The High Energy LHC (HE-LHC) is one option for a next generation hadron collider explored in the ... more The High Energy LHC (HE-LHC) is one option for a next generation hadron collider explored in the FCC-hh program. The core concept of the HE-LHC is to install FCC-hh technology magnets in the LHC tunnel. The higher beam rigidity and the increased radiation debris, however, impose severe challenges on the design of the triplet for the low beta insertions. In order to achieve 25 cm β * optics and survive a lifetime integrated luminosity of 10 ab −1 a new longer triplet was designed that provides sufficient shielding and enough beam stay clear. This triplet has been designed using complimentary radiation studies to optimise the shielding that will also be presented. The optics for the rest of the interaction region had to be adjusted in order to host this more rigid beam and longer triplet whilst leaving enough room for crab cavities. Moreover, the effects non-linear errors in this triplet have on the dynamic aperture will be outlined.
MD 1856 - Landau Damping: Beam Transfer Functions and diffusion mechanisms
In the 2012, 2015 and 2016 several instabilities were developing during the betatron squeeze wher... more In the 2012, 2015 and 2016 several instabilities were developing during the betatron squeeze where beam-beam interactions become stronger modifying the tune spread provided by the octupoles magnets. Studies of the stability area computed by evaluating the dispersion integral for different tune spread couldn’t explain the 2012 observed instabilities during the squeeze. The size of the stability area given by the computed dispersion integral depends on the transverse tune spread but its shape is defined by the particle distribution in the beams. Therefore any change of the particle distribution due to for instance a diffusion from excited resonances can lead to a deterioration of the Landau stability area. The Beam Transfer Functions (BTF) measurements are direct measurement of the Stability Diagrams (SD). They are sensitive to the particle distribution and contain information about the transverse tune spread in the beams. In this MD we wanted to verify the findings of MD 1407 and try to explain observed instabilities. A scan of the beam-beam separation and crossing angles have been performed to quantify the tune shift measured during the MD 1429
We present updated design parameters for a future High-Energy LHC. A more realistic turnaround ti... more We present updated design parameters for a future High-Energy LHC. A more realistic turnaround time has led to a revision of the target peak luminosity, as well as a choice of a larger IP beta function, and longer physics fills. Pushed parameters of the Nb₃Sn superconducting cable together with a modified layout of the 16 T dipole magnets resulted in revised field errors, updated dynamic-aperture simulations, and an associated re-evaluation of injector options. Collimators in the dispersion suppressors help achieve satisfactory cleaning performance. Longitudinal beam parameters ensure beam stability throughout the cycle. Intrabeam scattering rates and Touschek lifetime appear benign.
The High Energy Large Hadron Collider (HE-LHC), a possible successor of the High Luminosity Large... more The High Energy Large Hadron Collider (HE-LHC), a possible successor of the High Luminosity Large Hadron Collider (HL-LHC) aims at reaching a centre-of-mass energy of about 27 TeV using basically the same 16 T dipoles as for the hadron-hadron Future Circular Collider FCC-hh. Designing the HE-LHC results in a trade off between energy reach, beam stay clear as well as geometry offset with respect to the LHC. In order to best meet the requirements, various arc cell and dispersion suppressor options have been generated and analysed, before concluding on two baseline options, which are presented in this paper. Merits of each design are highlighted and possible solutions for beam stay clear minima are presented.
The High Energy LHC (HE-LHC) proton-proton collider is a proposed replacement of the LHC in the e... more The High Energy LHC (HE-LHC) proton-proton collider is a proposed replacement of the LHC in the existing 27-km tunnel, with the goal of reaching the centre-of-mass beam energy of 27 TeV. The required higher dipole field can be realized by using 16-T dipoles being developed for the FCC-hh design. A major concern is the dynamic aperture at injection energy due to degraded field quality of the new dipole based on Nb3Sn superconductor, the potentially large energy swing between injection and collision, and the slightly reduced magnet aperture. Another issue is the field in quadrupoles and sextupoles at top energy, for which it may be cost-effective, wherever possible, to stay with Nb-Ti technology. In this study, we explore design options differed by arc lattice, for three choices of injection energy, with the goal of attaining acceptable magnet field and maximum injection dynamic aperture with dipole non-linear field errors.
Long-range beam-beam interactions dictate the choice of operational parameters for the LHC, such ... more Long-range beam-beam interactions dictate the choice of operational parameters for the LHC, such as the crossing angle and β^{*} and therefore the luminosity reach for the collider. These effects can lead to particle losses, closed orbit effects and emittance growth. Defining how these effects depend on the beam-beam separation will determine the minimum crossing angle and the β^{*} the LHC can operate. In this article, analysis from a dedicated machine study is presented in which the crossing angle was reduced in steps and the impact on beam intensity and luminosity lifetimes were observed. Based on the observations during the machine study, the intensity decays are compared to expectations from models. Estimates of the luminosity reach in the LHC are also computed.
