Acceleration Of Bunches Research Articles

On the possibility of accelerating charged particles in the low-pressure acoustoplasma and plasma bunches in the air

In this paper obtained results of two experimental investigations are presented: on the acceleration of electrons in low-pressure acoustoplasma discharge and acceleration of plasma bunch-plasmoids in the air. The first experimental results on the acceleration of electrons in the low-pressure discharge were obtained in 2008. In the current paper an attempt to explain the obtained results by means of wake accelerations of particles in electromagnetic fields without utilization of usual drivers is made. Formerly calculated theoretical data for accelerated particles even in the energy range of 10–100 eV are experimentally confirmed. Experimental investigations on origination and initiating acceleration of plasma bunches in crossed fields in the air were conducted in 2023. In the current paper the obtained first results on acceleration of the originated long-life plasmoids in the air are presented as an announcement of our planned subsequent corresponding investigations. To carry out corresponding experiments a unique experimental setup, as well as appropriate devices and equipment were developed. A new conceptual model of a plasmoid is offered. The realization of this concept opens the possibility of carrying out the experimental investigations of the phenomena of origination of long-life plasmoids in air. During the experimental investigations, any ionizing additives into the discharge were not injected.

A novel approach to accelerating ultracold electron bunches, while still preserving their brightness.

Built upon a laser cooling and atomic gas trapping system, with additional sub-systems, the acceleration of ultracold electron bunches has proven successful without sacrificing quality.

RF acceleration of ultracold electron bunches.

The ultrafast and ultracold electron source, based on laser cooling and trapping of atomic gas and its subsequent near-threshold two-step photoionization, is capable of generating electron bunches with a high transverse brightness at energies of roughly 10 keV. This paper investigates the possibility of increasing the range of applications of this source by accelerating the bunch using radio frequency electromagnetic fields. Bunch energies up to 35 keV are measured by analyzing the diffraction patterns generated from a mono-crystalline gold sample. It is found that the normalized transverse emittance is largely preserved during acceleration.

Three-stage laser wakefield accelerator scheme for sub-Joule few-cycle laser pulses

Laser-driven electron acceleration in underdense plasma is a promising route towards the realization of reliable sources of relativistic electrons in the 0.1–1 GeV energy range. Generation of such electron bunches at high repetition rates is hindered by the limited energy per pulse, which inevitably results in very short pulse duration and tight focusing. Compressing the laser energy in time and space allows scientists to use higher plasma density to drive wakefieds, which in turn results in enhanced diffraction and dispersion of the broadband laser pulse. These features make difficult to control the acceleration in the plasma wave and to improve the beam quality. Here we propose a mm-long three-stage acceleration scheme, which allows for tunable injection and optimal acceleration of high-quality electron bunches. The full interaction length is modeled by 3D particle-in-cell simulations.

Analysis of frequency chirping on the electron bunch acceleration during Laguerre–Gauss laser interaction

We intend to examine the impact of frequency chirping on the efficient vacuum acceleration of an electron bunch using a chirped Laguerre–Gauss (LG) laser pulse. The study demonstrates that achieving high-energy electron acceleration relies not only on significant pulse asymmetry but also on ensuring phase synchronization in the LG laser interaction. The findings highlight the feasibility of generating outgoing electron bunches with high energy and low divergence through the selection of an optimal chirping value. Furthermore, we establish that chirping the LG laser pulse facilitates the acceleration of electrons to high energy using a lower laser intensity compared to the scenario without chirping.

Hybrid acceleration of compact ion bunches by few-cycle laser pulses in gas jets of two atomic species

Hybrid acceleration of compact ion bunches by few-cycle laser pulses in gas jets of two atomic species

Toward a Laser-Driven Traveling-Wave Linac on a Chip

Restricted by pulse dispersion, dephasing, and bunch deflection, it has been a challenging task to realize high-gain particle acceleration and bunch focusing by using an ultrashort-pulse laser to drive an integrable acceleration structure, which is necessary to develop an on-chip particle accelerator for practical applications. Here we propose a laser-driven traveling-wave linac (linear accelerator), which uses the cascade reflection and refraction of an ultrashort laser pulse on a microscale dielectric structure to achieve long-range laser-particle interaction, avoiding waveguide dispersion, and enhancing sustainable acceleration gradient. It is scalable and extensible, and can realize full-course particle acceleration by using a single laser source via the inverse Cherenkov effect. With this accelerator scheme, we further propose a dynamic synchronization and focusing method, which not only counteracts dephasing but also restrains the bunch spread and deflection caused by space-charge and emittance effects, realizing stable bunch transport and acceleration in a tiny-size bunch channel without resorting to the need for external focusing equipment. This accelerator scheme paves the way toward a high-efficiency laser-driven all-dielectric on-chip particle accelerator for practical applications.

Beam dynamics and space charge studies for the InnovaTron cyclotron

At IBA a high-intensity compact self-extracting cyclotron is being studied. There is no dedicated extraction device but instead, a special shaping of the magnetic iron and the use of harmonic coils to create large turn-separation. Proton currents up to 5 mA are aimed for. This would open new ways for large-scale production of medical radioisotopes. The main features of the cyclotron are presented. A major variable of the beam simulations is the space charge effect in the cyclotron centre. Using the SCALA-solver of Opera3D, we attempt to find the ion source plasma meniscus and the beam phase space and current extracted from it. With these properties known, we study the bunch formation and acceleration under high space charge condition with our in-house tracking code AOC. We also discuss a new tool that automates optimization of cyclotron settings for maximizing beam properties such as extraction efficiency.

Electron bunch acceleration by an azimuthally polarized laser pulse in the presence of a helical wiggler and external magnetic field

This study investigates the acceleration of a single electron and an electron bunch by an azimuthally polarized (AP) laser pulse in the presence of a helical wiggler and external magnetic field in the form of a hyperbolic tangent (HT) function. The wiggler parameters were optimized to retain betatron resonance for a long time, as a result of which it was found that the optimum values of HT magnetic field strength and its parameter increase the interaction length. The laser fields, the wiggler magnetic field, and the HT magnetic field cooperatively helped cause the generation of the high energetic electrons. Finally, highly energetic electrons were obtained with a mean energy of about 2 GeV and an extremely low mean scattering angle of [Formula: see text], and an acceleration gradient of about 42 GeV/m.

Surface plasmon-driven electron and proton acceleration without grating coupling

Surface plasmon (SP) excitation in intense laser interaction with solid target can be exploited for enhancing secondary emissions, in particular efficient acceleration of high charge electron bunches. Previous studies have mostly used grating coupling to allow SP excitation, which requires stringent laser contrast conditions to preserve the structural integrity of the target. Here we show via simulations that efficient SP electron acceleration for currently available short pulse lasers can occur in a flat foil irradiated at parallel or grazing incidence ( with the target surface) without a surface modulation. In turn, the accelerated electrons can be effective for generating proton beams with narrow spectra peaked at 100 MeV energies for currently available laser drivers.

COMPARATIVE ANALYSIS OF ACCELERATION GRADIENTS FOR CHIP STRUCTURES WITH DIFFERENT REFRACTIVE INDICES

The results of numerical studies of accelerating gradients in accelerators based on dielectric chip structures with different refractive indices, excited by a titanium-sapphire laser pulse, are presented. A comparative analysis of the influence of the refractive index on the rate of acceleration of electron bunches is carried out. Promising materials for the manufacture of dielectric laser accelerators are proposed.

Autoresonance phenomenon in a long mirror

The paper describes an implementation of a long mirror-based variant of cyclotron autoresonance which permits a local temporary change in the mirror`s induction and provides a mode for filling the trap with primary plasma, and for the generation of plasma bunches with an energetic electron component and their accumulation within a single cavity. The approach does not require injection of external particles into the acceleration zone as particles can be generated directly within the mirror using specialized conditions of electron cyclotron resonance (ECR) as part of the operational mode. A detailed study of the spectral-angular distribution of Bremsstrahlung in various operational modes has been undertaken. The results of this study permit the optimal value of the time sequence between the leading edge of the pulsed magnetic field and the microwave pulse to be determined, which ensures the optimal mode of electron trapping in the cyclotron autoresonance mode. Bremsstrahlung radiation recorded in the transverse direction has a significantly higher intensity of photons and energy compared to the longitudinal direction during the acceleration and subsequent confinement mode of plasma bunches. The observed changes in the intensity and spectral distribution of the Bremsstrahlung, which depend on the values of the operating parameters for acceleration, afford the possibility to define the dependence of the number of initial plasma particles trapped by cyclotron autoresonance for the different operating modes. The results will improve our understanding of the processes taking place at various stages of the operational modes. In general, such studies are important for gaining an improved understanding of the mechanisms of generation and confinement of hot electron plasma bunches with an energetic electron component for autoresonant interaction in a long mirror.

