Analysis of a direct-drive ignition capsule designed for the National Ignition Facility

McKenty, P. W.; Goncharov, V. N.; Town, R. P. J.; Skupsky, S.; Betti, R.; McCrory, R. L.

doi:10.1063/1.1350571

Cited by 155 publications

(137 citation statements)

References 33 publications

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“…The predicted gain of this 1D ignition design is 27. Figure 4(b) compares the density profiles of ignition designs with all-DT (dashed curve) [4] and glass-ablator (solid curve) targets taken near the end of their acceleration phases at the same distance traveled. The profile of the glass-ablator design shows a double ablation front [23]: the outer front is driven by the electron conduction (the same mechanism that drives all-DT and plastic targets), the inner ablation front is driven by the x rays generated in plasma corona and absorbed within a glass ablator.…”

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confidence: 99%

“…The highest ignition-relevant areal densities with a shell R of $200 mg=cm 2 were achieved in cryogenic D 2 -ice implosions with plastic ablators, when the hotelectron preheat was suppressed, at a moderate laser-drive peak intensity of $5 Â 10 14 W=cm 2 and a laser energy of $16 kJ on OMEGA [11]. Because of the moderate laserdrive intensity, the implosion velocity of $2:4 Â 10 7 cm=s was lower than required for ignition on the NIF (3.5 to 4 Â 10 7 cm=s) [4]. Increasing the peak intensity to $1 Â 10 15 W=cm 2 allows the implosion velocity to be raised to levels required for ignition, but hard x-ray signals, associated with TPD hot electrons, increase with laser intensity [6,10,11].…”

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“…In direct-drive spherical implosions, the target is driven by direct illumination with overlapped laser beams. To ignite DT fuel on the National Ignition Facility (NIF) [2] with a laser energy of E L ¼ 1:5 MJ and to achieve a gain of $40 to 50 will require high fuel compression with a total target areal density ( R) of $1500 mg=cm 2 [4]. As shown in Ref.…”

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Implosion Experiments using Glass Ablators for Direct-Drive Inertial Confinement Fusion

et al. 2010

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Direct-drive implosions with 20-m-thick glass shells were conducted on the Omega Laser Facility to test the performance of high-Z glass ablators for direct-drive, inertial confinement fusion. The x-ray signal caused by hot electrons generated by two-plasmon-decay instability was reduced by more than $40Â and hot-electron temperature by $2Â in the glass compared to plastic ablators at ignition-relevant drive intensities of $1 Â 10 15 W=cm 2 , suggesting reduced target preheat. The measured absorption and compression were close to 1D predictions. The measured soft x-ray production in the spectral range of $2 to 4 keV was $2Â to 3Â lower than 1D predictions, indicating that the shell preheat caused by soft x-rays is less than predicted. A direct-drive-ignition design based on glass ablators is introduced. DOI: 10.1103/PhysRevLett.104.165002 PACS numbers: 52.57.ÀzThe goal of inertial confinement fusion (ICF) [1,2] is to implode a spherical target to achieve high compression of the fuel and high temperature in the hot spot to trigger ignition and maximize the thermonuclear energy gain. To achieve high compression, the shell entropy and temperature must remain low because it is easier to compress the fuel at a low temperature than at a high temperature [2]. The entropy is defined [3] by adiabat ¼ PðMbÞ=½2:2 ðg=ccÞ 5=3 , the ratio of the plasma pressure to the Fermi pressure of a fully degenerate electron gas [3]. In direct-drive spherical implosions, the target is driven by direct illumination with overlapped laser beams. To ignite DT fuel on the National Ignition Facility (NIF) [2] with a laser energy of E L ¼ 1:5 MJ and to achieve a gain of $40 to 50 will require high fuel compression with a total target areal density ( R) of $1500 mg=cm 2 [4]. As shown in Ref.[3], Rðmg=cm 2 Þ % 2600E L ðMJÞ 1=3 À0:6 so high areal densities require low-adiabat, 3 implosions. The fuel adiabat is determined by shocks launched at the beginning of the implosion [2]. The shock waves must be precisely tuned to set the inner portion of the shell on a low adiabat. Adiabat control is critical to achieving the desired R at peak compression [1,2]. Shock mistiming was an important cause of R degradation in direct-drive, cryogenic implosions on OMEGA and a subject of intensive research [5,6]. Another area of concern to ICF is the unstable growth of target modulations caused by hydrodynamic instabilities [1,2]. While the areal densities at peak compression have been shown to be relatively insensitive to hydrodynamic instabilities, the fusion neutron yields are very sensitive [7]. Shell preheat, another source of compression degradation, is caused by hot electrons generated by two-plasmon-decay (TPD) instability [8,9]. This preheat was shown to be virulent in DT and D 2 ablators [6,10] and was reduced by using plastic ablators [6,11]. The highest ignition-relevant areal densities with a shell R of $200 mg=cm 2 were achieved in cryogenic D 2 -ice implosions with plastic ablators, when the hotelectron preheat was suppressed, at a moderate laser-dr...

