Diagnostic Beamline Research Articles

Scattered high-energy synchrotron radiation at theKARA visible-light diagnostic beamline.

To characterize an electron beam, visible synchrotron light is often used and dedicated beamlines at synchrotron sources are becoming a more common feature as instruments and methods for the diagnostics are, along with the accelerators, further developed. At KARA (Karlsruhe Research Accelerator), such a beamline exists and is based on a typical infrared/visible-light configuration. From experience at such beamlines no significant radiation was expected (dose rates larger than 0.5 µSv h-1). This was found not to be the case and a higher dose was measured which fortunately could be shielded to an acceptable level with 0.3 mm of aluminium foil or 2.0 mm of Pyrex glass. The presence of this radiation led to further investigation by both experiment and calculation. A custom setup using a silicon drift detector for energy-dispersive spectroscopy (Ketek GmbH) and attenuation experiments showed the radiation to be predominantly copper K-shell fluorescence and is confirmed by calculation. The measurement of secondary radiation from scattering of synchrotron and other radiation, and its calculation, is important for radiation protection, and, although a lot of experience exists and methods for radiation protection are well established, changes in machine, beamlines and experiments mean a constant appraisal is needed.

Automatic Analysis and Anomaly Detection System of Transverse Electron Beam Profile Based on Advanced and Interpretable Deep Learning Architectures

Abstract The National Synchrotron Radiation Center SOLARIS, ranked among the top infrastructures of that type worldwide, is the only one located in Central-Eastern Europe, in Poland. The SOLARIS Center, with six fully operational beamlines, serves as a hub for research across a diverse range of disciplines. This cutting-edge facility fosters innovation in fields like biology, chemistry, and physics as well as material engineering, nanotechnology, medicine, and pharmacology. With its advanced infrastructure and multidisciplinary approach, the SOLARIS Center enables discoveries and pushes the boundaries of knowledge. The most important aspect of such enormous research as well as industry infrastructure is to provide stable working conditions for the users and the conducted projects. Due to its unique properties, problem complexities, and challenges that require advanced approaches, the problem of anomaly detection and automatic analysis of signals for the beam stability assessment is still a huge challenge that has not been fully developed. To increase the effectiveness of centers with advanced research infrastructure we focus on the automatic analysis of transverse beam profiles generated by the Pinhole diagnostic beam-line. Pinhole beamlines are typically installed in the middle and high-energy synchrotrons to thoroughly analyze emitted X-rays and therefore assess electron beam quality. To address the problem we take advantage of AI solutions including up-to-date pre-trained convolutional neural network (CNN) models among others EfficientNetB0-B4-B6, InceptionV3 and DenseNet121. In this research, we propose the benchmark for Pinhole image classification including data preprocessing, model implementation, training process, hyperparameter selection as well as testing phase. Created from scratch database contains over one million transverse beam profile images. The proposed solution, based on the InceptionV3 architecture, classifies pinhole beamline images with 94.1% accuracy and 96.6% precision which is a state-of-the-art result in this research area. Finally, we employed interpretability algorithms to perform an analysis of the models and achieved results.

Free-electron laser temporal diagnostic beamline FL21 at FLASH.

A beamline for temporal diagnostics of extreme ultraviolet (XUV) femtosecond pulses at the free-electron laser in Hamburg (FLASH) at DESY was designed, built and put into operation. The intense ultra-short XUV pulses of FLASH fluctuate from pulse to pulse due to the underlying FEL operating principle and demand single-shot diagnostics. To cope with this, the new beamline is equipped with a terahertz field-driven streaking setup that enables the determination of single pulse duration and arrival time. The parameters of the beamline and the diagnostic setup as well as some first experimental results will be presented. In addition, concepts for parasitic operation are investigated.

Generation and characterization of magnetized electron beam from a DC high voltage photogun for electron beam cooling application

One of the most challenging requirements for the proposed Electron–Ion Collider is the strong cooling of the proton beam, which is key to achieving the collider’s desired luminosity of order 1033–1034 cm−2 s−1. Magnetized bunched-beam electron cooling could be a means to achieve the required high luminosity, where strong cooling is accomplished inside a cooling solenoid where the ions co-propagate with an electron beam generated from a source immersed in a magnetic field. To increase the cooling efficiency, a bunched electron beam with high bunch charge and high repetition rate is required. This work describes the production and characterization of magnetized electron beam using a compact 300 kV DC high voltage photogun and bi-alkali antimonide photocathode. Beam magnetization was studied using a diagnostic beamline that includes viewer screens for measuring the shearing angle of the electron beamlet passing through a narrow upstream slit. Simulations and corresponding measurements of beam magnetization are presented as a function of laser spot size and magnetic field strength. Correlated beam emittance with magnetic field (0–0.15 T) at the photocathode was measured for various laser spot sizes. Measurements of photocathode lifetime were carried out at different magnetized electron beam currents up to 28 mA, and bunch charge up to 0.7 nC (not simultaneously).