The HL-LHC project aims to reach larger peak luminosities, however this can lead to a high pile u... more The HL-LHC project aims to reach larger peak luminosities, however this can lead to a high pile up in the detectors. To control the pile up, luminosity levelling has been suggested. One proposed method is β*-luminosity levelling, in which beams collide at a larger than nominal β*. The β* is then reduced in steps as the beam intensity decays. This allows the luminosity to be kept constant over part of a physics fill. The use of round or flat optics will change the beam-beam effect of the head on collisions as well as the long range interactions. Here simulations of β* levelling are presented for the case of flat and round beam optics and the difference in terms of the beam-beam effect is highlighted.
One possible future hadron collider design investigated in the framework of the Future Circular C... more One possible future hadron collider design investigated in the framework of the Future Circular Collider (FCC) study is the High-Energy LHC (HE-LHC). Using the 16 T dipoles developed for the FCC-hh the center of mass energy of the LHC is set to increase to 27 TeV. To achieve this set energy goal, a new optics design is required, taking into account the constraint from the LHC tunnel geometry. In this paper, two different lattices for the HE-LHC are presented. Initial considerations take into account the physical aperture at the proposed injection energy as well as the energy reach of these lattices. The dynamic aperture at the injection energies is determined using latest evaluations of the field quality of the main dipoles.
The value of the luminosity at which levelling is performed is calculated assuming a visible cros... more The value of the luminosity at which levelling is performed is calculated assuming a visible cross-section of 81 mb (corresponding to the inelastic proton-proton crosssection at a center of mass energy of 14 TeV), and the cross-section for the burn-off is conservatively assumed to be 111 mb (corresponding to the total proton-proton crosssection at a center of mass energy of 14 TeV) [1,2]. For both scenarios the main assumptions for the first version of this note [3] were:
for the degree of Doctor of Philosophy by Matthew Paul Crouch Thesis title: Luminosity Performanc... more for the degree of Doctor of Philosophy by Matthew Paul Crouch Thesis title: Luminosity Performance Limitations Due To The BeamBeam Interaction In The Large Hadron Collider In the Large Hadron Collider (LHC), particle physics events are created by colliding high energy proton beams at a number of interaction points around the ring. One of the main performance indicating parameters of the LHC is the luminosity. The luminosity is limited by, amongst other things, the strength of the beam-beam interaction. In this thesis, the effect of the beam-beam interaction on the luminosity performance of the LHC and the proposed High Luminosity Large Hadron Collider (HL-LHC) is investigated. Results from a number of dedicated, long-range beam-beam machine studies are presented and analysed. In these studies, the minimum beam-beam separation for two different β∗ optics are identified. This separation defines the minimum operational crossing angle in the LHC. The data from these studies are then com...
MD 382: Beam Transfer Function and diffusion mechanisms
The Beam Transfer Function (BTF) measurements have been previously tested in the LHC during MD bl... more The Beam Transfer Function (BTF) measurements have been previously tested in the LHC during MD block 1 and 2. Different machine configurations (i.e. energy, beam intensity, emittance etc...) have been tested to determine a safe set-up (excitation amplitude) of the system to be completely transparent to the beam (no emittance blow-up neither losses). The aim of this experiment in MD block 3 was to characterize the Stability Diagram (SD) in the presence of diffusion mechanisms induced by excited resonances due to beam-beam long range and Landau octupole interplay. During the experiment, BTF measurements have been acquired at flat top for different settings of Landau octupole current, different chromaticity values and transverse feedback gains. In this note the description of the experiment is presented together with some preliminary results
The hourglass effect arises due to a coupling between the longitudinal and transverse bunch plane... more The hourglass effect arises due to a coupling between the longitudinal and transverse bunch planes. This coupling will result in a charge density distribution that will vary parabolically through the Interaction Point (IP). Here a method of analytically determining the electric field a particle receives from a charge density distribution which varies parabolically when centred at the IP, is derived for a 2D transverse model of a Gaussian bunch.
Identifying the minimum crossing angle achievable in the LHC is a key parameter to identify the c... more Identifying the minimum crossing angle achievable in the LHC is a key parameter to identify the collider luminosity reach. In this note, we summarise the observations collected during a dedicated experiment performed in 2015, where the strength of the long range beam-beam interaction is varied by reducing the crossing angle at IP1 and IP5. The crossing angle and the impact of the long range beam-beam interaction is analysed with respect to the beam and luminosity lifetimes. The effect of reducing Landau octupoles, initially operating at 476 [A] and high chromaticity values (15 units) are also shown. The minimum crossing angle achievable with collisions is identified, together with the impact on beam and luminosity lifetimes.
