Acceleration and focusing of relativistic electron beams in a compact plasma device

R. Pompili, M. P. Anania, A. Biagioni, M. Carillo, E. Chiadroni, A. Cianchi, G. Costa, A. Curcio, L. Crincoli, A. Del Dotto, M. Del Giorno, F. Demurtas, M. Galletti, A. Giribono, V. Lollo, M. Opromolla, G. Parise, D. Pellegrini, G. Di Pirro, S. Romeo, G. J. Silvi, L. Verra, F. Villa, A. Zigler, and M. Ferrario

Phys. Rev. E 109, 055202 – Published 3 May 2024

Abstract

Plasma wakefield acceleration represented a breakthrough in the field of particle accelerators by pushing beams to gigaelectronvolt energies within centimeter distances. The large electric fields excited by a driver pulse in the plasma can efficiently accelerate a trailing witness bunch paving the way toward the realization of laboratory-scale applications like free-electron lasers. However, while the accelerator size is tremendously reduced, upstream and downstream of it the beams are still handled with conventional magnetic optics with sizable footprints and rather long focal lengths. Here we show the operation of a compact device that integrates two active-plasma lenses with short focal lengths to assist the plasma accelerator stage. We demonstrate the focusing and energy gain of a witness bunch whose phase space is completely characterized in terms of energy and emittance. These results represent an important step toward the accelerator miniaturization and the development of next-generation table-top machines.

Received 19 February 2024
Accepted 11 April 2024

DOI:https://doi.org/10.1103/PhysRevE.109.055202

Physics Subject Headings (PhySH)

Beam injection, extraction & transport Particle acceleration in plasmas Plasma acceleration & new acceleration techniques Plasma discharges Plasma-beam interactions

Accelerators & BeamsPlasma Physics

Authors & Affiliations

R. Pompili ^1,*, M. P. Anania¹, A. Biagioni¹, M. Carillo², E. Chiadroni², A. Cianchi^3,4,5, G. Costa¹, A. Curcio¹, L. Crincoli¹, A. Del Dotto¹, M. Del Giorno¹, F. Demurtas³, M. Galletti^3,4,5, A. Giribono¹, V. Lollo¹, M. Opromolla¹, G. Parise³, D. Pellegrini¹, G. Di Pirro¹, S. Romeo¹, G. J. Silvi², L. Verra¹, F. Villa¹, A. Zigler⁶, and M. Ferrario¹

¹Laboratori Nazionali di Frascati, Via Enrico Fermi 54, 00044 Frascati, Italy
²University of Rome Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy
³University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
⁴INFN Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
⁵NAST Center, Via della Ricerca Scientifica 1, 00133 Rome, Italy
⁶Racah Institute of Physics, Hebrew University, 91904 Jerusalem, Israel

^*riccardo.pompili@lnf.infn.it

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Issue

Vol. 109, Iss. 5 — May 2024

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Images

Figure 1
Combined capillary adopted in the experiment. The picture shows the device consisting of two active-plasma lenses and an accelerator stage. The dashed blue lines indicate the flow of Nitrogen gas that fills up the three capillaries. The plasma is produced by ionizing the gas with three independent high-voltage discharge currents applied to the three capillaries. The polarity of the discharge current on each electrode is also shown. The electron bunches propagate from right to left (red arrows). Plastic shields are located in the two drift sections to avoid electric cross-talk due to the expanding plasma plumes. The inset shows the envelopes of the driver (D) and witness (W) bunches during the propagation in each stage. The total length of the device is 19 cm; a 1€ coin is included as reference size.
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Figure 2
Discharge current pulses. The accelerator stage (yellow) is triggered $\approx 8 μ s$ before the electron beam (dashed green line) so that the plasma density reaches the desired value $n_{p}$ during the recombination. Conversely, the two active-plasma lenses (red and blue lines) are turned on a few hundreds of ns before so that they experience the strongest focusing in correspondence of the current peak.
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Figure 3
Active-plasma lens scan. The data points (blue) show the horizontal (X) and vertical (Y) beam sizes measured on the screen downstream of the capillary. The scan is achieved by turning on only the second lens while delaying its discharge current with respect to the beam time of arrival. The errorbars are obtained as the standard deviations of the 50 shots collected for each delay. The corresponding discharge current (red) is shown on the right axis.
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Figure 4
Energy spectra with the accelerator stage turned off and on. The plots report the energy spectra of 200 consecutive acquisitions of the driver (D) and witness (W) beams. Each plot is obtained with the active-plasma lenses turned on and with the accelerator stage turned off (a) and on (b). The spectra are obtained in correspondence of the scintillator screen located downstream of the magnetic spectrometer.
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Figure 5
Start-to-end simulations of the driver-witness evolution along the three plasma stages. (a) Accelerating field ( $E_{z}$ ) generated in the PWFA stage. The positions of the driver (D) and witness (W) bunches are represented by the dashed lines. (b) Spot size and normalized emittance of the witness (solid) and driver (dashed). The three plasma stages are represented with gray dotted dashed lines. (c) Optimized configuration employing smaller spot sizes at the entrance.
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