POSTPONED: Plasma Wakefield Accelerator Experiments with CERN Proton Bunches

by Dr Patric Muggli (Max-Planck-Institut für Physik)

Thursday 31 May 2012, 14:30 → 15:30 Europe/Brussels

Large seminar room (IIHE (ULB-VUB))

The plasma wakefield accelerator or PWFA is a advanced accelerator using a plasma as the accelerating medium. The ionized plasma with a density a hundred times lower than the ambient air can sustain very large accelerating fields, exceeding 50GV/m in current experiments. In the PWFA the wakefield with transverse focusing and defocusing field, and longitudinal accelerating and decelerating fields are excited by a short, dense particle bunch (electrons, positrons or protons). The transverse fields allow for the propagation of the particle bunches over long plasma distances and they can therefore gain very large amounts of energy from the longitudinal fields. Recent experiments with the ultra-short, ultra-relativistic SLAC electron bunches have demonstrated an energy gain of 42GeV in only 85cm of plasma [Blumenfeld et al., Nature 445, 741 (2007)]. Proton bunches are attractive because they carry large amounts of energy (>100kJ, CERN LHC) enough to potentially produce an ILC-like electron bunch (~2kJ) in a single plasma cell. We are therefore proposing to study experimentally the proton-driven PWFA (or PDPWFA) using the CERN SPS bunches. However, these bunches are long (~12cm) and cannot drive large amplitude wakefields. Early experiments will therefore use the self-modulation of these long bunches [Kumar et al., PRL104, 255003 (2010)] in high-density plasmas (density~1e15/cc, plasma wavelength~1.5mm) to resonantly drive wakefields. Physics experiments with electron and positron bunches are also proposed for SLAC-FACET [Vieira et al., submitted 2011]. A full research program aimed at studying the PDPWFA in the context of a high-energy particle accelerator will be developed at CERN around these proof-of-principle experiments. The presentation will consist of an introduction to the PWFA, a presentation of key recent experimental results, as well as of a description of the experiments proposed at CERN and of its goals.