The effects of pre-mix on burn in ICF capsules

Wilson, D. C.; Kyrala, G. A.; Benage, J.F.; Wysocki, F. J.; Gunderson, Michael A.; Garbett, Warren; Glebov, V. Yu.; Frenje, J. A.; Yaakobi, B.; Herrman, H W; Cooley, J. H.; Welser‐Sherrill, L.; Horsfield, C. J.; Roberts, S.

doi:10.1088/1742-6596/112/2/022015

Cited by 25 publications

(28 citation statements)

References 12 publications

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“…Similar results were reported in Ref. 4 for Ar and Xe. These three yield discrepancies are summarized in Fig.…”

Section: Introductionsupporting

confidence: 92%

“…The differences reported in Ref. 4 were calculated using XSN LTE inline opacity calculations and were even greater for calculations using XSN non-LTE. It was also shown in Ref.…”

mentioning

confidence: 87%

“…Previously published modeling of these implosions 4,5 identified a discrepancy between experimental and calculated yields using a 1-D integrated model described below.…”

Section: Introductionmentioning

confidence: 99%

“…These new multipliers are then applied to the calculations for the set of Kr pre-mixed capsules reported in Ref. 4, which leads to better agreement with experiment. These improvements include: some improvement to the D(D, 3 He)n yield (Y DD-n ), an improvement to the calculated compression (or qR) measured by the ratio of neutron yields (Y DD-n /Y DT-n ), and improvement to the calculated ion temperature.…”

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confidence: 99%

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The effects of laser absorption on direct-drive capsule experiments at OMEGA

et al. 2012

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The yield of an inertial confinement fusion capsule can be greatly affected by the inclusion of high-Z material in the fuel, either intentionally as a diagnostic or from mixing due to hydrodynamic instabilities. To validate calculations of these conditions, glass shell targets filled with a D 2 and 3 He fuel mixture were fielded in experiments with controlled amounts of pre-mixed Ar, Kr, or Xe. The experiments were fielded at the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using 1.0 ns square laser pulses having a total energy 23 kJ and direct drive illumination of shells with an outer diameter of $925 lm and a thickness of $5 lm. Data were collected and compared to one-dimensional integrated models for yield and burn-temperature measurements. This paper presents a critical examination of the calculational assumptions used in our experimental modeling. A modified treatment of laser-capsule interaction improves the match to the measured scattered laser light and also improves agreement for yields, burn-temperatures, and the fuel compression as measured by the ratio of two yields. Remaining discrepancies between measurement and calculation will also be discussed. V C 2012 American Institute of Physics. [http://dx

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“…Similar results were reported in Ref. 4 for Ar and Xe. These three yield discrepancies are summarized in Fig.…”

Section: Introductionsupporting

confidence: 92%

“…The differences reported in Ref. 4 were calculated using XSN LTE inline opacity calculations and were even greater for calculations using XSN non-LTE. It was also shown in Ref.…”

mentioning

confidence: 87%

“…Previously published modeling of these implosions 4,5 identified a discrepancy between experimental and calculated yields using a 1-D integrated model described below.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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The effects of laser absorption on direct-drive capsule experiments at OMEGA

et al. 2012

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“…Multiple ion species are not treated separately: the ion mass and charge are set as a weighted average of the individual species. Recent experimental and theoretical work has questioned the validity of the average-ion assumption [5][6][7][8][9][10][11][12][13][14][15]. Anomalous reduction of the compression-phase nuclear yield has been observed in implosions filled with multiple fuel species, such as deuteriumhelium-3 (D 3 He) [5], DT [6], and other combinations [7,8].…”

mentioning

confidence: 99%

Ion Thermal Decoupling and Species Separation in Shock-Driven Implosions

Rinderknecht

Rosenberg

et al. 2015

Phys. Rev. Lett.