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Implosion Experiments using Glass Ablators for Direct-Drive Inertial Confinement Fusion

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“…Direct drive ignition target designs have been developed that calculate to have good performance making them attractive alternatives for NIF ignition experiments [2]. The NIF is being activated as an indirect drive facility and conversion to a direct drive facility is not planned before 2013.…”

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The ICF status and plans in the United States

2006

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Abstract. The United States continues to maintain its leadership in ICF as it moves toward the goal of ignition. The flagship of the program is the National Ignition Facility (NIF) presently under construction at LLNL. Experiments had begun on the first four beams of the National Ignition Facility just at the time of the last IFSA Conference. Several new successful campaigns have been conducted since then in planar hydrodynamics and hohlraums as well as activating the VISAR diagnostic for equation of state experiments. Highlights of these results will be reviewed. Presently, the four beam experimental capability has been suspended while the first eight beams are being installed as the first step in building out the project. Meanwhile, much progress has been made in developing ignition designs for using NIF. An array of designs having several ablator materials have been shown computationally to ignite with energies ranging from the design energy to as low as 1 MJ of laser energy. Alternative direct drive designs in the NIF indirect drive configuration have been developed by LLE. This wide array of design choices has increased the chance of achieving ignition sooner on the facility. Plans are now being developed to begin an ignition experimental campaign on NIF in 2010, a little over a year after completion of the facility. Other US facilities are also implementing improved capabilities. Petawatt lasers are now under construction at the University of Rochester and Sandia National Laboratory. The Z pulsed power machine at Sandia National Laboratory is being refurbished to improve its performance. The ongoing research program at the OMEGA laser at the University of Rochester and the Z machine at Sandia National Laboratory as well as at the Nike, Trident and Janus lasers remain strong, performing experiments supporting the NIF ignition plan and direct drive ignition. There also is an active program in the broader field of high energy density science on these facilities. These activities will be reviewed here as well as presented in talks throughout the conference.

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“…However, tens of MG are needed to achieve ! ce $ 1 in the hot spot of a typical, direct drive DT ignition target [4] with hot-spot density of $30 g=cc and a temperature of $7 keV. Such a field is higher than both the self-generated magnetic fields (see Ref.…”

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Laser-Driven Magnetic-Flux Compression in High-Energy-Density Plasmas

et al. 2009

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The demonstration of magnetic field compression to many tens of megagauss in cylindrical implosions of inertial confinement fusion targets is reported for the first time. The OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with a strong external field (>50 kG) from a specially developed magnetic pulse generator. This seed field was trapped (frozen) in the shock-heated gas fill and compressed by the imploding shell at a high implosion velocity, minimizing the effect of resistive flux diffusion. The magnetic fields in the compressed core were probed via proton deflectrometry using the fusion products from an imploding D 3 He target. Line-averaged magnetic fields between 30 and 40 MG were observed. In the magnetic fusion energy (MFE) concept, a strong magnetic field confines the plasma and reduces the electron thermal conduction to the vessel wall [1]. The magnetic pressure of typical $0:1-MG fields is higher than the total energy density of the plasma (with ¼ 2 0 p=B 2 < 1). MFE plasmas are fully magnetized and characterized by a Hall parameter ! ce > 1 since the modest gyrofrequency ! ce is matched by long collision times . In contrast, typical inertial confinement fusion (ICF) plasmas have collision frequencies higher by 10 to 12 orders of magnitude because of their extreme density. In such systems, thermal conduction losses are a major factor in the energy balance of an implosion. While it can be more difficult, magnetizing the hot spot in ICF implosions can lead to improved gains and to a reduction of the energy required for ignition. A similar approach is used in the magnetized target fusion concept [2], where the fusion burn requires relatively low-implosion velocities, provided there is an adequate magnetic thermal insulation. In ICF implosions, lower implosion velocities lead to higher gains [3]. However, tens of MG are needed to achieve ! ce $ 1 in the hot spot of a typical, direct drive DT ignition target [4] with hot-spot density of $30 g=cc and a temperature of $7 keV. Such a field is higher than both the self-generated magnetic fields (see Ref. [5]) and the external fields that can be generated by coils. Magnetic-flux compression [6] is a viable path to generating tens of MG magnetic fields with adequate size compression of a metal liner driven by high explosives [7,8] or by pulsed power. The latter approach has been pursued by the Z-pinch [9] communities. The results from the first experiments on a new approach that provides very effective flux compression are reported here. The field is compressed by the ablative pressure exerted on an imploding ICF capsule by the driving laser [10]. This approach was proposed in the 1980s [11] as a way to achieve record compressed fields with possible applications for fusion [12] but no laser experiments were performed. There are numerous advantages to this approach as the implosion velocity is high (a few 10 7 cm=s) and the hot plasma is an effective conductor that tra...

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Analysis of a direct-drive ignition capsule designed for the National Ignition Facility

Cited by 155 publications

References 33 publications

Implosion Experiments using Glass Ablators for Direct-Drive Inertial Confinement Fusion

Implosion Experiments using Glass Ablators for Direct-Drive Inertial Confinement Fusion

The ICF status and plans in the United States

Laser-Driven Magnetic-Flux Compression in High-Energy-Density Plasmas

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