Cryogenic Deuterium and Deuterium-Tritium Direct–Drive Implosions on Omega

Goncharov, V. N.

doi:10.1007/978-3-319-00038-1_7

Cited by 6 publications

(12 citation statements)

References 66 publications

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“…XVI. However, shock-velocity measurements in these designs 43 have shown that it is difficult to reproduce the adiabatic compression wave predicted by simulations. Because of this, current ignition designs are based on the generation of multiple shocks that can be accurately timed experimentally as described in Sec.…”

Section: A Triple-picket Ignition Design For the Nifmentioning

confidence: 99%

“…Assuming that a fluid with velocity v and density q is stopped by a strong shock, the resulting pressure of the stagnated material is P stag $ qv 2 : (3)(4)(5)(6)(7)(8)(9) This shows that the pressure at stagnation can be increased by increasing the shell density and velocity. For a given laser drive energy E L , the shell velocity scales as 43 v $ P a E L M shell I ; (3)(4)(5)(6)(7)(8)(9)(10) where P a is the drive (ablation) pressure created by the ablated plasma blowing off the target, M shell is the shell mass, and I is the intensity of the incident laser during the main portion of the pulse. Equation (3)(4)(5)(6)(7)(8)(9)(10) shows that the shell velocity increases by reducing the shell mass and increasing the drive pressure at a given laser intensity (by using, for example, more-efficient ablator materials).…”

Section: B Ignition Physicsmentioning

confidence: 99%

“…In addition, the generation of suprathermal electrons from laser-plasma instabilities can increase the adiabat in some designs when the laser intensity exceeds the instability thresholds. Calculations 43 show that ignition can fail if 1% to 2% of the shell kinetic energy is deposited in the main fuel due to suprathermal electron preheat. The design shown in Fig.…”

Section: B Ignition Physicsmentioning

confidence: 99%

“…XII B). Later work reported by Goncharov 43 showed that short-scale mix caused by the Rayleigh-Taylor instability at the ablation front was not the cause of the qR degradation-when beam smoothing was turned off, the yield dropped by a factor of 2 but the areal density remained unchanged.…”

mentioning

confidence: 95%

“…X A), once the quarter-critical surface moved into the DT. Other experimental data, 43 however, seemed to indicate that inaccuracy in the predicted shock timing was the dominant degradation mechanism. Difficulty in ensuring accurate shock timing also persisted in the design for the 10-lm-thick shell.…”

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confidence: 99%

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Direct-drive inertial confinement fusion: A review

et al. 2015

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The direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. The problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 μm—the third harmonic of the Nd:glass laser—and 0.248 μm (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be nonlocal in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [Haynam et al., Appl. Opt. 46(16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.

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Section: A Triple-picket Ignition Design For the Nifmentioning

confidence: 99%

Section: B Ignition Physicsmentioning

confidence: 99%

Section: B Ignition Physicsmentioning

confidence: 99%

mentioning

confidence: 95%

mentioning

confidence: 99%

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Direct-drive inertial confinement fusion: A review

et al. 2015

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Improving the hot-spot pressure and demonstrating ignition hydrodynamic equivalence in cryogenic deuterium–tritium implosions on OMEGA

et al. 2014

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Reaching ignition in direct-drive (DD) inertial confinement fusion implosions requires achieving central pressures in excess of 100 Gbar. The OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] is used to study the physics of implosions that are hydrodynamically equivalent to the ignition designs on the National Ignition Facility (NIF) [J. A. Paisner et al., Laser Focus World 30, 75 (1994)]. It is shown that the highest hot-spot pressures (up to 40 Gbar) are achieved in target designs with a fuel adiabat of a ' 4, an implosion velocity of 3.8 Â 10 7 cm/s, and a laser intensity of $10 15 W/cm 2. These moderate-adiabat implosions are well understood using two-dimensional hydrocode simulations. The performance of lower-adiabat implosions is significantly degraded relative to code predictions, a common feature between DD implosions on OMEGA and indirect-drive cryogenic implosions on the NIF. Simplified theoretical models are developed to gain physical understanding of the implosion dynamics that dictate the target performance. These models indicate that degradations in the shell density and integrity (caused by hydrodynamic instabilities during the target acceleration) coupled with hydrodynamics at stagnation are the main failure mechanisms in low-adiabat designs. To demonstrate ignition hydrodynamic equivalence in cryogenic implosions on OMEGA, the target-design robustness to hydrodynamic instability growth must be improved by reducing laser-coupling losses caused by cross beam energy transfer. V

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National direct-drive program on OMEGA and the National Ignition Facility

Goncharov

Regan

Campbell

et al. 2016

Plasma Phys. Control. Fusion

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A major advantage of the laser direct-drive (DD) approach to ignition is the increased fraction of laser drive energy coupled to the hot spot and relaxed hot-spot requirements for the peak pressure and convergence ratios relative to the indirect-drive approach at equivalent laser energy. With the goal of a successful ignition demonstration using DD, the recently established national strategy has several elements and involves multiple national and international institutions. These elements include the experimental demonstration on OMEGA cryogenic implosions of hot-spot conditions relevant for ignition at MJ-scale energies available at the National Ignition Facility (NIF) and developing an understanding of laser-plasma interactions and laser coupling using DD experiments on the NIF. DD designs require reaching central stagnation pressures in excess of 100 Gbar. The current experiments on OMEGA have achieved inferred peak pressures of 56 Gbar (Regan et al 2016 Phys. Rev. Lett. 117 025001). Extensive analysis of the cryogenic target experiments and two-and three-dimensional simulations suggest that power balance, target offset, and target quality are the main limiting factors in target performance. In addition, cross-beam energy transfer (CBET) has been identified as the main mechanism reducing laser coupling. Reaching the goal of demonstrating hydrodynamic equivalence on OMEGA includes improving laser power balance, target position, and target quality at shot time. CBET must also be significantly reduced and several strategies have been identified to address this issue.

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Cryogenic Deuterium and Deuterium-Tritium Direct–Drive Implosions on Omega

Cited by 6 publications

References 66 publications

Direct-drive inertial confinement fusion: A review

Direct-drive inertial confinement fusion: A review

Improving the hot-spot pressure and demonstrating ignition hydrodynamic equivalence in cryogenic deuterium–tritium implosions on OMEGA

National direct-drive program on OMEGA and the National Ignition Facility

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