Calculations show that 10 keV helium and carbon ions, injected midway between two identical 1 TW-power crossed laser beams of radial polarization, can be accelerated in vacuum to energies of utility in ion lithography. As examples, identical laser beams, crossed at 10° and focused to waist radii of $7.42\mu \mathrm{m}$, accelerate ${\mathrm{He}}^{2+}$ and ${\mathrm{C}}^{6+}$ ions to average kinetic energies near 75 and 165 keV over distances averaging less than 7 and 6 mm, respectively. The spread in kinetic energy in both cases is less than 1% and the particle average angular deflection is less than 7 mrad. More energy-demanding industrial applications require higher-power laser beams for their direct ion laser acceleration.

A set of one-dimensional equations has been deduced in the time domain from the Maxwell-Lorentz system with the aim of describing the free-electron laser radiation without using the slowly varying envelope approximation (SVEA). These equations are valid even in the case of arbitrarily short electron bunches and of current distributions with ripples on the scale of or shorter than the wavelength. Numerical examples are presented, showing that for long homogeneous bunches the new set of equations gives results in agreement with the SVEA free-electron laser theory and that the use of short or prebunched electron beams leads to a decrease of the emission lethargy. Furthermore, we demonstrate that in all cases in which the backward low frequency wave has negligible effects, these equations can be reduced to a form similar to the usual 1D SVEA equations but with a different definition of the bunching term.

A comparison of the two most prominent electron sources of high average current high brightness electron beams, dc and superconducting rf photoemission guns, is carried out using a large-scale multivariate genetic optimizer interfaced with space charge simulation codes. The gun geometry for each case is varied concurrently with laser pulse shape and parameters of the downstream beam line elements of the photoinjector to obtain minimum emittance as a function of bunch charge. Realistic constraints are imposed on maximum field values for the two gun types. The superconducting rf and dc gun emittances and beam envelopes are compared for various values of photocathode thermal emittance. The performance of the two systems is found to be largely comparable for up to 154 pC per bunch at 1.3 GHz or 200 mA provided low intrinsic emittance photocathodes can be employed.

A new way to generate intense attosecond x-ray pulses is discussed. It relies on coherent Thomson scattering (CTS) from relativistic electron sheets. A double layer technique is used to generate planar solid-density sheets of monochromatic high-$\gamma$ electrons with zero transverse momentum such that coherently backscattered light is frequency upshifted by factors up to $4{\gamma }^2$. Here previous work [H.-C. Wu et al., Phys. Rev. Lett. 104, 234801 (2010)] is extended to the regime of high-intensity probe light with normalized amplitude $a_0>1$ leading to nonlinear CTS effects such as pulse contraction and steepening. The results are derived both by particle-in-cell (PIC) simulation in a boosted frame and by analytic theory. PIC simulation shows that powerful x-ray pulses (1 keV, $<10\mathrm{\text{attosecond}}$, and $>10\mathrm{\text{gigawatt}}$) can be generated. They call for experimental verification. Required prerequisites such as manufacture of nanometer-thick target foils is ready and ultrahigh contrast laser pulses should be within reach in the near future.

High-resolution measurement of the longitudinal profile of a relativistic electron beam is of utmost importance for linac based free-electron lasers and other advanced accelerator facilities that employ ultrashort bunches. In this paper, we investigate a novel scheme to measure ultrashort bunches (subpicosecond) with exceptional temporal resolution (hundreds of attoseconds) and dynamic range. The scheme employs two orthogonally oriented deflecting sections. The first imparts a short-wavelength (fast temporal resolution) horizontal angular modulation on the beam, while the second imparts a long-wavelength (slow) angular kick in the vertical dimension. Both modulations are observable on a standard downstream screen in the form of a streaked sinusoidal beam structure. We demonstrate, using scaled variables in a quasi-1D approximation, an expression for the temporal resolution of the scheme and apply it to a proof-of-concept experiment at the UCLA Neptune high-brightness injector facility. The scheme is also investigated for application at the SLAC NLCTA facility, where we show that the subfemtosecond resolution is sufficient to resolve the temporal structure of the beam used in the echo-enabled free-electron laser. We employ beam simulations to verify the effect for typical Neptune and NLCTA parameter sets and demonstrate the feasibility of the concept.

