Beam Energy Spread Research Articles

Reduction of arrival time jitter or energy spread with arclike variable bunch compressors

Synchronizing free-electron laser pulses for time-resolved experiments is necessary as an unsynchronized system reduces the effective repetition rate of the experiment. Additionally, free-electron laser longitudinal coherence and spectral brightness are limited by electron beam energy spread. In this paper, a variable bunch compressor design and compression schemes were developed to: reduce klystron-induced arrival time jitter by 85% while preserving peak current and transverse emittance and to minimize electron beam correlated energy spread for potential self-seeding or HB-SASE modes. Published by the American Physical Society 2024

Beam energy spectra in the presence of cell-to-cell phase advance errors

The parameters of the accelerating structures of linear accelerators have a strong influence on the beam parameters such as the mean energy and the energy spread. One of the most common types the accelerating structures is based on disk loaded waveguides. Imperfections in such structure parameters may be critical for subsequent beam dynamics. We analytically study the influence of the errors of the cell-to-cell phase advance on the beam energy spread and the mean energy on the example of the constant gradient structure. Derived expressions were applied to the case of a large number of accelerating structures, which is relevant for GeV linacs, to obtain accelerated beam parameters in terms of the probabilistic analysis for several values of the injected beam duration.

Characterization of the PADME positron beam for the X17 measurement

This paper presents a detailed characterization of the positron beam delivered by the Beam Test Facility at Laboratori Nazionali of Frascati to the PADME experiment during Run III, which took place from October to December 2022. It showcases the methodology used to measure the main beam parameters such as the position in space, the absolute momentum scale, the beam energy spread, and its intensity through a combination of data analysis and Monte Carlo simulations. The results achieved include an absolute precision in the momentum of the beam to within ~1–2 MeV/c, a relative beam energy spread below 0.25%, and an absolute precision in the intensity of the beam at the level of 2%.

Three-dimensional theory of superradiant free-electron lasers

The solitonlike superradiant regime of free-electron lasers (FEL) offers a promising path towards ultrashort pulses, beyond the natural limit dictated by the bandwidth of the high-gain FEL instability. In this work we present a three-dimensional theory of the superradiant regime, including the effects of beam emittance and energy spread. Our work takes advantage of recent developments in nonlinear FEL theory to provide a fully analytical description of solitonlike superradiance. Our theory proves the existence of a diffraction-dominated steady-state regime in which the superradiant peak power grows indefinitely while leaving the pulse duration and on-axis intensity almost unchanged. These results are in excellent agreement with three-dimensional simulations and are supported by recent experimental results at the Linac Coherent Light Source. This work advances nonlinear FEL theory and provides a theoretical framework for the next generation of attosecond x-ray FELs. Published by the American Physical Society 2024

Analytical formulas of coherent-synchrotron-radiation induced microbunching gain and emittance growth in an arbitrary achromatic four-bend chicane

The coherent synchrotron radiations (CSR) emitted by a high-brightness electron beam during transport in a bending magnet is a double-edged sword in electron accelerators. While CSR contributes to a stronger radiation field than the incoherent radiation, it simultaneously leads to degradation of the electron beam quality. Specifically, CSR effects manifest in increases of the beam energy spread and the projected emittance, and amplification of the microbunching instability. A dedicated design of the multi-bend transport lines to mitigate CSR effects has recently become a crucial consideration in modern high-brightness electron accelerators. This paper presents analytical formulas for the CSR-induced microbunching instability gain and for the induced emittance growth in an arbitrary achromatic four-bend chicane with inclusion of both the steady-state and transient CSR effects. For the microbunching instability, an iterative method is employed to solve the integral equation for the bunching factor, providing satisfactory gain formulas. Regarding the CSR-induced emittance growth, based on the linear transfer matrices and incorporating the expressions of the CSR-induced energy spread, analytical formulas are derived for the projected emittance growth in an arbitrary four-bend transport section. The analytical formulas are compared and show good agreement with semi-analytical Vlasov calculations and particle tracking simulations. As an application, the obtained analytical formulas are applied to evaluate the CSR effects in the design of a general achromatic four-bend bunch compressor chicane, providing a quick estimate on the microbunching gain and the induced emittance growth. From the widely adopted symmetric C-shape chicane to a non-symmetric S-shape chicane, a design recently proposed by the co-authors, our analytical formulas offer insight into the evolution of the microbunching gain and the emittance growth with the variations of design parameters. In comparison to the time-consuming, full numerical particle tracking simulations currently employed for CSR effect analyses, the analytical formulas presented in this paper significantly reduce the evaluation time, enabling systematic study of parametric dependencies and comprehensive optimization with inclusion of CSR effects within specified design parameter ranges.

