Polygonal Complexes and Graphs for Crystallographic Groups

The paper surveys highlights of the ongoing program to classify discrete polyhedral structures in Euclidean 3-space by distinguished transitivity properties of their symmetry groups, focussing in particular on various aspects of the classification of regular polygonal complexes, chiral polyhedra, and more generally, two-orbit polyhedra.Comment: 21 pages; In: Symmetry and Rigidity, (eds. R.Connelly, A.Ivic Weiss and W.Whiteley), Fields Institute Communications, to appea

Second-order properties and central limit theorems for geometric functionals of Boolean models

Let $Z$ be a Boolean model based on a stationary Poisson process $\eta$ of compact, convex particles in Euclidean space ${\mathbb{R}}^d$. Let $W$ denote a compact, convex observation window. For a large class of functionals $\psi$, formulas for mean values of $\psi(Z\cap W)$ are available in the literature. The first aim of the present work is to study the asymptotic covariances of general geometric (additive, translation invariant and locally bounded) functionals of $Z\cap W$ for increasing observation window $W$, including convergence rates. Our approach is based on the Fock space representation associated with $\eta$. For the important special case of intrinsic volumes, the asymptotic covariance matrix is shown to be positive definite and can be explicitly expressed in terms of suitable moments of (local) curvature measures in the isotropic case. The second aim of the paper is to prove multivariate central limit theorems including Berry-Esseen bounds. These are based on a general normal approximation result obtained by the Malliavin--Stein method.Comment: Published at http://dx.doi.org/10.1214/14-AAP1086 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Traveling wave method for simulating geometric beam coupling impedance of a beamscreen with pumping holes

In particle accelerators, pumping holes in a vacuum chamber can be a source of unwanted broadband coupling impedance, leading to beam instabilities. Analytical methods have been previously developed to estimate the impedance of holes in circular-like chambers e.g. the beamscreen of the Large Hadron Collider (LHC). More sophisticated chamber designs like that of the High Energy LHC (HE-LHC) and the Future Circular Collider (FCC-hh) call for a different way to calculate the impedance. We propose using decomposition of the wakefield into synchronous traveling waves and employing a numerical solver to find the impedance of each wave. This method is compared to the direct time domain wakefield calculation method and its greater sensitivity to small impedances is shown

Pulse Shaping and Beam-Loading Compensation with the Delay Loop

In the drive-beam accelerator of the compact linear collider (CLIC) the trains fill every second bucket. If the bunches in the one train occupy even buckets they will occupy odd ones in the next train and vice versa. This encoding is achieved by a phase switch at the injector. An RF-kicker running at half the linac frequency and a delay loop are used to separate the trains after the acceleration. This paper shows how the delay loop and the phase switch can be used to compensate the main-linac beam loading. It is also possible to shorten the final pulse which would otherwise be fixed by geometry

Emittance Preservation in the Main LINAC of CLIC

The luminosity that can be achieved in a linear collider strongly depends on the vertical emittance of the beams at the interaction point. One of the most important sources of emittance growth is the accelerating part of the main linac especially in the case of the compact linear collider, CLIC, where the wakefields are strong due to the high frequency of the accelerating structures (30 GHz). Poss ible lattices for the main linacs for centre-of-mass energies of 1 TeV and 3 TeV are presented which allow the use of BNS-damping for emittance preservation. A new ballistic beam-based alignment techn ique to keep the emittance growth below the required limit is investigated. The influence of different prealignment and field errors on the correction efficiency is investigated

The CLIC Main Linac Lattice at 1 TeV

This paper presents the CLIC main linac lattice at a centre of mass energy of 1 TeV. Its aim is to show that such a lattice is feasible resulting only in a moderate emittance growth of the transported beam due to wakefield and dispersive effects. A correction method is presented that achieves this small growth. The emittance dilution due to static and dynamic effects is discussed. Finally the multibunch effects are estimated

Update of the Status of Machine Detector Interface Studies for CLIC

The Compact Linear Collider (CLIC) study team at CERN is working on the design of an electron-positron linear collider, with the main focus on a machine with a centre-of-mass energy of Ecm=3 TeV and a luminosity of 1035cm-2s-1. Because of the high energy and high luminosity, the background in this machine is expected to be higher than in low-energy linear colliders. These backgrounds need to be carefully investigated in order to verify that the experimental conditions are acceptable. For the same reason the luminsoity spectrum needs careful consideration. This paper gives a brief update on the status of the necessary machine/detector interface studies for CLIC

Background at Future Linear Colliders

Detector background in future e+e- colliders, as will arise for example from the beam-beam interaction, will strongly affect experimental conditions. A short overview of the main background sources is given. Numerical results are presented, mainly for TESLA at a centre-of-mass energy Ecm = 0.5 TeV and for CLIC at Ecm = 3 TeV

The Drive Beam Accelerator of CLIC

The drive beam of the Compact Linear Collider (CLIC) requires a current of several amperes. The time structure of this beam is discussed. First simulation results on longitudinal single bunch effects are presented and achievable bunch lengths and sensitivity to jitter of the gradient, initial energy and charge are analysed. The transverse stability of the beam is discussed based on the present structure model. Requirements on the damping and detuning of the cavities are given in detail. A beam-based alignment technique is presented and the stability with respect to jitter and ground motion is investigated

Simulations of an Intra-Pulse Interaction Point Feedback for NLC

Position and angle jitter of the beams at the interaction point are important sources of luminosity degradation in future linear colliders. In order to reduce their effect, intra-pulse feedbacks can be used. Some simulations are presented to evaluate a position feedback at the interaction point. The influence of angle jitter onto this feedback are investigated and possible fixes are discussed. A feedback is proposed that allows to also reduce the effect of angle jitter