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1. Observation of a non-uniform current distribution in stacked high temperature superconducting tapes

Author

N. Yanagi, T. A. J. Meulenbroeks, S. Matsunaga, and Y. Terazaki

Subjects
History, Materials science, Condensed matter physics, Current distribution, High temperature superconducting, Computer Science Applications, Education
Abstract

High Temperature Superconductors (HTS) improve upon low temperature superconductors in many ways and the ability to cope with a non-uniform current distribution might be one of those improvements. To put this to the test, an experimental setup is designed to force a non-uniform current upon a stack of 5 HTS tapes, using a worst case current feeding method. The experiment can help determine the potential of this conductor design and is part of the ongoing effort to develop a non-transposed stacked HTS conductor for the nuclear fusion reactor FFHR. The results clearly show that the conductor sample is able to stably conduct a current equal to its critical current, although at an elevated electric field of roughly 5 mV/m. This means non-transposed stacked tape conductors remain stable, even if a worst case nonuniform current is constantly forced upon them. A hypothesis to explain this abnormally high electric field is formulated on the basis of the results, however additional research is needed to verify it. It states that the electric field is necessary for the tapes to share current and would mean that in a properly engineered application, these losses due to the electric field, would only occur during start-up. Overall it is clear that this experiment proves the excellent stability of non-transposed stacked HTS tapes and their ability to conduct a non-uniform current.

Published
2019

2. Design and fabrication of forced-flow coils as an R&D program for Large Helical Device

Author

K., Takahata, N., Yanagi, T., Mito, J., Yamamoto, O., Motojima, Design Group, LHD, K., Nakamoto, S., Mizumaki, K., Kitamura, Y., Wachi, H., Shinohara, K., Yamamoto, M., Shibui, T., Uchida, and K., Nakayama

Subjects
Large Helical Device, Materials science, Nuclear magnetic resonance, Electromagnetic coil, Electrical equipment, Heat exchanger, Radius, Mechanics, Superconducting magnet, Electrical and Electronic Engineering, Electrical conductor, Current density, Electronic, Optical and Magnetic Materials
Abstract

Two forced-flow cooled NbTi superconducting coils (TOKI-TF, PF) have been designed and fabricated. The helical coil (TOKI-TF) is a 1/4-scale model of the Large Helical Device (LHD). It has a major radius of 0.9 m, a minor radius of 0.25 m, and a pitch number of 4. Nominal current and maximum field were designed to be 8 kA and 2.8 T, respectively. Another coil (TOKI-PF) was fabricated for the demonstration of LHD poloidal field coils. It consists of two double pancakes with an inner radius of 0.6 m and an outer radius of 0.82 m. The nominal current of 25 kA simulates that of LHD poloidal field coils. Cable-in-conduit-type conductors were used for the both coils. The test facility was also constructed with a vacuum vessel, a liquid nitrogen shield, 30-kA power leads, a heat exchanger, and cryogenic supports. Design concepts and details are presented.

Published
1991

3. Design and fabrication of module coil as an R&D program for Large Helical Device

Author

T. Mito, J. Yamamoto, K. Takahata, N. Yanagi, O. Motojima, T. Ichihara, K. Toyoda, T. Minato, and T. Sasaki

Subjects
Quantitative Biology::Biomolecules, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Abstract

A twisted solenoid coil (TOKI-MC) has been designed and fabricated in order to study the mechanical properties of the Large Helical Device (LHD). One of the most important R&D items of the LHD is the mechanical behavior of the helical coils under a large electromagnetic force. The TOKI-MC was wound obliquely on the 3D-machined elliptical bobbin with a maximum torsional rate of 36deg/m at the innermost conductor. The maximum field in the coil is 7.7 T with an operating current of 20 kA, an average current density of 40 A/mm^2, and a stored energy of 11 MJ. The TOKI-MC can simulate the electromagnetic force, conductor torsional rate, magnetic field, operating current, and current density of the LHD superconducting helical coils. The design and test results of the conductor and the design and fabrication of the coil are described

Published
1991

4. Performance of upgraded cooling system for LHD helical coils

Author

S. Hamaguchi, S. Imagawa, T. Obana, N. Yanagi, S. Moriuchi, H. Sekiguchi, K. Oba, T. Mito, O. Motojima, T. Okamura, T. Semba, S. Yoshinaga, H. Wakisaka, J. G. Weisend, John Barclay, Susan Breon, Jonathan Demko, Michael DiPirro, J. Patrick Kelley, Peter Kittel, Arkadiy Klebaner, Al Zeller, Mark Zagarola, Steven Van Sciver, Andrew Rowe, John Pfotenhauer, Tom Peterson, and Jennifer Lock

Subjects
Quantitative Biology::Biomolecules, business.industry, Nuclear engineering, Physics::Medical Physics, Electrical engineering, chemistry.chemical_element, Cryogenics, Superconducting magnet, Physics::Fluid Dynamics, Subcooling, Large Helical Device, chemistry, Heat exchanger, Physics::Atomic and Molecular Clusters, Water cooling, Physics::Atomic Physics, Lambda point refrigerator, business, Helium
Abstract

