Beam Diagnostics

As soon as the first particles emerge from an ion source, the source characteristics need to be determined. The total beam intensity, the transverse particle distributions, the beam divergence and emittance as well as the longitudinal parameters of the beam must be measured. This chapter provides an overview of typical measurement methods and the instruments used, and shows the results obtained.Comment: 12 pages, contribution to the CAS-CERN Accelerator School: Ion Sources, Senec, Slovakia, 29 May - 8 June 2012, edited by R. Bailey, CERN-2013-00

Beam diagnostics

Most beam measurements are based on the electro-magnetic interaction of fields induced by the beam with their environment. Beam current transformers as well as beam position monitors are based on this principle. The signals induced in the sensors must be amplified and shaped before they are converted into numerical values. These values are further treated numerically in order to extract meaningful machine parameter measurements. The lecture introduces the architecture of an instrument and shows where in the treatment chain digital signal analysis can be introduced. Then the use of digital signal processing is presented using tune measurements, orbit and trajectory measurements as well as beam loss detection and longitudinal phase space tomography as examples. The hardware as well as the treatment algorithms and their implementation on Digital Signal Processors (DSPs) or in Field Programmable Gate Arrays (FPGAs) are presented

Beam diagnostics

The instrumentation measuring beam parameters constitutes an important part of any particle accelerator. These lectures aim at giving an overview of detection and measurement techniques without going too much into details of implementation. Instruments for linear accelerators, transfer lines, and small synchrotrons are described with an emphasis on opportunities and problems specific to low-energy particle beams

A Single Pulse Beam Emittance Measurement for the CERN Heavy Ion Linac

A new device for transverse emittance measurement has been installed in the 4.2 MeV/u filter region of the CERN Heavy Ion Linac (Linac 3). It allows to obtain pulse-to-pulse (every 1.2 sec) visualisation of the Linac 3 beam parameters in order to tune the machine and to match the beam for injection into the first circular accelerator, the PS Booster. The system is based on the "multi-slit" technique similar to the well-known "pepper pot" method. A plate with a series of horizontal or vertical slits is placed in the beam, defining positions in the phase plane. Particles pass through the slits and drift to a scintillator screen where they produce light. The screen is looked at by an externally triggered high resolution CCD camera. For each slit position the light intensity distribution, in the limit of infinitesimal slit aperture, is proportional to the angle distribution of the particles and therefore, provides the angular distribution in the phase plane. The video signal from the camera is digitised and the result stored in a 512 x 512 x 8 frame store. An application program visualising slit images (raw data) as well as the calculated emittance ellipses has been developed. This program also delivers numerical values for the rms-emittance and the Twiss parameters. The paper discusses the method, the prototype realisation, the data treatment and first experimental results obtained during the running-in of Linac 3

Digital Beam Trajectory and Orbit System, for the CERN Proton Synchrotron

A new trajectory and orbit measurement system using fast signal sampling and digital signal processing in an FPGA is proposed for the CERN PS. The system uses a constant sampling frequency while the beam revolution frequency changes during acceleration. Synchronization with the beam is accomplished through a numerical PLL algorithm. This algorithm is also capable of treating RF gymnastics like bunch splitting or batch compression with the help of external timing signals. Baseline and position calculation are provided in the FPGA code as well. After having implemented the algorithms in C and MatLab and tested them with data from a test run at the PS, they have now been implemented in the FPGA for online use. Results of measurements on a single beam position monitor in the CERN PS and the SIS-18 at GSI will be presented

Wire scanners in low energy accelerators

Fast wire scanners are today considered as part of standard instrumentation in high energy synchrotrons. The extension of their use to synchrotrons working at lower energies, where Coulomb scattering can be important and the transverse beam size is large, introduces new complications considering beam heating of the wire, composition of the secondary particle shower and geometrical consideration in the detection set-up. A major problem in treating these effects is that the creation of secondaries in a thin carbon wire by a energetic primary beam is difficult to describe in an analytical way. We are here presenting new results from a full Monte Carlo simulation of this process yielding information on heat deposited in the wire, particle type and energy spectrum of secondaries and angular dependence as a function of primary beam energy. The results are used to derive limits for the use of wire scanners in low energy accelerators.Comment: 20 pages, 8 Postscript figures, uses elsart.cl

Injection Matching Studies using Turn by Turn Beam Profile Measurements in the CERN PS

The very small emittance beam needed for the LHC requires that the emittance blow-up in its injector machines must be kept to a minimum. Mismatch upon the beam transfer from one machine to the next is a potential source of such blow-up. The CERN PS ring is equipped with 3 Secondary Emission Grids (SEM-Grids) which are used for emittance measurement at injection. One of these has been converted to a multi-turn mode, in which several tens of consecutive beam passages can be observed. This allows the study of mismatch between the PS-Booster and the PS. This paper describes the instrument and experimental results obtained during the last year

Linac4 Beam Characterization before Injection into the CERN PS Booster

Construction work for the new CERN linear accelerator, Linac4, started in October 2008. Linac4 will replace the existing Linac2 and provide an H− beam at 160 MeV (as opposed to the present 50 MeV proton beam) for injection into the CERN PS Booster (PSB). The charge-exchange H− injection combined with the higher beam energy will allow for an increase in beam brightness required for reaching the ultimate LHC luminosity. Commissioning of Linac4 and of the transfer line to the PSB is planned for the last quarter of 2012. Appropriate beam instrumentation is foreseen to provide transverse and longitudinal beam characterization at the exit of Linac4 and in two dedicated measurement lines located before injection into the PSB. A detailed description of the diagnostics set, especially of spectrometer and emittance meter, and the upgrade of the measurement lines for Linac4 commissioning and operation is presented

A Comparative Study of Fast Wire Scanners, Beamscope and SEM-Grids for Emittance Measurements in the PS Booster

The tight emittance budget, imposed on the production of the high-brilliance beams in the LHC preinjectors, demands the elimination of all possible sources of beam blow-up. A prerequisite for this is reliable instrumentation and evaluation methods for comparison of their data. We have made a study of three methods for emittance measurement in the PS Booster: fast wire-scanners, BeamScope, and SEM-grids in a measurement line. For the fast wire-scanners, a full Monte-Carlo simulation was made of the beam-wire interaction, for an energy range from 100 MeV to 1 GeV, and compared to measured values. Data from a scraping method (BeamScope) are compared to profile measurements, using Abel-type integral transformations. Results will be presented