Transverse self-modulation of ultra-relativistic lepton beams in the plasma wakefield accelerator

Abstract

The transverse self-modulation of ultra-relativistic, long lepton bunches in high-density plasmas is explored through full-scale particle-in-cell simulations. We demonstrate that long SLAC-type electron and positron bunches can become strongly radially self-modulated over centimeter distances, leading to wake excitation in the blowout regime with accelerating fields in excess of 20 GV/m. We show that particles energy variations exceeding 10 GeV can occur in meter-long plasmas. We find that the self-modulation of positively and negatively charged bunches differ when the blowout is reached. Seeding the self-modulation instability mitigates the effect of the competing hosing instability. This work reveals that a proof-of-principle experiment to test the physics of bunch self-modulation can be performed with available lepton bunches and with existing experimental apparatus and diagnostics.

Numerical study of self modulation instability of 1 nC electron bunch at ATF

“…7 b)), no hosing is observed. This is consistent with the previous report that a sharp current-rising bunch can seed the SMI efficiently and therefore mitigate the development of hosing instability [6].…”

“…Originating from the interaction between the plasma electron sheath and the beam, this instability leads to spatio-temporally growing oscillations of the beam centroid of each axial slice, and therefore it may cause the bunch to break before SMI develops. Numerical simulations indicate that the seeding of the SMI may suppress the development of the hosing instability [6]. A number of methods could be used to seed the instability, including shaping the long bunch with a sharp (when compared to plasma wavelength) current rise at the front.…”

Coupled beam hose and self-modulation instabilities in overdense plasma

“…Tapered plasmas may be considered to control the phase velocity of the self-modulated beam-driven plasma wave, although sufficiently large background density variations will suppress the instability [13]. Proof-of-principle experiments to study the physics of beam self-modulation using lepton beams have also been proposed [14].…”

Physics of beam self-modulation in plasma wakefield accelerators

“…Another method involves beam micro-bunching in the plasma due to development of the self-modulation instability (SMI) [7,10,11]. The latter method is the cornerstone for the first experiment on proton driven plasma wakefield acceleration at CERN named AWAKE [1,[12][13][14] and for several supporting experiments with electron beams in other labs [15][16][17][18][19].…”