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The EUROfusion DEMO is being designed as the fusion machine to be built after ITER. During the preconceptual phase, several design options are investigated by theoretical analyses as well as tests on newly developed conductor prototypes. One design option for the toroidal field magnet (TF) and central solenoid (CS) is based on flat Nb3Sn forced-flow conductors made with react & wind technique. The usage of these conductors simplifies some steps in the conductor and coil manufacturing, and together with graded layer-winding allows approx. 50 & x0025; reduction of the required amount of Nb3Sn compared to ITER-like design based on wind-react-insulate pancake-winding. Two full-size prototype cables for DEMO TF coil were manufactured, jacketed and tested in several test campaigns in SULTAN test facility. The DC results for the second prototype, RW2, rated for 63 kA at 12.3 T, were presented and published in 2018. The AC loss data were collected over several test campaigns performed on various assemblies of RW2 at AC field parallel and perpendicular to the broad cable side. The measurements done at 4.5 K and 20 K allow us to decompose the AC loss contributions originating from the bundle of superconducting strands (hysteresis and coupling loss) and copper-matrix stabilizer located around the cable. The AC loss for sinusoidal and trapezoidal field variations are presented and discussed. The low AC loss of the flat cable makes the cable an attractive choice for the central solenoid operating in a pulse mode.

In 2013, the Swiss Plasma Center proposed a Toroidal Field (TF) layout for the DEMO-EUROfusion tokamak, based on a graded winding made of layers of Nb3 Sn (react&wind) and NbTi conductors. The R&D effort led in 2015 to a full size prototype conductor tested up to 82.4 kA at 12.35 T. The test continued in 2016 and new results are presented. In summer 2015 a new reference baseline was issued for the DEMO-EUROfusion tokamak, leading to an update of the TF requirements. The design update is presented in this paper, with the winding pack consisting of 12 single layers of Nb3 Sn with “invisible” (no protrusion) inter-layer joints. The high grade Nb3 Sn react&wind conductor operates at 63.3 kA, 12.23 T with T cs > 6.5 K. A new prototype conductor is being manufactured. The main advantages of the graded approach, applied to both the superconductor and the stainless steel conduit, are a substantial space and cost saving compared to the wind&react approach with pancake winding.

The Toroidal field coils (TFC) of the EUROFusion DEMO reactor call for Nb3Sn conductor with high field and high current. Another major requirement is cost-effectiveness, to keep the ratio of investment to electric power in the same range of the competing energy sources (fission, hydro, coal, gas, etc.). The TFC proposed by the Swiss Plasma Center (SPC) is based on a double-layer Nb3Sn/NbTi winding. A react-and-wind flat cable is the core of the Nb3Sn conductor, with six grades to minimize the cost and maintain a roughly constant temperature margin of 1.5 K over the winding cross section. A short length section of the high grade Nb3Sn conductor has been manufactured using relevant industrial cabling equipment. One hundred kilograms of 1.5-mm Nb3Sn strand has been procured at WST with average Jc up to 15% higher than specified (Jc≥ 1000A/mm2 at 12 T/4.2 K). A dedicated cabling line has been set up at TRATOS cavi (Italy), producing over 350 m of dummy cable and about 13 m of superconducting cable. The assembly of the cable into a conduit by longitudinal laser welding of two steel profiles is demonstrated, including the QA procedures. A test sample has been prepared at SPC by heat treating straight sections of the cable and encasing it into a steel jacket after the heat treatment to minimize the thermal strain. The test was carried out in three test campaigns at the EDIPO facility at SPC. The test program includes Dc performance at the relevant operating conditions. An assessment of the conductor test results in terms of strand performance suggests that the applicable thermal strain is less than -0.33%. The performance is stable upon load cycles. © 2002-2011 IEEE.

Five medium size cable‐in‐conduit conductors based on NbTi strands have been prepared at CRPP. The ac loss performance is investigated as a function of the layout parameters such as strand coating, bundle barriers (subcable wraps), copper segregation and Cu:non‐Cu ratio. The ac loss is measured in the SULTAN test facility with superimposed, transverse dc and ac field. Calorimetric and magnetization methods are used to explore a broad range of frequency. From the results discussion, the interstrand coupling loss is largely suppressed when Ni coating is applied. The copper segregation helps to reduce the overall ac loss, at the price of a lower take‐off voltage in dc mode. The subcable wraps marginally reduce the overall loss at the price of an impaired current re‐distribution, affecting the dc performance, and an increased friction factor. The non‐linearity observed in the loss curve at very low frequency is further investigated by a separate experiment with enhanced accuracy.

