Laser Fusion Reactor Research Articles

Feasibility study of tokamak, helical and laser reactors as affordable fusion volumetric neutron sources

The applicability of tokamak, helical and laser fusion reactors as a volumetric fusion neutron source has been examined using the systems codes that have been utilised for the conceptual design of DEMO and commercial reactors in Japan. This study has clarified the characteristics of reactor-based volumetric neutron sources that can be designed based on the current physics and engineering basis with a reasonable running cost (∼5B Yen/year). Although the achievable neutron flux is 2–3 orders lower than that of accelerator driven neutron sources, tokamak and helical neutron sources can provide a much larger irradiation area for the test of large components. Laser neutron sources have both high operability and tritium breeding capacity. These reactor-based neutron sources also serve as an integrated test bed of the entire reactor system.

Laser fusion reactor approaches ‘burning plasma’ milestone

Laser fusion reactor approaches ‘burning plasma’ milestone

Self-modulation and anomalous collective scattering of laser produced intense ion beam in plasmas

The collective interaction between intense ion beams and plasmas is studied by simulations and experiments, where an intense proton beam produced by a short pulse laser is injected into a pre-ionized gas. It is found that, depending on its current density, collective effects can significantly alter the propagated ion beam and the stopping power. The quantitative agreement that is found between theories and experiments constitutes the first validation of the collective interaction theory. The effects in the interaction between intense ion beams and background gas plasmas are of importance for the design of laser fusion reactors as well as for beam physics.

Fundamental Study of Wave Propagation on Liquid Surface Related IFE Mirror

A laser fusion reactor needs an optical mirror in its final optical system. This optical mirror is exposed to the neutron produced with fusion reaction. It is pointed out that the exposure to neutron will produce hydrogen gas in the mirror and cause swelling deformation of mirror. To avoid this swelling of mirror, a liquid-metal mirror is promising. High energy laser shots on the liquid mirror will cause the surface wave. These waves must be damped to under 1/10 of the laser wavelength in 250 ms or less. In this study, the hydrodynamic behavior of the liquid surface was investigated by experiment with water as surrogate liquid, the computational evaluation for the wave propagation with the MARS (Multi-interface Advection and Reconstruction Solver, 2001) was carried out, and the design window for the optical mirror based on the water experiment was discussed.

Simulated ablation of carbon wall by alpha particles for a laser fusion reactor

Thermal reactions of materials heated by charged particles may lead to serious damage in a laser fusion reactor. When charged particles irradiate and heat the wall material with high intensity like at above 109W/cm2, the material can be ablated. Once the wall is ablated, expanding gas or plasma can disturb the propagation of laser light irradiating the fuel target if it stagnates long enough for next laser shot. In order to understand the ablation dynamics in detail, we have performed 1-D hydro simulation to evaluate this ablation. As a new feature, we introduce the calculation of energy deposition by charged particles focusing on the interaction between ablated material and charged particles.

Proposal of an MFE-IFE cooperative system for a steady-state tritium balance

A new concept of a fusion reactor system, MFE-IFE cooperative system, is proposed. This concept combines the merits of a small-size MFE reactor and a dry-wall IFE reactor and aims at sufficient amount of tritium production and electricity generation without advanced technology. Design window analysis shows a NIF-scale (5m chamber radius) dry-wall laser fusion reactor with a ∼1GWth fusion output and net tritium breeding ratio (TBR) of 1.74 can sustain an MFE power plant with a fusion power of 3GWth and net TBR of 0.96. Although more detailed quantitative analyses are required, this concept can be a possible solution for a simultaneous achievement of tritium self-sufficiency and significant net electricity generation.

Investigation of Condensed Liquid Film Flow on Chamber Ceiling of Laser-Fusion Reactor

To protect from high-energy fluxes caused by nuclear fusion reaction to a first wall of a laser-fusion reactor such as “KOYO” reactor, the cascade-type falling liquid-metal film flow was proposed as a “liquid-wall” concept which was one of the reactor chamber cooling and wall protection schemes. In this concept, vapor released by fuel targets and the liquid wall will be condensed on the chamber ceiling which is kept relatively cold. The condensed liquid-metal vapor makes many droplets on the ceiling, and then the droplets will agglomerate, and eventually make the liquid film on the ceiling surface. The liquid-metal film will flow from the ceiling to the liquid first-wall. In this study, the proof-of-principal (POP) experiments and numerical simulations were conducted regarding the liquid-film flow on the ceiling wall. It is found that if the liquid film is formed on the ceiling surface, the liquid flows along the ceiling wall and from the ceiling wall down to the reactor core as long as the vapor is supplied. Moreover, the measurements of the liquid-film thickness were taken by using a confocal laser scanning microscopy, and the effects of the wettability of the wall on the liquid film flow behavior were obtained.

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.