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Anomalous reduction of the fusion yields by 50% and anomalous scaling of the burn-averaged ion temperatures with the ion-species fraction has been observed for the first time in D 3 He-filled shock-driven inertial confinement fusion implosions. Two ion kinetic mechanisms are used to explain the anomalous observations: thermal decoupling of the D and 3 He populations and diffusive species separation. The observed insensitivity of ion temperature to a varying deuterium fraction is shown to be a signature of ion thermal decoupling in shock-heated plasmas. The burn-averaged deuterium fraction calculated from the experimental data demonstrates a reduction in the average core deuterium density, as predicted by simulations that use a diffusion model. Accounting for each of these effects in simulations reproduces the observed yield trends. In inertial confinement fusion (ICF), targets are imploded to generate a high-density, high-temperature environment where fusion can occur [1,2]. In the current ignition design, four weak shocks compress the cryogenic deuterium-tritium (DT) fuel, then combine into a single strong shock with Mach number ∼10-50 in the central gas, a DT vapor with initial density 0.3 mg=cc [3]. Convergence of this shock at the implosion's center sets the initial entropy of the central plasma "hot spot" and generates a brief period of fusion production ("shock bang"). The rebounding shock strikes the imploding fuel, beginning the hot spot compression that generates the main period of nuclear production ("compression burn"). Understanding the evolution of the plasma during the shock transit phase is fundamentally important for achieving ICF ignition, as this sets the initial conditions for hot spot formation, compression, ignition, and burn [4].The simulations used to design ICF experiments generally assume a single average-ion hydrodynamic framework. The equations of motion for a single ion-species plasma are solved iteratively to model the implosion. Multiple ion species are not treated separately: the ion mass and charge are set as a weighted average of the individual species. Recent experimental and theoretical work has questioned the validity of the average-ion assumption [5][6][7][8][9][10][11][12][13][14][15]. Anomalous reduction of the compression-phase nuclear yield has been observed in implosions filled with multiple fuel species, such as deuteriumhelium-3 (D 3 He) [5], DT [6], and other combinations [7,8]. Anomalous reduction of the shock yield has been ambiguous in these studies. Diffusive ion species separation driven by gradients in pressure [9], electric potential [10,11], and temperature [12] is a potential cause of these observations [13]. Kinetic physics can impact the evolution and nuclear performance of multispecies plasmas in computational studies [14,15], although, to the best of our knowledge, no fully kinetic model is yet capable of simulating an entire ICF implosion.The experiments described in this Letter demonstrate, for the first time, signatures of two multiple-ion kinetic phys...

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Thermo-diffusion in inertially confined plasmas

Kagan

Tang

2014

Physics Letters A

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In a plasma of multiple ion species, thermodynamic forces such as pressure and temperature gradients can drive ion species separation via inter-species diffusion. Unlike its neutral mix counterpart, plasma thermo-diffusion is found comparable to, or even much larger than, baro-diffusion. It is shown that such a strong effect is due to the long-range nature of the Coulomb potential, as opposed to short-range interactions in neutral gases. A special composition of the tritium and 3 He fuel is identified to have vanishing net diffusion during adiabatic compression, and hence provides an experimental test in which yield degradation is minimized during ICF implosions.In inertial confinement fusion (ICF), the central "hotspot" plasma, assembled by laser-driven spherical implosion [1], contains multiple ion species. Common combinations include low-Z fuel mixtures such as deuterium (D)/tritium (T) and D 3 He with possible addition of high-Z pusher ions, such as carbon or silicon, due to plastic or glass shell mixing [2,3] into the gas fill. Sometimes high-Z gas dopants such as Ar [4] or Kr [5] are intentionally introduced for diagnostic purposes, as well as to specifically study the pre-mix effects [6,7]. The powerful thermodynamic forces (e.g. pressure [8][9][10] and temperature gradients [9,10]) in an imploding target can drive ion species separation via inter-species diffusion. Observation of the resulting fuel stratification in the DT implosion, which upsets the initially optimal arrangement of equal number densities of D and T, in experiments [11] and kinetic simulations [12][13][14][15] have recently been reported. The targets with high-Z dopants show a particularly strong yield anomaly [6,7,16], suggesting that even stronger fuel stratification may take place.Perhaps the most intriguing physics aspect of interion-species diffusion in a collisional plasma is the role of thermo-diffusion, which, as its name suggests, is driven by the gradients of ion and electron temperatures. The novelty comes through as a sharp contrast to the better-known case of a neutral mixture, where thermo-diffusion is substantially less important than baro-diffusion, though often counteracts it [9]. According to statistical physics, thermo-diffusion strongly depends on the details of the collisional exchange between and within the species [10]. Due to the long range nature of Coulomb collisions in plasmas, as opposed to short range collisions between neutral particles, one may expect thermo-diffusion in plasmas and neutral mixtures to be fundamentally different. This difference becomes particularly striking with the observation that plasma baro-diffusion ratio k p is identical to its neutral counterpart [17].

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The effects of pre-mix on burn in ICF capsules

Cited by 25 publications

References 12 publications

The effects of laser absorption on direct-drive capsule experiments at OMEGA

The effects of laser absorption on direct-drive capsule experiments at OMEGA

Ion Thermal Decoupling and Species Separation in Shock-Driven Implosions

Thermo-diffusion in inertially confined plasmas

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