Simulation observation of high effectiveness laser plasma wakefield accelerator using plasma telescope configuration

In the laser wakefield accelerators, the energy transfer efficiency from the laser to the electron beam and the energy spread of the electron beam are parameters of contradiction, which people have not been able to improve simultaneously for a long time. To generate quasi-monoenergetic electron beams, the energy transfer efficiencies are up to the 1% level, while for 10% or higher energy transfer efficiencies, the electron spectra are broad in general. In the series of particle-in-cell simulations shown in this paper, we observe the simultaneous improvement of these two parameters by the self-injection mechanism in uniform plasma using the plasma telescope configuration [Zeng et al., Phys. Plasmas 27, 023109 (2020)]. The energy transfer efficiency is increased to more than 10%, and the energy spread of the electron beam is less than 5%. We also show the possibility to produce an electron beam with the energy of 1.871 GeV, the charge of 2.13 nC, and the energy spread of 2.5% by a 30 J laser.

Energy stabilization of high-charge bunches from laser plasma accelerators

Laser plasma accelerators (LPAs) have become one of the frontiers of the accelerator community, mainly because they promise orders of magnitude improvement in the accelerating gradient. However, the energy stability and spread of the high-charge bunched beams (e.g. several hundred pC per bunch) from LPAs still strongly limit their application. In this work, we propose a novel method utilizing magnetic chicanes combined with both active and passive plasma dechirpers to simultaneously reduce the central energy deviation and the energy spread of high-charge bunched beams from LPAs. Start-to-end simulations demonstrate that the central energy deviation and the energy spread of approximately 500 pC bunches can be simultaneously reduced from approximately 2% and 1.2% to 0.1% and 0.5%, respectively, while maintaining almost perfect transmission efficiency (above 97%).

Laser polarization control of ionization-injected electron beams and x-ray radiation in laser wakefield accelerators

In this paper, we have studied the influence of laser polarization on the dynamics of the ionization-injected electron beams, and subsequently, the properties of the emitted betatron radiation in laser wakefield accelerators (LWFAs). While ionizing by strong field laser radiation, the generated photo-electrons carry a residual transverse momentum in excess of the ionization potential via the above threshold ionization (ATI) process. This ATI momentum explicitly depends on the polarization state of the ionizing laser and eventually governs the dynamics of the electron beam trapped inside the wake potential. In order to systematically investigate the effect of the laser polarization, here, we have employed complete three-dimensional particle-in-cell simulations in the nonlinear bubble regime of the LWFAs. We focus, in particular, on the effects the laser polarization has on the ionization injection mechanism, and how these features affect the final beam properties, such as beam charge, energy, energy spread, and transverse emittance. We have also found that as the laser polarization gradually changes from linear to circular, the helicity of the electron trajectory, and hence the angular momentum carried by the beam, increases significantly. Studies have been further extended to reveal the effect of laser polarization on the radiation emitted by the accelerated electrons. The far-field radiation spectra have been calculated for the linear and circular polarization states of the laser. It has been shown that the spatial distributions and the polarization properties (Stokes parameters) of the emitted radiation in the above two cases are substantially different. Therefore, our study provides a facile and efficient alternative to regulate the properties of the accelerated electron beams and x-ray radiation in LWFAs, utilizing ionization injection mechanism.

