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| MOPAB107 | A Method for Determining the Roll Angle of the CLIC Accelerating Structures From the Beam Shape Downstream of the Structure | collider, simulation, experiment, emittance | 368 |
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| The Compact Linear Collider (CLIC) accelerating structures have a four-fold symmetry from the radial waveguides for damping higher order modes. This symmetry allows for an octupole component of the rf fields to co-propagate with the main accelerating field. The effect of this octupole mode has been observed at the CLIC test facility 3. In CLIC the accelerating structures are mounted together on a moveable girders. There are four vertical and four horizontal actuators on the girder, which allows for 5D control in a limited range and for instance we can roll the girder. By observing the beam shape perturbed by the octupole field on a screen downstream from the structure we can determine the roll angle and thus align the structure azimuthally. Here we discuss a possible method and show some preliminary results. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPAB107 | ||
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| MOPAB108 | Beam-Based Alignment Studies at CTF3 Using the Octupole Component of CLIC Accelerating Structures | wakefield, experiment, alignment, collider | 371 |
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| The Compact Linear Collider (CLIC) uses normal-conducting accelerating structures that are sensitive to wakefield effects and therefore their alignment is extremely important. Due to the four-fold symmetry of the structures, they allow for an octupole component of the rf fields. By scanning the beam transversely we can determine the center of the structures from the shifts in beam position due to the kicks from the octupole field. We present some initial results from measurements at the CLIC test facility 3 at CERN. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPAB108 | ||
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| MOPIK038 | Initial Operation of the Low-Flux Proton Beamline at the KOMAC 100 MeV Linac | proton, target, vacuum, operation | 585 |
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Funding: This work was supported by the Ministry of Science, ICT and Future Planning of the Korean Government Korea multi-purpose Accelerator Complex (KOMAC) has been operating 20 MeV and 100 MeV proton beamlines to provide proton beams to users since 2013. The new beamline and target irradiation facility, which is proposed applicable to development of the detector and simulation of the space radiation, have being constructed for low-flux proton utilization at this year. The new beam lines have the 100 MeV of maximum beam energy and 10 nA of maximum beam current. The new beam line was designed to operate with maximum duty 8%, the flux density of proton beam can be reduced to the 1/10,000 by the graphite collimator. The extracted proton beam energy can be adjustable by the double wedge type energy degrader and also, the beam energy can be selected by dipole magnet. In addition to the two sets of the octupole magnets were prepared for uniform beam irradiation with the ± 5% uniformity. In this paper, the initial operation results of the constructed new beam line is be described. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPIK038 | ||
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| TUPVA009 | Multiparametric Response of the LHC Dynamic Aperture in Presence of Beam-Beam Effects | emittance, simulation, luminosity, optics | 2051 |
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| We performed extended simulations of LHC dynamic aperture (DA) in the presence of beam-beam effects in the weak-strong approximation, evaluating the contributions of parameters such as: tunes, optics, bunch intensity, crossing angle, emittance, chromaticity and current in the Landau octupoles. Here we present a summary of these studies, giving an overview of the amplitude of the LHC operational space and pointing out the remaining margins for mitigation of instabilities. These studies supported the actions deployed during the 2016 run of the LHC, which aimed at maximising its performances. Examples of such actions are the switch to lower emittance beams, the reduction of crossing angle and tune trims. More recently, DA scans have been used to help the definition of the operational scenarios for the 2017 run. Additional room for improvements, for instance by deploying crossing angle levelling, will be explained. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA009 | ||
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| TUPVA010 | Multiparametric Response of the HL-LHC Dynamic Aperture in Presence of Beam-Beam Effects | luminosity, simulation, beam-beam-effects, emittance | 2055 |
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| We performed extended simulations of HL-LHC dynamic aperture in the presence of beam-beam effects in the weak- strong approximation, evaluating the contributions of param- eters such as: bunch intensity, crossing angle, chromaticity, current in the Landau octupoles and multipole errors. From the beam dynamics point of view, the main differ- ence between the LHC (until 2017) and the HL-LHC is the deployment of the achromatic telescopic squeezing (ATS) optics, allowing not only for a smaller '' reach, but also modifying the phase advances between the lattice correctors (sextupoles, octupoles) and the main IPs, and increasing the peak ' functions in the arcs. These correctors become therefore more efficient for the chromatic correction, but also a mitigation of the beam-beam long range interactions using the Landau octupoles is enabled, resulting in a possible reduction of the normalised crossing angle. The limits have been investigated in a tracking simulation campaign aimed at exploring the operational space for the HL-LHC and two possible options for luminosity levelling. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA010 | ||
