Robert Appleby

JACoW : SPS Studies in Preparation for the Crab Cavity Experiment

A local Crab Cavity (CC) scheme will recover head-on collisions at the Interaction Points (IPs) of the High Luminosity LHC (HL-LHC), which aims to increase the LHC luminosity to L ∼ 5 · 1034 cm−2 · s−1. The first time that CC will ever be tested with proton beams will be in 2018 in the SPS machine. The available dedicated Machine Development (MD) time after the installation of the cavities will be limited and therefore good preparation is essential in order to ensure that the MDs are as efficient as possible. This paper presents the simulations and experimental studies performed in preparation for the future MDs and discusses the next steps.

The AC-MOT Cold Atom Electron Source (CAES)

Progress towards observing ultra-fast dynamics on atomic length scales is limited by the achievable brightness, or current per unit solid angle, of available electron beams. The brightness of an electron beam is related to its characteristic temperature [1], and hence by reducing the temperature of the electron beam, higher brightness beams can be produced. In a cold atom electron source (CAES), cold atoms held in a magneto-optical trap (MOT) are photo-ionized near threshold by a laser. This process yields electrons with an energy spread on the order of 1 meV, corresponding to a characteristic temperature of ~10 K [2]. Electrostatic fields are then used to extract the electrons into a bunched beam for delivery to experiments. The magnetic B-fields found in a conventional MOT perturb the electron beam trajectory and its quality. The new source described here uses an AC-MOT [3] to ensure the trapping fields are zero at the time of electron extraction. This allows field-free electron extraction whilst retaining a high source density. In the ACMOT, the trapping laser polarization is switched synchronously with an alternating Bfield. Once the B-fields are zero, the atoms are ionized using pulsed, two colour photoionisation, and an electron beam is extracted. To determine the brightness B of the CAES electron beam, its beam current J and characteristic temperature T are measured, since

High Luminosity LHC Hollow Electron Lens Collimation using MERLIN

The high luminosity large hadron collider (HL LHC) upgrade envisions an unprecedented stored beam energy of up to 700 MJ. To protect the machine during operation, an efficient collimation system is vital. The hollow electron lens (HEL) is being explored as a possible collimation enhancer for the LHC, based on Tevatron designs and operational experience [1], for active halo control. A HEL produces a hollow cylindrical beam of electrons through which the accelerator (proton) beam travels, particles that overlap undergo an electromagnetic interaction. As they can operate close to the beam core without being damaged, HELs may serve as soft scraper devices [2]. For the first time a HEL in high luminosity configuration is simulated in the HL LHC using the recently updated MERLIN 5 accelerator libraries [3–5]. The effects on the LHC beam halo are observed for various HEL operation modes.