An initial design of hohlraum driven by a shaped laser pulse

Lan, Ke; Gu, Peng; Ren, Guoli; Li, Xin; Wu, Congcong; Huo, Wenyi; Lai, Dongxian; He, X. T.

doi:10.1017/s026303461000042x

Cited by 23 publications

(6 citation statements)

References 28 publications

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“…As an example, we compare the laser energy required for generating an ignition radiation pulse of 300 eV inside a golden octahedral hohlraum with that inside a traditional cylinder. We consider the ignition target recently designed for NIF [13] and use the expended plasma-filling model [11,[17][18][19] to calculate the required laser energy and the plasma filling inside the hohlraums. According to Ref.…”

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High flux symmetry of the spherical hohlraum with octahedral 6LEHs at the hohlraum-to-capsule radius ratio of 5.14

et al. 2014

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In the present Letter, we investigate a spherical hohlraums with octahedral six laser entrance holes (LEHs) for inertial fusion, which has advantages over the conventional hohlraums of cylindrical geometry since it contains only one cone at each LEH and the problems caused by the beam overlap and crossed-beam energy transfer can be eliminated and the backscattering can be reduced. In particular, our study indicates that at a specific hohlraum-to-capsule radius ratio, i.e., the golden ratio, the flux asymmetry on capsule can be significantly reduced. From our study, this golden octahedral hohlraum has robust high symmetry, low plasma filling and low backscattering. Though the golden octahedral hohlraum needs 30% more laser energy than traditional cylinder for producing the ignition radiation pulse of 300 eV, it is worth for a robust high symmetry and low backscattering. The proposed octahedral hohlraum is also flexible and can be applicable to diverse inertial fusion drive approaches. As an application, we design an ignition octahedral hohlraum for the hybrid drive.PACS numbers: 52.70. La, 52.35.Tc, 47.40.Nm Introduction-The hohlraum is crucial for the inertial fusions of both indirect drive [1][2][3] and the hybrid indirectdirect drive proposed recently (HID) [4]. In the indirect drive approach, the hohlraum is first heated by laser beams to a few million Kelvin and then the energy flux of the transferred X-ray radiation compress the deuterium-tritium capsule at a convergence ratio of 25 to 45, making the nuclear fuel finally burn in a self-sustained way. In the corresponding hohlraum design, the hohlraum shape, size and the number of Laser Entrance Hole (LEH) are optimized to balance tradeoffs among the needs for capsule symmetry, the acceptable hohlraum plasma filling, the requirements for energy and power, and the laser plasma interactions. Among many requirements, the energy coupling and flux symmetry are of most concerned. A higher energy coupling will economize the input energy and increase the fusion energy gain. More importantly, a very uniform flux from the hohlraum on the shell of capsule is mandatory because a small drive asymmetry of 1% [2] can lead to the failure of ignition. Actually, the small flux asymmetry will be magnified during the compression process due to the varied kinds of instabilities and results in a serious hot-cold fuel mixture that can dramatically lessen the temperature or density of the hot spot for ignition.Various hohlraums with different shapes have been proposed and investigated, such as cylinder hohlraum [1,2], rugby hohlraum [5-10] and elliptical hohlraum [11]. These hohlraums are elongated with a length-to-diameter ratio greater than unity and have cylindrically symmetry with two LEHs on the ends. Among all above hohlraums, the cylindrical hohlraums are used most often in inertial fusion studies and are chosen as the ignition hohlraum on NIF [3,12,13], though it breaks the spherical symmetry and leads to cross coupling between the modes.Intuitively, spherical hohlraum h...

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High flux symmetry of the spherical hohlraum with octahedral 6LEHs at the hohlraum-to-capsule radius ratio of 5.14

et al. 2014

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“…1. The size of the spherical hohlraums is designed by using the extended plasma-filling model [19] with the criterion of n e ¼ 0.1. Here, n e is the average electron density in laser hot channel at filling time, which is normalized to the critical density.…”

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First demonstration of improving laser propagation inside the spherical hohlraums by using the cylindrical laser entrance hole

Huo

Yang

et al. 2016

Matter and Radiation at Extremes

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The octahedral spherical hohlraums have natural superiority in maintaining high radiation symmetry during the entire capsule implosion process in indirect drive inertial confinement fusion. While, in contrast to the cylindrical hohlraums, the narrow space between the laser beams and the spherical hohlraum wall is usually commented. In this Letter, we address this crucial issue and report our experimental work conducted on the SGIII-prototype laser facility which unambiguously demonstrates that a simple design of cylindrical laser entrance hole (LEH) can dramatically improve the laser propagation inside the spherical hohlraums. In addition, the laser beam deflection in the hohlraum is observed for the first time in the experiments. Our 2-dimensional simulation results also verify qualitatively the advantages of the spherical hohlraums with cylindrical LEHs. Our results imply the prospect of adopting the cylindrical LEHs in future spherical ignition hohlraum design.

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“…11,27 Shown in Fig. 9 is the initial design of laser energy and R H /R C by using the extended plasma-filling model.…”

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Octahedral spherical hohlraum and its laser arrangement for inertial fusion

Lan

Liu

et al. 2014

Physics of Plasmas

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A recent publication [K. Lan et al., Phys. Plasmas 21, 010704 (2014)] proposed a spherical hohlraum with six laser entrance holes of octahedral symmetry at a specific hohlraum-to-capsule radius ratio of 5.14 for inertial fusion study, which has robust high symmetry during the capsule implosion and superiority on low backscatter without supplementary technology. This paper extends the previous one by studying the laser arrangement and constraints of octahedral hohlraum in detail. As a result, it has serious beam crossing at h L 45 , and h L ¼ 50 to 60 is proposed as the optimum candidate range for the golden octahedral hohlraum, here h L is the opening angle that the laser quad beam makes with the Laser Entrance Hole (LEH) normal direction. In addition, the design of the LEH azimuthal angle should avoid laser spot overlapping on hohlraum wall and laser beam transferring outside hohlraum from a neighbor LEH. The octahedral hohlraums are flexible and can be applicable to diverse inertial fusion drive approaches. This paper also applies the octahedral hohlraum to the recent proposed hybrid indirect-direct drive approach. V C 2014 AIP Publishing LLC.

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An initial design of hohlraum driven by a shaped laser pulse

Cited by 23 publications

References 28 publications

High flux symmetry of the spherical hohlraum with octahedral 6LEHs at the hohlraum-to-capsule radius ratio of 5.14

High flux symmetry of the spherical hohlraum with octahedral 6LEHs at the hohlraum-to-capsule radius ratio of 5.14

First demonstration of improving laser propagation inside the spherical hohlraums by using the cylindrical laser entrance hole

Octahedral spherical hohlraum and its laser arrangement for inertial fusion

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