The consideration of transverse dynamics of relativistic space-charge dominated beams and halo growth due to bunch oscillations is based on variational approach to rational (in dynamical variables) approximation for rms envelope equations. It allows to control contribution from each scale of underlying multiscales and represent solutions via exact nonlinear eigenmodes expansions. Our approach is based on methods provided possibility to work with well-localized bases in phase space and good convergence properties of the corresponding expansions.
The mostly research fasten on high emission density of injector to study electron beam's brightness in LIA. Using the injector(2MeV) was built to research brightness of multi-pulsed high current(KA) electron beam, and researchs three measurement method (the pepper-pot method, beam collimator without magnetic field, beam collimator with magnetic field method) to detect beam's brightness with time-resolved measurement system.
Beam quality preservation during transport of high-brightness electron beams is of general concern in the design of modern accelerators. Methods to manage incoherent synchrotron radiation (ISR) have been in place for decades; as beam brightness has improved coherent synchrotron radiation (CSR) and the microbunching instability (uBI) have emerged as performance limitations. We apply the compensation analysis of diMitri, Cornacchia, and Spampinati - as previously used by Borland - to the design of transport systems for use with low-emittance beams, and find that appropriately configured second o…
We are developing a beam line which compresses the phase space of a standard surface $μ^+$ beam by 10 orders of magnitude with an efficiency of $10^{-3}$. Phase space compression occurs in a He gas target and consists of three consecutive stages: Transverse (perpendicular to the beam axis) compression, longitudinal compression and re-extraction into vacuum. Transverse compression was observed for the first time and longitudinal compression has been measured to occur within 2.5 $μ$s with high efficiency.
A comparison of the two most prominent electron sources of high average current high brightness electron beams, DC and superconducting RF photoemission guns, is carried out using a large-scale multivariate genetic optimizer interfaced with space charge simulation codes. The gun geometry for each case is varied concurrently with laser pulse shape and parameters of the downstream beamline elements of the photoinjector to obtain minimum emittance as a function of bunch charge. Realistic constraints are imposed on maximum field values for the two gun types. The SRF and DC gun emittances and beam e…
Increasing peak brightness is beneficial to various applications of Thomson scattering x-ray source. Higher peak brightness of scattered x-ray pulse demands shorter scattering electron beam realized by beam compression in electron beam-line. In this article, we study the possibility to compress electron beam in a typical S-band normal conducting photo-injector via ballistic bunching, through just adding a short RF linac section right behind the RF gun, so as to improve peak brightness of scattered x-ray pulse. Numerical optimization by ASTRA demonstrations that peak current can increase from ~…
Recent investigations of RF copper structures operated at cryogenic temperatures performed by a SLAC-UCLA collaboration have shown a dramatic increase in the maximum surface electric field, to 500 MV/m. We examine use of these fields to enable very high field cryogenic photoinjectors that can attain over an order of magnitude increase in peak electron beam brightness. We present beam dynamics studies relevant to X-ray FEL injectors, using start-to-end simulations that show the high brightness and low emittance of this source enables operation of a compact FEL reaching a photon energy of 80 keV…
The Free-Electron Laser Laboratory at the University of Hawai`i has constructed and tested a scanning wire beam position monitor to aid the alignment and optimization of a high spectral brightness inverse-Compton scattering x-ray source. X-rays are produced by colliding the 40 MeV electron beam from a pulsed S-band linac with infrared laser pulses from a mode-locked free-electron laser driven by the same electron beam. The electron and laser beams are focused to 60 μm diameters at the interaction point to achieve high scattering efficiency. This wire-scanner allows for high resolution measurem…
We present a conceptual design for a hybrid laser-to-beam-driven plasma wakefield accelerator. In this setup, the output beams from a laser-driven plasma wakefield accelerator (LWFA) stage are used as input beams of a new beam-driven plasma accelerator (PWFA) stage. In the PWFA stage a new witness beam of largely increased quality can be produced and accelerated to higher energies. The feasibility and the potential of this concept is shown through exemplary particle-in-cell simulations. In addition, preliminary simulation results for a proof-of-concept experiment at HZDR (Germany) are shown.
