Laser-plasma accelerators are expected to deliver electron bunches with high space charge fields. Several recent publications have addressed the impact of space charge effects on such bunches after the extraction into vacuum. Artifacts due to the approximation of retardation effects are addressed, which are typically either neglected or approximated. We discuss a much more appropriate calculation for the case of laser wakefield acceleration with negligible retardation artifacts due to the calculation performed in the mean rest frame. This presented calculation approach also aims at a validation of other simulation approaches.
An all-optical method of ultrafast spin rotation is put forward to precisely manipulate the polarization of relativistic charged particle beams of leptons or ions. In particular, laser-driven dense ultrashort beams are manipulated via single-shot interaction with a co-propagating moderate temporally asymmetric (frequency-chirped or subcycle THz) laser pulse. Using semi-classical numerical simulations, we find that in a temporally asymmetrical laser field, the spin rotation of a particle can be determined from the flexibly controllable phase retardation between its spin precession and momentum …
During low-energy operations below the regular injection energy in the Relativistic Heavy Ion Collider (RHIC), significant beam lifetime reductions due to the beam-beam interaction in conjunction with large space charge tune shifts have been observed. We report on dedicated experiments aimed at understanding this phenomenon as well as preliminary simulation results, and propose alternative working points to improve the beam lifetime in future lowenergy RHIC runs.
The RAON, a superconducting linear accelerator for RISP (Rare Isotope Science Project), will use a charge stripper in order to increase the charge states of the heavy ions for effective acceleration in the higher energy part of the linac. The charge stripper affects the beam qualities by scattering when the heavy ions go through the charge stripper. Moreover we have to select and accelerate proper charge states between 77+ and 81+ for uranium beam case in order to satisfy the beam power requirement at an IF (Inflight Fragmentation) target. This work focuses on the beam optics affected by the c…
Beam-beam interactions and space-charge effects belong to the category of the most long-standing issues in beam physics, and even today, after several decades of very active exploration and development of counter-measures, they still pose the most profound limitations on performance of accelerator facilities. In this brief review we consider past experience in active compensation of these effects and possible new schemes for further exploration in near-future, in particular, within the framework of the electron-ion collider R&D.
The SPIRAL1 charge breeder is now under operation. Radioactive beam has already been delivered [1] to Physicist for performing experiment. Although charge breeding efficiencies demonstrated high performances for stable ion beams, those efficiencies regarding radioactive ion beams were found, in the first experiments, lower than expected. The beam optics, prior to the injection of the 1+ ions into the SPIRAL1 charge breeder, is of prime importance [2] for getting such high efficiencies. Moreover, the intensities of the radioactive ion beams are so low, that it is really difficult to tune the ch…
A test of the acceleration of multiple charge-state uranium beams was performed at the ATLAS accelerator. A 238U+26 beam was accelerated in the ATLAS PII linac to 286 MeV (~1.2 MeV/u) and stripped in a carbon foil located 0.5 m from the entrance of the ATLAS Booster section. A 58Ni9+ 'guide' beam from the tandem injector was used to tune the Booster for 238U+38. All charge states from the stripping were injected into the booster and accelerated. Up to 94% of the beam was accelerated through the Booster linac, with losses mostly in the lower charge states. The measured beam properties of each c…
Transverse beam stability is strongly affected by the beam space charge. Usually it is analyzed with the rigid-beam model. However this model is only valid when a bare (not affected by the space charge) tune spread is small compared to the space charge tune shift. This condition specifies a relatively small area of parameters which, however, is the most interesting for practical applications. The Landau damping rate and the beam Schottky spectra are computed assuming that validity condition is satisfied. The results are applied to a round Gaussian beam. The stability thresholds are described b…
This paper studies the space charge impedances of a rectangular beam inside a rectangular chamber, and the limiting case, e.g., a rectangular beam between parallel plates, respectively. The charged beam has uniform density in vertical direction and arbitrary distribution in horizontal direction. The method of separation of variables is used to calculate the space charge potentials, fields, and impedances which are valid in the whole perturbation wavelength spectrum. Comparisons between the theoretical calculations and the numerical simulations are also provided and they match quite well. It is…
This paper analyzes the longitudinal space charge (LSC) impedances of a round uniform beam inside a rectangular and parallel plate chambers using the image charge method. This analysis is valid for arbitrary wavelengths and the calculation converges fast. The research shows that only a few of the image beams are needed to obtain a relative error less than 0.1%. The beam offset effect is also discussed in the analysis.
