The paper presents the analysis of the angular distributions of the incoherent Smith-Purcell radiation (SPR) generated by a charged particle passing over a periodic conducting structure (grating). The calculations were carried out for a grating which consists of conducting strips separated by vacuum gaps and a lamellar grating with the use of three models of this radiation: van den Berg‘s model, the surface current model, and the resonant diffraction radiation model. The two last models predict sufficiently close results for different geometries, while the results obtained with van den Berg‘s model predict primarily the SPR intensity which is by a few orders of magnitude lower for the electron energy $\approx 6\mathrm{MeV}$. The authors propose simple criteria to verify the SPR models by comparing the SPR yields between the volume (with the thickness comparable with a grating period) and flat (with the thickness which is much less than that of a period) gratings; by comparing the azimuth dependencies of the SPR intensities from the flat gratings; by comparing the dependencies of the SPR intensity on the Lorentz factor of a particle.

The longitudinal charge distribution of electron bunches in the Fermilab/NICADD photoinjector was determined using the coherent transition radiation produced by electrons passing through a thin metallic foil. The autocorrelation of the transition radiation signal was measured with a Michelson-type interferometer. The response function of the interferometer was determined from measured and simulated intensity spectra for low electron bunch charge and maximum longitudinal compression. Both pyroelectric and Golay detectors were used for these measurements. A Kramers-Kronig technique was used to determine longitudinal charge distribution. Measurements were performed for electron bunch lengths in the range from 0.3 to 2 ps (rms). To test the accuracy of this interferometric method, the longitudinal charge distribution was measured for double-peaked electron bunches with known distance between the two pulses. The agreement between measured bunch length and simulation is within 30%.

The current final focus systems of linear colliders have been designed based on the local compensation scheme proposed by Raimondi and Seryi. However, there exist remaining aberrations that deteriorate the performance of the system. This paper develops a general algorithm for the optimization of beam lines based on the computation of the high orders of the transfer map using MAD-X and Polimorphic Tracking Code. The algorithm is applied to the CLIC beam delivery system.

The Dragon-I injector based on the induction voltage adder technique is introduced. Twelve ferrite loaded induction cells are connected in a series through central conducting stalks to achieve a pulsed voltage higher than 3.5 MV across the diode. Electrons are extracted from the velvet emitter and guided through the anode pipe by the magnets placed inside the cathode and anode shrouds. Measurements at the exit of injector show that, with an electric field of $200\mathrm{kV}/\mathrm{cm}$ near the velvet surface and suitable magnetic field distribution, an electron beam up to 2.8 kA can be obtained with a normalized emittance of $1040\pi \mathrm{mm}\mathrm{mrad}$, and energy spread of 2.1% ($3\sigma$) around the central energy of 3.5 MeV.

An experimental study of crossing a third order uncoupled resonance was performed in a proof of principle fixed field alternating gradient with various widths of resonance and crossing speed. We observed that part of the beam is transported to a larger amplitude when the crossing speed is relatively small. We derived an “adiabatic parameter” from a “particle trapping” model as a useful index for avoiding beam deterioration due to resonance crossing. It relates the crossing speed to the resonance width and the amount of nonlinear detuning. When the adiabatic parameter is more than 7, resonance crossing will not affect a beam.

For a class of Vlasov-Fokker-Planck equations that have frequently been used to examine beam dynamic instabilities in accelerators and storage rings, it is shown that the stability of stationary distributions can be determined by studying reduced models defined by Smoluchowski equations. This is illustrated explicitly for longitudinal particle bunches in beams subjected to a particular class of wake fields, described by a Haïssinski distribution. For this class we find that continuous Haïssinski distributions are stable because they correspond to minima of appropriately defined free energy functionals. For parameters for which continuous distributions no longer exist, discontinuous distributions may still exist but correspond to free energy maxima and saddle points and are unstable.

In a first beam dynamics validation experiment for a new Pulse Line Ion Acceleration (PLIA) concept, the predicted energy amplification and beam bunching were experimentally observed. Beam energy modulation of $-80$ to $+150\mathrm{keV}$ was measured using a PLIA input voltage waveform of $-21$ to $+12\mathrm{kV}$. Ion pulses accelerated by 150 keV, and bunching by a factor of 4 were simultaneously achieved. The measured longitudinal phase space and current waveform of the accelerated beam are in good agreement with 3D particle-in-cell simulations.

Electron clouds sometimes limit accelerator performance by their appearance when the circulating bunch population exceeds a threshold value. Dynamical models of cloud buildup, and of the phase transition from “cloud off” to “cloud on”, are enhanced when simple coupling between electron and ion clouds is included. Maps are then capable of reproducing the first order phase transitions sometimes seen in practice. They also predict that hysteresis, period doubling, and chaotic phenomena may be observed.

