Visualizing fast electron energy transport into laser-compressed high-density fast-ignition targets

Jarrott, L. C.; Wei, M. S.; McGuffey, C.; Solodov, A. A.; Theobald, W.; Qiao, B.; Stoeckl, C.; Betti, R.; Chen, H.; Delettrez, J. A.; Döppner, T.; Giraldez, E.; Glebov, V. Yu.; Habara, H.; Iwawaki, T.; Key, M.H.; Luo, Rong; Marshall, F. J.; McLean, H. S.; Mileham, C.; Patel, P. K.; Santos, J. J.; Sawada, Hiroshi; Stephens, R. B.; Yabuuchi, T.; Beg, F. N.

doi:10.1038/nphys3614

Cited by 56 publications

(29 citation statements)

References 22 publications

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“…This result suggests that the use of Kα yields or Kα spectra as a Te diagnostic could be misinterpretation of data because (1) Kα emission correlates to <Z>, not Te, and (2) Kα photons can be produced by both non-thermal and a high-energy tail of thermal electrons. Because of the above reasons, care must be taken when Kα yields are used to estimate coupling efficiency from laser to a compressed core 74,75 for FI at moderately high densities where drag heating is ineffective (ne < ~10 25 [1/cm 3 ]).…”

Section: Kev Monochromatic X-ray Images For Shots (A) ~ (D) (H) Linementioning

confidence: 99%

Monochromatic 2DKαEmission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism

et al. 2019

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The rapid heating of a thin titanium foil by a high intensity, sub-picosecond laser is studied by using a 2D narrow-band x-ray imaging and x-ray spectroscopy. A novel monochromatic imaging diagnostic tuned to 4.51 keV Ti Kα was used to successfully visualize a significantly ionized area ( >17±1) of the solid density plasma to be within a ~ 35 μm diameter spot in the transverse direction and 2 μm in depth. The measurements and a 2D collisional Particle-in-cell simulation reveal that, in the fast isochoric heating of solid foil by intense laser light, such high ionization state in the solid titanium is achieved by thermal diffusion from the hot preplasma in a few picoseconds after the pulse ends. The shift of Kα and formation of a missing Kα cannot be explained with the present atomic physics model. The measured Kα image is reproduced only when a phenomenological model for the Kα shift with a threshold ionization of =17 is included. This work reveals how the ionization state and electron temperature of the isochorically-heated non-equilibrium plasma are independently increased.

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Section: Kev Monochromatic X-ray Images For Shots (A) ~ (D) (H) Linementioning

confidence: 99%

Monochromatic 2DKαEmission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism

et al. 2019

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“…Compared with the Cu foam target, the Cu doped CH sphere target has a smaller opacity for the Cu Ka photons; consequently, the transport of fast electrons inside the target could be detected by the Cu Ka imager. 28,29 This transport would benefit the estimation of the energy coupling efficiency from the short pulse laser to the compressed fuel core.…”

Section: -8mentioning

confidence: 99%

Confirmation of hot electron preheat with a Cu foam sphere on GEKKO-LFEX laser facility

et al. 2017

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Experiments with a solid Cu foam ($1.3 g/cm 3) sphere coated by a 20 lm CH ablator are performed on the GEKKO-LFEX laser facility to study the effect of hot electron preheat on the implosion performance. When the target is imploded by the GEKKO lasers ($1.2 Â 10 15 W/cm 2 in peak intensity), plenty of hot electrons are measured through the induced Cu Ka emission, indicating that the target could suffer strong preheat. This suffering of preheat is confirmed by the temporal evolution of the target self-emission, which is well reproduced by a 2D cylindrically symmetric radiative hydrodynamic code (FLASH) when a module handling the hot electron preheat is coupled. The results given by this benchmarked code indicate that, in the typical experiments with a small ($200 lm in diameter) solid sphere target conducted on the GEKKO-LFEX laser facility, the hot electron preheat greatly degrades the implosion performance, reducing the peak areal densities of a Cu foam sphere and a CD sphere by $20%

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“…Several breakthroughs were described in past articles on fast heating research: the invention of the cone-in-shell target 16 , high areal density core formation with the cone-in-shell target 17 , and efficient laser-to-core coupling after reduction of pre-plasma filling in the cone 18 . Our achievement, namely enhanced laser-to-core energy coupling with the magnetized fast isochoric heating enabled by an application of external kilo-Tesla-level magnetic field, is also a milestone as a demonstration of the efficient energy coupling, as a means to reduce the large radial spread of the REB.…”

Section: Introductionmentioning

confidence: 99%

“…The long-scale-length pre-plasma filling the cone is produced by prepulse and foot pulses of the heating laser and also by the cone breakup due to high pressure of a plasma surrounding the cone. The heating efficiency of 7% was attained at OMEGA laser facility with an ignition-scale large areal density ( ρR ~0.3 g cm −2 ) core 17 after reducing the pre-plasma formation in the cone 18 ; however, the aforementioned second and third critical problems still remain to be resolved.…”

Section: Introductionmentioning

confidence: 99%

Magnetized fast isochoric laser heating for efficient creation of ultra-high-energy-density states

et al. 2018

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Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in inertial confinement fusion (ICF) ignition sparks. Laser-produced relativistic electron beam (REB) deposits a part of kinetic energy in the core, and then the heated region becomes the hot spark to trigger the ignition. However, due to the inherent large angular spread of the produced REB, only a small portion of the REB collides with the core. Here, we demonstrate a factor-of-two enhancement of laser-to-core energy coupling with the magnetized fast isochoric heating. The method employs a magnetic field of hundreds of Tesla that is applied to the transport region from the REB generation zone to the core which results in guiding the REB along the magnetic field lines to the core. This scheme may provide more efficient energy coupling compared to the conventional ICF scheme.

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Visualizing fast electron energy transport into laser-compressed high-density fast-ignition targets

Cited by 56 publications

References 22 publications

Monochromatic 2DKαEmission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism

Monochromatic 2DKαEmission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism

Confirmation of hot electron preheat with a Cu foam sphere on GEKKO-LFEX laser facility

Magnetized fast isochoric laser heating for efficient creation of ultra-high-energy-density states

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