In its normal mode of operation the Argonne Wakefield Accelerator Facility uses a high charge (10-100 nC), short pulse (3-5 psec) drive bunch to excite high-gradient accelerating fields in various slow-wave structures. To generate this bunch, we designed a 1.5 cell, L-band, rf photocathode gun with an emittance compensating solenoid to give optimal performance at high-charge; it has recently completed commissioning. More recently, we have begun to investigate the possibility of using this gun in a high-brightness, low-charge operating mode, with charge equal to approximately 1 nC, for high-pre…
Progress on the Intensity Frontier of high energy physics critically depends on record high intensity charged particles accelerators. Beams in such machines become operationally limited by coherent beam instabilities, particularly enhanced in the regime of strong space charge (SC). Usual methods to control the instabilities, such as octupole magnets, beam feedback dampers and employment of chromatic effects, become less effective and insufficient. In [1] it was proposed to employ electron lenses for introduction of sufficient spread in particle oscillation frequencies needed for beam stabiliza…
The University of Maryland Electron Ring (UMER) has operated traditionally in the regime of strong space-charge dominated beam transport, but small-current beams are desirable to significantly reduce the direct (incoherent) space-charge tune shift as well as the tune depression. This regime is of interest to model space-charge effects in large proton and ion rings similar to those used in nuclear physics and spallation neutron sources, and also for nonlinear dynamics studies of lattices inspired on the Integrable Optics Test Accelerator (IOTA). We review the definition of space-charge intensit…
For booster synchrotrons, like the SIS at GSI, space charge is one of the main intensity limitations. At injection energy the space charge induced tune spreads in booster synchrotrons are large, reaching up to 0.5 and the ramping times are typically short. We study the effect of several localized electron lenses distributed equally around the circumference in order to compensate for the transverse space charge force.
This paper presents the approximate analytical solutions to the longitudinal space charge (LSC) impedances of a round beam with uniform transverse distribution and sinusoidal line density modulations under two boundary conditions: (a) between parallel plates (b) inside a rectangular chamber, respectively. When the ratio of beam diameter to chamber height is small, the image charge fields of the round beam can be approximated by those of a line charge, the approximate analytical LSC impedances can be obtained by image method. The derived theoretical LSC impedances are valid at any perturbation …
We present the results of transverse emittance and longitudinal current profile measurements of high bunch charge (greater than or equal to 100 pC) beams produced in the DC gun-based Cornell Energy Recovery Linac Photoinjector. In particular, we show that the cathode thermal and core beam emittances dominate the final 95% and core emittance measured at 9-9.5 MeV. Additionally, we demonstrate excellent agreement between optimized 3D space charge simulations and measurement, and show that the quality of the transverse laser distribution limits the optimal simulated and measured emittances. These…
Transverse instability of a bunched beam is investigated with synchrotron oscillations, space charge, and resistive wall wakefield taken into account. Boxcar model is used for all-round analysis, and Gaussian distribution is invoked for details. The beam spectrum, instability growth rate and effects of chromaticity are studied in a wide range of parameters, both with head-tail and collective bunch interactions included. Effects of the internal bunch oscillations on the of collective instabilities is investigated thoroughly. Landau damping caused by the space charge tune spread is discussed, an…
Space charge effects play significant role in modern-day accelerators. These effects frequently constrain attainable beam parameters in an accelerator - or - in an accelerator chain. They also could limit the luminosity of hadron colliders operating either at low energies or with a sub-TeV high brightness hadron beams. A number of schemes for compensating space charge effects in a coasting (e.g. continuous) hadron beam were proposed and some of them had been tested. But all of these methods do not address the issue of tune spread compensation of a bunched hadron beam, e.g. the tune shift depen…
We developed an exact analytical treatment for space-charge waves within a relativistic electron beam in terms of (self-reproducing) propagating eigenmodes. This result is of obvious theoretical relevance as it constitutes one of the few exact solution for the evolution of charged particles under the action of self-interactions. It also has clear numerical applications in particle accelerator physics where it can be used as the first self-consistent benchmark for space-charge simulation programs. Today our work is of practical relevance in FEL technology in relation with all those schemes wher…
