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The Muon g-2 Experiment at Fermi National Accelerator Laboratory (FNAL) has measured the muon anomalous precession frequency $\omega_a$ to an uncertainty of 434 parts per billion (ppb), statistical, and 56 ppb, systematic, with data collected in four storage ring configurations during its first physics run in 2018. When combined with a precision measurement of the magnetic field of the experiment's muon storage ring, the precession frequency measurement determines a muon magnetic anomaly of $a_{\mu}({\rm FNAL}) = 116\,592\,040(54) \times 10^{-11}$ (0.46 ppm). This article describes the multiple techniques employed in the reconstruction, analysis and fitting of the data to measure the precession frequency. It also presents the averaging of the results from the eleven separate determinations of \omega_a, and the systematic uncertainties on the result., Comment: 29 pages, 19 figures. Published in Physical Review D

Nonlinear problems in accelerator physics (Mais) Moment methods for nonlinear maps (Pusch) Differential algebraic formulation of normal form theory (Berz) Analytical determination of 5th-order transfer matrices of magnetic quadrupole fringing fields (Hartmann, et al ) Nonlinear beam transport effects in highly charged positive ion beams extracted from ECR ion sources (Antaya) Status of MAD (version 8.5) and future plans (Iselin) COSY INFINITY version 6 (Berz) The arbitrary order design code Tlie 1.0 (van Zeijts and Neri) The Chalk River differential algebra code "DACYC" and the role of differential and lie algebras in understanding the orbit dynamics of cyclotrons (Davies, et al) Optics programs at TRIUMF (Servranckx) A comparison of methods for long-term tracking using symplectic maps (Gjaja, et al) A generalization of the Henon map: stability of the orbits, symmetries and connections to accelerator physics (Todesco) Chaotic path at a nonlinear resonance (Lee) Third-order achromats based on mirror symmetries (Wan, et al) Design of modern high resolution magnetic spectrometers (Zeller) Alternating-phase focusing: a model to study nonlinear dynamics (Sagalovsky and Delayen) Review of the dynamic aperture experiment at the CERN SPS (Gareyte, Scandale and Schmidt) Review of nonlinear beam dynamics experiments (Lee).

We developed a highly accurate and fully Maxwellian conformal mapping method for calculation of main fields of electrostatic particle optical elements. A remarkable advantage of this method is the possibility of rapid recalculations with geometric asymmetries and mispowered plates. We used this conformal mapping method to calculate the multipole terms of the high voltage quadrupoles in the storage ring of the Muon [Formula: see text] Experiment (FNAL-E-0989). Next, we demonstrate that an effect where the observed tunes correspond to a voltage that is about [Formula: see text] higher compared to the voltage to which the Muon [Formula: see text] quadrupoles are set is explained by the conceptual and quantitative differences between the beam optics quadrupole voltage and the quadrupole voltage at the plates. Completing the methodological framework for field computations, we present a method for extracting multipole strength falloffs of a particle optical element from a set of Fourier mode falloffs. We calculated the quadrupole strength falloff and its effective field boundary (EFB) for the Muon [Formula: see text] quadrupole, which has explained the experimentally measured tunes, while simple estimates based on a linear model exhibited discrepancies up to [Formula: see text].

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a one standard deviation range of $\sigma = 0.21$ rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.

A frontier challenge in implementing femtosecond electron microscopy is to gain precise optical control of intense beams to mitigate collective space charge effects for significantly improving the throughput. Here, we explore the flexible uses of an RF cavity as a longitudinal lens in a high-intensity beam column for condensing the electron beams both temporally and spectrally, relevant to the design of ultrafast electron microscopy. Through the introduction of a novel atomic grating approach for characterization of electron bunch phase space and control optics, we elucidate the principles for predicting and controlling the phase space dynamics to reach optimal compressions at various electron densities and generating conditions. We provide strategies to identify high-brightness modes, achieving ∼100 fs and ∼1 eV resolutions with 106 electrons per bunch, and establish the scaling of performance for different bunch charges. These results benchmark the sensitivity and resolution from the fundamental beam brightness perspective and also validate the adaptive optics concept to enable delicate control of the density-dependent phase space structures to optimize the performance, including delivering ultrashort, monochromatic, high-dose, or coherent electron bunches.

