Diagnostic Beamline Research Articles

Development of a High-Heat-Load Compact Photon Absorber for SPring-8 Diagnostics Beamline II

Development of a high-heat-load compact photon absorber of the SPring-8 diagnostics beamline II (BL05SS), which can accept the power of 19 kW from a multi-pole wiggler, is presented. In order to make the whole system compact, the scheme which inserts two water-cooled absorber blocks made of Glidcop with a different tilt angle of surface into the photon beam axis in tandem has been adopted. When the absorber system was installed in the frontend of BL05SS and exposed to synchrotron radiation from an insertion device, the stainless steel chamber of the rear absorber block was heated rapidly by irradiation of the scattered X-rays from the absorber surface. A water-cooled absorber chamber made of oxygen-free high conductivity copper has been newly developed and the temperature rise of the chamber was successfully suppressed.

Transverse electron beam imaging system using visible synchrotron radiation at MAX III

The diagnostic beam line at the MAX III synchrotron light source utilizes the synchrotron radiation (SR) in the visible to ultraviolet range to form images of the transverse electron beam profile. The emission and subsequent propagation and focusing of the SR is modeled, taking into account effects such as diffraction and the longitudinally distributed SR generation. A detailed description of the setup of the beam line and method used to determine the transverse beam profile is given in the paper. In order to investigate the imaging method, a series of measurements were performed where the beam line configuration was varied to utilize different wavelengths and polarizations of the SR and different horizontal opening angles of the measurement system. A suggestion is made how to measure future small horizontal beam sizes.

An Indian test facility to characterise diagnostic neutral beam for ITER

The diagnostic neutral beam (DNB) line shall be used to diagnose the He ash content in the D–T phase of the ITER machine using the charge exchange recombination spectroscopy (CXRS). Implementation of a successful DNB at ITER requires several challenges related to the production, neutralization and transport of the neutral beam over path lengths of 20.665 m, to be overcome. The delivery is aided if the above effects are tested prior to onsite commissioning. As DNB is a procurement package for INDIA, an ITER approved Indian test facility, INTF, is under construction at Institute for Plasma Research (IPR), India and is envisaged to be operational in 2015. The timeline for this facility is synchronized with the RADI, ELISE (IPP, Garching), SPIDER (RFX, Padova) in a manner that best utilization of configurational inputs available from them are incorporated in the design. This paper describes the facility in detail and discusses the experiments planned to optimise the beam transmission and testing of the beam line components using various diagnostics.

Reconstruction of electron beam distribution using phase-retrieval algorithm

The shapes of light sources such as electron beams can be reconstructed by inverse Fourier transformation of the complex degree of spatial coherency, which can be measured using Young's interferometer. The application of the phase-retrieval algorithm to reduce phase measurement errors in the complex degree of spatial coherency is numerically studied using an electron beam with an asymmetric distribution. This application is demonstrated with experimental data measured at the diagnostic beamline at the Pohang Accelerator Laboratory.

Achievement of ultralow emittance coupling in the Australian Synchrotron storage ring

I. INTRODUCTIONThe Australian Synchrotron is a newly operating 3rdgeneration light source facility located in Melbourne,Australia. The 3 GeV storage ring is 216 meters in circum-ference and can store a beam of up to 200 mA current. Astorage ring design overview can be found in [1].The storage ring is a modified Chasman-Green–typelattice, designed for a horizontal emittance of 14 nmradwith dispersion free straights. For user operations a hori-zontal emittance of 10.4 nmrad is achieved by allowing a0.1 m dispersion in the straights. The 0.1 m dispersionsetting, while not the minimal horizontal emittance,achieves the minimal horizontal beam size when takinginto account both emittance and dispersion contributions.The storage ring is divided into 14 identical sectors, eachcontaining a 10.9 m arc and 4.5 m straight section. Of the14straights,twoareusedforrfcavities,onefordiagnosticsand onefor beam injection.Eacharc segmentcontains twodipole magnets (with defocusing gradients), six quadru-pole, and seven sextupole magnets, shown in Fig. 1. Orbitand coupling corrections are achieved via additional wind-ings on the sextupole magnets, fed by power suppliesindependent of the main magnet supply. Four sextupolemagnets in each arc have the required windings to act asskewquadrupoles,althoughonlytwoofthesearecurrentlypowered, giving a total of 28 skew quadrupole magnetsaround the storage ring. The power supplies for these skewquadrupoles are bipolar and can supply a current of up to5A,whichdeliversamaximumkstrengthof0.02perskewquadrupole.II. BEAM DIAGNOSTICSThere are two diagnostic beam lines at the AustralianSynchrotron, an x ray and an optical beam line. Details ofthe diagnostics beam lines can be found in Ref. [2].The x-ray diagnostic beam line (XDB) uses the x-raylight from a bending magnet and passes it through apinhole array. The multiple pinhole images formed arethen projected onto a fluorescent screen and imaged bya CCD camera. By measuring the beam size andknowing the beta functions and dispersion at the sourcepoint, it is possible to extract the beam emittance fromthis image. The CCD camera and beam line optics allowfor beam size measurements with 5 m resolution.However, the resolution limit from diffractive effects is60 m [3], which limits the resolution of vertical emit-tance measurements on this beam line to values above10 pm. Additional effects due to fast beam movementduring relatively slow CCD integration and uncertaintiesin the point spread function of the system make the beamline currently unsuitable for precision beam sizemeasurements.

