Experimental Evaluation of Inductance and Its Impact on Quench Detection of the KSTAR Coils

Yonekawa, H,Yong Chu,Young-ok Kim,Kaprai Park,Hoon-Kyun Na,Myeun Kwon IEEE 2011 IEEE transactions on applied superconductivity Vol.21 No.3

<P>Windings of Nb<SUB>3</SUB>Sn cable-in-conduit conductors of the toroidal field (TF) and the 1st-5th poloidal field (PF) coils of the Korea Superconducting Tokamak Advanced Research (KSTAR) have Incoloy-908 jackets, which exhibit weak ferromagnetism. The inductance of the PF coils was measured by monitoring the induced voltages on the coils while TF coils were steadily energized at 20 kA, and one of each pair of PF coils was charged up to 4 kA at 2 kA/s. At a large PF current, the measured self inductance was very close to the design value. In contrast, the measured self inductances of the PF1-PF5 coils increased 90-135% by decreasing their current below 2 kA; whereas those of the PF6-PF7 coils almost stayed at the same levels. On the other hand, the measured self inductances were much smaller than the other measurements obtained at no TF current. The self induced voltage was almost cancelled out by using a single Wheatstone bridge of the quench detectors; whereas, the mutually induced voltage was cancelled out by numerically subtracting outputs of two Wheatstone bridges for coils, which were symmetrically located in the assembled coils.</P>

Experimental Results of Simplified Balance Bridges for the KSTAR Quench Detection System

Yonekawa, Hirofumi,Yong Chu,Young-ok Kim,In-sik Woo,Kap-rai Park IEEE 2016 IEEE transactions on applied superconductivity Vol.26 No.4

<P>The primary quench detection system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device has been operated in technical and plasma experiments for eight years. Cowound-type quench detectors have exhibited distinct performance of compensation for both self-induction and mutual induction; on the other hand, some cowound strips tended to break in the long-term operation. In contrast, Wheatstone bridge (WB)-type quench detectors had no wire breakage, and their signal wires are still accessible and repairable. Therefore, WB-type quench detectors are very important to be a backup method of quench detection for the coils. New WBs using a half-bridge at a fixed ratio of resistances of 1: 1 were tested in the KSTAR operation. Upper-lower comparison of the new WBs performed good compensation for induced voltage. The new WBs clearly demonstrated that the bridge circuits may become very simple, and in situ calibration may be unnecessary if the arrangement of voltage taps and quench detectors is optimized with respect to the magnetic field of the tokamak device.</P>

Operational Results of a Thermal-Hydraulic Quench Detection System for the KSTAR TF Superconducting Coils

Yonekawa, Hirofumi,Young-ok Kim,Yong Chu Institute of Electrical and Electronics Engineers 2017 IEEE transactions on applied superconductivity Vol.27 No.4

<P>The Korea Superconducting Tokamak Advanced Research (KSTAR) device is equipped with a prototype of the safety quench detection system (SQD), making use of the variation of the pressure and flow rate in supercritical helium (SHe) in the event of a quench, for the toroidal field (TF) superconducting coils. The SQD prototype measures absolute and differential pressures on orifice flow meters at SHe supply manifolds by using radio-resistant pressure transducers, then variation of the measurements is discriminated by using analog signal interfaces and hard-wired logic solvers of a two-out-of-three (2oo3) voting configuration for validation. The SQD prototype is being operated to obtain technical expertise in KSTAR. TF coil charging and PF coil pulsed operation had a different impact on the temperature variations due to eddy current of the TF coils and structure. Accordingly, the inlet pressure of the TF coils increased by small amount in comparison to the quench detection criterion of the SQD prototype. The plasma current seemed to increase impulse voltage, but only, by ~10 mV in quench detection signals of normal-voltage detection method, and such a noise did not disturbed quench detectors. On the other hand application of the PF currents and plasma current increased outlet temperatures of the TF coils and structure by approximately 0.1 K. The inlet pressure variation due to the temperature variation was too small to achieve the quench detection criterion.</P>