The Muon Campus at Fermilab is a system through which muons are delivered to the storage ring of the Muon [Formula: see text] Experiment (E989). It consists of a set of 1 km beamlines that transport and prepare a highly polarized muon beam out of secondaries produced downstream a target station. Realistic simulations of this beam delivery system (BDS) using COSY INFINITY, and presented here, contribute to the understanding and characterization of the muon beam production in relation to the statistical and systematic uncertainties of the E989 measurement, intended to be smaller than 0.14 parts per million to achieve the goals of the experiment. The impact of nonlinearities from fringe fields and high-order contributions on the BDS performance are presented, as well as detailed studies of the interactions between secondaries and the beamline elements apertures, particle decay channels, spin dynamics and beamline misalignments.

The Muon [Formula: see text] Experiment at Fermilab (E989) is directed toward measuring the muon magnetic anomaly, [Formula: see text], with total statistical and systematic errors of 0.14 ppm. This new measurement will serve as strong probe of effects of as yet undiscovered particles beyond the Standard Model (SM), and perhaps validate or disprove other theoretical models beyond the SM. Of special interest is the reduction of muon losses from the storage ring to achieve the precision needed at the Muon [Formula: see text] Experiment. For this purpose, we have developed a detailed and precise symplectic model of the Muon [Formula: see text] Storage Ring using COSY INFINITY that considers measured inhomogeneities of the magnetic field; high-order representation of the Electrostatic Quadrupole System (EQS) electrostatic field at different stages of the experiment including fringe fields; injection to the ring based on measurements; and beam collimation. Specifically, we have performed numerical analyses of the rate of muons that are lost before they have a chance to decay for several possible configurations of the EQS in order to find the best possible scenarios that minimize muon losses and understand the resonance mechanisms that contribute to betatron and possibly spin resonances. Additionally, comparisons with measurements have permitted the determination of whether observed resonances come from anticipated features of the [Formula: see text] storage ring or from unexpected sources of error whose effect could be detrimental to the precision of E989.

Accelerators are playing increasingly important roles in basic science, technology, and medicine. Ultra high-intensity and high-energy (GeV) proton drivers are a critical technology for accelerator-driven sub-critical reactors (ADS) and many HEP programs (Muon Collider) but remain particularly challenging, encountering duty cycle and space-charge limits in the synchrotron and machine size concerns in the weaker-focusing cyclotrons; a 10–20 MW proton driver is not presently considered technically achievable with conventional re-circulating accelerators. One, as-yet, unexplored re-circulating accelerator, the Fixed-field Alternating Gradient or FFAG, is an attractive alternative to the other approaches to a high-power beam source. Its strong focusing optics can mitigate space charge effects and achieve higher bunch charges than are possible in a cyclotron, and a recent innovation in design has coupled stable tunes with isochronous orbits, making the FFAG capable of fixed-frequency, CW acceleration, as in the classical cyclotron but beyond their energy reach, well into the relativistic regime. This new concept has been advanced in non-scaling nonlinear FFAGs using powerful new methodologies developed for FFAG accelerator design and simulation. The machine described here has the high average current advantage and duty cycle of the cyclotron (without using broadband RF frequencies) in combination with the strong focusing, smaller losses, and energy variability that are more typical of the synchrotron. The current industrial and medical standard is a cyclotron, but a competing CW FFAG could promote a shift in this baseline. This paper reports on these new advances in FFAG accelerator technology and presents advanced modeling tools for fixed-field accelerators unique to the code COSY INFINITY.1

The Hefei light source (HLS) is a second generation synchrotron radiation light source, in which a superconducting wiggler is installed and operating. The effects of the wiggler on the beam dynamics on the HLS storage ring are studied, in order to make sure the wiggler can operate properly when the ring is working in the high brilliance mode. We generate a model of the magnetic field in the midplane of the wiggler. The 3D magnetic field model is also builded up by COSY infinity 9.0. Both the linear and nonlinear effects of the wiggler are discussed. The vertical tune is changed from 2.535 to 2.567 and the vertical beta function is heavily distorted, while a symplectic tracking study shows the dynamic aperture is only slightly affected by the wiggler. And the wiggler should be able to run on the high brilliance mode after the linear effects get compensated.