Quasi-monoenergetic electron beam from LWFA: analytical approach

Analytical dependence of the energy spread of electron beam on time and injection duration has been obtained with the 1D model of the quasi-linear laser wakefield electron acceleration, presented as phase portraits of electron energy relative to the plasma wave phase. The method for producing electron beams with variable energy and a lower energy spread compared to a standard bubble-like approach by transferring to a deaccelerating part with another phase trajectory (by reducing the plasma amplitude of a wave) has been developed. The analytically obtained results successfully describe key features of the previously obtained in Tsymbalov et al (2024 arXiv:2403.19828) experimental and numerical (PIC) data.

Towards Tests of an RFQ Cooler and Simulations

The cooling of secondary beams is important for accelerator-based nuclear physics. In the radiofrequency (RF) quadrupole cooler (RFQC), RF fields and ion-gas collisions may give a considerable increase or decrease of the beam transverse emittance and energy spread, depending on a delicate tuning of heating and cooling effects, dominated by the ion beam kinetic energy and the balance of collisions and confinement forces. An extra confinement may be added by a solenoid magnetic field, as in the RFQC prototype installed in the Eltrap machine. This provides a versatile test bench (distinct from a closed accelerator installation) for detailed studies of cooling dynamics and of several RFQC technical optimizations (for gas differential pumping and bias voltages). Modeling concepts and simulation results are summarized. The major RFQC parameters are reviewed, in particular for 133Cs+ collisions against He gas whose pressure pg ranges from 2 to 9 Pa in the reference case, with attention to the extraction, comparing triode/tetrode system, and to the bias voltages. Lower bias voltages request less pg , but provide less cooling of the energy spread.

Developing a penning ionization gauge ion source with a filament for a compact ion microbeam system

We present the development of a penning ionization gauge ion source with a filament (F-PIG) for producing submicron ion beams in a compact ion microbeam system. The conventional penning ionization gauge ion source (PIG) represents a viable choice for microbeam system due to its compact size and low power consumption. However, directly utilizing a PIG for generating submicron ion beam poses challenges, primarily from significant energy spread, causing substantial aberrations. Considering this, this study proposes a solving the generation of low-voltage discharge plasma, achieved using low-energy electrons from a filament by focusing on the development of F-PIG for this purpose. Experimental results demonstrate that the F-PIG exhibits considerable promise an ion source to forming submicron beam within a compact ion microbeams system. These findings indicate that F-PIG can effectively reduce the width of the beam energy spread, making it a valuable asset for microbeam applications.

Proton acceleration from optically tailored high-density gas jet targets

Laser-driven ion acceleration is well established using solid targets mainly in the target normal sheath acceleration regime. To follow the increasing repetition rate available on high-intensity lasers, the use of high-density gas targets has been explored in the past decade. When interacting with targets reaching densities close to the critical one, the laser pulse can trigger different acceleration mechanisms such as Collisionless Shock Acceleration (CSA) or hole boring. Particle-in-cell simulations using ideal target profiles show that CSA can accelerate a collimated, narrow energy spread and few hundreds of megaelectronvolts ion beam on the laser axis. Nevertheless, in real experiments, the laser will not only interact with an overcritical, thin plasma slab with sharp density gradients, but also with lower density regions surrounding the core of the gas jet, extending to several hundreds of micrometres. The interaction of the laser with these lower density wings will lead to nonlinear effects that will reduce the available energy to drive the shock in the high-density region of the target. Optically tailoring this target could mitigate that issue. Recent experiments conducted on different laser facilities aimed at testing several tailoring configurations. We first tested a scheme with a copropagating picosecond prepulse to create a lower density plasma channel to facilitate the propagation of the main pulse, while the second one was a transverse tailoring driven by nanosecond laser pulses to generate blast waves and form a high-density plasma slab. The main results will be presented here and the methods compared.