A conductor for ITER toroidal field (TF) coils is the cable-in-conduit conductor (CICC) type, which is made of Nb3Sn 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 T-cs 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.

Five medium size NbTi cable-in-conduit conductors with parametric variations in the cable layout were fabricated of three different strands to investigate their DC performance, AC loss behaviour and transient stability by means of the SULTAN facility. A comparison of measured strand data and the cable performances at the same background field indicates that the current carrying capacity of the conductors is limited by the total magnetic field on the high field side. Due to the self-field contribution the total magnetic field on the high field side is considerably larger than the background field at high currents. The take-off electric fields were found to decrease with increasing quench currents, resulting in sudden take-offs for large overall current densities. Effective self-field factors are used to describe the DC performance in the current range, where the critical current and the current sharing temperature are accessible. The quench behaviour of the conductors is discussed in the framework of a model based on peak-field-induced quenches. Differences in the DC performance of the conductors are related to the variation in the transverse resistance determining the ability of the conductors to redistribute the current in the case of a current imbalance originated at the joints. This aspect was studied in more detail by modifying one of the joints allowing a defined number of subcables to be disconnected. The voltage-current characteristics of strands and cable-in-conduit conductors are compared. The reasons for cable n values deviating from the strand n values are discussed. Moreover, the effect of different transverse resistances on the AC loss behaviour and the transient field stability was investigated. Ni coating of the strands was found to be sufficient to eliminate the interstrand coupling current loss. Thus, additional subcable wraps provided no significant further loss reduction. (c) 2005 Elsevier Ltd. All rights reserved.

Irreversible degradation, likely due to microscopic filament damage, has been observed in the past years for large size Nb3Sn cable‐in‐conduit conductors (CICC) exposed to high electromagnetic transverse load. An R&D program at CRPP is aimed to investigate, by comparison of six conductors with parametric layout variation, the effect of strand layout, thermal strain and cable pattern on the transverse load degradation, including cyclic load. The present work reports the test results in the SULTAN facility of two Nb3Sn cable‐in‐conduit conductor samples with identical parameters (144 strands, void fraction, jacket material) except the cabling pattern, either braid or triplet based. The pattern of strand crossovers affects the transverse load transmission. The dc performance difference due transverse load degradation is about 10% in favor of the braided CICC. Conclusion is drawn on the impact of conductor parameters on performance degradation.

Two Nb/sub 3/Sn cable-in-conduit conductors have been manufactured with identical non-Cu cross sections and the stabilizer either included in the Nb/sub 3/Sn composite or partly segregated as copper wires. The two conductors are series connected and wound as a bifilar, single layer solenoid, assembled in the high field bore (11 T) of the SULTAN test facility. Beside the DC and AC losses characterization, the key tests include stability under pulsed transversal field (dB/dt up to 180 T/s), at DC operating current up to 12 kA. The results show that strong, transverse field transients can be withstood by both conductors with small temperature margin. Cost reduction measures for fusion conductors are discussed.

A new generation of ITER TF conductor samples has been assembled and tested in SULTAN in 2007 following a common procedure agreed among the ITER parties. The test results of six SULTAN samples, made of twelve conductor sections manufactured in Europe, Japan, Korea and Russia, are reported here. The conductor layout reflects the ITER TF conductor design, with minor differences for the Nb3Sn strand characteristics, void fraction and twist pitch. The object of the test is a straight comparison with the ITER requirement of 5.7 K current sharing temperature at 68 kA current and 11.3 T field. A broad range of behavior is observed.

The test campaigns of the ITER conductors in the SULTAN test facility re-started in December 2011 after three months break. The main focus of the activities is about the qualification tests of the Central Solenoid (CS) conductors, with three different samples for a total six variations of strand suppliers and cable layouts. In 2012, five Toroidal Field (TF) conductor samples have also been tested as part of the supplier and process qualification phase of the European, Korean, Chinese and Russian Federation Agencies. A summary of the test results for all the ITER samples tested in the last period is presented, including an updated statistics of the broad transition, the performance degradation and the impact of layout variations. The role of SULTAN test facility during the ITER construction is reviewed, and the load of work for the next three years is anticipated. (c) 2013 Elsevier B.V. All rights reserved.