In response to recommendations in the 2013 update of the European Strategy for Particle Physics, ... more In response to recommendations in the 2013 update of the European Strategy for Particle Physics, a conceptual design effort for an energy upgrade of the Large Hadron Collider (LHC) at CERN, the so-called high-energy LHC (HE-LHC), was launched as part of the Future Circular Collider study. The HE-LHC machine, which is meant to use 16 T magnet technologies in the existing LHC tunnel, would provide proton collisions at a center-of-mass energy of 27 TeV (∼2 × LHC) with a total stored energy of 1.34 GJ (∼4 × LHC) per beam. By adapting the LHC collimation system, a first layout of the HE-LHC's betatron cleaning insertion was conceived, with the requirement to sustain-for at least 10 seconds-the impact of about 1.86 MW, corresponding to a beam lifetime of 12 minutes, without inducing any magnet quench nor any damage to other accelerator components. In this article, we evaluate the power deposition on the collimation insertion for proton beam operation in the HE-LHC machine at top energy, by means of particle tracking and interaction calculations. The beam loss effects on the warm elements as well as on the superconducting dispersion suppressor magnets are assessed through a three-step simulation approach. In particular, for the proposed future high-energy LHC, we demonstrate the necessity of adding local collimators in the dispersion suppressor, and we uncover the harmful consequences of a potential removal of the beam line "dogleg" in the collimation insertion.
In the 2012, 2015 and 2016 several instabilities were developing during the betatron squeeze wher... more In the 2012, 2015 and 2016 several instabilities were developing during the betatron squeeze where beam-beam interactions become stronger modifying the tune spread provided by the octupoles magnets. Studies of the stability area computed by evaluating the dispersion integral for different tune spread couldn’t explain the 2012 observed instabilities during the squeeze. The size of the stability area given by the computed dispersion integral depends on the transverse tune spread but its shape is defined by the particle distribution in the beams. Therefore any change of the particle distribution due to for instance a diffusion from excited resonances can lead to a deterioration of the Landau stability area. The Beam Transfer Functions (BTF) measurements are direct measurement of the Stability Diagrams (SD). They are sensitive to the particle distribution and contain information about the transverse tune spread in the beams. In this MD we wanted to verify the findings of MD 1407 and try...
The 2015 LHC run has shown the beauty of having weaker beam-beam effects with respect to 2012 phy... more The 2015 LHC run has shown the beauty of having weaker beam-beam effects with respect to 2012 physics run. The 2015 set-up has been defined to allow Landau octupole and chromaticity to be powered at maximum currents to fight coherent instabilities. Quantitative studies of the impact of reduced crossing angles on the beam and luminosity lifetimes have been used to compare to expectations from Dynamical Aperture studies. Possible scenarios for the 2016 RUN will be presented highlighting the beam-beam limits expected from long range and head-on. BEAM-BEAM EFFECTS IN THE LHC EXPERIENCE FROM 2012 PHYSICS RUN The 2012 Physics run of the LHC has shown losses and emittance blow-up which are related to beam-beam effects. The analysis of the bunch by bunch luminosity and specific luminosity decay rates during collisions has shown a clear dependency on the beam-beam interactions long-range and head-on [1]. An example of such relation is shown for the physics fill 2710 in Figure 1 and 2. In Fig...
Several machine development studies have been performed in 2016 at the LHC in order to evaluate t... more Several machine development studies have been performed in 2016 at the LHC in order to evaluate the effects of reducing the crossing angles in favour of defining the maximum achievable luminosity in the ATLAS and CMS experiments. At the end of the LHC proton-proton run at 6.5 TeV the reduction of the crossing angle from 370 μrad to 280 μrad was operationally implemented. The observation of beam losses and lifetimes during this process are analysed and discussed.
Preliminary results from simulations are presented using the COherent Multi-Bunch Interaction cod... more Preliminary results from simulations are presented using the COherent Multi-Bunch Interaction code (COMBI). Two bunches colliding head on, under the influence of an arbitrary sourced white noise are considered. The effect of noise on both flat and round beams is simulated and the emittance growth as a result is observed and studied. Preliminary results suggest that there is no significant difference in emittance growth due to the use of flat beams under the influence of uncoupled external white noise operating at HL-LHC parameters.
A design study for a future collider to be built in the LHC tunnel, the High-Energy Large Hadron ... more A design study for a future collider to be built in the LHC tunnel, the High-Energy Large Hadron Collider (HE-LHC), has been launched as part of the Future Circular Collider (FCC) study at CERN. It would provide proton collisions at a centre-of-mass energy of 27 TeV as well as collisions of heavy ions at the equivalent magnetic rigidity. HE-LHC is being designed under the stringent constraint of using the existing tunnel and therefore the resulting lattice and optics differ in layout and phase advance from the LHC. It is necessary to evaluate the performance of the collimation system for ion beams in HE-LHC in addition to proton beams. In the case of ion beams, the fragmentation and electromagnetic dissociation that relativistic heavy ions can undergo in collimators, as well as the unprecedented energy per nucleon of the HE-LHC, requires dedicated simulations. Results from a study of collimation efficiency for the nominal lead ion (208 Pb 82+) beams performed with the SixTrack-FLUKA coupling framework are presented. These include loss maps with comparison against an estimated quench limit as well as detailed considerations of loss spikes in the superconducting aperture for critical sections of the machine such as the dispersion suppressors.
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Papers by Matthew Crouch