W. Reiersen

Status of Conductor Qualification for the ITER Central Solenoid

The ITER central solenoid (CS) must be capable of driving inductively 30 000 15 MA plasma pulses with a burn duration of 400 s. This implies that during the lifetime of the machine, the CS, comprised of six independently powered coil modules, will have to sustain severe and repeated electromagnetic cycles to high current and field conditions. The design of the CS calls for the use of cable-in-conduit conductors made up of and pure copper strands, assembled in a five-stage, rope-type cable around a central cooling spiral that is inserted into a circle-in-square jacket made up of a special grade of high manganese stainless steel. Since cable-in-conduit conductors are known to exhibit electromagnetic cycling degradation, prior to the launch of production, the conductor design and potential suppliers must be qualified through the successful testing of full-size conductor samples. These tests are carried out at the SULTAN test facility. In this paper, we report the results of the on-going CS conductor performance qualification and we present the options under consideration for the different modules constituting the CS coil.

ITER Central Solenoid Insert Test Results

The ITER central solenoid (CS) is a highly stressed magnet that must provide 30 000 plasma cycles under the ITER prescribed maximum operating conditions. To verify the performance of the ITER CS conductor in conditions close to those for the ITER CS, the CS insert was built under a USA-Japan collaboration. The insert was tested in the aperture of the CSMC facility in Naka, Japan, during the first half of 2015. A magnetic field of up to 13 T and a transport current of up to 60 kA provided a wide range of parameters to characterize the conductor. The CS insert has been tested under direct and reverse charges, which allowed a wide range of strain variation and provided valuable data for characterization of the CS conductor performance at different strain levels. The CS insert test program had several important goals as follows. 1) Measure the temperature margin of the CS conductor at the relevant ITER CS operational conditions. 2) Study the effects of electromagnetic forces and strain in the cable on the CS conductor performance. 3) Study the effects of the warmup and cooldown cycles on the CS conductor performance. 4) Compare the conductor performance in the CS insert with the performance of the CS conductor in a straight hairpin configuration (hoop strain free) tested in the SULTAN facility. 5) Measure the maximum temperature rise of the cable as a result of quench. The main results of the CS insert testing are presented and discussed.

ITER Central Solenoid design

The Central Solenoid (CS) is a critical component in the ITER tokamak providing plasma current drive and shaping. The CS final design is being completed at the US ITER Project Office (USIPO) in Oak Ridge, TN under a Procurement Arrangement with the ITER Organization (IO). Key design decisions have been made and CAD models and drawings developed. Interfaces have been established. An extensive R&D program has been completed. Analyses have been conducted to verify the design meets requirements. Design documentation is being completed in anticipation of a Final Design Review in the fall of 2013. The paper describes the key features of the CS final design.

Moving Toward Manufacture of the ITER Central Solenoid

After several years of design optimization, the Central Solenoid (CS) of the ITER Magnet system is now moving towards manufacture. The design has evolved to take into account on one hand the results of the R&D carried out by the US ITER team in charge of the development of the design and on the other hand the feedback provided by the involvement of industry in preparation of the manufacture. To address specific issues, dedicated mock-ups have been manufactured and tested. Electromagnetic, structural and thermo-hydraulic analyses have been carried out to verify the compliance of the design with the ITER design criteria. A review of the Final Design is planned in 2013, preparing then to move into the manufacturing phase.

Addressing the Technical Challenges for the Construction of the ITER Central Solenoid

The Central Solenoid (CS) of the ITER Magnet system is split into six independently powered coils enclosed inside an external structure which provides vertical precompression thus preventing separation of the coils and acting as a support to net resulting loads. The analyses include an assessment of the mechanical behavior of the different components of the CS, under the normal and fault conditions, aiming at demonstrating the ability of the CS to achieve 30 000 cycles of plasma operation at nominal current (15 MA). A comprehensive material testing program is developed for the conductor jacket, the impregnated glass-epoxy insulation and the structure. The paper describes the architecture of the analysis and qualification programs and provides an overview of the results obtained so far.

Starting Manufacture of the ITER Central Solenoid

The central solenoid (CS) is a key component of the ITER magnet system to provide the magnetic flux swing required to drive induced plasma current up to 15 MA. The manufacture of its different subcomponents has now started, following completion of the design analyses and achievement of the qualification of the manufacturing procedures. A comprehensive set of analyses has been produced to demonstrate that the CS final design meets all requirements. This includes in particular structural analyses carried out with different finite-element models and addressing normal and fault conditions. Following the Final Design Review, held in November 2013, and the subsequent design modifications, the analyses were updated for consistency with the final design details and provide evidence that the Magnet Structural Design Criteria are fully met. Before starting any manufacturing activity of a CS component, a corresponding dedicated qualification program has been carried out. This includes manufacture of mockups using the real manufacturing tools to be tested in relevant conditions. Acceptance criteria have been established for materials and components, winding including joints, cooling inlets and outlets, insulation, precompression, and support structure elements.

