Passive Ballistic Microbunching of Nonultrarelativistic Electron Bunches Using Electromagnetic Wakefields in Dielectric-Lined Waveguides

F. Lemery, P. Piot, G. Amatuni, P. Boonpornprasert, Y. Chen, J. Good, B. Grigoryan, M. Groß, M. Krasilinikov, O. Lishilin, G. Loisch, A. Oppelt, S. Philipp, H. Qian, Y. Renier, F. Stephan, and I. Zagorodnov

Phys. Rev. Lett. 122, 044801 – Published 30 January 2019

Abstract

Temporally modulated electron beams have a wide array of applications ranging from the generation of coherently enhanced electromagnetic radiation to the resonant excitation of electromagnetic wakefields in advanced-accelerator concepts. Likewise producing low-energy ultrashort microbunches could be useful for ultrafast electron diffraction and new accelerator-based light-source concepts. In this Letter we propose and experimentally demonstrate a passive microbunching technique capable of forming a picosecond bunch train at $\sim 6 MeV$ . The method relies on the excitation of electromagnetic wakefields as the beam propagates through a dielectric-lined waveguide. Owing to the nonultrarelativistic nature of the beam, the induced energy modulation eventually converts into a density modulation as the beam travels in a following free-space drift. The modulated beam is further accelerated to $\sim 20 MeV$ while preserving the imparted density modulation.

Received 25 June 2018
Revised 17 December 2018

DOI:https://doi.org/10.1103/PhysRevLett.122.044801

Physics Subject Headings (PhySH)

Plasma acceleration & new acceleration techniques Radiation from moving charges

Accelerators & Beams

Authors & Affiliations

F. Lemery^1,*, P. Piot^2,3, G. Amatuni^4,5, P. Boonpornprasert⁴, Y. Chen⁴, J. Good⁴, B. Grigoryan^4,5, M. Groß⁴, M. Krasilinikov⁴, O. Lishilin⁴, G. Loisch⁴, A. Oppelt⁴, S. Philipp⁴, H. Qian⁴, Y. Renier⁴, F. Stephan⁴, and I. Zagorodnov¹

¹Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607 Hamburg, Germany
²Northern Illinois Center for Accelerator & Detector Development and Department of Physics, Northern Illinois University, DeKalb Illinois 60115, USA
³Accelerator Physics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
⁴Deutsches Elektronen-Synchrotron, Platannenallee 6, 15738 Zeuthen, Germany
⁵Center for the Advancement of Natural Discoveries using Light Emission, Yerevan 0040, Armenia

^*francois.lemery@gmail.com

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Vol. 122, Iss. 4 — 1 February 2019

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Images

Figure 1
Overview of the passive ballistic-bunching experiment implemented at the PITZ facility. (a) Simulated evolutions of the longitudinal-phase-space density distribution $(ζ, δ)$ at the different stages of the bunching process (b)–(d) with associated current profile [ $Λ (ζ)$ ], evolution of the transverse and longitudinal emittances (e) and rms beam size (f) along the accelerator beamline with (dashed trace) and without (solid trace) DLW2 present, and development of the bunch current profile [ $I (ζ)$ ] along the beam line (g). The nominal parameters for these simulations are listed in Table 1 for the case of DLW2. Values $ζ > 0$ correspond to the head of the bunch. Note that in plots (e) and (f) the dashed and solid traces overlap for the transverse parameters. For the “optimized configuration” an additional solenoid was located at $z = 2.7 m$ .
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Figure 2
Green’s function for the two considered DLW structures. (a) Simulated evolution of the compression factor $| ξ | (z - z_{c})$ along the beam line downstream of the DLW location for different booster-linac accelerating voltage $V_{b}$ (b) and final LPS distribution obtained for the nominal accelerator settings for the cases without DLW (c) and with DLW1 (d) or DLW2 (e) inserted along with corresponding current profiles (f).
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Figure 3
Measured $Q (ζ, x)$ charge-density distribution without DLW (a) and with DLW1 (b) or DLW2 (c) inserted, along with associated current profiles $I (ζ)$ (d). Locations of local maxima for the current profiles measured with the DLW structures inserted (e) and associated bunch form factors (f).
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Figure 4
Simulated evolution of the LPS for booster linac injection phases $φ_{b} = - 22.5 °$ (a), 0° (b), and $+ 22.5 °$ (c). The traces correspond to the peak-normalized charge distribution as a function of longitudinal (energy) $Λ (ζ)$ [ $Λ^{'} (δ)$ ] coordinate. Evolution of the charge distribution $Λ^{''} (p_{z})$ for different injection phases $φ_{b}$ (d) with labeled lines referring to phase settings associated with plots (a),(b), and (c). The simulations are performed with DLW2 (similar results are obtained with DLW1 albeit with a different modulation period).
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Figure 5
Mosaic image of measured LPS-distribution snapshots (a) for different settings of the booster linac injection phases $φ_{b}$ (columns) corresponding to the three cases of DLW operation (rows). Comparison of the simulated (traces) and measured (symbols) modulation period along the longitudinal $Δ ζ$ (b) and fractional energy $Δ δ$ (c) coordinates. The shaded areas reflect uncertainties in the simulated values.
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