Current Feeder System Research Articles

Preliminary design and analysis of 20 K helium cooled MgB2 based superconducting current feeder system for Tokamak application

Current feeders system (CFS) is one of the most critical part of a large-scale superconducting (SC) magnets based machines like a tokamak or accelerator. One end of the SC feeder is connected to magnets and another end is connected to the power supply via optimised current leads (CL) for energizing the magnets. So far, low temperature superconductor (LTS) is the popular choice for such applications. For high temperature superconductor (HTS) applications, cuprate oxide based coated conductors or magnesium diboride (MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) wires are the options. MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> despite of its superconducting transition temperature of 39 K,is now gaining wide attention for SC feeders system due to its lower raw material cost and ease of availability than 2G HTS tapes. To assess its suitability, we report 1-D thermo-hydraulic study of 10 kA rated MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> current feeders system cooled with 20 K helium for SST-1 tokamak as a case study. For varying mass flow rate, temperature margin along the feeder are calculated considering helium at 20 K, 4 bar (a) with cooling inlet from magnet side. Such a feeder yields a temperature margin of 6 K–16 K across its entire length depending up on mass flow rate of helium. There is also a possibility of cooling the binary current lead (HTS + MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) from cold helium coming out from the feeder. From our study, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> current feeder system provides benefits of higher temperature margin, lower mass flow requirement and cryogenic savings by use of 20 K helium as coolant compared to LTS based feeders. In future, it could provide a safe, reliable and cryogenic operational cost saving solution for SC current feeders for Tokamak applications.

Insulation of Current Leads for Superconducting PF-3 Coils of SST-1

Conventional copper current leads (CLs) for superconducting magnets of SST-1 are fabricated to operate in dc condition for Toroidal field coils and fast current ramp up to 10 kA for Poloidal field (PF) coils at low temperature under vacuum. Two pairs of CLs are required to be installed with PF-3 coil terminals in current feeder system chamber (CFSC) for shaped plasma operation in SST-1.The PF coils of SST-1 are subjected to the induced voltages of around 1 kV due to Ohmic coil discharge. In past few campaigns, high induced voltages on PF coils due to Ohmic coil discharge have caused arcing inside the CFSC between high potential PF CLs and grounded thermal shield. This arcing resulted in severe damage to the PF current leads and helium hydraulic lines. We report the development and implementation of Paschen leak tight electrical insulation for cylindrical CLs with variations in diameter and geometry along its length. The developmental procedures include the sample preparations and optimization of insulation processes. The scales down version of CLs samples were prepared after the investigation of curing kinetics of insulation resin at 140 &#x00B0;C and 110 &#x00B0;C. The high voltage testing of these insulation samples was carried out up to 28 kV at room temperature (RT) before and after multiple thermal shocks. These insulation samples were also tested up to 5 kV dc and 80 K temperature in Paschen test setup. The insulation resistance and breakdown voltage of these samples found to be more than 100 G&#x03A9; and 28 kV, respectively at RT.

Reliable long-term operation of superconducting bus lines for the LHD

The Large Helical Device (LHD) is an experimental device for helical type fusion plasma in National Institute for Fusion Science and plasma experiments over 150,000 shots have been successfully conducted during twenty long-term plasma experimental campaigns. The LHD has two kinds of superconducting magnets and nine flexible superconducting bus lines with an average length of 55 m, which are utilized as a part of the current feeder system between the coils and the power sources. The superconducting bus lines consist of a pair of aluminum stabilized NbTi/Cu compacted stranded cable insulated electrically and coaxial five corrugated stainless steel tubes with two layers of vacuum insulations. The nominal current is 32 kA and the withstand voltage is 5 kV in 77 K gas helium. From the first experimental campaign, the superconducting bus lines have been stably operated at steady state by using automatic control. It is also confirmed that the status of the superconducting bus lines are kept good thanks to appropriate maintenances. As the results, the reliable operation of the superconducting bus lines has been achieved during the plasma experimental campaigns without any serious failure and the total operational time of the steady state cooling is approximately 58,000 hours.

Performance of Superconducting Current Feeder System for SST-1

Superconducting (SC) Current Feeder System (CFS) for SST-1 (Steady state superconducting Tokamak was installed and commissioned in 2012. Since then, it has been operating successfully in successive plasma campaigns. The aim of this system is to transfer electric current from power supply at ambient temperature to SC magnets which are at 4.5 K. It consists of 10 kA vapour cooled current leads, Nb-Ti/Cu bus-bars, liquid nitrogen cooled radiation shield and liquid/vapour helium circuits. This system had been operated reliably in different scenario such as initial cool- down, electric current (ramp-up, ramp down and long-time steady state condition), cold with no current and in quench etc. In addition to this, it has fulfilled the long term operation with SST-1 with current flat top of 4.7 kA for more than 20,000 seconds. This paper highlights operational performance along with results in different aspects.

