. We stress that the frequency maps, and therefore the dynamics optimization, are highly sensitive to sextupolar strengths and vary in a large amount from one machine to another. The frequency maps can thus be used to characterize the different machines.

A study of round-to-flat configurations, and vice versa, of angular-momentum-dominated beams is presented. The beam propagation in an axial magnetic field is described in terms of the familiar Courant-Snyder formalism by using a rotating coordinate system. The discussion of the beam transformation is based on the general properties of a cylindrically symmetric beam matrix and the existence of two invariants for a symplectic transformation in 4D phase space.

Coherent synchrotron radiation (CSR) can play an important role by not only increasing the energy spread and emittance of a beam, but also leading to a potential instability. Previous studies of the CSR induced longitudinal instability were carried out for the CSR impedance due to dipole magnets. However, many storage rings include long wigglers where a large fraction of the synchrotron radiation is emitted. This includes high-luminosity factories such as DAPHNE, PEP-II, KEK-B, and CESR-C as well as the damping rings of future linear colliders. In this paper, the instability due to the CSR impedance from a wiggler is studied assuming a large wiggler parameter $K$. The primary consideration is a low-frequency microwavelike instability, which arises near the pipe cutoff frequency. Detailed results are presented on the growth rate and threshold for the damping rings of several linear collider designs. The different scaling between the wiggler CSR impedance and the dipole CSR impedance suggests an optimization for the damping ring design.

At the interaction point of a storage ring collider each beam is subject to perturbations due to the electromagnetic field of the counterrotating beam. For flat beams, a well-known approximation models the beam by a current sheet which is uniform in the horizontal plane, restricting the particle motion to the vertical direction. In this classical model a water-bag beam distribution has been used to find working points and beam-beam tune shift parameters which lead to a stable beam distribution. We investigate the stability of a more realistic Gaussian equilibrium distribution. A linearized Vlasov equation written in action-angle variables is used to compute the radial and angular modes of a perturbation in two-dimensional phase space to first order in the displacement from the design trajectory. We find that the radial modes, which are often neglected, can have a stabilizing effect on the beam motion.

Phase advance and $\beta$ function are basic lattice functions characterizing the linear properties of an accelerator lattice. Accurate and efficient measurements of these quantities are important for commissioning and operating a machine. For rings with little coupling, we report a new method to measure these lattice functions based on the model-independent analysis technique, which uses beam histories of excited betatron oscillations measured simultaneously at a large number of beam position monitors. It is simple, fast, accurate, and robust. Measurements done at the storage ring of the Advanced Photon Source are reported. Comparisons among various methods are made.

Bunch shortening causes an electron-cooled beam to be space charge dominated at low energies. Instability during the bunch shortening has been studied using a particle-tracking program where the 3D space-charge field due to the beam is calculated with a simplifying model.

A novel rf shield structure for bellows chambers or gate valves in high-current accelerators is proposed. The rf shield has no thin fingers, but nested comb teeth instead at the inner surface of the beam duct. The comb-type rf shield has a higher thermal strength structurally than the conventional finger-type one. A simulation also indicates its lower impedance. Especially, the leak of a TE modelike higher order mode through the axial slits, which causes mainly heating of these components, is almost suppressed due to thick teeth. An abrasion test in a vacuum using a test piece of the comb-type rf shield shows less dust generation compared to the finger type. Another preliminary test transmitting 508 MHz microwaves through a prototype rf shield in the atmosphere found no abnormal heating or arcing. A trial model of bellows chambers with the comb-type rf shield will be installed and tested using a real beam in the KEK $B$-factory positron ring this year.