Increasing demands for luminosity in existing and future colliders have made lattice design and error tolerance and correction critical to achieving performance goals. The current state of the Tevatron collider is an example, with a strong skew quadrupole error present in the operational lattice. This work studies the high-order performance of the Tevatron and the strong nonlinear behavior introduced when a significant skew quadrupole error is combined with conventional sextupole correction, a behavior still clearly evident after optimal tuning of available skew quadrupole circuits. An optimization study is performed using different skew quadrupole families, and, importantly, local and global correction of the linear skew terms in maps generated by the code COSY INFINITY [M. Berz, COSY INFINITY version 8.1 user's guide and reference manual, Department of Physics and Astronomy MSUHEP-20704, Michigan State University (2002). URL http://cosy.pa.msu.edu/cosymanu/index.html]. Two correction schemes with one family locally correcting each arc and eight independent correctors in the straight sections for global correction are proposed and shown to dramatically improve linearity and performance of the baseline Tevatron lattice.

In the US scenario for a Neutrino Factory presented in “A feasibility study of a neutrino source based on a muon storage ring”, N. Holtkamp (Ed.), D. Finley (Ed.), Fermilab, April 15th, 2000), a large percentage of the cost is related to an induction linac for phase-energy rotation and bunching of the muon beam collected after the production target and decay channel. A more cost-effective adiabatic buncher and phase-energy rotator has been proposed to replace the induction linac system (D. Neuffer, A. Van Ginneken, High-frequency bunching and ( φ - δ E ) rotation for a muon source, Proceedings of the 2001 Particle Accelerators Conference, Chicago, 2001, p. 2029). The new method uses consecutive RF cavities with differing frequencies. The frequencies are changed to enable bunching and phase-energy rotation. In this paper, the theoretical concept is developed and demonstrated with simulation results obtained with the map code COSY Infinity ( http://cosy.pa.msu.edu ). An optimization strategy is also explored.

All schemes to produce intense sources of high-energy muons—Neutrino factories, beta beams, Colliders—require collection, RF capture, and transport of particle beams with unprecedented emittances, both longitudinally and transversely. These large initial emittances must be reduced or “cooled” both in size and in energy spread before the muons can be efficiently accelerated to multi-GeV energies. The acceleration stage becomes critical in formulating and optimizing muon beams; individual stages are strongly interlinked and not independent as is the case in most conventional acceleration systems. Most importantly, the degree of cooling, or cooling channel, depends on the choice of acceleration. In the current US baseline scenario, the cooling required for acceleration is about a factor of 10 in transverse emittance per plane. Longitudinal cooling is also required. In the proposed Japanese scenario, using an alternative acceleration scheme, no cooling is presumed. This work discusses two basic, but different approaches to a Neutrino Factory and how the optimal strategy depends on beam parameters and method of acceleration.

Schemes to produce intense sources of high-energy muons, Neutrino Factories, beta beams, and colliders, require collection, rf capture, and transport of particle beams with unprecedented emittances, both longitudinally and transversely. These large initial emittances must be reduced or cooled both in size and in energy spread before the muons can be efficiently accelerated to multi-GeV energies. The acceleration stage becomes critical in formulating and optimizing muon beams; individual stages are strongly interlinked and not independent as is the case in most conventional acceleration systems. Most importantly, the degree of cooling, or cooling channel, depends on the choice of acceleration. This work discusses two basic, but different approaches to a Neutrino Factory and how the optimal strategy depends on beam parameters and method of acceleration.

In a scenario for either a Neutrino Factory or Muon Collider, the anticipated transverse beam emittance subsequent to capture and phase rotation is so large that it permits a relaxation of the requirements on beam spot size in the early stages relative to the final stages of ionization cooling. Staging the cooling process according to initial emittances, coupled with modest cooling factors, permits more optimal and efficient cooling channel designs and avoids much of the difficulty encountered with channels which attempt to maintain strong focusing (large, 300–500 mrad, divergences) across ultra-large momentum ranges (⩾±20% δ p / p ). Relaxation of spot size at the absorber, especially in the “precooling” stage, allowed development of an efficient transverse cooling channel based simply on a quadrupole FODO cell. This work describes the design of such a cooling channel and its application as an upstream stage of beam cooling. Being a linear channel with no bends, it serves to reduce the large transverse beam size delivered from muon-beam capture and bunching before entering more restricted optical structures such as transverse plus longitudinal cooling channels or accelerators.