Upgradation in SCADA and PLC of existing LN2 control system for SST-1

Helium Refrigerator/Liquefier system of Steady State Superconducting Tokamak (SST-1) incorporates Liquid Nitrogen (LN2) pre-cooling system. LN2 is used for 80K thermal shields of SST-1, current feeder system and integrated flow distribution and control system. The LN2 management system is distributed system and requires automatic control. Initially LN2 control system had Citect based Supervisory Control and Data Acquisition (SCADA) and Koyo make Programmable Logic Controller (PLC). With the passage of time and due to unavailability of their hardware, it is being obsoleted. So, the requirements of new PLC and SCADA systems have been envisaged to make uninterruptable operation of SST-1 cryogenic system. Therefore, Wonderware SCADA and Schneider Electric make PLC is programmed to replace Citect SCADA and Koyo PLC. New control features have been added in upgraded control system for better management of LN2 system. This upgradation of SCADA and PLC is completed, tested successfully and in operation. Operational performance highlights of the new upgraded system are presented in this paper.

Electrospun Polyacrylonitrile-Based Nanofibers Maintain Embryonic Stem Cell Stemness via TGF-Beta Signaling.

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are capable of self-renewal and differentiation into any cell type, thus making them the focus of many clinical application studies. Culturing ESCs on mouse embryonic fibroblast-derived and cell-based feeder layers to maintain pluripotency is a standard laboratory procedure. However, xenogeneic contamination and the large amount of time required for feeder cell preparation are two challenges that encourage the use of a murine-based feeder layer. A novel biomaterial is required to replace the current cell-based feeder system. Toward this goal, we applied a combination of biocompatible polyacrylonitrile (PAN) and electrospinning technology to establish a non-cell-based feeder layer. According to results from stem cell marker staining, scanning electron microscopy, and embryoid body formation tests, optimal ESC stemness and pluripotency were noted in three electrospun groups (2, 4, and 8 minutes), with the longer electrospinning times producing higher feeder-layer densities. KEGG pathway microarray results identified TGF-beta signaling as one of the major deregulatory pathways on electrospun-based feeder layers. Western blot data indicate significant increases in TGF-beta receptor II, phosphorylated Smad3, and Nanog protein levels in the 4- and 8-minute electrospun-based feeder layer groups compared to the non-feeder layer group. Combined, the data suggest that electrospun-based feeder layers are good candidates for maintaining ESC and iPSC pluripotency in clinical applications.

Instrumentation and DAQ aspects of SST-1 current feeder and 80 K thermal shield systems

The operational requirement of Steady State Superconducting Tokamak (SST-1) Current Feeder System (CFS) and 80 K thermal shield demands large number of parameters to be measured and monitored. The parameter includes the temperature, pressure, liquid level, fluid flow and voltage across different current carrying components of SST-1. In refurbished SST-1 CFS which is equipped with (+/-) 10 pairs of conventional vapor cooled current leads (VCCL), superconducting (SC) feeders, actively cooled LN2 shield etc. All these components are installed with suitable and sufficient instrumentation and diagnostics. Similarly, 80 K thermal shield of SST-1, also need a large number of temperature sensors to monitor the temperature profile of the shield. We have carried out the online measurement and monitoring of these parameters to smoothen the operation of both the above systems during the recent commissioning of SST-1. This paper describes the details of instrumentation and data acquisition systems of the current feeder and 80 K thermal shield.

Design and engineering validation of venturi flow meter for current feeder system of SST 1

Current feeder system (CFS) of steady state superconducting tokamak 1 (SST-1) consists of ten pair of vapour cooled current leads (VCCL). Helium vapour consumption of a VCCL is an important parameter to be measured accurately during operation of current leads. To measure flow precisely and accurately, we use venturi type flow element. A venturi flow element was designed for required flow rate with accuracy of approximately +/-1% and the same was machined, finally it was calibrated and validated to define its discharge co efficient and found to be in agreement with the designed value. These venturi flow elements with Differential pressure transmitter (DPT) have been installed in helium gas return network of current feeder system of SST-1. This paper describes design, validation and installation and commissioning of venturi flow element with its DPT.

