Long-Term Survival of Grazing-Incidence Metal Mirrors for Laser Fusion

Tillack, M. S.; Pulsifer, J.

doi:10.13182/fst09-32

Cited by 8 publications

(5 citation statements)

References 5 publications

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“…Research has shown that a reflector made of a solid solution alloy of aluminum with 5% copper can withstand well above 3.5 J/cm 2 for over 10 7 pulses with no damage. 886 Neutrons scattering off the GIMM will be incident on the upstream optics. GIMMs are large (typically 3.44 m Â 4.05 m, at a distance of 24 m from the target 884 ), so it is desirable to make these upstream optics using something other than a GIMM.…”

Section: Final Optics and Illumination Geometrymentioning

confidence: 99%

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: Final Optics and Illumination Geometrymentioning

confidence: 99%

Direct-drive inertial confinement fusion: A review

et al. 2015

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“…For the case of silica ∂n/∂T n−1 ∼ 3×10 −5 K −1 [24], and α ∼ 5×10 −7 K −1 [13], i.e. two orders of magnitude lower 4 .…”

Section: Temperature Variationmentioning

confidence: 99%

“…An alternative to the cassette of lenses is the use of grazing incidence metallic mirrors (GIMM). GIMM have been designed and tested during the high average power laser program [4]. The real drawback of the metallic mirrors (apart of radiation-resistance considerations) is the distance from the target: 24 m to the focal point, which is three times longer than the NIF/LMJ focal length (8 m); so far it is almost impossible to reach the same beam pointing accuracy on the target [5].…”

Section: Introductionmentioning

confidence: 99%

Transmission final lenses in the HiPER laser fusion power plant: system design for temperature control

Páramo¹,

Sordo²,

Garoz³

et al. 2014

Nucl. Fusion

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The European laser fusion project HiPER is developing technologically feasible components for a laser fusion power plant with an evacuated dry wall chamber which is likely to operate with a shock ignition scheme and direct targets. One of the key components is the final optics. In this work, we consider silica transmission final lenses and address the major issues regarding the unavoidable neutron irradiation they must withstand. For pre-commercial power plants (150 MJ target yield at 10 Hz) a distance of 16 m between the final lenses and target leads to maximum lens temperatures within tolerable limits. However, a non-uniform steady-state temperature profile is a major concern because it is the origin of unacceptable aberrations that severely affect the target spots. We have devised an active intervention system based on a heat-transfer fluid to keep the temperature profile as smooth as possible. The main characteristics of the temperature control system are defined throughout this work and enable the operation of the plant, both for the start-up procedure and for normal operation.

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“…Other designs, for example HAPL 17 , propose the use of mirrors far away from the target. Such a scheme assures a minimum radiation load onto the mirrors at the expense of using long focal lengths.…”

Section: Hiper Final Optics Assembly (Foa)mentioning

confidence: 99%

Lifetime of silica final lenses subject to HiPER irradiation conditions

et al. 2011

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The goal of the European laser fusion project, is to build an engineering facility for repetitive laser operation (HiPER 4a) and later a fusion reactor (HiPER 4b). A key aspect for laser fusion energy is the final optics. At the moment, it is based on silica transmission lenses located 8 m away from the chamber center. Lens lifetime depends on the irradiation conditions. We have used a 48 MJ shock ignition target for calculations. We have studied the thermo-mechanical effects of ions and X-rays on the lenses. Ions lead to lens melting and must therefore be mitigated. On the other hand, X-rays (~1% of the energy) does not produce either a significant temperature rise or detrimental stresses. Finally, we calculated the neutron flux and gamma dose rate on the lenses. Next, based on a simple model we studied the formation of color centers in the sample, which lead to optical absorption. Calculations show that simultaneous neutron and gamma irradiation does not significantly increase the optical absorption during the expected lifetime of the HiPER 4a facility. Under severe conditions (HiPER 4b), operation above 800 K or lens refreshing by thermal annealing treatments seem to assure adequate behavior.

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Long-Term Survival of Grazing-Incidence Metal Mirrors for Laser Fusion

Cited by 8 publications

References 5 publications

Direct-drive inertial confinement fusion: A review

Direct-drive inertial confinement fusion: A review

Transmission final lenses in the HiPER laser fusion power plant: system design for temperature control

Lifetime of silica final lenses subject to HiPER irradiation conditions

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