Seeding of proton bunch self-modulation by an electron bunch in plasma

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Preprint
Report number	arXiv:2106.12414
Title	Seeding of proton bunch self-modulation by an electron bunch in plasma
Author(s)	Verra, L. (CERN ; Munich, Max Planck Inst. ; Munich, Tech. U.) ; Zevi Della Porta, G. (CERN) ; Moon, K.-J. (UNIST, Ulsan) ; Bachmann, A.-M. (Munich, Max Planck Inst.) ; Gschwendtner, E. (CERN) ; Muggli, P. (Munich, Max Planck Inst.)
Imprint	2021-06-23
Number of pages	4
Presented at	37th International Cosmic Ray Conference (ICRC 2021), Berlin, Germany, 15 - 22 Jul 2021, pp.
Subject category	physics.plasm-ph ; Other Fields of Physics ; physics.acc-ph ; Accelerators and Storage Rings
Accelerator/Facility, Experiment	CERN AWAKE
Abstract	The AWAKE experiment relies on the self-modulation instability of a long proton bunch to effectively drive wakefields and accelerate an electron bunch to GeV-level energies. During the first experimental run (2016-2018) the instability was made phase reproducible by means of a seeding process: a short laser pulse co-propagates within the proton bunch in a rubidium vapor. Thus, the fast creation of plasma and the onset of beam-plasma interaction within the bunch drives seed wakefields. However, this seeding method leaves the front of the bunch not modulated. The bunch front could self-modulate in a second, preformed plasma and drive wakefields that would interfere with those driven by the (already self-modulated) back of the bunch and with the acceleration process. We present studies of the seeded the self-modulation (SSM) of a long proton bunch using a short electron bunch. The short seed bunch is placed ahead of the proton bunch leading to self-modulation of the entire bunch. Numerical simulations show that this method have other advantages when compared to the ionization front method. We discuss the requirements for the electron bunch parameters (charge, emittance, transverse size at the focal point, length), to effectively seed the self-modulation process. We also present preliminary experimental studies on the electron bunch seed wakefields generation.
Other source	Inspire
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0)

$\it \small Schematic of the electron bunch seeding process. a) Beams at the injection and initial wakefields; b) Fully modulated train of microbunches and transverse wakefields at saturation.$ $\it \small a) Electron bunch imaged onto the spectrometer screen after propagation through vacuum. b) Electron bunch imaged onto the spectrometer screen after propagation through $10\,$ meters of plasma. The horizontal axis is the dispersive plane. The counts of each image are normalized to the respective maximum. c) and d) show a waterfall plot of the energy projections of the electron beam imaged on the spectrometer screen. c) 30 events with the smallest beam size at the plasma entrance; d) 30 events with the largest beam size at the plasma entrance. e) sums of the energy distributions for the two cases: (c) in blue and (d) in orange. For all images, the electron bunch charge at the plasma entrance is $150\,$pC and the energy is $\sim18.5\,$MeV.$

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Record created 2024-08-07, last modified 2024-08-15

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