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Description
High intensity (≥1018 W/cm2) short pulse (≤ps) lasers allow the efficient generation of MeV energy protons from thin foils. Since the protons are emitted perpendicular to the rear surface of the foil, hemispherical foils may act to focus the protons [1-3]. This focusing is crucial to achieving sufficient proton flux on target for the proton fast ignition scheme of inertial confinement fusion. [4]
To study the generation and focusing of protons beams, a secondary thin foil target can be placed in their path. The protons will heat the secondary target to several eV temperatures, which in turn will radiate Planckian blackbody emission. To study the proton heating a diagnostic system has been developed to image a narrow band of XUV emission, with photon energies around 93 eV, from the rear surface of the secondary target. This technique was used to study proton focusing at the ZEUS Petawatt laser facility at the University of Michigan using a laser focal spot of similar size to the hemispherical radius and laser energies of around 40 J. The time-integrated brightness of emission can be used to calculate the spatial distribution of the temperature [5,6] and from this the amount of proton heating which has occurred. Time-dependent hydrodynamic modeling coupled with radiation emission calculations are used to compare to the measurements. The XUV imaging system design, sample data, and analysis techniques are discussed with some initial proton heating images obtained.
1 – C. McGuffey, et. al. “Focussing Protons from a Kilojoule Laser for Intense Beam Heating using Proximal Target Structure”, Sci. Rep. Vol. 10, No. 9415, (2020)
2 – T. Bartal, et. al. “Focusing of short-pulse high-intensity laser-accelerated proton beams”, Nat. Phys. Vol. 8, pp. 139-142, (2012)
3 - P.K. Patel, et al. "Isochoric heating of solid-density matter with an ultrafast proton beam." Phys. Rev. Lett. Vol. 91, No. 12, (2003)
4 – M. Roth, et. al. “Fast Ignition by Intense Laser-Accelerated Proton Beams”, Phys. Rev. Lett. Vol. 86, 436, (2001)
5 – P. Gu, et. al. “Measurements of electron and proton heating temperatures from extreme-ultraviolet light images at 68 eV in petawatt laser experiments”, Rev. Sci. Inst. 77, 113101, (2006)
6 – R. Snavely et. al. “Laser generated proton beam focusing and high temperature isochoric heating of solid matter”, PoP. 14, 092703, (2007)
| Keyword-1 | XUV |
|---|---|
| Keyword-2 | Proton |
| Keyword-3 | Heating |