We have developed an empirical electrical-breakdown relation that can be used to design large-area water-insulated pulsed-power systems. Such systems often form an integral part of multiterawatt pulsed-power accelerators, and may be incorporated in future petawatt-class machines. We find that complete dielectric failure is likely to occur in water between a significantly field-enhanced anode and a less-enhanced cathode when $E_p{\tau }_{\mathrm{eff}}^{0.330\pm 0.026}=0.135\pm 0.009$. In this expression $E_p\equiv V_p/d$ is the peak value in time of the spatially averaged electric field between the anode and cathode (in $\mathrm{MV}/\mathrm{cm}$), $V_p$ is the peak voltage across the electrodes, $d$ is the distance between the anode and cathode, and ${\tau }_{\mathrm{eff}}$ is the temporal width (in $\mu \mathrm{s}$) of the voltage pulse at 63% of peak. This relation is based on 25 measurements for which $1\le V_p\le 4.10\mathrm{MV}$, $1.25\le d\le 22\mathrm{cm}$, and $0.011\le {\tau }_{\mathrm{eff}}\le 0.6\mu \mathrm{s}$. The normalized standard deviation of the differences between these measurements and the associated predictions of the relation is 12%.

ILC (International Linear Collider) is aiming to conduct electron-positron collisions at 1 TeV center-of-mass energy. One bunch train will contain up to 2800 3.2 nC bunches with a 308 ns bunch spacing or 5600 1.6 nC bunches with a 154 ns spacing. The bunch-train length will be 0.9 ms. Because of this extremely large amount of beam in a train, serious damage to a positron production target driven by 6 GeV incident electron beam is of concern. As the ILC positron source, several different methods have been proposed. The target hardness is a key point concerning the selection. In this article, we report on a test experiment to examine the target hardness by using a stored electron beam in KEKB HER (High Energy Ring). The project name is IPPAK (ILC Positron Project At KEKB). By manipulating the abort kicker, a condition similar to that of the ILC positron production target can be reproduced. The experiment was carried out on June 29 and 30, 2005. The target was seriously damaged under the heaviest condition (KEKB mode), but the damage was less and nothing for those of the ILC mode. Possible impacts to the ILC positron production scheme are also discussed.

Spin-resonance strength produced by a localized rf field has been a focus of recent publications [V. S. Morozov et al., Phys. Rev. ST Accel. Beams 7, 024002 (2004).; M. A. Leonova et al. (to be published).; T. Roser, in Handbook of Accelerator Physics and Engineering, edited by A. W. Chao and M. Tigner (World Scientific, Singapore, 1999), p. 151.; M. Bai, W. W. MacKay, and T. Roser, Phys. Rev. ST Accel. Beams 8, 099001 (2005).; V. S. Morozov et al., Phys. Rev. ST Accel. Beams 8, 099002 (2005).]. This paper discusses the debated factor of 2, and provides a formula to calculate the component enhanced by the induced betatron motion.

The optical klystron enhancement to self-amplified spontaneous emission (SASE) free electron lasers (FELs) is studied in theory and in simulations. In contrast to a seeded FEL, the optical klystron gain in a SASE FEL is not sensitive to any phase mismatch between the radiation and the microbunched electron beam. The FEL performance with the addition of four optical klystrons located at the undulator long breaks in the Linac Coherent Light Source (LCLS) shows significant improvement if the uncorrelated energy spread at the undulator entrance can be controlled to a very small level. In addition, FEL saturation at shorter x-ray wavelengths (around $1.0\AA$) within the LCLS undulator length becomes possible. We also discuss the application of the optical klystron in a compact x-ray FEL design that employs relatively low electron beam energy together with a shorter-period undulator.

We have measured the absolute radiant flux of synchrotron radiation as a function of the angle above and below the orbital plane with high accuracy at the Synchrotron Ultraviolet Radiation Facility (SURF III) at the National Institute of Standards and Technology (NIST), and the results were compared with theoretical calculations. The radiant flux of synchrotron radiation was measured at effective wavelengths of 256.5, 397.8, and 799.8 nm using three calibrated narrow-band filter radiometers with electron energies ranging from 180 to 380 MeV at SURF III. The filter radiometers were positioned inside a beamline with an unobstructed view of synchrotron radiation. The measured radiant flux agrees with theoretical Schwinger formulation to better than 0.5% for angles up to several milliradians.

Fundamental advances in experimental nuclear physics will require ion beams with orders of magnitude luminosity increase and temperature reduction. One of the most promising particle accelerator techniques for achieving these goals is electron cooling, where the ion beam repeatedly transfers thermal energy to a copropagating electron beam. The dynamical friction force on a fully ionized gold ion moving through magnetized and unmagnetized electron distributions has been simulated, using molecular dynamics techniques that resolve close binary collisions. We present a comprehensive examination of theoretical models in use by the electron cooling community. Differences in these models are clarified, enabling the accurate design of future electron cooling systems for relativistic ion accelerators.

