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1
Dewald, E. L., S. A. MacLaren, D. A. Martinez, J. E. Pino, R. E. Tipton, D. D. M. Ho, C. V. Young et al. "First graded metal pushered single shell capsule implosions on the National Ignition Facility". Physics of Plasmas 29, n. 5 (maggio 2022): 052707. http://dx.doi.org/10.1063/5.0083089.
Testo completoAbstract (sommario):
Graded metal pushered single shell (PSS) capsules are predicted to be a viable alternative to low-Z capsule indirect drive inertial confinement fusion (ICF) implosions for achieving high fusion yields [MacLaren et al., Phys. Plasmas 28, 122710 (2021)]. The first experiments with Be/Cr-graded metal PSS capsules indicate that the implementation of the principle design feature, the graded density inner metal layer, has succeeded in producing a stable implosion with performance in agreement with predictions. With 50% Cr concentration in the pusher, PSS capsules have greater than ∼2× higher shell densities during stagnation for enhanced core confinement and radiation trapping at ∼35% lower shell implosion velocities than low-Z capsules. High-energy >30 keV inflight shell radiography recorded 215 km/s implosion velocities and show that implosion Legendre mode P2 asymmetry can be tuned via inner-to-outer beam wavelength separation, similar to other implosions. Shell radiographs and neutron core images show similar P2 asymmetry, suggesting no symmetry swings between peak implosion velocity and stagnation times. Despite the modest implosion velocities, gas-filled deuterium–tritium capsule implosions generate 1015 neutron yields at relatively modest core ion temperatures of 2.75 keV, indicating that in spite of the high-density inner layer, the implosions have been stabilized by the design density gradient. When compared with hydrodynamic simulations, the measured yield-over-simulated is 35% due to fuel–pusher mix and other perturbations such as the capsule fill tube. Simple analytical scalings of hot spot pressure and neutron yield show that PSS implosions reach similar performance at lower implosion velocities and higher shell densities to low-Z ICF capsules.
2
Choe, W. H., e R. C. Venkatesan. "Self-similar solutions of screw-pinch plasma implosion". Laser and Particle Beams 8, n. 3 (settembre 1990): 485–91. http://dx.doi.org/10.1017/s0263034600008727.
Testo completoAbstract (sommario):
A self-similar analysis of supersonic compression of a “screw-pinch” plasma is carried out that generalizes earlier analyses of pure θ-pinch and Z-pinch implosions. Solutions are found for various implosion modes. It is shown that the screw-pinch plasma implosion differs qualitatively from θ-pinch and Z-pinch implosions.
3
Lindl, John D., Steven W. Haan e Otto L. Landen. "Impact of hohlraum cooling on ignition metrics for inertial fusion implosions". Physics of Plasmas 30, n. 1 (gennaio 2023): 012705. http://dx.doi.org/10.1063/5.0113138.
Testo completoAbstract (sommario):
This paper extends the evaluation of ignition metrics to include the impact of hohlraum cooling before peak implosion velocity in radiation driven implosions. First, we provide an extension of the results for the key hot spot stagnation quantities from the 2018 paper [Lindl et al., Phys Plasmas 25, 122704 (2018)]. The modified analytic expressions presented here match the Hydra results for these National Ignition Facility scale implosions both with and without hohlraum cooling before peak velocity if the effective ablation pressure Pabl(effective) = Pabl(tpv − 0.5 ns) is used in the analytic formulas, where tpv is the time of peak implosion velocity. Second, we provide an analysis that enables a comparison of the Hydra radiation hydrodynamics code calculations utilized here with the predictions of the analytic piston model [Hurricane et al., Phys. Plasmas 29, 012703 (2022)] of an ICF implosion, which focused on sensitivity to time duration of the hohlraum cooling phase before peak velocity (often called the “coast time”) and the shell radius at peak velocity Rpv. Third, we provide a set of ignition metrics that are valid across a wide range of capsule designs valid for implosions both with and without hohlraum cooling before peak implosion velocity is reached.
4
Manheimer, W., e D. Colombant. "Effects of viscosity in modeling laser fusion implosions". Laser and Particle Beams 25, n. 4 (dicembre 2007): 541–47. http://dx.doi.org/10.1017/s0263034607000663.
Testo completoAbstract (sommario):
AbstractThis paper examines the necessity of including ion viscosity in modeling laser fusion implosions. Using the Naval Research Laboratory one-half Mega Joule laser fusion target as an example, it is shown that for virtually the entire implosion up to maximum compression, and the entire rebound after the implosion, ion viscosity is unimportant. However for about half a nanosecond before peak implosion, ion viscosity can have a significant, but by no means dominant effect on both the one-dimensional flow and on the Rayleigh-Taylor instability.
5
Baker, K. L., O. Jones, C. Weber, D. Clark, P. K. Patel, C. A. Thomas, O. L. Landen et al. "Hydroscaling indirect-drive implosions on the National Ignition Facility". Physics of Plasmas 29, n. 6 (giugno 2022): 062705. http://dx.doi.org/10.1063/5.0080732.
Testo completoAbstract (sommario):
A goal of the laser-based National Ignition Facility (NIF) is to increase the liberated fusion energy “yield” in inertial confinement fusion experiments well past the ignition threshold and the input laser energy. One method of increasing the yield, hydrodynamic scaling of current experiments, does not rely on improving compression or implosion velocity, but rather increases the scale of the implosion to increase hotspot areal density and confinement time. Indirect-drive ( Hohlraum driven) implosions carried out at two target sizes, 12.5% apart, have validated hydroscaling expectations. Moreover, extending comparisons to the best-performing implosions at five different capsule sizes shows that their performance also agrees well with hydroscaling expectations even though not direct hydroscales of one another. In the future, by switching to a reduced loss Hohlraum geometry, simulations indicate that we can drive 20% larger-scale implosions within the current power and energy limitations on the NIF. At the demonstrated compression and velocity of these smaller-scale implosions, these 1.2× hydroscaled implosions should put us well past the ignition threshold.
6
Li, Chuanying, Jianfa Gu, Fengjun Ge, Zhensheng Dai e Shiyang Zou. "Impact of different electron thermal conductivity models on the performance of cryogenic implosions". Physics of Plasmas 29, n. 4 (aprile 2022): 042702. http://dx.doi.org/10.1063/5.0066708.
