AWAKE readiness for the study of the seeded self-modulation of a 400 GeV proton bunch

Abstract

AWAKE is a proton-driven plasma wakefield acceleration experiment. We show that the experimental setup briefly described here is ready for systematic study of the seeded self-modulation of the 400 GeV proton bunch in the 10 m-long rubidium plasma with density adjustable from 1 to 10×10 14 cm −3 . We show that the short laser pulse used for ionization of the rubidium vapor propagates all the way along the column, suggesting full ionization of the vapor. We show that ionization occurs along the proton bunch, at the laser time and that the plasma that follows affects the proton bunch.

Experimental Observation of Plasma Wakefield Growth Driven by the Seeded Self-Modulation of a Proton Bunch

“…When satisfying k pe σ z ∼ = √ 2, these proton bunches are therefore much too long to drive GV/m wakefield amplitudes. However, when the bunch is much longer than the plasma wavelength it is subjected to a transverse instability called the self-modulation instability (SMI) [8][9][10] or, when seeded, the seeded self-modulation (SSM) [11,12].…”

Accelerating field enhancement due to ion motion in plasma wakefield accelerators

“…The effect of wakefield enhancement was first noticed in numerical simulations of the AWAKE experiment. In AWAKE [18][19][20], a long proton bunch undergoes seeded self-modulation in the plasma [21][22][23] and transforms into a train of short micro-binches that resonantly drive the plasma wave [24,25]. The number of micro-bunches depends on the plasma density and is typically about one hundred, so the plasma wave exists sufficiently long to move the ions.…”

External Electron Injection for the AWAKE Experiment

“…Since the 400 GeV/c proton drive bunch (γ = 427) -as delivered by the CERN Super Proton Synchrotron-has a rms bunch length on the order of ∼6-12 cm, it is much too long to effectively drive wakefields at these plasma densities. Thus, the experiment relies on the seeded self-modulation [11] to modulate the proton bunch density at the plasma electron wavelength. The bunch train then resonantly excites a plasma wave with hundreds of MV/m field amplitudes.…”