A multi-physics approach to simulate the RF heating 3D power map induced by the proton beam in a beam intercepting device

The project High Luminosity Large Hadron Collider (HL-LHC) calls for a streaking beam intensity and brightness in the LHC machine. In such a scenario, beam-environment electromagnetic interactions are a crucial topic: they could lead to uneven power deposition in machine equipment. The resulting irregular temperature distribution would generate local thermal gradients, this would create mechanical stresses which could lead to cracks and premature failure of accelerator devices. This work presents a method to study this phenomenon by means of coupled electro-thermomechanical simulations. Further, an example of application on a real HL-LHC device is also discussed

Analysis on the mechanical effects induced by beam impedance heating on the HL-LHC target dump injection segmented (TDIS) absorber

The High Luminosity Large Hadron Collider (HL-LHC) Project at CERN calls for increasing beam brightness and intensity. In such a scenario, critical accelerator devices need to be redesigned and rebuilt. Impedance is among the design drivers, since its thermo-mechanical effects could lead to premature device failures. In this context, the current work reports the results of a multiphysics study to assess the electromagnetic and thermo-mechanical behaviour of the Target Dump Injection Segmented (TDIS). It first discusses the outcomes of the impedance analysis performed to characterise the resistive wall and the high order resonant modes (HOMs) trapped in the TDIS structures. Then, their RF-heating effects and the related temperature distribution are considered. Finally, mechanical stresses induced by thermal gradients are studied in order to give a final validation on the design qualit

Impedance study on HL-LHC’s collimation and protection system

In this thesis work the coupling impedance of the foreseen HL-LHC’s (High Luminosity Large Hadron Collider) collimation and protection system will be analyzed in detail. In particular the devices of interest will be the TCSPM and the TDIS, which are a secondary collimator and an injection protection system. This work is structured in two parts, the first one is composed by three chapters in which it will be explained: what are the LHC and the collimators, which formulas were used in order to carry out this study, which tools and measurements techniques were adopted to characterize the different materials. The second part is composed of two chapters and it will show and comment the results obtained during a year of studies

Single-Collimator Tune Shift Measurement of the Three-Stripe Collimator at the LHC

Several options of low resistivity coating have been proposed for the collimator upgrade of the Large Hadron Collider. In order to study their effect on the beam dynamics a special collimator has been built and installed in the machine. Its jaws are coated with three different materials and can be moved transversely to selectively expose the beam to the chosen coating. We have measured the resistive wall tune shifts of each coating material and compared them with that of a standard Carbon Fibre Composite (CFC) collimator jaw. A resolution of the tune shift of the order of $10^{-5}$ has been achieved in the measurement. The results show a significant reduction of the resistive wall tune shift with novel materials. The largest improvement is obtained with a 5 $\mu$m Molybdenum coating of a Molybdenum-Graphite jaw. The observed tune shifts show a good agreement with the impedance model and the bench impedance and resistivity measurements. Obtained results can be used to further improve the precision of the impedance model

Single bunch stability threshold with at orbit (MD2870)

The results of an experiment demonstrating the absence of impact of the crossing angle in all IPs on the coherent stability of the beams at top energy in the LHC are presented

The Ghost Train Instability (MDs 2066 and 2936)

This notes describes experimental studies of the octupole strength required to stabilise bunch trains at 6.5 TeV in the LHC, performed over 3 MD blocks in 2017. An instability affecting the bunches at the head of the train in the horizontal plane of B1 was observed and could not be stabilised with the maximum octupole current available in the first 2 MD tests. The instability was no longer observed in the last experiment in similar conditions. Eventually, the measured octupole threshold for 25 ns trains was found slightly above the single bunch stability threshold, within a factor ≈2.2 with respect to predictions based on the impedance model

HL-LHC impedance and related effects

This note aims at gathering the work done by CERN and collaborators on the HL-LHC beam coupling impedance in the recent years and identifying the next steps. The note describes the status of the impedance, beam stability and beam induced heating at the moment of writing with the present design and layout (HL-LHCv1.3)