Testo completoAbstract (sommario):
The electron thermal conduction strongly affects the hot-spot formation and the hydrodynamic instability growth in inertial confinement fusion implosions. A harmonic-mean flux-limited conductivity model has been widely used in implosion simulations. In this paper, using the high foot implosion N140520 as an example, we have performed a series of one-dimensional (1D) no-alpha simulations to quantify the impact of different conductivity models including the Spitzer–Harm model, the Lee–More model, and the recently proposed coupled Gericke-Murillo-Schlanges model [Ma et al., Phys. Rev. Lett. 122, 015001 (2019)] with the flux limiter fe ranging from 0.03 to 0.15 on the performance of cryogenic implosions. It is shown that varying fe has a bigger impact on the performance than changing conductivity models. Therefore, we have only performed two-dimensional (2D) no-alpha simulations using the Lee–More model with different flux limiters [Formula: see text] to quantify the effect of the electron thermal conduction on the performance, with single-mode velocity perturbations with different mode numbers L seeded on the inner shell surface near the peak implosion velocity. We find that in both the 1D implosions and the 2D implosions with the same L, increasing fe leads to more hot-spot mass and lower hot-spot-averaged ion temperature, resulting in approximately constant hot-spot internal energy. In addition, the no-alpha yield [Formula: see text] is dominated by the neutron-averaged ion temperature Tn in these two cases. Increasing [Formula: see text] from 0.0368 to 0.184 reduces Tn by ∼15% in 1D and by ∼20% for the 2D implosions with the same L, both leading to a ∼20% reduction in [Formula: see text].
7
Roycroft, R., J. P. Sauppe e P. A. Bradley. "Double cylinder target design for study of hydrodynamic instabilities in multi-shell ICF". Physics of Plasmas 29, n. 3 (marzo 2022): 032704. http://dx.doi.org/10.1063/5.0083190.
Testo completoAbstract (sommario):
Cylindrical implosions are used to study hydrodynamic instability growth for inertial confinement fusion (ICF) applications, as the cylindrical geometry allows for easier diagnostic access while retaining convergence effects. In this work, we use the established cylindrical implosion platform [Palaniyappan et al., Phys. Plasmas 27, 042708 (2020)] to inform the double shell ICF campaign [Montgomery et al., Phys. Plasmas 25, 092706 (2018)]. We present a design for a double cylindrical target as an analogue to the double shell ICF capsule in order to study hydrodynamic instability growth on the high-Z inner shell. Our design work is done with two-dimensional (2D) Eulerian radiation-hydrodynamics simulations, considering the axial uniformity of the implosion and feasibility of measuring the instability growth of pre-seeded single mode sinusoidal perturbations. We discuss in depth the design for a target to be directly driven at the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)]. We evaluate the design for axial implosion symmetry and visibility of instability growth using synthetic radiographs constructed from the simulations, as the instability growth on the inner cylinder is experimentally measured using x-ray radiography of the implosion. We find that the seeded perturbation growth on the inner cylinder should be visible in an experiment, even with axial implosion asymmetry and preheat. We compare our 2D simulations with linear theory predictions for perturbation growth and show that a cylinder with lower azimuthal mode number (mode-20) perturbations compares more favorably with linear theory, while a cylinder with higher azimuthal mode number (mode-40) perturbations at the same starting amplitude saturates and is over-predicted by linear theory.
8
Barlow, D., T. Goffrey, K. Bennett, R. H. H. Scott, K. Glize, W. Theobald, K. Anderson et al. "Role of hot electrons in shock ignition constrained by experiment at the National Ignition Facility". Physics of Plasmas 29, n. 8 (agosto 2022): 082704. http://dx.doi.org/10.1063/5.0097080.
Testo completoAbstract (sommario):
Shock ignition is a scheme for direct drive inertial confinement fusion that offers the potential for high gain with the current generation of laser facility; however, the benefits are thought to be dependent on the use of low adiabat implosions without laser–plasma instabilities reducing drive and generating hot electrons. A National Ignition Facility direct drive solid target experiment was used to calibrate a 3D Monte Carlo hot-electron model for 2D radiation-hydrodynamic simulations of a shock ignition implosion. The [Formula: see text] adiabat implosion was calculated to suffer a 35% peak areal density decrease when the hot electron population with temperature [Formula: see text] and energy [Formula: see text] was added to the simulation. Optimizing the pulse shape can recover [Formula: see text] of the peak areal density lost due to a change in shock timing. Despite the harmful impact of laser–plasma instabilities, the simulations indicate shock ignition as a viable method to improve performance and broaden the design space of near ignition high adiabat implosions.
9
Nishimura, H., H. Shiraga, T. Endo, H. Takabe, M. Katayama, Y. Oshikane, M. Nakamura, Y. Kato e S. Nakai. "Radiation-driven cannonball targets for high-convergence implosions". Laser and Particle Beams 11, n. 1 (marzo 1993): 89–96. http://dx.doi.org/10.1017/s0263034600006947.
Testo completoAbstract (sommario):
In the last few years, systematic studies on radiation hydrodynamics in the X-ray confining cavity and a fuel capsule have attained remarkable progress. This makes it possible to analyze quantitatively the energy transfer processes from laser to the fusion capsule and find uniform irradiation conditions of the fusion capsule driven by thermal X rays. As a result, reproducible and stable implosions were achieved. Throughout implosion experiments with the Gekko XII blue laser system (351 nm, kJ, 0.8 ns), good agreement of implosion has been obtained between the experiment and numerical simulations, assuming perfectly spherical symmetry, up to a radial convergence ratio of 15. Described are particularly the issues of (1) energy transfer processes from laser to a fuel capsule and conditions for uniform irradiation, (2) properties of the X-ray propagation through aluminum heated by X-ray radiation, and (3) dependence of the convergence ratio of Ri/Rf (where Ri and Rf are the initial and final radii) of the capsule on the initial fill pressure of D–T gas and its influence on the core parameters and fusion products to evaluate implosion sphericity.
10
Christopherson, A. R., R. Betti, C. J. Forrest, J. Howard, W. Theobald, E. M. Campbell, J. Delettrez et al. "Inferences of hot electron preheat and its spatial distribution in OMEGA direct drive implosions". Physics of Plasmas 29, n. 12 (dicembre 2022): 122703. http://dx.doi.org/10.1063/5.0091220.
Testo completoAbstract (sommario):
Hot electrons generated from laser plasma instabilities degrade performance of direct drive implosions by preheating the deuterium and tritium (DT) fuel resulting in early decompression and lower areal densities at stagnation. A technique to quantify the hot electron preheat of the dense DT fuel and connect it to the degradation in areal density is described in detail. Hot electrons are measured primarily from the hard x-rays they emit as they slow down in the target. The DT preheat is inferred from a comparison of the hard x-ray signals between a DT-layered implosion and its mass equivalent ablator only implosion. The preheat energy spatial distribution within the imploding shell is inferred from experiments using high Z payloads of varying thicknesses. It is found that the electrons deposit their energy uniformly throughout the shell material. For typical direct-drive OMEGA implosions driven with an overlapped intensity of [Formula: see text], approximately [Formula: see text] of the laser energy is converted into preheat of the stagnated fuel which corresponds to areal density degradations of 10%–20%. The degradations in areal density explain some of the observed discrepancies between the simulated and measured areal densities.
11
Ikeda, C. M., J. Wilkerling e J. H. Duncan. "The implosion of cylindrical shell structures in a high-pressure water environment". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469, n. 2160 (8 dicembre 2013): 20130443. http://dx.doi.org/10.1098/rspa.2013.0443.
