Wakefield Effects Research Articles

Strong–strong simulations of combined beam–beam and wakefield effects in the Electron–Ion-Collider

Collective wakefield and beam–beam effects play an important role in accelerator design and operation. These effects can cause beam instability, emittance growth, and luminosity degradation, and warrant careful study during accelerator design. In this paper, we studied the combined wakefield and beam–beam effects in an Electron Ion Collider design using strong–strong simulations. The simulation results show that the nonlinear beam–beam effects help suppress wakefield driven instability in the nominal working tune regime. In other tune regimes, the coherent beam–beam modes interact with the wakefields and cause a beam instability. The simulation results also show the importance of maintaining nominal crab cavity voltage. If the crab cavity voltage drops significantly the beam can become unstable.

Experimental Observation of Space-Charge Field Screening of a Relativistic Particle Bunch in Plasma.

The space-charge field of a relativistic charged bunch propagating in plasma is screened due to the presence of mobile charge carriers. We experimentally investigate such screening by measuring the effect of dielectric wakefields driven by the bunch in a uncoated dielectric capillary where the plasma is confined. We show that the plasma screens the space-charge field and therefore suppresses the dielectric wakefields when the distance between the bunch and the dielectric surface is much larger than the plasma skin depth. Before full screening is reached, the effects of dielectric and plasma wakefields are present simultaneously.

Laser Wakefield Effect: A Comparative Study of Gaussian and Sinh-Gaussian Pulse Characteristics

Laser Wakefield Effect: A Comparative Study of Gaussian and Sinh-Gaussian Pulse Characteristics

Manipulation and Wakefield Effects on Multi-Pulse Driver Beams in PWFA Injector Stages

Particle-driven plasma wakefield acceleration (PWFA) exploits the intense wakefields excited in a plasma by a high-brightness driver beam in order to accelerate a trailing, properly delayed witness electron beam. Such a configuration offers notable advantages in achieving very large accelerating gradients that are suitable for applications in particle colliders and photon production. Moreover, the amplitude of the accelerating fields can be enhanced by resonantly exciting the plasma using a multi-pulse driver beam with a proper time structure. Before the injection into the plasma stage, the pulsed electron beam, conventionally termed the comb beam, is usually produced and pre-accelerated in a radio-frequency (RF) linear accelerator (linac). In this pape, we discuss challenging aspects of the dynamics that comb beams encounter in the RF injector stage preceding the plasma. In particular, the examples we analyze focus on the use of velocity bunching to manipulate the time structure of the beam and the impact of dipole short-range wakefields on the transverse emittances. Indeed, both processes crucially affect the phase space distribution and its quality, which are determinant features for an efficient acceleration in the plasma. In addition, the analyses we present are performed with the custom tracking code MILES, which utilizes semi-analytical models for a simplified evaluation of wakefield effects in the presence of space charge forces.

Evaluation of beam coupling impedance by generating a dedicated database in an ultra-low emittance storage ring

The evaluation and accurate understanding of the cause of collective effects and the related instabilities using corrective measures, which may limit the achievable current per bunch, is significant for a prosperous design of charged particle accelerators. We describe in detail two dominant collective effects, i.e. space-charge and wakefield effects for a multi-bend achromat (MBA) storage ring lattice under design. We have developed a detailed impedance model, which is used to study the beam dynamics, including the wakefield effects. The beam coupling impedances due to the wakefields were calculated to construct a coupling impedance database, with the wakefields of each vacuum component being maintained in a standard format. The Self-Describing Data Sets (SDDS) toolkit was used to calculate the wake potentials for all coupling impedance contributing vacuum components, to be used for an ultra-low emittance lattice design. The ELEGANT code was utilized for the particle tracking in an element-by-element procedure along the lattice. A bunch with the Gaussian distribution was assumed to calculate the model for a distributed resistive-wall impedance and the impedance generated by geometrical discontinuities for the various accelerator elements. Moreover, we evaluated the potential-well distortion effect due to longitudinal phase space motion for a system of electron bunches. The collective effects in multi-particle systems have been evaluated for the estimation of the beam instability with more accurate results, defined by their sources in the designed lattice and describing their effects on beam instabilities with remarkable consequences like energy loss and betatron tune shift.

Advanced Studies for the Dynamics of High Brightness Electron Beams with the Code MILES

High brightness electron beams enable a wide spectrum of applications ranging from short wavelength radiation sources to high gradient wakefield acceleration. The rich dynamics that are intrinsic in charged particles accelerated in complex systems require a careful description in the analysis and design of a given machine, particularly regarding its stability. Numerous computer codes are in use by the accelerator community for such purposes. In particular, MILES is a simple tracking code we have developed that allows fast evaluations of collective effects in RF linacs. In this paper we extend the simple models previously developed to describe specific, diverse applications that can benefit from the fast simulation tools developed in MILES. Examples of this kind include particle driven acceleration schemes in a plasma where driver and witness beams propagate in the “comb” pulse-train configuration. Specifically, we investigate the self-induced fields excited within the X-band rf-linac stage of EuPRAXIA@SPARC_LAB. Further, we discuss additional advanced topics such as resistive wall wakefield effects in planar FEL undulators and their impact on the radiation emitted.