Measurement and calculation of scattered Synchrotron Radiation processes at the KARA visible light beamline

At KARA a visible light diagnostic beamline is in use to analyse the stored electron beam. Synchrotron light is deflected 90 degrees upwards by a cooled copper mirror, passes through a Quartz UHV window and is then reflected back into the horizontal plane but sideways through a hole in the wall to the diagnostics. Based on experience from similar Infrared beamlines no significant radiation (doserates larger than 0.5µSv/hr) was expected. Nevertheless, a higher radiation level exists but can be shielded with 0.3mm Aluminium foil or 2.0mm of Pyrex reducing the rate to an acceptable level. The presence of the radiation led to further investigation by experiment and calculation. A custom setup using a silicon drift detector (SDD) for energy dispersive spectroscopy showed the radiation to be predominantly Copper K-alpha and is confirmed by FLUKA and other calculations of the scattered Synchrotron radiation.

Simulation of synchrotron radiation from electron beams affected by vibrations and drifts

This paper presents results of simulations of synchrotron radiation from electron beams affected by instabilities in position and angle at the source point. The goal of this work is to develop and test instrumentation for studies of the effects of the electron beam's vibrations and drifts on beamline performance at synchrotron light sources. To perform these simulations, numerical methods were developed and implemented in the Python version of the Synchrotron Radiation Workshop (srw) code. The simulation results were compared against analytical formulas and experimental results obtained from an x-ray pinhole-camera diagnostics beamline at NSLS-II. We compared the measured data with the prediction by our code for amplitudes of orbit oscillation from $6--60\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ and frequencies between 1 and 40 Hz, also taking into account the effects of misalignment of the pinhole. The simulation results are in good agreement with both analytical estimates and experimental data.

High-Fidelity Prediction of Megapixel Longitudinal Phase-Space Images of Electron Beams Using Encoder-Decoder Neural Networks

Modeling of large-scale research facilities is extremely challenging due to complex physical processes and engineering problems. Here, we adopt a data-driven approach to model the longitudinal phase-space diagnostic beamline at the photoinector of the European XFEL with an encoder-decoder neural network model. A deep convolutional neural network (decoder) is used to build images measured on the screen from a small feature map generated by another neural network (encoder). We demonstrate that the model trained only with experimental data can make high-fidelity predictions of megapixel images for the longitudinal phase-space measurement without any prior knowledge of photoinjectors and electron beams. The prediction significantly outperforms existing methods. We also show the scalability and interpretability of the model by sharing the same decoder with more than one encoder used for different setups of the photoinjector, and propose a pragmatic way to model a facility with various diagnostics and working points. This opens the door to a new way of accurately modeling a photoinjector using neural networks and experimental data. The approach can possibly be extended to the whole accelerator and even other types of scientific facilities.

Status of the Dedicated Electron Diagnostic Beamline at AXSIS

Status of the Dedicated Electron Diagnostic Beamline at AXSIS

Design of High Energy Photon Source Booster beam size monitor

High Energy Photon Source (HEPS) Booster is designed to ramp up the energy of the beam from linac and inject high quality electron beam to the storage ring. To measure the transverse beam size, emittance and energy spread of HEPS Booster, we designed two beam diagnostic beamlines at visible-UV spectrum region. The source points are at two bending magnets with different chromatic dispersion, one has no dispersion while the other has large dispersion. By measuring the transverse beam sizes with synchrotron imaging system, beam emittance and energy spread can also be calculated. This paper introduces the extraction of visible-UV light, and the optical imaging system, the spatial resolution. It also introduces the design of beam spot changes measurement during beam ramping process.