Testo completoAbstract (sommario):
The implosion of cylindrical shell structures in a high-pressure water environment is studied experimentally. The shell structures are made from thin-walled aluminium and brass tubes with circular cross sections and internal clearance-fit aluminium end caps. The structures are filled with air at atmospheric pressure. The implosions are created in a high-pressure tank with a nominal internal diameter of 1.77 m by raising the ambient water pressure slowly to a value, P c , just above the elastic stability limit of each shell structure. The implosion events are photographed with a high-speed digital movie camera, and the pressure waves are measured simultaneously with an array of underwater blast sensors. For the models with larger values of length-to-diameter ratio, L / D 0 , the tubes flatten during implosion with a two-lobe (mode 2) cross-sectional shape. In these cases, it is found that the pressure wave records scale primarily with P c and the time scale (where R i is the internal radius of the tube and ρ is the density of water), whereas the details of the structural design produce only secondary effects. In cases with smaller values of L / D 0 , the models implode with higher-mode cross-sectional shapes. Pressure signals are compared for various mode-number implosions of models with the same available energy, P c V , where V is the internal air-filled volume of the model. It is found that the pressure records scale well temporally with the time scale , but that the shape and amplitudes of the pressure records are strongly affected by the mode number.
12
Haines, Brian M., J. P. Sauppe, B. J. Albright, W. S. Daughton, S. M. Finnegan, J. L. Kline e J. M. Smidt. "A mechanism for reduced compression in indirectly driven layered capsule implosions". Physics of Plasmas 29, n. 4 (aprile 2022): 042704. http://dx.doi.org/10.1063/5.0083299.
Testo completoAbstract (sommario):
High-yield implosions on the National Ignition Facility rely on maintaining low entropy in the deuterium–tritium fuel, quantified by its adiabat, in order to efficiently couple energy to the hot spot through high compression of the fuel layer. We present very-high-resolution xRAGE simulation results that study the impacts of interfacial mixing and the jetting of materials due to surface defects, defects on internal interfaces, voids, and engineering features on fuel layer compression. Defects and voids are typically neglected in implosion simulations due to their small size and three-dimensional geometry. Our results showed that supersonic jets of material arise through weak spots in the shell at peak implosion velocity that prevent uniform compression of the fuel layer even when they do not introduce contaminant into the hot spot. This occurs despite maintaining low fuel entropy, since the formation of the weak spots involves nonradial displacement of fuel mass. In contrast, simulations show that fuel–ablator mixing due to interfacial instabilities has a much smaller impact on compression. We show that defects on interior interfaces of plastic capsules decrease compression by 15% to 25% and interfacial mixing between the ablator and fuel decreases compression by less than 1% for implosions with plastic or high-density carbon (HDC) ablators. For low adiabat implosions, the impact of jetting seeded by the support tent can also decrease the compression by 25%. We demonstrate that the inclusion of interior defects in simulations can explain the inferred compression in two fielded plastic capsule implosions and that the inclusion of voids, for which available characterization has large uncertainties, in simulations of HDC capsule implosions has a qualitatively consistent impact. This mechanism offers a potential explanation for persistently overestimated fuel compression in design simulations of layered implosions on the National Ignition Facility.
13
Sugitani, Koji, Yasuo Fukui e Katsuo Ogura. "Bright-rimmed clouds with IRAS point sources: candidates for star formation by radiation-driven implosion". Symposium - International Astronomical Union 147 (1991): 498–99. http://dx.doi.org/10.1017/s0074180900240163.
Testo completoAbstract (sommario):
We present preliminary results of a survey of bright-rimmed clouds associated with IRAS point sources.Bright-rimmed globules associated with old HII regions have long been suspected as a potential site for star formation. Physical conditions of such clouds seem to well match to models of radiation-driven implosion, which have been studied as an effective process for induced star formation (e.g. Klein et al. 1985, Bertoldi 1989). Bright-rimmed globules associated with IRAS point sources are good candidates for the sites of induced star formation. Three well-established cases of radiation-driven implosions in bright-rimmed globules (Ori I-2, IC1396-n, and L1206) were reported (Sugitani et al. 1989). Similar examples were also reported in HH46/47 (Olberg et al. 1989) and in GN21.38.9 (Duvert et al. 1990). However, the samples are still not numerous enough to establish comprehensive understanding of star formation by such implosion process.
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Sugitani, Koji, Yasuo Fukui e Katsuo Ogura. "Bright-rimmed clouds with IRAS point sources: candidates for star formation by radiation-driven implosion". Symposium - International Astronomical Union 147 (1991): 498–99. http://dx.doi.org/10.1017/s0074180900199541.
Testo completoAbstract (sommario):
We present preliminary results of a survey of bright-rimmed clouds associated with IRAS point sources.Bright-rimmed globules associated with old HII regions have long been suspected as a potential site for star formation. Physical conditions of such clouds seem to well match to models of radiation-driven implosion, which have been studied as an effective process for induced star formation (e.g. Klein et al. 1985, Bertoldi 1989). Bright-rimmed globules associated with IRAS point sources are good candidates for the sites of induced star formation. Three well-established cases of radiation-driven implosions in bright-rimmed globules (Ori I-2, IC1396-n, and L1206) were reported (Sugitani et al. 1989). Similar examples were also reported in HH46/47 (Olberg et al. 1989) and in GN21.38.9 (Duvert et al. 1990). However, the samples are still not numerous enough to establish comprehensive understanding of star formation by such implosion process.
15
Baltazar, J., R. Betti, K. Churnetski, V. Gopalaswamy, J. P. Knauer, D. Patel, H. G. Rinderknecht et al. "Diagnosing low-mode (ℓ < 6) and mid-mode (6 ≤ ℓ ≤ 60) asymmetries in the post-stagnation phase of laser-direct-drive deuterium–tritium cryogenic implosions on OMEGA". Review of Scientific Instruments 93, n. 12 (1 dicembre 2022): 123513. http://dx.doi.org/10.1063/5.0101653.
Testo completoAbstract (sommario):
Low- and mid-mode perturbations are possible candidates for performance limitations in cryogenic direct-drive implosions on the OMEGA laser at the Laboratory of Laser Energetics. Simulations with a 3D hydrocode demonstrated that hotspot imagers do not show evidence of the shell breakup in the dense fuel. However, these same simulations revealed that the low- and mid-mode perturbations in the dense fuel could be diagnosed more easily in the post-stagnation phase of the implosion by analyzing the peak in the x-ray emission limb at the coronal–fuel interface than before or at the stagnation phase. In experiments, the asymmetries are inferred from gated images of the x-ray emission of the implosion by using a 16-pinhole array imager filtered to record x-ray energies >800 eV and an x-ray framing camera with 40-ps time integration and 20- μm spatial resolution. A modal analysis is applied to the spatial distribution of the x-ray emission from deuterium and tritium cryogenic implosions on OMEGA recorded after the bang time to diagnose the low- and mid-mode asymmetries, and to study the effect that the beam-to-target ratio ( Rb/ Rt) has on the shell integrity.
16
Köpcke, Maris. "Positivism’s Implosion". American Journal of Jurisprudence 66, n. 2 (25 novembre 2021): 355–71. http://dx.doi.org/10.1093/ajj/auab017.