A method has been developed to calculate accurate high-order ion-optical maps for electrostatic and radio-frequency accelerating elements. The method has been incorporated into the arbitrary-order map-based beam optics code COSY Infinity. The treatment is restricted to the case of negligible magnetic fields, as is typical of heavy-ion accelerating cavities, and does not include space charge. For validation purposes, the beam dynamics calculated for these elements is compared against ray tracing for typical beam and cavity parameters. Different from the ray-tracing approach, parameter changes of individual components typically require only recalculation of the maps of the particular components and not the entire system, and thus the method is particularly suitable for optimization. The approach developed for accurate analytical representation of the on- and off-axis electric fields of cylindrically symmetric electrostatic lenses and radio-frequency cavities is described. Some of the many possible applications for using accurate high-order map representations of Einzel lenses, electrostatic accelerating gaps, and radio-frequency accelerating structures are discussed.

With the U.S. experimental effort in HEP largely located at laboratories supporting the operations of large, highly specialized accelerators, colliding beam facilities, and detector facilities, the understanding and prediction of high energy particle accelerators becomes critical to the success, overall, of the DOE HEP program. One area in which small businesses can contribute to the ongoing success of the U.S. program in HEP is through innovations in computer techniques and sophistication in the modeling of high-energy accelerators. Accelerator modeling at these facilities is performed by experts with the product generally highly specific and representative only of in-house accelerators or special-interest accelerator problems. Development of new types of accelerators like FFAGs with their wide choices of parameter modifications, complicated fields, and the simultaneous need to efficiently handle very large emittance beams requires the availability of new simulation environments to assure predictability in operation. In this, ease of use and interfaces are critical to realizing a successful model, or optimization of a new design or working parameters of machines. In Phase I, various core modules for the design and analysis of FFAGs were developed and Graphical User Interfaces (GUI) have been investigated instead of the more general yet less easily manageable console-typemore » output COSY provides.« less

A recent effort is underway to design an efficient match of a Muon Collider to the Fermilab site, potentially using the Tevatron tunnel after decommissioning. This work represents a new design for such a collider with emphasis on shortened IR and systematic high-order correction and dynamics studies. With a 1 cm beta*, simultaneous control of geometric and chromatic aberrations is critical and can only be achieved through the deliberate addition of nonlinear fields in the Interaction Region itself. This work studies both the correction schemes and the unavoidable impact of high-order correctors - sextupoles, octupoles and even duodecapoles - located in the Interaction Region close to the low-beta quadrupoles or focusing elements. This study proposes and systematically addresses the aberrations for different systems of nonlinear correctors and optimizes performance of an advanced IR.

Progress in the development of interaction regions (IR) for advanced future colliders, in particular the Muon Collider and the International Linear Collider, require a systematical high-order dynamics study. The effects from high-order beam dynamics become more and more pronounced as the spot size at the interaction point decreases to very small values, 14 cm and 4 cm for the 50 on 50 GeV Muon Collider and Higgs Factory, respectively, and even less for the International Linear Collider. Simultaneous control of geometric and chromatic aberrations is critical to the success of future machines and can only be achieved through the deliberate addition of nonlinear fields in the interaction region itself. This work studies both the correction schemes and the unavoidable impact of high-order correctors - sextupoles, octupoles and even duodecapoles - located in the interaction region close to the low-beta quadrupoles or focusing elements. This study proposes and systematically addresses the evolution of aberrations for different systems of nonlinear correctors and optimizes performance of advanced IRs.

There exists now a large demand in better neutrino beams in particle physics community. Studying of such beams could reveal interesting and important properties of the observed neutrino oscillations. A high intensity source of a single flavor of neutrinos with reduced backgrounds, a known energy spectrum and intensity is needed for this research. Such intense source of neutrinos is supposed to be provided by the Neutrino Factory. A Neutrino Factory, as proposed, relies on formation and acceleration of ultra-large emittance muon beams with subsequent decay of the muons into a well-collimated, well-characterized neutrino beam. The muon beam creating section of the lattice is originally based on capturing, bunching and phase rotation in an expensive induction linac. A recently proposed different scheme bunches particles and reduces their energy spread in an array of high-frequency rf cavities whose rf frequency varies along the length of the channel. The cost reduction and simplicity of the proposed approach is extensive but is still not at its optimum. Different variations of the design paramaters leading to different properties of the beam and cost are possible. This work explores the approach, variations and develops an optimization scheme for rf parameters based on the underlying beam dynamics.