Investigation of liquid-film formation along first wall of laser-fusion reactor

To protect the first wall of a laser-fusion reactor from extremely high energy/particle fluxes, a cascade-type falling liquid-film flow along the first wall has been proposed as one of realistic liquid-wall concept designs. On the cascade-typed liquid-wall concept, the first wall has multistage structure for renewal of starting point of liquid-film flow on it. Both experiments and numerical simulations have been conducted on liquid-film flow along the surface corresponding to the first wall. The experiments, which satisfy the Weber number coincident condition, were carried out using water as the working fluid. Numerical simulations are well simulated on liquid-film behavior observed in flow visualization experiment. Measurement of liquid-film thickness by using a confocal laser scanning microscopy gives information for evaluation on the heat transfer rate. For avoiding increase of vapor concentration in the center region of reactor chamber, saw-shaped wall design is also investigated. The POP (proof-of-principle) experiments and numerical simulations are conducted for the investigation on saw-shaped structure. Both results of experiments and simulations show that it is considerably difficult to cover the small-angle corner entirely with liquid film. Several modified wall surface with smart micro-structure are tested in order to prevent uncovering of the solid wall surface. Such modification has the possibility to cover entire area of the wall surface with liquid film.

Activities on the Laser Fusion Reactor KOYO-F in Japan

Current status of elemental research on a laser fusion reactor with a liquid wall in Japan is summarized. Cascade scheme was found to be useful to obtain a continuous protective liquid LiPb layer. Formation of micro particles in a plume ablated by alpha particle heating is discussed based on experimental results obtained by backside irradiation of a lead membrane. Our numerical simulation results for formation of aerosols matched experimental results obtained with electric discharge through a thin lead membrane. Protection of beam port is described. A magnetic field generated with a pulse current successfully shields the tip of beam port from alpha particles. Tracking of cone target with diverging beam showed 0.2 m resolution at 10m separation.

Comparison of Two Types of Blanket Concepts for a Fast Ignition ICF Reactor FALCON-D

A Fast ignition Advanced Laser fusion reactor CONcept with a Dry first-wall and a high repetition laser (FALCON-D) has been proposed to investigate the potential of the fast ignitionin the reactor concepts. For the blanket system, two types of blanket concepts, i.e.asolid and a liquid metal breeder types using the reduced activation ferritic steel (F82H) were proposed. In this study, two types of blankets were designed, where the thickness of the blankets was minimized while keeping the net TBR larger than 1.07. One of the blanket concepts for FALCON-D is based on the solid breeder (Li2TiO3) with beryllium (Be) neutron multiplier and water cooling. The second blanket concept is based on liquid metal breeder (Li17Pb83) with water cooling. The maintenance method for FALCON-D is applicable to both blanket types. The net electric power of the solid breeder blanket is 110 MW larger than that of the liquid metal breeder blanket. This is mainly caused by the differences in the neutron energy multiplication. In the case of the liquid metal breeder blanket with water cooling, the net TBR 1.09 is achieved without Be as the neutron multiplier. Such design without Be can remove a risk of accident due to the chemical reaction between beryllium and water. From the economical point of view, the solid breeder blanket with water cooling, which generates a larger electric power, is desirable. On the other hand, if the combination of beryllium and water cooling was not acceptable from a viewpoint of safety, the blanket system with the liquid metal would be another possible option.

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.

Investigation of cascade-type falling liquid-film along first wall of laser-fusion reactor

To protect the first wall of an inertia fusion reactor from extremely high heat flux, X-rays, alpha particles and fuel debris caused by a nuclear fusion reaction, a “cascade-type” falling liquid-film flow is proposed as a “liquid-wall” concept. The flow visualization experiment to investigate the feasibility of this liquid-wall concept has been conducted. The preliminary numerical simulation results suggest that the current cascade structure design should be improved because less thermal-mixing is expected. The cascade-type structure has, therefore, been redesigned. This new cascade-type first wall consists of a liquid reservoir which has a free-surface to maintain a constant water head in the rear, and connects to a slit composed of two plates, i.e., the first wall is connected to a slit which is partially made up of the first wall to begin with it. The numerical simulations were performed on the new cascade-type first wall and they show the stable liquid-film flow on it. Moreover, the POP (proof-of-principle) flow visualization experiments, which satisfy the Weber number coincident condition, are carried out using water as the working fluid. By comparing the numerical and experimental results, it was found that the liquid-film flow with 3–5 mm thickness could be stably established. According to these results for the new cascade-type first wall concept, it was confirmed that the coolant flow rate and the thickness of the liquid-film could be controlled if the Weber number coincident condition was satisfied.