The coherency of synchrotron radiation at Pohang Accelerator Laboratory

The coherency of the synchrotron radiation at Pohang Accelerator Laboratory has been investigated using Young's interferometer. The electron beam size can be measured precisely using the interferometer. An interferogram using 650 nm light at the diagnostics beamline at Pohang Light Source (PLS) has been measured to determine the electron beam distribution and the spatial coherence length. Interferograms obtained by numerical study are compared with experimental results in order to understand the measured data. From this comparison, the electron beam at PLS is revealed to be a Gaussian distribution with a standard deviation of 210 microm. The spatial coherency length of 650 nm light at PLS is measured to be 0.57 cm, and that of 0.1 nm light at PLS is predicted to be 0.88 microm by the same numerical study.

Electron beam diagnostics for a superconducting radio frequency photoelectron injector

A superconducting radio frequency (SRF) photoelectron injector is currently under construction by a collaboration of BESSY, DESY, FZD, and MBI. The project aims at the design and setup of a continuous-wave SRF injector including a diagnostics beamline for the ELBE free electron laser (FEL) and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development, serving a multitude of operation settings. In this paper the layout and the rationale of the diagnostics beamline are described. Furthermore detailed information on specific components is given, together with results from laboratory tests and data taking.

A high-brightness SRF photoelectron injector for FEL light sources

Most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources require electron beams with an unprecedented combination of high brightness, low emittance, and high average current. In all projects photoguns will be applied: DC-photoguns, normal conducting RF-photoguns (NC-guns), and superconducting RF photoguns (SRF-guns). While the concepts of DC- and NC-guns are well proofed, the SRF-gun development still possesses a high risk. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high average power into the gun, and, finally, the risk of beam excitation of higher-order cavity modes. In combination with SRF linacs, the SRF-guns seem to be the best solution for high average currents. Several R&D projects of SRF-gun have been launched. In this paper, we will give an overview of the progress of the SRF photoinjector development. In detail, the technical concept, the performance and the status of the Dresden Rossendorf SRF-gun project, a collaboration of BESSY, DESY, MBI and FZD, will be presented. The main design parameters of this SRF-gun are the final electron energy of 9.5 MeV, 1 mA average current, and transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. The 1.3 GHz cavity consists of three TESLA-shaped cells, a specially designed half-cell where the photocathode is placed and a choke filter in order to prevent RF losses at the cathode side. The normal-conducting photocathode with a Cs 2Te photoemission layer is cooled by liquid nitrogen. The SRF-gun cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid nitrogen-cooled thermal shield and a titanium He tank with a two-phase supply tube. The 10 kW fundamental power coupler is adopted from the ELBE cryomodule. In a first commissioning and test period the gun will be operated in parallel to the accelerator. A diagnostic beamline will allow beam parameter measurement and further optimization of the SRF-gun. In a final step, the gun will be connected to the ELBE superconducting linear accelerator to deliver an improved electron beam to the user labs.

The X-ray diagnostic beamline at the Canadian Light Source

Beam characterizations at the Canadian Light Source (CLS) are provided by two independent diagnostic beamlines called the optical synchrotron radiation (OSR) and the X-ray synchrotron radiation (XSR) beamlines, respectively. The XSR beamline, which operates in the X-ray region, is the subject of this report. The beamline is comprised of a variable-aperture pinhole camera with an intrinsic r.m.s. resolution at the source point of σ≈11 μm. Image analysis employs a Fresnel-based algorithm that encompasses both geometric and diffractive aspects within a common framework. Other instruments on the XSR beamline include a position-sensitive detector (PSD) and an Avalanche photodiode (APD). A fill-pattern monitor based on the APD has a bunch-charge resolution of at least 1 part in 10 7.

