In this paper we report on start-to-end simulation of a next generation light source based on a high repetition rate free electron laser (FEL) driven by a CW superconducting linac. The simulation integrated the entire system in a seamless start-to-end model, including birth of photoelectrons, transport of electron beam through 600 m of the accelerator beam delivery system, and generation of coherent x-ray radiation in a two-stage self-seeding undulator beam line. The entire simulation used the real number of electrons ($\sim 2$ billion electrons/bunch) to capture the details of the physical shot noise without resorting to artificial filtering to suppress numerical noise. The simulation results shed light on several issues including the importance of space-charge effects near the laser heater and the reliability of x-ray radiation power predictions when using a smaller number of simulation particles. The results show that the microbunching instability in the linac can be controlled with 15 keV uncorrelated energy spread induced by a laser heater and demonstrate that high brightness and flux 1 nm x-ray radiation ($\sim {10}^{12}\mathrm{photons}/\mathrm{pulse}$) with fully spatial and temporal coherence is achievable.

The current paper discusses possible designs for a stand alone muon target for MuSR studies of condensed matter science. Considering the ISIS 7 mm graphite target as a reference, Geant4 simulations have been performed in order to optimize the target parameters with respect to muon and pion yield. Previous studies suggested that the muon production can be optimized by using a thin graphite slab target with an incident proton energy significantly lower than initially considered. Surface muon production obtained by firing an 800 MeV proton beam energy onto the target is simulated and potential improvements to the target material, geometry and angle orientation with respect to the incoming proton beam as well as an estimated performance of the muon target are presented in this paper. Implications for the ISIS muon facility are also discussed. A comparison of the pion production cross section between experimental data and three theoretical models for the latest four Geant4 versions is also included in this paper.

A 7 cm cathode has been deployed for use on a 3.8 MV, 80 ns (FWHM) Blumlein, to increase the extracted electron current from the nominal 1.7 to 2.9 kA. The intense relativistic electron bunch is accelerated and transported through a nested solenoid and ferrite induction core lattice consisting of 64 elements, exiting the accelerator with a nominal energy of 19.8 MeV. The principal objective of these experiments is to quantify the space-charge limitations on the beam quality, its coupling with the beam breakup (BBU) instability, and provide an independent validation of the BBU theory in a higher current regime, $\mathrm{I}>2\mathrm{kA}$. Time resolved centroid measurements indicate a reduction in BBU $>10\times$ with simply a 50% increase in the average B-field used to transport the beam through the accelerator. A qualitative comparison of experimental and calculated results are presented, which include time resolved current density distributions, radial BBU amplitude relative to the calculated beam envelope, and frequency analyzed BBU amplitude with different accelerator lattice tunes.

Nonaxially symmetric superconducting deflecting cavities are under development for a variety of purposes, but breaking the symmetry adds more complexity to wakefield characterization. This paper considers the influence of cavity asymmetry on the wakefield. Based on the TM-type deflecting cavity, we investigated how the polarized cell and the damper coupling affect the wake impedances. An improved method to characterize the wake impedances in asymmetric cavities is proposed by combining the time-domain and frequency-domain calculations. Compared to conventional methods, the new method decomposes the wake potential in terms of beam moments, which provides more information about the wakefield, and significantly reduces the simulation time with better accuracy. Using this method, we analyzed the wakefield of the deflecting cavity and the wakefield coupling between the cavities for the advanced photon source. Bench measurements were performed on a fabricated copper prototype; the measured mode field distributions and the $Q_{\text{ext}}$ values agreed well with calculations.

Development of a new type of vibrating wire monitor (VWM), which has two mechanically coupled wires (vibrating and target), is presented. The new monitor has a much larger aperture size than the previous model of the VWM, and thus allows us to measure transverse beam halos more effectively. A prototype of such a large aperture VWM with a target wire length of 60 mm was designed, manufactured, and bench-tested. Initial beam measurements have been performed at the Fermilab High Intensity Neutrino Source facility, and key results are presented.