CW photoinjectors operating at high accelerating gradients promise to revolutionize many areas of science and applications. They can establish the basis for a new generation of monochromatic X-ray free electron lasers, high brightness hadron beams, or a new generation of microchip production. In this letter we report on the record-performing superconducting RF electron gun with $\textrm{CsK}_{2}\textrm{Sb}$ photocathode. The gun is generating high charge electron bunches (up to 10 nC/bunch) and low transverse emittances, while operating for months with a single photocathode. This achievement o…
We consider the maximum of the Wigner distribution (WD) of synchrotron radiation (SR) fields as a possible definition of SR source brightness. Such figure of merit was originally introduced in the SR community by Kim. The brightness defined in this way is always positive and, in the geometrical optics limit, can be interpreted as maximum density of photon flux in phase space. For undulator and bending magnet radiation from a single electron, the WD function can be explicitly calculated. In the case of an electron beam with a finite emittance the brightness is given by the maximum of the convol…
The production of ultra-bright electron bunches using ionization injection triggered by two transversely colliding laser pulses inside a beam-driven plasma wake is examined via three-dimensional (3D) particle-in-cell (PIC) simulations. The relatively low intensity lasers are polarized along the wake axis and overlap with the wake for a very short time. The result is that the residual momentum of the ionized electrons in the transverse plane of the wake is much reduced and the injection is localized along the propagation axis of the wake. This minimizes both the initial 'thermal' emittance and …
Plasma photocathodes open a path towards tunable production of well-defined, compact electron beams with normalized emittance and brightness many orders of magnitude better than state-of-the-art. Such beams could have a far-reaching impact on applications such as light sources, but also open up new vistas on high energy physics and high field physics. We report on challenges and details of the proof-of-concept demonstration of a plasma photocathode in 90$^\circ$ geometry at SLAC FACET within the "E-210: Trojan Horse" program. Using this experience, alongside theoretical and simulation-supporte…
The use of existing linacs, and in particular light source injectors, for free-electron laser (FEL) experiments is becoming more common due to the desire to test FELs at ever shorter wavelengths. The high-brightness, high-current beams required by high-gain FELs impose technical specifications that most existing linacs were not designed to meet. Moreover, the need for specialized diagnostics, especially shot-to-shot data acquisition, demands substantial modification and upgrade of conventional linacs. Improvements have been made to the Advanced Photon Source (APS) injector linac in order to pr…
Presently large efforts are conducted towards the development of highly brilliant gamma beams via Compton back scattering of photons from a high-brilliance electron beam, either on the basis of a normal-conducting electron linac or a (superconducting) Energy Recovery Linac (ERL). Particularly ERL's provide an extremely brilliant electron beam, thus enabling to generate highest-quality gamma beams. A 2.5 MeV gamma beam with an envisaged intensity of 10^15 s^-1, as ultimately envisaged for an ERL-based gamma-beam facility, narrow band width (10^-3), and extremely low emittance (10^-4 mm^2 mrad^2…
In an effort to increase spatial and temporal resolution of ultrafast electron diffraction and microscopy, ultra-high brightness photocathodes are actively sought to improve electron beam quality. Beam dynamics codes often approximate the Coulomb interaction with mean-field space charge, which is a good approximation in traditional beams. However, point-to-point Coulomb effects, such as disorder induced heating and the Boersch effect, can not be neglected in cold, dense beams produced by such photocathodes. In this paper, we introduce two new numerical methods to calculate the important effect…
A design study of the diagnostics of a high brightness linac, based on X-band structures, and a plasma accelerator stage, has been delivered in the framework of the EuPRAXIA@SPARC_LAB project. In this paper, we present a conceptual design of the proposed diagnostics, using state of the art systems and new and under development devices. Single shot measurements are preferable for plasma accelerated beams, including emittance, while $μ$m level and fs scale beam size and bunch length respectively are requested. The needed to separate the driver pulse (both laser or beam) from the witness accelera…
We describe use of the Advanced Photon Source (APS) rf thermionic gun, alpha magnet beamline, and linac to produce a stable high-brightness beam in excess of 100 amperes peak current with normalized emittance of 10 pi mm-mrad. To obtain peak currents greater than 100 amperes, the rf gun system must be tuned to produce a FWHM bunch length on the order of 350 fs. Bunch lengths this short are measured using coherent transition radiation (CTR) produced when the rf gun beam, accelerated to 40 MeV, strikes a metal foil. The CTR is detected using a Golay detector attached to one arm of a Michelson in…
Producing high-brightness and high-charge (>100 pC) electron bunches at blowout regime requires ultrashort laser pulses with high fluence. The effects of laser pulse heating of the copper photocathode are analyzed in this paper. The electron and lattice temperature is calculated using an improved two-temperature model, and an extended Dowell-Schmerge model is employed to calculate the thermal emittance and quantum efficiency. A time-dependent growth of the thermal emittance and the quantum efficiency is observed. For a fixed amount of charge, the projected thermal emittance increases with decr…
In this paper we discuss the design choices and construction strategy of the tapered undulator system designed for a high energy extraction efficiency experiment in the ultraviolet region of the electromagnetic spectrum planned for installation at the Argonne National Laboratory Linac Extension Area (LEA) beamline. The undulator is comprised of 4 sections pure permanent magnet Halbach array separated by short break sections, each one of them housing a focusing quadrupole doublet and a phase shifter. The quadrupoles use a novel hybrid design which allows one to vary the gradient and match the b…
We present the application of variational-wavelet analysis to numerical/analytical calculations of Wigner functions in (nonlinear) quasiclassical beam dynamics problems. (Naive) deformation quantization and multiresolution representations are the key points. We construct the representation via multiscale expansions in generalized coherent states or high-localized nonlinear eigenmodes in the base of compactly supported wavelets and wavelet packets.