Testo completoAbstract (sommario):
Abstract: Kletzer’s recent book The Idea of a Pure Theory illustrates the incoherence of a legal theory’s methodological commitment to “purity,” and hence to independence from moral and empirical concerns. Unlike other self-styled “positivist” accounts that pay mere lip service to this methodological agenda, Kletzer helpfully spells it out and follows it through, to the point of expunging from his account anything bearing the resemblance of an argument from first principles. He associates moral with theological reasoning, and theological reasoning in turn with legal reasoning by appeal to validating criteria. But his account pays a high price for purity. The price is the account’s internal contradiction and inconsistency with a legal theory’s criteria of success. Reflection on Kletzer’s enterprise suggests that we have reason to reject a “pure” method in doing legal theory.
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Peters, Han, e Liz Vivas. "Parabolic Implosion". Notices of the American Mathematical Society 67, n. 08 (1 settembre 2020): 1. http://dx.doi.org/10.1090/noti2132.
Testo completo
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Zavattaro, Staci M. "Organizational Implosion". Administration & Society 46, n. 9 (20 ottobre 2014): 1071–91. http://dx.doi.org/10.1177/0095399714554681.
Testo completoAbstract (sommario):
Detroit, Michigan, is on the brink: Financial mismanagement, population exodus, increasing legacy costs, and out-of-control debt have driven it to bankruptcy. City actors, both administrative and elected, making politically driven decisions invited the disaster. This article uses the concepts of organizational implosion and image management to examine the degree to which the city indeed suffered organization implosion and how the city presented its image, internally and externally. The article synthesizes the administrative and communication literature streams to find that despite an overall rebranding effort, city actors still are falling short when generating positive narratives and trying to change organizational culture.
19
Yen, Nai‐chyuan. "Implosion sound". Journal of the Acoustical Society of America 98, n. 5 (novembre 1995): 2876. http://dx.doi.org/10.1121/1.413179.
Testo completo
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Guillemin, Victor, Lisa Jeffrey Jeffrey e Reyer Sjamaar Sjamaar. "Symplectic Implosion". Transformation Groups 7, n. 2 (1 maggio 2002): 155–85. http://dx.doi.org/10.1007/s00031-002-0009-y.
Testo completo
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André, M., D. Babonneau, C. Bayer, M. Bernard, J.-L. Bocher, J. Bruneau, A. Coudeville et al. "Progress in inertial confinement fusion physics at Centre d'Etudes de Limeil-Valenton". Laser and Particle Beams 12, n. 3 (settembre 1994): 329–42. http://dx.doi.org/10.1017/s0263034600008181.
Testo completoAbstract (sommario):
The laser program developed at the Centre d'Etudes de Limeil-Valenton, Saint-Georges, France (CEL-V) is concentrated on a systematic investigation of indirect drive fusion; by comparison with direct drive, this process is expected to provide the required irradiation uniformity with relaxed constraints on laser beam quality. The main concerns are radiative transfer and preheat, hydrodynamic instabilities, and high-density X-ray driven implosions. Ablative implosion experiments have been conducted with the two beams at the Phebus facility (5 kJ, 1.3 ns, 0.35 μm). Symmetry was proved to be controlled by the casing structure, following scaling laws describing hohlraum physics. A compressed DT density ∼100 ρ0 (ρ0 liquid DT density) has been deduced from activation measurements. Different aspects of the soft X-ray transfer processes, and particularly of the ablation of a low-Z material, which drives the capsule implosion, are dealt with in detailed investigations. Reported here are results on X-ray reemission and penetration in several materials, and on induced hydrodynamics of accelerated foils. The laser energy required to reach fuel ignition conditions has been evaluated from numerical simulations as well as from analytical models, taking into account hohlraum physics, capsule implosion, hot spot formation, and burn propagation. Several crucial parameters have been drawn, the most important being the radiation temperature. A target gain in the order of 10 appears achievable with a 2-MJ laser.
22
Sio, H., O. Larroche, A. Bose, S. Atzeni, J. A. Frenje, N. V. Kabadi, M. Gatu Johnson et al. "Fuel–shell mix and yield degradation in kinetic shock-driven inertial confinement fusion implosions". Physics of Plasmas 29, n. 7 (luglio 2022): 072710. http://dx.doi.org/10.1063/5.0087905.
Testo completoAbstract (sommario):
Fuel–shell mix in kinetic plasma conditions is probed using nuclear and x-ray self-emission in shock-driven, D3He-gas-filled inertial confinement fusion implosions. As initial gas fill density decreases, measured nuclear yields and ion temperatures are lower than expected as compared to radiation-hydrodynamic simulations. Spatially and temporally resolved x-ray emissions indicate significant mixing at the fuel–shell interface in implosions with low initial gas fill density. This observed fuel–shell mix introduces a substantial amount of shell ions into the center of the implosion prior to and during shock flash and is the key mechanism needed in the kinetic-ion simulations to match experimental nuclear yields.
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HEYA, MANABU, HIROYUKI SHIRAGA, ATSUSHI SUNAHARA, MIKIO NAKASUJI, MASAHARU NISHIKINO, HIROSHI HONDA, KAZUHISA FUJITA et al. "Implosion experiments of gas-filled plastic-shell targets with [ell ] = 1 drive nonuniformity at the Gekko-XII glass laser". Laser and Particle Beams 19, n. 2 (aprile 2001): 267–84. http://dx.doi.org/10.1017/s0263034601192177.
Testo completoAbstract (sommario):
Effects of an implosion nonuniformity with [ell ] = 1 ([ell ]: Legendre polynomial mode number) on the hot spark formation were investigated in a series of direct-drive implosion experiments at the Gekko-Xll glass laser (Yamanaka et al., 1987). The implosion dynamics and the performance from the early to final stage of the implosion were observed with a variety of X-ray imaging and neutron diagnostics. A drive nonuniformity in the implosion with [ell ] = 1 was observed in the shape of the accelerated target at the early stage of the implosion. At the final stage of the implosion, the resultant nonuniformity with [ell ] = 1 was also observed as a geometrical shift of core plasmas from the center of the chamber. The observed neutron yield and X-ray emission properties at the final stage of the implosion were significantly degraded with an increase of the implosion nonuniformity with [ell ] = 1. The experimental results were compared with one-dimensional (1-D) and two-dimensional (2-D) hydrodynamic simulations. As a result, it was found that the implosion nonuniformity with [ell ] = 1 shifts the whole implosion dynamics towards its direction and prevents the confinement of the gas fuel considerably. However, the experimentally observed degradation in the hot spark formation, such as reductions in neutron yield and features in X-ray emission, can be reproduced in 2-D simulations not with an asymmetric perturbation of [ell ] = 1 only but with multimode nonuniformities such as [ell ] = 1 coupled with some additional middle-mode ones (e.g., [ell ] = 6). Such a complex spike structure caused by the multimode nonuniformities was found to be essential for the experimentally observed rapid cooling of the hot spark.