We present a new design study of the neutrino Super Beam based on the Superconducting Proton Linac at CERN. This beam is aimed at megaton mass physics, a large water Cherenkov detector, proposed for the Laboratoire Souterrain de Modane in France, with a baseline of 130 km. The aim of this proposed facility is to study $CP$ violation in the neutrino sector. In the study reported here, we have developed the conceptual design of the neutrino beam, especially the target and the magnetic focusing device. Indeed, this beam presents several unprecedented challenges, related to the high primary proton beam power (4 MW), the high repetition rate (50 Hz), and the low kinetic energy of the protons (4.5 GeV). The design is completed by a study of all the main components of the system, starting from the transport system to guide the beam to the target up to the beam dump. This is the first complete study of a neutrino beam based on a pebble-bed target capable of standing the large heat deposition of MW class proton beams.

We report modeling results for electron cloud buildup and instability in the International Linear Collider positron damping ring. Updated optics, wiggler magnets, and vacuum chamber designs have recently been developed for the 5 GeV, 3.2-km racetrack layout. An analysis of the synchrotron radiation profile around the ring has been performed, including the effects of diffuse and specular photon scattering on the interior surfaces of the vacuum chamber. The results provide input to the cloud buildup simulations for the various magnetic field regions of the ring. The modeled cloud densities thus obtained are used in the instability threshold calculations. We conclude that the mitigation techniques employed in this model will suffice to allow operation of the damping ring at the design operational specifications.

We report on the first results of experiments with a new laser-based proton beam line at the GSI accelerator facility in Darmstadt. It delivers high current bunches at proton energies around 9.6 MeV, containing more than ${10}^9$ particles in less than 10 ns and with tunable energy spread down to 2.7% ($\mathrm{\Delta }\mathrm{E}/{\mathrm{E}}_0$ at FWHM). A target normal sheath acceleration stage serves as a proton source and a pulsed solenoid provides for beam collimation and energy selection. Finally a synchronous radio frequency (rf) field is applied via a rf cavity for energy compression at a synchronous phase of $-90\mathrm{deg}$. The proton bunch is characterized at the end of the very compact beam line, only 3 m behind the laser matter interaction point, which defines the particle source.

The stability of beams of laser wakefield accelerated electrons in dielectric capillary tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.

In free-electron lasers, it is essential to characterize the beam parameters as a function of the longitudinal position along the bunch, i.e., to determine the so-called slice parameters. Conventional measurements utilize transverse deflector structures to deflect the beam transversely as a function of time. Such structures are expensive and only allow the measurement of slice parameters in one transverse plane. Alternatively, the correlation between time and transverse position can be generated by introducing transverse dispersion to an energy-chirped beam. Dedicated dispersive sections can be used to measure the slice beam parameters in one transverse plane at one location. To extend the applicability of such measurements, we propose to actively generate the dispersion in the two transverse directions wherever required, thus enabling the measurement of beam slice parameters in both transverse planes at potentially any location of the accelerator. Our strategy does not incur any additional cost since it utilizes components already built into the accelerator for other purposes. The application of the method is illustrated with the SwissFEL injector test facility: we show simulations and measurements and we experimentally verify our proposal with the well-established transverse deflector approach.

Hadron therapy motivates research dealing with the production of particle beams with $\sim 100\mathrm{MeV}/\text{nucleon}$ energy and relative energy fluctuation on the order of 1%. Laser-driven accelerators produce ion beams with only tens of $\mathrm{MeV}/\text{nucleon}$ energy and an extremely broad spectra. Here, a novel method is proposed for postacceleration and monochromatization of particles, leaving the laser-driven accelerator, by using intense THz pulses. It is based on further developing the idea of using the evanescent field of electromagnetic waves between a pair of dielectric crystals. Simple model calculations show that the energy of a proton bunch can be increased from 40 to 56 MeV in five stages and its initially broad energy distribution can be significantly narrowed down.

The traditional linear envelope model is widely used in linac design and on-line tuning. However, for the simultaneous acceleration of multicharge states, the associated transfer matrix acts differently on each species with different charge to mass ratios and the traditional linear envelope model cannot be utilized. A direct way to handle multicharge state acceleration is by using multiparticle tracking, which can be high in model detail, but is typically lacking in computational efficiency to the extent where it is not suitable for on-line beam tuning of a linac. In this paper, a new approach of adapting a conventional linear envelope model to multicharge state acceleration is developed. The lattice of the proposed Facility for Rare Isotope Beams (FRIB) is used to test this technique in both the linac and the bend/folding segments of the machine. Results are benchmarked with the multiparticle tracking code IMPACT to both verify the accuracy of the model and clarify improvements in computational efficiency.

