Horizontal Beam Size Research Articles

Determination of microwave instability threshold of storage ring based on longitudinal bunch asymmetry characterization

In this study, a novel method is proposed to measure the microwave instability (MWI) threshold of the storage ring by means of the ultrafast photon detection streak camera system. It provides an additional and complementary diagnostic tool for determination of the MWI threshold of the current storage ring. Compared to other conventional measurement methods, this scheme can realize the more accurate measurement of the MWI threshold current with the remarkable advantages of simple optical architecture, good robustness, and high accuracy. In the experiment, the MWI threshold current of the Hefei Light Source-II (HLS-II) is obtained as 12.77 ± 0.54 mA corresponding to 123.6 kV of the nominal radio-frequency (RF) voltage by measuring the current dependence of the bunch asymmetry factor, under single-bunch operation mode. With a further adjust RF voltage to 100.2, 110.2, 130.3, and 140.2 kV, the turbulent threshold currents are acquired to be 11.11 ± 0.90, 11.74 ± 0.47, 13.21 ± 0.68, and 13.78 ± 0.82 mA, respectively. Additionally, the applicability, feasibility, and reliability of this method are further verified by experimentally observing the beam characteristic behaviors of the energy spread broadening and horizontal beam size widening. From experimental verification and comparative analysis, it is proved that this reported approach is valid for measuring the MWI threshold of the storage ring. This method is importance for the study of the beam instability mechanisms and related longitudinal beam dynamics in storage ring, which is also useful for machine debugging and beam status analysis.

Electron Energy Spectrometer for MIR-THz FEL Light Source at Chiang Mai University

The linear accelerator system of the PBP-CMU Electron Linac Laboratory has been designed with the aim of generating free-electron lasers (FELs) in the mid-infrared (MIR) and terahertz (THz) regions. The quality of the radiation is strongly dependent on the properties of the electron beam. Among the important beam parameters, the electron beam energy and energy spread are particularly important. To accurately measure the electron beam energy, the first dipole magnet in the bunch compressor system and the downstream screen station are employed as an energy spectrometer. The A Space Charge Tracking Algorithm (ASTRA) software is used for the design and optimization of this system. Simulation results demonstrate that the developed spectrometer is capable of accurately measuring the energy within the 5–25 MeV range. The screen station system is designed and constructed to have the ability to capture a beam size with a resolution of 0.1 mm per pixel. This resolution is achieved with a screen-to-camera distance of 1.2 m, which proves sufficient for precise energy measurement. The systematic error in energy measurement is found to be less than 10%, with a minimum energy spread of 0.4% achievable when the horizontal beam size remains below 3 mm.

Two-dimensional electron beam size measurements with x-ray heterodyne near field speckles

In this paper we report on recent two-dimensional (2D) electron beam size measurements with a nonconventional synchrotron radiation interferometric technique based on x-ray heterodyne near field speckles (HNFS). The method relies on Fourier analysis of the random speckle patterns generated by a water suspension of nanospheres to assess the full 2D transverse coherence of the incoming x rays. The horizontal and vertical electron beam sizes are then retrieved by means of statistical optics approaches. The manuscript thoroughly describes the HNFS technique, and shows experimental results obtained at the ALBA Synchrotron Light Source. By changing the machine coupling, beam sizes as small as $5\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ are measured, thus improving on past measurements reported in the literature and proving the HNFS diagnostics suitable for low-emittance particle beams.

A proof-of-principle experiment on a new diagnostic tool for determining beam sizes from angular distributions of parametric X-ray radiation

A previously proposed technique for measuring the transverse sizes of an electron beam was verified experimentally by comparing the angular distributions of parametric X-ray radiation in a thin crystal for two distances between the crystal and the detector. The measurements were performed on a 255-MeV electron beam incident on a 20 μm-thick silicon crystal. The angular distributions of parametric X-ray radiation were measured using an imaging plate as a two-dimensional position-sensitive detector. The obtained horizontal and vertical beam sizes were in good agreement with the results of measurements by optical transition radiation. The proposed method would be useful for electron beam diagnostics for recently advanced linear accelerators where optical transition radiation cannot be used as a beam profile monitor owing to the coherent effect.

Design and relative calibration of a beam profile measurement system for the SC200 superconducting cyclotron

The SC200 superconducting cyclotron promoted by the ASIPP (Hefei, China) and the Joint Institute for Nuclear Research (Dubna, Russia) has made significant progress. A new beam profile measurement system (BPMS) has been developed to operate inside the cyclotron to acquire information of the transverse beam profile. We present the structural layout of the BPMS in frame of the SC200 superconducting cyclotron operating scenario with many details, e.g. high magnetic field, compact structure, high radio frequency interference and strong irradiation, etc. The influences of the magnetic field, heat-dissipating method, and other factors on the BPMS were described in detail and solved. The energy loss, spectral matching, and the temperature dependency of the scintillation screen, as well as the directional characteristic of the imaging system were all taken into account for a relative calibration of the BPMS. The BPMS was adopted for beam diagnosis during the initial commissioning phase of the SC200, and the experimental results of light output and horizontal beam sizes were calibrated to provide quantitative information. Furthermore, the beam loss and vertical distribution of the beam were calculated, which provide important basis for beam tuning and optimization of the cyclotron. The successful application of the BPMS inside the compact cyclotron is of great significance for further shimming and optimization of the isochronous field.

