Shunji Tsuji-Iio

Wind farms linked by SMES systems

The objective of this paper is to introduce the concept of wind farms linked by SMES systems. In this work, the SMES system is applied to a wind farm that is interconnected with a grid through a back-to-back DC link for the variable speed operation of the wind turbines. This system enables the output power leveling of the wind farm depending on the power demand and can reduce the capacity of the converter system by selecting an optimal discharge/charge rate of the SMES. By using the stored energy of the SMES, this system can also compensate the inertia of the blades so that the wind turbine speed can be rapidly controlled depending on the wind condition. This paper describes the design condition of the SMES for the output power leveling of the wind farm and discusses the SMES configuration for a 100-MW class wind farm.

Flexible Power Interconnection With SMES

Electric power networks are usually interconnected with each other through a back-to-back direct-current (DC) link to increase reliability of electric power networks and to improve system operations. The objective of this work is to discuss the concept of a superconducting magnetic energy storage (SMES) incorporated into a back-to-back interconnection. In this case, the back-to-back system is used as a power conditioning system for the SMES coils. Since the AC/DC converter can be designed independently of the frequency of the power system, a two-way switch is connected to the AC side of each converter. This two-way switch can select the interconnected power system. By using the two-way switches, this system can increase the availability factor of the back-to-back interconnection during the SMES operations and also enables the flexible power interchange between interconnected power networks with an optimal time interval for the power demand of each interconnected power network. This work discusses the design considerations of the back-to-back interconnection with the SMES that enables the replacement of a pumped hydro storage. In this case, the SMES system is composed of a number of superconducting coils in order to decrease the risk of the superconducting coil constructions by the effect of mass production. In this work, the SMES coils are optimized from the required mass of the structure and the leakage magnetic field

Internal transport barrier with improved confinement in the JT-60U tokamak

Characteristics of the internal transport barrier (ITB) were studied. The region of steep and , i.e. the ITB front, propagated from the core outwards. The thickness of the ITB front was about 3 cm. The ITB worked as a particle transport barrier as well as a thermal transport barrier for ions. The threshold heating power for ITB formation strongly increased with electron density and was independent of the toroidal magnetic field. ITB with was sustained for twice the global energy confinement time . A repetitive relaxation phenomenon at ITB was observed, which induced spikes like ELMs but had a different poloidal distribution.

Objectives and design of the JT-60 superconducting tokamak

A fully superconducting tokamak named JT-60SC is designed for the modification programme of JT-60 to enhance economical and environmental attractiveness in tokamak fusion reactors. JT-60SC aims at realizing high-β steady-state operation in the use of low radio-activation ferritic steel in a low ν* and ρ* regime relevant to the reactor plasmas. Objectives, research issues, plasma control schemes and a conceptual design for JT-60SC are presented.

CO2 laser polarimeter for electron density profile measurement on the Large Helical Device

We developed a three-channel tangential CO2 laser polarimeter to measure electron densities on the Large Helical Device. Our system aims to obtain not only the line averaged electron density but also the electron density profile. The achieved resolution of the Faraday rotation angle was 0.01° with a response time of 3 ms by digital complex demodulation combined with digital filtering. The phase fluctuations whose amplitude is typically 0.05° with a time constant of several seconds were observed. It was found that they were caused by beam axis fluctuations from bench top experiments. In the case of pellet injected plasmas it was demonstrated that the polarimeter could measure the time evolution of the Faraday rotation with high reliability and resolution. The calibrated rotation angle of all chords were well consistent with interferometer data. Assuming the functional dependence of the density profile, we estimated the density profile after pellet injections from three-channel polarimeter data iteratively....

Helically wound coils for high field magnets

The winding current density of a superconducting coil is one of the key parameters to realize high field magnet systems with smaller sized superconducting coil. Force-balanced coil (FBC) which is a helically wound toroidal coil can control the distribution of working stresses and minimize the structure requirements by selecting an optimal number of poloidal turns. The winding current density of a superconducting coil is estimated from the relationship between ampere-meters of conductor and structure requirements based on the virial theorem. In this case, the FBC can obtain the stored energy for the same winding current density 20 times larger than that in the toroidal field coils case and about 120 times larger than that in the solenoid case. By applying the FBC concept, superconducting magnets will be realized in smaller size.

Force-balanced coil for large scale SMES

In large scale SMES, huge electromagnetic force caused by high magnetic fields and coil currents is a serious problem. In order to solve this problem, we propose a concept of force-balanced coil (FBC) applied to the SMES. The FBC balances the centering force with the hoop force, both of which are exerted in the major radius direction. Moreover, for the optimization of large aspect ratio superconducting coils, we propose a stress-balanced coil (SEC) concept, improving the concept of FBC, which balances magnetic pressures at the coil nose part where the produced magnetic field reaches its maximum value. Comparing the toroidal magnetic field coil (TFC) and FBC with SEC, the last can reduce coil stresses and obtain large stored energy with shorter length conductors and/or lower magnetic fields.

Variations of force-balanced coils for SMES

Strong electromagnetic force caused by high magnetic fields and coil current is a serious problem in superconducting magnetic energy storage (SMES) systems. In facing this problem, we proposed the concept of the force-balanced coil (FBC) which is a helically wound toroidal coil applied to SMES. This paper shows the variations of the helical windings in order to reduce structure requirements. We discuss the relationship between the shape of SMES coils and the structure requirements based on the virial theorem. From this result, the FBC can minimize the working stresses by selecting the optimal number of poloidal turns.

Design considerations for force-balanced coil applied to SMES

Strong electromagnetic force caused by high magnetic field and large coil current is a serious problem in superconducting magnetic energy storage (SMES) systems. In facing this problem, we propose the concept of force-balanced coil (FBC) which is a helical-winding toroidal coil and can reduce the centering force of toroidal field coil (TFC). The helical-winding of the FBC is modulated in order to reduce the torsional force. This paper describes the cost-related parameters of the FBC in terms of the dimension of the coil, the ampere-meters of superconductors and the surface area of the coil compared with the TFC and the solenoid. Moreover, we discuss the structure requirements by the virial theorem and improve the concept of FBC in terms of the further optimization of SMES through the structural analysis.

Application of parallel connected power-MOSFET elements to high current d.c. power supply

The low aspect ratio spherical torus (ST), which has single turn toroidal field coil, requires the extremely high d.c. current like as 20 MA to energize the coil. Considering the ratings of such extremely high current and low voltage, power-MOSFET element is employed as the switching device for the a.c./d.c. converter of power supply. One of the advantages of power-MOSFET element is low on-state resistance, which is to meet the high current and low voltage operation. Recently, the capacity of power-MOSFET element has been increased and its on-state resistance has been decreased, so that the possibility of construction of high current and low voltage a.c./d.c. converter with parallel connected power-MOSFET elements has been growing. With the aim of developing the high current d.c. power supply using power-MOSFET, the basic characteristics of parallel operation with power-MOSFET elements are experimentally investigated. And, the synchronous rectifier type and the bi-directional self commutated type a.c./d.c. converters using parallel connected power-MOSFET elements are proposed.