Experimental characterization of the optical klystron effect to measure the intrinsic energy spread of high-brightness electron beams

The intrinsic energy spread of electron beams needs to be measured to characterize and optimize high-brightness electron beam sources such as those driving x-ray free-electron lasers (FELs). We demonstrate the use of the optical klystron effect as a precise and high-resolution method to measure the electron beam energy spread. The optical klystron setup consists of undulator modules and magnetic chicanes placed between them. The energy spread is found by measuring the radiation power produced in the undulators as a function of the chicanes’ strengths. High resolution and simplicity are the advantages of this approach, in contrast to the standard method, which measures the longitudinal phase space of the electron beam with a transverse deflector. The demonstration was performed at Athos, the soft x-ray FEL beamline of SwissFEL, for which we measured energy spreads below 1 MeV at a central beam energy of 3.4 GeV. We have verified the consistency of the method for different parameters (radiation wavelengths, undulator polarization configurations, and electron bunch durations) and we have benchmarked it against the standard measurement approach using a transverse deflector. Our results confirm the optical klystron as a valid approach to measure the electron beam energy spread. The method can be especially useful to reconstruct low energy spread values, where the conventional approach may be resolution limited, such as in ultra high-brightness radiofrequency photoinjectors or plasma sources, or when transverse deflectors are not available. Published by the American Physical Society 2024

Tuning methods for multigap drift tube linacs.

Multigap cavities are used extensively in linear accelerators to achieve velocities up to a few percent of the speed of light, driving nuclear physics research around the world. Unlike for single-gap structures, there is no closed-form expression to calculate the output beam parameters from the cavity voltage and phase. To overcome this, we propose to use a method based on the integration of the first and second moments of the beam distribution through the axially symmetric time-dependent fields of the cavity. A beam-based calibration between the model's electric field scaling and the machine's rf amplitudes is presented, yielding a fast online energy change method, returning cavity amplitude and phase necessary for a desired output beam energy and energy spread. The method is validated with 23Na6+ beam energy measurements.

Design and study of cavity quadrupole moment and energy spread monitor

A nondestructive method to measure beam energy spread using the quadrupole modes within a microwave cavity is proposed. Compared with a button beam position monitor (BBPM) or a stripline beam position monitor (SBPM), the cavity monitor is a narrow band pickup and therefore has better signal-to-noise ratio (SNR) and resolution. In this study, a rectangular cavity monitor is designed. TM220 mode operating at 4.76 GHz in the cavity reflects the quadrupole moment of the beam. The cavity plans to be installed behind a bending magnet in Dalian Coherent Light Source (DCLS), an extreme ultraviolet FEL facility. In this position, the beam has a larger dispersion, which is beneficial to measure the energy spread. A quadrupole magnet, a fluorescent screen, and a SBPM with eight electrodes is installed near the cavity for calibration and comparison. The systematic framework and simulation results are also discussed in this paper.

Three-pole wigglers at NSLS-II

The National Synchrotron Light Source-II (NSLS-II) at Brookhaven National Lab (BNL) is a third-generation medium-energy storage ring with 3 GeV and sub-nm-rad horizontal emittance, equipped with a top-off capability of 500 mA. It is designed to deliver an extremely intense photon beam across a wide spectral range, from the far-infrared to the very hard X-ray region. This outstanding performance is achieved through a combination of bending magnets (BM), three-pole wigglers (3 PW), and advanced insertion device (ID) sources. Six three-pole wigglers have been constructed at the NSLS-II IDs Lab. These devices are used to produce broadband radiation with lower angular power density and to monitor the electron beam emittance and energy spread. This paper describes the R&D activities focused on developing the required magnetic and mechanical designs, along with magnetic field optimization and the final magnetic measurement results. It also covers the spectral brightness, flux, power density, spatial and angular output properties of the 3 PWs, including their commissioning results and their effects on the performance of the NSLS-II storage ring.

The Influence of Increased Electron Energy Spread on the Radiation of the Second Harmonic in Free Electron Lasers

Free electron lasers (FELs) are becoming more and more popular as sources of radiation for research purposes in many fields of science. They are frequently employed in second harmonic generation (SHG) studies. SHG is an important effect of nonlinear responses of matter to irradiation. It should be separated from the second harmonic of the radiation source, FELs, for correct analysis of the response. Using an analytical model for harmonic powers evolution in a single-pass FEL, we demonstrate the dependence of FEL harmonics on the key parameters of beams and undulators and show that it is possible to reduce the second FEL harmonic content if the energy spread of an electron beam is increased. For LEUTL FEL radiation in the visible range, we analytically demonstrate a reduction in the second harmonic power by an order of magnitude if electron energy spread is increased twice, which still allows efficient bunching at the fundamental wavelength. The method is valid regardless of the photon energy and, therefore, the absorption edge of the target material, and as such, it is valid also in the X-ray band.