Helical coils of the Large Helical Device (LHD) are large scale superconducting magnets for heliotron plasma experiments. The helical coils had been cooled by saturated helium at 4.4 K, 120 kPa until 2005. An upgrade of the cooling system was carried out in 2006 in order to improve the cryogenic stability of the helical coils and then it has been possible to supply the coils with subcooled helium at 3.2 K, 120 kPa. A designed mass flow of the supplied subcooled helium is 50 g/s. The subcooled helium is generated at a heat exchanger in a saturated helium bath. A series of two centrifugal cold compressors with gas foil bearing is utilized to lower the helium pressure in the bath. The supplied helium temperature is regulated by rotational speed of the cold compressors and power of a heater in the bath. The mass flow of the supplied helium is also controlled manually by a supply valve and its surplus is evaporated by ten heaters at the outlet above the coils. In the present study, the performance of the cooli...

Published
2007

6. Conceptual design of a compact helical fusion reactor FFHR-c1 for the early demonstration of year-long electric power generation.

Author

T. Goto, J. Miyazawa, H. Tamura, T. Tanaka, R. Sakamoto, C. Suzuki, R. Seki, S. Satake, M. Nunami, M. Yokoyama, N. Yanagi, A. Sagara, and Group, the FFHR Design

Subjects
ELECTRIC power production, FUSION reactors, CONCEPTUAL design, SUPERCONDUCTING magnets
Abstract

Conceptual design of a compact large helical device (LHD)-type helical fusion reactor FFHR-c1 has been conducted. This design focuses on a year-long electric power generation with as small a reactor size as possible by adopting the operation with auxiliary heating and innovative ideas for the design of the superconducting magnet, divertor and blanket system. The primary design parameters, which have been selected by extrapolation from the previous design FFHR-d1B using simple scalings, has been examined by the systems code and the 1D integrated physics analysis code from the viewpoint of plant power balance and the achievable plasma operation regime. The design feasibility of the proposed design point has been confirmed with the physics parameters that are consistent with the LHD experiment. Further improvement of the plasma performance is expected by the optimisation of the helical coil winding law. Although intensive R&D is needed to realise the innovative ideas of the engineering design, this design ensures the path to helical commercial power plants and provides more options and increases the probability of solving critical issues of fusion reactors. [ABSTRACT FROM AUTHOR]

Published
2019
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18. Core plasma design of the compact helical reactor with a consideration of the equipartition effect.

Author

T Goto, J Miyazawa, N Yanagi, H Tamura, T Tanaka, R Sakamoto, C Suzuki, R Seki, S Satake, M Nunami, M Yokoyama, A Sagara, and Group, the FFHR Design

Subjects
PLASMA gases, EQUIPARTITION theorem, HELICAL structure, MAGNETIC fields, ELECTROMAGNETIC theory
Abstract

Integrated physics analysis of plasma operation scenario of the compact helical reactor FFHR-c1 has been conducted. The DPE method, which predicts radial profiles in a reactor by direct extrapolation from the reference experimental data, has been extended to implement the equipartition effect. Close investigation of the plasma operation regime has been conducted and a candidate plasma operation point of FFHR-c1 has been identified within the parameter regime that has already been confirmed in LHD experiment in view of MHD equilibrium, MHD stability and neoclassical transport. [ABSTRACT FROM AUTHOR]

Published
2018
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19. Development of remountable joints and heat removable techniques for high-temperature superconducting magnets.

Author

H. Hashizume, S. Ito, N. Yanagi, H. Tamura, and A. Sagara

Subjects
SUPERCONDUCTING magnets, FUSION reactors, HIGH-temperature superconducting filters, LIQUID nitrogen, THERMAL stability
Abstract

Segment fabrication is now a candidate for the design of superconducting helical magnets in the helical fusion reactor FFHR-d1, which adopts the joint winding of high-temperature superconducting (HTS) helical coils as a primary option and the ‘remountable’ HTS helical coil as an advanced option. This paper reports on recent progress in two key technologies: the mechanical joints (remountable joints) of the HTS conductors and the metal porous media inserted into the cooling channel for segment fabrication. Through our research activities it has been revealed that heat treatment during fabrication of the joint can reduce joint resistance and its dispersion, which can shorten the fabrication process and be applied to bent conductor joints. Also, heat transfer correlations of the cooling channel were established to evaluate heat transfer performance with various cryogenic coolants based on the correlations to analyze the thermal stability of the joint. [ABSTRACT FROM AUTHOR]

Published
2018
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24. First Cool-down Performance of the LHD

Author

T., Mito, R., Maekawa, S., Yamada, A., Nishimura, K., Takahata, S., Imagawa, K., Watanabe, N., Yanagi, H., Tamura, A., Iwamoto, T., Baba, S., Moriuchi, K., Oba, H., Sekiguchi, I., Ohtake, T., Satow, S., Satoh, O., Motojima, and Group, LHD

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