High-brightness electron beams provided by modern accelerators require several measures to preserve their high quality and to avoid instabilities. The mitigation of the impact of residual ions is one of these measures. It is particularly important if high bunch charges in combination with high repetition rates are aimed for. This is because ions can be trapped in the strong negative electrical potential of the electron beam causing emittance blow-up, increased beam halo and longitudinal and transverse instabilities. Over the last decades three ion-clearing strategies have been applied to count…
Most present and future electron accelerators require bright sources. Invented less than ten years ago, the photo-injector the principle of which is briefly recalled, has already demonstrated that it can provide very bright beams. In this paper, the most advanced photo-injector projects are reviewed, their specific features are outlined, and their major issues are examined. The state-of-the-art in photocathode and laser technologies is presented. Beam dynamics issues are also considered since they are essential in the production of bright beams. Finally, the question of the maturity of photo-i…
In this article, we share our experience related to the new photo-injector commissioning at the SPARC\_LAB test facility. The new photo-injector was installed into an existing machine and our goal was not only to improve the final beam parameters themselves but to improve the machine handling in day-to-day operations as well. Thus, besides the pure beam characterization, this article contains information about the improvements, that were introduced into the new photo-injector design from the machine maintenance point of view, and the benefits, that we gained by using the new technique to assem…
We show using particle-in-cell (PIC) simulations and theoretical analysis that a high-quality electron beam whose density is modulated at angstrom scales can be generated directly using density downramp injection in a periodically modulated density in nonlinear plasma wave wakefields. The density modulation turns on and off the injection of electrons at the period of the modulation. Due to the unique longitudinal mapping between the electrons' initial positions and their final trapped positions inside the wake, this results in an electron beam with density modulation at a wavelength orders of …
New high current accelerator facilities like proposed for HIDIF or ESS require a beam with a high brilliance. These beams can not be produced by a single pass rf-linac. The increase in brightness in such a driver linac is done by several funneling stages at low energies, in which two identically bunched ion beams are combined into a single beam with twice the frequency current and brightness. Our Two-Beam-RFQ funneling experiment is a setup of two ion sources, a two beam RFQ, a funnel deflector and beam diagnostic equipment to demonstrate funneling of ion beams as a model for the first funneli…
The development of compact accelerator facilities providing high-brightness beams is one of the most challenging tasks in field of next-generation compact and cost affordable particle accelerators, to be used in many fields for industrial, medical and research applications. The ability to shape the beam longitudinal phase-space, in particular, plays a key role to achieve high-peak brightness. Here we present a new approach that allows to tune the longitudinal phase-space of a high-brightness beam by means of a plasma wakefields. The electron beam passing through the plasma drives large wakefie…
Recent studies of the performance of radio-frequency (RF) copper cavities operated at cryogenic temperatures have shown a dramatic increase in the maximum achievable surface electric field. We propose to exploit this development to enable a new generation of photoinjectors operated at cryogenic temperatures that may attain, through enhancement of the launch field at the photocathode, a significant increase in five-dimensional electron beam brightness. We present detailed studies of the beam dynamics associated with such a system, by examining an S-band photoinjector operated at 250 MV/m peak e…
The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy…
We determine the limit of the lowest achievable photoemitted electron temperature, and therefore the maximum achievable electron brightness, due to heating just after emission into vacuum, applicable to dense relativistic or nonrelativistic photoelectron beams. This heating is due to poorly screened Coulomb interactions equivalent to disorder induced heating seen in ultracold neutral plasmas. We first show that traditional analytic methods of Coulomb collisions fail for the calculation of this strongly coupled heating. Instead, we employ an N-body tree algorithm to compute the universal scalin…
SHINE, as the first hard x-ray free-electron-laser (FEL) facility in China, is designed to provide high-brightness FEL lasing under high-repetition-rate operation mode. In order to drive x-ray FEL pulses with high qualities, the photoinjector section is deployed to provide the specified electron beam with low transverse emittance and high brightness. Normally the multi-objective optimization algorithm is employed in the injector beam dynamics design. In this paper, the many-objective optimization algorithm NSGA-III is introduced to the injector physical design for optimizing the 4 beam quality…