We analyze the possibility of producing two-color x or $\gamma$ radiation by Thomson/Compton backscattering between a high intensity laser pulse and a two-energy level electron beam, constituted by a couple of beamlets separated in time and/or energy obtained by a photoinjector with comb laser techniques and linac velocity bunching. The parameters of the Thomson source at SPARC_LAB have been simulated, proposing a set of realistic experiments.

We present a unified model and analysis of radiation modes excitation in free-electron lasers with a periodically premodulated electron beam. The formulation characterizes superradiant coherent radiation emission from electron beam prebunched at the synchronous frequency, including the case of stimulated superradiant where in addition to a prebunched electron beam an electromagnetic wave is injected into the undulator region. The derived formulation of radiation mode excitation by currents is applicable to general structures that can support orthogonal eigenmodes.

The interaction of a charge with its own electromagnetic field in the case of traveling into a circular semi-infinite waveguide is considered. The total work performed by the field on the charge is calculated analytically and presented as an integral over frequency. The typical spectral density of the work performed by the field is demonstrated. The total work depending on the velocity of the charge is computed. It is shown that the kinetic energy gain of the charge is positive if the velocity is less than a certain limiting value, which is independent of the waveguide radius.

The magnetic field of a staggered-array undulator using a bulk high-temperature superconductor is calculated by analytical and numerical methods. Analytical formulas for the undulator field and the solenoid field required to generate the undulator field are derived from a simple two-dimensional model. The analytical calculation shows the degree of dependence of these fields on the undulator parameters, the generation of a high undulator field proportional to the critical current density of the bulk superconductor, and the good tunability of the undulator field over a wide range of values. The numerical calculation is performed in a three-dimensional geometry by two methods: the center field and energy minimization methods. The latter treats the current distribution inside the bulk, whereas the former neglects it as a natural extension of the analytical model. The calculation also reveals the dependence of the fields on the undulator parameters arising from the current distribution. From the comparison with experimental results, we find that the latter method reproduces the experimental results well, which indicates the importance of the current distribution inside the bulk. Therefore, we derive a semiempirical formula for the required solenoid field by modifying the analytical formula using the numerical results so as to include the effect of the current distribution. The semiempirical formula reproduces the numerical result with an error of 3%. Finally, we estimate the magnetic performance of the undulator as an example of using the formulas and values presented in this paper. The estimation shows that an undulator field twice as large as that of the present in-vacuum undulator but with an equal period and gap can be obtained at a temperature of approximately 20–40 K, and that deflection parameters ($K$ values) of 1 and 2 can be achieved with periods of 5 and 10 mm at approximately 4–20 K.

Nested head-tail is a Vlasov solver for transverse oscillations in multibunch beams. It takes into account azimuthal, radial, coupled-bunch, and beam-beam degrees of freedom affected by arbitrary dipole wakes, feedback damper,beam-beam effects and Landau damping.

The correct functioning of a collimation system is crucial to safely operate highly energetic particle accelerators, such as the Large Hadron Collider (LHC). The requirements to handle high intensity beams can be demanding. In this respect, investigating the consequences of LHC particle beams hitting tertiary collimators (TCTs) in the experimental regions is a fundamental issue for machine protection. An experimental test was designed to investigate the robustness and effects of beam accidents on a fully assembled collimator, based on accident scenarios in the LHC. This experiment, carried out at the CERN High-Radiation to Materials (HiRadMat) facility, involved 440 GeV proton beam impacts of different intensities on the jaws of a horizontal TCT. This paper presents the experimental setup and the preliminary results obtained, together with some first outcomes from visual inspection and a comparison of such results with numerical simulations.

Collimators with embedded beam position monitor (BPM) button electrodes will be installed in the Large Hadron Collider (LHC) during the current long shutdown period. For the subsequent operation, BPMs will allow the collimator jaws to be kept centered around the beam orbit. In this manner, a better beam cleaning efficiency and machine protection can be provided at unprecedented higher beam energies and intensities. A collimator alignment algorithm is proposed to center the jaws automatically around the beam. The algorithm is based on successive approximation and takes into account a correction of the nonlinear BPM sensitivity to beam displacement and an asymmetry of the electronic channels processing the BPM electrode signals. A software implementation was tested with a prototype collimator in the Super Proton Synchrotron. This paper presents results of the tests along with some considerations for eventual operation in the LHC.