The Canadian Light Source: The newest synchrotron in the Americas

The Canadian Light Source (CLS) is a 2.9 GeV synchrotron facility. It consists of seven user beamlines (not including two facility diagnostic beamlines), seven more under construction, and five additional beamlines for which funding has been announced. This article describes some details of the initial stages of operation.

Canadian Macromolecular Crystallography Facility (CMCF) 08ID-1 status update

The Canadian Macromolecular Crystallography Facility (CMCF) 08ID-1 beamline at the Canadian Light Source (CLS) is in the later stages of commissioning. The photon source is a small-gap in-vacuum undulator (SGU), which was designed in-house with a support structure and vacuum chamber from RMP of Italy. The undulator magnets were shimmed at the CLS and the SGU was installed in the 2.9 GeV storage ring. The storage ring has had currents up to 300 mA safely injected and stored since its first light in the diagnostic beamline in December of 2003. At these storage ring currents, the 7th harmonic of the SGU will yield a photon flux on the sample at the endstation on the order of ∼ 5 × 10 12 at 12 keV. The overall design of the beamline includes white beam slits, indirectly cryo-cooled first crystal of the DCM and sagittally focusing second crystal, and vertically focussing ULE mirror. The endstation of the beamline is innovative and robust, and was manufactured by ACCEL according to CLS specifications. The beamline controls, are being developed based on EPICS, and complemented with a user-friendly interface. The scientific goal of the 08ID-1 beamline is to operate a protein crystallography MAD beamline suitable for studying small crystals and crystals with large unit cells.

The optical diagnostic beamline at the Canadian Light Source

Beam characterizations at the Canadian Light Source are provided by two independent diagnostic beamlines called the Optical Synchrotron Radiation (OSR) and the X-ray Synchrotron Radiation (XSR) beamlines, respectively. The OSR beamline, which operates in the visible region, is the subject of this report. Issues discussed include the general design philosophy, choice of instrumentation, limits to resolution, and actual performance. The primary pick-off mirror intercepts only half of the dipole light-cone, with unique consequences for the diffraction limit and polarization degrees of freedom. Instrumentation includes a CCD camera, a gated MCP-intensified CCD camera, a streak camera, and a position-sensitive detector. The three cameras complement each other very nicely as diagnostic tools.

Results of beam parameter measurement of the ELBE electron accelerator after commissioning

The ELBE accelerator, an electron linac with superconducting cavities, is designed for a beam energy of 40MeV, a CW current up to 1mA, and a maximum bunch charge of 77pC. The electron beam will be used to generate a variety of electromagnetic radiations with different wave length. For the first commissioning tests, the injector with a thermionic electron gun, one cryomodule with two nine-cell cavities and a diagnostic beamline were in operation. Energy and energy spread were measured with a magnetic spectrometer. Transverse emittance measurements were carried out with a pepper-pot mask in the injector and with the quadrupole scan method for the accelerated beam. Bunch length was determined from the autocorrelation function of the coherent transition radiation with a Martin–Puplett interferometer.

Helium doped hydrogen or deuterium beam as cost effective and simple tool for plasma spectroscopy

Energetic neutral particles from neutral hydrogenic beam heating systems are widely used for active spectroscopic measurements of key plasma parameters in fusion experiments. Helium beams are used in dedicated diagnostic beamlines offering deeper penetration and resonant double charge exchange with alpha particles. Neutral beam systems using pure helium either require specialised helium gas pumping with a pumping speed in excess of 1000 m 3/h or are restricted to short pulses (normally less than 1 s). A doped hydrogen/helium beam combines the requirements for plasma heating and diagnostics without the need for sophisticated helium pumping. A small flow of helium gas is injected into the plasma source for the time helium particles are required. The helium current is typically 10% of the total extracted current. The reduction in heating power of the doped beam can be kept below 5%. Doped deuterium/helium beams have been successfully tested and routinely used at JET. HeI beam emission spectra obtained with a doped deuterium/helium beam offer sufficiently strong visible lines for spectroscopic applications.