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| TUPVA018 | Macroparticle Simulation Studies of the LHC Beam Dynamics in the Presence of Electron Cloud | simulation, electron, dipole, quadrupole | 2081 |
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| Beam quality degradation caused by the Electron Cloud (EC) effects has been identified as one of the main performance limitations for the high intensity 25 ns beams in the Large Hadron Collider (LHC). When a proton bunch passes through an EC, electrons are attracted towards the transverse center of the beam resulting into an increasing electron density within the bunch. The effects driven by the interaction of the electrons with the bunch have been studied with macroparticle simulations in order to evaluate, in different operational scenarios, the threshold for the coherent instabilities as well as the incoherent tune spread. This contribution will summarize the main findings of the simulation study and compare them with the available experimental observations. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA018 | ||
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| TUPVA027 | Study of Beam-Beam Long Range Compensation with Octupoles | optics, dynamic-aperture, resonance, beam-beam-effects | 2113 |
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Funding: The European Circular Energy-Frontier Collider Study (EuroCirCol), EU's Horizon 2020 grant No 654305. Long range beam-beam effects are responsible for particle losses and define fundamental operational parameters of colliders (i.e. crossing angles, intensities, emittances, β*). In this study we propose octuple magnets as a possible scheme to efficiently compensate long-range beam-beam interactions with a global correction scheme. The impact and improvements on the dynamic aperture of colliding beams together with estimates of the luminosity potentials are discussed for the HL-LHC upgrade and extrapolations made for the FCC project. Results are compared to other compensating schemes. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA027 | ||
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| TUPVA031 | Impact of Incoherent Effects on the Landau Stability Diagram at the LHC | betatron, damping, coupling, simulation | 2125 |
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| Instability thresholds are explored at the Large Hadron Collider (LHC) by means of the computation of the Landau Stability Diagrams (SD). In the presence of diffusive mechanisms, caused by resonance excitations or noise, the SD can be reduced due to the modification of the particle distribution inside the beam. This effect can lead to a possible lack of Landau damping of the coherent modes previously damped by lying within the unperturbed SD area. The limitations deriving from coherent instabilities in the LHC is crucial in view of future projects that aim to increase the performance of the LHC such as the High-Luminosity upgrade (HL-LHC). Simulation tools for the computation of the SD have been extended in order to take into account the incoherent effects from long tracking through the detailed model of the accelerator machine. The model includes among others beam-beam interactions and octupoles and the interplay between both is addressed. Finally the simulation results are compared to the Beam Transfer Function (BTF) measurements in the LHC. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA031 | ||
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| WEPAB011 | High Order Magnetic Field Components and Non-Linear Optics at the ANKA Storage Ring | wiggler, resonance, sextupole, betatron | 2586 |
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| The Karlsruhe Institute of technology operates the 2.5 GeV electron storage ring ANKA as an accelerator test facility and synchrotron radiation source. A superconducting wiggler is installed in a short straight section of the ring where vertical beta-function is large (13 m). The life time of the electron beam was reduced from 15 to 12 hours at a high field level of the wiggler (2.5 T) even though the coherent shift of vertical tune was compensated locally. Computer simulations show the non-linear nature of the effect. The ANKA storage ring operates with strong sextupoles at a positive chromaticity of +2/+6. Even residual octupole components of the wiggler field, set at the tolerance limit of fabrication conditions, could reduce the dynamic aperture for off-momentum particles providing the betatron tune is located in the vicinity of a weak octupole resonance and the chromaticity is high. Also the vertical betatron tune is close to the sextupole resonance Qy=8/3. Large resonance stop-band and proximity of sextupole resonance affect the life time as well. Betatron tunes of ANKA have been shifted away of suspected high-order resonances and beam life time was essentially improved. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB011 | ||
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| WEPIK070 | Nonlinear Lattice Optimization for the SPring-8 Upgrade | sextupole, lattice, betatron, injection | 3091 |
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| The SPring-8 upgrade project has adopted the hybrid MBA lattice to achieve the emittance of about 100 pmrad at 6 GeV with damping effects by insertion devices. This optics has two dispersion bumps in one unit cell where chromaticity-correcting sextupoles locate. The horizontal and vertical betatron phases between these bumps are tuned to be 3PI and PI, respectively, to cancel the low order contributions of nonlinear kicks due to sextupoles. However, it is not easy to obtain a sufficiently large dynamic aperture (DA) since (i) the cancellation is incomplete due to a nested arrangement, (ii) sextupoles are very strong, and (iii) the number of tuning knobs is limited. The DA is quite small due to the leakage of nonlinear kicks by nested sextupoles. We hence proposed to install additional weak sextupoles between the dispersion bumps to suppress the leakage kick further. Simulations show that this simple scheme is very effective for suppressing ADTS and for enlarging DA. We present details of this scheme and some numerical examples together with a newly developed fourth-order formula of ADTS for describing and controlling the lattice nonlinearity. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK070 | ||
