Hot spots and dark current in advanced plasma wakefield accelerators

Open Access

Hot spots and dark current in advanced plasma wakefield accelerators

G. G. Manahan, A. Deng, O. Karger, Y. Xi, A. Knetsch, M. Litos, G. Wittig, T. Heinemann, J. Smith, Z. M. Sheng, D. A. Jaroszynski, G. Andonian, D. L. Bruhwiler, J. B. Rosenzweig, and B. Hidding

Phys. Rev. Accel. Beams 19, 011303 – Published 29 January 2016

Abstract

Dark current can spoil witness bunch beam quality and acceleration efficiency in particle beam-driven plasma wakefield accelerators. In advanced schemes, hot spots generated by the drive beam or the wakefield can release electrons from higher ionization threshold levels in the plasma media. These electrons may be trapped inside the plasma wake and will then accumulate dark current, which is generally detrimental for a clear and unspoiled plasma acceleration process. Strategies for generating clean and robust, dark current free plasma wake cavities are devised and analyzed, and crucial aspects for experimental realization of such optimized scenarios are discussed.

Received 3 November 2015

DOI:https://doi.org/10.1103/PhysRevAccelBeams.19.011303

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Laser wakefield acceleration

Accelerator applications

Accelerators & BeamsPlasma Physics

Authors & Affiliations

G. G. Manahan^1,*, A. Deng², O. Karger³, Y. Xi², A. Knetsch³, M. Litos⁴, G. Wittig³, T. Heinemann³, J. Smith⁵, Z. M. Sheng¹, D. A. Jaroszynski¹, G. Andonian⁶, D. L. Bruhwiler^6,7, J. B. Rosenzweig², and B. Hidding^1,3,†

¹Scottish Universities Physics Alliance, Department of Physics, University of Strathclyde, Glasgow G4 0NG, United Kingdom
²Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
³Institute of Experimental Physics, University of Hamburg, 22761 Hamburg, Germany
⁴SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
⁵Tech-X UK Ltd., Daresbury, Cheshire WA4 4FS, United Kingdom
⁶RadiaBeam Technologies LLC, Santa Monica, California 90404, USA
⁷RadiaSoft LLC, Boulder, Colorado 80304, USA

^*grace.manahan@strath.ac.uk
^†bernhard.hidding@strath.ac.uk

Article Text

Click to Expand

References

Click to Expand

Issue

Vol. 19, Iss. 1 — January 2016

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Illustration of the plasma blowout time evolution ( $t_{0} < t_{1}$ ), depicting sources of huge electric field spikes or hot spots (blue shade) in PWFA. (a) The blowout vertex, where recoalescing plasma electrons generate an electric field spike and (b) the one concurrent with the drive beam, which is subject to plasma lensing and betatron oscillations.
Reuse & Permissions
Figure 2
Plasma generation via (a) self-field ionization, (b) partial preionization and (c) complete preionization. The top snapshots show the longitudinal electric field, and the bottom snapshots depict the total electric field, thus rendering the laser pulse(s) visible. The longitudinal current profile of the driver bunch (green) is given with the green lineout. The green dashed line in (a) indicates the effective current profile, where self-ionization begins close to the peak charge density. The laser- and wake-ionized He electrons are shown in blue shades.
Reuse & Permissions
Figure 3
PIC simulation results showing step-wise reduction of dark current formation processes in controlled laser injection PWFA. Plots in the top row show the vector sum of the electric field, while those in the middle row show the longitudinal electric fields $E_{z}$ , and those in the bottom row show the potential $Φ$ . All snapshots are taken approximately at the onset of the laser release. The green shade is the drive beam, propagating to the right, the ionization-released He electrons released by lensing drive beam, injector laser and by the blowout wake hot spot are shown color coded (red: high energy, blue: low energy), and the red solid ellipse in the bottom row is the estimated trapping isoregion ( $Φ = - 1.0$ ).
Reuse & Permissions
Figure 4
Blowout and drive beam at different interaction times (i.e., the arrival of the injector laser) in a dark current free TH-PWFA scenario with relaxed requirements on pre-ionization ( $n_{e} = 1.1 \times 10^{17} {cm}^{- 3}$ , $λ_{p} = 100 μ m$ ) and drive bunch density. In (a) $t = 18 ps$ ( $z = 5 mm$ ), the TH injector laser releases electrons at the beginning of the interaction, while at (b) $t = 54 ps$ ( $z = 16 mm$ ) and (c) $t = 107 ps$ ( $z = 32 mm$ ), the release position is located later, where plasma lensing and betatron oscillations have distorted the drive bunch shape and local charge density, leading to increased trapping but at the same time avoids dark current generation. The top snapshots show the sum of the electric field, while the bottom snapshots show the longitudinal field, where the on-axis lineout of the field is shown in black solid line.
Reuse & Permissions
Figure 5
(a) Ray trace of a beam passing through an annular aperture and axicon lens system. (b) Intensity distribution of a Gaussian beam ( $λ_{L} = 800 nm$ , 500 mJ, 70 fs), after passing through the focusing system described in (a) with $γ = 0.25 °$ , $R_{1} = 5 mm$ and $R_{2} = 15 mm$ . The corresponding on-axis E-field is shown at the top inset, while the transverse intensity profile is shown at the right inset. (c) Estimated hydrogen ( $H_{2}$ ) plasma from the configuration in (b), where a plasma width of $\sim 120 μ m$ is generated, as shown with the (black) line out. The calculation is based on ADK ionization rates [21] of $H_{2}$ and integrated over the entire laser pulse duration.
Reuse & Permissions

Physical Review Accelerators and Beams