Laser wakefield excitation in the interaction of femtosecond laser pulse with an underdense thin magnetized plasma slab is studied by one dimensional relativistic Vlasov-Maxwell system of equations. The interaction is modeled by relativistic Vlasov equation in propagation direction of laser pulse and fluid equations in transverse direction. Backward semi-Lagrangian method (BSL) is used for numerical solution of Vlasov equation. Generation of wakefields by a right and left handed circularly polarized (RCP) and (LCP) laser pulses in the interaction with nonmagnetized and magnetized plasma slab are examined and compared. Two directions are considered for external magnetic field, parallel and antiparallel to direction of laser pulse propagation. The results show that applying magnetic field along (opposite to) the propagation direction of RCP (LCP) laser pulse increases amplitude of density steepening and consequently wakefields amplitude, and mean kinetic energy of electrons compared with nonmagnetized plasma. The results are in complete agreement with previous analytical and numerical reports.

In the past years, several studies, numerical and experimental, have been carried out for enlightening the effect of space charge and resonances on particle beams stored in accelerators. The last effort of this quest focused on the third-order coupled resonances, emphasizing the existence of the periodic crossing of fixed lines induced by space charge. In this article, the theory of nonlinear sum resonances in coasting beams in the presence of space charge is presented and applied to unravel the key features of the four-dimensional coupled dynamics in high-intensity bunched beams.

Efficient tuning of complex accelerator chains requires automated procedures, themselves reliant upon beam physical models. The Isotope Separator and ACcelerator (ISAC) facility at TRIUMF requires frequent changes of beam species (isotope), mass to charge ratio and beam energy tailored to experiment requirements, which demands rapid beam tuning. In addition, emergent effects such as long term changes of energy or energy spread require beam optimization that must be based on a complete model of the accelerator. Using an envelope code to build an end-to-end simulation of the accelerator facility for operational purposes reduces computing times by 3 or 4 orders of magnitude, when compared to particle tracking codes, so that the requisite simulations may be carried out in real time, by polling control system data. Herein described is the second order Hamiltonian for an radio frequency quadrupole (RFQ), presented within the framework of the envelope code transoptr. To benchmark the transoptr model, envelope simulations of the TRIUMF-ISAC RFQ have been performed and compared with the multiparticle code parmteq.

Transverse beam instabilities are a major cause of emittance dilution and beam losses in high intensity hadron accelerators. This paper presents an overview of the system that has been developed for automatic detection of transverse beam instabilities in the Large Hadron Collider at CERN. It relies on the detection of very small transverse beam oscillations using a high sensitivity tune measurement system. These oscillations are then processed online in a field programmable gate array to monitor the growth of any instabilities. When an instability is detected, the acquisition of intrabunch beam position data with a multi-gigahertz bandwidth is triggered. This data allows identification of unstable bunches within bunch trains and provides information on the temporal signature of the instability. The design of these systems and the different algorithms for instability detection that have been tested with beam will be presented along with a detailed description of their performance.

A method proposed to preserve the electron beam polarization at the VEPP-4M collider during acceleration with crossing the integer (imperfection) spin resonance at energy $E=1763\mathrm{MeV}$ has been successfully applied. It is based on full decompensation of the $0.6\times 3.3\mathrm{Tesla}\times \text{meter}$ integral of the KEDR detector longitudinal magnetic field due to the antisolenoid being “switched off.”

We propose a simple scheme to compress an electron beam with an optical laser, which can potentially achieve a bunch length much shorter than what is currently available with a conventional radio-frequency technique. Instead of an energy chirp, the optical laser induces an energy modulation whose amplitude linearly changes along the longitudinal axis, which effectively compresses the electron beam after it passes through an optimized magnetic chicane. Numerical simulations performed to demonstrate the proposed scheme show that a free electron laser pulse with the peak power of 16 GW and the pulse length of 470 as (attosecond) can be generated, if this scheme is applied to a 2-GeV and 2-kA electron beam.

The beam dump facility (BDF) project is a proposed general-purpose facility at CERN, dedicated to beam dump and fixed target experiments. In its initial phase, the facility is foreseen to be exploited by the Search for Hidden Particles Experiment. Physics requirements call for a pulsed $400\mathrm{GeV}/c$ proton beam as well as the highest possible number of protons on target each year of operation ($4.0\times {10}^{19}/\mathrm{year}$), in order to search for feebly interacting particles. The target/dump assembly lies at the heart of the facility, with the aim of safely absorbing the full high intensity Super Proton Synchrotron beam, while maximizing the production of charmed and beauty mesons. High-Z materials are required for the target/dump, in order to have the shortest possible absorber and reduce muon background for the downstream experiment. The design of the production target is one of the most challenging aspects of the facility design, due to the high energy and power density deposition that are reached during operation, and the resulting thermomechanical loads. The nature of the beam pulse induces very high temperature excursions between pulses (up to $100°\mathrm{C}$), leading to considerable thermally induced stresses and long-term fatigue considerations. The high average power deposited on target (305 kW) creates a challenge for heat removal. During the BDF facility comprehensive design study, launched by CERN in 2016, extensive studies have been carried out in order to define and assess the target assembly design. These studies are described in the present contribution, which details the proposed design of the BDF production target, as well as the material selection process and the optimization of the target configuration and beam dilution. One of the specific challenges and novelty of this work is the need to consider new target materials, such as a molybdenum alloy as core absorbing material and Ta2.5W as cladding. Thermostructural and fluid dynamics calculations have been performed to evaluate the reliability of the target and its cooling system under beam operation. In the framework of the target comprehensive design, a preliminary mechanical design of the full target assembly has also been carried out, assessing the feasibility of the whole target system.

