Tetsuya Uchimoto

On the exploration of innovative concepts for fusion chamber technology

Abstract This study, called APEX, is exploring novel concepts for fusion chamber technology that can substantially improve the attractiveness of fusion energy systems. The emphasis of the study is on fundamental understanding and advancing the underlying engineering sciences, integration of the physics and engineering requirements, and enhancing innovation for the chamber technology components surrounding the plasma. The chamber technology goals in APEX include: (1) high power density capability with neutron wall load >10 MW/m 2 and surface heat flux >2 MW/m 2 , (2) high power conversion efficiency (>40%), (3) high availability, and (4) simple technological and material constraints. Two classes of innovative concepts have emerged that offer great promise and deserve further research and development. The first class seeks to eliminate the solid “bare” first wall by flowing liquids facing the plasma. This liquid wall idea evolved during the APEX study into a number of concepts based on: (a) using liquid metals (Li or Sn–Li) or a molten salt (Flibe) as the working liquid, (b) utilizing electromagnetic, inertial and/or other types of forces to restrain the liquid against a backing wall and control the hydrodynamic flow configurations, and (c) employing a thin (∼2 cm) or thick (∼40 cm) liquid layer to remove the surface heat flux and attenuate the neutrons. These liquid wall concepts have some common features but also have widely different issues and merits. Some of the attractive features of liquid walls include the potential for: (1) high power density capability; (2) higher plasma β and stable physics regimes if liquid metals are used; (3) increased disruption survivability; (4) reduced volume of radioactive waste; (5) reduced radiation damage in structural materials; and (6) higher availability. Analyses show that not all of these potential advantages may be realized simultaneously in a single concept. However, the realization of only a subset of these advantages will result in remarkable progress toward attractive fusion energy systems. Of the many scientific and engineering issues for liquid walls, the most important are: (1) plasma–liquid interactions including both plasma–liquid surface and liquid wall–bulk plasma interactions; (2) hydrodynamic flow configuration control in complex geometries including penetrations; and (3) heat transfer at free surface and temperature control. The second class of concepts focuses on ideas for extending the capabilities, particularly the power density and operating temperature limits, of solid first walls. The most promising idea, called EVOLVE, is based on the use of a high-temperature refractory alloy (e.g. W–5% Re) with an innovative cooling scheme based on the use of the heat of vaporization of lithium. Calculations show that an evaporative system with Li at ∼1u2008200°C can remove the goal heat loads and result in a high power conversion efficiency. The vapor operating pressure is low, resulting in a very low operating stress in the structure. In addition, the lithium flow rate is about a factor of ten lower than that required for traditional self-cooled first wall/blanket concepts. Therefore, insulator coatings are not required. Key issues for EVOLVE include: (1) two-phase heat transfer and transport including MHD effects; (2) feasibility of fabricating entire blanket segments of W alloys; and (3) the effect of neutron irradiation on W.

Profile reconstruction of simulated natural cracks from eddy current signals

Based upon the fact that internal conductivity of the crack has a serious effect on the eddy current signals, two kinds of inversion schemes that can reconstruct cracks with non-vanishing conductivity from eddy current signals are proposed in this paper. One is a physics-based approach that modifies crack parameters iteratively and the other is a neuronet-based approach. Two models that are supposed to be appropriate models of a natural crack are also proposed. After detailed explanation of the schemes, several reconstruction results using simulated data are presented. The results show these schemes can reconstruct crack profile with high accuracy where not only shape of the crack but also internal conductivity is unknown. Advantages and disadvantages of both schemes are discussed at the end of the paper.

Experimental and numerical evaluation of rotation speed degradation of radial type superconducting magnetic bearing

The degradation of levitation force and rotation speed is one of the most significant problems for the practical use of superconducting magnetic bearing (SMB) for flywheel energy storage system. The degradation are called the rotation losses caused by the AC magnetic field due to the inhomogeneous distribution of magnetic flux density of the permanent magnet (PM) rotor. In this research, our simulation method was improved so that the eddy current flowing in the cryostat around the superconductor was taken into account. The dependency of the rotation losses of radial type SMB with cryostat was evaluated by this new simulation method concerning the amplitude of inhomogeneous component of PM rotors field.

