Diamond, Oxfordshire
JAI, Egham, Surrey
UCL, London
Royal Holloway, University of London, Surrey
This paper describes the design of a cavity BPM for use in single pass machines. The design was modelled using a number of different EM codes to allow cross comparison of the simulation results. Furthermore, in addition to existing designs, the geometry has been modified to introduce a frequency separation between the horizontal and vertical dipole signals, as well as a reduction of the sensitivity of the position monitor to the monopole sum signal. The next stage of this project will be the manufacture of a prototype for tests in the transfer path at Diamond Light Source.
BNL, Upton, Long Island, New York
An internal R&D program has been undertaken at BNL to develop an RF BPM to meet all requirements of both the injection system and storage ring. The RF BPM architecture consists of an Analog Front-End (AFE) board and a Digital Front-End board (DFE) contained in a 1U 19" chassis. An external passive RF signal processor has been developed that will be located near the RF BPM pickups. The partitioning into two boards enables a flexible Software Defined Instrument. A model-based design flow has been adopted utilizing AWR VSS, Simulink, and Xilinx System Generator for algorithm development and AFE impairment performance analysis. The DFE architecture consists of a Virtex-6 with MicroBlaze embedded processor. An optional Intel Atom SBC is also supported. The AFE is based on a bandpass sampling architecture utilizing 16-bit ADCs. Long-term drift is corrected by inclusion of an out-of-band calibration tone. An RF BPM Calibration Tool is being developed for removal of systematic errors and performance verification. In this contribution we will present a detailed overview of the architecture, compare simulation results to laboratory performance, and report beam test results.
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.
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.
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.
NewPath, Salt Lake City, Utah
Others have shown that the voltages induced on one uniformly-wound toroidal coil and two sinusoidally-wound toroidal coils may be used to determine the current in a single filament and its coordinates. We have extended this technique to show that the voltages measured on a group of sinusoidally-wound toroidal coils may be used to approximate the distribution of current within their common aperture. This is possible because each measured voltage is proportional to the product of unique functions of the radial and azimuthal coordinates of each increment of the current [1,2]. We have developed matrix methods to determine the transverse distribution of the current and determined the sensitivity of these calculations to measurement errors. Shielded sinusoidally-wound coils with a precision of 0.02 cm have been prepared using rapid prototyping, and methods have been defined to prepare the next generation of these coils, which will have a precision of 0.001 cm, by using an engraving tool with the 4th axis of a vertical milling machine.
LBNL, Berkeley, California
LLNL, Livermore, California
The versatility of the beams that ECR ion sources can provide make them the injector of choice for many heavy ion accelerators. However, the design of the LEBT* systems for these devices is challenging because the LEBT has to be matched for a wide variety of ions. In addition, due to the magnetic confinement fields, the ion density distribution across the extraction aperture is inhomogeneous and charge state dependent, and the ion beam is extracted from a region of high axial magnetic field, which adds a rotational component to the beam. In this presentation a simulation model for ECR ion source beams is described. The initial conditions (i.e., spatial and velocity distribution of the ions prior to extraction from the ion source) are obtained semi-empirically. Extraction from the plasma is then simulated with the particle-in-cell code WARP. The same code is used for the actual simulation of ion transport through the beam line. Simulations of a beam containing uranium ions of charge state 18+ to 42+, as well as other ions due to the use of support gases, extracted from VENUS**, are presented and compared to emittance measurements.
SLAC, Menlo Park, California
Measurement of time-of-arrival or instantaneous longitudinal position is a fundamental beam diagnostic. We present results from a stripline transversal periodic coupler structure which forms the heart of a sub-ps beam timing detector. This filter structure approximates a sinx/x response in the frequency domain which corresponds to a limited pulse length response in the time domain. These techniques have been used extensively in beam feedback systems at 3 GHz center frequencies with operational single-shot resolutions of 200 fs[1]. We present a new design, based on a 11.424 GHz center frequency, which is intended to offer a factor of four improvement in time resolution. Two-dimensional electromagnetic simulation results are shown, and the design optimization approach leading to the final circuit implementation is illustrated. The prototype circuit has been fabricated on 60mil Rogers 4003 and lab frequency domain and time domain data are compared to the 2-D simulation results. Performance of the prototype circuit is shown with applicability to sub-ps beam measurements in LINAC and FEL applications.
CERN, Geneva
The LHC Beam Loss Monitoring (BLM) system is one of the most complex instrumentation systems deployed in the LHC. In addition to protecting the collider, the system also needs to provide a means of diagnosing machine faults and deliver feedback of losses to the control room as well as to several systems for their setup and analysis. It has to transmit and process signals from over 4,000 monitors, and has nearly 3 million configurable parameters. In a system of such complexity, firmware reliability is a critical issue. The integrity of the signal chain of the LHC BLM system and its ability to correctly detect unwanted scenarios and thus provide the required protection level must be ensured. In order to analyze the reliability and functionality, a test bench has been developed that emulates different types of loss signals and monitors the performance and response of the FPGA-based data analysis firmware. This paper will report on the numerous tests that have been performed and on how the results are used to quantify the reliability of the system.
ANL, Argonne
SLAC, Menlo Park, California
A large-solid-angle Cherenkov detector beam loss monitor has been built and tested as part of the Linac Coherent Light Source machine protection system (MPS). The MPS is used to protect the undulator magnets from high-energy electron beam loss that can lead to demagnetization. Lost primaries create a shower of secondary electrons that transit through the radiator medium. The radiator consists of an Al-coated plate of high-purity, fused silica, formed into a tuning fork geometry that envelopes the beam pipe preceding each undulator. The radiator transports Cherenkov photons via internal reflection through a tapered neck into a compact photomultiplier tube (PMT). A simple model based on line sources summed across image planes is used to calculate the radiator optical coupling efficiency etac as a function of the electron's transverse position. The results are compared for the case of normally incident electrons with a more detailed Monte Carlo random-walk simulation called RIBO. Both analytical and numerical models show etac to be relatively uniform over the full range of transverse positions in the radiator and to be a strong function of surface reflectivity.
LBNL, Berkeley, California
A hardware system that acquires and stores a large buffer of bunch-by-bunch 16-bit data has been realized. A high resolution (up to 16-bit) analog-to-digital converter (ADC), or bank of ADCs, samples the analog signal at the bunch frequency. The digitized data is fed into a Field Programmable Gate Array (FPGA), which contains an interface to a bank of double data rate (DDR) SDRAM type memory. With appropriate data bus widths, the FPGA bursts the ADC data into the DDR SDRAM fast enough to keep up with the bunch-by-bunch ADC data continuously. The realized system demonstrates continuous data transfer at a rate of 1 GByte/sec, or 16-bit data at 500 MHz, into a 64MByte SDRAM. This paper discusses the implementation of this system and the future of this architecture for bunch-by-bunch diagnostics.