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Walsh, C. A., R. Florido, M. Bailly-Grandvaux, F. Suzuki-Vidal, J. P. Chittenden, A. J. Crilly, M. A. Gigosos et al. "Exploring extreme magnetization phenomena in directly driven imploding cylindrical targets". Plasma Physics and Controlled Fusion 64, n. 2 (12 gennaio 2022): 025007. http://dx.doi.org/10.1088/1361-6587/ac3f25.
Testo completoAbstract (sommario):
Abstract This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realizable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10 kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally driven or current-driven transport is dominating.
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Lees, A., R. Betti, J. P. Knauer, V. Gopalaswamy, D. Patel, K. M. Woo, K. S. Anderson et al. "Understanding the fusion yield dependencies in OMEGA DT-layered implosion experiments using a physics-based statistical mapping model". Physics of Plasmas 30, n. 1 (gennaio 2023): 012709. http://dx.doi.org/10.1063/5.0106515.
Testo completoAbstract (sommario):
Improving the performance of inertial confinement fusion implosions requires physics models that can accurately predict the response to changes in the experimental inputs. Good predictive capability has been demonstrated for the fusion yield using a statistical mapping of simulated outcomes to experimental data [Gopalaswamy et al., Nature 565(771), 581–586 (2019)]. In this paper, a physics-based statistical mapping approach is used to extract and quantify all the major sources of degradation of fusion yield for direct-drive implosions on the OMEGA laser. The yield is found to be dependent on the age of the deuterium tritium fill, the [Formula: see text] asymmetry in the implosion core, the laser beam-to-target size ratio, and parameters related to the hydrodynamic stability. A controlled set of experiments were carried out where only the target fill age was varied while keeping all other parameters constant. The measurements were found to be in excellent agreement with the fill age dependency inferred using the mapping model. In addition, a new implosion design was created, guided by the statistical mapping model by optimizing the trade-offs between increased laser energy coupling at larger target size and the degradations caused by the laser beam-to-target size ratio and hydrodynamic instabilities. When experimentally performed, an increased fusion yield was demonstrated in targets with larger diameters.
26
KYRALA, GEORGE A., NORMAN DELAMATER, DOUGLAS WILSON, JOYCE GUZIK, DON HAYNES, MARK GUNDERSON, KENNETH KLARE, ROBERT W. WATT, WILLIAM M. WOOD e WILLIAM VARNUM. "Direct drive double shell target implosion hydrodynamics on OMEGA". Laser and Particle Beams 23, n. 2 (giugno 2005): 187–92. http://dx.doi.org/10.1017/s0263034605050330.
Testo completoAbstract (sommario):
Imploding indirect-drive double shell targets may provide an alternative, non-cryogenic path to ignition at the National Ignition Facility (NIF). Experiments are being pursued at OMEGA to understand the hydrodynamics of these implosions and the possibility of scaling it to the NIF design. We have used 40 beams from the OMEGA laser to directly drive the capsules, and we have used the remaining 20 beams to backlight the imploding shells from two different directions at multiple times. We will review the recent experiments to measure the hydrodynamics of the targets using two-view X-ray radiography of the capsules. We will present data on measured yields from the targets. We will present a measured time history of the hydrodynamics of the implosion. Experiments were pursued using direct drive in which the M-band effect (experienced in the indirect drive experiments) could be eliminated or controlled. It was learned in the direct drive experiments that the best performing capsules were those that had a thin outer layer of gold. This effectively causes M-band pre-heat effects giving implosion hydrodynamics and performance closer to the indirect drive case. We will review the methods used to radiograph the targets and the techniques used to extract useful information to compare with calculations. The effect of imperfections in the target construction will be shown to be minimal during the initial stage of implosion. The yields from the targets were observed to be uniformly low compared to indirect-drive.
27
Yanagawa, T., H. Sakagami, A. Sunahara e H. Nagatomo. "Asymmetric implosion of a cone-guided target irradiated by Gekko XII laser". Laser and Particle Beams 33, n. 3 (30 aprile 2015): 367–78. http://dx.doi.org/10.1017/s0263034615000427.
Testo completoAbstract (sommario):
AbstractIn implosion experiments of a cone-guided target using Gekko XII laser, the lasers on the cone side are not irradiated to avoid the irradiation of the cone. In such condition, the implosion process is done highly asymmetrically. Thus we evaluated the effects of the asymmetric implosion on the compression ratio of the fuel in Gekko XII irradiation orientation by three-dimensional hydro simulations. In this paper, we discuss the degradation of the compression ratio by asymmetric implosion and show that the compression ratio can be enhanced by adjusting the laser intensity between each beam to reduce the asymmetry of the implosion.
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Joshi, T. R., R. C. Shah, W. Theobald, K. Churnetski, P. B. Radha, D. Cao, C. A. Thomas, J. Baltazar e S. P. Regan. "Diagnosis of the imploding shell asymmetry in polar-direct-drive deuterium–tritium cryogenic target implosions on OMEGA". Review of Scientific Instruments 93, n. 9 (1 settembre 2022): 093524. http://dx.doi.org/10.1063/5.0101567.
Testo completoAbstract (sommario):
We discuss the analyses of gated, x-ray imaging data from polar-direct-drive experiments with cryogenically layered deuterium–tritium targets on the OMEGA laser. The in-flight shell asymmetries were diagnosed at various times during the implosion, which was caused by the beam pointing geometry and preimposed variations in the energy partition between the different groups of laser beams. The shape of the ablation surface during the acceleration phase of the implosion was measured along two different lines of sight, and a Legendre mode ( ℓ-mode) decomposition was applied for modes of up to ten to investigate shell asymmetries. A clear causal relationship between the imposed beam imbalance and the shape of the in-flight shell asymmetries was observed. The imploded shell with a balanced energy ratio shows smaller values of the amplitudes of ℓ-mode 2 compared to that from implosions with an imbalanced ring energy ratio. The amplitudes of ℓ-modes 4 and 6 are the same within the measurement uncertainty with respect to the change in beam energy ratio.
29
Kunimune, J. H., H. G. Rinderknecht, P. J. Adrian, P. V. Heuer, S. P. Regan, F. H. Séguin, M. Gatu Johnson et al. "Knock-on deuteron imaging for diagnosing the morphology of an ICF implosion at OMEGA". Physics of Plasmas 29, n. 7 (luglio 2022): 072711. http://dx.doi.org/10.1063/5.0096786.