Experimental Evaluation of the Influence of External Current on the KSTAR TF Quench Detection System

Yonekawa, Hirofumi,Yong Chu,Young-Ok Kim,Soo-Hwan Park,Kap-Rai Park IEEE 2014 IEEE transactions on applied superconductivity Vol.24 No.3

<P>The quench detection system (QDS) for 16 toroidal field (TF) coils of the Korea Superconducting Tokamak Advanced Research (KSTAR) is using Wheatstone bridges to naturally reduce induced voltage in the quench detection circuits. The TF coils have to be quickly discharged to save the superconductors from thermal runaway if quench occurs; on the other hand, the fast discharge brings about many side effects. Thus, malfunction of the TF QDS should be avoided. According to the results of the TF QDS operation in KSTAR campaigns, the single Wheatstone bridges can sufficiently reduce self-induced voltage even though the induced voltage may remain due to unbalancing the bridges by ferromagnetism of the cable-in-conduit conductor (CICC) jackets at small TF coil current. In contrast, mutually induced voltage by central solenoid (CS) and poloidal field (PF) coils may not be sufficiently reduced by using a single Wheatstone bridge comparing voltages across a number of TF coils due to larger electric circuits in the cryostat. On the other hand, a single Wheatstone bridge comparing single TF coil voltages could not effectively reduce the sharp impulse voltage caused by locally induced current on the vacuum vessel at the end of plasma current with vertical displacement event (VDE).</P>

Electric Resistance Measurement of the KSTAR Superconducting Coils With Small Resistive Joints

Yonekawa, H.,Yong Chu,Young-ok Kim,Kap-rai Park,Hoon-kyun Na IEEE 2012 IEEE transactions on applied superconductivity Vol.22 No.3

<P>An electric resistance of lap joints assembled with Korea Superconducting Tokamak Advanced Research (KSTAR) poloidal field 1 (PF1) superconducting coils and bus lines was measured by 4-wire method with some improvements to reduce induced noise in measurements at cryogenic temperature. Generally, a large current has to flow through the joints in order to measure its resistance by electrical methods; however, an induced voltage generated by a DC power supply is much higher than a voltage drop on the joints. The improved method used a bypass resistor installed in parallel to the DC power supply and the coils in order to naturally reduce ripples of the coil current. Transitional waveforms of the coil current and tap voltages were approximated by non-linear curve fitting with constraints based on an electric circuit equation. The resistance and inductance were evaluated by solving simultaneous equations of an applied voltage on the conductors. The induced noise reduction by this method was helpful to evaluate the joint resistance.</P>

A Study of the Possibility of Positioning Using Small Number of Satellite

Masashi Yonekawa,Toshiyuki Tanaka 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8

Nowadays, positioning system using satellite is used in car-navigation, the cellular phone and the survey work. In addition, the demand of use is high. But, a new usage of satellite positioning has not been announced since then. One of the reasons, which is also the biggest problem, is because that positioning method is difficult to use. The positioning system using satellite requires more than four satellites. We consider the conditions of general living environments. The condition where the sky is completely free from obstacles is rare because obstacles like buildings, trees and etc are commonly present in our daily life environment. Therefore, it is difficult to always meet the requirement of more than 4 satellites. We study the ongoing possibility of positioning using less than four satellites. Whether or not the measurement was possible by four data was examined in this paper. If the data of the same satellite is used, the error margin grows.

