Collisionless shocks in laser-produced plasma generate monoenergetic high-energy proton beams


Compact and affordable ion accelerators based on laser-produced plasmas have potential applications in many fields of science and medicine. However, the requirement of producing focusable, narrow-energy-spread, energetic beams has proved to be challenging. Here we demonstrate that laser-driven collisionless shocks can accelerate proton beams to 20 MeV with extremely narrow energy spreads of about 1% and low emittances. This is achieved using a linearly polarized train of multiterawatt CO2 laser pulses interacting with a gas-jet target. Computer simulations show that laser-heated electrons launch a collisionless shock that overtakes and reflects the protons in the slowly expanding hydrogen plasma, resulting in a narrow energy spectrum. Simulations predict the production of 200 MeV protons needed for radiotherapy by using current laser technology. These results open a way for developing a compact and versatile, high-repetition-rate ion source for medical and other applications.

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Figure 1: Experimental setup, the CO2 laser pulse profile and an image of a CR39 detector.
Figure 2: Proton energy spectra.
Figure 3: Laser-produced plasma profile.
Figure 4: Simulation results.
Figure 5: Simulated proton spectra.


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Work supported by DOE Grant DE-FG02-92-ER40727, NSF grant PHY-0936266 at UCLA, European Research Council ERC-2010-AdG Grant 267841 and FCT (Portugal) grants PTDC/FIS/111720/2009 and SFRH/BD/38952/2007. We thank A. Pak, N. Lemos and K. A. Marsh for characterizing the gas-jet targets. Computing resources provided by PRACE (Tier 0) on Jugene based in Germany, the Hoffman Cluster (UCLA) and the IST Cluster (IST Lisbon).

Author information

D.H., S.T., C.G. and C.J. conceived and designed the experiments, carried out the experiments, analysed the data, contributed analysis tools and wrote the paper. F.F., L.O.S., R.A.F. and W.B.M. carried out the numerical simulations and wrote the paper.

Correspondence to Chan Joshi.

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Haberberger, D., Tochitsky, S., Fiuza, F. et al. Collisionless shocks in laser-produced plasma generate monoenergetic high-energy proton beams. Nature Phys 8, 95–99 (2012) doi:10.1038/nphys2130

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