DESY, Hamburg
By using magnetic chicane bunch compressors, high-gain free-electron lasers are capable of generating femtosecond electron bunches with peak currents in the kilo-ampere range. For accurate control of the longitudinal dynamics during this compression process, high-precision beam energy and arrival-time monitors are required. Here we present an electro-optical detection scheme that uses the signal of a beam pickup to modulate the intensity of a femtosecond laser pulse train. By detecting the energies of the laser pulses, the arrival-time of the pickup signal can be deduced. Depending on the choice of the beam pickup, this technique allows for high-resolution beam position measurements inside of magnetic chicanes and/or for femtosecond-resolution bunch arrival-time measurements. In first prototypes we realized a beam position monitor with a resolution of 3 μm (rms) over a many-centimeter dynamic range and a bunch arrival-time monitor with a resolution of 6 fs (rms) relative to a pulsed optical reference signal.
UniDo/IBS, Dortmund
iThemba LABS, Somerset West
FZJ, Jülich
DELTA, Dortmund
The interaction of an ion beam with the residual gas might lead to a photon emission of the excited residual gas molecule. These photons can be used to monitor the beam profile. Therefore a multichannel photomultiplier is used together with an optical system. Measurements at the COSY synchrotron are presented. The usability of the method is discussed by comparing to measurements at the iThemba Labs beam line and the JESSICA experiment, a spallation source prearrangement at COSY.
LANL, Los Alamos, New Mexico
The Accelerator Operations & Technology Division operates a half-mile linear particle accelerator which utilizes 110 wire scanning diagnostics devices to gain position and intensity information of the proton beam. In the upcoming LANSCE improvements, 51 of these wire scanners are to be replaced with a new design, up-to-date technology and off-the-shelf components. This document outlines the requirements for the mechanical design of the LANSCE wire scanner and presents the design currently being worked on. Additionally, it presents the decision making process for the selected components and sub-systems within the wire scanner such as the drive system, frame, mounting interface, and vacuum components. This is done by comparing design alternatives and comparing them to the objectives of the project. Similarly, a comparison between the use of a stepper motor and a servo motor is detailed in this document; this is mostly done through motor-torque calculations, back-drive calculations, and a comparison of the inherent properties of both types of motors, such as detent torque and torque capabilities. Lastly, the paper concludes with a plan for future work on the wire scanner development.
LANL, Los Alamos, New Mexico
The primary goal of this newly installed beam profile measurement is to provide the facility operators and physicists with a reliable horizontal and vertical projected beam distribution and location with respect to the proton beam target and beam aperture. During a 3000-hour annual run cycle, 5 microcoulombs of charge is delivered every 50 milliseconds through this harp to the downstream 1L target. The resulting radioactive annual dose near this harp is at least 600 MRads. Because of this harsh environment, the new harp design has been further optimized for robustness. For example, compared to an earlier design, this harp has half of the sensing wires and utilizes only a single bias plane. The sensing fibers consist of a 0.078-mm diameter SiC fiber. To hold these fibers to a rigid ceramic structure, a “collet” fiber-clamping device accomplishes the three goals of maintaining a mechanical fiber clamp, holding the sense fiber under a slight tensile force, and providing a sensing fiber electrical connection. This paper describes the harp analysis and design, and provides fabrication, assembly, and installation information, and shows how facility wiring was altered.
LANL, Los Alamos, New Mexico
The goal of the design LANSCE-R Wire-Scanner Analog Front-end Electronics is to develop a high-performance, dual-axis wire-scanner analog front-end system implemented in a single cRIO module. This new design accommodates macropulse widths as wide as 700 us at a maximum pulse rate of 120 Hz. A lossey integrator is utilized as the integration element to eliminate the requirement for providing gating signals to each wire scanner. The long macropulse and the high repetition rate present conflicting requirements for the design of the integrator. The long macropulse requires a long integration time constant to assure minimum integrator droop for accurate charge integration, and the high repetition rate requires a short time constant to assure adequate integrator reset between macropulses. Also, grounding is a serious concern due to the small signal levels. This paper reviews the basic Wire Scanner AFE system design implemented in the cRIO-module form factor to capture the charge information from the wire sensors and the grounding topology to assure minimum noise contamination of the wire signals.
