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Yannis Papaphilippou

Publications and source records attributed to Yannis Papaphilippou.

17 recordsLinked to original sources
arXiv2025

The Compact Linear e$^+$e$^-$ Collider (CLIC)

The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear e$^+$e$^-$ collider studied by the international CLIC and CLICdp collaborations. CLIC uses a two-beam acceleration scheme, in which normal-conducting high-gradient 12 GHz accelerating structures are powered via a high-current drive beam. CLIC is foreseen to be built and operated in stages. The initial 380 GeV stage, with a site length of 11 km, optimally combines the exploration of Higgs and top-quark physics, including a top threshold scan near 350 GeV. A higher-energy stage, still using the initial single drive-beam complex, can be optimised for any energy up to 2 TeV. Parameters are presented in detail for a 1.5 TeV stage, with a site length of 29 km. Since the 2018 ESPPU reporting, significant effort was invested in CLIC accelerator optimisation, technology developments and system tests, including collaboration with new-generation light sources and free-electron lasers. CLIC implementation aspects at CERN have covered detailed studies of civil engineering, electrical networks, cooling and ventilation, scheduling, and costing. The CLIC baseline at 380 GeV is now 100 Hz operation, with a luminosity of 4.5$\times 10^{34}$ cm$^{-2}$s$^{-1}$ and a power consumption of 166 MW. Compared to the 2018 design, this gives three times higher luminosity-per-power. The new baseline has two beam-delivery systems, allowing for two detectors operating in parallel. The cost estimate of the 380 GeV baseline is approximately 7.2 billion CHF. The construction of the first CLIC energy stage could start as early as ~2034/35 with first beams following a decade later. This report summarises the CLIC project, its implementation and running scenarios, with emphasis on new developments and recent progress. It concludes with an update on the CLIC detector studies and on the physics potential in light of the improved accelerator performance.

physics.acc-ph↗
arXiv2024

Interplay of space charge, intrabeam scattering and synchrotron radiation in the Compact Linear Collider damping rings

Future ultra-low emittance rings for electron/positron colliders require extremely high beam brightness and can thus be limited by collective effects. In this paper, the interplay of effects such as synchrotron radiation, intra-beam scattering (IBS) and space charge in the vicinity of excited betatron resonances is assessed. In this respect, two algorithms were developed to simulate IBS and synchrotron radiation effects and integrated in the PyORBIT tracking code, to be combined with its widely used space charge module. The impact of these effects on the achievable beam parameters of the Compact Linear Collider (CLIC) Damping Rings was studied, showing that synchrotron radiation damping mitigates the adverse effects of IBS and space charge induced resonance crossing. The studies include also a full dynamic simulation of the CLIC damping ring cycle starting from the injection beam parameters. It is demonstrated that a careful working point choice is necessary, in order to accommodate the transition from a non-linear lattice induced detuning to a space-charge dominated one and thereby avoid excessive losses and emittance growth generated in the vicinity of strong resonances.

physics.acc-ph↗
arXiv2024

Particle Motion in Hamiltonian Formalism

The goal of this contribution is to introduce the Hamiltonian formalism of theoretical mechanics for analysing motion in generic linear and non-linear dynamical systems, including particle accelerators. This framework allows the derivation and integration of equations of motion, in order to describe the particle trajectory evolution with respect to time. First, basic concepts are re-visited for describing particle propagation through the resolution of differential equations, applied to linear and non-linear motion. These equations of motion can be obtained by the Lagrangian of the system, which is the natural step leading to Hamiltonian Formalism and its properties. The accelerator ring Hamiltonian is derived, starting with the relativistic Hamiltonian of particles in the influence of E/M fields and a series of canonical (or symplectic) transformations and approximations. Thereby, introductory concepts of beam dynamics such as invariants and transport matrices are revisited and extended towards generic concepts such as action-angle variables and symplectic maps. To this end, the ground is prepared for the advanced methods and tools used for studying non-linear motion in particle accelerators.

physics.acc-ph↗
arXiv2023

Interplay of space charge and intrabeam scattering in the LHC ion injector chain

The ion injectors of the CERN accelerator chain, in particular the Super Proton Synchrotron (SPS) and the Low Energy Ion Ring (LEIR), operate in a strong space charge (SC) and intrabeam scattering (IBS) regime, which can degrade beam quality. Optimizing the ion beam performance therefore requires studying the interplay of these two effects in tracking simulations by incorporating both SC and IBS effects interleaved with lattice nonlinearities. In this respect, the kinetic theory approach of treating IBS effects has been deployed. A modified stochastic IBS kick is introduced, with friction and diffusion coefficients derived in two forms: an efficient Nagaitsev formulation based on complete elliptic integrals of the second kind, and a complete Bjorken-Mtingwa formulation. This IBS kick is implemented in PyORBIT and extensively benchmarked against analytical models. Results of combined space charge and intrabeam scattering simulations for the SPS and LEIR are presented and compared with observations from beam measurements.

