Nonlinear dynamics of proton beams with hollow electron lens in the CERN high-luminosity LHC

The design stored beam energy in the CERN high-luminosity large hadron collider (HL-LHC) upgrade is about 700 MJ, with about 36 MJ in the beam tails, according to estimates based on scaling considerations from measurements at the LHC. Such a large amount of stored energy in the beam tails poses serious challenges on its control and safe disposal. In particular, orbit jitters can cause significant losses on primary collimators, which can lead to accidental beam dumps, magnet quenches, or even permanent damage to collimators and other accelerator elements. Thus, active control of the diffusion speed of halo particles is necessary and the use of hollow electron lenses (HELs) represents the most promising approach to handle overpopulated tails at the HL-LHC. HEL is a very powerful and advanced tool that can be used for controlled depletion of beam tails, thus enhancing the performance of beam halo collimation. For these reasons, HELs have been recently included in the HL-LHC baseline. In this paper, we present detailed beam dynamics calculations performed with the goal of defining HEL specifications and operational scenarios for HL-LHC. The prospects for effective halo control in HL-LHC are presented.

Layouts for fixed-target experiments and dipole moment measurements of short-lived baryons using bent crystals at the LHC

Several studies are on-going at CERN in the framework of the Physics Beyond Collider study group, with main aim of broadening the physics research spectrum using the available accelerator complex and infrastructure. The possibility to design a layout that allows fixed-target experiments in the primary vacuum of the CERN Large Hadron Collider (LHC), without the need of a dedicated extraction line, is part of these studies. The principle of the layouts presented in this paper is to deflect beam halo protons on a fixed-target placed in the LHC primary vacuum, by means of the channeling process in bent crystals. Moreover, the presence of a second bent crystal adjacent to the target opens a unique opportunity for the first direct measurement of electric and magnetic dipole moments of short-lived baryons. Two possible layouts are reported, together with a thorough evaluation on their expected performance and impact on LHC operations.

Suppression of beam halo in an RF linac using a hollow electron beam

High-intensity electron linacs have severe space-charge effects that lead to the production of beam halo which degrade the beam quality. For a given charge per bunch, hollow beams have a weaker nonlinear space-charge force. In this paper, we have investigated the possibility of using hollow beam to control halo growth in linacs. We simulate the dynamics of such a beam in a 17 MeV radio frequency linac using ASTRA beam dynamics code and show that it experiences a smaller emittance growth as well as reduced beam halo. The results suggest that using a hollow beam, high charge per bunch could be propagated and accelerated in a radio frequency linac.

Development of the LHCb VELO Detector Modules into a Standalone, Non-Invasive Online Beam Monitor for Medical Accelerators

Knowledge of the beam properties in proton therapy through beam monitoring is essential, ensuring an effective dose delivery to the patient. In clinical practice, currently used interceptive ionisation chambers require daily calibration and suffer from a slow response time. A new non-invasive method for dose online monitoring is under development based on the silicon multi-strip sensor LHCb VELO (VErtex LOcator), originally used for the LHCb experiment at CERN. The proposed method relies on proton beam halo measurements. Several changes in the system setup were necessary to operate the VELO module as a standalone system outside of the LHC environment and are described in this paper. A new cooling, venting and positioning system was designed. Several hardware and software changes realised a synchronised readout with a locally constructed Faraday Cup and the RF frequency of a medical cyclotron with quasi-online monitoring. The adapted VELO module will be integrated at the 60 MeV proton therapy beamline at the Clatterbridge Cancer Centre (CCC), UK and the capability as a beam monitor will be assessed by measuring the beam current and by monitoring the beam profile along the beamline in spring 2019.