SULTAN Facility Research Articles

The performance test and analysis of the third and fourth China PF conductor for ITER

The third Chinese PF conductor for ITER PF5 (PFCN3) and the fourth Chinese PF conductor for ITER PF2/3/4 (PFCN4) conductor in Phase II were manufactured in ASIPP and tested in the SULTAN facility. This paper introduces the PFCN3 and PFCN4 sample manufacture, including strand, sample preparation, current sharing temperature (Tcs), AC loss and Minimum Quench Energy (MQE) test performance of PFCN3 and PFCN4 conductors. The Tcs test result of PFCN4 conductor is consistent with the calculated result used the strand scaling and the Tcs test result of PFCN3 conductor is a little larger than calculated result, whose maximum difference is about 0.2K. According to the SULTAN test result, the Tcs performance of both PFCN3 and PFCN4 conductor sample could meet the ITER requirement.

Neutron diffraction measurement of internal strain in the first Japanese ITER CS conductor sample

Several conductor samples were fabricated and tested in the SULTAN facility at CRPP for ITER Central Solenoid (CS) conductor qualification. From the result of the cyclic testing on the first and second conductor samples named CSJA01 and CSJA02, continuous linear degradation of the current sharing temperature (Tcs) was found. From the result of the visual inspection, a large deflection on the lower loading side (LLS) in the high field zone (HFZ) was observed. The bending strain of the strands cannot be evaluated from only the deflection obtained visually. To evaluate the strain of strands in CSJA01 quantitatively, a neutron diffraction measurement of the CSJA01 left leg was performed using the engineering materials diffractometer ‘Takumi’ in J-PARC. From the result, the large bending strain at the LLS in the HFZ was found. Therefore, the Tcs degraded position in the conductor sample due to the cyclic testing can be determined.

Experimental and Analytical Approaches on JT—60SA TF Strand and TF Conductor Quality Control During Qualification and Production Manufacture Stages

In the framework of the JT-60SA project, aiming at upgrading the present JT-60U tokamak, Europe as part of its in-kind contribution within the Broader Approach agreement, will provide the full Toroidal Field (TF) magnet system. For this purpose, Fusion for Energy is committed to procure about 27 km of TF conductor. The TF conductor is cable-in-conduit type and includes 486 strands (2/3 NbTi-1/3 copper) wrapped with a thin stainless steel foil and embedded into a rectangular stainless steel jacket. The procurement is split into two main contracts: one for strand manufacturing and the other for cabling and jacketing. After having successfully passed the qualification stage, strand and conductor are now in mass production stage. In the present paper, we emphasize on the scientific and quality control approaches of both TF strand and TF conductor productions. For the NbTi strand, the focus is on design and measurement of performance critical aspects (CuNi barrier design optimization, AC losses, TCS performance, etc.). For Cu strand the main issue is RRR. For the TF conductor, the topics presented cover hydraulic correlation validation measurements (pressure drop tests), geometrical advanced controls, and electromagnetic behavior (hotspot checks and mainly the experimental results of the TF conductor full-size samples tested in SULTAN facility). The article presents comparisons of numerical simulation and experimental results used to confirm the design and the manufacturing processes.

Testing of RF 100 m TF Qualification Conductor in the SULTAN Test Facility

A conductor for ITER toroidal field (TF) coils is the cable-in-conduit conductor (CICC) type, which is made of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting strands encased in a stainless steel tubular jacket. A 120-m-long prototype has been designed in accordance with ITER requirements and manufactured prior to production of 26 full-sized CICC lengths that are the contribution of Russia to the ITER TF magnet system. Ten meters of the prototype have been used to produce a sample for testing in the SULTAN facility in order to qualify the strand/cable/jacket combination. A test aimed at qualifying the conductor performance based on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cs</sub> measurements in representative condition regarding the transport current and magnetic field has been carried out. At the same time, the test was used to compare the conductor behavior after different heat treatment cycles. Each of two legs has been reacted in accordance with one of the specified heat treatment cycles for the ITER TF conductor. Test results are presented and discussed. Based on the test results, the eligibility of the conductor for the ITER TF magnet system has been assessed.