An existing Nb3Sn laboratory magnet generating a magnetic field of 12 T is intended to be upgraded to 16 T by means of the use of a high temperature superconductor (HTS) insert coil. An outline design of the HTS insert coil is presented. In the design, the aspects of the maximum achievable operation current, the required copper cross-section to ensure a hot spot temperature below 200 K and the resulting forces and stresses have been considered. The length of the insert coil has been selected in such a way that the field uniformity will be better than 1% within a sphere of 3 cm diameter. The protection of the whole magnet system (LTS & HTS insert) is briefly described. (C) 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.

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 (T-cs), AC loss and Minimum Quench Energy (MQE) test performance of PFCN3 and PFCN4 conductors. The T-cs test result of PFCN4 conductor is consistent with the calculated result used the strand scaling and the T-cs test result of PFCN3 conductor is a little larger than calculated result, whose maximum difference is about 0.2 K. According to the SULTAN test result, the T-cs performance of both ElsevierPFCN3 and PFCN4 conductor sample could meet the ITER requirement. (C) 2014 Elsevier B. V. All rights reserved.

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 Nb3Sn 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.

In the scope of the qualification tests of the ITER TF conductors, four samples for the SULTAN facility have been prepared, each consisting of two conductor sections manufactured by the US ITER Domestic Agency. The samples are nicknamed USTF1, USTF2, USTF3 and USTF4. The conductor sections used for USTF1 and USTF3, as well as those for USTF2 and USTF4, are identical. The conductor terminations for the samples USTF1 and USTF4 are prepared by the "solder filling" method, where a copper sleeve is swaged on the dismantled conductor before the heat treatment, and the cable space is filled with a soldering alloy by siphon after the heat treatment. In USTF2 and USTF3, the conductor terminations are dismantled after the heat treatment, and the cable ends are dipped into a bath of molten solder. The main test of the conductor characterization in SULTAN is the current sharing temperature (Tcs) test at 10.78 T background field. The current is raised up to 68 kA current in steps of 10 kA. Then, the coolant temperature is raised in steps of 0.25 K till quench occurs. Early voltage is observed during the current ramp before heating even at relatively low current. Due to the broad voltage-temperature (V-T) transition, the early voltage causes an uncertainty in the assessment of the conductor performance. The comparison of the test result of USTF1 vs. USTF3 and USTF2 vs. USTF4 enables to clarify the impact of the termination preparation procedure on the early voltage. In the case the early voltage is caused by non-uniform current distribution and high inter-strand resistance at the joints, the V-T behavior should be clearly different. In this paper, the joint preparation procedures are described, and the impact of the joint preparation on the conductor performance is discussed.

The conductor for the ITER correction coils (CCs) is manufactured in China and is tested in the SULTAN facility. The third China CC conductor for the qualification SULTAN test sample (CCCN3) was prepared from a 200-m-long CC conductor unit length (Phase II). The fourth and fifth China CC conductor samples for SULTAN testing (CCCN4 and CCCN5) were prepared from the 576-m-long production unit lengths (Phase III). The current sharing temperature $T_{cs}$ test results show that the sections of CCCN3, CCCN4, and CCCN5 have high $T_{cs}$ performance. Using the electrical method, the $T_{cs}$ was 7.13 K for CCCN3, 7.10 K for CCCN4, and 7.09 K for CCCN5 at the ITER reference test conditions, i.e., at ${B}_{\mathrm{sultan}}=3.7\ \text{T}$ and current equal to 10 kA $({B}_{\mathrm{peak}}=4.0\ \text{T})$ . Even after the 2000 electromagnetic load cycles for CCCN3 conductor and 1000 electromagnetic load cycles for CCCN4 and CCCN5, the $T_{cs}$ performance of all samples did not changed appreciably. Based on the CC conductor sample test results at 10 kA and at different fields, the $T_{cs}$ was extrapolated to the peak field ${B}_{\mathrm{peak}}= 4.1\ \text{T}$ and current equal to 10 kA. The extrapolated $T_{cs}$ is 7.07 K for CCCN3, 7.05 K for CCCN4, and 7.03 K for CCCN5. The $T_{cs}$ performance for all conductors is higher than the ITER acceptance criteria of 7.00 K.