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| WEPIK084 | Approximating Nonlinear Forces with Phase-Space Decoupling | simulation, proton, linac, sextupole | 3120 |
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| Beam tracking software for accelerators typically falls into two categories: fast envelope simulations limited to linear beam optics, and slower multiparticle simulations that can model nonlinear effects. To find a middle ground between these approaches, we introduce virtual coordinates in position and momentum which have a cross-dependency (i.e. p*=f(x) where x is an initial position and p* is a virtual projection of momentum onto the position axis).This technique approximates multiparticle simulations with a significant reduction in calculation cost. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK084 | ||
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| WEPIK085 | Beam Shaping with 4N-order Multipole Magnets | focusing, multipole, electron, quadrupole | 3124 |
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| A uniformly irradiating beam is beneficial in spallation for preventing irregular wear on the target. For octupoles (n = 4) and higher-order (n = 4N) magnets, passing charged-particle bunches undergo symmetric shaping effects along the x and y axes. Using a Lie-mapping formalism, we illustrate how well Gaussian distributions can be flattened symmetrically in 2D with single, dual-pulse, and RF magnets of 4N order. Incidental shaping effects are also discussed. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK085 | ||
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| WEPIK091 | Amplitude Dependent Closest Tune Approach Generated by Normal and Skew Octupoles | coupling, simulation, resonance, injection | 3147 |
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| Amplitude dependent closest tune approach, an action dependent analogue of the DQmin generated by linear coupling, was observed in the LHC during Run1. It restricts the accessible resonance free area of the tune diagram and by altering tune spread has the potential to impact upon Landau damping. A theoretical description of such behaviour, generated by normal octupoles and linear coupling has recently been validated in the LHC, however simulation has established that amp-dependent closest approach may also be generated by a combination of normal and skew octupoles. This paper summarizes these simulation based observations. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK091 | ||
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| WEPIK092 | Effect of Linear Coupling on Nonlinear Observables at the LHC | coupling, dynamic-aperture, injection, simulation | 3151 |
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| Simulation work during LHC Run 1 established that linear coupling had a large impact on nonlinear observables such amplitude detuning and dynamic aperture. It is generally taken to be the largest single source of uncertainty in the modelling of the LHC's nonlinear single particle dynamics. Measurements in 2016 sought to confirm this impact of linear coupling with beam. This paper summarizes the observed influence of linear coupling on various nonlinear observables in the LHC. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK092 | ||
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| THPAB040 | Destabilising Effect of Linear Coupling in the LHC | coupling, simulation, damping, operation | 3791 |
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| During operation in 2015 and 2016, some transverse instabilities were observed when either the coupling (or closest tune approach) C- was large, or when the tunes were moved closer together. This motivated a campaign of simulations on the effect of linear coupling on the transverse stability. Measurements made during operation and with dedicated beam time have been found to confirm the predictions. This paper will detail the results of the linear coupling studies and relate them to operation of the LHC in the future. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB040 | ||
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| THPAB041 | Implementation of Hollow Electron Lenses in SixTrack and First Simulation Results for the HL-LHC | electron, simulation, collimation, proton | 3795 |
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Funding: Fermilab is operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the US Department of Energy. Electron lenses have found a wide range of applications for hadron colliders, where the main applications are machine protection and beam-beam compensation. This paper summarizes the status of the current electron lens implementation in SixTrack with the focus on hollow electron beams for beam collimation and shows some first simulation results of the High-Luminosity upgrade of the LHC (HL-LHC). |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB041 | ||
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| THPVA026 | Practical Stabilisation of Transverse Collective Instabilities with Second Order Chromaticity in the LHC | simulation, damping, sextupole, impedance | 4477 |
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| The study reports on dedicated measurements made with a single nominal bunch in the LHC at 6.5 TeV. First, we show that a significant amount of second order chromaticity Q'' can be introduced in the machine in a well-controlled manner. Second, we demonstrate that the incoherent betatron tune spread from Q'' can provide beam stability through the Landau damping mechanism. This is a first step in the development of a Q'' knob to be potentially applied during regular physics operation in the LHC. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPVA026 | ||
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