LHC Dynamic Aperture Including the Beam-Beam Force

The LHC dynamic aperture in collision is constrained mainly by the beam-beam encounters, and by the field errors in the low-beta triplet quadrupoles. The nominal field errors were used and have been corrected with a local corrector scheme at each IP. The correction algorithm is explained, and the resulting dynamic aperture is shown. In the calculations, the effect of the crossing angle geometry, the beta-function, the bunch intensity and the pacman bunches on the dynamic aperture are studied. It is, however, also necessary to study how the unavoidable long range beam-beam encounters influence the dynamic aperture

Dynamic aperture studies for the LHC version 4

The limitations of the dynamic aperture due to field errors of the super-conducting magnets is a notorious problem for the LHC. Given the large amount of independent studies performed by a sizeable research team it becomes necessary to define a common tracking strategy. The emphasis is placed on an elaborate on - and off - line processing of the tracking data making use of all tools presently available. To manage the very time-comsuming investigations our approach is two-fold: firstly we are maximising the computing power running optimised code on state of the art equipment which is continuously upgraded and secondly we speed up the studies by using reliable and automated early indicators for long-term losses. The procedure is exemplified with a series of tracking runs for the LHC version 4 at injection

The upgrade of GEO600

The German / British gravitational wave detector GEO 600 is in the process of being upgraded. The upgrading process of GEO 600, called GEO-HF, will concentrate on the improvement of the sensitivity for high frequency signals and the demonstration of advanced technologies. In the years 2009 to 2011 the detector will undergo a series of upgrade steps, which are described in this paper.Comment: 9 pages, Amaldi 8 conference contributio

Quantum Collective QCD String Dynamics

The string breaking model of particle production is extended in order to help explain the transverse momentum distribution in elementary collisions. Inspired by an idea of Bialas', we treat the string using a collective coordinate approach. This leads to a chromo-electric field strength which fluctuates, and in turn implies that quarks are produced according to a thermal distribution.Comment: 6 pages. Presented at SQM 2006. Submitted to J. Phys. G for publication in proceedings. Vers. 2: Minor revisions; final hadron spectrum calculation include

Contributions of the SL Division to the Workshop on Beam-beam Effects at Fermilab, June 2001

This is a compilation of the papers and presentations contributed to the workshop on beam-beam effects, held from 25-28.6 2001 at Fermilab, Batavia, Illinois, US

Tracing drought effects from the tree to the stand growth in temperate and Mediterranean forests: insights and consequences for forest ecology and management

How drought affects tree and stand growth is an old question, but is getting unprecedented relevance in view of climate change. Stress effects related to drought have been mostly studied at the individual tree level, mostly investigating dominant trees and using their responses as indicator for the impact at the stand level. However, findings at tree and stand level may differ, as the stand responses include interactions and feedbacks that may buffer or aggravate what is observed at the individual tree level. Here, we trace drought effects on growth and development from tree to the stand scale. Therefore, we analyse annually measured data from long-term experiments in temperate and Mediterranean forests. With this analysis, we aim to disclose how well results of dominant tree growth reflect stand-level behaviour, hypothesizing that drought resistance of dominant trees’ can strongly deviate from the overall sensitivity of the stand. First, we theoretically derive how drought responses at the stand level emerge from the tree-level behaviour, thereby considering that potential drought resistance of individual trees is modulated by acclimation and tree–tree interactions at the stand level and that the overall stress response at the stand level results from species-specific and size-dependent individual tree growth and mortality. Second, reviewing respective peer-reviewed literature (24 papers) and complementing findings by own measurements (22 experiments) from temperate and Mediterranean monospecific and mixed-species forests, we are able to reveal main causes for deviations of tree-level and stand-level findings regarding drought stress responses. Using a long-term experiment in Norway spruce (Picea abies (L.) KARST.) and European beech (Fagus sylvatica L.), we provide evidence that the species-dependent and size-dependent reactions matter and how the size–frequency distribution affects the scaling. We show by examples that tree-level derived results may overestimate growth losses by 25%. Third, we investigate the development of the growth dominance coefficient based on measurements gathered at the Bavarian forest climate stations. We show that drought changes stand biomass partitioning in favour of small trees, reduce social differentiation, and homogenize the vertical structure of forests. Finally, we discuss the drought-related consequences of the social class-specific growth reaction patterns for inventory and monitoring and highlight the importance of these findings for understanding site-specific stand dynamics, for forest modelling, and for silvicultural management

Subtraction of test mass angular noise in the LISA Technology Package interferometer

We present recent sensitivity measurements of the LISA Technology Package interferometer with articulated mirrors as test masses, actuated by piezo-electric transducers. The required longitudinal displacement resolution of 9 pm/sqrt[Hz] above 3 mHz has been demonstrated with an angular noise that corresponds to the expected in on-orbit operation. The excess noise contribution of this test mass jitter onto the sensitive displacement readout was completely subtracted by fitting the angular interferometric data streams to the longitudinal displacement measurement. Thus, this cross-coupling constitutes no limitation to the required performance of the LISA Technology Package interferometry.Comment: Applied Physics B - Lasers and Optics (2008

Long-term stable squeezed vacuum state of light for gravitational wave detectors

Currently, the German/British gravitational wave detector GEO600 is being upgraded in course of the GEO-HF program. One part of this upgrade consists of the integration of a squeezed light laser to nonclassically improve the detection sensitivity at frequencies where the instrument is limited by shot noise. This has been achieved recently [1]. The permanent employment of squeezed light in gravitational wave observatories requires a long-term stability of the generated squeezed state. In this paper, we discuss an unwanted mechanism that can lead to a varying squeezing factor along with a changing phase of the squeezed field. We present an extension of the implemented coherent control scheme [2] that allowed an increase in the long-term stability of the GEO600 squeezed light laser. With it, a quantum noise reduction by more than 9 dB in the frequency band of 10 Hz - 10 kHz was observed over up to 20 hours with a duty cycle of more than 99%

Photon pressure induced test mass deformation in gravitational-wave detectors

A widely used assumption within the gravitational-wave community has so far been that a test mass acts like a rigid body for frequencies in the detection band, i.e. for frequencies far below the first internal resonance. In this article we demonstrate that localized forces, applied for example by a photon pressure actuator, can result in a non-negligible elastic deformation of the test masses. For a photon pressure actuator setup used in the gravitational wave detector GEO600 we measured that this effect modifies the standard response function by 10% at 1 kHz and about 100% at 2.5 kHz