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…
There is demand for the construction of a medium-energy ion linear accelerator based on superconducting rf (SRF) technology. It must be capable of producing several hundred kilowatts of CW beams ranging from protons to uranium. A considerable amount of power is required in order to generate intense beams of rare isotopes for subsequent acceleration. At present, however, the beam power available for the heavier ions would be limited by ion source performance. To overcome this limit, we have studied the possibility of accelerating multiple-charge-state (multi-Q) beams through a linac. We show th…
Electric current fluctuations are one type of unavoidable machine imperfections,and induce magnetic-field perturbations as a source of instabilities in accelerators. This paper presents measurement-based methodology of modeling the fluctuating electric current arising from the power system of Fermilab's Booster synchrotron to discuss the ramifications of the presence of ripple current and space-charge defocusing effects. We also present the method of generating stochastic noise and the measurement and analysis methods of ripple current and offending electromagnetic interferences residing in th…
The formation of beam halos has customarily been described in terms of a particle-core model in which the space-charge field of the oscillating core drives particles to large amplitudes. This model involves parametric resonance and predicts a hard upper bound to the orbital amplitude of the halo particles. We show that the presence of colored noise due to space-charge fluctuations and/or machine imperfections can eject particles to much larger amplitudes than would be inferred from parametric resonance alone.
Flat-beam transforms (FBTs) provide a technique for controlling the emittance partitioning between the beam's two transverse dimensions. To date, nearly all FBT studies have been in regimes where the beam's own space-charge effects can be ignored, such as in applications with high-brightness electron linacs where the transform occurs at high, relativistic, energies. Additionally, FBTs may provide a revolutionary path to high power generation at high frequencies in vacuum electron devices where the beam emittance is currently becoming a limiting factor, which is the focus of this paper. Electro…
Electron-cooling offers a relatively simple scheme to enable high-luminosity collisions in future electron-ion and hadron colliders. Contemplated TeV-energy hadron colliders require relativistic (sub 100 MeV) high-charge [${\cal O}(\mbox{nC})$] electron beams with a specific transverse eigenemittance partition. This paper discusses the generation of high-charge ($Q\le 3.2$~nC) 40 MeV electron bunches with eigenemittance partition consistent with requirements associated with electron-cooling option for future electron-ion colliders. The supporting experiment was performed at the FAST facility a…
Electron cooling as a method of creating intense ion beams has a practical upper limit when it comes to the peak phase space density of ion beams which can be achieved in practice. We describe a new experiment to study electron cooling of 2.5 MeV protons at the intensity limit using the Integrable Optics Test Accelerator (IOTA), which is a storage ring dedicated to beam physics research at Fermilab. This system will enable the study of magnetized electron cooling of a proton beam with transverse incoherent tune shifts approaching -0.5 due to the presence of intense space-charge forces. We pres…
Asymmetrical Alternate Phase (A-APF) focusing realized in a sequence of 36 Superconducting Quarter Wave Resonators has been shown to accelerate almost 81 % of input Uranium beam before foil stripper to an energy of 6.2 MeV/u from 1.3 MeV/u. Ten charge states from 34+ to 43+ could be simultaneously accelerated with the phase of resonators tuned for 34+. A-APF structure showed unique nature of large potential bucket for charge states higher than that of tuned one. Steering inherent to QWRs can be mitigated by selecting appropriate phase variation of the APF periods and optimization of solenoid f…
For modern high-intensity linear accelerators, the well-known envelope instability and recently reported fourth-order particle resonance impose a fundamental operational limit (i.e., zero-current phase advance should be less than 90 deg). Motivated by the stability of spinning flying objects, we propose a novel approach of using spinning beams to surpass this limit. We discovered that spinning beams have an intrinsic characteristic that can suppress the impact of the fourth-order resonance on emittance growth and the associated envelope instability.