The commissioning of the European DIPOle (EDIPO) test facility at the Center for Research in Plasma Physics in Villigen was completed in Spring 2015, and the first test of a 60-kA/12-T high-temperature superconductor (HTS) was carried out in June 2015. User specifications are issued to allow external users to prepare their own sample matching the interface of the test facility. EDIPO offers a background magnetic field up to 12.35 T in a rectangular test well with a cross section of 89 mm $\times$ 138 mm (sample dimension). The homogeneous high field length is 910 mm (±1%) or 680 mm (±0.5%) at full current. A set of small copper coils provides a superimposed ac field with amplitude up to ±0.3 T and frequency up to 1 Hz. A superconducting transformer provides steady-state operating current for the sample up to 100 kA. The cooling circuit of the sample supplies supercritical helium at 10-bar inlet pressure. The mass flow rate, which is adjustable by cryogenic valves, is up to 8 g/s in each branch of the sample at 4.5 K. The operating temperature ranges from 4.5 to 60 K (at high temperature, the range of mass flow rate is reduced). To test samples at temperature higher than 10 K, an HTS “adapter” connects the sample to the NbTi transformer plates, which must remain cold. In such case, the length of the sample is reduced from 3600 mm (typical low-temperature superconductor sample) to 2900 mm (HTS sample with adapter).

In the period between August 2010 and August 2011 the SULTAN test facility has been continuously operated, with over one dozen test campaigns. Among the ITER conductors, five Toroidal Field (TF) samples, two Central Solenoid (CS) samples and four NbTi samples for Poloidal Field (PF), Correction Coil and Main Busbar coming from Japan, Russia, Korea and China have been tested with duration of test campaign ranging from two to nine weeks each. Two non-ITER conductor samples are also tested in the same period, a high current NbTi cable-in-conduit (CICC) for the secondary winding of the EDIPO flux pump and a prototype high field conductor for the hybrid magnet of the Radboud University (NL). The possibility to apply “off-SULTAN” thermal cycles from room temperature to liquid nitrogen has been realized for two samples. A novel method for in-situ measurement of the critical temperature in CICC has been successfully applied in SULTAN, opening the possibility to experimentally assess the thermal strain of the filaments at various stages of the test campaign, i.e. as a function of the load cycles and degradation. Residual strain measurements on the steel jacket of the TF conductors have been carried out at RT and 77 K.

This paper reports the main outcomes of the 2013 design activities for the toroidal field magnet of the European nuclear fusion reactor DEMOnstration Power Plant (DEMO). Within the current project plan, the manufacture of full-size conductor prototypes during 2014 and their test during 2015 are foreseen, aimed at the assessment of the proposed cable-in-conduit-conductor technologies. Industrial partners have been thus already involved at this early stage, and the preliminary cabling trials performed are illustrated here. As far as the coil design assessment is concerned, one of the main aspects to be investigated is the mechanical performance of the magnet, considering its large size and the high electromagnetic forces involved. An overall 3-D finite-element model of the coil has been set up, and mechanical stress analysis has been carried out for a selected instant of the plasma scenario after the computation of the electromagnetic loads within a full 3-D system model, including central solenoid and poloidal field coil contributions. The resulting loads have been mapped on the finite-element-method model, making use of a novel mesh-independent interpolator based on radial basis functions. The results reported here highlight a quite high level of stress, which is close to the acceptance limits, in some regions of the steel casing. Further investigations and assessments are required, but the most critical areas are clearly identified.

High Temperature Superconductors (HTS) are promising materials for future fusion magnets. One of HTS conductors' main issues is the quench protection: the quench develops much slower than in LTS, delaying the quench detection by voltage monitoring and causing a massive temperature increase before detection. The Swiss Plasma Center (SPC), with the support of EUROFusion, has upgraded the SULTAN facility to test large current conductors during the whole quench evolution. The 100 kA superconducting transformer has been replaced by an 18 kA direct power supply, which allows sustaining the operating current in the sample during a quench. Five HTS conductors have been manufactured at SPC: they are sub-size of the HTS high-current cables designed by the group for an HTS high current high field cable proposed for EU-DEMO Central Solenoid (CS) hybrid magnet. Every conductor has a specific feature. The aim is to compare the quench behavior of the five conductors “parametrically”. The commissioning of the upgraded facility and the preliminary results of the measurements are presented in this work.

