Sorting strategies for the arc quadrupoles of the LHC

The variation in the field gradient of the LHC arc quadrupoles can not be corrected by the dedicated trim quadrupole circuits. This may result to a beta function beating larger than the one accepted by the machine budget. In this respect, sorting strategies for the installation of these magnets were implemented in order to eliminate this effect, as locally as possible. Special care was taken for quadrupoles whose warm measurements showed large gradient errors due to an excessive magnetic permeability. The figures of merit used in the sorting and the results obtained for all 8 sectors of the LHC are detailed. The global optics function beating foreseen, as computed by analytical estimates are finally presented

A primary electron beam facility at CERN

This document describes the concept of a primary electron beam facility at CERN, to be used for dark gauge force and light dark matter searches. The electron beam is produced in three stages: A Linac accelerates electrons from a photo-cathode up to 3.5 GeV. This beam is injected into the Super Proton Synchrotron, SPS, and accelerated up to a maximum energy of 16 GeV. Finally, the accelerated beam is slowly extracted to an experiment, possibly followed by a fast dump of the remaining electrons to another beamline. The beam parameters are optimized using the requirements of the Light Dark Matter eXperiment, LDMX, as benchmark

Detecting chaos in particle accelerators through the frequency map analysis method

The motion of beams in particle accelerators is dominated by a plethora of non-linear effects which can enhance chaotic motion and limit their performance. The application of advanced non-linear dynamics methods for detecting and correcting these effects and thereby increasing the region of beam stability plays an essential role during the accelerator design phase but also their operation. After describing the nature of non-linear effects and their impact on performance parameters of different particle accelerator categories, the theory of non-linear particle motion is outlined. The recent developments on the methods employed for the analysis of chaotic beam motion are detailed. In particular, the ability of the frequency map analysis method to detect chaotic motion and guide the correction of non-linear effects is demonstrated in particle tracking simulations but also experimental data.Comment: Submitted for publication in Chaos, Focus Issue: Chaos Detection Methods and Predictabilit

Space-Charge and resonance considerations for choosing the SNS ring working points

The beam power of the SNS is an order of magnitude higher than that of existing accelerator facilities. This imposes a strict requirement on the uncontrolled beam loss at a $10^{-4}$ level. The major source of beam loss is associated with machine resonances. Thus, the first step towards reaching low beam loss is to find the best suitable working points on the tune diagram. In this note, we explore the tune space by considering machine resonances and the effect of space charge, which can drive particles into these excited resonances.In addition, space charge itself can induce resonances. Our present studies were driven by these facts and by the fact that previous working points [1] were identified for the shorter ring with 220 m circumference. Also, the combined effects of space charge and magnet errors raised concern for the nominal working point [2-3]

Self-consistent models of cuspy triaxial galaxies with dark matter haloes

We have constructed realistic, self-consistent models of triaxial elliptical galaxies embedded in triaxial dark matter haloes. We examined three different models for the shape of the dark matter halo: (i) the same axis ratios as the luminous matter (0.7:0.86:1); (ii) a more prolate shape (0.5:0.66:1); (iii) a more oblate shape (0.7:0.93:1). The models were obtained by means of the standard orbital superposition technique introduced by Schwarzschild. Self-consistent solutions were found in each of the three cases. Chaotic orbits were found to be important in all of the models,and their presence was shown to imply a possible slow evolution of the shapes of the haloes. Our results demonstrate for the first time that triaxial dark matter haloes can co-exist with triaxial galaxies.Comment: Latex paper based on the AASTEX format, 20 pages, 11 figures, 2 tables. Paper submitted to Ap

A primary electron beam facility at CERN

This paper describes the concept of a primary electron beam facility at CERN, to be used for dark gauge force and light dark matter searches. The electron beam is produced in three stages: A Linac accelerates electrons from a photo-cathode up to 3.5 GeV. This beam is injected into the Super Proton Synchrotron, SPS, and accelerated up to a maximum energy of 16 GeV. Finally, the accelerated beam is slowly extracted to an experiment, possibly followed by a fast dump of the remaining electrons to another beamline. The beam parameters are optimized using the requirements of the Light Dark Matter eXperiment (LDMX) as benchmark.Comment: 3 pages, 3 figure