We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma.

Ions are produced in an accelerator when the beam ionizes residual gas inside the vacuum chamber. If the beam is negatively charged, ions can become trapped in the beams potential, and their density will increase over time. Trapped ions can cause a variety of undesirable effects, including instability and emittance growth. This paper will discuss the possibility of ion trapping and instability in the APS-Upgrade storage ring. The question of where ions will be trapped is addressed using simple analytical calculations, while the instability is modeled with computer simulations. A scheme is proposed for mitigating the ion instability, by using train gaps with a high charge bunch before and after the gap to minimize rf transients. The reduction in ion density due to nonevaporable getter coating is also discussed.

We present a quantitative experimental analysis of the radiation emission of 12.6 GeV electrons moving along and across the (111) planes of a strongly bent silicon crystal with a bending radius of 0.15 m. We have measured the radiation emitted during volume reflection, which has shown to strongly enhance the emission of low-energy photons, and a convincing agreement between simulations and experimental data is found.

In our previous publications, we introduced a concept of complex bend, which is a bending element consisting of dipole poles, interleaved with strong focusing and defocusing quadrupole poles. An electron ring built from such elements features low emittance while preserving substantial room for insertion devices and associated lattice elements. In this paper, we present two new optics solutions for the complex bend which offer to substantially reduce the device length by removing the dipole poles. In the first of the solutions, the bending is realized by shifting the quadrupole poles along the curved horizontal axis. For the second solution, we use permanent magnet quadrupole poles installed into a wide gap of the conventional electromagnet. In this case, the resulting bending field in the magnet gap is a superposition of the quadrupole field from the poles and the dipole field from the conventional magnet. We present an analysis of the particle motion and synchrotron radiation emitted in such fields, as well as an assessment of the ring linear lattice that is composed of complex bend elements.

We present a design study of an innovative scheme to generate high rep rate (MHz-class) GeV electron beams by adopting a two-pass two-way acceleration in a superconducting (SC) linac operated in continuous wave (CW) mode. The electron beam is accelerated twice by being reinjected in opposite direction of propagation into the linac after the first passage. Acceleration in opposite directions is accomplished thanks to standing waves supported in rf cavities. The task of recirculating the electron beam when it leaves the linac after first pass is performed by a bubble-shaped arc compressor composed by a sequence of double bend achromat. In this paper we address the main issues inherent to the two-pass acceleration process and the preservation of the electron beam quality parameters (emittance, energy spread, peak current) required to operate x-ray free electron lasers (FEL) with low jitters in the amplitude, spectral and temporal domain, as achieved by operating in seeding and/or oscillator mode a CW FEL up to 1 MHz rep rate. Detailed start-to-end simulations are shown to assess the capability of this new scheme to double the electron beam energy as well as to compress the electron bunch length from picoseconds down to tens of femtoseconds. The advantage of such a scheme is to halve the requested linac length for the same final electron beam energy, which is typically in the few GeV range, as needed to drive an x-ray FEL. The AC power to supply the cryogenic plant is also significantly reduced with respect to a conventional single-pass SC linac for the same final energy. We are reporting also x-ray FEL simulations for typical values of wavelengths of interest (in the 200 eV–8 keV photon energy range) to better illustrate the potentiality of this new scheme.

This contribution describes the latest milestones of a multiyear program to build and operate a compact $-300\mathrm{kV}$ dc high voltage photogun with inverted insulator geometry and alkali-antimonide photocathodes. Photocathode thermal emittance measurements and quantum efficiency charge lifetime measurements at average current up to 4.5 mA are presented, as well as an innovative implementation of ion generation and tracking simulations to explain the benefits of a biased anode to repel beam line ions from the anode-cathode gap, to dramatically improve the operating lifetime of the photogun and eliminate the occurrence of micro-arc discharges.

