NewPath, Salt Lake City, Utah
We have shown that a group of sinusoidally-wound coaxial toroids can be used to determine the transverse distribution of a time-dependent current that passes through their common aperture. The current is expressed in a basis of chapeau (pulse) functions over an array of pixels, and matrix methods are used to determine the current in each pixel from measurements of the voltages that are induced on the toroids. Optimum configurations of pixels are used, for which the condition number of the matrix is bounded by the number of pixels. For example, with a resolution of 50 pixels, the fractional errors in determining the current at each pixel are approximately 50 times the fractional errors in the measurements of the induced voltages as well as imperfections in the fabrication of the toroids and their placement. Our algorithms were tested numerically by specifying the currents, calculating the voltages that would be induced on the toroids, adding Gaussian noise to these voltages, and then using the algorithms to calculate the currents from the simulated voltage measurements. These simulations confirm that the condition number of the matrix is bounded by the number of pixels.
Northern Illinois University, DeKalb, Illinois
Electrons crossing the boundary between different media generate bursts of transition radiation. In the case of bunches of N electrons, the radiation is coherent and has an N-squared enhancement at wavelengths related to the longitudinal bunch distribution. This coherent transition radiation has therefore attracted attention as an interceptive charged particle beam diagnostic technique. Many analytical descriptions have been devised describing the spectral distribution generated by electron bunches colliding with thin metallic foils making different simplifying assumptions. For typical bunches having lengths in the sub-millimeter range, measurable spectra are generated up into the millimeter range. Analysis of this THz radiation is performed using optical equipment tens of millimeters in size. This gives rise to concern that optical diffraction effects may spread the wavefront of interest into regions larger than the optical elements and partially escape detection, generating a wavelength-dependent instrument response. In this paper we present a model implementing vector diffraction theory to analyze these effects in bunch length diagnostics based on coherent transition radiation.
INFN/LNF, Frascati (Roma)
LAL, Orsay
roma3, Rome
INFN-Roma, Roma
INFN Gruppo di Cosenza, Arcavacata di Rende (Cosenza)
The test of the crabbed waist scheme, undergoing at the Frascati DAΦNE accelerator complex, needs a fast and accurate measurement of the absolute luminosity, as well as a full characterization of the background conditions. Three different monitors, a Bhabha calorimeter, a Bhabha GEM tracker and a gamma bremsstrahlung proportional counter have been designed, tested and installed on the accelerator at the end of January 2008. Results from beam-test measurements, comparison with the Monte Carlo simulation and preliminary data collected during the SIDDHARTA run are presented.
KEK, Ibaraki
Button electrodes with good time response are essential for the bunch-by-bunch feedback / diagnostic systems needed for future short-bunch-spacing accelerators, such as energy recovery linacs (ERL) or a super B-factory. The impedance matching and time-domain response of electrodes, particularly around the vacuum seal, have been studied using 3-D electromagnetic codes (HFSS, MAFIA and GdfidL). Several candidates have been fabricated to examine the tolerance for mechanical pressures and heat stress due to the welding process. The real beam response from a short bunch has also been studied using a test-beam line at the KEK-PF injector beam transport section.
UMD, College Park, Maryland
ANL, Argonne
We have used an optical diffraction-transition radiation interferometer (ODTRI) in a transmission mode to measure the divergence of the low energy 8 MeV ANL-AWA electron beam. The interferometer employs a metallic micromesh first foil, which is used to overcome the inherent limitation due to scattering in the solid first foil of a conventional OTR interferometer, and an optically transparent dielectric foil. The interferences of forward directed ODR from the mesh and radiation from the dielectric foil is observed in transmission. This geometry allows a small gap between the foils (0.9 mm), which is required to observe fringes from two foils at low beam energies. The measured beam divergence is in a good agreement with that obtained using the standard pepper pot technique and simulation code calculations. ODTRI measurements indicate that a single Gaussian distribution is insufficient to describe the angular distribution of the measured beam and that a second Gaussian beam faction or halo beam component is required to fit the data.
LBNL, Berkeley, California
The superconducting, electron cyclotron resonance (ECR) ion source VENUS has been designed for the dual roles of ion injector for the 88-Inch Cyclotron at LBNL and prototype high current, medium charge state injector for the driver linac of a proposed U.S. radioactive ion beam facility. Ion beam extraction and transport from an ECR is complicated as the plasma-confining solenoidal and sextupolar fields produce beams lacking axial symmetry, these beams are composed of multiple charge states with varied distributions at extraction, and the beams undergo species-dependent rotation while leaving the confining magnetic fields. We are developing an accurate, adaptable simulation model to aid in both understanding the current VENUS system and optimizing the source and transport system for the future facility. VENUS has been outfitted with various beam diagnostics such as viewing screens, a multi-wire harp, emittance scanners, and energy analyzers, and these play an essential role in correlating simulation with experiment. We will describe in detail the diagnostics employed in the VENUS beam line. Measurements with these devices will be presented and compared with ion beam simulations.
CERN, Geneva
Wire scanners are instruments to measure the transverse beam profile. The measurement is performed by moving a thin wire across the path of the particle beam while monitoring the secondary particles. One of the limiting factor in application of wire scanners for high-intensity beams is the wire resistance to high temperature. In this work a heat flow equation for a carbon wire passing through a particle beam is solved. The equation contains modeling of wire heating induced by electromagnetic field of the beam and by electronic energy loss of the protons passing through the wire. The cooling processes considered are conduction, radiation, thermionic emission and sublimation enthalpy. Due to the equation nonlinearity a numerical approach based on discretization of the wire movement is used. An estimation of the wire sublimation rate is made. The model is tested on SPS and LEP data. An other limitation of a wire scanner application is a superconducting environment. The energy deposition in the magnet coils of downstream superconducting LHC magnets is estimated using Geant4 simulation package. In conclusions the limits of Wire Scanner operation on LHC beams are drawn.
CERN, Geneva
Field Programmable Gate Arrays (FPGAs) have become a central enabling technology for the design of fast digital signal processing systems. This tutorial starts with an introduction to digital signal processing and a comparison with analog techniques. We then treat the problem of choosing between the two key technologies for digital systems: Digital Signal Processors (DSPs) and FPGAs. Once the advantages of FPGAs for very demanding systems have been laid out, we go on with a survey of digital design techniques of general nature, followed by tips and tricks more directly applicable to FPGA implementations. Digital signal processing in FPGAs typically uses a fixed-point number representation. We explain how different fixed-point arithmetic operations can be implemented, and the trade-offs regarding speed, silicon area and precision. Finally, all the concepts are applied to a set of examples in beam instrumentation.