Testo completoAbstract (sommario):
Knock-on deuteron imaging is a new diagnostic technique that is being implemented at the OMEGA laser facility to diagnose the morphology of an inertial confinement fusion (ICF) implosion. It utilizes the fact that some of the neutrons from deuterium–tritium (DT)-fusion reactions generated in the central hot-spot of an ICF implosion elastically scatter deuterons as they traverse the surrounding shell layer. The energy of these “knock-on” deuterons depends on the scattering angle, where the most energetic deuterons are forward-scattered and probe the shape of the central hot-spot, while lower-energy deuterons are made by side-scattering or slowing down in the fuel and carry information about the distribution of the dense DT-fuel layer surrounding the hot-spot. The first proof-of-concept tests have been conducted successfully. In these tests, three penumbral imagers with different views on an implosion recorded deuterons scattered from the dense shell of DT-gas-filled deuterated plastic shell implosions with prescribed offsets. Data from these experiments are presented here, along with novel analysis techniques that iteratively reconstruct the deuteron source from the data. Reconstructed hot-spot and shell radii agree with 1D hydro simulations and indicate a P1 asymmetry in the direction of the offset. A comparison of coaxial deuteron and x-ray images suggests the presence of a mix between the hot-spot and shell on the order of 15 μm. This new diagnostic capability will allow us to study asymmetries in unprecedented detail at OMEGA.
30
Rinderknecht, H. G., P. V. Heuer, J. Kunimune, P. J. Adrian, J. P. Knauer, W. Theobald, R. Fairbanks et al. "A knock-on deuteron imager for measurements of fuel and hotspot asymmetry in direct-drive inertial confinement fusion implosions (invited)". Review of Scientific Instruments 93, n. 9 (1 settembre 2022): 093507. http://dx.doi.org/10.1063/5.0099301.
Testo completoAbstract (sommario):
A knock-on deuteron imager (KoDI) has been implemented to measure the fuel and hotspot asymmetry of cryogenic inertial confinement fusion implosions on OMEGA. Energetic neutrons produced by D–T fusion elastically scatter (“knock on”) deuterons from the fuel layer with a probability that depends on ρR. Deuterons above 10 MeV are produced by near-forward scattering, and imaging them is equivalent to time-integrated neutron imaging of the hotspot. Deuterons below 6 MeV are produced by a combination of side scattering and ranging in the fuel, and encode information about the spatial distribution of the dense fuel. The KoDI instrument consists of a multi-penumbral aperture positioned 10–20 cm from the implosion using a ten-inch manipulator and a detector pack at 350 cm from the implosion to record penumbral images with magnification of up to 35×. Range filters and the intrinsic properties of CR-39 are used to distinguish different charged-particle images by energy along the same line of sight. Image plates fielded behind the CR-39 record a 10 keV x-ray image using the same aperture. A maximum-likelihood reconstruction algorithm has been implemented to infer the source from the projected penumbral images. The effects of scattering and aperture charging on the instrument point-spread function are assessed. Synthetic data are used to validate the reconstruction algorithm and assess an appropriate termination criterion. Significant aperture charging has been observed in the initial experimental dataset, and increases with aperture distance from the implosion, consistent with a simple model of charging by laser-driven EMP.
31
Phillips, J. C. "American physics implosion". Physics Today 60, n. 10 (ottobre 2007): 16. http://dx.doi.org/10.1063/1.2800083.
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Roncayolo, Marcel. "Dilution et implosion". Espaces Temps 33, n. 1 (1986): 13–14. http://dx.doi.org/10.3406/espat.1986.3311.
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33
Loizeaux, J. Mark, e Douglas K. Loizeaux. "Demolition by Implosion". Scientific American 273, n. 4 (ottobre 1995): 146–53. http://dx.doi.org/10.1038/scientificamerican1095-146.
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Qadeer, Mohammad A. "Urbanization by implosion". Habitat International 28, n. 1 (marzo 2004): 1–12. http://dx.doi.org/10.1016/s0197-3975(02)00069-3.
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35
Yamanaka, C. "Laser driven implosion". Laser and Particle Beams 8, n. 1-2 (gennaio 1990): 3–17. http://dx.doi.org/10.1017/s0263034600007783.
Testo completoAbstract (sommario):
Inertial confinement fusion (ICF) has made great progress. In fact several significant scientific firsts have been achieved in the last year. These developments have presented the ICF community with an opportunity to embark on a new phase in ICF research. The key issues of laser fusion are to attain a high absorption of laser light in a plasma, to prevent preheating of fuel during the compression, and to achieve highly efficient implosion by uniform compression of fuel due to the homogeneous deposition of laser energy on the pellet surface. Direct drive and indirect drive have been investigated. The progress in both schemes is remarkable. The neutron yield by the stagnation free compression of the LHART target has attained 1013 which corresponds to a pellet gain of 1/500. The plastic shell target has reached a fuel density as large as 600 times the liquid density which is measured by the Si activation method as well as the D knockon method. A cryogenic foam target is now under investigation.
36
Eberstadt, Nicholas. "The Population Implosion". Foreign Policy, n. 123 (marzo 2001): 42. http://dx.doi.org/10.2307/3183154.
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37
Winthrop-Young, Geoffrey. "Implosion and Intoxication". Theory, Culture & Society 23, n. 7-8 (dicembre 2006): 75–91. http://dx.doi.org/10.1177/0263276406069884.
Testo completoAbstract (sommario):
Focusing on Kittler’s reading of Goethe’s ‘Wanderer’s Nightsong’ and Pink Floyd’s ‘Brain Damage’, the article traces Kittler’s development from discourse analysis to media theory. Where more traditional approaches would stress notions of self-reflexivity (both the poem and the song elaborate on their effects and foreground their own construction), Kittler performs, in his own words, a kind of ‘implosion’: The words of Goethe’s poem collapse back into the discursive order they evoke, and Pink Floyd’s song performs its own technology. But it is precisely this implosion that has an intoxicating effect, which paves the way for a more political, or at least politicized, reading of Kittler’s work that highlights his indebtedness to the cultural transgressions of the 1960s.
38
Weidenfeld, Ursula. "Implosion einer Krisenkanzlerin?" Indes 10, n. 1-2 (14 novembre 2022): 127–35. http://dx.doi.org/10.13109/inde.2022.10.1-2.127.
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SOMEYA, TETSUO, KENTAROU MIYAZAWA, TAKASHI KIKUCHI e SHIGEO KAWATA. "Direct-indirect mixture implosion in heavy ion fusion". Laser and Particle Beams 24, n. 3 (settembre 2006): 359–69. http://dx.doi.org/10.1017/s0263034606060526.
Testo completoAbstract (sommario):
In order to realize an effective implosion, the beam illumination non-uniformity and implosion non-uniformity must be suppressed to less than a few percent. In this paper, a direct-indirect mixture implosion mode is proposed and discussed in heavy ion beam (HIB) inertial confinement fusion (HIF) in order to release sufficient fusion energy in a robust manner. On the other hand, the HIB illumination non-uniformity depends strongly on a target displacement (dz) in a reactor. In a direct-driven implosion mode dz of ∼20 μm was tolerance and in an indirect-implosion mode dz of ∼100 μm was allowable. In the direct-indirect mixture mode target, a low-density foam layer is inserted, and radiation is confined in the foam layer. In the foam layer the radiation transport is expected in the lateral direction for the HIB illumination non-uniformity smoothing. Two-dimensional implosion simulations are performed and show that the HIB illumination non-uniformity is well smoothed. The simulation results present that a large pellet displacement of ∼300 μm is tolerable in order to obtain sufficient fusion energy in HIF.