Effect of a Wake-Field on the Dissociation of Quarkonium in Collisional Quark–Gluon Plasma

We have studied wake effects on the dissociation of heavy quarkonia states J/ψ and Y by introducing an in-medium modification to the inter-quark potential. The wakes in the quark–gluon plasma were modeled using linear response theory using a dynamic dielectric function obtained from kinetic theory (Boltzmann equation) with a Bhatnagar–Gross–Krook (BGK) collision term. The in-medium modified potential was used to investigate the dissociation character depending on various parameters such as the velocity of quarkonium moving through the medium and the collision frequency. We have also calculated critical values of the dissociation temperature. Modifications of the dissociation energy due to wake-field effects were found.

Study on the influence of shaft brackets on the scale effect of the four-screw ship wake field

In the four-screw ship navigation, the load difference between the inner and outer propeller is found to be more than twice of that in the model test, indicating a serious scale effect. The stern attachment of the four-screw ship has a significant impact on the inner and outer propeller wake which directly affecting the load distribution. Thus, to investigate the impact of the brackets on the scale effect of the four-screw ship flow field, this paper conducted multi-scale simulations of a four-screw ship with and without bracket using the Reynolds-averaged Navier-Stokes (RANS) method. The feasibility and accuracy of the numerical method was verified by comparing with PIV test results. The result shows that the scale effect is more pronounced in the outer propeller compared to the inner propeller. The presence of bracket reduces the wake fraction difference between the inner and outer propellers, but significantly affects the inner radius region of the outer propeller disk, more than doubling the wake fraction in this region at full-scale. When the bracket Reynolds number falls below its critical Reynolds number, the inner radius region of the outer propeller flow field deviates notably from the full-scale results and loses its practical significance.

Status and future plans for C3 R&D

C3 is an opportunity to realize an e + e - collider for the study of the Higgs boson at √s = 250 GeV, with a well defined upgrade path to 550 GeV while staying on the same short facility footprint [2,3]. C3 is based on a fundamentally new approach to normal conducting linear accelerators that achieves both high gradient and high efficiency at relatively low cost. Given the advanced state of linear collider designs, the key system that requires technical maturation for C3 is the main linac. This paper presents the staged approach towards a facility to demonstrate C3 technology with both Direct (source and main linac) and Parallel (beam delivery, damping ring, ancillary component) R&D.The primary goal of the C3 Demonstration R&D Plan is to reduce technical and cost risk by building and operating the key components of C3 at an adequate scale. This R&D plan starts with the engineering design, and demonstration of one cryomodule and will culminate in the construction of a 3 cryomodule linac with pre-production prototypes. This R&D program would also demonstrate the linac rf fundamentals including achievable gradient and gradient stability over a full electron bunch train and breakdown rates. It will also investigate beam dynamics including energy spread, wakefields, and emittance growth. This work will be critical to confirm the suitability of the C3 beam parameters for the physics reach and detector performance in preparation for a Conceptual Design Report (CDR), as well as for follow-on technology development and industrialization.The C3 Demonstration R&D Plan will open up significant new scientific and technical opportunities based on development of high-gradient and high-efficiency accelerator technology. It will push this technology to operate both at the GeV scale and mature the technology to be reliable and provide high-brightness electron beams.The timeline for progressing with C3 technology development will be governed by practical limitations on both the technical progress and resource availability. It consists of four stages: Stage 0) Ongoing fundamental R&D on structure prototypes, damping and vibrations. Stage 1) Advancing the engineering maturity of the design and developing start-to-end simulations including space-charge and wakefield effects. This stage will include testing of strucutres operating at cryogenic temperatures. Beam tests would be performed with high beam current to test full beam loading. Stage 2) Production and testing of the first cryomodule at cryogenic temperatures. This would provide sufficient experimental data to compile a CDR and it is anticipated for Stage 2 to last 3 years and to culminate with the transport of photo-electrons through the first cryomodule. Stage 3) Updates to the engineering design of the cryomodules, production of the second and third cryomodule and their installation. Lower charge and lower emittance beams will be used to investigate emittance growth. The successful full demonstration of the 3 cryomodules to deliver up to a 3 GeV beam and achieve the C3five gradient will allow a comprehensive and robust evaluation of the technical design of C3 as well as mitigate technical, schedule, and cost risks required to proceed with a Technical Design Report (TDR).