Experimental study on broadband bistable energy harvester with L-shaped piezoelectric cantilever beam

This paper presents an experimental study of the broadband energy harvesting and dynamic responses of an L-shaped piezoelectric cantilever beam. Experimental results show that the L-shaped piezoelectric beam generates two optimal voltage peaks when the horizontal beam size is similar to the vertical beam size. Several optimized L-shaped piezoelectric cantilever beam structures are proposed. Power generation using the inverted bistable L-shaped beam is better. It is observed experimentally that the inverted bistable L-shaped beam structure shows obvious bistable characteristics and hard spring characteristics. Furthermore, the corresponding relationship between the bistable phase portrait and the potential energy curve is found in the experiment. This is the first time that a phase portrait for stiffness hardening of an L-shaped beam has been found experimentally. These results can be applied to analysis of new piezoelectric power generation structures.

Profile measurement of circulating electrons in a synchrotron by inserting a carbon wire

An internal radiator made of a carbon wire is employed to produce bremsstrahlung-photon beams for meson photoproduction experiments from circulating electrons in a synchrotron at the Research Center for Electron Photon Science, Tohoku University. The horizontal electron-beam size at the radiator location is determined from the decay rate of the resultant photon intensity as a function of the distance between the fixed position of the radiator and the centroid of the electron beam. The horizontal beam size at the radiator location is determined to be 0.74 mm with a statical error less than 0.01 mm for 1.3-GeV circulating electrons. The horizontal correlation between the position and momentum direction of the electron beam is also measured. The horizontal size and correlation are well-reproduced by the design values of the parameters of the synchrotron.

Transverse beam profile measurement system for the Duke storage ring

The transverse beam emittance is a crucial parameter determining the brightness of an electron storage ring based synchrotron radiation source. The beam emittance is typically determined using the transverse electron beam size and the beta function at a particular location. For a low energy storage ring, the direct imaging method using visible/UV light has many advantages, including being simple, straightforward, and cost-effective. The resolution of such a system can be quite adequate for measuring electron beams with a reasonably large transverse beam size. In this work, we present the development of a new transverse beam profile measurement system for the Duke storage ring. This new system has been characterized to allow absolute measurements of the electron beam size while achieving better system resolution than previously thought possible for the direct imaging technique. The preliminary measurement results show that this system is capable of measuring the horizontal beam size over a wide range of the electron beam energies and currents. The system has also been demonstrated as a useful tool to study the intra-beam scattering related emittance increase in the storage ring.

Performance of beam size monitor based on Kirkpatrick–Baez mirror at SSRF

High-energy photon source (HEPS) is a 6 GeV ultralow emittance storage ring light source to be built in Beijing, China. Both the horizontal and vertical beam sizes of the HEPS storage ring are below 10 µm. It is a challenge to measure such a small beam size in both directions. To this end, measurement by a Kirkpatrick–Baez (KB) mirror imaging system was evaluated. A test KB system for the Shanghai Synchrotron Radiation Facility storage ring was designed and tested. Two crossed cylindrical mirrors were used to image the dipole source point. Both mirrors can be moved in and out so that the monitor is interchangeable with the original X-ray pinhole monitor. The aberration and point spread function, which would cause image blur, were evaluated. A beam-based calibration scheme was used by varying the beam size with different quadrupole settings and fitting them with the corresponding theoretical values. We updated the original X-ray camera with a new camera having a 5-μm-thick LuAG/Ce scintillator, and the imaging result shows greatly decreased image blur.

Variable focusing system for neutrons

We have developed a variable focusing system for neutrons that allows varying the vertical and horizontal beam size at the sample position independently. It is based on a focusing parabolic neutron guide coated with supermirror m = 6 times the critical angle of reflection of Ni. The divergence of the incident beam is adjusted by solid-state collimators with horizontally and vertically arranged absorbing blades. The performance of the prototype set-up has been benchmarked at the beamline BOA at SINQ confirming the expected behavior. In particular we show that the beam size at the sample position can be varied between 0.6 and 2 mm without exchanging the focusing guide or by introducing a beam-defining aperture between the exit of the guide and the sample, i.e. the beam size can be adapted more than half a meter away from the sample.

