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Drive beam depletion with multi-Joule energy transfer in a plasma wakefield accelerator

R. Ariniello, V. Lee, D. Storey, C. Emma, S. Gessner, M. J. Hogan, A. Knetsch, M. D. Litos, N. Majernik, B. O'Shea

TL;DR

This work tackles the challenge of achieving collider-relevant drive-to-wake energy transfer in beam-driven PWFA by employing an all-optical, laser-ionized hydrogen plasma source that can support large drive energies without overheating. Using a $10\ \mathrm{GeV}$, $1.52\ \mathrm{nC}$ drive beam and a novel diffractive-optics plasma source, the authors demonstrate at least $5.6\ \mathrm{J}$ of energy transfer over a $0.85\ \mathrm{m}$ plasma, corresponding to a drive-to-wake efficiency of $37\pm3\%$ with more than $90\%$ of the drive charge participating. The energy depletion is evidenced by decelerated electrons concentrated in a narrow spectral peak, and some shots show energy depletion below $0.93\ \mathrm{GeV}$ for significant fractions of the beam. Scaling toward collider parameters appears feasible by increasing drive beam charge to $2.1\ \mathrm{nC}$ and extending the plasma length, potentially achieving efficiencies $>60\%$ and energy deposition around $12.6\ \mathrm{J}$ (or higher) per meter, while the plasma source demonstrated robust operation over extended runs.

Abstract

A collider based on beam-driven plasma wakefield acceleration will require the drive beam to transfer 10-100s of Joules to the plasma in each stage, with a drive-to-wake energy transfer efficiency exceeding 70%. Using an all-optical plasma source, we demonstrate significant progress towards these parameters, transferring at least 5.6 J from a 1.52 nC, 10 GeV electron beam to a $4.5\times 10^{16}\,\mathrm{cm^{-3}}$ hydrogen plasma while achieving at least $37\pm 3\%$ drive-to-wake energy transfer efficiency. We observe deceleration of some particles to less than 0.93 GeV with up to 90% of the charge participating in the interaction.

Drive beam depletion with multi-Joule energy transfer in a plasma wakefield accelerator

TL;DR

This work tackles the challenge of achieving collider-relevant drive-to-wake energy transfer in beam-driven PWFA by employing an all-optical, laser-ionized hydrogen plasma source that can support large drive energies without overheating. Using a , drive beam and a novel diffractive-optics plasma source, the authors demonstrate at least of energy transfer over a plasma, corresponding to a drive-to-wake efficiency of with more than of the drive charge participating. The energy depletion is evidenced by decelerated electrons concentrated in a narrow spectral peak, and some shots show energy depletion below for significant fractions of the beam. Scaling toward collider parameters appears feasible by increasing drive beam charge to and extending the plasma length, potentially achieving efficiencies and energy deposition around (or higher) per meter, while the plasma source demonstrated robust operation over extended runs.

Abstract

A collider based on beam-driven plasma wakefield acceleration will require the drive beam to transfer 10-100s of Joules to the plasma in each stage, with a drive-to-wake energy transfer efficiency exceeding 70%. Using an all-optical plasma source, we demonstrate significant progress towards these parameters, transferring at least 5.6 J from a 1.52 nC, 10 GeV electron beam to a hydrogen plasma while achieving at least drive-to-wake energy transfer efficiency. We observe deceleration of some particles to less than 0.93 GeV with up to 90% of the charge participating in the interaction.

Paper Structure

This paper contains 5 sections, 1 equation, 3 figures.

Table of Contents

  1. Introduction
  2. Experimental Setup
  3. Estimate of Plasma Length
  4. Drive Depletion and Energy Transfer
  5. Conclusion

Figures (3)

  • Figure 1: Experimental setup. The laser pulse reflected off a holed mirror to co-propagate with the electron beam where it ionized the $\mathrm{H_2}$ gas filling the beamline. The gas was contained between two holed Be windows by a differential pumping system. The FACET-II electron beam was focused into the plasma with a pair of quadrupole triplets. After the plasma, the beam was imaged by three quadrupoles into a dipole spectrometer. (a) The laser focal region was characterized by scanning a camera (Rail camera) through the leakage light from a turning mirror. (b) The on-axis fluence was distorted at high power by nonlinear phase picked up in the $\mathrm{CaF_2}$ that isolates the laser compressor from the beamline. (c) Electron beam spectra with the laser off, showing minimal interaction between the beam and the $\mathrm{H_2}$ gas. (d) With the laser on, significant deceleration due to the laser ionized plasma was visible. Shots were recorded sequentially, with pauses for saving data every 100 shots. (e) A representative shot [shot 15 in (d)] is shown, measured using two detectors: a scintillator screen for particles from 0.93GeV to 3GeV and a Cherenkov based detector for particles from 3.25GeV to 11.30GeV.
  • Figure 2: Estimate of the plasma length. (a) Energy spectra recorded from scanning the location of the incoming beam waist at the plasma entrance, black lines separate the scan steps. (b) The energy loss is maximized when the waist is positioned at the start of the plasma, as this position minimizes emittance growth. (c) Transverse projection of a 20MeV energy slice centered at 3.4GeV as the spectrometer imaging plane is scanned. (d) Fitting Eq. (\ref{['eq:vacProp']}) gives both the $\beta$ function and location of the waist at the exit of the plasma.
  • Figure 3: Energy depletion of the electron beam (a and b) and high drive-to-wake energy transfer efficiency (c and d). (a) Spectrum of all shots taken with the spectrometer set to image $\leq\qty{1.5}{GeV}$, sorted by minimum energy. (b) An example spectrometer image and spectrum (shot 0) showing depletion of significant charge below the spectrometer's lower limit of 0.93GeV. The orange shading depicts the amount of charge that remains at 10GeV and does not participate in driving the wake, here $236\pm\qty{3}{pC}$. (c) The 600 shots with the greatest drive-to-wake energy transfer efficiency, taken with the spectrometer set to image 3.5GeV. (d) Spectrum of a shot with high efficiency (shot 2, $35\pm 3\%$ drive-to-wake efficiency) showing a significant fraction of the charge located in a single peak around 3.75GeV.