High-throughput injection–acceleration of electron bunches from a linear accelerator to a laser wakefield accelerator

Plasma-based accelerators (PBAs) driven by either intense lasers (laser wakefield accelerators, LWFAs) or particle beams (plasma wakefield accelerators, PWFAs), can accelerate charged particles at extremely high gradients compared to conventional radio-frequency (RF) accelerators. In the past two decades, great strides have been made in this field, making PBA a candidate for next-generation light sources and colliders. However, these challenging applications necessarily require beams with good stability, high quality, controllable polarization and excellent reproducibility. To date, such beams are generated only by conventional RF accelerators. Therefore, it is important to demonstrate the injection and acceleration of beams first produced using a conventional RF accelerator, by a PBA. In some recent studies on LWFA staging and external injection-acceleration in PWFA only a very small fraction (from below 0.1% to few percent) of the injected charge (the coupling efficiency) was accelerated. For future colliders where beam energy will need to be boosted using multiple stages, the coupling efficiency per stage must approach 100%. Here we report the first demonstration of external injection from a photocathode-RF-gun-based conventional linear accelerator (LINAC) into a LWFA and subsequent acceleration without any significant loss of charge or degradation of quality, which is achieved by properly shaping and matching the beam into the plasma structure. This is an important step towards realizing a high-throughput, multi-stage, high-energy, hybrid conventional-plasma accelerator.

Cavity tilt measurement using beam excited higher order mode signals at the Free Electron Laser FLASH

At the Free Electron Laser in Hamburg (FLASH), TESLA-type superconducting (SC) cavities are used for the acceleration of electron bunches. Higher Order Modes (HOMs) excited by electron bunches may cause emittance growth and decrease the FEL performance. The misalignment of the SC cavities housed inside cryo-modules is one of the main factors which enhance the coupling of HOMs to the bunches. We consider the cavity offset and tilt as the two most relevant misalignments. These can be measured by utilizing the beam excited HOM signals. The cavity offset has been measured before in several modules at FLASH, while the tilt has so far proved to be much more difficult to be measured. This is because the beam trajectory tilt excited modes are much weaker than the ones excited by offset. We used a method for measuring cavity tilt by carefully targeting the beam through the middle of a cavity. An efficient data processing routine based on signal fitting was applied. For the first time, the tilts of all cavities inside a cryo-module are measured. The ratio between the offset and angle dependence of the HOMs agrees well among the different cavities.

Direct electron bunch acceleration by Laguerre–Gauss laser pulse

Acceleration of a rest electron bunch in vacuum by a Laguerre–Gauss (LG) laser pulse is studied using three-dimensional test-particle simulations. It is found that the ponderomotive force and the phase synchronization process, with the help of each other, cause rest electrons to reach high energies in the laser interaction. The ponderomotive force due to the spatial distribution of a high-intensity LG laser pulse pushes electrons from the rest and accelerates them at first. Then, the accelerated electrons are trapped in the pulse and continue to gain more energy through the phase synchronization process. Unlike the interaction with a Gaussian laser pulse in which to maintain the beam quality was not possible without the intervention of an external factor, using the LG laser pulse reveals the feasibility of generating a GeV high-quality electron bunch with low spread in energy and radial deflection, without applying any external agent.

