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Atomic and Laser Physics
Credit: Jack Hobhouse

Dr Benjamin Greenwood

Postdoctoral Research Assistant

Research theme

  • Plasma physics

Sub department

  • Atomic and Laser Physics

Research groups

  • Laser-plasma accelerator group
ben.greenwood@physics.ox.ac.uk
Clarendon Laboratory, room Simon Room
  • About
  • Publications

Multi-parametric characterization of proton bunches above 50 MeV generated by helical coil targets

High Power Laser Science and Engineering Cambridge University Press (CUP) 12 (2024) e88

Authors:

P Martin, H Ahmed, O Cavanagh, S Ferguson, JS Green, B Greenwood, B Odlozilik, M Borghesi, S Kar

Abstract:

Abstract Tightly focused proton beams generated from helical coil targets have been shown to be highly collimated across small distances, and display characteristic spectral bunching. We show, for the first time, proton spectra from such targets at high resolution via a Thomson parabola spectrometer. The proton spectral peaks reach energies above 50 MeV, with cutoffs approaching 70 MeV and particle numbers greater than 10 ${}^{10}$ . The spectral bunch width has also been measured as low as approximately 8.5 MeV (17% energy spread). The proton beam pointing and divergence measured at metre-scale distances are found to be stable with the average pointing stability below 10 mrad, and average half-angle beam divergences of approximately 6 mrad. Evidence of the influence of the final turn of the coil on beam pointing over long distances is also presented, corroborated by particle tracing simulations, indicating the scope for further improvement and control of the beam pointing with modifying target parameters.
More details from the publisher

Dual stage approach to laser-driven helical coil proton acceleration

New Journal of Physics IOP Publishing 25:1 (2023) 013006-013006

Authors:

S Ferguson, P Martin, H Ahmed, E Aktan, M Alanazi, M Cerchez, D Doria, JS Green, B Greenwood, B Odlozilik, O Willi, M Borghesi, S Kar

Abstract:

Abstract Helical coil accelerators are a recent development in laser-driven ion production, acting on the intrinsically wide divergence and broadband energy spectrum of laser-accelerated protons to deliver ultra-low divergence and quasi-monoenergetic beams. The modularity of helical coil accelerators also provides the attractive prospective of multi-staging. Here we show, on a proof-of-principle basis, a two-stage configuration which allows optical tuning of the energy of the selected proton beamlet. Experimental data, corroborated by particle tracing simulations, highlights the importance of controlling precisely the beam injection. Efficient post-acceleration of the protons with an energy gain up to ∼16 MeV (∼8 MeV per stage, at an average rate of ∼1 GeV m−1) was achieved at an optimal time delay, which allows synchronisation of the selected protons with the accelerating longitudinal electric fields to be maintained through both stages.
More details from the publisher

Multi-parametric characterization of proton bunches above 50 MeV generated by helical coil targets

High Power Laser Science and Engineering Cambridge University Press (CUP) 12 (2024) e88

Authors:

P Martin, H Ahmed, O Cavanagh, S Ferguson, JS Green, B Greenwood, B Odlozilik, M Borghesi, S Kar

Abstract:

Abstract Tightly focused proton beams generated from helical coil targets have been shown to be highly collimated across small distances, and display characteristic spectral bunching. We show, for the first time, proton spectra from such targets at high resolution via a Thomson parabola spectrometer. The proton spectral peaks reach energies above 50 MeV, with cutoffs approaching 70 MeV and particle numbers greater than 10 ${}^{10}$ . The spectral bunch width has also been measured as low as approximately 8.5 MeV (17% energy spread). The proton beam pointing and divergence measured at metre-scale distances are found to be stable with the average pointing stability below 10 mrad, and average half-angle beam divergences of approximately 6 mrad. Evidence of the influence of the final turn of the coil on beam pointing over long distances is also presented, corroborated by particle tracing simulations, indicating the scope for further improvement and control of the beam pointing with modifying target parameters.
More details from the publisher

Dual stage approach to laser-driven helical coil proton acceleration

New Journal of Physics IOP Publishing 25:1 (2023) 013006-013006

Authors:

S Ferguson, P Martin, H Ahmed, E Aktan, M Alanazi, M Cerchez, D Doria, JS Green, B Greenwood, B Odlozilik, O Willi, M Borghesi, S Kar

Abstract:

Abstract Helical coil accelerators are a recent development in laser-driven ion production, acting on the intrinsically wide divergence and broadband energy spectrum of laser-accelerated protons to deliver ultra-low divergence and quasi-monoenergetic beams. The modularity of helical coil accelerators also provides the attractive prospective of multi-staging. Here we show, on a proof-of-principle basis, a two-stage configuration which allows optical tuning of the energy of the selected proton beamlet. Experimental data, corroborated by particle tracing simulations, highlights the importance of controlling precisely the beam injection. Efficient post-acceleration of the protons with an energy gain up to ∼16 MeV (∼8 MeV per stage, at an average rate of ∼1 GeV m−1) was achieved at an optimal time delay, which allows synchronisation of the selected protons with the accelerating longitudinal electric fields to be maintained through both stages.
More details from the publisher

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