Effects of a 4.3T superconducting wiggler on the electron beam optics and dynamics at NSLS-II

A superconducting wiggler (SCW) with a peak field of 4.3 T has recently been installed at NSLS-II. The wiggler generates a high-flux X-ray beam with a photon energy range from 20 keV to 200 keV for the High Energy Engineering X-ray Scattering beamline. This device induces significant distortions in the electron beam orbit and optics. We have corrected these adverse effects using feed-forward tables. The effects of the SCW on the electron beam emittance, energy spread, and bunch length were calculated and measured. The beam-induced heating of the cryogenic vacuum chamber was also studied. Finally, the superconducting wiggler has been commissioned for user operations.

Technical Infrastructure for Clinical Translation of Electron FLASH

For safe clinical translation of electron FLASH, hardware tools for real-time beam control and software tools for treatment planning are necessary. The purpose of this study is to prototype high-throughput hardware for real-time beam control, along with accurate beam modeling of a modern clinical Linac configured to deliver FLASH dose-rates. For real-time beam current monitoring, a beam current transformer (BCT) was initially coupled to a fast digitizer and its linearity was established by varying dose per pulse. The radiation pulse width was modified, and this change was measured using the BCT. The BCT was then used to measure the variability of dose per pulse and pulse width due to a mistuned linear accelerator system. Next, the BCT was interfaced with a field programmable gate array (FPGA) which provides the ability for high-throughput and deterministic control of the Linac based on dose accumulation. For beam modeling, the program, TOol for PArticle Simulation (TOPAS), was used to obtain beam parameters by using Bayesian optimization of the beam energy, source size, angular, and energy spread via comparison of simulated and representative dose profiles. The beam model would then be employed to calculate 3D dose distribution in a CT scan of a 3D-printed anatomically realistic mouse phantom. The area under the current-time curve from the BCT exhibited excellent linearity (response = 12.80 nC/Gy) up to 2.5 Gy/Pulse (R2 = 0.99). The peak beam current for the electron FLASH beam was measured to be ∼10 mA for an instantaneous dose-rate of ∼5×105 Gy/s. The measured radiation pulse width agreed with the expected value (3.7 μs). The pulse width was then shortened and the measurement by the BCT indicated pulse widths of 1.8 μs and 0.5 μs corresponding to 0.7 Gy/pulse and 0.3 Gy/pulse, respectively. The beamline exhibited a ramp-up in dose per pulse and pulse width when using the automatic frequency controller (AFC). For the first pulse, the dose delivered was ∼0.1-0.3 Gy and the pulse width was 0.6 μs. The output stabilized to nominal values of dose and pulse width after 3-4 pulses. This ramp-up was mitigated by manually tuning the RF resonance with the AFC disabled, after which the BCT exhibited constant output and pulse width. The beam modeling work is in progress. We demonstrated that a BCT can provide real-time measurement of per-pulse output suitable as input for FLASH beam control based on dose accumulation. The next steps are to quantify the accuracy of the dose control mechanism with the FPGA-based hardware. Potential failure modes will be identified and mitigated in parallel with the development of the hardware. A 3D-printed mouse phantom has been constructed to facilitate beam modeling work for treatment planning (in progress). On completion of this work, it is expected that we will have key infrastructure elements needed to move towards an eventual FDA investigational device exemption for clinical trials.

A boosted muon collider

A muon collider could produce the heavier Standard Model particles with a boost, for example in resonant processes such as μ−μ+→ h or μ−μ → Z. We propose machine configurations that produce the boost (asymmetric beam energies, tilted beams) and estimate how much the luminosity is reduced or perhaps enhanced. The feasibility of the proposed configurations, as well as an estimation of the beam-induced backgrounds and beam energy spread, needs to be evaluated in order to derive more solid conclusions on the physics potential of such boosted collider configurations. If achievable, the boost can provide new interesting observational opportunities. For example it can significantly enhance the sensitivity to long-lived new particles decaying in a far-away detector, such as dark higgses or sterile neutrinos produced in h or Z decays.