Laser wakefield acceleration of GeV electrons is becoming a mature technique, so that a reliable accelerator delivering stable beams to users communities can now be considered. In such a context, two plasma stages, one injector and one booster stage, offer a flexible solution for optimization. For the injector we consider here the resonant multipulse ionization injection (ReMPI) that can be optimized to generate electron bunches with high enough quality to be efficiently transported to the second stage. In order to better control the beam-loading effect and optimize the beam manipulation after the plasma downramp, a quasiround beam is preferable. In this respect, we present analytical and particle-in-cell results concerning the tunnel-ionization process in presence of two, orthogonally polarized, laser pulses with different wavelengths. We also show, by means of hybrid fluid/PIC numerical simulations, that a stable working point with the ReMPI injector exists at 32 pC, 4 kA peak current, with mean energy of 150 MeV, energy spread of 1.65% rms, normalized emittance ${\epsilon }_n=0.23\mu \mathrm{m}$ and divergence of 0.6 mrad. The scheme relies on a 150 TW Ti:Sa laser modified to achieve a four-pulses driver train and a third harmonics ionization pulse.

Recent progress in plasma based accelerator technology has demonstrated its ability to deliver high energy (GeV) beams in compact structures (centimeter to meter scale plasmas). Current developments of that technology are oriented toward producing beams with quality and energy spread comparable to those obtained using standard accelerating structures. In plasma based accelerators, the beam energy spread can be improved during the acceleration process through beam loading. To achieve optimum beam loading, the beam has to be shaped such that the superposition of its space charge fields and plasma fields result in a uniform accelerating field. In this work we show how beam-induced-ionization injection can be used to shape and inject a trailing beam suitable for beam loading. Our particle-in-cell numerical simulations done with OSIRIS show the ionization injection of a shaped 340 pC, 13 kA and $3\mu \mathrm{m}$ long electron beam accelerated to 900 MeV in less than 3 cm of plasma. The configurations considered numerically were based on the beams and plasmas that have been and will be available at the FACET facility.

The combined zero degree structure (KONUS) is a quasiperiodic structure. It was developed for the low-energy part of multigap drift tube linacs with H-type cavities. Their rf efficiency depends very much on a low electrical capacity of the drift tube structure, while in E-type structures like the Alvarez-DTL this is a minor effect. Therefore, instead of having quadrupole singlets integrated in voluminous drift tubes, KONUS allows one to develop a separated function drift tube linac (DTL) with a large voltage gain between two lenses. Very low beam injection energies can be realized, as the drift tube lengths can range down to around 10 mm. One KONUS period consists of a triplet lens, a rebuncher with a few gaps at a synchronous phase around $-35°$, and the main multigap acceleration designed for a hypothetical zero degree synchronous particle. The longitudinal beam dynamics along this main acceleration section and the layout of the quadrupole triplet channel are explained in detail. Two examples for pulsed high current proton and heavy ion acceleration are included.

The study of magnetized electron beam has become a high priority for its use in ion beam cooling as part of electron ion colliders and the potential of easily forming flat beams with a large aspect ratio. In this paper, a new diagnostic is described with the purpose of studying longitudinal and transverse magnetized beam properties. The device is a modification to a typical pepper-pot. Specifically, this 1D pepper-pot was designed for use with a transverse deflecting cavity for longitudinal bunch profile measurements of magnetized beams.

In a previous paper we showed that dynamical density shocks occur in the nonrelativistic expansion of dense single component plasmas relevant to ultrafast electron microscopy; and we showed that fluid models capture these effects accurately. We show that the nonrelativistic decoupling of the relative and center of mass motions ceases to apply and this coupling leads to novel behavior in the relativistic dynamics under planar, cylindrical, and spherical symmetries. In cases where the relative motion of the bunch is relativistic, we show that a dynamical shock emerges even in the case of a uniform bunch with cold initial conditions; and that density shocks are in general enhanced when the relative motion becomes relativistic. Furthermore, we examine the effect of an extraction field on the relativistic dynamics of a planar symmetric bunch.

We present a laser-ionized, beam-driven, passive thin plasma lens that operates in the nonlinear blowout regime. This thin plasma lens provides axisymmetric focusing for relativistic electron beams at strengths unobtainable by magnetic devices. It is tunable, compact, and it imparts little to no spherical aberrations. The combination of these features make it more attractive than other types of plasma lenses for highly divergent beams. A case study is built on beam matching into a plasma wakefield accelerator at SLAC National Accelerator Laboratory’s FACET-II facility. Detailed simulations show that a thin plasma lens formed by laser ionization of a gas jet reduces the electron beam’s waist beta function to half of the minimum value achievable by the FACET-II final focus magnets alone.

Next-generation light sources based on the multibend achromat concept place great reliance on the accuracy of beam dynamics modeling. To ensure the success of such light sources, confirmation of design performance with at least two independent codes is prudent. The APS Upgrade (APS-U) lattice has been designed using the code elegant, which has existing and new features that are needed by the design. Corresponding, independent improvements have recently been made to the accelerator toolbox (at), in order to permit an independent check of nonlinear dynamics predictions. The new developments include the modeling of combined-function bending magnets with straight geometry and improved fringe field effects of quadrupole magnets. Calculations of linear and nonlinear lattice parameters and particle tracking results were compared, showing remarkable agreement was found between the two independently developed codes. This provides significant confirmation of the feasibility of the APS-U design.