In this paper we discuss representations of charge particle densities in particle-in-cell simulations, analyze the sources and profiles of the intrinsic numerical noise, and present efficient methods for their removal. We devise two alternative estimation methods for charged particle distribution which represent significant improvement over the Monte Carlo cosine expansion used in the 2D code of Bassi et al. [G. Bassi, J. A. Ellison, K. Heinemann, and R. Warnock, Phys. Rev. ST Accel. Beams 12, 080704 (2009); G. Bassi and B. Terzić, in Proceedings of the 23rd Particle Accelerator Conference, Vancouver, Canada, 2009 (IEEE, Piscataway, NJ, 2009), TH5PFP043], designed to simulate coherent synchrotron radiation (CSR) in charged particle beams. The improvement is achieved by employing an alternative beam density estimation to the Monte Carlo cosine expansion. The representation is first binned onto a finite grid, after which two grid-based methods are employed to approximate particle distributions: (i) truncated fast cosine transform; and (ii) thresholded wavelet transform (TWT). We demonstrate that these alternative methods represent a staggering upgrade over the original Monte Carlo cosine expansion in terms of efficiency, while the TWT approximation also provides an appreciable improvement in accuracy. The improvement in accuracy comes from a judicious removal of the numerical noise enabled by the wavelet formulation. The TWT method is then integrated into the CSR code [G. Bassi, J. A. Ellison, K. Heinemann, and R. Warnock, Phys. Rev. ST Accel. Beams 12, 080704 (2009)], and benchmarked against the original version. We show that the new density estimation method provides a superior performance in terms of efficiency and spatial resolution, thus enabling high-fidelity simulations of CSR effects, including microbunching instability.

Electron cloud buildup is a major limitation for high-energy particle accelerators such as the CERN Super Proton Synchrotron (SPS). Amorphous carbon thin films with low initial secondary electron yield ($\mathrm{SEY}\cong 1.0$) have been applied as a mitigation material in the SPS vacuum chambers. This paper summarizes the experimental setups for electron cloud monitoring, coating procedures, and recent measurements performed with amorphous carbon coated vacuum chambers in the SPS. The electron cloud measured by dedicated monitors is completely suppressed for LHC-type beams. Even after more than one year’s exposure in the SPS with the machine in operation, the coating does not show any increase in the secondary electron yield. The study of coated vacuum chambers for the SPS dipole magnets is in progress; the correlation between electron cloud reduction and pressure rises is not yet fully understood. Some prototypes have already been installed in the accelerator and plans for the implementation of an optimized coating technique are under development.

The 3 GeV rapid cycling synchrotron (RCS) at Japan Proton Accelerator Research Complex is already in user operation stage, delivering a stable and relatively high power beam to the Material and Life Science Experimental Facility as well as to the main ring. RCS utilizes multiturn ${\mathrm{H}}^{-}$ charge-exchange injection for which a hybrid-type boron doped carbon stripper foil known as HBC foil with a thickness of around $200\mu \mathrm{g}/{\mathrm{cm}}^2$ is used at the present injection beam energy of 181 MeV. It will be changed to $290\mu \mathrm{g}/{\mathrm{cm}}^2$ at the near future upgrade and design injection beam energy of 400 MeV. The stripping efficiencies are expected to be 99.6% and 99.7% in the present and the later case, respectively. The remaining 0.4% or 0.3% of the beam is called the waste beam and is transported to the injection beam dump with a capacity of only 4 kW. The full power of the injected beam at 400 MeV is 133 kW, while the waste beam power is calculated to be about 0.4 kW. The raw signal measured by a current transformer placed downstream of the waste beam dump line contains a large noise and it is practically very hard to identify the beam signal. However, a fast Fourier transformation analysis of the raw signal made it possible to clearly identify the beam signal. The power spectrum is calibrated with respect to the known injected beam current. The absolute error of the monitor system is 0.2 mV, which gives the ratio of the waste beam to the injected beam as $(0.38\pm 0.03)\%$. Such an accurate and realtime monitoring system provides quite an efficient method to know the conditions of the stripper foil and the incoming linac beam during the user operation.