The ITER Toroidal Field (TF) conductor qualification phase has been carried out by testing short sample prototype conductors in the SULTAN test facility. This phase, started in 2007, has been substantially completed after minor adjustment of the conductor specification and test procedures. All the parties involved in the TF conductor procurement passed the qualification phase. Starting 2010, the samples for TF process qualification phase are tested in SULTAN. A summary of the results for all the ITER Qualification samples and an updated statistics are presented for the V-I and V-T characteristics of the cable-in-conduit conductors (CICC), including Nb3Sn and NbTi samples assembled with either a "bottom joint" or a "U-bend".

Within the R&D program on the International Thermonuclear Experimental Reactor (ITER) Poloidal Field (PF) coils, a full size conductor sample was tested in the SULTAN facility (CRPP Villigen, Switzerland). This sample is composed of two straight ITER-like cable-in-conduit conductors, using the same NbTi strand. The two conductors are identical except that one leg has a cable containing steel wraps around the main subcables as in the ITER design, while the other has no wraps inside. The paper presents conductor DC test results compared to predictions given by various models developed within ITER-associated laboratories. These models aim to predict the DC behavior of the cable from the experimental performances of the single strand. They have to explain the observed voltage-current (V-I) or voltage-temperature (V-T) characteristics, including the thermal runaways. The lower experimental performances compared to all expectations have shown the necessity to revise the models and to introduce a possible uneven current distribution among the strands of the cables.

The Korean Domestic Agency (KODA) for the International Thermonuclear Experimental Reactor (ITER) project has taken the responsibility of the procurement of cable-in-conduit conductors for the ITER toroidal field magnet. While procuring 27 conductor unit lengths, which are the Korean sharing, 10 conductors have gone through the superconducting performance test, under low temperature and high magnetic field, as one of the final acceptance tests. The sample assembly and instrumentation of various voltage taps and temperature sensors have been done according to the specified procedure, which had been agreed between domestic agencies and the ITER International Organization. The performance test program, which has also been agreed, was carried out. For the assessment of the current sharing temperature (Tcs), the standard analysis procedure has been adopted. Tcs of all samples, at 68 kA and a background field of 10.78 T, after 1000 cyclic current loads are well above the acceptance criterion. By analyzing the electric field as a function of temperature, the effective strain (eeff) and transition index (n-value) were reduced, and the behavior of eeff will be discussed in terms of the electromagnetic load, i.e., I × B. The effective strain was compared with the physical strain and results with a numerical simulation.

This paper describes a new method to determine the equivalent heat transfer coefficients, i.e., radial and azimuthal, in CICC's with parallel cooling channels. The method is based on the measurement of the steady state temperature response to a step heating. The experiment is modelled by a set of transport equations for the temperature distribution that contain explicitly the parametric dependence on the transverse heat transfer coefficients. The equations are solved analytically and the values of the equivalent transverse heat transfer coefficients are obtained as the best fit of the experimental temperature distributions. We show the results obtained with the method by application to a short length sample experiment in the SULTAN test facility using an ITER-type CICC with special instrumentation, and with heaters to generate a variety of heat slugs. The values of heat transfer coefficient are consistent with expected values, based in particular on the theory of dispersion in porous media. (c) 2007 Elsevier Ltd. All rights reserved.

The index n of the voltage-current characteristic of large superconductors is a crucial parameter to assess the allowed range for coil operation. In the tests of the Insert coils at the CSMC as well as in the short sample test in the SULTAN facility, it is observed that the index n dramatically decreases from the Nb/sub 3/Sn strands extracted from cable-in-conduit provide the evidence of a permanent performance drop in the strands, likely due to the transverse load accumulation at the strand crossovers in the cable. This effect is not observed in NbTi conductors. The immediate implications for the Nb/sub 3/Sn conductor design are discussed and layout modifications to mitigate the effect are proposed.

A parametric study of the ac loss behavior and the stability of 3 NbTi subsize cable-in-conduit conductors has been performed in the SULTAN test facility. Two of the conductors are distinguished only by the SnAg and the Ni coating of the strands. The effective transverse resistance in the SnAg conductor is considerably lower than that found for the conductor with Ni coated strands. Hence, the coupling loss in the SnAg coated conductor is considerably higher than that in the Ni coated conductor. Cyclic loading of the conductor reduces the coupling loss in the SnAg coated conductor, whereas the ac loss of the Ni coated conductor is unchanged. The stability of the conductors has been found to be closely related to the ac loss. Due to the smaller ac loss in the Ni coated conductor the minimum field integral of (dB/dt)/sup 2/dt required to initiate a quench is considerably larger than that for the SnAg coated conductor.