Staging and optimization in the design of a Neutrino Factory are critically dependent on the choice and format of accelerator. Possibly the simplest, lowest-cost scenario is a nonscaling FFAG (Fixed-Field Alternating Gradient) machine coupled to a linear (no bending) transverse cooling channel constructed from the simplest quadrupole lens system, a FODO cell. In such a scenario, transverse cooling demands are reduced by a factor of 4 and no longitudinal cooling is required relative to acceleration using a Recirculating Linac (RLA). Detailed simulations further show that a quadrupole-based channel cools efficiently and over a momentum range which is well-matched to FFAG acceleration. Details and cooling performance for a quadrupole channel are summarized in this work.

Increasing demands for luminosity in existing and future colliders have made both lattice design and error tolerance and correction critical to achieving performance goals. The current state of the Tevatron collider is an example, with a strong skew quadrupole error present in the operational lattice. This work studies the high order performance of the Tevatron and the strong nonlinear behavior introduced when a significant skew quadrupole error is combined with conventional sextupole correction, a behavior still clearly evident after optimal tuning of available skew quadrupole circuits. An optimization study is performed using different skew quadrupole families, and, importantly, local and global correction of the linear skew terms in maps generated by the code COSY. This correction scheme is compared with the present Tevatron operational lattice and corrector configuration.

The Tevatron accelerator, currently the particle accelerator with the highest energy in the world, consists of a ring with circumference of four miles in which protons are brought into collision with antiprotons at speeds very close to the speed of light. The accelerator currently under development at Fermilab represents a significant upgrade, but experienced significant limitations during initial operation. The correction of some of the problems that appeared using techniques of automatic differentiation are described. The skew quadrupole correction problems are addressed in more detail, and different schemes of correction are proposed.

In this paper we present simulations using COSY INFINITY to study the behavior of muon beams in a ring cooler designed by V. Balbekov[1]. Because of the substantial transversal emittance, the nonlinearities play a very important limiting role that must be understood and controlled well, which leads to the requirement of high order computation. We describe the system, the approaches for the simulations of the large aperture solenoids and magnetic sectors, and we show the nonlinear transfer maps as well as tracking simulations for different field models, and compare with other methods based on various approximations.

Summary form only given. Particle optical systems are usually comprised of electric and magnetic bending elements, focusing elements, and high-order multipoles for correction of aberrations. However, various modern systems for the transport and manipulation of large acceptance beams of rare and short-lived particles require the detailed treatment of more advanced optical elements. In particular, in recent years the reduction of the emittance of such beams has become of prime importance. The systems performing such reduction of emittance usually consist of combinations of absorbers that uniformly reduce the components of the momenta of the particles, as well as cavities that increase predominately the longitudinal components, which overall leads to a reduction of transversal emittance. For purposes of optimal focusing, frequently both cavities and absorbers are placed inside the body or at least the fringe fields of quadrupole or solenoidal focusing elements, which leads to the requirement of treating the nonlinear optics of acceleration, absorption, and focusing in a combined approach. The treatment of such systems in ray-tracing scenarios based on integration through fields and matter is very laborious and time consuming, and does not lend itself well to optimization and correction of undesirable nonlinear effects. We describe a differential algebraic method for the treatment of such nonlinear dynamics, based on the spatial and temporal form of the accelerating fields, any superimposed focusing magnetic fields, and the geometry and physical properties of the absorbing material and its possible vessel. Described by a Bethe-Bloch-Vavilov formalism, the bulk of the effects are described in terms of a high order nonlinear transfer maps. The also occurring scattering and straggling, which are inherently non-deterministic and hence not representable in the map formalism, are described in terms of a set of stochastic kicks in the transversal and longitudinal dynamics. The stochastics is propagated to the center of the occurring absorbers and thus allows a combined treatment of the tracking of both deterministic and random effects in an efficient way. ne method is implemented in the high-order code COSY INFINTIY. Examples for the application and performance of the method are given.

A tetra ring muon beam cooler designed by V. Balbekov consists of large aperture magnets. Because the original design is based on the hard edge model, the realistic field description has to be considered in the simulations. Using the code COSY INFINITY, which can treat realistic fields, we studied the dynamics of muon beam in the tetra cooler ring.