At EuPRAXIA@SPARC_LAB, the unique combination of an advanced high-brightness RF injector and a plasma-based accelerator will drive a new multi-disciplinary user-facility. The facility, that is currently under study at INFN-LNF Laboratories (Frascati, Italy) in synergy with the EuPRAXIA collaboration, will operate the plasma-based accelerator in the external injection configuration. Since in this configuration the stability and reproducibility of the acceleration process in the plasma stage is strongly influenced by the RF-generated electron beam, the main challenge for the RF injector design i…
High brightness, high repetition rate electron beams are key components for optimizing the performance of next generation scientific instruments, such as MHz-class X-ray Free Electron Laser (XFEL) and Ultra-fast Electron Diffraction/Microscopy (UED/UEM). In the Advanced Photo-injector EXperiment (APEX) at Berkeley Lab, a photoelectron gun based on a 185.7 MHz normal conducting re-entrant RF cavity, has been proven to be a feasible solution to provide high brightness, high repetition rate electron beam for both XFEL and UED/UEM. Based on the success of APEX, a new electron gun system, named APE…
We present the applications of variational--wavelet approach for the analytical/numerical treatment of the effects of insertion devices on beam dynamics. We investigate the dynamical models which have polynomial nonlinearities and variable coefficients. We construct the corresponding wavelet representation for wigglers and undulator magnets.
The beam parameters of complete prototype of the bERLinPro injector that consisted of a lead cathode in an 1.6 cell superconducting cavity were measured. The measurements are discussed in chapter 2 and indicate that the beam emittance is governed by a multitude of contributions from the cathode and the injector. Cathodes for practical use must have a high enough QE to deliver the required current at moderate illumination intensities and be able to sustain the operation for several days. Alkali antimonides are good candidates for this purpose, as discussed in chapter 3.2. The preparation of suc…
Particle acceleration in plasma creates a possibility of exceptionally high accelerating gradients and appears as a very attractive option for future linear electron-positron and/or photon-photon colliders. These high accelerating gradients were already demonstrated in a number of experiments. However, a linear collider requires exceptionally high beam brightness which still needs to be demonstrated. In this article we discuss major phenomena which limit the beam brightness of accelerated beam and, consequently, the collider luminosity.
Space charge is typically one of the performance limitations for the operation of high intensity and high brightness beams in circular accelerators. In the Proton Synchrotron (PS) at CERN, losses are observed for vertical tunes above $Q_y=6.25$, especially for beams with large space charge tune shift. The work presented here shows that this behaviour is associated to structure resonances excited by space charge due to the highly symmetric accelerator lattice of the PS, typical for first generation alternating gradient synchrotrons. Experimental studies demonstrate the dependency of the losses …
X-ray free-electron laser oscillator (XFELO) is expected to be a cutting edge tool for fully coherent X-ray laser generation, and undulator taper technique is well-known for considerably increasing the efficiency of free-electron lasers (FELs). In order to combine the advantages of these two schemes, FEL amplifier seeded by XFELO is proposed by simply using a chirped electron beam. With the right choice of the beam parameters, the bunch tail is within the gain bandwidth of XFELO, and lase to saturation, which will be served as a seeding for further amplification. Meanwhile, the bunch head whic…
Since the introduction of the radio-frequency (rf) photoinjector electron source over thirty years ago, peak performance demands have dictated the use of high accelerating electric fields. With recent strong advances in obtainable field values, attendant increases in beam brightness are expected to be dramatic. In this article, we examine the implementation of very high gradient acceleration in a high frequency, cryogenic rf photoinjector. We discuss in detail the effects of introducing, through an optimized rf cavity shape, rich spatial harmonic content in the accelerating modes in this devic…
Reducing the intrinsic emittance of photocathodes is one of the most promising routes to improving the brightness of electron sources. However, when emittance growth occurs during beam transport (for example, due to space-charge), it is possible that this emittance growth overwhelms the contribution of the photocathode and, thus, in this case source emittance improvements are not beneficial. Using multi-objective genetic optimization, we investigate the role intrinsic emittance plays in determining the final emittance of several space-charge dominated photoinjectors, including those for high r…
Large area carbon nanotube (CNT) cathodes made from yarns, films or fibers have long been promising as next generation electron sources for high power radio frequency (rf) and microwave vacuum electronic devices. However, experimental evidence have been pointing out spatial incoherence of the electron beam produced by such cathodes that, in turn, impeded the progress toward high brightness CNT electron sources and their practical applications. Indeed, typically large area CNT fibers, films or textiles emit stochastically across their physical surface at large emission angles and with large tra…