Results of the TFEU6 Sample Tested in SULTAN

This paper presents the results of the latest European Conductor Performance Qualification Sample for the ITER toroidal field coils. The standard qualification test was performed in the SULTAN facility at CRPP. The sample consisted of two 3.5-m lengths of cable in conduit conductor (CICC), which utilized bronze route Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands from Bruker-EAS. The sample was prepared at CRPP with the conductor terminations and the bottom joint fabricated by the solder filling method. In order to prevent slippage between the jacket and cable, SULTAN samples systematically have crimping rings added to the extremity of each leg. In this case, one leg also had additional crimping rings on both sides of the high field region, which experiences a greater electromagnetic load during the test. As per a standard SULTAN sample, temperature sensors and voltage taps were installed along each conductor. In order to monitor the strain effects of the electromagnetic load cycles on the sample, strain gauges were bonded to each leg both in the high and low field regions. Pickup coils were wound on the high field region of each leg for critical temperature measurements via the magnetization method. The results of the SULTAN test are described in this paper and the effect of the additional crimping rings in the high field region discussed. Additional investigative work into residual jacket strain of CICCs is also presented.

Preliminary Performance Test Results of First CICC From Korea Destined for an ITER TF Magnet

The Republic of Korea is participating in the ITER project to construct and operate the ITER tokamak for the purpose of demonstrating the feasibility of fusion power. ITER Korea, the implementing agency for the Republic of Korea that is procuring items for the ITER project on behalf of the Korean government, has established domestic and international contracts for the procurement of cable-in-conduit conductor (CICC) that will be used in the ITER toroidal field (TF) magnets. The CICC for the ITER TF magnets is made of superconducting and copper strand cable inside a cylindrical stainless steel jacket, and is designed to operate at a nominal peak field of 11.8 T at 4.5 K with 68 kA of nominal operating current. Recently, the first CICC from Korea, which will be installed in an ITER TF magnet, has been manufactured and tested including testing performed on a 4 m sample near ITER operating conditions at the CRPP-EPFL SULTAN facility in Villigen, Switzerland under the coordination of the ITER International Organization. This paper provides a brief description of the CICC along with preliminary results of the tests and the conductor performance characteristics derived from the results.

The performance test and analysis of ITER Main and Correction Busbar conductor

The first ITER Main Busbar (MBCN1) and Correction Busbar (CBCN1) conductor samples were manufactured in ASIPP and tested in the SULTAN facility. This paper introduces the sample manufacture, including strand, cabling, jacketing and sample preparation, and discusses the performance of MBCN1 and CBCN1 conductors. The testing results show that both samples have high Tcs, and meet the ITER requirement.Due to the ITER acceptance standard Tcs of MB conductor was changed to 6.7K at 45.5kA/3.9T. The performance of MBCN1 conductor after cyclic load fits the ITER requirement, but the sample was only tested at 57kA/2.75T before cycling test. Using some hypothesis and equation to extrapolate the Tcs performance of MBCN1 conductor before cycling test, the result also fits the ITER requirement.For CBCN1 conductor, the central line of the central cooling spiral shifted about 1.3mm during the cabling. The deviation causes an increase of the max self-field by about 0.005T, which could not influence the CBCN1 conductor real Tcs performance at peak field.

Results of the TF conductor performance qualification samples for the ITER project

The performance of the toroidal field (TF) magnet conductors for the ITER machine are qualified by a short full-size sample (4 m) current sharing temperature (Tcs) test in the SULTAN facility at CRPP in Villigen, Switzerland, using the operating current of 68 kA and the design peak field of 11.8 T. Several samples, including at least one from each of the six ITER Domestic Agencies participating in TF conductor fabrication (China, European Union, Japan, Russia, South Korea and the United States), have been qualified by the ITER Organization after achieving Tcs values of 6.0–6.9 K, after 700–1000 electromagnetic cycles. These Tcs values exceed the ITER specification and enabled the industrial production of these long-lead items for the ITER tokamak to begin in each Domestic Agency. Some of these samples did not pass the qualification test. In this paper, we summarize the performance of the qualified samples, analyze the effect of strand performance on conductor performance, and discuss the details of the test results.

Manufacture and Acceptance Test of the Full Size ITER PF5 Conductor Sample

In the R&D process of the International Thermonuclear Experimental Reactor (ITER) Poloidal Field (PF) coils, 16 m PF5 Cable-in-Conduit Conductor (CICC) was integrated at Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The manufacture process of the qualification conductor was according to the ITER design. As required by the ITER Procurement Arrangement (PA), full size PF5 qualification conductor sample was manufactured and delivered to SULTAN facility (CRPP Villigen, Switzerland) for acceptance test. The PF5 conductor sample was made of two legs by one conductor bending, bottom hairpin box, upper terminations, support clamps, insulation, cryogenic piping and instrumentations. The concept of hairpin box and comb-type terminations configuration for ITER PF conductor sample which was co-contributed by ENEA and CEA was successfully verified by the first China PF2 conductor sample tested in SULTAN facility May 2010. The PF5 conductor sample test was initiated at the end of Feb. 2011. The test program included DC performance, cyclic loading, AC loss and MQE test. The conductor manufacture process, conductor sample assembly and test results were presented in this paper.

JT-60SA TF Magnet Joints Developments and Prequalification

In the framework of the so-called “broader approach” in connection with the International Thermonuclear Experimental Reactor ITER, the European and Japanese part- ners have agreed to in kind contribute to the construction of the JT-60SA tokamak in Naka (Japan). JT-60SA is a major upgrade of the former tokamak JT-60U, equipped with, in particular, superconducting coils. France and Italy, as European Voluntary Contributors, are sharing the supply of the 18 superconducting Toroidal Field coils, along with the corresponding mechanical structures and supports. These D shaped coils use a NbTi Cable-In-Conduit Conductor (CICC) and are electrically connected in series. Each coil is composed of double pancakes connected in series and two coil terminals, all located in a joint area at their outer radius at the upper part of the outer leg. The joints proposed by CEA is the twin box design which was initially developed by CEA for ITER Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn conductors and which is now adapted to the NbTi conductor. This design relies on the use of copper/steel explosion bonded plate as base material to constitute each conductor termination, the joint being assembled by soldering of the adjacent terminations. Such a design was successfully qualified on a pre-prototype sample in the CRPP SULTAN facility. To simplify the inner joints regarding the winding pack manufacture process, an evolution towards a monobloc twin box concept is proposed. After production and qualification of the needed prototype steel/copper/steel 3-layer explosion bonded plate, a dedicated joint mock-up was used to define the corresponding manufacture process. Specific processes were also developed for the coil terminals which have to be connected in a dismountable way for the cold acceptance tests of the coils in Europe, as well as in a definitive way at the Japan site. A low cost dedicated facility was developed to measure the DC resistance in order to perform a simple prequalification in cryogenic conditions on the produced mock-ups. A benchmark of the facility using the previously prequalified sample was done to validate this facility as a simple tool usable for this resistance measurement. The paper reports the different joint proposals and the manufacture processes developed as well as the pre-qualification results.

Minimum quench power dissipation and current non-uniformity in international thermonuclear experimental reactor type NbTi cable-in-conduit conductor samples under direct current conditions

The level of current non-uniformity in NbTi cable-in-conduit conductors (CICCs) sections near the joints in combination with the magnetic field profile needs attention in view of proper joint design. The strand joule power and current distribution at quench under DC conditions of two samples of ITER poloidal field coil conductors, as tested in the SULTAN facility, and of the so called PFCI model coil insert, have been analyzed with the numerical cable model JackPot. The precise trajectories of all individual strands, joint design, cabling configuration, spatial distribution of the magnetic field, sample geometry, and experimentally determined interstrand resistance distributions have been taken into account. Although unable to predict the quench point due to the lack of a thermal-hydraulic routine, the model allows to assess the instantaneous strand power at quench and its local distribution in the cable once the quench conditions in terms of current and temperature are experimentally known. The analysis points out the relation of the above mentioned factors with the DC quench stability of both short samples and coils. The possible small scale and local electrical-thermal interactions were ignored in order to examine the relevance of such effects in the overall prediction of the CICC performance. The electromagnetic code shows an excellent quantitative predictive potential for CICC transport properties, excluding any freedom for matching the results. The influence of the local thermal effects in the modeling is identified as being marginal and far less than the generally accepted temperature margin for safe operation.

Current sharing temperature of NbTi SULTAN samples compared to prediction using a single pinning mechanism parametrization for NbTi strand

NbTi strands to be used in four of the six ITER poloidal field (PF) coils, all the correction coils (CC) and all the superconducting feeder busbars are being produced in China. Short full-size qualification conductor (cabled and jacketed) samples have been developed at ASIPP and tested at CRPP. Single pinning mechanism parametrization for this Chinese strand (type S2) has been obtained using the Bottura scaling law. The determination of the scaling parameters using a Kramer-type regression method will be described. A comparison between the critical temperature at the operating current and field of a single strand as determined by the parametrization and the current sharing temperature (TCS) of a few conductor samples tested at the SULTAN facility will be made. The validity and limitation of the estimation will be discussed. The estimated TCS dependence on various (superconducting critical as well as geometric and volumetric) parameters will be assessed using the modelled critical surface. Errors propagated from critical current (Ic) measurements of the strands and parameter fitting, and other uncertainties, will be quantified.

Current Sharing Temperature Test and Simulation with GANDALF Code for ITER PF2 Conductor Sample

Cable-in-conduit conductor (CICC) conductor sample of the PF2 coil for ITER was tested in the SULTAN facility. According to the test results, the CICC conductor sample exhibited a stable performance regarding the current sharing temperature. Under the typical operational conditions of a current of 45 kA, a magnetic field of 4 T and a temperature of 5 K for PF2, the test result for the conductor current sharing temperature is 6.71 K, with a temperature margin of 1.71 K. For a comparison thermal-hydraulic analysis of the PF2 conductor was carried out using GANDALF code in a 1-D model, and the result is consistent with the test one.

Numerical analysis of the DC performance of ITER TF samples with different cablingpattern based on resistance measurements on terminations

The DC transport properties of ITER TF conductors are analyzed inthe SULTAN facility, but their associated current sharing temperature(Tcs) can give scope for different interpretations. To extract the conductor’s pureperformance during such short sample tests requires a detailed quantitative modelsuch as JackPot, for which as many as possible input parameters are based onexperimentally verified data. The crucial interstrand contact resistance data of theTFPRO-2 and TFJA-3 samples, which have a different cabling and joint layout,has recently become available. With only three parameters for JackPot’s jointmodel, we were able to find a good match between the measured and simulatedinterstrand resistances for all terminations, despite their different layout. ForNb3Sn conductors, the axial strain is the only free model parameter left for matching the simulations withSULTAN Tcs tests. We were able to find a match with the measured voltage–temperature characteristicfor all but one conductor. The simulation results indicate that the termination layout canbe the cause of lower sample performance due to current imbalance. The outcome of thisanalysis also confirms that transverse load degradation can be significantly mitigated byfinding an optimal set of cable twist pitches.

Effects of Mass Flow Rate Imbalance Among Petals During ${\rm T}_{\rm CS}$ Measurements of ITER TF Short Samples in SULTAN

Since year 2009, the joint of the toroidal field (TF) conductor samples tested in the SULTAN facility at PSI Villigen, CH, is solder-filled, so that the helium coolant can only flow axially inside the central channel. The latter is however plugged starting ~ 40-45 mm downstream of the joint. The helium has then to pass from the central channel into the annular cable region over such a short length that the desired homogeneity of the flow distribution among the petals in the high field region is not guaranteed a priori, since central helix and petal wrappings act as azimuthally non-uniform obstacles to the radial flow. In the paper we first present a geometrical model for estimating this interference to the radial flow, and combine it with a CFD (ANSYS-FLUENT) model of the hydraulic effect of the plug, in order to estimate the mass flow rate imbalance among the petals at the beginning of the plug. This is then used as boundary condition by the THELMA code, to parametrically assess the results of a TCS measurement.