Measurement of the Electric Properties of the KSTAR CS Model Coil

Hirofumi Yonekawa,G. M. Moon,G. S. Lee,J. S. Bak,J. S. Kim,박갑래,K. W. Cho,박수환,W. S. Han,W. W. Park,Y. Chu,Y. J. Lee,Y. K. Oh,Y. M. Park,Y. S. Kim,KSTAR Team 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2

The maximum current, the self inductance and the lap joint resistance of a split-pair superconducting pulse magnet were experimentally inspected. The pulse magnet mainly consists of two KSTAR central solenoid (CS) model coils, which are wound, continuous Nb₃Sn cable-in-conduit conductors (CICC) with Incoloy 908 jackets. The pulse magnet initially could not achieve its rated current over several days whereas the temperature of the magnet surfaces and coolant outlets stayed at 5 ~ 8 K. A training effect and a ramp rate limitation were suspected of being the cause at the beginning. However the magnet's supporting structure was found to have been exceedingly warm in that period, and the maximum current clearly corresponded to the temperature of the supporting structure. The self inductance of the pulse magnet was measured with an LCR meter at 0.1 ~ 1 kHz at room temperature, but the inductance was nearly double the design value. The self inductance was also measured by means of a decay time constant method at 5 K and, at values of current above 200 A, was found to be originally the same as the design value, however, it dynamically increased below that current. Supplemental calculation showed that the permeability of Incoloy 908 could have a detrimental impact upon the dynamic variation of the self inductance. The lap joint resistance was successfully obtained by measuring the voltage drops between two CICCs at 5 K. Another trial measuring the voltage drops between the two outer surfaces of the lap joint resulted in a nonphysical result that violated Ohm's law.

RELATIONS BETWEEN POSITIONING RESULT AND EACH ERROR FACTOR IN GPS

Masashi Yonekawa,Toshiyuki Tanaka 제어로봇시스템학회 2006 제어로봇시스템학회 국제학술대회 논문집 Vol.2006 No.10

Industry-Academia-Government Collaboration Activities and Human Resources Development Program at the University of Tokushima (ACDDE 2010)

Takahiro Yonekawa,Shigekazu Kanehira,HIroshi Noda,Fumika Oi,Hiromu Satake,Teruaki Ito (사)한국CDE학회 2010 한국CAD/CAM학회 국제학술발표 논문집 Vol.2010 No.8

Industry-academia-government collaboration activities of the University of Tokushima started in 1991 when its Regional Joint Research Center was set up. Since then, the university developed the organization and activities concerning industry-academia-government collaboration. Number of the staff member has been increased since then from one person at first to 33 at present and the activities were strengthened remarkably and became extensive. This paper describes our basic policies, outline of major activities; Technology Licensing, Research Promotion, Intellectual Property Management, and Information Management and Utilization, and outline of a technology matching system called TPAS-Net that helps and facilitates industry-academia-government collaboration activities. Then it shows our human resources development program that was introduced in 2005 to secure leading engineers for local companies. The program consists of three courses: Production Management Course, Advanced Technology Course and Internship Course. The outline of these courses and the result of the training are explained. Finally the content of a subject on simulation and modeling is presented briefly as an example of the development program.

Pressure Drop of CICC From Manufacturing Stage to Plasma Operation in KSTAR Superconducting Magnet System

Park, S.,Yonekawa, H.,Woo, I.,Kim, Y.,Chu, Y.,Park, K.,Kwag, J. IEEE 2013 IEEE transactions on applied superconductivity Vol.23 No.3

<P>The Korea Superconducting Tokamak Advanced Research (KSTAR) is a superconducting tokamak that consists of cable-in-conduit conductors (CICCs) and has been successfully operated since 2008. KSTAR toroidal field (TF) and poloidal field (PF) coils are cooled by forced-flow supercritical helium of about 4.5 K. The complicated behaviors of the supercritical helium affect the plasma operation and the efficiency of the helium refrigerator system by means of, for instance, pressure drop. The annual measurements of pressure drop of PF coils are carried out including the manufacturing stage at room temperature to check the inside status of the cable-in-conduit conductor. The mass flow distribution of TF coils has also been checked since the individual coil stage. During current charging of the TF coil, we confirmed the change of pressure drop, and the friction factor of PF coils are compared to the ITER case. In this paper, the latest hydraulic behaviors based on pressure drop of the KSTAR superconducting magnet are presented.</P>