The resonant laser cooling of circular accelerator beams of relativistic charged particle is studied. It is shown that in the approximation of the given external electromagnetic wave amplitude (small gain free electron laser) the emittance of a beam of charged particles decreases. In the field of particle energy about 100 in the mass energy units the beam energy losses are negligible. The discovered effect can be used for cooling of charged particle beams in various accelerators. The significant cooling rates are possible to achieve by placing of the cooling device in the appropriate points of…
The energy recovery linac test facility (ERL-TF), a compact ERL-FEL (free electron laser) two-purpose machine, was proposed at the Institute of High Energy Physics, Beijing. As one important component of the ERL-TF, the photo-injector started with a photocathode direct-current gun has been designed. In this paper optimization of the injector beam dynamics in low-charge operation mode is performed with iterative scans using Impact-T. In addition, the dependencies between the optimized beam quality and the initial offset at cathode and element parameters are investigated. The tolerance of alignm…
The GSI Unilac was upgraded as a high current injector for the SIS in 1999. Therefore, the stripping section [1] at 1.4 MeV/u, where a beam transport under highest space charge conditions and multi beam operation had to be established, was completely new designed. Results of the commissioning of the stripper section will be presented. The beam transport to the new gas stripper, and the charge state analysis under space charge conditions confirmed the calculations. A 238U4+ beam - coming from a MEVVA ion source and accelerated by the new injector linac- was stripped (with the expected stripping…
A detailed experimental and simulation study of the extraction of a 24 keV He-ion beam from an ECR ion source and the subsequent beam transport through an analyzing magnet is presented. We find that such a slow ion beam is very sensitive to space-charge forces, but also that the neutralization of the beam's space charge by secondary electrons is virtually complete for beam currents up to at least 0.5 mA. The beam emittance directly behind the extraction system is 65 pi mm mrad and is determined by the fact that the ion beam is extracted in the strong magnetic fringe field of the ion source. Th…
We developed a model to calculate the stability of Gaussian beam distributions with non-linear space-charge forces in the presence of random and skew-quadrupole errors. The effect of the space-charge force on the beam matrix is calculated analytically including full cross-plane coupling in 4D phase space, which allows us to perform fast parameter studies. For stability analysis, we find the fixed points of the beam including the space-charge forces and construct a Jacobi-matrix by slightly perturbing the periodic solution. The stability of envelope oscillations is inferred by eigenvalue analys…
An electron lens is planned for the Fermilab Integrable Optics Test Accelerator as a nonlinear element for integrable dynamics, as an electron cooler, and as an electron trap to study space-charge compensation in rings. We present the main design principles and constraints for nonlinear integrable optics. A magnetic configuration of the solenoids and of the toroidal section is laid out. Single-particle tracking is used to optimize the electron path. Electron beam dynamics at high intensity is calculated with a particle-in-cell code to estimate current limits, profile distortions, and the effec…
Laser-assisted stripping is a novel approach to H- charge exchange that overcomes long-standing limitations associated with the traditional, foil-based method of producing high-intensity, time-structured beams of protons. This paper reports on the first successful demonstration of the laser stripping technique for microsecond duration beams. The experiment represents a factor of 1000 increase in the stripped pulse duration compared with the previous proof-of-principle demonstration. The central theme of the experiment is the implementation of methods to reduce the required average laser power …
In work is considered average transverse dynamics of an electron beam in the autoresonant laser. It is shown, that in approach of the given external electromagnetic wave (small gain free electron laser) transverse emittance of a beam of the charged particles decreases. This for the first time found out effect can be used for cooling beams of various accelerators of the charged particles. In the field of particle energy about 100 in the mass energy units, beam energy losses are negligible. This method of charge beams cooling may be applied to electron, muon and various heavy particle beams.
We develop a universal framework which allows quickly solve a wide class of problems for longitudinal space charge effects in beams and plasmas in cylindrical geometry. We introduce the longitudinal dielectric permittivity for the beam of charged particles, which describes its collective space charge response. The analyis yields an effective plasma frequency, which depends on the transverse geometry of the system. This dielectric permittivity mirrors the dielectric permittivity of plasma and matches the one dimensional (1D) expression once the transverse size of the beam is large. Several part…
To achieve high focal spot intensities in heavy ion fusion, the ion beam must be compressed longitudinally by factors of ten to one hundred before it is focused onto the target. The longitudinal compression is achieved by imposing an initial velocity profile tilt on the drifting beam. In this paper, the problem of longitudinal drift compression of intense charged particle beams is solved analytically for the two important cases corresponding to a cold beam, and a pressure-dominated beam, using a one-dimensional warm-fluid model describing the longitudinal beam dynamics.
Laser accelerators can provide proton beams with unique qualities, such as micron size, picosecond pulse duration and high peak current, and have been demonstrated for various applications and for scientific research purposes. The effect of the space charge force in high peak current beams is strong and raises challenges for application after beam transportation. We performed two-dimensional particle-in-cell simulations and studied the influence of electrons that have velocities close to that of the protons after laser acceleration. We employed ellipsoid models with different charge distributi…
The effect of conducting pipes on the equilibrium of intense nonaxisymmetric continuous beams of charged particles is investigated. For a cylindrical pipe and an elliptical beam, we obtain an exact closed form analytical expression for the electrostatic potential. Using a variational principle, we then explore the distortions that equilibrium beams suffer due to the conducting channel. Finally, we present an exact proof that despite the nonlinear forces acting on beams of arbitrary cross section inside conducting pipes of arbitrary shape, the density of these beams remains homogeneous and thei…
There has been much interest in the blowout regime of plasma wakefield acceleration (PWFA), which features ultra-high fields and nonlinear plasma motion. Using an exact analysis, we examine here a fundamental limit of nonlinear PWFA excitation, by an infinitesimally short, relativistic electron beam. The beam energy loss in this case is shown to be linear in charge even for nonlinear plasma response, where a normalized, unitless charge exceeds unity. The physical basis for this effect is discussed, as are deviations from linear behavior observed in simulations with finite length beams.
A process of energy transfer is demonstrated in non-equilibrium charged particle beams with anisotropy and space charge. Equipartitioning of energy between available degrees of freedom occurs in just a few betatron wavelengths, without halo formation. Collective space charge modes similar to those observed in recent experiments provide the underlying coupling mechanism. Since laboratory beams are commonly far from equilibrium, the traditional K-V stability analysis does not necessarily apply, implying that selection of an operating point based on theory does not necessarily avoid equipartition…
Breaking of a plasma wave driven by a long beam of charged particles results in electron jets escaping from the plasma column and forming an electron halo. For plasma densities less than or of the order of the beam density, this process is well described by a semi-analytical model, which agrees with simulations and allows to calculate the position of wavebreaking points and determine the regions around the plasma column occupied by the halo.