Measurements of transverse profiles using Ionization Profile Monitors (IPMs) for high brightness beams are affected by the electromagnetic field of the beam. This interaction may cause a distortion of the measured profile shape despite strong external magnetic field applied to impose limits on the transverse movement of electrons. The mechanisms leading to this distortion are discussed in detail. The distortion itself is described by means of analytic calculations for simplified beam distributions and a full simulation model for realistic distributions. Simple relation for minimum magnetic fie…
The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamic code is developed based on a Lagrangian method for the calculation of the particles' radiation near-fields using wavefront/wavelet me…
We have developed an efficacious algorithm for simulation of the beam-beam interaction in synchrotron colliders based on the nonlinear $δf$ method, where $δf$ is the much smaller deviation of the beam distribution from the slowly evolving main distribution $f_0$. In the presence of damping and quantum fluctuations of synchrotron radiation it has been shown that the slowly evolving part of the distribution function satisfies a Fokker-Planck equation. Its solution has been obtained in terms of a beam envelope function and an amplitude of the distribution, which satisfy a coupled system of ordina…
We consider modeling for strong-strong beam-beam interactions beyond preceding linearized/perturbative methods such as soft gaussian approximation or FMM (HFMM) etc. In our approach discrete coherent modes, discovered before, and possible incoherent oscillations appear as a result of multiresolution/multiscale fast convergent decomposition in the bases of high-localized exact nonlinear modes represented by wavelets or wavelet packets functions. The constructed solutions represent the full multiscale spectrum in all internal hidden scales from slow to fast oscillating eigenmodes. Underlying var…
In recent years, intense efforts have been devoted to studying how nonlinear effects can be used to shape the transverse beam distribution by means of an adiabatic crossing of nonlinear resonances. By this approach, it is possible to split the beams in the transverse plane, so that the initial single-Gaussian beam is divided into several distinct distributions. This is at the heart of the multiturn extraction process that is successfully in operation at the CERN Proton Synchrotron. Nonlinear effects can also be used to cool a beam by acting on its transverse beam distribution. In this paper, w…
Photoinjectors are the main high brightness electron sources for X-ray free electron lasers (XFEL). Photoinjector emittance reduction is one of the key knobs for improving XFEL lasing, so precise emittance measurement is critical. It's well known that rms emittance is very sensitive to low intensity tails of particle distributions in the phase space, whose measurement depend on the signal to noise ratio (SNR) and image processing procedures. Such sensitivities make the interpretations of beam transverse brightness challenging, leading to different emittance definitions to reduce the impact of …
An intense non-uniform particle beam exhibits strong emittance growth and halo formation in focusing channels due to nonlinear space charge forces of the beam. This phenomenon limits beam brightness and results in particle losses. The problem is connected with irreversible distortion of phase space volume of the beam in conventional focusing structures due to filamentation in phase space. Emittance growth is accompanied by halo formation in real space, which results in inevitable particle losses. A new approach for solving a self-consistent problem for a matched non-uniform beam in two-dimensi…
We propose a new method for self-injection of high-quality electron bunches in the plasma wakefield structure in the blowout regime utilizing a "flying focus" produced by a drive beam with an energy chirp. In a flying focus the speed of the density centroid of the drive bunch can be superluminal or subluminal by utilizing the chromatic dependence of the focusing optics. We first derive the focal velocity and the characteristic length of the focal spot in terms of the focal length and an energy chirp. We then demonstrate using multidimensional particle-in-cell simulations that a wake driven by …
This paper presents X-ray spectra of channeling radiation (CR) expected at the FAST (Fermi Accelerator Science and Technology) facility in Fermilab. Our purpose is to produce high brightness quasi-monochromatic X-rays in an energy range from 40 keV to 110 keV. We will use a diamond crystal and low emittance electrons with an energy of around 43 MeV. The quality of emitted X-rays strongly depends on parameters of the electron beam at the crystal. We present simulations of the beam optics for high brightness and high yield operations with bunch charges of 1 pC, 20 pC, and 200 pC. We estimate the…
We present a clear signature of the Schottky effect in a RF photoinjector using photons with energy lower than the Mg cathode work function. This signature is manifested by the shift in the RF phase angle for the onset of the detection of photoelectrons via single-photon absorption and allows for a reasonable estimate of the field enhancement factor. This is a viable method to generate an electron beam with very low thermal emittance and thus, a high brightness beam.