SPARC (acronym of “Sorgente Pulsata ed Amplificata di Radiazione Coerente”, i.e. Pulsed and Amplified Source of Coherent Radiation) is a single pass free-electron laser designed to obtain high gain amplification at a radiation wavelength of 500 nm. Self-amplified spontaneous emission has been observed driving the amplifier with the high-brightness beam of the SPARC linac. We report measurements of energy, spectra, and exponential gain. Experimental results are compared with simulations from several numerical codes.

For injection of beams into circular machines with different horizontal and vertical emittance acceptance, the injection efficiency can be increased if these beams are flat, i.e., if they feature unequal transverse emittances. Generation of flat electron beams is well known and has been demonstrated already in beam experiments. It was proposed also for ion beams that were generated in an electron-cyclotron-resonance (ECR) source. We introduce an extension of the method to beams that underwent charge state stripping without requiring their generation inside an ECR source. Results from multiparticle simulations are presented to demonstrate the validity of the method.

We calculate the impedance and wake functions for laminated structures with parallel-plane and circular geometries in the ultrarelativistic limit. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between flat and circular geometry impedances is presented. We apply our calculation in a state-of-the-art beam dynamics simulation of the Fermilab Booster which includes nonlinear optics, laminated wakefields, and space charge impedance. The latter can have a significant effect away from the ultrarelativistic limit. Even though the simulations and the comparison with the experiment are done at the Booster injection energy, where the relativistic factor $\gamma =1.42$, we find good agreement between our calculation of the coherent tune shift and recent experimental measurements.

Multiturn (or turn-by-turn) data acquisition has proven to be a new source of direct measurements for Twiss parameters in storage rings. On the other hand, closed-orbit measurements are a long-known tool for analyzing closed-orbit perturbations with conventional beam position monitor (BPM) systems and are necessarily available at every storage ring. This paper aims at combining the advantages of multiturn measurements and closed-orbit data. We show that only two multiturn BPMs and four correctors in one localized drift space in the storage ring (diagnostic drift) are sufficient for model-independent and absolute measuring of $\beta$ and $\phi$ functions at all BPMs, including the conventional ones, instead of requiring all BPMs being equipped with multiturn electronics.

The longitudinal coherence of free-electron laser (FEL) radiation can be enhanced by seeding the FEL with high harmonics of an optical laser pulse. The radiation produced by high-harmonic generation (HHG), however, has a fast-varying temporal profile that can violate the slowly varying envelope approximation and limited frequency window that is employed in conventional free-electron laser simulation codes. Here we investigate the implications of violating this approximation on the accuracy of simulations. On the basis of both analytical considerations and 1D numerical studies, it is concluded that, for most realistic scenarios, conventional FEL codes are capable of accurately simulating the FEL process even when the seed radiation violates the slowly varying envelope approximation. We additionally discuss the significance of filtering the harmonic content of broadband HHG seeds.

A comprehensive study of charge diagnostics is conducted to verify their validity for measuring electron beams produced by laser plasma accelerators (LPAs). First, a scintillating screen (Lanex) was extensively studied using subnanosecond electron beams from the Advanced Light Source booster synchrotron, at the Lawrence Berkeley National Laboratory. The Lanex was cross calibrated with an integrating current transformer (ICT) for up to the electron energy of 1.5 GeV, and the linear response of the screen was confirmed for charge density and intensity up to $160\mathrm{pC}/{\mathrm{mm}}^2$ and $0.4\mathrm{pC}/(\mathrm{ps}{\mathrm{mm}}^2)$, respectively. After the radio-frequency accelerator based cross calibration, a series of measurements was conducted using electron beams from an LPA. Cross calibrations were carried out using an activation-based measurement that is immune to electromagnetic pulse noise, ICT, and Lanex. The diagnostics agreed within $\pm 8\%$, showing that they all can provide accurate charge measurements for LPAs.

