The Linac Coherent Light Source (LCLS) is the first x-ray laser user facility based upon a free electron laser (FEL). In addition to many other stringent requirements, the LCLS XFEL requires extraordinary beam quality to saturate at 1.5 angstroms within a 100 meter undulator.[1] This new light source is using the last kilometer of the three kilometer linac at SLAC to accelerate the beam to an energy as high as 13.6 GeV and required a new electron gun and injector to produce a very bright beam for acceleration. At the outset of the project it was recognized that existing RF guns had the potential to produce the desired beam but none had demonstrated it. This paper describes the analysis and design improvements of the BNL/SLAC/UCLA s-band gun leading to achievement of the LCLS performance goals.
Although accelerator technology has matured sufficiently, state-of-the-art X-ray linacs for radiotherapy and cargo-scanning capture merely 30-50% of the electrons from a thermionic cathode, requiring a higher cathode current and leaving uncaptured electrons to cause problems due to back bombardment, shortening of cathode life, etc. Any solution to increase capture should be effective, simple, reliable, compact, and low cost in order to be adopted by industry. To address this, we present the design of a 6 MeV high capture efficiency S-band electron linac that captures 90% of the initial DC beam…
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…
Due to the various applications of THz sources, we developed a pure permanent magnet (PPM) undulator with 8 periods and min/max values of gap equal to 15/25, to use at the end of our current 10 MeV linear accelerator (linac) in order to produce THz coherent radiation. We used RADIA for simulation and calculation of our magnet and B2E code for calculation of its radiation harmonics. After fabrication, we also measured the magnetic field via high precision Hall probes. Calculations and measurements are in good agreements. These calculations show that it is possible to reach photon energies from …
Energy recovery linac (ERL) holds great promise for generating high repetition-rate and high brightness electron beams. The application of ERL to drive a free-electron laser is currently limited by its low peak current. In this paper, we consider the combination of ERL with the recently proposed angler-dispersion induced microbunching technique to generate fully coherent radiation pulses with high average brightness and tunable pulse length. Start-to-end simulations have been performed based on a low energy ERL (600 MeV) for generating coherent EUV radiation pulses. The results indicate an ave…
We present design and simulation results on the electron source for 2856 MHz technological electron linac. This device is a combination of an RF gun and a DC diode gun. The designed gun consists of a thermionic cathode, which is mounted on the wall of the TM010 cavity that is under negative high voltage potential relatively to an anode. The use of such an electron source makes it possible to exclude the high-voltage gun modulator and resonator for beam prebunching from the accelerator circuit. Duration and position of an electron beam pulse within a RF power supply pulse of the accelerating se…
本文介绍了一种适用于短波长直线加速器自由电子激光器的高亮度电子源的设计方案。该项目的目标是开发一种多电池集成的光注入器，能够提供发射度低于1 mm mrad的1 nC聚束。这将是在现有的里雅斯特直线加速器基础上开发第四代光源测试设施的第一步。为此目的，的里雅斯特新克罗特公司和INFN米兰公司之间开展了一项共同计划。本文简要介绍了ELETTRA直线加速器上射频电子枪电磁结构和束流动力学的初步结果。
The treatment of flue gases from power plants and municipal or industrial wastewater using electron beam irradiation technology has been successfully demonstrated in small-scale pilot plants. The beam energy requirement is rather modest, on the order of a few MeV, however the adoption of the technology at an industrial scale requires the availability of high beam power, of the order of 1 MW, in a cost effective way. In this article we present the design of a compact superconducting accelerator capable of delivering a cw electron beam with a current of 1 A and an energy of 1 MeV. The main compo…
Accelerators produce too many signals for a small operations team to monitor in real time. In addition, many of these signals are only interpretable by subject matter experts with years of experience. As a result, changes in accelerator performance can require time-intensive consultations with experts to identify the underlying problem. Herein, we focus on a particular anomaly detection task for radio-frequency (RF) stations at the Linac Coherent Light Source (LCLS). The existing RF station diagnostics are bandwidth limited, resulting in slow, unreliable signals. As a result, anomaly detection…
LCLS-II is currently in its commissioning phase at SLAC. It is an X-ray FEL driven by a CW superconducting LINAC. The beam injector plays a crucial role in the overall performance of the accelerator, and is critical to the final electron beam performance parameters. The LCLS-II injector comprises of a 185.7 MHz VHF copper gun cavity, and a 1.3 GHz two-cell L-band copper buncher cavity. The FPGA-based controller employs feedback and Self-Excited Loop logic in order to regulate the cavity fields. It also features several other functionalities, such as live detune computation, active frequency tr…
