Laser Fusion Power Plant Research Articles

Conceptual design of a ceramic breeding blanket for laser fusion power plants with online tunable tritium breeding ratio based on a variable neutron reflector: Remarkable no need of isotopic enrichment

Abstract An essential component of nuclear fusion power plants is the breeding blanket. Its main roles include neutron thermalization and tritium breeding. Tritium shortage is a problem for plant operation, while excess tritium production constitutes a serious safety issue. It has been recognized that tritium demand can vary during the plant lifetime. In addition, the estimation of the tritium breeding ratio and tritium inventories is subject to considerable uncertainties. A way to overcome these difficulties is to design a breeder blanket with capabilities to easily tune the tritium breeding ratio during operation. In this paper, we describe for the first time a novel conceptual design of a breeding blanket to operate under laser fusion power plant conditions based on lithium ceramics with beryllium multiplier and surrounded by a (heavy) water neutron reflector. Varying the reflector thickness (equivalent to vary the filling level of a tank), we demonstrate that the tritium breeding ratio can be tuned at will in a broad range compatible with the requirements of a power plant. Importantly, the resulting design turns out to be compact and does not require lithium enrichment.

Efficient Energy Transfer and Enhanced Near‐IR Emission in Cu+/Nd3+‐Activated Aluminophosphate Glass

The development of photonic materials for efficient energy conversion and high‐power solid‐state lasers is currently pursued given the wide range of applicable technologies and the possibility to help meet global energy demands in laser fusion power plants. In this work, Cu+ ions successfully incorporated in aluminophosphate glass are recognized as near‐ultraviolet (UV) sensitizers of Nd3+ ions resulting in remarkable near‐infrared (IR) 4F3/2 → 4I11/2 emission at 1.06 μm. Optical absorption, solid‐state 31P nuclear magnetic resonance, Raman, and photoluminescence spectroscopies characterizations are employed and assessment methods for material optical and structural properties are proposed. The spectroscopic data indicates an efficient (>50%) nonradiative energy transfer where the Cu+ ions first absorb photons broadly around 360 nm, and subsequently transfer the energy from the Stokes‐shifted emitting states to resonant Nd3+ energy levels. Then, the Nd3+ electronic excited states decay and the upper lasing state 4F3/2 is populated, leading to enhanced near‐IR emission. It is suggested that the physico‐chemically robust Cu+/Nd3+ codoped aluminophosphate glass is a suitable candidate as solid‐state laser material with enhanced pump range in the near‐UV part of the spectrum and for solar spectral conversion in photovoltaic cells.

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

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.

Viability of the ESS-Bilbao neutron source for irradiation of nuclear fusion materials

The ESS-Bilbao neutron source, currently under construction, is conceived as a multipurpose facility. It will offer a fast neutron beam line for materials irradiation. In this paper we discuss the viability of ESS-Bilbao for experimental studies of fusion materials. Making use of the already designed target station we have calculated the neutron spectrum expected in the fast neutron line. Then, we have studied the neutron irradiation effects in two model materials: iron and silica. We have calculated the expected PKA (primary knock-on atom) spectra and light species production as well as the damage production in these materials. Regarding structural materials, we conclude that the ESS-Bilbao neutron irradiation facility will play a minor role due to the resulting low neutron fluxes (about two orders of magnitude lower than in fusion reactors). On the other hand, ESS-Bilbao turns out to be relevant for studies of final lenses in laser fusion power plants. A comparison with the conditions expected for HiPER final lenses shows that the fluxes will be only a factor 5 smaller in ESS-Bilbao and the PKA spectra will be very similar. Taking into account, in addition, that relevant effects on lenses occur from the onset of irradiation, we conclude that an appropriate irradiation cell with in situ characterisation techniques will make ESS-Bilbao very attractive for applied neutron damage studies of laser fusion final lenses. Finally, we compare ESS-Bilbao with other facilities.