A few years ago, Andrews and Brau (AB) presented the dispersion relation for a lamellar grating in two dimensions (2D) as a step in understanding coherent Smith-Purcell radiation. This involved solving Maxwell’s equations both in the grooves and in the region above the grooves, where Floquet theory was used. The coupling with an electron beam was studied, and an expression for the gain as a function of current was derived. Their approach has been supported by 2D simulations using particle-in-cell (PIC) codes, and more recently by a demonstration experiment that used a wide grating. We present here the dispersion relation (in the absence of beam) of a grating in three dimensions, which turns out to be a relatively straightforward extension of the AB results. The predictions of this theory are compared with PIC simulations, and also with measurements of the transmission coefficient as a function of frequency. Extremely good agreement is observed.

Shot noise can affect the performance of free-electron lasers (FELs) by driving instabilities (e.g., the microbunching instability) or by competing with seeded density modulations. Recent papers have proposed suppressing shot noise to enhance FEL performance. In this paper we use a one-dimensional (1D) model to calculate the noise amplification from an energy modulation (e.g., electron interactions from space charge or undulator radiation) followed by a dispersive section. We show that, for a broad class of interactions, selecting the correct dispersive strength suppresses shot noise across a wide range of frequencies. The final noise level depends on the beam’s energy spread and the properties of the interaction potential. We confirm and illustrate our analytical results with 1D simulations.

The Spallation Neutron Source accelerator utilizes ${\mathrm{H}}^{-}$ charge exchange injection to merge a 1 GeV, 1 MW beam from a linac into an accumulator ring. The design calls for the 545 keV foil-stripped electrons to be absorbed by an electron catcher located below the foil. However, multiple observations of hardware damage caused by stripped electrons indicate that at least a fraction of the electrons are reflected back into the vacuum chamber. This paper presents the results of a 3D computational model employed to simulate the dynamics of foil-stripped electrons, including a surface interaction model for the catcher. Simulation results are compared with experimental observations, and the implications for high power beam operations are discussed.

The back bombardment (BB) effect limits wide usage of thermionic rf guns. The BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during a macropulse. This paper presents a comparison of the BB effect for the case of dispenser tungsten-base (DC) and lanthanum hexaboride (${\mathrm{LaB}}_6$) thermionic rf gun cathodes. For each, particle simulation codes are used to simulate the BB effect and electron beam dynamics in a thermionic rf gun cathode. A semiempirical equation is also used to investigate the stopping range and deposited heat power of BB electrons in the cathode material. A numerical simulation method is used to calculate the change of the cathode temperature and current density during a single macropulse. This is done by solving two differential equations for the rf gun cavity equivalent circuit and one-dimensional thermal diffusion equation. High electron emission and small beam size are required for generation of a high-brightness electron beam, and so in this work the emission properties of the cathode are taken into account. Simulations of the BB effect show that, for a pulse of $6\mu \mathrm{s}$ duration, the DC cathode experiences a large change in the temperature compared with ${\mathrm{LaB}}_6$, and a change in current density 6 times higher. Validation of the simulation results is performed using experimental data for beam current beyond the gun exit. The experimental data is well reproduced using the simulation method.

Cavity accumulation of coherent undulator synchrotron radiation emitted by a train of periodic electron bunches is investigated. Phase-matching conditions for accumulation of radiation emitted by successive bunches are analyzed and numerically confirmed. While the coherent emission of a single bunch is optimal at grazing resonance, the accumulated radiation targeted at the upper resonant frequency of the waveguide mode is found to have much broader bandwidth and higher efficiency as the resonance steps away from the grazing condition. Numerical results confirm that stimulated superradiance is responsible for the accumulated radiation.

We present and discuss the properties of the coherent electromagnetic fields of a very short, ultrarelativistic bunch in a rectangular vacuum chamber inside a bending magnet. The analysis is based on the results of a direct numerical solution of Maxwell’s equations together with Newton’s equations. We use a new dispersion-free time-domain algorithm which employs a more efficient use of finite element mesh techniques and, hence, produces self-consistent and stable solutions for very short bunches. We investigate the fine structure of the coherent synchrotron radiation fields. We also discuss coherent edge radiation. We present a clear picture of the field using the electric field lines constructed from the numerical solutions. This method should be useful in the study of existing and future concepts of particle accelerators and ultrafast coherent light sources, where high peak currents and very short bunches are envisioned.