SLAC National Accelerator Laboratory is collaborating with Arizona State University to design a LLRF system towards the advancement of the ASU Compact X-ray Light Source (CXLS). The CXLS is a phased project to develop small brilliant x-ray sources that may produce coherent x-rays appropriate as a seed source for LCLS and LCLS II. The CXLS electron beam is produced by an x-band photoinjector and linac operating at 9.3 GHz RF frequency and 1 kHz repetition rate with up to 300 pC per bunch. The linac consists of 3 short 20-cell sections of standing wave linac. The RF gun and linac sections are po…
Asymmetric Dual Axis Energy Recovery Linac for Ultra-High Flux sources of coherent X-ray/THz radiation: Investigations Towards its Ultimate Performance
The AXSIS project (Attosecond X-ray Science: Imaging and Spectroscopy) aims to develop a THz-driven compact X-ray source for applications e.g. in chemistry and biology by using ultrafast coherent diffraction imaging and spectroscopy. The key components of AXSIS are the THz-driven electron gun and THz-driven dielectric loaded linear accelerator as well as an inverse Compton scattering scheme for the X-rays production. This paper is focused on the prototype of the THz-driven electron gun which is capable of accelerating electrons up to tens of keV. Such a gun was manufactured and tested at the t…
Compact DC high-voltage photo-electron guns are able to meet the sophisticated demands of high-current applications such as energy recovery linacs. A main design parameter for such sources is the electric field strength, which depends on the electrode geometry and is limited by the field emission threshold of the electrode material. In order to minimize the maximum field strength for optimal gun operation, isogeometric analysis (IGA) can be used to exploit the axisymmetric geometry and describe its cross section by non-uniform rational B-splines, the control points of which are the parameters …
Over the last years, the generation and acceleration of ultra-short, high quality electron beams has attracted more and more interest in accelerator science. Electron bunches with these properties are necessary to operate and test novel diagnostics and advanced high gradient accelerating schemes such as plasma accelerators or dielectric laser accelerators. Furthermore, several medical and industrial applications require high-brightness electron beams. The dedicated R&D facility ARES at DESY will provide such probe beams in the upcoming years. After the setup of the normal-conducting RF photoin…
With a low emittance and short-bunch electron beam at a high repetition rate realized by a superconducting linac, stimulated excitation of an optical cavity at the terahertz spectrum range has been shown. The electron beam passed through small holes in the cavity mirrors without being destroyed. A sharp resonance structure which indicated wide-band stimulated emission via coherent diffraction radiation was observed while scanning the round-trip length of the cavity.
A superconducting linear accelerator operating in continuous-wave mode could produce X-ray free electron lasers (XFEL) at megahertz repetition rate, with the capability that delivering wide spectral range coherent radiation to multi end stations. In this Letter, the energy recovery Linac (ERL) mode is proposed to flexibly control the electron beam energy for a continuous-wave superconducting Linac. Theoretical investigations and multi-dimensional numerical simulations are applied to the Linac case of Shanghai high-repetition-rate XFEL and extreme light facility. The results show that, with ERL…
A superconducting radio-frequency (SRF) photo injector is in operation at the electron linac for beams with high brilliance and low emittance (ELBE) radiation center and generates continuous wave (CW) electron beams with high average current and high brightness for user operation since 2018. The speed of emittance measurement at the SRF gun beamline can be increased by improving the slit-scan system, thus the measurement time for one phase space mapping can be shortened from about 15 minutes to 90 seconds. A parallel algorithm and machine learning have been used to reduce the beamlet image noi…
Superconducting RF (SRF) photo-injectors are one of the most promising devices for generating continuous wave (CW) electron beams with record high brightness. Ultra-high vacuum of SRF guns provides for long lifetime of the high quantum efficiency (QE) photocathodes, while SRF technology provides for high accelerating gradients exceeding 10 MV/m. It is especially true for low frequency SRF guns where electrons are generated at photocathodes at the crest of accelerating voltage. Two main physics challenges of SRF guns are their compatibility with high QE photocathodes and multipacting. The first…
Accelerator-based terahertz (THz) radiation has been expected to realize a high-power broadband source. Employing a low-emittance and short-bunch electron beam at a high repetition rate, a scheme of coherent diffraction-radiation in an optical cavity layout is proposed. The scheme's stimulated radiation process between bunches can greatly enhance the efficiency of the radiation emission. We performed an experiment with a superconducting linac constructed as an energy recovery linac (ERL) test facility. The electron beam passes through small holes in the cavity mirrors without being destroyed. …