The PF1 coil manufactured in the Russian Federation is one of the six poloidal field (PF) coils of the ITER electromagnetic system. The PF1 winding represents a stack of eight double pancakes (DPs). Each DP is wound from niobium–titanium “cable-in-conduit” conductors using the “two in hand” technique. The PF1 unidirectional winding is provided by connecting the ends of DPs into a single electric circuit by “shaking hands” low-resistance joints. An acceptance criterion for manufactured joints is an active resistance of less than 5 nΩ in the range of PF1 operating temperatures and applied magnetic fields. The initial joint design was updated on the basis of deviation requests of the ITER Organization. As a result, the previously developed techniques and tools were upgraded. To verify the modifications made, the preliminary joint sample was manufactured and tested in the NIIEFA test facility. Despite the limited current (up to 20 kA) and magnetic field, the results of the NIIEFA test verified the possibility of meeting the acceptance criterion and allowed us to start the manufacturing of the qualification joint sample. The final electrical test was performed in the “SULTAN” test facility of the Swiss Plasma Center (Switzerland). The test results are presented in this paper.

For the secondary winding of the flux pump (super- conducting transformer) of the EDIPO test facility at CRPP Villigen, a NbTi cable-in-conduit conductor (CICC) was designed at CRPP and procured at the industry. From a left section of the CICC a SULTAN sample, nicknamed TRASEK, has been assembled and tested. In the conductor design, high Cu:non-Cu ratio in the strand (no copper segregation), low void fraction and SnAg5 coating of the strand surface are selected to allow smooth current redistribution and enhance the take-off voltage. The DC tests are carried out be- fore and after solder filling the sample termination and current sharing is observed up to 80 kA. Eventually, the DC conductor performance is limited by the self field of the sample in the U-bend region. In normal operation, the secondary coil of the transformer is not exposed to significant magnetic field sweeps. The AC loss is expected to be large according to the design choices (tin coating, low void fraction). The AC loss characterization in SULTAN includes over 400 load cycles. The pressure drop vs. mass flow rate is measured in SULTAN to complement the data base for friction factor of CICC's.

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 Nb3Sn 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 cable-in-conduit-conductors (CICC) for the ITER Toroidal Field (TF) Coils are tested in the Sultan test facility in order to estimate their AC and DC performances under operating conditions. The tests are carried out on different stages of conductor procurement implementation starting from Nb3Sn superconducting strand layout and process development to regular checks of production unit lengths. Four TF samples provided by Russia have been successfully tested in the Sultan facility by now in the framework of the ITER collaboration, including Strand Performances Qualification Sample, Qualification Conductor Sample, Pre-production and Production Conductors sample. The test results of all four samples shows pretty good reproducibility of the conductor performances from sample to sample and at the same time good stability of conductor performance under mechanical loading caused by Lorenz force during electromagnetic (EM) cycling can be observed. In the present work a comparison of the conductors and their performance was carried out to show the development of conductor performances from R&D stage to mass production.

Five subsize NbTi cable-in-conduit conductors with parametric variations were fabricated and their DC performance was tested in the SULTAN facility. A comparison of the measured strand data and the cable performances clearly indicates that the current carrying capacity of the conductors is considerably reduced due to the self-field effect. This result reflects that because of the high transverse resistance the interstrand current sharing is not very efficient. Furthermore, the take-off electric field was found to decrease monotonously with increasing quench currents. In the case of large overall current densities, sudden take-offs occur before the critical current criterion (0.1 /spl mu/V/cm) has been reached. The observed quench behavior is a consequence of the large contribution of the self-field to the total magnetic field, which leads to strongly enhanced electric fields in the strands on the high field side of the conductor. As soon as the heat generated in the peak field region exceeds the locally available cooling power a quench is initiated. Considering insulated strands and a uniform current distribution the quench behavior has been reproduced by simulations.