Supervisory control and data acquisition system development for superconducting current feeder system of SST-1

The Current Feeders System (CFS) is essentially an optimized bridge between the power supply at room temperature and Super Conducting Magnet System (SCMS) of the SST- 1 machine at 4.5 K.CFS is a complex electrical and cryogenic network which consists of ten pairs of 10 KA rating helium Vapor cooled Conventional Current Leads (VCCLs), superconducting (SC) current feeder and associated components. For the safe and reliable operation of CFS, it is equipped with different physical process parameters measuring instruments like flow, pressure, temperature, level, vacuum, voltage taps and final control element like control valves, heaters, vacuum pumps etc. PLC program is developed in ladder language for acquiring and controlling the process parameters. Independent SCADA applications developed in Wonderware Intouch software for data communication from PLC, front-end Graphical User Interface (GUI), auto-manual interface, real time trends, history trends, events and alarm pages. Time synchronized communication established between CFS control system and Industrial SQL server (InSQL) Historian for centralized storage of CFS process parameters which intern provides the CFS process data to SST-1 central control room. SCADA based data acquisition and data retrieval system is found to be satisfactory during the recent SST-1 cool down experiment. This paper describes the SCADA and PLC application development and their communication to InSQL server.

Up-graded Control System of Liquid Nitrogen Management System of SST-1

Liquid Nitrogen (LN2) is used for 80 K thermal shield of Steady-state Super-conducting Tokamak (SST-1), Integrated Fluid Distribution and Control System, Current Feeder System and 80 K refrigerant in Helium Liquefier/Refrigerator. A dedicated storage and distribution system for LN2was installed at IPR. The present system includes 3-nos of storage tanks, sub-cooler dewar, vacuum jacketed cryo-lines and instrumentation. This system employs PLC based supervisory control system with smart process instrumentation. Considering nonupgradability and lack of reliability due to obsolesce of components of automation system and future plan of 80 K single phase distribution system for thermal shield of SST-1, new control system is required. Various control schemes are employed for sub-cooler dewar, evaporators and storage tanks. The up-graded control system will offer ease of operation with improved automation, better maintainability and reliability. This paper describes design and development of up-graded control system of LN2 system.

Experience of superconducting current feeders system of SST-1

The superconducting current feeder system for SST-1 which has been installed and commissioned recently along with SST-1, felicitates to energize the SST-1. The CFS consists of ten pairs of 10,000 Ampere (A) rating helium vapor cooled conventional current leads, interconnecting Cu-SC joints, three numbers of cryo-compatible SC feeders ducts, current leads assembly chamber, hydraulic network and three numbers of joint boxes operated at different current rating to charge Toroidal Field and Poloidal Field coils separately. During the last three campaigns, it was possible to achieve a controlled cool down up to 4 K and showed its rated operational performance. Actively cooled liquid nitrogen shield showed temperature profile in the temperature range of80-85K and the whole system was evacuated up to 6×10−6 mbar. The measured LHe consumption rates from TF VCCL were 0.3 g/s and 0. 35 g/s at zero current and 1kA respectively.

The maintenance record of the KSTAR helium refrigeration system

Korea Superconducting Tokamak Advanced Research (KSTAR) has a helium refrigeration system (HRS) with the cooling capacity of 9 kW at 4.5 K. Main cold components are composed of 300 tons of superconducting (SC) magnets, main cryostat thermal shields, and SC current feeder system. The HRS comprises six gas storage tanks, a liquid nitrogen tank, the room temperature compression sector, the cold box (C/B), the 1st stage helium distribution box (DB#1), the PLC base local control system interconnected to central control tower and so on. Between HRS and cold components, there's another distribution box (DB#2) nearby the KSTAR device. The entire KSTAR device was constructed in 2007 and has been operated since 2008. This paper will present the maintenance result of the KSTAR HRS during the campaign and discuss the operation record and maintenance history of the KSTAR HRS.

Design, fabrication and commissioning of the KSTAR TF current feeder system

The 16 toroidal field (TF) coils of the Korea Superconducting Tokamak Advanced Research (KSTAR) device are connected in series through inter-coil buses. The 15 inter-coil buses connecting nearby TF coils used the superconducting cable-in-conduit conductor (CICC) that is identical to the conductor of the main TF bus-lines. In addition, two half-turn buses are connected to the remaining two TF coil terminals, and finally routed to the vicinity of the inter-coil buses to minimize the cross-sectional area of the closed loop between inter-coil buses and half-turn buses. Strand-to-strand (STS) joints are utilized to join the TF coil terminals to the end parts of inter-coil buses. The TF current feeder system (CFS) has two pairs of superconducting (SC) bus-lines and current leads. This arrangement has an advantage in the reliable current discharging of SC bus-lines because one half of the current (17.5 kA) flows through each bus-line. In this paper, general design features, manufacturing and operational results of the superconducting TF bus-line are reported in detail, including analysis results for the quench-safety of the half-turn bus.

