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Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA
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Image of FIG. 1.
FIG. 1.

An Aitoff projection of the OMEGA target chamber. The 60 beams are split into three legs. In typical experiments, Legs 1 and 3 (blue) are used to drive a target and Leg 2 (red) drives the proton backlighter source. Ports used to field proton fluence diagnostics are also shown (green) and labeled. Other diagnostic ports not used are labeled for reference.

Image of FIG. 2.
FIG. 2.

(a) Sample fusion proton spectra from an exploding pusher backlighter capsule taken from OMEGA shot 51237. DD protons were measured at 3.6 MeV with FWHM of 320 keV and D3He protons were measured at 15.3 MeV with FWHM of 670 keV. (b) Sample emission profile for D3He protons over laid on the 1 ns square pulse used to drive the capsule on OMEGA shot 51237. Bang time was measured at 420 ps after laser onset with FWHM of 140 ps.

Image of FIG. 3.
FIG. 3.

Summary of backlighter proton emission isotropy data. (a) and (b) DD and D3He-proton yield measurements from different ports; error bars are calculated standard deviations. (c) and (d) Global (long-scale) variance of yield measurements as a function of mean yield. Average variance Σ is shown by the solid line and the dashed lines are ± one standard deviation. (e) and (f) Local proton variance σ measured from radiographs in TIM2 (10 cm squares) and TIM3 (7 cm circles) as a function of mean proton fluence Γ. (g) and (h) Average power density spectrum plotted as a function of angular frequency for two points in each of (e) and (f) (outlined in black) with corresponding radiographs where darker pixels indicate higher fluence. Frequencies ≳50 rad−1 are shown to have amplitudes of ⩽3% relative to the mean proton fluence level (normalized to 1). These data indicate that most of the local variance stems from long-scale perturbations.

Image of FIG. 4.
FIG. 4.

(a) Schematic of sample laser interaction with a CH foil of initial density 1.04 g/cc. (b) Plasma parameters predicted by DRACO for the sample interaction in (a). The solid (green) line in each plot represents a path through this sample plasma. Contour plots of quantities relevant to Coulomb collisions for 3 MeV (dotted) and 15 MeV (dashed) protons in the temperature-density parameter space of a CH (1:1.38) plasma. (d) The ratio of mean square scattering angle in a plasma to that in cold matter. The difference between 3 and 15 MeV protons is negligible, because the ratio is dependent only on ln Λ. (d) The ratio of stopping power in a plasma to that in cold matter.

Image of FIG. 5.
FIG. 5.

(a) Experimental setup for capsule radiographs. Synthetic and experimental data are shown for 3 MeV (b) and 15 MeV (c) proton radiographs of an unimploded CH capsule from OMEGA shot 46531. The top half of either radiograph is from experimental data and the bottom half is simulated. Corresponding radial lineouts are shown by the solid line (experiment) and the dashed line (simulated).

Image of FIG. 6.
FIG. 6.

(a) Experimental setup for mesh radiography experiments. (b) Measured RMS amplitude modulation (□) through the nickel mesh only is plotted as a function of hole spacing with simulated results (solid line). The experimental radiograph shown is from OMEGA shot 44429 and illustrates the three different mesh frequencies. (c) Normalized proton fluence lineouts from data taken on OMEGA shot 44431. Amplitude modulation is shown to decrease for the λ ∼ 230 μm mesh as CH thickness is increased from 25 to 100 μm. (d) Measured RMS amplitude modulation (○) is plotted as a function of CH thickness with simulated results (solid line) for the λ ∼ 230 μm mesh hole spacing. The proton fluence radiograph of the mesh through 25 μm CH is shown with other mesh frequencies visible.


Generic image for table
Table I.

Integration limits for the mean square scattering angle ⟨θ2⟩ calculation under cold-matter and plasma conditions.

Generic image for table
Table II.

Comparison of proton source parameters for exploding-pusher- and TNSA- generated MeV protons. Quantities given for the TNSA proton source are nominal and in many cases, as in pulse duration, peak energy, and source size, the values are dependent on the laser and target parameters. Additionally, CR-39 could be used as a detecting medium for TNSA-generated protons, though due to high fluences, saturation can be a problem.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA