[en] In the framework of the JT60 project, a 4.5 K cryogenic loop, dedicated to the tests of the JT60 Toroidal Field Coils, is planned to be installed at CEA-Saclay. For this purpose, the existing 'CELLO' cold box is foreseen. In this paper, we present the results of the cryogenic performance tests carried out in pure 'refrigeration mode' and 'unbalanced mode' in which a 3.6 g/s mass flow, required to cool HTS current leads, is taken on the high pressure branch at the 50 K level. A 500-watt power has been measured in pure refrigeration mode; a slight power decline down to 487 watts had been measured in unbalanced mode. Measurements are compared to computations. (author)

[en] The W7-X magnet system consists of 50 non-planar coils of five different types and 20 planar coils of two different types. Factory acceptance tests of the non-planar coils are carried out at the manufacturer site of Babcock-Noell, Germany, and for the planar coils at Tesla Engineering, UK. They consist of electrical insulation checks, mass flow measurements and leak tests. In the test facility of CEA Saclay, France, each coil is cooled down to ∼ 6 K and operated at nominal current. At least one coil of each type is quenched by increasing the inlet temperature. The characteristic parameters of the quench tests (temperature, pressure, speed of normal-conducting zone, etc.) will be presented. Coils of the same type show a uniform behavior. The occurrences of leaks during cool-down on planar coils revealed quality problems with aluminum welds and stress corrosion of stainless steel tubes at the soldered connections with copper heat sinks. AC tests (impulse and impedance tests) were applied to detect short circuits during the fabrication of the winding packs. High voltage DC tests under vacuum and low gas pressure (Paschen-minimum conditions) revealed electrical insulation defects, which had not been found using standard high-voltage tests. These were mainly due to voids and cavities present in the winding pack after vacuum impregnation, insufficient glass-epoxy wrapped insulation and inappropriate design of the Kapton insulated quench detection cables. The mass flow measurements of the superconductor showed that the deviation between individual double layers of the coils is within acceptable limits. Two winding packs were given up by the supplier because of a superconductor blockage with resin and a short circuited winding, respectively. All other quality issues could be resolved by repair or changes in the components. The coil instrumentation with temperature sensors seems to be adequate. The strain gauges need improvements in temperature compensation and gluing technique. The displacement transducers used temporarily during the cold tests showed reproducible results but a relatively high failure rate. In conclusion, the scope of the tests, augmented in due course by new elements as Paschen tests and dedicated AC tests, allows a very strict quality control. This experience is highly beneficial for the construction of similar components for future superconducting fusion experiments. (author)

[en] The construction, commissioning, and operation phases of the W7-X cryo-magnetic test facility in CEA Saclay lasted ten years. The large diversity of equipments called, specialties involved and problems solved attest the expertise that was required to operate the test facility and test the coils. Nearly one hundred cryogenic tests were performed on the seventy W7-X coils, at a rate always increasing, using two cryostats each holding two coils. This paper presents the test facility and its operation first, the cryogenic difficulties that were confronted with their solutions, the electro-magnetic difficulties encountered along with corrective actions, and finally the instrumentation and data acquisition aspects. (authors)

[en] Highlights: • The Cold Test Facility’s instrumentation/operation are designed for JT60SA TF coils. • Four quench dynamic phases are identified for studying the coil’s performance. • Four quench-back effects are proposed to understand the coil's performance. • Some key physical parameters are estimated for TF coil's quench phenomena. - Abstract: In order to check the performance of the JT-60SA Toroidal Field (TF) coils and hence mitigate their possible fabrication risks, a series of tests have been carried out in the Cold Test Facility (CTF) at CEA Saclay in nominal conditions at 5 K and 25.7 kA. One major test performed is the so called “temperature margin test” during which the inlet helium temperature of the Winding Pack (WP) is controlled to increase progressively to the calculated current sharing temperature of 7.3 K in the high field region to launch the quench. The measurements of voltage, pressure and temperature signals allow us to study the thermo-hydraulic behavior of the JT-60SA coils during a quench. This paper will present the 6 quench tests on 5 TF coils accomplished between February and September 2016, of which the first manufactured coil TFC10 has carried out two quench tests and two pure Fast Discharges without any quenches. It will analyze in particular the temperature and pressure rise in helium, the corresponding physical phenomena after each voltage variation, the four quench dynamic phases, the quench propagation velocity and the dissipated power in the coils.

[en] A new plasma fusion experiment, Wendelstein 7-X (W7-X), is built in the Max-Planck Institute for Plasma Physics in Greifswald (IPP), Germany. This experiment employs superconducting coils, allowing for plasma discharges up to 30 minutes duration. W7-X will be an 'optimized' stellarator with respect to plasma transport and stability. The W7-X magnet consists of 70 individual coils in a toroidal arrangement. Each coil of W7-X is thoroughly tested before installation in a cryogenic test facility at the Commissariat a I'Energie Atomique (CEA) in Saclay, France. The tests are essential, because no access is foreseen to the magnetic system during the entire operation period of W7-X. The test procedure will be described briefly, and some test results will be presented. (authors)

[en] WENDELSTEIN 7-X (W7-X) is a superconducting stellarator which uses 50 non-planar coils for the main confinement field and 20 planar coils for the magnetic configuration. All 70 coils are subject to an extensive test program after manufacturing and before assembly, realised at the cryomagnetic test facility at CEA Saclay. The tests are part of a well-advanced quality assurance plan attesting the specified coil performance. The test program is mainly divided in warm and cold tests. Various tests have to be performed such as visual inspections, hydraulic measurements, electrical tests and the check of sensors. The most elaborate test is the cryogenic temperature margin test using current up to 17.6 kA including the quench or fast discharge test and the evaluation of the specified interlayer joint resistance. Up to now 75% of the coils have been tested and accepted. The last acceptance tests at CEA are scheduled to be performed beginning of 2009. The test program has been enhanced permanently in its course, due to further improvement as well as considering aspects of the time schedule. This paper will present a short description of the test program done at CEA, their aim and background.

[en] Highlights: • The tests of the first JT-60SA TF coils in the CTF have started beginning of 2016. • The quench test of the coils had to be modified using a transient scenario so as to allow testing conductor at peak field. • CEA/IRFM has developed a dedicated thermal-hydraulic and electrical model to simulate the whole quench experiment. • The first two tested coils have shown very similar behaviors with a quench initiated on a side double-pancake at an inlet temperature around 7.5 K. • The estimated local quench temperature is in good agreement with CEA model, which is very promising for the operation of the coils in the tokamak. - Abstract: The Toroidal Field system of the JT-60SA tokamak is composed of 18 NbTi superconducting coils all individually tested in the Cold Test Facility (CTF, CEA/IRFU Saclay, France). The test program includes for each coil a progressive operating temperature increase at nominal current (25.7 kA) up to quench followed by a safety discharge. To account for the heat coming from the casing to the winding pack (WP), a transient test procedure was settled so as to trigger the quench at peak field in the coil; nevertheless the quench location was identified on a side double-pancake in the first two tested coils. We present the CEA analyses for the quench test of the second coil which showed similar behavior as the first one but received a more extensive instrumentation. The coil performance is analyzed in light of the NbTi strand superconducting properties coming from the strand characterization program and of the full-size conductor tests carried out by CEA in the SULTAN facility. These analyses involve cable thermal and electrical modelling developed at CEA and already used in ITER R&D, design and characterization programs.

[en] Highlights: • The 5 first JT-60SA TF coils have been successfully tested at 5 K and 25.7 kA. • One major insulation problem was detected, analyzed and repaired. • Cooling down problems like clogging and temperature gradient were solved. • The inter pancakes joint resistances are below the 2 nΩ specified value. • The quench temperature of each coil is above the 7.3 K specified value. - Abstract: JT-60SA is a fusion experiment which is jointly constructed by Japan and Europe and which shall contribute to the early realization of fusion energy, by providing support to the operation of ITER, and by addressing key physics issues for ITER and DEMO. In order to achieve these goals, the existing JT-60U experiment will be upgraded to JT-60SA by using superconducting coils. The 18 TF coils of the JT-60SA device are provided by European industry and tested in a Cold Test Facility (CTF) at CEA Saclay. The first coils were tested at the nominal current of 25.7 kA and at a temperature between 5 K and 7.5 K. The main objective of these tests is to check the TF coils performances and hence mitigate the fabrication risks. These first tests allowed checking a certain number of performances of the first TF coils: DC/AC insulation, cooling down characterization, RRR of the conductor, pressure drop in the winding pack and temperature margin against a quench. This paper will give an overview of the main experimental results obtained during these tests. These results will be analyzed and discussed in the light of the expected TF coils performances.

[en] The 18 D-shaped Nb-Ti toroidal field (TF) coils for the JT-60SA tokamak will each be 7 m high and 4.5 m wide. Together they will generate an on-axis field of 2.25 T. All the main contracts for their manufacture are now in place, with manufacturing split primarily between sites in Japan (superconducting strand), Italy (conductor cabling and jacketing, casings fabrication and coil winding, and integration), and France (support structures, coil winding and integration, and final coil cold testing). This paper will summarize the key aspects of the design of the coils and the current status of manufacture on each area of the manufacture of the TF coils. A simple overview of the overall schedule for their completion is included. (authors)

[en] In the framework of the EU-JA Broader Approach agreement, the 20 Toroidal Field (TF) coils (18 coils for the tokamak + 2 spares) produced for the JT-60SA tokamak were qualified in cold conditions and at full current (25.7 kA) in self-field conditions and heated up until quench occurs, along standardized testing procedures, at the Cold Test Facility (CTF) installed at CEA-IRFU (Saclay, France). The analysis of the tests results will be presented using simple dynamic models for the coolant exchange with cable in the steady-state regime. In addition to this approach, the coils operating limits in CTF conditions will be explored, integrating the global statistics of their strands' critical performances. The latter are built by processing TF strand performances data obtained during strand production phase. Those statistical data will be used to calculate the TF coils performances in the CTF configuration. Results will be discussed and compared to the TF coils experimental statistics, followed by a tentative quantified interpretation: The results will be transposed into variation of effective macroscopic parameters such as local heat load on pancakes or temperature margin potential increase. Once this macroscopic study is assessed, it stands as the first step toward more refined future analyses. Finally, using the above method, a first predictive application will be conducted on the JT-60SA tokamak operation configuration. (authors)