Parameter optimization and start-to-end simulation for the phase-merging enhanced harmonic generation free electron laser

Recently, a novel scheme called the phase-merging enhanced harmonic generation (PEHG) free-electron laser (FEL) has been developed to achieve higher harmonic bunching in a single stage set up. However, previous studies of the PEHG mechanism ignored the practical lattice configuration, leaving out the impact of the intrinsic beam divergence on the phase-merging effect. In this paper, a new method based on the beam transport matrix is proposed to comprehensively study the optimization conditions of the harmonic generation FELs. On the basis of this method, the new optimization conditions of the PEHG are obtained by taking into account both the intrinsic horizontal beam size and the intrinsic horizontal beam divergence. The parameter optimization and three dimensional start-to-end simulations are carried out using the typical beam parameters of the Shanghai Soft X-ray Free Electron Laser user facility. The simulation results are in agreement with the theoretical analysis and demonstrate the validity of the PEHG-FEL.

Design of a side coupled standing wave accelerating tube for NSTRI e-Linac

The design and construction of a 6 MeV electron linear accelerator (e-Linac) was defined in the Institute of Nuclear Science and Technology (NSTRI) for cargo inspection and medical applications. For this accelerator, a side coupled standing wave tube resonant at a frequency of 2998.5 MHZ in π/2 mode was selected. In this article, the authors provide a step-by-step explanation of the process of the design for this tube. The design and simulation of the accelerating and coupling cavities were carried out in five steps; (1) separate design of the accelerating and coupling cavities, (2) design of the coupling aperture between the cavities, (3) design of the entire structure for resonance at the nominal frequency, (4) design of the buncher, and (5) design of the power coupling port. At all design stages, in addition to finding the dimensions of the cavity, the impact of construction tolerances and simulation errors on the electromagnetic parameters were investigated. The values obtained for the coupling coefficient, coupling constant, quality factor and capture efficiency are 2.11, 0.011, 16203 and 36%, respectively. The results of beam dynamics study of the simulated tube in ASTRA have yielded a value of 5.14 π-mm-mrad for the horizontal emittance, 5.06 π-mm-mrad for the vertical emittance, 1.17 mm for the horizontal beam size, 1.16 mm for the vertical beam size and 1090 keV for the energy spread of the output beam.

Beam parameter optimization at CLIC using the process [formula omitted] at 380 GeV

At CLIC and the ILC beam–beam forces lead to the emission of beamstrahlung photons and a reduction of the effective center-of-mass energy. This degradation is controlled by the choice of the horizontal beam size. A reduction of this parameter would increase the luminosity but also the beamstrahlung. In this paper the optimum choice for the horizontal beam size is investigated for one of the most important physics processes. The Higgsstrahlung process e+e−→HZ is identified in a model-independent manner by observing the Z boson and determining the mass against which it is recoiling. The physics analysis for this process is performed for constant running times, assuming different beam size and taking into account the resulting levels of integrated luminosity and the associated luminosity spectra.

Study of alternative ILC final focus optical configurations

The current design of ILC final focus achieves perfect first order chromaticity correction in both horizontal and vertical planes. Based on RDR FFS optics a set of alternative optical configurations were studied in which the horizontal beam size at the IP is increased while at the same time the vertical one is decreased, with the goal of reducing beamsstrahlung emission. Luminosity reduction due to the hour glass effect must be considered because βy⁎/σz⁎ becomes much smaller in this case. The beam–beam interaction simulation by Guineapig++ was used for evaluation. Reduced bunch lengths are used to make sure that the obtained luminosities are not lower than those of the ILC RDR configuration.

Noninvasive emittance and energy spread monitor using optical synchrotron radiation

We propose a design for a minimally perturbing diagnostic minichicane, which utilizes optical synchrotron radiation (OSR) generated from magnetic bends in the chicane, to measure the rms horizontal and vertical beam sizes, divergences, emittances, Twiss parameters and energy spread of a relativistic electron beam. The beam is externally focused to a waist at the first bend and the OSR generated there can be used to measure the rms beam size. Subsequent pairs of bends produce far field OSR interferences (OSRI) whose visibility depends on the beam energy spread and the angular divergence. Under proper conditions, one of these two effects will dominate the OSRI visibility from a particular pair of bends and can be used to diagnose the dominant effect. The properties of different configuration of bends in the chicane have been analyzed to provide an optimum diagnostic design for a given set of beam parameters to: (1) provide a sufficient number of OSR interferences to allow a measurement of the fringe visibility; (2) minimize the effect of coherent synchrotron radiation and space charge forces on the particles motion; and (3) minimize the effect of compression on the bunch length as the beam passes through the chicane. A design for the chicane has been produced for application to the FERMI free electron laser facility and by extension to similar high brightness linear accelerators. Such a diagnostic promises to greatly improve control of the electron beam optics with a noninvasive measurement of beam parameters and allow on-line optics matching and feedback.