Test Result of a Full-Size &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;${\rm Nb}_{3}{\rm Sn}$&lt;/tex&gt;&lt;/formula&gt; Conductor Developed for the ITER TF Coils

The Japan Atomic Energy Agency (JAEA) developed ITER TF Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn conductors that fulfill ITER requirements and has commenced fabricating the conductors to be used in the ITER TF coils. As a qualification of conductor fabrication, two full-size conductor samples, named as JATF4, were prepared and tested by the SULTAN facility at CRPP in Switzerland. Temperature sensors and voltage taps were attached on the three meter-long conductor samples to measure the current sharing temperature (Tcs). Measurements were performed at the beginning of the testing campaign, during cyclic test, and at the end of the campaign following a warm up and cool down. The Tcs values electrically assessed by the agreed procedure at outer magnetic fields of 10.78 T initially were 6.5 K and 6.2 K, and then 6.1 K and 6.0 K at the end of the campaign for each conductor, respectively. These results demonstrate that the conductors have a sufficient Tcs margin to satisfy the ITER TF conductor criterion of 5.7 K, and conductor fabrication is qualified. Details of the test results are presented and discussed.

Evaluation of Effective Strain and $n$-Value of ITER TF Conductor Samples

The acceptance tests of the Cable in Conduit Conductors for the Toroidal Field coils of the ITER magnet system are being performed at the SULTAN facility in Villigen, Switzerland. The main physical quantity measured in these tests is the current sharing temperature, Tcs . In Tcs measurements, the E-T characteristic curve of the conductor is traced. This curve is utilized here to evaluate the equivalent n-index and the effective strain of the superconducting Nb3Sn cable, under the simplifying assumptions of a uniform strain, current density and temperature distribution in the cable cross section. The variations of n-index and effective strain with mechanical cycling and their sensitivity to the applied transverse load and to the warm up-cooldown process are presented for various conductor samples tested recently.

Preparation of PF1/6 and PF2 Conductor Performance Qualification Sample

The ITER Conductor Procurement Arrangement requires that all the conductors have to be qualified before the production phase. The objects of the work here presented are the Poloidal Field Coils conductors, specifically the PF1/6 and the PF2 conductors. The realization of the samples comprised the jacketing, the compaction and the straightening of the CICC, together with the design and manufacturing of the bottom hairpin box and the upper termination. The instrumentation and the related jacket machining completed the preparation of the samples. The samples have been assembled according to the specification defined by ITER and have been shipped to SULTAN facility. This paper describes all the activities performed during the preparation, the features of the samples and all the related issues.

Status Report of the EDIPO Project

The aim of this paper is to present an up to date review of the status of the European DIPOle (EDIPO) project whose objective is to build a new facility to perform both DC and AC tests of large superconductor samples in high magnetic background field (up to ~12.5 T). EDIPO was designed by EFDA, is being built by BNG (Babcock-Noell) and, once completed, it shall be installed near the existing SULTAN facility at the Paul-Scherer-Institute, (CRPP, Villigen, Switzerland). The results presented focus on the manufacture of the dummy coil (which is a 1:1 model of one of the EDIPO poles) that was completed in spring 2009. Details are given about the dummy coil winding results, coil reaction heat treatment, impregnation and acceptance tests. Moreover, a progress status is provided about the manufacturing of the other parts of the EDIPO magnet assembly, in particular with respect to the manufacturing of the test-well, AC coils, yoke sheets cutting and assembly, the outer cylinder production and welding (316 LN steel, 35 mm thick) and the coils ends preparation. Some results regarding the R&D studies are also reported about the winding trials carried out to improve the winding accuracy and the numerical simulations made to support coil winding (e.g. conductor spring back).

The results of the second Chinese TF conductor sample

In the framework of the ITER qualification tests the second Chinese sample (CNTF2) was tested in the SULTAN facility. The sample was made of two identical ITER TF type cable-in-conduit conductor sections. Internal Sn strands offered by Western Superconducting Technologies Company (WST) were used for the conductor fabrication. The main characteristics of the conductor and the strand are presented as well as the sample assembly details. The test was performed in accordance with the ITER International Organization specified program. In order to evaluate the conductor performance, the current sharing temperature was measured at specified electromagnetic load cycling steps. Few voltage–current characteristics were measured with the aim of n-value estimation. Before cycling load, both conductor sections of CNTF2 showed different performance, but after 1200 cycles and warmed up and cool down, they showed identical performance: the current sharing temperature ( T cs ) was 6.36 K, which exceeds ITER requirement of 5.7 K.