Transverse Emittance Measurement with the Three-Monitor-Method at the CERN Linac4

This report evaluates the applicability of the Three-Monitor-Method to determine the transverse emittance of the CERN Linac4 160 MeV H- -beam. The Three-Monitor-Method is a linear formalism allowing to calculate transverse emittance values from beam size measurements at three different positions along a beam line, assuming that the transfer matrix elements between these locations are known. It is planned to build two of these measurement systems, which should operate from 2013/14 immediately behind the exit of the linear accelerator in the dump line and close to the end of the transfer line to the PS Booster synchrotron in the LBE line. At first, the mathematical formalism and the simulation tools are briefly introduced. Then, the method is applied for both measurement lines. Results on measurement precisions and systematic errors are presented. Final conclusions are drawn at the end, and a summary of the equipment to be installed or modified will be given

PS Booster Orbit Correction

At the end of the 2007 run, orbit measurements were carried out in the 4 rings of the PS Booster (PSB) for different working points and beam energies. The aim of these measurements was to provide the necessary input data for a PSB realignment campaign during the 2007/2008 shutdown. Currently, only very few corrector magnets can be operated reliably in the PSB; therefore the orbit correction has to be achieved by displacing (horizontally and vertically) and/or tilting some of the defocusing quadrupoles (QDs). In this report we first describe the orbit measurements, followed by a detailed explanation of the orbit correction strategy. Results and conclusions are presented in the last section

Non relativistic Broad Band wake fields and potential-well distortion

The study of the interaction between a particle beam and wake fields is usually based on the assumption of ultra relativistic beams. This is not the case, for example, for the Proton Synchrotron Booster(PSB), in which protons cover the energy range. There are some examples in literature which derive nonultra relativistic formulae for the resistive wall impedance. In this paper we have extended the Broad-Band resonator model, allowing the impedance to have poles even in the upper half complex plane, in order to obtain a wake function different from zero for. The Haissinski equation has been numerically solved showing longitudinal bunch shape changes with. In addition some longitudinal bunch profile measurements, taken for two different bunch intensities at the PSB, are shown

Single Photon Detection with Semiconductor Pixel Arrays for Medical Imaging Applications

This thesis explores the functioning of a single photon counting pixel detector for X-ray imaging. It considers different applications for such a device, but focuses mainly on the field of medical imaging. The new detector comprises a CMOS read-out chip called PCC containing 4096 identical channels each of which counts X-ray hits. The conversion of the X-rays to electric charge takes place in a semiconductor sensor which is segmented into 4096 matching square diodes of side length 170 um, the 'pixels'. The photon counting concept is based on setting a threshold in energy above which a hit is registered. The immediate advantages are the elimination of background and the in principle unlimited dynamic range. Moreover, this approach allows the use of an electronic shutter for arbitrary measurement periods. As the device was intended for operation in the energy range of ~10-70 keV, gallium arsenide was selected as the preferred sensor material. The development of this detector followed on from about 10 years of research aimed at developing hybrid silicon pixel detectors for the future Large Hadron Collider at CERN. A general overview of the requirements for medical imaging is presented. Semiconductor detectors and in particular GaAs detectors are discussed. Charge deposition and charge collection simulations were carried out. Minimum threshold, threshold spread, noise and spatial resolution measurements are presented and finally some images are shown. The combination of the detector simulations and the measurements of the device give important information about the limits of single photon counting devices and indicators for future developments

Temperature Behaviour and Uniformity of SCT Barrels during Assembly and Reception Testing

This note presents temperature studies of the barrel SemiConductor Tracker (SCT) modules during the barrel assembly at Oxford University and the barrel reception at CERN. At Oxford, warm and/or cold tests have been performed on each of the four SCT barrels comprising a total of 2112 silicon strip modules. After macro-assembly, the barrels were shipped to CERN where reception tests took place before the inner detector integration phase. We present the temperature uniformity of the different barrels under changing operating conditions. Estimates of the errors contributing to the temperature measurements will be discussed. We introduce corrections for several systematic effects. We finally identify modules operating at higher temperatures and discuss possible reasons for their deteriorated thermal performance

Characterisation of a single photon counting pixel system for imaging of low-contrast objects

In the framework of the Medipix collaboration the PCC, a single photon counting pixel chip, has been developed with the aim of improving the contrast resolution in medical imaging applications. The PCC consists of a matrix of 64x64 square pixels with 170 mm side length, each pixel comprising a 15 bit counter and a pulse height discriminator. The chip has been bump bonded to equally segmented 200 mm thick SI-LEC GaAs detectors showing a very high absorption energy for X-rays used in diagnostics. An absolute calibration of the system with a radioactive source and a synchrotron beam are described resulting in the value of the test input capacitance of ~24.7 fF. Using this value a full characterisation of the system from electrical measurements is presented. The entire system can reach a minimum threshold of ~2100 e- with ~250e- rms noise. One of the characteristics of the PCC is the possibility to adjust the thresholds of all pixels on a pixel-by-pixel basis with 3-bit precision. The threshold distribution after adjustment is ~120 e- rms. The spatial resolution of the system has been measured to be 3.61p/mm. A comparison of a tooth image taken with the PCC and with a screen-CDD system demonstrates its imaging capabilities

Coherent tune shift and instabilities measurements at the CERN Proton Synchrotron Booster

To understand one of the contributions to the intensity limitations of the CERN Proton Synchrotron Booster (PSB) in view of its operation with beams from Linac 4, the impedance of the machine has been characterized. Measurements of tune shift as a function of the intensity have been carried out in order to estimate the low frequency imaginary part of the impedance. Since the PSB is a low energy machine, these measurements have been done at two different energies, so as to enable us to disentangle the effect of the indirect space charge and resistive wall from the contribution of the machine impedance. An estimation of the possible resonant peaks in the impedance spectrum has been made by measuring a fast instability in Ring4

LHC Beams from the CERN PS Booster

The CERN PS Booster (PSB) produces a variety of beam flavours for the LHC. While the nominal LHC physics beams require 6 Booster bunches with intensities up to 1.6·1012 protons per bunch, during the LHC commissioning single bunch beams with variable intensities as low as 5·109 protons have to be provided reproducibly. The final transverse and in many cases also the final longitudinal beam characteristics have to be achieved already in the PSB and can be very demanding in terms of beam brightness and stability. The optimized production schemes for the different LHC beam flavours in the PSB and the achieved machine performance are presented. Experience with the first beams sent to the LHC in September 2008 is discussed. An overview of the first measured results with a new production scheme of the nominal LHC beam using single instead of double-batch beam transfer from the PSB to the PS is also given

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

High Intensity Beams from the CERN PS Booster

The CERN Proton Synchrotron Booster (PSB) has been running for more than 30 years. Originally designed to accelerate particles from 50 to 800 MeV, later upgradedto an energy of 1 GeV and finally 1.4 GeV, it is steadily being pushed to its operational limits. One challenge is the permanent demand for intensity increase, in particular for CNGS and ISOLDE, but also in view of Linac4. As it is an accelerator working with very high space charge during the low energy part of its cycle, its operational conditions have to be precisely tuned. Amongst other things resonances must be avoided, stop band crossings optimised and the machine impedance minimised. Recently, an operational intensity record was achieved with >4.25×1013 protons accelerated. An orbit correction campaign performed during the 2007/2008 shutdown was a major contributing factor to achieving this intensity. As the PSB presently has very few orbit correctors available,the orbit correction has to be achieved by displacing and/or tilting some of the defocusing quadrupoles common to all 4 PSB rings. The contributing factors used to optimise performance will be reviewed