Solaris synchrotron performance and operational status

Solaris is a third generation light source operating since 2015 in Krakow, Poland. Between 2015 and 2018 the synchrotron as well as two beamlines were commissioned. During the commissioning phases the good performance of Solaris storage ring was reached. The beam optics was brought close to the design one. Since October 2018 the Solaris storage ring is in the user operation mode. Moreover, two other beamlines (PHELIX and XMCD) with elliptically polarized undulators used as source have been installed, currently under commissioning. In 2019 the total beam availability of 91.9% was reached with the average circulating current of 280 mA and the total lifetime of 25 h. Over the last year few improvements of the storage ring were done in order to optimize the storage ring performance. The Landau cavities were tuned to improve the Touschek lifetime and to suppress the instabilities. Two diagnostic beamlines were set up and commissioned, allowing for the beam size and the emittance measurements. The storage ring optics was fine-tuned to increase the dynamic aperture.

Thermal emittance and lifetime of alkali-antimonide photocathodes grown on GaAs and molybdenum substrates evaluated in a −300 kV dc photogun

${\mathrm{Cs}}_{x}{\mathrm{K}}_{y}\mathrm{Sb}$ photocathodes grown on GaAs and molybdenum substrates were evaluated using a $\ensuremath{-}300\text{ }\text{ }\mathrm{kV}$ dc high voltage photogun and diagnostic beam line. Photocathodes grown on GaAs substrates, with varying antimony layer thickness (estimated range from $<20\text{ }\text{ }\mathrm{nm}$ to $>1\text{ }\text{ }\mathrm{um}$), yielded similar thermal emittance per rms laser spot size values ($\ensuremath{\sim}0.4\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}/\mathrm{mm}$) but very different operating lifetime. Similar thermal emittance was obtained for a photocathode grown on a molybdenum substrate but with markedly improved lifetime. For this photocathode, no decay in quantum efficiency was measured at 4.5 mA average current and with peak current 0.55 A at the photocathode.

Upgrade of diagnostics beamline BL7B at Pohang Light Source for a photon BPM and CRL X-ray imaging

A Photon Beam Position Monitor (PBPM) and Compound Refractive Lens (CRL) have been implemented in the diagnostics beamline to measure photon beam stability and beam profile from X-ray imaging, respectively. Synchrotron radiation with 8.6-keV critical photon energy from bending magnet is available in the diagnostics beamline at PLS-II [1]. The most common PBPM is a simple structure equipped with two blades; it enables the beam diagnostics beamline to measure photon beam stability up to 500-Hz photon beam motion. The electron beam size can be measured and beam profile can be monitored in real time by CRL X-ray imaging. The beam diagnostics beamline BL7B provides important information on the condition of the photon beam in PLS-II.

Beam Dump Fabrication and Simulation by Using PHITS Code and an ANSYS Analysis

The design of a beam dump for the energy range less than 20 MeV is reported. The beam dump was developed for the beam extraction commissioning stage of the Korea Basic Science Institute’s( KBSI’s) heavy ion facility. At present, the downstream section design of the diagnostic chamber of the beam line was completed, as has the fabrication of a radio-frequency quadrupole(RFQ) section. We are now performing frequency tuning for optimization. For reduction and elimination of the generated beam, the beam dump will be located downstream of the diagnostic beam line, and the beam dump was designed to withstand a heavy-ion beam energy of less than 20 MeV. The PHITS code and ANSYS steady-state thermal analysis were adapted for simulating the heat transfer and determining the numbers and types of secondary particles produced by bombardment of the beam’s dump material, respectively.

Upgrade of the X-ray pinhole camera system at SSRF

An X-ray pinhole camera has been used to determine the transverse beam size and emittance on the diagnostic beam line of the storage ring at SSRF since 2009. The performance of the beam size measurement is determined by the width of the point spread function of the X-ray pinhole camera. Beam-based calibration was carried in 2012 out by varying the beam size at the source point and measuring the image size. However, this calibration method requires special beam conditions. In order to overcome this limitation, the pinhole camera was upgraded and an X-ray quasi-monochromator was installed. A novel experimental method was introduced by combining the pinhole camera with the monochromator to calibrate the point spread function. The point spread function can be accurately resolved by adjusting the angle of the monochromator and measuring the image size. The X-ray spectrum can also be obtained. In this work, the X-ray quasi-monochromator and the novel beam-based calibration method will be presented in detail.