Conceptual design of a fast-ignition laser fusion reactor based on a dry wall chamber

The fast ignition is quite attractive for a compact laser fusion reactor, because a sufficiently high pellet gain is available with a small input energy. We designed an inertial fusion reactor based on Fast-ignition Advanced Laser fusion reactor CONcept, called FALCON-D, where a dry wall is employed for a chamber wall. A simple point model shows that the pellet gain G∼100 is available with laser energies of 350kJ for implosion, 50kJ for heating. This results in the fusion yield of 40 MJ in one shot. By increasing the repetition rate up to 30 Hz, the fusion power of 1.2 GWth becomes available. Plant system analysis shows the net electric power to be about 0.4 GWe In the fast ignition it is available to employ a low aspect ratio pellet, which is favorable for the stability during the implosion phase. Here the pellet aspect ratio is reduced to be 2 ∼ 4, and the optimization of the pulse shape for the implosion laser are carried out by using the 1-D hydrodynamic simulation code ILESTA-1D. A ferritic steel with a tungsten armour is employed for the chamber wall. The feasibility of this dry wall concept is studied from various engineering aspects such as surface melting, physical and chemical sputtering, blistering and exfoliation by helium retention, and thermo-mechanical fatigue, and it is found that blistering and exfoliation due to the helium retention and fatigue failure due to cyclic thermal load are major concerns. The cost analysis shows that the construction cost is moderate but the cost of electricity is slightly expensive.

Maintenance method and its critical issues for a fast-ignition laser fusion reactor based on a dry wall chamber

The neutronics analysis has been carried out for feasibility study of the FALCON-D concept by Monte Carlo N-paticle transport code (MCNP), in order to inspect the cooling performance of in-vessel and ex-vessel components, and a connection pipe between Vacuum Vessel and reactor room. The nuclear heating rate in the Vacuum Vessel was at the same level as that of NBI duct of the ITER. The temperature of the connection pipe was found to be 345·, ·which was smaller than the melting point of structure materials (F82H). Moreover, the radiation damage of the final optics was also investigated. We propose a sliding changer concept for replacement. This method could be adapted for the replacement of one FPY cycle in the final optics system.

Experimental investigation of aerosol formation in laser fusion reactor chamber by discharge method

Liquid wall chambers are one of the most critical technologies in inertial fusion energy (IFE) plants. The critical problem for the liquid wall IFE chamber is the chamber clearance after laser shots. This paper presents preliminary results from an experimental simulation of ablation processes induced by alpha-particle heating.

Design Study of Dry Wall Fast Ignition Laser Fusion Reactor with High Repetition Laser

The design of a laser fusion reactor with a dry wall chamber has been carried out. According to a simple point model calculation, sufficient pellet gain (G > 100) can be achieved with the injection energy of 400kJ under relatively conservative parameters (α = 2, ηc = 0.05, ηh = 0.2). Assuming the pulse heat load limit of a dry wall to be 2J/cm2, chamber radius of R = 5.64m is achievable. 1-D thermal analysis also supports the feasibility of this design. Then a medium scale plant (400MWe electric output) can be designed with moderate construction cost, which suits for the first-step reactor, if the laser repetition rate can be increased to 30 Hz. Since laser fusion reactors have flexibility in changing its output, this design enables them to be in flexible use according to the time-varying electric demand as the present fossil fuel power plants. This design is remarkable because it gives a new property to the fusion reactors.

Development of a system code for an IFE reactor and investigation of a design regime for a dry wall chamber concept

A system code for designing laser fusion reactors has been developed, and the design possibility of the laser fusion commercial plant with a single dry wall chamber and a high repetition laser has been examined. In a fast ignition concept, it is confirmed that the target gain G ≥ 100 is achievable with the fusion pulse energy of 40 MJ. If we assume the laser repetition rate of 30 Hz and the pulse heat load limit of 2 J/cm 2, the plant which has moderate electric power ( ∼ 400 MW e) can be designed with a dry wall chamber of which radius R = 5.6 m. Although there are several technological issues needed to be solved, this design point can be characterized as a first-step reactor of the laser fusion study because of its relatively low construction cost.

Conceptual design of laser fusion reactor KOYO-fast – Target design and the fueling system

Target design and the fabrication scheme are discussed aiming an application for the future laser fusion reactor KOYO-F that has 4 modular chambers with a wet wall operated with fast ignition scheme. Gain estimation and load of fusion output from the non-symetric burn on the first wall are shown.

Conceptual design of laser fusion reactor KOYO-fast

A conceptual design of the laser fusion reactor KOYO-F based on the fast ignition scheme is reported including the target design, the laser system and the design for chamber. A Yb-YAG ceramic laser operated at 200K is the primary candidate for the compression laser and an OPCPA system is the one for the ignition laser. The chamber is basically a wet wall type but the fire position is vertically off-set to simplify the protection scheme of the ceiling. The target consists of foam insulated, cryogenic DT shells with a LiPb, reentrant guide-cone.