Chen-yu Gung

Test of a 10 kA HTS Current Lead for ITER

The ITER Organization (IO) and the Institute of Plasma Physics at the Chinese Academy of Sciences (ASIPP) are jointly developing the design of the 10 kA Current Leads (CL) using High Temperature Superconductors (HTS) for the Correction Coil (CC) Magnet System of the International Thermonuclear Experimental Reactor, ITER. The proposed design combines a conventional helium cooled heat exchanger operating between 65 K and 300 K with a HTS module covering the low temperature end using Bi-2223 tapes. The details of the design and test results obtained on a first prototype lead will be discussed in this paper.

Progress in Design, Analysis, and Manufacturing Studies of the ITER Feeders

The feeder design has been improved by the feeder teams at the ITER Organization (IO) and the Institute of Plasma Physics, Chinese Academy of Science (ASIPP) by incorporating the results of mechanical and thermal analyses as well as the system integration and assembly tolerances in the present CAD model. The feeder design is being finalized progressively, and will be delivered to the Chinese Domestic Agent (CNDA) for further procurement arrangement (PA) activities. Pre-PA manufacturing studies and tests performed at ASIPP have been effective in clarifying feeder design feasibility and component manufacturability. This paper reports the recent advancements on feeder design, analysis and manufacturing studies.

Development of the ITER PF Coils

The ITER Poloidal Field (PF) magnet system consists of six coils. Niobium-Titanium (NbTi) is used as superconducting material and cable-in-conduit conductor(CICC) type are used as a conductor. All coils are fabricated by stacking 6 to 9 double-pancakes wound by two-in-hand winding scheme. The six PF coils (PF1 to PF6) are attached to the Toroidal Field (TF) coil cases through flexible plates or sliding supports to allow small radial and vertical displacements. The outer diameters of the coils vary between 8 m and 24 m. Since the PF coil system provides magnetic field for plasma shaping and position control together with the Central Solenoid (CS) coil, it needs to operate in fast pulse mode, leading to induced voltages of up to 14 kV on the coil terminals during operation.

High Voltage Test of ITER Feeder Components Under Paschen Condition

As an important method of quality confirmation for the ITER Feeder system insulated components, high voltage test at Paschen condition need to be carried out once after these components are manufactured. The Paschen test is much more efficient for detecting the micro cracks or defects in solid multi-composite high polymer insulation materials than the conventional high voltage test done in atmospheric condition, and almost without any damage for the qualified components. For this purpose and the task agreement of Feeder R&D with ITER IO, a cryogenic vacuum Paschen test facility, which was modified by the Feeder prototype of Coil Termination Box (CTB), was established in ASIPP (China) in October of 2010, it is suitable to test typical critical high voltage components in Feeder, such as S-bend busbar, superconducting joint, and current lead. The test voltage can be up to 30 kV and provide pressure lower than 10-3. This paper describes the detailed configurations of the insulation mock-ups for Feeder and the test facility, also presents and discusses the test procedure and results acquired up to now.

Status of Design and R&D for the ITER Feeder System Procurement in China

The Procurement of the feeder system for The International Thermonuclear Experimental Reactor (ITER) tokamak device started in ASIPP (China) in 2006. The relevant tasks of structural design and analysis have now come to an end, but the R&D activities started in 2009 for critical feeder components and key technology are still ongoing. Following the signature of the Procurement Arrangement between China and the ITER Organization (IO) in 2010, a great number of R&D tasks have been launched with the purpose of testing and verifying the original design, leading to design changes and optimizations. This paper mainly discusses the progress of the feeder design and R&D activities; it also presents some test results.

Key Components of the ITER Magnet Feeders

Now that ITER is entering construction, many of its systems are in the final stages of design and analysis. Among them the 31 feeders, which will be supplied in-kind by the Chinese ITER partner. The feeders supply the electrical power and cryogens through the warm-cold barrier to the ITER superconducting magnet systems. They are complex systems with their independent cryostats and thermal shields, densely packed with many components, such as the current feeds, the cryogenic valves and High-Voltage (HV) instrumentation hardware. Some of the feeder components are particularly critical and have been designed with great care. Among them the High-Temperature Superconductor (HTS) current leads, designed for unprecedented currents, the 30 kV class, Paschen-hard HV insulation and the bus bar support system, designed to react the multi-ton Lorentz-forces from the bus bars at minimal heat load. This paper discusses the design challenges for these (and other) key components of the ITER magnet feeders.

Busbar System for ITER Magnets

The superconducting busbar system for ITER magnets includes the NbTi cable-in-conduit busbars themselves, the support structure consisting of rigid ducts and clamps to take the electromagnetic loads experienced by the busbars, and the joints for electrical and hydraulic connection. The main challenges arise from considerable displacements of the coil terminals relative to the cryostat, and high electromagnetic, thermal and seismic loads on the busbars, and supporting system. In addition, the busbar ground insulation has to withstand a voltage of up to 30 kV in fault conditions. This article describes how the individual engineering challenges have been met. This includes design concepts and the analysis method for the iterative design of a support structure complying with different, often contradictory, requirements.

Cryogenic Engineering Design of the ITER Superconducting Magnet Feeders

The ITER magnet system is to be operated at about 4.5 K. It has 31 feeders for high-current power supply, helium distribution and instrumentation cable routing. The feeders (except the smaller ones which are for instrumentation only) are 25 to 30 m long for about 40 tons. They have 3 main components: coil terminal box-cum-S-bend box (CTB-SBB), Cryostat feedthrough (CFT) and in-cryostat feeder (ICF). The CTB is the feeder component placed farthest from the coil (about 25 m away from the magnet center) and outside the bio-shield (the nuclear radiation restriction wall) so that it can be easily accessible in case the critical elements placed within it need maintenance: high-temperature superconducting current leads (HTSCL), large number of cryogenic control valves and pressure-release valves for quench protection. This paper explains the cryogenic design that considers these factors and main components.

Design and Qualification of Joints for ITER Magnet Busbar System

The joints connecting the ITER magnet busbars and coils utilize the twin-box “shaking hands” concept: inside a helium leak tight box, a bare cable is pressed in an indium-tinned copper base. To form the joint, two boxes are tightly compressed against each other on the copper side with a layer of indium in between. This concept was chosen to address the different requirements of the joints: to provide low electrical resistance without degradation and need of maintenance during ITER lifecycle, to sustain cyclic electromagnetic and pressure loads, to be easily dismountable in case of failure, to be tolerant to manufacturing and assembly misalignments, to provide low coolant flow impedance, and to limit ac losses and at the same time to facilitate current redistribution in the busbars. This paper presents the design; the key results of the electromagnetic, thermal, and stress analysis; and the major manufacturing and qualification steps. The latter includes cryogenic fatigue test of the joint welds and joint resistance measurements.

Progress of the ITER Feeder in China

The Procurement of Feeder system in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) for The International Thermonuclear Experimental Reactor (ITER) Tokamak device has been carrying out after the signature of Procurement Arrangement in October 2011. The relevant main tasks in 2012 and 2013 are the qualification of some key subcomponents, including high temperature superconducting current leads (HTS-CL), superconducting joints, 80-K thermal shield (TS), vacuum barrier, in-cryostat feeder, cold mass support, etc. The production of manufacturing drawings, preparation of manufacturing plan, manufacture and qualification of tooling, and qualification of subcomponents are all involved in this phase. This paper describes the progress made by ASIPP and some sub-contractors for the feeders qualification work.