GSI, Darmstadt
LBNL, Berkeley, California
TU Darmstadt, Darmstadt
As conventional intercepting diagnostics will not withstand high intensity ion beams, Beam Induced Fluorescence (BIF) profile monitors constitute a preeminent alternative for non-intercepting profile measurements. This diagnostic technique makes use of optical emission of beam-excited gases. Recently BIF became an important diagnostic technique for beam profile measurement with applicability in beam tuning over a wide range of beams and accelerator conditions. Beam induced fluorescence spectra in the range of 300 - 800 nm were recorded with an imaging spectrograph for 5 MeV/u proton, S(6+) and Ta(24+) beams in nitrogen, Xe, Kr, Ar, Ne and He at 10-3 mbar gas pressure. Optical transitions were identified and associated with corresponding beam profiles. Effective light yields, normalized to the differential energy loss, are presented for all gas-species investigated. Since residual gas ionization is the basic process for BIF-monitors as well as for Ionization Profile Monitors (IPM), BIF-results are compared to IPM measurement data.
BNL, Upton, Long Island, New York
Modes with transverse electric field (TE-modes) in the NSLS-II multipole vacuum chamber can be generated at frequencies above 450 MHz due to its geometric dimensions. Since the NSLS-II BPM system is triggered by the RF at 500 MHz, frequencies of higher-order modes (HOMs) can be generated within the transmission band of the band pass filter. In order to avoid systematic errors in the NSLS-II BPM system, we introduced frequency shift of HOMs by using RF metal shielding located in the antechamber slot.
BNL, Upton, Long Island, New York
The NSLS-II Light Source is being built at Brookhaven National Laboratory. It will provide users with ultimate brightness beam and the full realization of its capabilities requires corresponding stability of the beam orbit. The small aperture BPMs, located at the ends of a insertion device, will provide better sensitivity to the beam position but also requires thorough design. In this paper we present the results of the optimization including signal power levels and button heating.
DESY, Hamburg
To control the beam position at the entrance of the FLASH dump a position monitor is required outside of the vacuum. When a charged particle travels through a gas it will ionize the atoms. Therefore the signal from a capacitive button monitor is caused not only by the electric field of the beam but also by the ionized atoms which add high background to the usable signal. To avoid the ionization signal a magnetic coupled monitor is designed. The monitor consists of four longitudinal loops symmetrically arranged at the tube wall. An analytical expression of the signal for this monitor is derived and compared with simulation. Raw data are compared with the expectation.
KEK, Ibaraki
Button-type beam position monitors for SuperKEKB rings have been designed. The RF characteristics such as beam response, trapped modes or wake functions have been simulated using 3-D E-M codes such as GdfidL and HFSS. The estimated instability threshold from the trapped modes was much higher than the radiation damping time. The prototype units have been tested in the prototype-antechambers installed in KEKB and KEK-PF BT line. The mechanical reliability and the beam responses are also reported.
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
For beam profile monitoring applications where low beam perturbation together with bi-dimensional imaging is required, ionization monitors based on neutral gas-jet targets shaped into a thin curtain are an interesting option. When integrated in ultra-high vacuum systems, such as in the Ultra-low energy Storage Ring (USR), where local vacuum preservation is of primary concern, such systems present severe difficulties linked to the creation and proper shaping of a high quality gas-jet curtain. In this contribution, investigations into the generation and evolution of the jet with the Gas Dynamics Tool (GDT) software and purpose-written C++ analysis modules are presented. By means of extensive numerical analysis, the advantages of a novel nozzle-skimmer system in terms of curtain quality are summarized as compared to traditional axisymmetric gas-jet creation and curtain shaping by means of scrapers. It is also shown that variable nozzle-skimmer geometries allow for modifying the gas-jet characteristics in a wide range, including jet splitting and local density modulation. Finally, the layout of a test stand that will be used for an experimental benchmark of these studies is shown.
Cockcroft Institute, Warrington, Cheshire
The University of Liverpool, Liverpool
For destructive beam intensity measurements, electrostatic Faraday cups will be incorporated into the Ultra-low energy Storage Ring (USR) and its transfer lines at the Facility for Low-energy Antiproton and Ion Research (FLAIR). This multipurpose machine will offer both slow and fast extracted beams resulting in a wide range of intensities and varying time structure of the beam. In this contribution we present the particular challenges of measuring the beam intensity in the USR, results from numerical optimization studies, as well as the design of the cup.
ANL, Argonne
The Advanced Photon Source (APS) storage ring rf beam position monitors (BPMs) are impacted by the presence of beam-excited transverse electric (TE) modes. These modes are excited in large-aperture vacuum chambers and become trapped between the bellow end flanges. The TE modes are vertically oriented and are superimposed on the TEM beam position signals, corrupting the BPM measurements. Erroneous step changes in beam position measurements and systematic intensity dependence in the vertical plane have been traced to these modes, placing a fundamental limitation on vertical beam position stabilization. Experiments were conducted suppressing these modes on a test vacuum chamber. These experiments were simulated with MAFIA and Microwave Studio, confirming experimental results. We will describe the measurements, simulations, and prototype test results.