Fast models for the evaluation of self-induced field effects in linear accelerators

Advanced applications of modern linear accelerators (linacs) strongly rely on the quality of the particle beams produced by such machines. Key examples of this kind include particle-driven radiation sources, plasma wakefield acceleration and lepton colliders for high energy physics. Such systems require use of high brightness electron beams implying the simultaneous coexistence of high peak currents, small transverse emittances and narrow energy spectra. The associated high phase space density results in strong self-induced electromagnetic fields, causing mutual interaction of the charged particles through space-charge and wakefield forces. These two sources of collective effects may be both present at significant levels, along with the strong applied fields, both longitudinal and transverse, found in high gradient linacs. As a result, beam dynamics studies capable of investigating the performance of a given device, as well as its operational limits, are crucial. However, the modeling of collective effects in simulation codes tracking large particle ensembles often requires significant, time-intensive numerical resources. In this paper we thus present alternative, simplified approaches for the description of space-charge and wakefield effects that permit streamlined computations. The features of such models are discussed, including their limitations and validating comparisons with existing tracking codes that utilize standard but more time-consuming approaches are shown. The beamlines we consider in our analyses are part of state-of-the-art facilities now under design for which new, challenging beam physics properties due to high fields and high beam brightness are expected. Thus, in addition to the introduction of new modeling techniques, our results provide an useful insight into advanced applications.

Experimental exploration of compressed beam dynamics in an energy recovery linac with comparison to simulations

The compact energy recovery linac (cERL) has been developed for industrial applications since 2017. Applications such as free electron laser require a compressed beam with a small energy spread and transverse emittance. The typical operation energy of cERL is an intermediate energy region close to 17.5 MeV; therefore, the electron bunch is easily affected by the longitudinal space-charge effects and the coherent synchrotron radiation wakefield effects. Bunch compression is demonstrated by optimizing a combination of a longitudinally chirped electron bunch and the arcs with nonzero ${R}_{56}$ parameters. When the bunch compression procedure is applied for a bunch charge of 60 pC, an increase in energy spread is observed at the short bunch length. We systematically explored the chirp phase to determine the best condition. The measurement results of the energy spread, bunch length, and transverse emittance were compared with the tracking simulation results to understand the compressed beam dynamics.

Goubau-Line Set Up for Bench Testing Impedance of IVU32 Components

The worldwide first in-vacuum elliptical undulator, IVUE32, is being developed at Helmholtz-Zentrum Berlin. The 2.5 m long device with a period length of 3.2 cm and a minimum gap of about 7 mm is to be installed in the BESSY II storage ring. It will deliver radiation in the soft X-ray range to several beamlines. The proximity of the undulator structure to the electron beam makes the device susceptible to wakefield effects which can influence beam stability. A complete understanding of its impedance characteristics is required prior to installation and operation, as unforeseen heating of components could have catastrophic consequences. To understand and measure the IVU’s impedance characteristics a Goubau-line test stand is being designed. A Goubau-line is a single wire transmission line for high frequency surface waves with a transverse electric field resembling that of a charged particle beam out to a certain radial distance. A concept optimized for bench testing IVUE32-components will be discussed, microwave simulations will be presented, and progress towards a test bench prototype will be shown.

Submacropulse electron-beam dynamics correlated with higher-order modes in a Tesla-type cryomodule

Experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility to elucidate the effects of long-range wakefields (LRWs) in TESLA-type superconducting rf cavities. In particular, we investigated the higher-order modes (HOMs) generated in the eight cavities of a cryomodule (CM) due to off-axis steering with correctors located ~4 m upstream of the CM. We have observed correlated submacropulse centroid slews of a few-hundred microns and centroid oscillations at ~240 kHz in the rf BPM data after the CM. The entrance energy into the CM was 25 MeV, and the exit energy was 100 MeV with 125 pC/b and 400 pC/b in 50-bunch pulse trains. These experimental results were evaluated for machine learning training aspects which will be used to inform the commissioning plan for the Linac Coherent Light Source-II injector CM.

On the synergy manipulation between the activation temperature, surface resistance and secondary electron yield of NEG thin films

The operation of the modern accelerators has long been challenged with the problems associated with distributed vacuum profile and electron multipacting. Applying a Ti-Zr-V based non-evaporable getter (NEG) film provides an ideal solution to these problems, except that TiZrV thin film may deteriorate the wakefield effect because of the increased wall resistivity. To deal with the trade-offs between those effects, an innovative quaternary TiZrVCu NEG film was prepared using magnetron sputtering technique in the present study. Through comparative study on the activation behavior, secondary electron yields and the surface resistivity of the novel TiZrVCu getter film with that of the conventional TiZrV film, it is found that alloying Cu into the TiZrV film would encouragingly eliminate the secondary electron yield and the d.c. resistivity of the NEG films, with a minor deterioration on the activation kinetics. The present study provides insights for optimizing the composition of NEG films from the aspect of realizing synergy manipulation of the activation kinetics, SEY and d.c resistivity.

Observation of Wakefield Effects with Wideband Feedthrough-BPM at the Positron Capture Section of the SuperKEKB Injector Linac

Observation of Wakefield Effects with Wideband Feedthrough-BPM at the Positron Capture Section of the SuperKEKB Injector Linac

A Sub-Micron Resolution, Bunch-by-Bunch Beam Trajectory Feedback System and Its Application to Reducing Wakefield Effects in Single-Pass Beamlines

A Sub-Micron Resolution, Bunch-by-Bunch Beam Trajectory Feedback System and Its Application to Reducing Wakefield Effects in Single-Pass Beamlines

Beam performance of the SHINE dechirper

A corrugated structure is built and tested on many FEL facilities, providing a ‘dechirper’ mechanism for eliminating energy spread upstream of the undulator section of X-ray FELs. The wakefield effects are here studied for the beam dechirper at the Shanghai high repetition rate XFEL and extreme light facility (SHINE), and compared with analytical calculations. When properly optimized, the energy spread is well compensated. The transverse wakefield effects are also studied, including the dipole and quadrupole effects. By using two orthogonal dechirpers, we confirm the feasibility of restraining the emittance growth caused by the quadrupole wakefield. A more efficient method is thus proposed involving another pair of orthogonal dechirpers.

A sub-micron resolution, bunch-by-bunch beam trajectory feedback system and its application to reducing wakefield effects in single-pass beamlines

A high-precision intra-bunch-train beam orbit feedback correction system has been developed and tested in the ATF2 beamline of the Accelerator Test Facility at the High Energy Accelerator Research Organization in Japan. The system uses the vertical position of the bunch measured at two beam position monitors (BPMs) to calculate a pair of kicks which are applied to the next bunch using two upstream kickers, thereby correcting both the vertical position and trajectory angle. Using trains of two electron bunches separated in time by 187.6 ns, the system was optimised so as to stabilize the beam offset at the feedback BPMs to better than 350 nm, yielding a local trajectory angle correction to within 250 nrad. The quality of the correction was verified using three downstream witness BPMs and the results were found to be in agreement with the predictions of a linear lattice model used to propagate the beam trajectory from the feedback region. This same model predicts a corrected beam jitter of c. 1 nm at the focal point of the accelerator. Measurements with a beam size monitor at this location demonstrate that reducing the trajectory jitter of the beam by a factor of 4 also reduces the increase in the measured beam size as a function of beam charge by a factor of c. 1.6.

Wakefield effects and mitigation techniques for nanobeam production at the KEK Accelerator Test Facility 2

The ATF2 beam line at KEK was built to validate the operating principle of a novel final-focus scheme devised to demagnify high-energy beams in future linear lepton colliders; to date vertical beam sizes as small as 41 nm have been demonstrated. However, this could only be achieved with an electron bunch intensity $\ensuremath{\sim}10%$ of nominal, and it has been found that wakefield effects limit the beam size for bunch charges approaching the design value of ${10}^{10}{e}^{\ensuremath{-}}$. We present studies of the impact of wakefields on the production of ``nanobeams'' at the ATF2. Wake potentials were evaluated for the ATF2 beam line elements and incorporated into a realistic transport simulation of the beam. The effects of both static (component misalignments and rolls, magnet strength errors and beam position monitor resolution) and dynamic (position and angle jitter) imperfections were included and their effects on the beam size evaluated. Mitigation techniques were developed and applied, including orbit correction, dispersion-free steering, wakefield-free steering, and interaction point tuning knobs. Explicit correction knobs to compensate for wakefield effects were studied and applied, and found to significantly decrease the intensity dependence of the beam size.

Conceptual design for an hard X-ray Free Electron Laser based on CLIC X-band structure

In this paper, a conceptual design of a hard X-ray Free-Electron Laser (FEL) facility based on CLIC-like X-band accelerating structure has been presented. The injector, based on an X-band rf gun, the main accelerating sections, using high-gradient CLIC-like structures including rf power distribution, and the two bunch compressors have been discussed. Simulations of the rf gun, of the injector, and of the linac have been performed, successfully meeting the stringent requirements in terms of minimum projected emittance, sliced emittance, and minimum bunch length. Full 6-D start-to-end linac simulations have been performed taking into account wakefield effects, misalignment of accelerator components, Coherent Synchrotron Radiation (CSR), and small dynamic variations of phase, voltage, and injection time. The performance of FEL at λ=1 Angstrom (Å) has also been evaluated for self-amplified spontaneous emission (SASE) FEL mode. A radiation power of about 10 GW has been achieved with a photon pulse length of 30 fs. The main advantage of the proposed design is that it achieved the required beam parameters in very short length, rendering the facility quite compact.