40
ROSCH, R., D. FRIART, M. DARRIGOL, L. CHATRIEUX, P. ZEHNTER, P. ROMARY e J. M. CHEVALIER. "The implosion dynamics and emission characteristics of Al liner-on-wire implosions". Laser and Particle Beams 18, n. 2 (aprile 2000): 307–13. http://dx.doi.org/10.1017/s0263034600182217.
Testo completoAbstract (sommario):
Previous experiments at 0.1 TW level have shown that stability and X-ray emission of fast Z-pinch could be significantly improved by imploding an Al vapor jet onto a very thin coaxial wire (Wessel et al., 1992). Here we present the first results of an Al Z-pinch using a similar liner but at mega-ampere level. The pinch is driven by AMBIORIX facility, a 2 TW, 0.5 Ω, 2 MA, and a 50-ns pulse-line generator. We study the effect of an Al wire and its diameter (20–50 μm) on the implosion dynamics, on X-ray yield, on-axis magnetohydrodynamics (MHD) stability, and on Rayleigh–Taylor instability of the column at stagnation. Analysis of an Al jet on Al wire shots demonstrates that X-ray yield due to emission processes in the H- and He-like ionization stages (i.e., the K-shell) is enhanced, relative to the ones with Al jet only. The wire leads also to a better symmetrization of the implosion, and to better reproducibility of the shots. X-ray signals exhibit two similar pulses, 10-ns-wide and separated by 15 ns. To discern spectrally the origin of each pulse, further experiments have been performed with stainless steel wire (25 μm in diameter). Results show that liner and wire radiate simultaneously and contribute to both pulses. Full analysis of a typical Al jet on Al wire shot, using detailed collisional-radiative equilibrium (CRE) model is given in this paper. A sketch of the pinch at stagnation, with a cold dense core embedded in a hot low density corona, reproduces well all features of X-ray emission.
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Singh, Shailendra, e Ritam Mallick. "Time-like detonation in presence of magnetic field". Laser and Particle Beams 37, n. 01 (marzo 2019): 30–37. http://dx.doi.org/10.1017/s0263034619000041.
Testo completoAbstract (sommario):
AbstractWe study the effect of magnetic field in an implosion process achieved by radiation. A time-varying sinusoidal magnetic field is seen to affect the continuous transition of space-like detonation to time-like detonation at the core of implosion region. The oscillating varying magnetic field has a significant effect in increasing the volume of the time-like detonation of the core of implosion and also modifies the time of the implosion process. This transition can have significant outcome both theoretically and experimentally in the areas of high-energy hadronization of quark–gluon plasma matter and inertial confinement fusion efforts of fuels.
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Paddock, R. W., H. Martin, R. T. Ruskov, R. H. H. Scott, W. Garbett, B. M. Haines, A. B. Zylstra et al. "One-dimensional hydrodynamic simulations of low convergence ratio direct-drive inertial confinement fusion implosions". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, n. 2189 (7 dicembre 2020): 20200224. http://dx.doi.org/10.1098/rsta.2020.0224.
Testo completoAbstract (sommario):
Indirect drive inertial confinement fusion experiments with convergence ratios below 17 have been previously shown to be less susceptible to Rayleigh–Taylor hydrodynamic instabilities, making this regime highly interesting for fusion science. Additional limitations imposed on the implosion velocity, in-flight aspect ratio and applied laser power aim to further reduce instability growth, resulting in a new regime where performance can be well represented by one-dimensional (1D) hydrodynamic simulations. A simulation campaign was performed using the 1D radiation-hydrodynamics code HYADES to investigate the performance that could be achieved using direct-drive implosions of liquid layer capsules, over a range of relevant energies. Results include potential gains of 0.19 on LMJ-scale systems and 0.75 on NIF-scale systems, and a reactor-level gain of 54 for an 8.5 MJ implosion. While the use of 1D simulations limits the accuracy of these results, they indicate a sufficiently high level of performance to warrant further investigations and verification of this new low-instability regime. This potentially suggests an attractive new approach to fusion energy. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.
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Sreedhar, V. V., e Amitabh Virmani. "Maximal Kinematical Invariance Group of Fluid Dynamics and Applications". Universe 8, n. 6 (7 giugno 2022): 319. http://dx.doi.org/10.3390/universe8060319.
Testo completoAbstract (sommario):
The maximal kinematical invariance group of the Euler equations of fluid dynamics for the standard polytropic exponent is larger than the Galilei group. Specifically, the inversion transformation (Σ:t→−1/t,x→→x→/t) leaves the Euler equation’s invariant. This duality has been used to explain the striking similarities observed in simulations of the supernova explosions and laboratory implosions induced in plasma by intense lasers. The inversion symmetry extends to discontinuous fluid flows as well. In this contribution, we provide a concise review of these ideas and discuss some applications. We also explicitly work out the implosion dual of the Sedov’s explosion solution.
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Xia, Tian Xiang, Tong Zhao, Liang Zou, Li Zhang e Feng Zhu. "Research on Two-Dimensional MHD Simulations of X-Pinch Implosion and its Physical Aspects". Applied Mechanics and Materials 525 (febbraio 2014): 316–19. http://dx.doi.org/10.4028/www.scientific.net/amm.525.316.
Testo completoAbstract (sommario):
Based on a large quantity of experimental work and study of the two-dimensional MHD (Magnetohydrodynamic) simulation describing the implosion dynamics of X-pinch, at the same time taking basic physical processes of implosion into account, this paper seeks to build a two-dimensional MHD simulation model on implosion dynamics throughout the whole constriction evolution (including formation of dense plasma, compression, generation of hot spot, X-ray pulsed radiation), determine the target area for numerical simulation, as well as the initial time for simulation and plasma initial state. As for two-dimensional MHD models which indicate the physical process during different stages, a clear boundary condition is explored along with Lagrange-Euler numerical method which strives to reproduce the dynamics of the X-pinch implosion and better study the physical properties during the X-pinch implosion dynamics. Results of this thesis will enrich the X-pinch research areas of basic theories and analytical methods, which is of great theoretical significance and application value.
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Iinuma, T., T. Karino, S. Kondo, T. Kubo, H. Kato, T. Suzuki, S. Kawata e A. I. Ogoyski. "Control of fuel target implosion non-uniformity in heavy ion inertial fusion". Laser and Particle Beams 34, n. 4 (2 novembre 2016): 729–34. http://dx.doi.org/10.1017/s0263034616000677.
Testo completoAbstract (sommario):
AbstractIn inertial fusion, one of scientific issues is to reduce an implosion non-uniformity of a spherical fuel target. The implosion non-uniformity is caused by several factors, including the driver beam illumination non-uniformity, the Rayleigh–Taylor instability (RTI) growth, etc. In this paper, we propose a new control method to reduce the implosion non-uniformity; the oscillating implosion acceleration δg(t) is created by pulsating and dephasing heavy-ion beams (HIBs) in heavy-ion inertial fusion (HIF). The δg(t) would reduce the RTI growth effectively. The original concept of the non-uniformity control in inertial fusion was proposed in [Laser Part. Beams (1993) 11, 757–768]. In this paper, it was found that the pulsating and dephasing HIBs illumination provide successfully the controlled δg(t) and that δg(t) induced by the pulsating HIBs reduces well the implosion non-uniformity. Consequently the pulsating HIBs improve a pellet gain remarkably in HIF.