With the emergence of neutron and proton irradiation facilities for cancer therapy, substantial interest has developed in compact gantry beamlines which can be rotated around the patient and guide the beam from the rotation axis to the perpendicular irradiation axis. We propose a new type of beamline which differs from other approaches by giving up midplane symmetry but requiring only three bending magnets. Compared to other designs, this layout increases the amount of room for patient and instrumentation while maintaining rather compact exterior dimensions. The lack of midplane symmetry conceptually complicates the design in several aspects. However, using solenoids for linear decoupling and focusing, the system can be made linearly achromatic in both planes. In order to achieve the required beam spot size in the transport, careful higher-order correction is necessary, in particular because of the coupling aberrations that arise from lack of midplane symmetry. In the proposed system, the relevant second- and third-order aberrations have been corrected.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs Factories and compact high energy lepton colliders. The status and timescale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons., Comment: 112 pages, Large report

Recently there has been renewed interest in the influence of fringe fields on particle dynamics, due to studies that revealed their importance in some cases, as, for example, the proposed Neutrino Factory and muon colliders. In this paper, we present a systematic study of generic fringe field effects. Using as an example a lattice of the proposed Neutrino Factory, we show that fringe fields influence the dynamics of particles at all orders, starting with the linear motion. It is found that the widely used sharp cutoff approximation leads to divergences regardless of the specific fall-off shape of the fields. The results suggest that a careful consideration of fringe field effects in the design stage of small machines for large emittances is always recommended.

Because of the predominance of large emittances, muon storage rings have a tendency to being rather sensitive to nonlinear effects. In this paper we study the effects of the nonlinearities due to the lattice elements’ fringe fields, which have a fundamentally different behavior from normal multipole terms. It is found that for given scenarios for lattices and emittances, the fringe field effects have dramatic influences on the dynamics and stability of particles and hence require careful study of correction options.

Among many other challenges faced by muon accelerators and storage rings, the influence of nonlinear effects has to be studied carefully compared to conventional proton and electron machines. The short lifetime of muons as well as their production mechanism make the cooling of muon beams a necessity; however, in many scenarios still rather large transversal emittances persist, which makes nonlinear effects more pronounced than usual. There are a variety of sources for nonlinear effects besides deliberate and random nonlinear multipoles; particularly, there are nonlinear effects due to fringing fields, which have been known in the design of high-resolution spectrographs and recently have also been studied for storage rings [1]. Details of some first estimates of their effects are given in an accompanying paper [2]. In this paper we address another nonlinear effect that is directly connected to the presence of large emittances, namely the so-called kinematic correction, and report first results of the effects on some current muon storage ring designs.

The Super-FRS will be a large-acceptance two-stage superconducting fragment separator with three exit branches serving different experimental areas. Due to the high primary-beam intensity of up to 1012 ions/s a challenging design of the target area and the components used in the first dipole Super-FRS is necessary. These efforts include high-power production targets, beam-dumps to catch the remaining primary beam, and radiation resistant magnets. In this contribution we summarize the recent developments on these issues.

Using a multilevel fast multipole method, coupled with the shadow imaging of femtosecond photoelectron pulses for validation, we quantitatively elucidate the photocathode, space charge, and virtual cathode physics, which fundamentally limit the spatiotemporal and spectroscopic resolution and throughput of ultrafast electron microscope (UEM) systems. We present a simple microscopic description to capture the nonlinear beam dynamics based on a two-fluid picture and elucidate an unexpected dominant role of image potential pinning in accelerating the emittance growth process. These calculations set theoretical limits on the performance of UEM systems and provide useful guides for photocathode design for high-brightness electron beam systems.

The transport systems required to feed a beam of highly relativistic electrons into a free electron laser have to satisfy very stringent requirements with respect to isochronicity and achromaticity. In addition, the line has to be tunable to match different operating modes of the free electron laser. Various beamlines emphasizing different aspects, such as quality of isochronicity and achromaticity, simplicity of the design, and space configurations are shown and compared. Solutions are presented having time resolution in the range of 2 to less than 0.5 ps for 1% of energy spread.

The European physical journal / A 56(8), 211 (2020). doi:10.1140/epja/s10050-020-00215-8, Published by Springer, Berlin ; Heidelberg