Electron Cloud Mitigation by Fast Bunch Compression in the CERN PS

A fast transverse instability has been observed with nominal LHC beams in the CERN Proton Synchrotron (PS) in 2006. The instability develops within less than 1 ms, starting when the bunch length decreases below a threshold of 11.5 ns during the RF procedure to shorten the bunches immediately prior to extraction. An alternative longitudinal beam manipulation, double bunch rotation, has been proposed to compress the bunches from 14 ns to the 4 ns required at extraction within 0.9 ms, saving some 4.5 ms with respect to the present compression scheme. The resultant bunch length is found to be equivalent for both schemes. In addition, electron cloud and vacuum measurements confirm that the development of an electron cloud and the onset of an associated fast pressure rise are delayed with the new compression scheme. Beam dynamics simulations and measurements of the double bunch rotation are presented as well as evidence for its beneficial effect from the electron cloud standpoint

Jejunal gene expression patterns correlate with severity of systemic infection in chicken

<p>Abstract</p> <p>Background</p> <p>Not much is known about the effect of <it>Salmonella enteritidis</it> on changes in the developmental processes occurring in the intestine of young chicken. Therefore we investigated the correlation of intestinal gene expression patterns with the severity of systemic Salmonella infections.</p> <p>Methods</p> <p>The number of Salmonella colony forming units (CFUs) in the liver of infected chicken were plotted against the average intestinal expression profiles of previously identified gene expression clusters. The functional properties of all the genes taken together present in 3 clusters exhibiting positive correlation at early time-points were compared with the functional properties of the genes displaying antagonistic correlations in 1 cluster. The top 5 ranking functional groups were analysed in further detail.</p> <p>Results</p> <p>Three clusters showed gene expression profiles which were positively correlated with the severity of systemic disease as measured by the number of Salmonella colony forming units in the liver. In these clusters, genes involved in morphological processes were predominantly present. One cluster had a profile that was negatively correlated with the severity of systemic disease, as measured by numbers of CFUs in the liver. The genes in the latter cluster were mostly involved in cell turn-over and metabolism.</p> <p>Conclusions</p> <p>In the developing jejunum of young chicken, both stimulatory and inhibitory gene expression mechanisms are correlated with the severity of systemic Salmonella infections.</p

Disc shaped compact tension (DCT) specifications development for asphalt pavement

The disc-shaped compact tension (DCT) fracture energy test has been shown to discriminate between asphalt mixtures with respect to their thermal cracking potential. This research refines the DCT fracture energy testing procedure, identifies needed adjustments in asphalt mixture to increase fracture energy, determines the suitability of DCT-test-based parameters as indicators of reflective cracking, and proposes threshold values to lower the potential for premature reflective cracking in asphalt overlays. A number of recommendations have been developed to implement outcomes of this research as well as to fill knowledge gaps identified through this study

SPS Impedance

For many years several measurements of the beam coupling impedance have been performed each year in both longitudinal and transverse planes of the CERN Super Proton Synchrotron to keep track of the evolution of its hardware. Copious types of equipments had to be modified or added in the past to allow the SPS to produce the nominal LHC beam. The next challenge would be the operation of the SPS with higher intensity for the LHC luminosity upgrade, which requires a good knowledge of the machine impedance and in particular of its major contributors. The current understanding of the measurements performed over the last few years is presented in this paper. In particular, this analysis reveals that the longitudinal impedance is reasonably well understood, while the situation is less satisfactory in the transverse planes, where about half of the measured impedance still needs to be identified

CERN SPS Impedance in 2007

Each year several measurements of the beam coupling impedance are performed in both longitudinal and transverse planes of the CERN Super Proton Synchrotron to keep track of its evolution. In parallel, after the extensive and successful campaign of identification, classification and cure of the possible sources of (mainly longitudinal) impedance between 1998 and 2001, a new campaign (essentially for the transverse impedance this time) has started few years ago, in view of the operation of the SPS with higher intensity for the LHC luminosity upgrade. The present paper summarizes the results obtained from the measurements performed over the last few years and compares them to our predictions. In particular, it reveals that the longitudinal impedance is reasonably well understood and the main contributors have already been identified. However, the situation is quite different in the transverse plane: albeit the relative evolution of the transverse impedance over the last few years can be well explained by the introduction of the nine MKE kickers necessary for beam extraction towards the LHC, significant contributors to the SPS transverse impedance have not been identified yet

LHC Transverse Feedback System and its Hardware Commissioning

A powerful transverse feedback system ("Damper") has been installed in LHC. It will stabilise coupled bunch instabilities in a frequency range from 3 kHz to 20 MHz and at the same time damp injection oscillations originating from steering errors and injection kicker ripple. The transverse damper can also be used as an exciter for purposes of abort gap cleaning or tune measurement. The power and lowlevel systems layouts are described along with results from the hardware commissioning. The achieved performance is compared with earlier predictions and requirements for injection damping and instability control

LHC Transverse Feedback System: First Results of Commissionning

A powerful transverse feedback system ("Damper") has been installed in LHC. It will stabilise the high intensity beam against coupled bunch transverse instabilities in a frequency range from 3 kHz to 20 MHz and at the same time damp injection oscillations originating from steering errors and injection kicker ripple. The LHC Damper can also be used as means of exciting transverse oscillations for the purposes of abort gap cleaning and tune measurement. The LHC Damper includes 4 feedback systems on 2 circulating beams (in other words one feedback system per beam and plane). Every feedback system consists of 4 electrostatic kickers, 4 push-pull wide band power amplifiers, 8 preamplifiers, two digital processing units and 2 beam position monitors with low-level electronics. The power and low-level subsystem layout is described along with first results from the commissioning of 16 power amplifiers and 16 electrostatic kickers located in the LHC tunnel. The achieved performance is compared with earlier predictions and requirements for injection damping and instability control. Requirements and first measurements of the performance of the power and low-level subsystems are summarized