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Huneault, Justin, David Plant e Andrew J. Higgins. "Rotational stabilisation of the Rayleigh–Taylor instability at the inner surface of an imploding liquid shell". Journal of Fluid Mechanics 873 (25 giugno 2019): 531–67. http://dx.doi.org/10.1017/jfm.2019.346.
Testo completoAbstract (sommario):
A number of applications utilise the energy focussing potential of imploding shells to dynamically compress matter or magnetic fields, including magnetised target fusion schemes in which a plasma is compressed by the collapse of a liquid metal surface. This paper examines the effect of fluid rotation on the Rayleigh–Taylor (RT) driven growth of perturbations at the inner surface of an imploding cylindrical liquid shell which compresses a gas-filled cavity. The shell was formed by rotating water such that it was in solid body rotation prior to the piston-driven implosion, which was propelled by a modest external gas pressure. The fast rise in pressure in the gas-filled cavity at the point of maximum convergence results in an RT unstable configuration where the cavity surface accelerates in the direction of the density gradient at the gas–liquid interface. The experimental arrangement allowed for visualisation of the cavity surface during the implosion using high-speed videography, while offering the possibility to provide geometrically similar implosions over a wide range of initial angular velocities such that the effect of rotation on the interface stability could be quantified. A model developed for the growth of perturbations on the inner surface of a rotating shell indicated that the RT instability may be suppressed by rotating the liquid shell at a sufficient angular velocity so that the net surface acceleration remains opposite to the interface density gradient throughout the implosion. Rotational stabilisation of high-mode-number perturbation growth was examined by collapsing nominally smooth cavities and demonstrating the suppression of small spray-like perturbations that otherwise appear on RT unstable cavity surfaces. Experiments observing the evolution of low-mode-number perturbations, prescribed using a mode-6 obstacle plate, showed that the RT-driven growth was suppressed by rotation, while geometric growth remained present along with significant nonlinear distortion of the perturbations near final convergence.
47
Kawata, S., K. Noguchi, T. Suzuki, T. Karino, D. Barada, A. I. Ogoyski e Y. Y. Ma. "Uniformity of fuel target implosion in heavy ion fusion". Laser and Particle Beams 33, n. 4 (9 luglio 2015): 591–99. http://dx.doi.org/10.1017/s026303461500066x.
Testo completoAbstract (sommario):
AbstractIn inertial confinement fusion the target implosion non-uniformity is introduced by a driver beams’ illumination non-uniformity, a fuel target alignment error in a fusion reactor, the target fabrication defect, etc. For a steady operation of a fusion power plant the target implosion should be robust against the implosion non-uniformities. In this paper the requirement for the implosion uniformity is first discussed. The implosion uniformity should be less than a few percent. A study on the fuel hotspot dynamics is also presented and shows that the stagnating plasma fluid provides a significant enhancement of vorticity at the final stage of the fuel stagnation. Then non-uniformity mitigation mechanisms of the heavy-ion beam (HIB) illumination are also briefly discussed in heavy ion inertial fusion (HIF). A density valley appears in the energy absorber, and the large-scale density valley also works as a radiation energy confinement layer, which contributes to a radiation energy smoothing. In HIF a wobbling HIB illumination was also introduced to realize a uniform implosion. In the wobbling HIBs illumination, the illumination non-uniformity oscillates in time and space on a HIF target. The oscillating-HIB energy deposition may contribute to the reduction of the HIBs’ illumination non-uniformity by its smoothing effect on the HIB illumination non-uniformity and also by a growth mitigation effect on the Rayleigh–Taylor instability.
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Haines, Brian M., D. E. Keller, K. P. Long, M. D. McKay, Z. J. Medin, H. Park, R. M. Rauenzahn et al. "The development of a high-resolution Eulerian radiation-hydrodynamics simulation capability for laser-driven Hohlraums". Physics of Plasmas 29, n. 8 (agosto 2022): 083901. http://dx.doi.org/10.1063/5.0100985.
Testo completoAbstract (sommario):
Hohlraums are hollow cylindrical cavities with high-Z material walls used to convert laser energy into uniform x-ray radiation drives for inertial confinement fusion capsule implosions and high energy density physics experiments. Credible computational modeling of hohlraums requires detailed modeling and coupling of laser physics, hydrodynamics, radiation transport, heat transport, and atomic physics. We report on improvements to Los Alamos National Laboratory's xRAGE radiation-hydrodynamics code in order to enable hohlraum modeling. xRAGE's Eulerian hydrodynamics and adaptive mesh refinement make it uniquely well suited to study the impacts of multiscale features in hohlraums. In order to provide confidence in this new modeling capability, we demonstrate xRAGE's ability to produce reasonable agreement with data from several benchmark hohlraum experiments. We also use xRAGE to perform integrated simulations of a recent layered high density carbon capsule implosion on the National Ignition Facility in order to evaluate the potential impacts of the capsule support tent, mixed cell conductivity methodologies, plasma transport, and cross-beam energy transfer (XBT). We find that XBT, seeded by plasma flows in the laser entrance hole (LEH), causes a slight decrease in energy coupling to the capsule and that all of these impact the symmetry of the x-ray drive such that they have an appreciable impact on the capsule implosion shape.
49
SREBRO, YAIR, DORON KUSHNIR, YONI ELBAZ e DOV SHVARTS. "Modeling turbulent mixing in inertial confinement fusion implosions". Laser and Particle Beams 21, n. 3 (luglio 2003): 355–61. http://dx.doi.org/10.1017/s0263034603213100.
Testo completoAbstract (sommario):
Recent direct drive implosion experiments, performed on the OMEGA laser, have been analyzed by comparing full two-dimensional (2D) and one-dimensional (1D) numerical simulations. The 2D simulations result in a fusion yield higher than experimental results. A simple full-mixing model, leaving only the clean region, overestimates yield degradation. Fully turbulent mixing is expected to develop in most of the mixing region; however regions slightly beyond the radius of the most penetrating spike are expected to remain clean and to contribute to fusion yield. One can correct the mixing model by redefining the clean region. Accounting for this unmixed region results in improved agreement with experimental results. Differences in central pressure, density, temperature, and fusion rate in implosions dominated by low mode number perturbations imply that mix effects might not be limited to the mix region, and that 2D simulations are necessary to describe the large scale flow affecting the central region. The same analysis has been undertaken for implosions with different convergence ratios, but with similar initial perturbation spectra. These implosions should be compared to implosions dominated by high mode number perturbations, which might be described by models based on 1D simulations.
50
Niu, Keishiro. "Implosion by Ion Beam". Kakuyūgō kenkyū 58, n. 4 (1987): 332–42. http://dx.doi.org/10.1585/jspf1958.58.332.
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