Numerical Study for Laser Source Protection from Alpha Particles by Magnetic Fields in a Laser Fusion Reactor

A possible method for protecting beam ports and laser sources from alpha particles which are produced by a nuclear fusion in the fast ignition laser fusion power plant (KOYO-Fast) is proposed. Two simple dipolar magnetic fields generated by two coils installed at the tip of the beam port and at the side of the beam port are used for protecting the alpha particles coming into the inside of the beam port and colliding to the tip surface of the beam port. To calculate the behavior of alpha particles in the magnetic field, we use a 3D hybrid numerical simulation code. As a result, the intensity of 0.9 T of the magnetic flux density at the tip of the beam port is large enough for achieving the 10% reduction of the collision energy of the alpha particles to the tip surface of the beam port compared with the case without protection. Furthermore, the intensity of 1.35 T of the magnetic flux density at the center of the coil installed at the side of the beam port can guide the alpha particles coming into the inside of the beam port to the outside liquid wall perfectly.

Nuclear Assessment of Shielding Configuration Options for Final Optics of HAPL Laser Fusion Power Plant

The High Average Power Laser (HAPL) power plant has targets that are directly driven by forty KrF laser beams. Three-dimensional neutronics calculations were performed directly in the exact CAD model of the HAPL final optics system to assess the impact of the biological shielding configuration on the nuclear environment at the GIMM and dielectric focusing and turning mirrors. In the initial configuration, the biological shield fully encloses the GIMM sand associated dielectric mirrors. We assessed another configuration where the shield is moved farther from the target to fully enclose the dielectric mirrors leaving the GIMM in the open space between the chamber and the biological shield. A variation of this configuration utilizes 40 neutron traps attached to the inner surface of the biological shield behind the GIMMs. It is concluded that the shielding configuration with all optics including the GIMM being fully enclosed in the biological shield is the preferred option since it results in the lowest nuclear environment at the dielectric mirrors, provides better GIMM support, reduces the volume to be maintained under vacuum, and requires the least amount of concrete shield.

A Laser Based Fusion Test Facility

The Fusion Test Facility (FTF) is a high repetition rate ignition facility that would bridge the gap between single shot facilities (such as NIF and LMJ) and a fully functioning laser fusion power plant. It would allow development of science and technologies so that follow-on power plants could have predictable performance. The FTF would need to have enough fusion power, about 100 MW, to rigorously test materials and components for the power plants. Because inertial fusion provides a “point” source for neutrons, it can provide very high fluxes for test objects placed close to the target, while the reaction chamber walls remain at conservatively large distances. Simulations indicate that direct-drive designs can achieve 100 MW fusion power with laser energies well below 1 MJ with a 5 Hz driver. High-resolution 2-D simulations of high-velocity direct-drive implosions utilizing a Krypton-Fluoride (KrF) laser give gains of >60× at 500 kJ, and shock-ignited targets may allow higher gains at even lower driver energy. Utilizing designs that require relatively small driver energy is the most straightforward path to reducing cost and development time for a practical laser fusion energy power plant. A program to develop an FTF would build upon the science and technologies developed in the existing National Ignition Campaign and the High Average Power Laser (HAPL) program, as well as the magnetic fusion technology program.

Conceptual design of fast-ignition laser fusion reactor FALCON-D

A new conceptual design of the laser fusion power plant FALCON-D (Fast-ignition Advanced Laser fusion reactor CONcept with a Dry wall chamber) has been proposed. The fast-ignition method can achieve sufficient fusion gain for a commercial operation (∼100) with about 10 times smaller fusion yield than the conventional central ignition method. FALCON-D makes full use of this property and aims at designing with a compact dry wall chamber (5–6 m radius). 1D/2D simulations by hydrodynamic codes showed a possibility of achieving sufficient gain with a laser energy of 400 kJ, i.e. a 40 MJ target yield. The design feasibility of the compact dry wall chamber and the solid breeder blanket system was shown through thermomechanical analysis of the dry wall and neutronics analysis of the blanket system. Moderate electric output (∼400 MWe) can be achieved with a high repetition (30 Hz) laser. This dry wall reactor concept not only reduces several difficulties associated with a liquid wall system but also enables a simple cask maintenance method for the replacement of the blanket system, which can shorten the maintenance period. The basic idea of the maintenance method for the final optics system has also been proposed. Some critical R&D issues required for this design are also discussed.

