A. Minato

A simulated plasma disruption experiment using an electron beam as a heat source

An experimental study was made on the behavior of a solid surface subjected to an extremely high heat flux similar to that expected during a plasma disruption. An electron beam was used as the heat source to simulate the high heat flux. The beam was defocused in an attempt to give as much uniform heat flux as possible on the test surface. The 5-mm-diameter test pieces were made of 304 stainless steel, aluminum, and zinc. Heat fluxes from 10 to 110 MW/m2 were applied on the test pieces for durations of 90 to 180 msec. Special attention was paid to the measurement of the surface heat flux on the test surface. Comparison between experimental and analytical results on melt layer thickness and evaporation loss is made. An improved thermal analysis code (DAT-K) was developed for the analysis. Agreement between the experimental and analytical results on melt layer thickness is good. For evaporation loss, experimental and analytical results are in fair agreement. Features of the experiments and analysis that lead to the differences in the results are discussed.

Improvement of an electron beam facility as a heat source for disruption simulation experiments

To perform simulated plasma disruption experiments, a heat source which can provide fast rise and high heat flux on a target surface is required. An existing electron beam facility has been improved to provide higher heat fluxes uniformly over a wider area by installing a high speed beam rastering system. The beam rastering coils can provide a beam oscillation angle of 4.4° with a frequency of up to 400 kHz. The high frequency ensures temporal uniformity of the heat flux on a test surface. Triangular wave shaped current is supplied to excite the coils to provide spatially uniform heat flux over a test surface. Using this electron beam facility, we can provide uniform heat fluxes as high at 160 MW/m2 on an area of 13 mm × 13 mm, and 20 MW/m2 on 38 m × 38 mm.

Lifetime analysis for fusion reactor first walls and divertor plates

Lifetime analysis of fusion reactor first walls and divertor plates is performed by (1) a one-dimensional analytical plate model, and (2) a two-dimensional elastic-plastic finite element method. Life-limiting mechanisms and the limits of applicability for these analysis methods are examined. Structural design criteria are also discussed.

A thermal cycling durability test of tungsten copper duplex structures for use as a divertor plate

A tungsten-copper (W—Cu) duplex structure is the reference divertor plate design concept for the Fusion Experimental Reactor (FER). In the present study, a durability test of the W—Cu duplex structure against thermal cycling was performed. A tungsten disk was bonded to a copper disk by means of brazing or direct casting. The tungsten surface of the test piece was periodically heated by a high temperature argon plasma jet. Before and after the tests, the test pieces were examined with the aid of a scanning electron microscope and the Knoop hardness was measured. Grain boundary microcracks were observed after 200 and 1100 thermal cycles in brazed tungsten samples which contained a small amount of nickel and phosphorus. A cast tungsten specimen subjected to 2200 thermal cycles also contained microcracks. However, microcracks were not observed in a brazed tungsten sample containing an extremely small amount of impurities for thermal cycles up to 3700 times. Microcracks were observed in the brazing material of this test piece. None of the test specimens were broken. It is found that brazing is a valid bonding method and that W—Cu duplex structure, especially with high purity tungsten, is able to endure a practical number of thermal cycles.

Analysis and experiments on lifetime predictions for first wall and divertor plate structures in JAERI

Analysis and experiments on lifetime predictions of the first wall and divertor plate of fusion reactors have been performed. The analysis is based on both a one-dimensional plate model and a two-dimensional elastic-plastic finite element method. The experiments consist of mechanical fatigue tests, thermal fatigue tests, and tests of vaporized loss of materials. From these results, discussions of lifetime prediction procedures for fusion reactor components are made.

Analysis of magnetomechanical behavior of ferromagnetic first wall component

Ferritic stainless steel(HT-9) is a prospective candidate for a first wall material of a fusion reactor. It experiences magnetic stress due to magnetization in magnetic field. A ferromagnetic cantilever of mild steel was provided to carry out a test on magnetomechanical behavior and to compare with theoretical prediction. The theoretical prediction was made for an infinitely wide beam plate and magnetic stiffness was taken into account. Field distribution of the finite specimen is very different from one of an infinite specimen. It is made clear that deformation is proportional to the squared field for smaller applied field while linear with the field for larger one.

Analysis of the magnetomechanical behavior of a ferromagnetic beam plate

Ferritic stainless steel, hereafter called HT-9, is a prospective candidate material for the first wall of a fusion power reactor because of its high resistance to irradiation swelling due to 14 MeV neutrons. The large increase of the transition temperature has been proven to be in a range of 50°C even for a neutron fluence of more than 50 dpa. However, since it is magnetized in a magnetic field, it experiences magnetic stress due to magnetization when it is used in the field. The magnetomechanical behavior is not simple because its relative permeability is very high (∼1000) and the B-H curve is nonlinear and followed by saturation of the magnetization. Beam-plates of HT-9 and mild steel were provided to carry out tests on the magnetomechanical behavior and compare it to the theoretical prediction. The theoretical prediction of the mechanical behavior was made for the configuration of the beam-plate based on non-linear numerical analysis of magnetization. The field distribution of the finite specimen is very different from that of an infinite specimen. It is also found that the deformation is proportional to the squared field for a very small applied field and increases monotonously to a peak. For a specimen with small inclination to the incident field, the deformation decreases very rapidly after the peak.

Thermohydraulic and mechanical design assessment of tube-panel first wall for Tokamak Fusion Power Reactor

A first wall structural concept cooled by high temperature and pressurized water has been proposed for the Tokamak Fusion Power Reactor (SPTR-P). Among a number of candidate design concepts, a tube-panel structure was selected for the first wall design. Stainless steel serves as the first wall structural material. The first wall is separated from the blanket wall and has a circular cross-section coolant channel since this shape is the most desirable for resisting the mechanical load due to the pressurized cooling water. Feasibility of the thermohydraulic and mechanical design has been established by analyses under steady-state operating conditions. The effect of the heat load during plasma disruptions on the thermomechanical characteristics of the first wall has been clarified. The mechanical strength of the first wall of power reactor is inadequate to withstand the thermal load expected during plasma disruption in an experimental reactor.