Electromagnetic fields induced by the space charge in relativistic beams play an important role in Accelerator Physics. They lead to emittance growth, slice energy change, and the microbunching instability. Typically, these effects are modeled numerically since simple description exists only in the limits of large- or small-scale current variations. In this paper we consider an axially symmetric charged beam inside a round pipe and find the solution of the space charge problem that is valid in the full range of current variations. We express the solution for the field components in terms of Gr…
Longitudinal charge profile measurements or bunch shape measurements is a challenge for temporally short non-relativistic bunches. The field profile has a larger longitudinal extent compared to the charge profile for such beams. This affects the ability of field sensing devices such as phase pick-ups or wall current monitors to measure charge distribution. Here we evaluate the feasibility for usage of coherent transition and diffraction radiation from non-relativistic beams for bunch shape measurements.
Laser-driven Plasma Accelerators (LPA) have successfully generated high energy, high charge electron bunches which can reach many kA peak current, over short distances. Space charge issues, even in transport lines as simple as a drift section, have to be carefully taken into account since they can degrade the beam quality, preventing any further application of such electron beams. We analyse the space charge effects within an electron bunch with numerical simulations in order to assess their effect on the beam. We use LPA beam parameters published in previous experimental studies. These studie…
Design of a Storage Ring based on a Fixed Field Alternating Gradient Configuration with an Internal Target for Heavy-Ion Beams with Stochastic Charge State Conversions
Institute for Integrated Radiation and Nuclear Science, Kyoto University（京都大学辐射核科学综合研究所）；Advanced Science Research Center, Japan Atomic Energy Agency（日本原子能研究机构先进科学研究中心）
In the present paper we study the role of particle interactions on the evolution of a high energy beam. The interparticle forces taken into account are due to space charge alone. We derive the collision integral for a charged particle beam in the form of Balescu-Lenard and Landau and consider its further simplifications. Finally, the transition to the generalized kinetic equation has been accomplished by using the method of adiabatic elimination of fast variables.
Within the framework of the thermal wave model, an investigation is made of the longitudinal dynamics of high energy charged particle beams. The model includes the self-consistent interaction between the beam and its surroundings in terms of a nonlinear coupling impedance, and when resistive as well as reactive parts are included, the evolution equation becomes a generalised nonlinear Schroedinger equation including a nonlocal nonlinear term. The consequences of the resistive part on the propagation of particle bunches are examined using analytical as well as numerical methods.
A new method able to transport charged particle beams along curved paths is presented. It is based on curved capillary-discharge waveguides in which the induced azimuthal magnetic field is used both to focus the beam and keep it close to the capillary axis. We show that such a solution is highly tunable, it allows to develop compact structures providing large deflecting angles and, unlike conventional solutions based on bending magnets, preserves the beam longitudinal phase space. The latter feature, in particular, is very promising when dealing with ultra-short bunches for which non-trivial m…
We have developed and tested a direct-sampling RF receiver capable of measuring the amplitude of a 1497 MHz sinusoidal signal in 0.5 ms integration windows to within <10 ppm relative uncertainty. The receiver is intended for measuring signals from beam current monitoring cavities on the beamline of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory. The signal strength, frequency, and integration window are consistent with the thus far unmet requirements of the upcoming MOLLER experiment to measure the beam charge for different helicity states.
Space charge effects can be very important for the dynamics of intense particle beams, as they repeatedly pass through nonlinear focusing elements, aiming to maximize the beam's luminosity properties in the storage rings of a high energy accelerator. In the case of hadron beams, whose charge distribution can be considered as "frozen" within a cylindrical core of small radius compared to the beam's dynamical aperture, analytical formulas have been recently derived \cite{BenTurc} for the contribution of space charges within first order Hamiltonian perturbation theory. These formulas involve dist…
A hydrodynamical description of coherent instabilities that take place in the longitudinal dynamics of a charged-particle coasting beam in a high-energy accelerating machine is presented. This is done in the framework of the Madelung fluid picture provided by the Thermal Wave Model. The well known coherent instability charts in the complex plane of the longitudinal coupling impedance for monochromatic beams are recovered. The results are also interpreted in terms of the deterministic approach to modulational instability analysis usually given for monochromatic large amplitude wave train propag…