Coupling control and optimization at the Canadian Light Source

We present a detailed study using the skew quadrupoles in the Canadian Light Source storage ring lattice to control the parameters of a coupled lattice. We calculate the six-dimensional beam envelop matrix and use it to produce a variety of objective functions for optimization using the Multi-Objective Particle Swarm Optimization (MOPSO) algorithm. MOPSO produces a number of skew quadrupole configurations that we apply to the storage ring. We use the X-ray synchrotron radiation diagnostic beamline to image the beam and we make measurements of the vertical dispersion and beam lifetime. We observe satisfactory agreement between the measurements and simulations. These methods can be used to adjust phase space coupling in a rational way and have applications to fine-tuning the vertical emittance and Touschek lifetime and measuring the gas scattering lifetime.

The development of W-PBPM at diagnostic beamline

The photon beam position monitor (PBPM) plays a critically important role in the accurate monitoring of the beam position. W (Wire)-PBPMs are installed at the front end and photon transfer line (PTL) of the diagnostic beamline and detect the change of position and angle of the beam orbit applied to the beamline. It provides beam stability and position data in real time, which can be used in feedback system with BPM in storage-ring. Also it provides beam profile, which makes it possible to figure out the specifications of beam. With two W-PBPMs, the angle information of beam could be acquired and the results coupled with beam profile are used with orbit correction. The W-PBPM has been designed and installed in the diagnostic beamline at Pohang Light Source. Herein the details of the design, analysis and performance for the W-PBPM will be reported.

Methods for measuring sub-pm rad vertical emittance at the Swiss Light Source

We report on methods capable of measuring a rms vertical electron beam size of 3μm with a rms error of less than 10% at a diagnostic beamline at the Swiss Light Source (SLS). This corresponds to a vertical emittance of 0.6pmrad with a 20% rms error. We showed this capability by presenting the theoretical basis for, and the data from, a series of measurements on a stable beam at 1.6pmrad vertical emittance at the SLS. The methods presented utilized either π- or σ-polarized synchrotron radiation (SR) in the visible to ultra violet (vis-UV) spectral range. In addition to the established π-polarization method, we introduced a diffraction method with a potentially high resolution capability. Also an intensity imbalanced diffraction scheme was introduced, but was found to be prone to SR induced carbon contamination on optical elements.

Design of x-ray diagnostic beam line for a synchrotron radiation source and measurement results

Indus-2 is a 2.5GeV synchrotron radiation source (SRS) operational at the Raja Ramanna Centre for Advanced Technology (RRCAT) in India. We have designed, developed and commissioned x-ray diagnostic beam line (X-DBL) at the Indus-2. It is based on pinhole array imaging (8–18keV). We have derived new equations for online measurements of source position and emission angle with pinhole array optics. Measured values are compared with the measurements at an independent x-ray beam position monitor (staggered pair blade monitor) installed in the X-DBL. The measured values are close to the theoretical expected values within ±12µm (or ±1.5μrad) for sufficiently wide range of the beam movements. So, beside the beam size and the beam emittance, online information for the vertical position and angle is also used in the orbit steering. In this paper, the various design considerations of the X-DBL and online measurement results are presented.

Experimental studies of dark current in a superconducting rf photoinjector

A superconducting rf photoinjector (SRF gun) has been put in operation successfully at the radiation source ELBE. It produces a 13 MHz, low emittance, cw beam with beam current up to $400\text{ }\text{ }\ensuremath{\mu}\mathrm{A}$ and energy of 3 MeV. During the gun operation, the field emission from the niobium cavity and the ${\mathrm{Cs}}_{2}\mathrm{Te}$ cathodes produces dark current. In this paper, we study the dark current of the SRF gun by using the existing diagnostics beam line. The dependency of the intensity and the energy spectrum on the cavity gradient and the cathode voltage are examined, and the emission sources are analyzed. Furthermore, the new project of installing a strip line kicker to reduce the dark current effect is presented.

Measurements of aperture and beam lifetime using movable beam scrapers in Indus-2 electron storage ring

In this paper, the measurements of vertical and horizontal aperture which are available for stable beam motion in Indus-2 at beam energy 2.5 GeV using movable beam scrapers are presented. These beam scrapers are installed in one of the long straight sections in the ring. With the movement of beam scrapers towards the beam centre, the beam lifetime is measured. The beam lifetime data obtained from the movement of vertical and horizontal beam scrapers are analyzed. The contribution of beam loss due to beam-gas scattering (vacuum lifetime) and electron-electron scattering within a beam bunch (Touschek lifetime) is separated from the measured beam lifetime at different positions of the beam scrapers. Vertical and horizontal beam sizes at scrapers location are estimated from the scraper movement towards the beam centre in quantum lifetime limit and their values closely agree with measured value obtained using X-ray diagnostic beamline.