Coherent seeding of self-modulated plasma wakefield accelerators

Abstract

The growth of the beam self-modulation and hosing instabilities initiated by a seed wakefield is examined. Although the growth rates for the self-modulation and hosing instabilities are comparable, it is shown that an externally excited wakefield can be effective in selectively seeding the beam radial self-modulation, enabling the beam to fully modulate before strong beam hosing develops. Methods for coherent seeding are discussed.

Hosing Instability Suppression in Self-Modulated Plasma Wakefields

“…In addition, beam tilts that seed hosing lead to W ⊥,HI = k 2 β k p σ z δ HI . Hence the stable propagation condition W ⊥,SMI / W ⊥,HI 1 holds as long as δ HI r b /σ z (x c0 = δ HI ξ), consistent with [24]. Stable propagation then occurs for all beamlets whose centroid initially resides within the bunch radius, at the bunch front.…”

“…This is the same as having the seed for x w being smaller than the seed for δn p /n 0 . Among several SMI seeding mechanisms [22][23][24] we consider seeding by bunches with short rise times [25] for which W ⊥,SMI ∝ k 2 β k p r b0 . In addition, beam tilts that seed hosing lead to W ⊥,HI = k 2 β k p σ z δ HI .…”

Physics of beam self-modulation in plasma wakefield accelerators

“…The interplay between hosing and SMI is studied in Refs. [29][30][31] and is by now limited to the analytically tractable case of narrow and constant emittance beams. No detailed numerical studies of mode interaction has been done yet, as this problem is essentially three-dimensional and computationally heavy due to long beams and long interaction distances of interest.…”

Electron trapping and acceleration by the plasma wakefield of a self-modulating proton beam

“…28 By performing 2D cylindrically symmetric simulations, we preclude the physics associated with the hosing instability, which can lead to beam breakup. 11,29,30 It has been shown, however, that the hosing instability can be suppressed after the saturation of the selfmodulation instability if wakefield excitation is in the linear regime. 31 Since the baseline AWAKE variant will lead to plasma wakefields excited in the linear regime, cylindrically symmetric simulations are well suited for our research.…”