Probing the diffusive behaviour of beam-halo dynamics in circular accelerators

Circular particle accelerators at the energy frontier are based on superconducting magnets that are extremely sensitive to beam losses as these might induce quenches, i.e. transitions to the normal-conducting state. Furthermore, the energy stored in the circulating beam is so large that hardware integrity is put in serious danger, and machine protection becomes essential for reaching the nominal accelerator performance. In this challenging context, the beam halo becomes a potential source of performance limitations and its dynamics needs to be understood in detail to assess whether it could be an issue for the accelerator. In this paper, we discuss in detail a recent framework, based on a diffusive approach, to model beam-halo dynamics. The functional form of the optimal estimate of the perturbative series, as given by Nekhoroshev’s theorem, is used to provide the functional form of the action diffusion coefficient. The goal is to propose an effective model for the beam-halo dynamics and to devise an efficient experimental procedure to obtain an accurate measurement of the diffusion coefficient

Baseline LHC machine parameters and configuration of the 2015 proton run

This paper shows the baseline LHC machine parameters for the 2015 start-up. Many systems have been upgraded during LS1 and in 2015 the LHC will operate at a higher energy than before and with a tighter filling scheme. Therefore, the 2015 commissioning phase risks to be less smooth than in 2012. The proposed starting configuration puts the focus on feasibility rather than peak performance and includes margins for operational uncertainties. Instead, once beam experience and a better machine knowledge has been obtained, a push in $\beta^*$ and performance can be envisaged. In this paper, the focus is on collimation settings and reach in $\beta^*$---other parameters are covered in greater depth by other papers in these proceedings.Comment: submitted for publication in a CERN yellow report (Proceedings of the LHC Performance Workshop - Chamonix 2014

Trajectory Correction in the Transfer Line TT2-TT10 for the Continuous Transfer (CT)

A new scheme for the trajectory correction in the TT2-TT10 transfer line for the Continuous Transfer (CT) extraction from the PS to the SPS has been developed together with a new software application, PS-CT-Check. In this note the algorithm, the software, and the results of the tests performed during the 2007 run are summarized. The PS-CT-Check user's manual is also provided. The scheme, with minor modifications, will be applied to the new Multi-Turn Extraction (MTE)

WISE: A Simulation of the LHC Optics including Magnet Geometrical Data

The beam dynamics in the LHC require a tight control of the field quality and geometry of its magnets. At the EPAC06 we presented the simulation tool WISE which generates magnetic field errors to be used as input to the MAD-X program. This paper describes the evolution in the WISE software since EPAC06. The allocation of magnets to lattice positions is completed, and therefore there is no more need for simulated allocations. Geometric axis measurements are now available for all cryostats. Furthermore, survey data is available to estimate the precision of the magnet installation (alignment). This paper discusses how the new data is used in connection with MAD-X simulations to give the most recent figures for beta-beating at injection (450 GeV) and collision energy (7 TeV)

CERN Proton Synchrotron working point control using an improved version of the pole-face-windings and figure-of-eight loop powering

The working point of the CERN Proton Synchrotron, which is equipped with combined function magnets, is controlled using pole-face-windings. Each main magnet consists of one focusing and one de-focusing half-unit on which four pole-face-winding plates are mounted containing two separate coils each, called narrow and wide. At present they are connected in series, but can be powered independently. In addition, a winding called the figure-of-eight loop, contours the pole faces and crosses between the two half units, generating opposite fields in each half-unit. The four optical parameters, horizontal and vertical tune and chromaticity, are adjusted by acting on the pole-face-winding currents in both half units and in the figure-of-eight loop, leaving one physical quantity free. The power supply consolidation project opened the opportunity to use five independent power supplies, to adjust the four parameters plus an additional degree of freedom. This paper presents the results of the measurements that have been made in the five-current mode together with the influence of the magnetic nonlinearities, due to the unbalance in the narrow and wide winding currents, on the beam dynamics

Experimental evidence of adiabatic splitting of charged particle beams using stable islands of transverse phase space

Recently, a novel technique to perform multi-turn extraction from a circular particle accelerator was proposed. It is based on beam splitting and trapping, induced by a slow crossing of a nonlinear resonance, inside stable islands of transverse phase space. Experiments at the CERN Proton Synchrotron started in 2002 and evidence of beam splitting was obtained by summer 2004. In this paper the measurement results achieved with both a low- and a high-intensity, single-bunch proton beam are presented