Measurement of Resonance Driving Terms from Turn-by-Turn Data

It has been shown that the Fourier analysis of recorded turn-by-turn tracking data can be used to derive resonance terms of an accelerator. Besides the resonance driving terms, the non-linear one-turn map can be obtained with all non-linearities arising from magnetic imperfections and correction elements. This could be interesting for the LHC which will be a machine that is dominated by strong non-linear fields. The methods works very well for tracking data and is expected to work equally well for turn-by-turn beam data. The precision to which these terms can be determined relies on the frequency analysis tool. To demonstrate the feasibility of the method, measurements of real accelerators are presented in which the beam is kicked once and the beam oscillations are recorded over several thousand turns. Besides the tune, the strengths of resonance driving terms have been measured and the results are compared with numerical calculation

Efficient queue-balancing switch for FPGAs

This paper presents a novel FPGA-based switch design that achieves high algorithmic performance and an efficient FPGA implementation. Crossbar switches based on virtual output queues (VOQs) and variations have been rather popular for implementing switches on FPGAs, with applications to network-on-chip (NoC) routers and network switches. The efficiency of VOQs is well-documented on ASICs, though we show that their disadvantages can outweigh their advantages on FPGAs. Our proposed design uses an output-queued switch internally for simplifying scheduling, and a queue balancing technique to avoid queue fragmentation and reduce the need for memory-sharing VOQs. Our implementation approaches the scheduling performance of the state-of-the-art, while requiring considerably fewer FPGA resources

Generation of short Proton bunches in the CERN Accelerator Complex

Short high-energy proton bunches have been proposed as efficient drivers for single-stage electron-beam plasma accelerators. We discuss some very preliminary ideas if and how the desired proton bunches could be obtained in the CERN accelerator complex, considering various bunchshortening schemes, such as a fast non-adiabatic lattice change prior to extraction from a storage ring or the use of transversely deflecting cavities, as well as the possibility of introducing, in a longer bunch, a microstructure that might resonantly excite a plasma wake field

A unified framework for the orbital structure of bars and triaxial ellipsoids

We examine a large random sample of orbits in two self-consistent simulations of N-body bars. Orbits in these bars are classified both visually and with a new automated orbit classification method based on frequency analysis. The well-known prograde x1 orbit family originates from the same parent orbit as the box orbits in stationary and rotating triaxial ellipsoids. However, only a small fraction of bar orbits (~4%) have predominately prograde motion like their periodic parent orbit. Most bar orbits arising from the x1 orbit have little net angular momentum in the bar frame, making them equivalent to box orbits in rotating triaxial potentials. In these simulations a small fraction of bar orbits (~7%) are long-axis tubes that behave exactly like those in triaxial ellipsoids: they are tipped about the intermediate axis owing to the Coriolis force, with the sense of tipping determined by the sign of their angular momentum about the long axis. No orbits parented by prograde periodic x2 orbits are found in the pure bar model, but a tiny population (~2%) of short-axis tube orbits parented by retrograde x4 orbits are found. When a central point mass representing a supermassive black hole (SMBH) is grown adiabatically at the center of the bar, those orbits that lie in the immediate vicinity of the SMBH are transformed into precessing Keplerian orbits that belong to the same major families (short-axis tubes, long-axis tubes and boxes) occupying the bar at larger radii. During the growth of an SMBH, the inflow of mass and outward transport of angular momentum transform some x1 and long-axis tube orbits into prograde short-axis tubes. This study has important implications for future attempts to constrain the masses of SMBHs in barred galaxies using orbit-based methods like the Schwarzschild orbit superposition scheme and for understanding the observed features in barred galaxies