Development of HTS Current Feeder Quench Detection System for the EAST Tokamak

A high temperature superconductor (HTS) current feeder system is used as the current transmission lines for EAST Tokamak. It consists of a pair of 16 kA HTS current feeder for the Toroidal Field (TF) coils, 6 pairs of 15 kA current feeders for Central Solenoid (CS) coils and 6 pairs of 15 kA current feeders for the Poloidal Field (PF) coils. The HTS magnets are made of Bi-2223/Ag-Au alloy tapes supplied by American Superconductor Corporation. Several methods have been used for quench detection in the EAST HTS current feeder. For the investigated conditions, detecting resistance voltage shows the best performance as the main quench detection method due to the fastest response time. This paper describes the design of HTS current feeder quench detection system for EAST and emphasizes the development of detecting system in the recent EAST operating scenarios. The relevant upgrade woke for the detecting system has also been assessed in the various operating conditions especially including quench events.

Construction and Commissioning of the KSTAR Current Feeder System

The function of the current feeder system (CFS) is for conducting large currents from the power supplies to the KSTAR superconducting (SC) magnets. The CFS consists of SC bus-lines, joints, and current leads. The bus-line conductor is a circular cable-in-conduit conductor (CICC), which consists of a 4.5 mm thick stainless steel 316L seamless pipe containing 324 strands of chrome coated NbTi superconductor and 243 strands of OFHC. The ends of the CICC are assembled with specially designed lap joints. The joining resistance is controlled to less than 2.5 nano-ohm to minimize Joule heating. The outer surfaces of the CICC were electrically insulated up to 15 kV with jackets made of Kapton film and prepreged E-glass tape. Helically wrapped conducting fiber was used to measure the voltages of bus-line quenches. Two pairs of prototype brass leads for poloidal field (PF) and toroidal field (TF) coils have been fabricated and tested up to the currents of 26 kA for the PF leads and 35 kA for the TF leads. The test results satisfied all the requirements so that all 18 leads were manufactured and assembled on site. This paper will describe the detailed manufacturing progress and commissioning results of the KSTAR CFS.

Quench Characteristics of an NbTi CICC With Non-Uniform Current Distribution

The effect of non-uniform current distribution (NUCD) on stability and quench characteristics of an NbTi/Cu cable-in-conduit conductor (CICC) with non-insulated or bare strands has been investigated by artificially introducing NUCD among the strands using a sophisticated current feeder system with thin-film resistive heaters. The stability margin or minimum quench energy (MQE) has been found to decrease significantly, especially in the transition region between so-called well-cooled and ill-cooled regions, due to the introduction of NUCD. The experimental results of stability margin with uniform current distributions have been compared with numerical calculations using the 1-D finite element code GANDALF, whereas the non-uniform current distribution cases have been treated by another code developed by the authors, which models the last two twisting stage of the conductor with uniform contact resistances between sub-cables. The numerical calculation results also simulate the similar behaviors as found in experiments. The quench propagation velocities deduced from voltage tap signals are also discussed.