ANL, Argonne
As the Advanced Photon Source (APS) prepares for a large-scale upgrade, many of the fundamental limitations on beam stability have to be identified. Studies have been conducted to measure thermal mechanical effects of both the water and air handling systems impacting insertion device vacuum chambers (IDVES). Mechanical stability of beam position monitor pickup electrodes mounted on these small-gap IDVES places a fundamental limitation on long-term x-ray beam stability for insertion device beamlines. Experiments have been conducted on an ID vacuum chamber indicating that the BPM blocks are moving with water temperature cycles at the level of 10 microns/degree C. Measurements and potential engineering solutions will be described.
IAP, Frankfurt am Main
In beam diagnostics optical techniques had become increasingly important as they provide information with the advantage to have only minimal effect on the beam. The planned Frankfurt Neutron Source will consist of a proton driver LINAC providing beam energies up to 2.0 MeV. The rotatable diagnosis tank hybrid ion beam tomography tank HIBTT will be placed at the end of the low energy beam transport section (LEBT) to provide beam tomography based on the visible radiation of the ion beam in front of the RFQ. The beam energy in this section will be 120keV and the current 200 mA. Additional to the CCD camera that takes optical data for the tomography, other non-interceptive devices could be used to gain additional information. The question behind this hybrid approach on non invasive beam diagnostics is: which and how much information can be extracted from an ion beam without disturbing or destroying it. The actual contribution deals with the information of profile width in beam profile measurements. The presentation introduces a definition and an information sensitive method for profile width determination and verifies them using experimental and numerical data.
HIT, Heidelberg
GSI, Darmstadt
The transverse emittance of the ion beam at the Heidelberg Ion Therapy Center (HIT) will be measured within the Low Energy Beam Transport (LEBT) using a pepper-pot measurement system. At HIT, two ECR sources produce ions (H, He, C and O) at an energy of 8keV/u with different beam currents from about 80 μA to 2mA. The functionality and components of the pepper-pot device is reviewed as well as the final design and the choice of the scintillator. For that, results from recent beam test at the Max Planck Institute für Kernphysik at Heidelberg are presented. The material investigation was focused on inorganic doped crystal, inorganic undoped crystal, borosilicate glass and quartz glass with the following characteristics: availability, prior use in beam diagnostics, radiation hardness, fast response, spectral matching to CCD detectors.
LBNL, Berkeley, California
CLASSE, Ithaca, New York
The experimental study of the electron cloud dynamics and mitigation techniques is one of the main objectives of the CESR Damping Ring Test Accelerator (Cesr-TA) program. Shielded pick-up buttons are a relatively simple diagnostic device for obtaining time-resolved information on the electron cloud density. They have been already successfully employed on the SPS at CERN, although with different resolution parameters due to the different type of beams. We present the initial results obtained using such a detector in the Cesr-TA electron/positron ring. By carefully designing the read-out electronics we were able to resolve the individual bunch contribution to the electron cloud formation process along a bunch train and gain useful information on its decay time. Alternatively, by increasing the electronics integration time, we could use our device as a sensitive detector of the average electron cloud density level generated by the passage of a bunch train.
CELLS-ALBA Synchrotron, Cerdanyola del Vallès
Beam position monitors (BPM) characterization has been widely studied at ALBA Synchrotron Light Source. Special care has been taken on the analysis of their electrical offset in order to achieve submicron beam stabilities. This paper shows the results of the BPMs offset study for Booster and Storage Ring. The electrical effect of the different vacuum vessels housings the BPMs is also reported.
DESY, Hamburg
DESY Zeuthen, Zeuthen
Additional beam diagnostics has been installed in the dump line at FLASH in 2009. Its purpose is to prevent damage by long high current electron beam pulses, as happened in autumn 2008, when a vacuum leak occurred near the dump vacuum window. Beam position monitors (BPM), scintillator-based loss monitors and temperature sensors have been installed thus far in the dump area. Additional BPMs and loss monitors have meanwhile been installed. These include a magnetic BPM placed after the vacuum window. Magnetic loops are used in order to prevent the influence of the ions on the pick-up signals. Four ionization chambers, consisting of air-filled tubes, and 4 glass fibers have been installed parallel to the vacuum pipe, along the last 2 m of beam pipe. Beam halo monitors were installed next to the magnetic BPM. These consist of 4 diamond and 4 sapphire sensors operating as solid state ionization chambers. The halo monitors are sensitive to very small losses. These additional diagnostic monitors were commissioned in autumn 2009, and have contributed to the successful run of long pulses with 3-9 mA current and up to 800 microsecond length. Their performance will be summarized in this paper.