Lasers for inertial confinement fusion driven by high explosives

Proposed laser fusion power plant concepts suffer from the huge size and expense of the lasers needed for compression and ignition. In a 1969 study (classified in 1970 and declassified in 2007), the idea to use chemical high explosives for the pumping of megajoule lasers was explored. Apart from being less expensive by orders of magnitude, such lasers are expected to be much more compact, and with their large energy, output could simultaneously drive several thermonuclear micro-explosion chambers. Because of its topical importance, I accepted the journal's invitation to publish a previously classified work, but with new unpublished ideas, with the previously classified paper put into the appendix.

Conceptual Design of Fast Ignition Power Plant KOYO-F Driven by Cooled Yb:YAG Ceramic Laser

Recent progress on fast ignition (FI) and cooled Yb:YAG ceramic laser enable us to design an IFE power plant with a 1MJ-class, compact laser whose output energy is 1/4 of previous central ignition scheme. Basing on the FI scheme, we conceptually designed a laser fusion power plant driven with cooled-Yb:YAG, ceramic lasers. The cooled Yb-YAG ceramic was newly chosen as the laser material. We found that the heating laser for ignition could be constructed with the cooled Yb:YAG ceramics as well as the compression laser with acceptable electricity-laser conversion efficiencies including the electric power for the cooling system. A new reactor scheme for a liquid wall reactor that has no stagnation point of ablated gas was proposed.

Laser Fusion Chamber Design

A laser fusion chamber must absorb the energy emitted by the target in such a way that the plant can achieve a commercially viable power conversion efficiency. This must be accomplished with a design that can reliably withstand on the order of a billion shots. For a dry chamber wall, the key lifetime issues are thermo-mechanical effects resulting from the rapid heating, ion effects, such as blistering and sputtering, and radiation effects. These issues define the chamber size by providing flux limits for the various threats. In cases where a dry, unprotected wall cannot provide an adequate lifetime, measures must be taken to reduce the threat to the wall. Previously proposed approaches include filling the chamber with sufficient gas to stop the majority of the ions before they reach the wall or redirection of the ions by a cusp field. Other design trade-offs that must be addressed include the need to reduce heating of the target during injection and the need for adequate clearing of the chamber between shots. In this paper we provide a review of the chamber design approaches required for commercially viable laser fusion power plants, the issues driving those designs, and some system-level analyses that provide insight into the implications of these design issues for the overall economics of a commercial plant.

Conceptual design of laser fusion reactor KOYO-fast – Concepts of reactor system and laser driver

We have carried out the design studies of KOYO-Fast laser fusion power plant, using fast ignition cone targets, DPSSL lasers, and LiPb liquid wall chambers. Using fast ignition targets, we could design a middle sized 300 MWe reactor module, with 200 MJ fusion pulse energy and 4 Hz rep-rates, and 1200MWe modular power plants with 4 reactor modules and a 16 Hz laser driver. The liquid wall chambers with free surface cascade flows are proposed for cooling surface quickly enough to a 4 Hz pulse operation. We examined the potential ofYb-YAG ceramic lasers operated at 150 ∼ 225 K for both implosion and heating laser systems required for a 16-Hz repetition and 8 % total efficiency.

