| Thesis | |
| Report number | CERN-THESIS-2022-366 |
| Title | Compensation of residual field from hollow electron lens asymmetries in the Large Hadron Collider |
| Author(s) | Rakic, Milica (Ecole Polytechnique, Lausanne) |
| Publication | 45. |
| Thesis note | Master : Ecole Polytechnique, Lausanne : 2022 |
| Thesis supervisor(s) | Hermes, Pascal ; Seidel, Mike |
| Note | Presented 2022 |
| Subject category | Accelerators and Storage Rings |
| Accelerator/Facility, Experiment | CERN HL-LHC CERN LHC |
| Abstract | The Large Hadron Collider (LHC) is currently the largest hadron collider in the world. It consists of a 27-kilometre ring, filled with superconducting mag- nets and beams stored in two separate beam pipes. The accelerator houses four main experiments; ATLAS, CMS, ALICE and LHCb, installed in four beam interaction/collision points. Within the LHC, two beams consisting of 2808 bunches each and around 1.2 × 10$^{11}$ protons per bunch, are accelerated up to top energy of 7 TeV and peak luminosity of ∼ 2 × 10$^{34}$ cm$^{-2}$ s$^{-1}$. Tiny fractions of the circulating beam particles lost in the LHC hardware can cause severe damage. Therefore, the LHC is equipped with a sophisticated collimation system, composed of more than 100 collimators that intercept parti- cles at large amplitudes which risk to be in the LHC hardware otherwise. With the upcoming LHC upgrade towards High Luminosity LHC (HL-LHC), the peak luminosity is intended to raise to 5 × 10$^{34}$ cm$^{-2}$ s$^{-1}$, such that the integrity of the collimation system itself is at risk if key devices in HL-LHC would fail. In particular, particles at large transverse amplitudes are threatening the machine availability and safety, which is why it is desirable to remove them se- lectively from the beam core, while particles at small amplitudes should be kept to produce the luminosity at the experiments. Hollow electron lenses (HEL) are devices that are going to be installed in HL-LHC to serve this purpose. They create a hollow shaped electron beam that is moving co-axially and inversely directed to the circulating hadron beam. The hollow shape of the electron beam causes particles at large transverse amplitudes to become unstable, while par- ticles in the beam core should stay unaffected. Given the importance for safe operation of HL-LHC, the HELs were included in the baseline of HL-LHC. However, in real operation, the electron beam is not perfectly symmetric, which results in the existence of electromagnetic fields, creating, in first order, a small dipolar kick acting on the beam core. If no measures are taken to counter- act, this residual kick might lead to an increase of the beam dimensions, with detrimental effects on the LHC physics program. This effect could be inhib- ited by employing the transverse damper (ADT) and inducing a deterministic compensating dipolar kick at each turn the HEL is switched on. This approach might have an impact on the halo depletion efficiency, as well as on the beam core population, which must be understood in simulations. To explore these questions, tracking tool XSuite – a Python framework used to simulate particle motion in the beam line elements of particle accelerators – was used and adapted. In this work, the physical figures of merit for the im- plementation and testing of different operational ADT-HEL approaches in the simulation framework, were derived. The results were used to draw conclusions on the effect of possible ADT compensation schemes on the halo depletion and the particle density in the beam core (and how the latter affects the LHC lu- minosity). These results deliver an important input on the choice of the final compensation scheme to be applied in HL-LHC. |
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Записът е създаден на 2023-06-27, последна промяна на 2024-02-21
