CsBr photocathodes have 10 times higher quantum efficiency with only 3 times larger intrinsic transverse emittance than copper. They are robust and can withstand $80\mathrm{MV}/\mathrm{m}$ fields without breaking down or emitting dark current. They can operate in $2\times {10}^{-9}\mathrm{torr}$ vacuum and survive exposure to air. They are well suited for generating high pulse charge in rf guns without a photocathode transfer system.

Charged particle beam diagnostics is a key task in modern and future accelerator installations. The diagnostic tools are practically the “eyes” of the operators. The precision and resolution of the diagnostic equipment are crucial to define the performance of the accelerator. Transition and diffraction radiation (TR and DR) are widely used for electron beam parameter monitoring. However, the precision and resolution of those devices are determined by how well the production, transport and detection of these radiation types are understood. This paper reports on simulations of TR and DR spatial-spectral characteristics using the physical optics propagation (POP) mode of the Zemax advanced optics simulation software. A good consistency with theory is demonstrated. Also, realistic optical system alignment issues are discussed.

The buildup of low-energy electrons has been shown to affect the performance of a wide variety of particle accelerators. Of particular concern is the persistence of the cloud between beam bunch passages, which can impose limitations on the stability of operation at high beam current. We have obtained measurements of long-lived electron clouds trapped in the field of a quadrupole magnet in a positron storage ring, with lifetimes much longer than the revolution period. Based on modeling, we estimate that about 7% of the electrons in the cloud generated by a 20-bunch train of 5.3 GeV positrons with 16-ns spacing and $1.3\times 10^{11}$ population survive longer than $2.3\mu \mathrm{s}$ in a quadrupole field of gradient $7.4\mathrm{T}/\mathrm{m}$. We have observed a nonmonotonic dependence of the trapping effect on the bunch spacing. The effect of a witness bunch on the measured signal provides direct evidence for the existence of trapped electrons. The witness bunch is also observed to clear the cloud, demonstrating its effectiveness as a mitigation technique.

With a nominal beam power of nearly 1 MW on target, the Swiss Spallation Neutron Source (SINQ), ranks among the world’s most powerful spallation neutron sources. The proton beam transport to the SINQ target is carried out exclusively by means of linear magnetic elements. In the transport line to SINQ the beam is scattered in two meson production targets and as a consequence, at the SINQ target entrance the beam shape can be described by Gaussian distributions in transverse $x$ and $y$ directions with tails cut short by collimators. This leads to a highly nonuniform power distribution inside the SINQ target, giving rise to thermal and mechanical stresses. In view of a future proton beam intensity upgrade, the possibility of homogenizing the beam distribution by means of a fast beam rotation system is currently under investigation. Important aspects which need to be studied are the impact of a rotating proton beam on the resulting neutron spectra, spatial flux distributions and additional—previously not present—proton losses causing unwanted activation of accelerator components. Hence a new source description method was developed for the radiation transport code MCNPX. This new feature makes direct use of the results from the proton beam optics code TURTLE. Its advantage to existing MCNPX source options is that all phase space information and correlations of each primary beam particle computed with TURTLE are preserved and transferred to MCNPX. Simulations of the different beam distributions together with their consequences in terms of neutron production are presented in this publication. Additionally, a detailed description of the coupling method between TURTLE and MCNPX is provided.