Helium doped hydrogen or deuterium beam as cost effective and simple tool for plasma spectroscopy

Energetic neutral particles from neutral beam heating systems are widely used for active spectroscopic measurements of key plasma parameters in fusion experiments. Both the plasma discharges and the neutral beam systems are normally operated with hydrogen or deuterium. Helium beams are used in dedicated diagnostic beam lines as they offer deeper penetration and are subject to less background radiation and enable resonant double charge exchange with alpha particles. Neutral beam systems using pure helium either require specialized helium gas pumping with a pumping speed in excess of 1000 m3/h or are restricted to short pulses (normally less than 1 s). A doped hydrogen/helium beam combines the requirements for plasma heating and diagnostics without the need for sophisticated helium pumping. A small flow of helium gas is injected into the plasma source for the time helium particles are required. The helium current is typically 10% of the total extracted current. The reduction in heating power of the doped beam can be kept below 5%. The small amount of helium gas does not cause an excessive pressure rise along the beam line and does not reduce the reliability of the beam heating system. Doped deuterium/helium beams have been successfully tested and routinely used at JET. The Hel beam emission spectra obtained with a doped deuterium/helium beam produce sufficiently strong visible lines for spectroscopic applications. Furthermore, the simultaneous availability of helium and hydrogenic particles in the beam allows us to extend spectroscopic measurements to another atomic system and hence cross-check results from helium beams with those from hydrogenic beams. The only investment required is an additional helium gas inlet system into the ion source.

Spatio-temporal measurement of beam properties in the PLS diagnostic beamline.

A diagnostic beamline is being constructed in the PLS storage ring for measurement of electron- and photon-beam properties. It consists of two 1:1 imaging systems: a visible-light imaging system and a soft X-ray imaging system. In the visible-light imaging system, the transverse beam size and beam position are measured with various detectors: a CCD camera, two photodiode arrays and a photon-beam position monitor. Longitudinal bunch structure is also investigated with a fast photodiode detector and a picosecond streak camera. On the other hand, the soft X-ray imaging system is under construction to measure beam sizes with negligible diffraction-limited error. The X-ray image optics consist of a flat cooled mirror and two spherical focusing mirrors.

High precision, high-heat-load mirror for the APS diagnostics beamline (abstract)

A high precision mirror for measuring the storage ring beam size is under fabrication for the APS diagnostics beamline. The mirror, which will be located at 12.9 meters from the bending magnet source, is required to maintain less than 1.6 microradian slope error. The mirror design consists of a slot in the center in order to reduce incident power from the 300-mA, 7-GeV beam during normal operation. Water channels with fins are machined in the GlidCop mirror body to protect it against extremely high heat loads under accidental beam deviations. The mechanical design of the mirror, and results from a thermal analysis are presented in this paper.

Design and performance of the ALS diagnostic beamline

The design and operation of an imaging beamline at the Advanced Light Source used for providing diagnostic information on the electron beam for the accelerator and experimental groups is described. This system is based on a Kirkpatrick-Baez mirror pair and utilizes a carbon filter to give a bandpass in the soft x-ray region. The focused x-rays are viewed on a single-crystal scintillator through an optical microscope and the image recorded on a CCD camera. This system, together with other instruments to evaluate beam size, stability, and other time-dependent information, is described, data are presented, and the operation of the overall beamline is evaluated.

Thermal effects and mirror surface figure requirements for a diagnostic beamline at the advanced light source

Abstract An imaging beamline based on a Kirkpatrick-Baez mirror configuration has been designed to image the electron beam in the ALS storage ring, to measure its size and shape. The electron beam emittance will be small ( ϵ h = 3.4×10 −9 m rad) and the quality of the image is extremely sensitive to surface figure distortion of the mirrors. Thermal distortions and surface temperatures have been calculated for radiatively cooled mirrors of various materials in a search for a simple design which avoids water cooling. The choice of mirror material and the thermal and mechanical design is discussed.

Diagnostic beamline for a third generation storage ring

A knowledge of the position, size, and stability of the source and the angle of emission of synchrotron radiation (SR) from the storage ring are essential for optimizing the operation of storage ring, insertion devices and monochromators. Berkeley’s Advanced Light Source (ALS) has a natural emittance of 3.4×10−9 mrad, and has beam sizes σh and σv (assuming a 10% emittance ratio into the vertical direction) in bending magnet 1 (BM1) of 44 and 83 μm, respectively. Simple diffractive optical calculations show that imaging this beam using visible light optics is not feasible and imaging must be performed using photon energies greater than 50 eV. This will be the same for all third generation low emittance storage rings. The synchrotron radiation diagnostics at ALS will consist of an imaging system for 200 eV photons and a ‘‘white beam’’ port with a streak camera to obtain the timing information. The imaging system will employ two crossed spherical mirrors in a Kirkpatrick–Baez configuration, to eliminate astigmatism. Use of 1:1 imaging will eliminate coma, resulting in an image of the source which is only limited by the residual aberrations of the optics. Real time imaging of the beam is deemed feasible by the use of a high resolution charged coupled device (CCD), and the associated electronics necessary to read the CCD. The design of the imaging system of the diagnostic beamline for ALS and the detection system will be discussed with a view toward applications in other third generation SR sources.