physics.acc-ph↗
arXiv2020

Numerical analysis techniques for non-linear dynamics

The content of this contribution is based on the course on numerical analysis techniques for non-linear dynamics. After introducing basic concepts as the visual analysis of trajectories in phase space and the importance of the nature of fixed points in their topology and dynamics, the motion close to a resonance is presented, with simple non-linear map examples. The onset of chaotic motion and the modern methods used for their detection are detailed with a focus on frequency map analysis and concrete examples for a variety of rings and non-linear effects.

physics.acc-ph↗
arXiv2020

Extracting chromatic properties of electron beams from spectral analysis of turn-by-turn beam position data

A method to estimate linear chromaticity, RMS energy spread, and chromatic beta-beating, directly from turn-by-turn beam position data in a circular electron accelerator, is presented. This technique is based on frequency analysis of a transversely excited beam, in the presence of finite chromaticity. Due to the turn-by-turn chromatic modulation of the beam's envelope, betatron sidebands appear around the main frequency of the Fourier spectra. By determining the amplitude of both sidebands, chromatic properties of the beam can be estimated. In this paper, analytical derivations justifying the proposed method are given, along with results from tracking simulations. To this end, results from practical applications of this technique at the KARA electron ring are demonstrated.

physics.acc-ph↗
arXiv2020

Origin of the 50 Hz harmonics in the transverse beam spectrum of the Large Hadron Collider

Since the beginning of the Large Hadron Collider (LHC) commissioning, spectral components at harmonics of the mains frequency (50 Hz) have been observed in the transverse beam spectrum. This paper presents an overview of the most important observations, collected during the latest physics operation of the LHC in 2018, which clearly indicates that the harmonics are the result of a real beam excitation rather than an instrumental feature. Based on these findings, potential sources of the perturbation are discussed and a correlation with power supply ripple originating from the magnets' power supplies is presented.

physics.acc-ph↗
arXiv2020

Impact of the 50 Hz harmonics on the beam evolution of the Large Hadron Collider

Harmonics of the mains frequency (50 Hz) have been systematically observed in the transverse beam spectrum of the Large Hadron Collider (LHC) since the start of its operation in the form of dipolar excitations. In the presence of strong non-linearities such as beam-beam interactions, as many of these power supply ripple tones reside in the vicinity of the betatron tune they can increase the tune diffusion of the particles in the distribution, leading to proton losses and eventually to a significant reduction of the beam lifetime. The aim of this paper is to determine whether the 50~Hz harmonics have an impact on the beam performance of the LHC. A quantitative characterization of the ripple spectrum present in the operation of the accelerator, together with an understanding of its source is an essential ingredient to also evaluate the impact of the 50~Hz harmonics on the future upgrade of the LHC, the High Luminosity LHC (HL-LHC). To this end, simulations with the single-particle tracking code, SixTrack, are employed including a realistic ripple spectrum as extracted from experimental observations to quantify the impact of such effects in terms of tune diffusion, Dynamic Aperture and beam lifetime. The methods and results of the tracking studies are reported and discussed in this paper.

physics.acc-ph↗
arXiv2020

Identification and characterization of high order incoherent space charge driven structure resonances in the CERN Proton Synchrotron

Space charge is typically one of the performance limitations for the operation of high intensity and high brightness beams in circular accelerators. In the Proton Synchrotron (PS) at CERN, losses are observed for vertical tunes above $Q_y=6.25$, especially for beams with large space charge tune shift. The work presented here shows that this behaviour is associated to structure resonances excited by space charge due to the highly symmetric accelerator lattice of the PS, typical for first generation alternating gradient synchrotrons. Experimental studies demonstrate the dependency of the losses on the beam brightness and the harmonic of the resonance, and simulation studies reveal the incoherent nature of the resonance. Furthermore, the calculation of the Resonance Driving Terms (RDT) generated by the space charge potential shows that the operational working point of the PS is surrounded by multiple space charge driven incoherent resonances. Finally, measurements and simulations on both lattice driven and space charge driven resonances illustrate the different behaviour of the beam loss depending on the source of the resonance excitation and on the beam brightness.