Power Plant Concepts and Chamber Issues for Fast Ignition Direct-Drive Targets

We have analyzed the design windows for laser fusion power plants based on direct-drive fast ignition concepts and have examined the issues of chamber technologies and the feasibility of a small laser fusion experimental reactor suitable for developing their power plants. Target gain curves are assessed for power plants having 90- to 200-MJ fusion yields with 600-kJ to 1-MJ lasers, and for an experimental reactor [the laser fusion experimental reactor (LFER)], having a 10-MJ fusion yield with a 200-kJ laser, i.e., 100 kJ for implosion and 100 kJ for heating. The fast ignition LFER can produce its fusion output approximately one order of magnitude smaller than that of the central ignition design, so that we can use a rather small solid-wall chamber for the first stage of the LFER operation. We can also expect to decrease laser cost drastically, although for the heating laser we must develop a long-life final optics system. Using fast ignition direct-drive targets, we could design a smaller ~300-MW(electric) reactor, with 200-MJ fusion pulse energy and 4-Hz repetition rates. The smaller pulse energies mitigate pulse loads on the chamber walls and the final optics; then, we can flexibly design large 1200-MW(electric) modular plants by using multiple reactor modules. We identified the issues of liquid-wall and solid-wall chambers and proposed basic reactor concepts for a power plant (KOYO-Fast) and an experimental reactor using fast ignition direct-drive cone targets.

An overview of the development of the first wall and other principal components of a laser fusion power plant

This paper introduces the JNM Special Issue on the development of a first wall for the reaction chamber in a laser fusion power plant. In this approach to fusion energy a spherical target is injected into a large chamber and heated to fusion burn by an array of lasers. The target emissions are absorbed by the wall and encapsulating blanket, and the resulting heat converted into electricity. The bulk of the energy deposited in the first wall is in the form of X-rays (1.0–100 keV) and ions (0.1–4 MeV). In order to have a practical power plant, the first wall must be resistant to these emissions and suffer virtually no erosion on each shot. A wall candidate based on tungsten armor bonded to a low activation ferritic steel substrate has been chosen as the initial system to be studied. The choice was based on the vast experience with these materials in a nuclear environment and the ability to address most of the key remaining issues with existing facilities. This overview paper is divided into three parts. The first part summarizes the current state of the development of laser fusion energy. The second part introduces the tungsten armored ferritic steel concept, the three critical development issues (thermo-mechanical fatigue, helium retention, and bonding) and the research to address them. Based on progress to date the latter two appear to be resolvable, but the former remains a challenge. Complete details are presented in the companion papers in this JNM Special Issue. The third part discusses other factors that must be considered in the design of the first wall, including compatibility with blanket concepts, radiological concerns, and structural considerations.

Estimating and projecting operating fields for liquid dielectrics in KrF laser fusion power plants

Krypton fluoride (KrF) laser fusion power plant designs include pulsed oil and water dielectrics with very large electrode areas that must operate continuously and reliably for years at 5-10 pulses per second. Operating electric fields must be maximized to minimize size and cost. To obtain a better understanding of design criteria for the electric fields the authors discuss the statistical treatment of breakdown probability. They also examine the use of the published area effects for breakdown of oil and water; the authors suggest that at very large areas the results may have been controlled by the presence of large impurities and that engineering criteria for limiting the type and size of these can allow reliable operation at fields higher than those predicted by the accepted area effects in oil and water. Other factors that might raise or lower safe operating fields are discussed, as are polarity effects. A system is described that will be used for accelerated tests of oil and water insulation to reduce the uncertainties in the choice of operating fields for fusion power plants.

Overview of new high gain target design for a laser fusion power plant

We have developed a new direct-drive target design that has a predicted energy gain of 127 using a 1.3 MJ KrF laser, and a gain of 155 using 3.1 MJ. The DT fuel is surrounded by an ablator consisting of a low density CH foam filled with frozen DT. The ablator is then surrounded by a thin CH coating and a very thin high-Z overcoat. The energy gain of 127–155 is possible through the use of (1) direct-drive laser-target coupling; (2) controlled levels of radiative preheating that keeps the DT fuel on a low isentrope; (3) a short 1/4 μm laser wavelength for maximum absorption and rocket efficiencies; (4) reduction of the laser beam focal spot size during the implosion (zooming) so that the focal spot size better matches the imploding target size; and (5) ISI optical smoothing to minimize the laser nonuniformities at both high and low mode numbers. In addition to its high energy gain, this target design has several other attractive features: a low target fabrication cost; the potential for a modest-size 300 MWe power plant; the physical strength to withstand the acceleration into the chamber; and a high infrared albedo to better protect the target from preheating during the injection into the chamber.