Electromagnetic and Beam Dynamics Studies for High Gradient Accelerators at Terahertz Frequencies

THz radiation is one of the most appealing portion of the electromagnetic spectrum in terms of multi-disciplinary use in basic science and technology. Beyond the numerous applications, a great interest is its potential for future, compact linear accelerators.Conventional radio-frequency accelerating structures operating at the S and C band can reach gradients up to 30 - 50MV/m, respectively; higher accelerating gradients, of the order of 100MV/m, have been obtained with X-band cavities. THz-based accelerating structures enable operation at even higher gradient, potentially up to the GV/m scale, holding great potential for their application to free-electron lasers and linear colliders, for instance.Here we present electromagnetic and beam dynamics studies about the use of a dielectric loaded waveguide to accelerate electron bunches by mean of a narrow-band multi-cycle THz pulse. The excitation of the accelerating structure by the THz pulse and the bunch acceleration in the excited field are investigated through CST Microwave Studio and GPT simulations.

Transformer Ratio at Wakefield Excitation by Train of Electron Bunches with Linear Growth of Current in Dielectric Resonator Electron–Positron Collider

The efficiency of electron bunch acceleration by wakefield, excited in two-beam electron-positron dielectric resonator collider by train of electron bunches is determined by transformer ratio (TR). The train of homogeneous bunches, in which current grows linearly along a train, is considered. The length of homogeneous bunch equals to half of excited wavelength 0.5λ. Interval between bunches is ρλ, p = 1, 2,… The conditions have been formulated, when the wakefield pulses from all electron bunches are added. Bunch is injected in dielectric resonator, when the back wavefront of the wakefield pulse is on the bunch-injection boundary of the resonator/cavity. Bunch leaves the resonator, when the first wavefront of wakefield pulse is on the end of the resonator. The conditions for a large TR have been formulated. The wakefield and TR have been derived after N bunch. The computer simulation has been performed taking into account wakefield pulse dispersion spreading and electron bunch transition radiations. The results of analytical investigation are compared with the results of computer simulation. It has been shown that the dependence TR = 2N is performed. Advantage of this mode with large transformer ratio that some injected bunch with decreased current becomes witness. When this bunch is injected it gets in maximum accelerating field.The infinite periodical mode of accelerator operation has been proposed. In this mode, witness-bunches and driver-bunches are injected according to periodic mode. In the infinite periodical mode, short shaped trains of driver-bunches are alternated with witnesses. Large transformer ratio and identical decelerating field for all driver-bunches are provided by this long periodic train.

A MHz-repetition-rate hard X-ray free-electron laser driven by a superconducting linear accelerator

The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created.

Charge coupling in multi-stage laser wakefield acceleration

The multi-stage technique in the laser driven acceleration of electrons has become a critical part for full-optical jitter-free accelerators. Several independent laser drivers and shorter plasma targets allow the stable and reproducible acceleration of electron bunches (or beam) at the GeV energies with narrower energy spreads. Moreover, the charge coupling, necessary for efficient acceleration in the consecutive acceleration stages, depends collectively on the parameters of the injected electron beam, the booster stage, and the nonlinear transverse dynamics of the electron beam in the laser pulse wake. An unmatched electron beam injected in the booster stage and its nonlinear transverse evolution may result in perturbations and even a reduction of the field strength in the acceleration phase of the wakefield. Thus, the analysis and characterization of charge coupling in multi-stage laser wakefield acceleration (LWFA) are important. Here, we investigate acceleration of an externally injected electron beam in the laser wakefield, emulating two-stage LWFA, using fully relativistic multi-dimensional particle-in-cell simulations. We also study the underlying critical parameters that affect the efficient coupling and acceleration of the injected electron beam in the booster stage.

Terahertz accelerator based electron and x-ray sources

The generation and use of THz radiation for electron acceleration and manipulation of electron bunches has progressed over the last decade to a level where practical devices for THz guns, acceleration and a wide range of beam manipulations have become possible. Here, we present our progress on generation of single-cycle THz pulses at the two-hundred micro-Joule level to drive advanced acceleration and beam manipulation devices. Specifically, we use pulses centered at 0.3 THz to power a segmented terahertz electron accelerator and manipulator (STEAM) capable of performing multiple high-field operations on the 6D-phase-space of ultrashort electron bunches. Using this STEAM device, we demonstrate record THz-acceleration of >60 keV, streaking with <10 𝑓s resolution, focusing with >2 kT/m strength, compression to ~100 𝑓s as well as real-time switching between these modes of operation. The STEAM device demonstrates the feasibility of THz-based electron accelerators, manipulators and diagnostic tools enabling science beyond current resolution frontiers with transformative impact.