New challenges in beamline instrumentation for theESRF Upgrade Programme Phase II.

Although beamline instrumentation is by nature driven by science, some recent examples serve as reminders that new technologies also enable new science. Indeed, exploiting the full scientific potential of forthcoming new storage rings with unprecedented source characteristics will, in many cases, require the development and implementation of novel instrumentation. In comparison with present synchrotron radiation facilities, the majority of beamlines should reap immediate performance benefits from the improved source emittance, principally through increased flux and/or horizontal beam size reduction at the sample. Instrumentation will have to develop along similar quantitative and qualitative trends. More speculative and more challenging is anticipating instrumentation that will be required by the new science made possible thanks to the unique coherence properties of diffraction-limited storage rings (DLSRs). ESRF has recently carried out a detailed feasibility study for a new ultra-low-emittance 6 GeV hybrid multibend storage ring, identified as ESRF Upgrade Programme Phase II. Although its performance is not expected to be equivalent to a DLSR source, the successful implementation of the ESRF Phase II project has to address scientific instrumentation issues that are also common to DLSRs. This article aims at providing a comprehensive review of some of the challenges encountered by the ESRF, in the context of the preparation of PhaseII of its upgrade programme.

SHIKA: a fast and accurate spot finder for raster scan on microfocus beamlines

On BL32XU, a microfocus beamline at SPring-8, oscillation data are collected with typical horizontal beam size of 1 μm. Hence it requires very accurate crystal centering, which is difficult especially for invisible crystals e.g. LCP crystals. Therefore, we perform raster diffraction scan to find crystal positions based on their diffractivity using low-dose exposure. It had been time consuming process due to two reasons; i) slow readout time of CCD, ii) manual inspection of hundreds of diffraction images. To tackle this problem, we installed new fast-readout CCD detector, MX225HS (Rayonix, L.L.C.), and developed support tool for raster scan based crystal centering. The tool visually shows possible crystal position on 2D map based on spot populations, and therefore it is named SHIKA (Spot-wo Hirotte Ichiwo Kimeru Application; a Japanese abbreviation which means the application for crystal positioning by picking up spots). SHIKA automatically detects new images when raster scan started and finishes just after raster scan ends. On GUI, user can find and pass the crystal position information to KUMA (a tool suggesting helical data collection strategy with predicted radiation damage) to start data collection immediately. User can also see picked spots on diffraction images with GUI. SHIKA has been developed based on DISTL [1] and modified to be faster and more accurate, especially for LCP crystal which is an important target on BL32XU. SHIKA picks up spots after subtracting smoothed pseudo-background which is a key for better separation of spots and ring-like diffuse background of lipids. Smoothing is time-consuming, but SHIKA now uses GPUs for almost all process including high-speed median filter [2] so that it can be done within ~100 msec. Further development is under way for faster processing. Now SHIKA can be also used on BL41XU, a high flux beamline at SPring-8 with some adjustment for PILATUS3 (Detectris Ltd.) detector.

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.

Efficiency Enhancement of Indirect Transverse Laser Cooling with Synchro-Betatron Resonant Coupling by Suppression of Beam Intensity

The efficiency of indirect transverse laser cooling with synchro-betatron resonance coupling has been improved with the reduction in beam intensity by scraping the tail part of the beam. In order to measure the beam size at a low beam intensity, a new scheme to measure the beam profile by observation of the survival ratio with changing the scraper position has been established. With 104 particles, the transverse cooling time was reduced to 1.2 s, and the cooled horizontal and vertical beam sizes were 0.19 and 0.61 mm, corresponding to temperatures of 20 and 29 K, respectively, which is largely improved compared with that in our previous experiment [Nakao et al.: Phys. Rev. ST Accel. Beam 15 (2012) 110102].

Resonance coupling induced enhancement of indirect transverse cooling in a laser-cooled ion beam

We report the first observation of indirect resonantly enhanced transverse laser cooling of a bunched, stored ion beam of 40 keV $^{24}\mathrm{Mg}^{+}$. The longitudinal velocity distribution and the horizontal beam size of the laser-cooled $^{24}\mathrm{Mg}^{+}$ ion beam with 280 nm laser light were simultaneously observed by the use of standard fluorescence-based techniques. Keeping the operation point at (2.068, 1.105), the synchrotron tune (${\ensuremath{\nu}}_{s}$) was changed from 0.0376 to 0.1299. A strong decrease in the cooled horizontal beam size and a corresponding increase in the equilibrium cooled momentum spread were observed at the expected synchrobetatron resonance coupling condition of ${\ensuremath{\nu}}_{s}=0.068$, which is the first observation of a resonantly induced coupling for enhanced indirect transverse laser cooling of an ion beam, and is an important step towards creating a crystalline ground state of the beam.