physics.acc-ph↗
arXiv2020

Tune modulation effects in the High Luminosity Large Hadron Collider

Several transverse noise sources, such as power supply ripples, can potentially act as an important limiting mechanism for the luminosity production of the Large Hadron Collider (LHC) and its future High-Luminosity upgrade (HL-LHC). In the presence of non-linearities, depending on the spectral components of the power supply noise and the nature of the source, such a mechanism can increase the diffusion of the particles in the distribution through the excitation of sideband resonances in the vicinity of the ones driven by the lattice non-linearities. For the HL-LHC, due to the reduction of the beam size in the Interaction Points (IP) of the high luminosity experiments (IP1 and 5), increased sensitivity to noise effects is anticipated for the quadrupoles of the inner triplets. The modulation that may arise from the power supply ripples will be combined with the tune modulation that intrinsically emerges from the coupling of the transverse and longitudinal plane for off-momentum particles through chromaticity. To this end, the aim of this paper is to study the impact of tune modulation effects on the transverse beam motion resulting from the interplay between quadrupolar power supply ripples and synchro-betatron coupling. A power supply noise threshold for acceptable performance is estimated with single-particle tracking simulations by investigating the impact of different modulation frequencies and amplitudes on the Dynamic Aperture. The excitation of sideband resonances due to the modulation is demonstrated with frequency maps and the higher sensitivity to specific modulation frequencies is explained. Finally, a power supply noise spectrum consisting of several tones is considered in the simulations to determine whether the presence of power supply ripples in the quadrupoles of the inner triplet will limit the luminosity production in the HL-LHC era.

physics.acc-ph↗
arXiv2019

Refined betatron tune measurements by mixing beam position data

The measurement of the betatron tunes in a circular accelerator is of paramount importance due to their impact on beam dynamics. The resolution of the these measurements, when using turn by turn (TbT) data from beam position monitors (BPMs), is greatly limited by the available number of turns in the signal. Due to decoherence from finite chromaticity and/or amplitude detuning, the transverse betatron oscillations appear to be damped in the TbT signal. On the other hand, an adequate number of samples is needed, if precise and accurate tune measurements are desired. In this paper, a method is presented that allows for very precise tune measurements within a very small number of turns. The theoretical foundation of this method is presented with results from numerical and tracking simulations but also from experimental TbT data which are recorded at electron and proton circular accelerators.

physics.acc-ph↗
arXiv2018

Luminosity Scans for Beam Diagnostics

A new type of fast luminosity separation scans ("Emittance Scans") was introduced at the CERN Large Hadron Collider (LHC) in 2015. The scans were performed systematically in every fill with full-intensity beams in physics production conditions at the Interaction Point (IP) of the Compact Muon Solenoid (CMS) experiment. They provide both emittance and closed orbit measurements at a bunch-by-bunch level. The precise measurement of beam-beam closed orbit differences allowed a direct, quantitative observation of long-range beam-beam PACMAN effects, which agrees well with numerical simulations from an improved version of the TRAIN code.

physics.acc-ph↗
arXiv2014

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.

nlin.CD↗
arXiv2013

Analytical considerations for linear and nonlinear optimization of the TME cells. Application to the CLIC pre-damping rings

The theoretical minimum emittance cells are the optimal configurations for achieving the absolute minimum emittance, if specific optics constraints are satisfied at the middle of the cell's dipole. Linear lattice design options based on an analytical approach for the theoretical minimum emittance cells are presented in this paper. In particular the parametrization of the quadrupole strengths and optics functions with respect to the emittance and drift lengths is derived. A multi-parametric space can be then created with all the cell parameters, from which one can chose any of them to be optimized. An application of this approach are finally presented for the linear and non-linear optimization of the CLIC Pre-damping rings.

physics.acc-ph↗
arXiv2011

Efficient control of accelerator maps

Recently, the Hamiltonian Control Theory was used in [Boreux et al.] to increase the dynamic aperture of a ring particle accelerator having a localized thin sextupole magnet. In this letter, these results are extended by proving that a simplified version of the obtained general control term leads to significant improvements of the dynamic aperture of the uncontrolled model. In addition, the dynamics of flat beams based on the same accelerator model can be significantly improved by a reduced controlled term applied in only 1 degree of freedom.

physics.acc-ph↗
arXiv2003

Deflections in Magnet Fringe Fields

A transverse multipole expansion is derived, including the longitudinal components necessarily present in regions of varying magnetic field profile. It can be used for exact numerical orbit following through the fringe field regions of magnets whose end designs introduce no extraneous components, {\it i.e.} fields not required to be present by Maxwell's equations. Analytic evaluations of the deflections are obtained in various approximations. Mainly emphasized is a ``straight-line approximation'', in which particle orbits are treated as straight lines through the fringe field regions. This approximation leads to a readily-evaluated figure of merit, the ratio of r.m.s. end deflection to nominal body deflection, that can be used to determine whether or not a fringe field can be neglected. Deflections in ``critical'' cases (e.g. near intersection regions) are analysed in the same approximation.

physics.acc-ph↗