Reduction of toroidal ripple by using high Tc superconductors

Abstract In this paper we present a new method to reduce the toroidal ripple with use of high T c superconductors. High T c superconductors can behave as ferromagnetic or diamagnetic materials depending on their magnetic hysteresis. If they are appropriately arranged and magnetized between the toroidal field coils, they possibly decrease the toroidal field ripple. Here, the preliminary design of ITER is taken as an example, and the effect of the high T c superconductors on the ripple is evaluated. The magnetic induction due to the superconductors is calculated by the current vector potential method based on the critical state model. Several arrangements of the high T c superconductors were quantitatively examined in order to reduce the ripple. The results obtained by the calculation show that the maximum ripple value can be reduced to be the required value.

Design Study on High Tc Superconducting Plasma Stabilizer

This paper presents design study on application of high Tc superconductors (HTSCs) as a stabilizer for improvement of the plasma vertical instability. For this purpose, an numerical simulation of the overall system including the plasma, the structures and the HTSCs was carried out taking an example of the configuration of the ITER tokamak reactor. Through this simulation, arrangements and parameters of the high Tc superconducting stabilizer are optimized with the consideration of various constraints from the technological viewpoint of the fusion reactor.

132 Nondestructive Evaluation of Austenitic Stainless Steel Residual Strain with EMAT and ECT Dual Probe

and electromagnetic properties can be evaluated with the dual probe at the same time. This advantage makes the probe hasa wide range of application and good testing performance, In theory, the dual probe can improve the testing speed and accuracy ofresidual strain, To figure out the feasibility of the dual probe in residual strain evaluation, in this study, the EMAT-ECT dual probe is applied te the evaluation of residual strain of austenitic stainless steels. Ultrasonic velocities and eddy current signals are evaluated from stainless steel

AC Loss of YBCO Magnetic Bearing Covered with HTSC Thin Films

The decreases of rotation speed and levitation force are ones of the most significant problems for the practical use of HTSC bearing. It is caused by AC field due to the inhomogeneous magnetization of the rotor’s PMs. In this research, we propose the HTSC bearing covered with the HTSC thin films that have much larger Jc for suppression of rotation loss, and its effects are investigated by experimental and computational works.

Design of compact tokamak reactor with HTSC plasma stabilizing coils

Abstract This paper presents a design of tokamak plasma with use of the high temperature superconducting coils as plasma stabilizer. Having regard to the current situation of the ITER project, two cases of designs were investigated: a smaller machine which has the same mission of the ITER/RCO (Q=10), and an ignition machine which has the same major radius as ITER/RCO (R=6.1 m). The same data base and formulas as ITER are here used and any innovative technology other than the HTSC stabilizing coils is not assumed.

Evaluation of flux flow resistivity of high Tc superconducting cable for application to fusion reactors

Abstract A new method for improving plasma positional instability was proposed by using high Tc superconductors (HTSCs) and its feasibility was numerically demonstrated. In order to estimate the stabilizing effect of HTSCs with high accuracy, a flux flow and creep (FFC) model should be adopted as the model of shielding current. Here, a flux flow resistivity plays an important role in the evaluation, due to the induction change in HTSCs being large. In this paper, it was verified experimentally that a numerical analysis applying the FFC model is valid, and the flux flow resistivity was evaluated. Furthermore, the dependence of the stabilizing effect on the flux flow resistivity was evaluated by the analysis based on the FFC mode, and a design guideline of high Tc superconducting cable was also indicated.

Study on High Tc Superconducting Ripple Reducer

This paper presents study on application of high Tc superconductors as a ripple reducer for reduction of the toroidal field (TF) ripple without changing the design of TF coils. The feasibility of the ripple reducer is first demonstrated on the basis of experiments. Next, parameter survey of the ripple reducer is performed for the configuration of the outline design of ITER, and a guideline for the design of the ripple reducer is presented with the consideration of constraints from the technological viewpoint of the fusion reactor.