The variation of mass ablation rate with laser wavelength and target geometry

Goldsack, T.J.; Kilkenny, J. D.; MacGowan, B. J.; Veats, Stephen Alan; Cunningham, P. F.; Lewis, Ciaran; Key, M.H.; Rumsby, P.T.; Toner, W.T.

doi:10.1016/0030-4018(82)90089-x

Cited by 56 publications

(8 citation statements)

References 14 publications

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“…This fact raises the question of whether or not the delta function absorption is a sufficient treatment of the system. Several experiments have attempted to measure the ablation pressure or mass ablation rate either directly or through derived quantities [22][23][24][25] . Although there is an abundance of experimental results, most of the measurements utilized short pulse times and therefore the results are valid where c s t is small.…”

Section: B Validity Of the Modelmentioning

confidence: 99%

The role of incidence angle in the laser ablation of a planar target

Scheiner

Schmitt

2019

Physics of Plasmas

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The effect of the laser ray incidence angle on the mass ablation rate and ablation pressure of planar inertial confinement fusion (ICF) targets is explored using an idealized model. Polar direct drive (PDD) on the National Ignition Facility (NIF) requires the repointing of its 192 beams clustered within 50 degrees of the poles to minimize the imparted polar varying payload kinetic energy of the target. Due to this repointing, non-normal incidence angles of the beam centerlines are encountered in any PDD design. The formulation of a PDD scheme that minimizes non-uniformity is a significant challenge that requires an understanding of the induced differences in ablation including those of incidence angle. In this work, a modified version of the textbook model of laser ablation [Manheimer et al. Phys. Fluids 25, 1644(1982] is used to demonstrate that the mass ablation rate and ablation pressure scale with the 4/3 and 2/3 power of the cosine of the laser ray incidence angle for the planar case during the beginning portion of the laser ablation. This result is considered with an idealized 1-D two segment planar model using rays at different incidence angles for each segment. Within the model, the segments cannot have equal mass and velocity simultaneously without tailoring the ray's time-dependent intensity for each segment. However, with the correct segment-to-segment time-independent ray intensities, equal velocity and dynamic pressure can be achieved approximately without tailoring. Additionally, an analytic prediction for the conduction zone width as a function of incidence angle is provided. It is predicted that this width increases with incidence angle, resulting in a decrease in laser imprint, an effect which has been previously observed in experiments. These results, when generalized to spherical geometry, may provide insight into the implosion dynamics encountered in PDD.

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Section: B Validity Of the Modelmentioning

confidence: 99%

The role of incidence angle in the laser ablation of a planar target

Scheiner

Schmitt

2019

Physics of Plasmas

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“…The classical theories of thermal transport by Spitzer-Härm (SH) [1] and Braginskii [2] specify the heat flux by a local expression, in terms of the thermal conductivity κ and the electron temperature gradient (e.g., q SH = −κ∇T e ). This theory breaks down in the presence of large temperature gradients [8][9][10][11], turbulence [12], or return current instabilities [13][14][15][16]: classical theory does not include nonlocal effects where energetic electrons travel distances comparable with the temperature scale length before colliding.…”

Section: Pacs Numbersmentioning

confidence: 99%

“…In laser-produced plasmas, classical theory predicts unphysically large thermal transport and hydrodynamic simulations of these plasmas require an ad hoc limiter on the heat flux to match experimental observables. Historically these limiters were set by kinetic simulations [17,[25][26][27], integrated experiments [10,11,28,29], or more-focused Thomson scattering measurements of the local plasma conditions (i.e., electron temperature and density) [8,13,30,31]. More recently, the nonlocal Schurtz, Nicolaï, and Busquet (SNB) model [23] was introduced as a computationally efficient method for calculating the nonlocal heat flux in large-scale multidimensional hydrodynamic simulations.…”

Section: Pacs Numbersmentioning

confidence: 99%

Observation of Nonlocal Heat Flux Using Thomson Scattering

et al. 2018

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“…Streak-time-resolved X-ray spectroscopy of layered target burn-through was used to determine mass ablation rates and ablation pressures for wavelengths of 1.05 Mm, 0.53 Mm and 0.35 Mm [20][21][22].…”

Section: Energy Transportmentioning

confidence: 99%