An x-ray free-electron laser oscillator (XFELO) is a next-generation x-ray source, similar to free-electron laser oscillators at VUV and longer wavelengths but using crystals as high-reflectivity x-ray mirrors. Each output pulse from an XFELO is fully coherent with high spectral purity. The temporal coherence length can further be increased drastically, from picoseconds to microseconds or even longer, by phase-locking successive XFELO output pulses, using the narrow nuclear resonance lines of nuclei such as ${}^{57}\mathrm{Fe}$ as a reference. We show that the phase fluctuation due to the seismic activities is controllable and that due to spontaneous emission is small. The fluctuation of electron-bunch spacing contributes mainly to the envelope fluctuation but not to the phase fluctuation. By counting the number of standing-wave maxima formed by the output of the nuclear-resonance-stabilized (NRS) XFELO over an optically known length, the wavelength of the nuclear resonance can be accurately measured, possibly leading to a new length or frequency standard at x-ray wavelengths. A NRS-XFELO will be an ideal source for experimental x-ray quantum optics as well as other fundamental physics. The technique can be refined for other, narrower resonances such as ${}^{181}\mathrm{Ta}$ or ${}^{45}\mathrm{Sc}$.

With the improvement of acceleration techniques, the intrinsic emittance of the cathode has a strong impact on the final brightness of a free electron laser. The systematic studies presented in this paper demonstrate for the first time in a radiofrequency photocathode gun a reduction of the intrinsic emittance when tuning the laser photon energies close to the effective work function of copper. The intrinsic emittance was determined by measuring the core slice emittance as a function of the laser beam size at laser wavelengths between 260 and 275 nm. The results are consistent with the measured effective work function of the cathode. Slice emittance values normalized to the laser beam size reached values down to $500\mathrm{nm}/\mathrm{mm}$, close to that expected from theory. A 20% reduction of the intrinsic emittance was observed over the spectral range of the laser.

The Iranian Light Source Facility (ILSF) is a new 3 GeV third generation synchrotron light source facility which is in the design stage. As the main radiation source, design of the ILSF storage ring emphasizes an ultralow electron beam emittance, great brightness, stability and reliability. The storage ring is based on a five-bend achromat lattice providing an ultralow horizontal beam emittance of 0.48 nm rad. In this paper, we present the design feature of the ILSF storage ring, give the linear and nonlinear dynamic properties of the lattice and discuss the related beam dynamic specifications.

A two-dimensional finite element beam coupling impedance solver for arbitrary transverse geometries and material distribution is presented. The solver is based on open source software and is applicable to space charge and resistive wall longitudinal and transverse impedances. The frequency and the beam velocity can be chosen arbitrarily and also dispersively lossy materials are supported. Space charge impedance, a thin resistive beam pipe, a ferrite ring, and a carbon collimator are presented as application examples.

We present electromagnetic models aiming to calculate the variation of the inductance in a magnet due to dynamic effects such as the variation of magnetization or the coupling with eddy currents. The models are studied with special regard to the calculation of the inductance in superconducting magnets which are affected by interfilament coupling currents. The developed models have been compared with experimental data coming from tests of prototype ${\mathrm{Nb}}_3\mathrm{Sn}$ magnets designed for the new generation of accelerators. This work is relevant for the quench protection study of superconducting magnets: quench is an unwanted event, when part of the magnet becomes resistive; in these cases, the current should be discharged as fast as possible, in order to maintain the resistive zone temperature under a safe limit. The magnet inductance is therefore a relevant term for the description of the current discharge, especially for the high-field new generation superconducting magnets for accelerators, and this work shows how to calculate the correct value during rapid current changes, providing a mean for simulations of the reached temperature.

Beam lifetimes of stored ${\mathrm{U}}^{28+}$ ions with kinetic energies of 30 and $50\mathrm{MeV}/\mathrm{u}$, respectively, were measured in the experimental storage ring of the GSI accelerator facility. By using the internal gas target station of the experimental storage ring, it was possible to obtain total projectile electron loss cross sections for collisions with several gaseous targets ranging from hydrogen to krypton from the beam lifetime data. The resulting experimental cross sections are compared to predictions by two theoretical approaches, namely the CTMC method and a combination of the DEPOSIT code and the RICODE program.

A high-resolution, low-latency beam position monitor (BPM) system has been developed for use in particle accelerators and beam lines that operate with trains of particle bunches with bunch separations as low as several tens of nanoseconds, such as future linear electron-positron colliders and free-electron lasers. The system was tested with electron beams in the extraction line of the Accelerator Test Facility at the High Energy Accelerator Research Organization (KEK) in Japan. It consists of three stripline BPMs instrumented with analogue signal-processing electronics and a custom digitizer for logging the data. The design of the analogue processor units is presented in detail, along with measurements of the system performance. The processor latency is $15.6\pm 0.1\mathrm{ns}$. A single-pass beam position resolution of $291\pm 10\mathrm{nm}$ has been achieved, using a beam with a bunch charge of approximately 1 nC.

A metallic pipe with corrugated walls supports propagation of a high-frequency mode that is in resonance with a relativistic beam propagating along the axis of the pipe. This mode can be excited by a beam whose length is a fraction of the wavelength. In this paper, we study another option of excitation of the resonant mode—via the mechanism of the free electron laser instability. This mechanism works if the bunch length is much longer than the wavelength of the radiation and, hence, does not require bunch compression. It provides an alternative to excitation by short bunches that can be realized with relatively low energy and low peak-current electron beams.

Beginning with Maxwell’s equations and assuming only that the wall interaction can be approximated by a surface impedance, we derive formulas for the generalized longitudinal and transverse impedance in flat geometry, from which the wakefields can also be obtained. From the generalized impedances, by taking the proper limits, we obtain the normal longitudinal, dipole, and quad impedances in flat geometry. These equations can be applied to any surface impedance, such as the known dc, ac, and anomalous skin models of wall resistance, a model of wall roughness, or one for a pipe with small, periodic corrugations. We show that, for the particular case of dc wall resistance, the longitudinal impedance obtained here agrees with a known result in the literature, a result that was derived from a very general formula by Henke and Napoly.

One obstacle in plasma accelerator development is the limitation of techniques to diagnose and measure plasma wakefield parameters. In this paper, we present a novel concept for the density measurement of a plasma wakefield using photon acceleration, supported by extensive particle in cell simulations of a laser pulse that copropagates with a wakefield. The technique can provide the perturbed electron density profile in the laser’s reference frame, averaged over the propagation length, to be accurate within 10%. We discuss the limitations that affect the measurement: small frequency changes, photon trapping, laser displacement, stimulated Raman scattering, and laser beam divergence. By considering these processes, one can determine the optimal parameters of the laser pulse and its propagation length. This new technique allows a characterization of the density perturbation within a plasma wakefield accelerator.

We present an experimental study aimed at exploring integer resonance crossing with a focus on nonscaling fixed field alternating gradient accelerators. The method uses the Simulator of Particle Orbit Dynamics system at Hiroshima University based on a compact ion trap known as a Paul trap. In a setup that mimics the Electron Model for Many Applications nonscaling fixed field alternating gradient accelerator, we have verified the theoretical prediction of the coherent excitation of dipole motion over a wide range of errors and crossing speeds. In addition, the cancellation of amplitude growth dependent on the relative betatron oscillation phase between two consecutive resonances is observed and studied. We also explore nonlinear effects and, in particular, the effects of amplitude-dependent tune shifts and find that these nonlinear effects are a key factor in understanding our experimental results.

Self-seeding is a promising approach to significantly narrow the self-amplified spontaneous emission bandwidth of X-ray free-electron lasers (FELs) and hence to produce nearly transform-limited pulses. We study the radiation propagation through a grating monochromator installed at the Linac Coherent Light Source (LCLS). The monochromator design is based on a toroidal VLS grating working at a fixed incidence angle mounting without an entrance slit. It covers the spectral range from 500 eV to 1000 eV. The optical system was studied using a wave optics method to evaluate the performance of the self-seeding scheme. Our wave optics analysis takes into account the finite size of the coherent source, third-order aberrations and height error of the optical elements. Two propagation approaches are studied with time-dependent FEL simulations. In addition, the pulse-front tilt phenomenon effect is illustrated.