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

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

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

Noiseless, kilohertz-frame-rate, imaging detector based on micro-channel plates readout with the Medipix2 CMOS pixel chip

A new hybrid imaging detector is described that is being developed for the next generation adaptive optics (AO) wavefront sensors. The detector consists of proximity focused microchannel plates (MCPs) read out by pixelated CMOS application specific integrated circuit (ASIC) chips developed at CERN ("Medipix2"). Each Medipix2 pixel has an amplifier, lower and upper charge discriminators, and a 14-bit chounter. The 256x256 array can be read out noiselessly (photon counting) in 286 us. The Medipix2 is buttable on 3 sides to produce 512x(n*256) pixel devices. The readout can be electronically shuttered down to a terporal window of a few microseconds with an accuracy of 10 ns. Good quantum efficiencies can be achieved from the x-ray (open faced with opaque photocathodes) to the optical (sealed tube with multialkali or GaAs photocathode)

Photon counting arrays for AO wavefront sensors

Future wavefront sensors for AO on large telescopes will require a large number of pixels and must operate at high frame rates. Unfortunately for CCDs, there is a readout noise penalty for operating faster, and this noise can add up rather quickly when considering the number of pixels required for the extended shape of a sodium laser guide star observed with a large telescope. Imaging photon counting detectors have zero readout noise and many pixels, but have suffered in the past with low QE at the longer wavelengths (>500 nm). Recent developments in GaAs photocathode technology, CMOS ASIC readouts and FPGA processing electronics have resulted in noiseless WFS detector designs that are competitive with silicon array detectors, though at ~40% the QE of CCDs. We review noiseless array detectors and compare their centroiding performance with CCDs using the best available characteristics of each. We show that for sub-aperture binning of 6x6 and greater that noiseless detectors have a smaller centroid error at fluences of 60 photons or less, though the specific number is dependent on seeing conditions and the centroid algorithm used. We then present the status of a 256x256 noiseless MCP/Medipix2 hybrid detector being developed for AO

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

Coherent Single Charge Transport in Molecular-Scale Silicon Nanowire Transistors

We report low-temperature electrical transport studies of molecule-scale silicon nanowires. Individual nanowires exhibit well-defined Coulomb blockade oscillations characteristic of charge addition to a single nanostructure with length scales up to at least 400 nm. Further studies demonstrate coherent charge transport through discrete single particle quantum levels extending the whole device, and show that the ground state spin configuration follows the Lieb-Mattis theorem. In addition, depletion of the nanowires suggests that phase coherent single-dot characteristics are accessible in a regime where correlations are strong.Comment: 4 pages and 4 figure