We present detailed calculations of RMS-envelope matching over a broad range of beam intensities for the University of Maryland Electron Ring (UMER). Containment of beams from zero current to extreme space charge, all without changing the strength of external focusing in the periodic lattice, is possible thanks to the high density of quadrupoles in UMER. In turn, the small-aspect ratio of the UMER magnets results in gradient or field profiles that are “all edges,” thus requiring special treatment when constructing accurate hard-edge models. Further, the results of matching calculations, for both symmetric and asymmetric FODO (alternating gradient) schemes, are compared with calculations from simple general expressions valid in the uniform-focusing approximation of the periodic lattice. Finally, some aspects of the source-to-FODO matching calculation/optimization problem are discussed, together with sensitivity studies of the matching solutions under realistic conditions. The examples from the UMER project, which include experimental results, emphasize the practical aspects of beam envelope matching.

The interaction between high-brilliance electron beams and counterpropagating laser pulses produces x rays via Thomson backscattering. If the laser source is long and intense enough, the electrons of the beam can bunch on the scale of the emitted x-ray wavelength and a regime of collective effects can establish. In this case of dominating collective effects, the FEL instability can develop and the system behaves like a free-electron laser based on an optical undulator. Coherent x rays can be irradiated, with a bandwidth very much thinner than that of the corresponding incoherent emission. The emittance of the electron beam and the distribution nonuniformity of the laser energy are the principal quantities that limit the growth of the x-ray signal. In this work we analyze with a 3D code the transverse effects in the emission produced by a relativistic electron beam when it is under the action of an optical laser pulse and the x-ray spectra obtained. The scalings typical of the optical wiggler, characterized by very short gain lengths and overall time durations of the process, make possible considerable emission also in violation of the Pellegrini criterion for static wigglers. A generalized form of this criterion is validated on the basis of the numerical evidence.

In recirculating accelerators, and, in particular, energy-recovery linacs, the maximum current can be limited by multipass, multibunch beam breakup (BBU), which occurs when the electron beam interacts with the higher-order modes (HOMs) of an accelerating cavity on the accelerating pass and again on the energy recovering pass. This effect is of particular concern in the design of modern high average current energy-recovery accelerators utilizing superconducting rf technology. Experimental characterization and observations of the instability at the Jefferson Laboratory 10 kW free electron laser (FEL) are presented. Measurements of the threshold current for the instability are made under a variety of beam conditions and compared to the predictions of several BBU simulation codes. This represents the first time in which the codes have been experimentally benchmarked. With BBU posing a threat to high current beam operation in the FEL driver, several suppression schemes were developed. These include direct damping of the dangerous HOM using cavity feedback and modifying the electron beam optics so as to reduce the coupling between the beam and mode. Both methods were shown to increase the threshold current for stability. Beam optical suppression techniques, in particular, have proved to be so effective that they are routinely used in the normal operations of the FEL Upgrade Driver.

A new representation of the external-$Q$ $(Q_{\mathrm{ext}})$ calculations for cavities coupled to waveguides is derived based on a circuit model. The $Q_{\mathrm{ext}}$ value is obtained by solving analytical equations of the input impedance of a cavity provided as a function of the frequency; large numerical simulations are not necessary. The derivation starts with a fundamental expression of the ratio of the stored energies of two loss-free circuits forming a parallel resonant circuit. By applying this expression to the input impedance of a cavity seen from the detuned-short-circuit plane, as well as to those of open- and short-end waveguides, a precise estimation of $Q_{\mathrm{ext}}$ is given. It is then explained that the result is almost independent of the choice of the cavity boundary. This method is an alternative to the electromagnetic representation of the $Q_{\mathrm{ext}}$ calculation [P. Balleyguier, in Proceedings of the XIX International Linac Conference, Chicago, Illinois, USA, edited by C. E. Eyberger, R. C. Pardo, and M. M. White (ANL-98/28, 1998), pp. 133–135.]. It is also shown why this estimation provides a good approximation when $Q_{\mathrm{ext}}$ is high. Formulas for the TEM, TE, and TM modes of waveguides are presented along with a simple example of a loop-coupled cavity.

Metal photocathodes are commonly used in high-field rf guns because they are robust, straightforward to implement, and tolerate relatively poor vacuum compared to semiconductor cathodes. However, these cathodes have low quantum efficiency (QE) even at UV wavelengths, and still require some form of cleaning after installation in the gun. A commonly used process for improving the QE is laser cleaning. In this technique the UV-drive laser is focused to a small diameter close to the metal’s damage threshold and then moved across the surface to remove contaminants. This method does improve the QE, but can produce nonuniform emission and potentially damage the cathode. Ideally, an alternative process which produces an atomically clean, but unaltered, surface is needed. In this paper we explore using a hydrogen ion (H-ion) beam to clean a copper cathode. We describe QE measurements over the wavelength range of interest as a function of integrated exposure to an H-ion beam. We also describe the data analysis to obtain the work function and derive a formula of the QE for metal cathodes. Our measured work function for the cleaned sample is in good agreement with published values, and the theoretical QE as a function of photon wavelength is in excellent agreement with the cleaned copper experimental results. Finally, we propose an in situ installation of an H-ion gun compatible with existing s-band rf guns.