CRPP has been selected to host the EDIPO test facility for the quality control tests of the ITER conductors. The new facility will be erected next to the existing SULTAN test facility at CRPP (Villigen) in Switzerland and will share the same cryo-plant. Operation of the two facilities is planned in parallel starting 2009. The new facility is designed to test short length samples built to the same specification as for SULTAN. EFDA procures 17 tons superconducting winding under industrial contract that will be delivered to CRPP in late 2008. The preparatory work at CRPP includes the design and procurement of several items as well as the final assembly and commissioning of the facility. An overview and the progress are reported, with focus on the main components: the vacuum vessel, the superconducting transformer and sample holder unit, the cryogenic cooling loop, the power supply and quench protection system, the HTS current leads and the magnetic screen.

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 T-cs, and meet the ITER requirement. Due to the ITER acceptance standard T-cs of MB conductor was changed to 6.7 K at 45.5 kA/3.9 T. The performance of MBCN1 conductor after cyclic load fits the ITER requirement, but the sample was only tested at 57 kA/2.75 T before cycling test. Using some hypothesis and equation to extrapolate the T-cs 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 1.3 mm during the cabling. The deviation causes an increase of the max self-field by about 0.005 T, which could not influence the CBCN1 conductor real T-cs performance at peak field. (C) 2013 Elsevier B.V. All rights reserved.

Previous studies indicated that the use of high-temperature superconductors (HTS) in the highest field allows us achieving the required magnetic flux in the central solenoid (CS) of the European DEMO at a reduced outer diameter, which would enable a reduced overall size and cost of DEMO. The proposed winding pack design of the CS1 module is based on ten layer-wound subcoils using an HTS, react and wind Nb3Sn, and NbTi conductors in the high, medium, and low field sections, respectively. The design utilizes a stainless steel and a superconductor grading leading to different overall current densities in each of the ten subcoils. Both, the hoop stress and the vertical loads are taken into consideration for determination of the required stainless steel cross-section in the winding pack. The stainless steel grading has been found to have an even more pronounced effect on the overall subcoil current densities than the superconductor grading. A preliminary estimation of the space required for the precompression structure is also reported.

In the last few years, the critical current densities of long commercially available REBa2Cu3O7-x (RE-123, where RE represents Y or a rare earth element) coated conductors have reached values of 250 A/cm-width at 77K and zero applied field. Even higher values of 600 A/cm-w (77 K, B = 0) have been demonstrated in shorter lengths. The attractive features of the use of these high-T-c superconductors (HTS) are operation temperatures above 20K and/or magnetic fields higher than those envisaged for the ITER TF coils. Possible operation conditions for HTS fusion magnets have been studied taking into consideration the possible further improvements of RE-123 coated conductors. Investigations of stability and quench behavior indicate that stability is not a problem, whereas quench detection and protection need attention. Because of the high currents necessary for fusion magnets, many tapes need to be assembled into a transposed conductor. The qualification of HTS conductors for fusion magnets would require their test at magnetic fields of 11 land currents well above 10 kA. The possibilities to test straight HIS conductor samples in SULTAN have been considered. For a test at 4.5 K, only the development of a low resistance joint between the HTS conductor under test and the NbTi transformer of SULTAN would be necessary. Tests up to 20K would require that the HTS sample is connected with the NbTi transformer by a conduction-cooled HTS bus bar of large thermal resistance similar to the HIS module of a current lead. HIS conductor tests at temperatures around 50K would be possible with modified cryogenics. (C) 2013 Elsevier B.V. All rights reserved.

An R&D program at CRPP investigates the design of large size Nb3Sn conductors, with the aim to improve the effectiveness and hence the cost of large size, force flow conductors. A design based on a solder filled flat cable, by react wind method, is selected for a demonstration prototype, built at CRPP and tested in the SULTAN facility. In the new conductor, the longitudinal strain is similar to the strand intrinsic strain because the cable is heat treated without steel jacket. The transverse load degradation is suppressed thank to effective mechanical support of the strands by the solder matrix. The test in SULTAN includes dc test, ac loss in superimposed dc and ac field and transient field stability. At 48 kA (430 A/mm(2)) and 11.15 T the current sharing temperature is 6.3 K, i.e. the new conductor provides a higher temperature margin and saves about 50% of the Nb3Sn cross section, in comparison to ITER. The transient stability largely fulfils the ITER requirement.