KSTAR 전류전송계통 진공배기계 구축 및 시운전

KSTAR (Korea Superconducting Tokamak Advanced Research) 전류전송계 (Current Feeder System)는 4.5 K의 저온에서 운전되는 초전도자석과 300 K의 실온에서 운전되는 전원장치 (Magnet Power Supply)를 전기적으로 연결하는 장치이다. 전류전송계는 최대 35 kA의 DC 전류가 인가되는 TF 자석용 및 350초간 20<TEX>$\sim$</TEX>26 ㎄의펄스 전류가 인가되는 PF 자석용으로 분리되어 있으며 리드박스 내부는 전류인입선, 초전도버스라인, 열차폐체 및 냉각라인 등이 설치되어 있다. 리드박스와 초전도버스라인 진공덕트는 KSTAR 주장치와는 별도로 진공배기 시스템이 구축되어있으며, 전체적으로 아령 형상을 하고 있는 진공공간을 효율적으로 진공배기하기 위하여 버스라인 덕트와 주장치 저온용기 사이에 진공 분리막 (Vacuum Separator)이 설치되어 있다. 진공배기를 위한 초벌배기계는 로터리펌프 및 부스터펌프 (Mechanical Booster Pump)로 구축되었으며 고진공 배기계는 4대의 크라이오펌프 (Cryo-pump)로 구축되었다. 진공장치 운전을 위해 PLC 기반의 로컬 제어시스템을 구축하였고 장치 안전을 위한 자체 인터록과 중앙인터록 시스템 및 중앙제어연계시스템이 함께 구축되어 있다. 전류전송계 설치완료 후 진공배기 시운전을 통해 배기시스템의 자가진단 및 리드박스 내부에 설치되어 있는 헬륨배관의 진공누설검사를 완료하였으며, 액체질소를 사용하여 전류인입선 냉각시험을 완료하였다. Current feeder system (CFS) for Korea superconducting tokamak advanced research(KSTAR) project plays a role to interconnect magnet power supply (MPS) and superconducting (SC) magnets through the normal bus-bar at the room temperature(300 K) environment and the SC bus-line at the low temperature (4.5 K) environment. It is divided by two systems, i.e., toroidal field system which operates at 35 kA DC currents and poloidal field system wherein 20<TEX>$\sim$</TEX>26 kA pulsed currents are applied during 350 s transient time. Aside from the vacuum system of main cryostat, an independent vacuum system was constructed for the CFS in which a roughing system is consisted by a rotary and a mechanical booster pump and a high vacuum system is developed by four cryo-pumps with one dry pump as a backing pump. A self interlock and its control system, and a supervisory interlock and its control system are also established for the operational reliability as well. The entire CFS was completely tested including the reliability of local/supervisory control/interlock, helium gas leakage, vacuum pressure, and so on.

Conceptual design of a High Temperature Superconductor current feeder system for ITER

The International Thermonuclear Experimental Reactor (ITER) project envisages a techno-economically feasible solution of its current feeder system in order to reduce the overall cryogenic requirements and operational costs. Since the ITER magnet system has a long stand-by time with respect to its operation duty cycle, it is essential to optimize the operational costs of the current feeder system taking into consideration both, the full current and stand-by modes. The present HTS technology has reached the maturity that HTS conductors are applicable for the current feeder system of ITER. The replacement of the actually planned conventional current leads by HTS current leads would provide considerable savings in the refrigeration investment and operational costs. Another option is the substitution of the water cooled high current aluminum feeders by HTS feeders, so called HTS bus bars. In this paper, the different design options of Bi-2223/Ag HTS based bus bars as prototype unit modules for ITER are discussed. The performance of different cooling schemes for HTS bus bars is studied and the design related critical issues e.g. metallic transition (65 K −300 K) and bending of bus bar, AC loss, thermal loss and reliability of the cooling system are investigated.

Superconducting Current Feeder System With Associated Test Results for SST-1 Tokamak

The current feeder system (CFS) consists of 20 numbers 10 kA current leads assembled inside a specially designed cryostat, superconducting bus bars assembled in a vacuum duct with bends and the joint box interface in cryogenic environment at 4.5 K. Support structure between room temperature and 4.5 K surfaces with an intercept at 80 K has been designed specially to minimize the conduction heat load as well as to take care of the electromagnetic forces. The hydraulics design of the CFS has been optimized in order to be able to interface with the liquid helium refrigerator/liquefier. A sophisticated instrumentation and control system has been designed and developed as well as tested. The paper describe the design concepts, mechanical and hydraulic analysis, instrumentation & control system as well as some test results of the current feeder system.

Current feeder system for the KSTAR device

The current feeder system consisting of superconducting (SC) bus-lines, SC bus-line interface terminal, and current leads is used as the current transmission system for the KSTAR SC coils. The current lead system consists of 11 pairs of vapor-cooled leads for the PF coils and a pair of leads for the TF coils. The PF coils are operated at full currents only during a portion of the entire time. The heat loads of current leads in idle mode, when it carries no current, depend quite strongly on the using material. We have measured the heat load and temperature profile when the overload current was charged in 200 A optimum brass lead. Also, the current feeder system requires a long bus-line that must supply a large amount of current from a current lead to SC coils. We have designed a SC bus-line with NbTi cable-in-conduit conductor (CICC) to reduce Joule heating loss. The CICC is cooled with forced-flow supercritical helium (SHe). The bus-line requires higher reliability and safety than those of the SC coils of the KSTAR. The KSTAR bus-line has been designed to have an independent vacuum space and consist of SHe return and 60 K thermal shield line for shielding. To connect the bus-line with a cryostat of the KSTAR and current lead box, we have developed a prototype SC bus-line interface terminal.