J. C. Molendijk | Searcharxiv

arXiv2019

Achievements and New Challenges for CERN's Digital LLRF Family

An innovative digital Low-Level RF (LLRF) family has been developed at CERN and deployed on several circular machines. Operation of CERN's PS Booster (PSB), Low Energy Ion Ring (LEIR) and Extra Low ENergy Antiproton (ELENA) ring all reaped great benefit from the flexibility and processing power of this new family. Beam and cavity feedback loops have been implemented, as well as bunch shaping, longitudinal blowup and bunch splitting. For ELENA, longitudinal diagnostics such as bunched beam intensity and bunch length measurements have also been deployed. During Long Shutdown 2 (LS2) the ferrite-based High-Level RF (HLRF) systems of the Antiproton Decelerator (AD) and of the four-ring PSB will be replaced with Finemet-based HLRF. This will require a new LLRF system for the AD and deep upgrades to the existing PSB LLRF systems. This paper gives an overview of the main results achieved by the digital LLRF family so far and of the challenges the LLRF team will take on during LS2.

physics.acc-ph↗

arXiv2019

Experimental observation of proton bunch modulation in a plasma, at varying plasma densities

We give direct experimental evidence for the observation of the full transverse self-modulation of a relativistic proton bunch propagating through a dense plasma. The bunch exits the plasma with a density modulation resulting from radial wakefield effects with a period reciprocal to the plasma frequency. We show that the modulation is seeded by using an intense laser pulse co-propagating with the proton bunch which creates a relativistic ionization front within the bunch. We show by varying the plasma density over one order of magnitude that the modulation period scales with the expected dependence on the plasma density.

physics.acc-ph↗

arXiv2018

Acceleration of electrons in the plasma wakefield of a proton bunch

High energy particle accelerators have been crucial in providing a deeper understanding of fundamental particles and the forces that govern their interactions. In order to increase the energy or reduce the size of the accelerator, new acceleration schemes need to be developed. Plasma wakefield acceleration, in which the electrons in a plasma are excited, leading to strong electric fields, is one such promising novel acceleration technique. Pioneering experiments have shown that an intense laser pulse or electron bunch traversing a plasma, drives electric fields of 10s GV/m and above. These values are well beyond those achieved in conventional RF accelerators which are limited to ~0.1 GV/m. A limitation of laser pulses and electron bunches is their low stored energy, which motivates the use of multiple stages to reach very high energies. The use of proton bunches is compelling, as they have the potential to drive wakefields and accelerate electrons to high energy in a single accelerating stage. The long proton bunches currently available can be used, as they undergo self-modulation, a particle-plasma interaction which longitudinally splits the bunch into a series of high density microbunches, which then act resonantly to create large wakefields. The AWAKE experiment at CERN uses intense bunches of protons, each of energy 400 GeV, with a total bunch energy of 19 kJ, to drive a wakefield in a 10 m long plasma. Bunches of electrons are injected into the wakefield formed by the proton microbunches. This paper presents measurements of electrons accelerated up to 2 GeV at AWAKE. This constitutes the first demonstration of proton-driven plasma wakefield acceleration. The potential for this scheme to produce very high energy electron bunches in a single accelerating stage means that the results shown here are a significant step towards the development of future high energy particle accelerators.

physics.acc-ph↗