Status of design and manufacturing of the ITER Central Solenoid and Correction Coils

The Final Design of the Central Solenoid (CS) of the ITER Magnet system is currently being completed by the US ITER Domestic Agency (USDA) and the manufacturing line of the coil under installation at the suppliers premises in the USA. The Central Solenoid includes 6 identical Nb3Sn coil modules independently powered and enclosed inside a precompression structure preventing their separation. The CS structure includes 9 subsets, made of Nitronic 50 high strength austenitic stainless steel, evenly distributed around the stack of the 6 modules.

ITER central solenoid module fabrication

General Atomics (GA) was awarded the first phase of the ITER Central Solenoid (CS) Module Fabrication (CSMF) contract by US ITER in July 2011. The ITER CSMF is managed by the US ITER Project Office (USIPO) at Oak Ridge National Laboratory, under the sponsorship of the Department of Energy Office of Science. Goals of the base contract include definition and qualification of manufacturing processes and tooling necessary to fabricate seven CS modules (6 + 1 spare) that constitute the ITER CS. Qualification is completed at each manufacturing station with the production of a mockup coil using dummy conductor. A subsequent, second phase manufacturing effort produces the CS Modules which will be delivered to the ITER site in Cadarache, France during 2016-2018. GA is developing an integrated manufacturing process along with specialized tooling based on the USIPO requirements. An integrated management system utilizes proven risk management, configuration management, quality assurance, and earned value management tools to identify and manage program efforts. Regular interaction between the USIPO and GA teams review and address program issues. Formal Tooling Requirements Reviews (TRR), Preliminary Design Reviews (PDR), Final Design Reviews (FDR) and Manufacturing Readiness Reviews (MRR) for eleven (11) manufacturing stations are the key milestones in the tooling development phase of the program. Seven (7) CS Module deliveries are the primary milestones in the manufacturing phase of the program. The critical path for the tooling development phase is driven primarily by the Winding System design and fabrication, and the qualification of processes on a mockup of the CS Module. The manufacturing phase is driven by the delivery of the production conductor. GA has established a fabrication facility that combines 1,500 m2 of offices with 6,000 m2 of fabrication space. Extensive building modifications are complete with the first manufacturing tooling arriving in late 2013. The facility utilizes several cranes with up to 35 T capacity to handle and move delivered conductor and wound hex and quad pancakes during the winding, joint and lead fabrication, and stacking operations. Once the CS Module is stacked, it is moved between manufacturing stations on an air bearing moving tool on a high capacity floor for the nearly 200 tonnes CS module and tooling. The manufacturing process flow uses primarily one set of tools per station, except for the critical Winding and Turn Insulation Stations which require two sets of tools to meet delivery requirements and to minimize program schedule risk. Most tools are unique to the ITER CSMF and are designed and built by GA and tooling suppliers. GA is performing manufacturing development tasks to reduce program risks and to support the generation of process and tooling requirements. GA has placed contracts for the design and fabrication of time critical systems. Tauring S.p.A is designing and fabricating the Winding Station and Ridgway Machines LTD has been selected for the insulation wrapping heads used in the Turn Insulation Stations. The Reaction Heat Treatment Furnace contract has been issued to Seco Warwick.

Qualification of the U.S. Conductors for ITER TF Magnet System

The U.S. Domestic Agency is one of the six suppliers of the toroidal field (TF) conductor for ITER. To qualify conductors per ITER requirements, we prepared or provided to the Swiss Plasma Center (SPC) eight test articles, sixteen conductors total, that were tested in the SULTAN facility at SPC in the ITER relevant conditions. The strands that were used in these SULTAN samples were fully characterized in the laboratories. In this paper, we report both test results and analysis of the conductors’ performance against expected strand performance. The U.S. TF conductors showed a slightly better than average current sharing temperature and a relatively low sensitivity to warm up-cooldown cycles in comparison with other suppliers’ conductors. However, the trend in current sharing temperature versus cycles and warm ups did not saturate, which means a continuing slow degradation of the conductor performance if the number of warm up and cooldown cycles will be significantly higher than expected. The ac losses in the U.S. TF conductors are in line with losses in the other TF conductor suppliers.

R&D effort for ITER Central Solenoid

The US ITER organization is responsible for supply of the Central Solenoid (CS) to the ITER collaboration. This 1,000 t object is the largest pulsed superconducting magnet ever built.