Dry wall chamber issues for the SOMBRERO laser fusion power plant

A reassessment of the SOMBRERO laser driven fusion power plant that was designed in 1990–91 has been conducted. New information and analysis has confirmed most of the original design decisions except that the tritium inventory in the blanket may be larger than originally calculated. Possible methods of lowering the tritium inventory are described along with a discussion of the critical issues that still remain 10 years after the original design was completed.

Exploration of the Fundamental “Damage Limit” Light Flux for Grazing Incidence Liquid Metal Mirrors

One definition for the “damage limit” of a liquid metal surface used as a final optic for laser fusion power plants is the maximum energy flux that the liquid metal can withstand without any resulting spallation. Some preliminary calculations were performed by Moir to roughly estimate the damage limit by imposing the restriction of a 200°C surface temperature rise. Here, new 1D calculations that account for hydro-motion on the compressible time scales are presented, along with revised estimates of the damage limits for liquid aluminum, sodium, and mercury. Slow compression time scales (~20 ns) produced negative pressures in the liquid film on the order of MPa, and fast ignition time scales (~10 ps) yielded GPa pressures for the laser energy densities set out by Moir. For Na and Al the peak energy densities normal to the beam on the order of 5 to 10 J/cm2 were acceptable for fast ignition when 85° grazing incidence is assumed. Some experimental data on the generation and damping of surface waves resulting from surface ablation recoil is also presented, where large waves are seen to damp out after about 50 ms following the laser pulse.

Prospects for Inertial Fusion Energy with a KrF Laser

Previous reactor studies indicate that a practical laser fusion power plant will require target gains of about 100. This level of energy gain appears possible with direct-drive targets now being designed and optimized at the Naval Research Laboratory (NRL). With direct-drive, the light is absorbed directly on the pellet shell, thereby maximizing the coupling efficiency. The current status of NRL's high gain target designs will be presented.To obtain sufficiently high target gains for a fusion reactor, NRL has had to take advantage of three optimizations. First, the laser beam illumination on the pellet has to be extremely uniform. High-mode beam nonuniformities in the range of 0.2% rms are required, along with low-mode nonuniformities of about 1%. The equivalent non-uniformity levels have already been achieved, in planar geometry, with NRL's KrF laser. Second, the rocket efficiency has to be maximized by depositing the laser energy deeply into the pellet. KrF, with 1/4 micron wavelength light, deposits at a high plasma density. Third, the target gain is optimized by “zooming” the laser beam inward during the implosion, thereby matching the laser spot size to the decreasing pellet diameter. This optical zooming is easily implemented on KrF lasers.Although the laser-target physics leads us to KrF, there are several engineering challenges in developing a laser of this type with sufficient energy, rep-rate, reliability, and economy for a practical reactor. Some of these challenges are the lifetime of the emitter and pressure foil in the electron-beam pumped amplifiers, the ability to clear the laser gas between pulses without sacrificing beam quality, and the overall efficiency of the system. Technologies and techniques which might meet these challenges have been partially developed elsewhere, but they are not necessarily in a parameter range appropriate for laser fusion, and they have yet to be integrated into a single system. We have a conceptual design for a 400-Joule, 5-Hz KrF laser which would serve as a test bed for these technologies.There are also engineering challenges in the design of a target chamber for a laser fusion reactor, including the protection of the first wall from the transient x-ray flux, and the final grazing incidence metal mirror which will be in direct line of sight of high energy neutrons from the burning pellet.

Laser Fusion Research at Ile Osaka University

The progress of laser fusion research at the Institute of Laser Engineering, Osaka University is reviewed. They are physics investigations on target implosion, development of laser technologies, and R&D for laser fusion power plants. The long term strategy of Inertial Fusion Energy (IFE) development has been reexamined taking into account the recent progress of implosion physics and reactor related technologies. 15 refs., 12 figs.