In the past decade, the bunch lengths of electrons in accelerators have decreased dramatically to the range of a few picoseconds \cite{Uesaka94,Trotz97}. Measurement of the length as well as the longitudinal profile of these short bunches have been a topic of research in a number of institutions \cite{Uesaka97,Liu97,Hutchins00}. One of the techniques uses the electric field induced by the passage of electrons in the vicinity of a birefringent crystal to change its optical characteristics. Well-established electro-optic techniques can then be used to measure the temporal characteristics of the electron bunch. In this paper we present a novel, non-invasive, single-shot approach to improve the resolution to tens of femtoseconds so that sub-millimeter bunch length can be measured.
Electron accelerators and synchrotrons can be operated to provide short emission pulses due to longitudinally compressed or sub-structured electron bunches. Above a threshold current, the high charge density leads to the micro-bunching instability and the formation of sub-structures on the bunch shape. These time-varying sub-structures on bunches of picoseconds-long duration lead to bursts of coherent synchrotron radiation in the terahertz frequency range. Therefore, the spectral information in this range contains valuable information about the bunch length, shape and sub-structures. Based on …
High-repetition-rate sources of bright electron bunches have a wide range of applications. They can directly be employed as probes in electron-scattering setups, or serve as a backbone for the generation of radiation over a broad range of the electromagnetic spectrum. This paper describes the development of a compact sub-Mega-electronvolt (sub-MeV) electron-source setup capable of operating at MHz repetition rates and forming sub-picosecond electron bunches with transverse emittance below 20~nm. The setup relies on a conduction-cooled superconducting single-cell resonator with its geometry alt…
We briefly compare in numerical simulations the relativistic ionization front and electron bunch seeding of the self-modulation of a relativistic proton bunch in plasma. When parameters are such that initial wakefields are equal with the two seeding methods, the evolution of the maximum longitudinal wakefields along the plasma are similar. We also propose a possible seeding/injection scheme using a single plasma that we will study in upcoming simulations works.
In AWAKE a self-modulated proton bunch drives wakefields in a plasma. Recent experiments successfully demonstrated many aspects of the self-modulation of the drive bunch as well as acceleration of test electrons. Next experiments will focus on producing a multi-GeV accelerated electron bunch with low emittance and low energy spread. The experiment requires a variety of advanced beam diagnostics to characterize the self-modulated proton bunch at the picosecond time scale. These include optical transition radiation and a streak camera for short and long time scale detailed imaging of self-modula…
Plasma-based accelerators have made remarkable progress over the last two decades. Their unique characteristics make them tools that can revolutionize fields of science and applications. AWAKE takes advantage of the availability of high-energy, relativistic proton bunches to drive large amplitude wakefields ($\sim$GV/m) in a single plasma over distances sufficient to produce hundreds of GeV to TeV electron bunches.
Charged particle bunch length detection is one of the most challenging measurements in particle and accelerator physics, especially when the bunch length reduces below tens of femtoseconds. Since these measurements are most critical in high energy electron accelerators and devices with ultrashort electron bunches - such as the plasma wakefield and related accelerators - this discussion is limited to electron bunch detection, although the results clearly have significance for any ultra-relativistic particle bunches.
Knowledge of longitudinal electron bunch profiles is vital to optimize the performance of plasma wakefield accelerators and x-ray free electron laser linacs. Because of their importance to these novel applications, noninvasive frequency domain techniques are often employed to reconstruct longitudinal bunch profiles from coherent synchrotron, transition, or undulator radiation measurements. In this paper, we detail several common reconstruction techniques involving the Kramers-Kronig phase relationship and Gerchberg-Saxton algorithm. Through statistical analysis, we draw general conclusions abo…
University of Chicago（芝加哥大学）；Brookhaven National Laboratory（布鲁克海文国家实验室）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；SLAC National Accelerator Laboratory（斯坦福直线加速器中心）
The equations, which describe generation of coherent radiation by a relativistic electron bunch moving in a photonic crystal, are obtained. Spectral-angular distribution of radiation and intensity of radiation in time-domain are derived. The interaction of the bunch electrons with the electromagnetic field induced by bunch itself at the initial stage of producing coherent radiation is shown contributing to the expression for the bunch current with the terms proportional to particle acceleration (proportional to interaction time and strength of electric field induced by bunch itself) along with…
We present the design of a high repetition rate MeV energy ultrafast electron diffraction instrument based on a DC photoelectron gun and an SRF linac with multiple independently controlled accelerating and bunching cavities. The design is based on the existing Cornell photoinjector, which can readily be applied to the presented findings. Using particle tracking simulations in conjunction with multiobjective genetic algorithm optimization, we explore the smallest bunch lengths, emittance, and probe spot sizes achievable. We present results for both stroboscopic conditions (with single electrons…
The development of fast detection methods for comprehensive monitoring of electron bunches is a prerequisite to gain comprehensive control over the synchrontron emission in storage rings with their MHz repetition rate. Here, we present a proof-of-principle experiment with at detailed description of our implementation to detect the longitudinal electron bunch profiles via single-shot, near-field electro-optical sampling at the Karlsruhe Research Accelerator (KARA). Our experiment is equipped with an ultra-fast line array camera providing a high-throughput MHz data stream. We characterize statis…
At SwissFEL, a fully non-invasive characterization of the beam energy distribution can be performed by means of a Synchrotron-Radiation-Monitor (SRM) imaging in the visible the transverse profile of the electron beam in a magnetic chicane. Under conditions of off-crest acceleration in the SwissFEL injector, according to a first order Taylor series expansion, the distribution of the relative energy of the electron beam can be linearly expressed as a function of the distribution of the electron longitudinal coordinates via the coefficient of the rf induced beam energy chirp. It is hence possible…
Temporally-shaped electron bunches at ultrafast time scales are foreseen to support an array of applications including the development of small-footprint accelerator-based coherent light sources or as probes for, e.g., ultrafast electron-diffraction. We demonstrate a method where a transversely-segmented electron bunch produced via photoemission from a transversely-patterned laser distribution is transformed into an electron bunch with modulated temporal distribution. In essence, the presented transformation enables the mapping of the transverse laser distribution on a photocathode surface to …
In the presence of longitudinal coherent electron cooling, the evolution of the line-density profile of a circulating ion bunch can be described by the 1-D Fokker-Planck equation. We show that, in the absence of diffusion, the 1-D equation can be solved analytically for certain dependence of cooling force on the synchrotron amplitude. For more general cases with arbitrary diffusion, we solved the 1-D Fokker-Planck equation numerically and the numerical solutions have been compared with results from macro-particle tracking.