Two identical conductor samples were fabricated from 110 m length cable prepared for qualification of the manufacturing process for Phase II procurement of ITER TF conductor. Superconducting strand characteristics, cabling specifications, and the stainless steel jacket sections are described. Sample assembly and instrumentation of various voltage taps and temperature sensors have been prepared according to specified procedures for conductor performance qualification. The performance test program which was agreed to by the SULTAN working group was applied to the conductor samples. To assess the current sharing temperature (T-cs), standard analysis procedures were adopted. The T-cs of both samples at 68 kA with a background field of 10.78 T after a 1000 cyclic load are well above the acceptance criteria. Behavior of individual "star" voltage taps which are located at different positions and which are possible origins of rather large discrepancies in the T-cs of identical samples is discussed. The effective strain and the transition index of the samples are obtained from the experimental data.

In the last decade, a large number of high current, force flow superconductors have been tested as short length samples in the SULTAN facility. The object of the test ranged over transient stability, thermal-hydraulic behavior, AC losses, joint resistance and proof-of-principle for innovative conductor design. Recently, with the ITER cable-in-conduit conductors (CICC), the basic DC transport properties have been the focus of the SULTAN test. The critical steps of the sample assembly and instrumentation are described, with emphasis on the application of the temperature sensors, verification of the signal treatment chain and calibration. The post-processing and the data reduction are focused on the assessment of the current sharing temperature, T cs: the conventional method of electrical field threshold detection by voltage taps is compared with the current sharing power detection by steady state gas-flow calorimetry. The longitudinal strain state of the conductors is discussed through the results of strain gauges applied on the jacket. Eventually, the value of a certified conductor test is highlighted in the frame of the quality control for the ITER magnets.

The fourth China TF conductor sample (TFCN4) for Phase II, the left leg of the fifth China TF conductor sample (TFCN5) for Phase III, as well as the right leg of the TFCN5 conductor for Phase IV, were made of the WST strands, cabled by Baosheng, jacketed at ASIPP, and prepared by CRPP following the IO-approved procedure and tested in the SULTAN facility. The Tcs test results show that both legs of the TFCN4 and TFCN5 have high Tcs performance. Using the electrical method, the Tcs was 6.56 K for the left leg of TFCN4 and 6.58 K for the right leg of TFCN4 at 68 kA/10.78 T in the first test and 6.36 K for both legs after 1000 electromagnetic load cycles. In the case of TFCN5, Tcs was 6.56 K for the left leg and 6.30 K for the right leg at 68 kA/10.78 T in the first test and 6.33 K for the left leg and 6.02 K for the right leg after 1000 electromagnetic load cycles. According to the SULTAN test result, Tcs values of TFCN4 and TFCN5 conductor samples meet the ITER acceptance criteria.

In the framework of the conductor optimisation task (CONDOPT) five NbTi subsize cable-in-conduit conductors with parametric variations were fabricated. The DC performance of these conductors tested in the SULTAN test facility [IEEE Trans. Appl. Supercond. 12 (2002) 520] and the strand properties including the voltage-current characteristic, are compared. The results clearly indicate that the current carrying capacity of the conductors is considerably reduced due to the self-field. In conductors with a hindered interstrand current sharing, the critical current has been found to be even below the predicted value at the peak field, suggesting an uneven current distribution among the strands. (C) 2003 Elsevier B.V. All rights reserved.

Coated conductors could be promising materials for the fabrication of the large magnet systems of future fusion devices. Two prototype conductors (flat cables in steel conduits), each about 2 m long, were manufactured using coated conductor tapes (4 mm wide) from Super Power and SuperOx, with a total tape length of 1.6 km. Each flat cable is assembled from 20 strands, each strand consisting of a stack of 16 tapes surrounded by two half circular copper profiles, twisted and soldered. The tapes were measured at 12 T and 4.2 K and the results of the measurements were used for the assessment of the conductor electromagnetic properties at low temperature and high field. The two conductors were assembled together in a sample that was tested in the European Dipole (EDIPO) facility. The current sharing temperatures of the two conductors were measured at background fields from 8 T up to 12 T and for currents from 30 kA up to 70 kA: the measured values are within a few percent of the values expected from the measurements on tapes (short samples). After electromagnetic cycling, T-cs at 12 T and 50 kA decreased from about 12 K to 11 K (about 10%), corresponding to less than 3% of I-c.