Francesca Cau

Test Results of Two European ITER TF Conductor Samples in SULTAN

Four conductor lengths were prepared according to the ITER TF conductor design and assembled into two SULTAN samples. The four lengths are not fully identical, with variations of the strand supplier, void fraction and twist pitch. Lower void fractions improve the strand support and increased twist pitches also lower the strand contact pressure but both tend to increase the AC loss and the lower void fraction also increases the pressure drop so that the mass flow rate in the strand bundle area of the cable is reduced. The assembly procedure of the two samples is described including the destructive investigation on a short conductor section to assess a possible perturbation of the cable-to-jacket slippage during the termination preparation. Based on the DC performance and AC loss results from the test in SULTAN, the impact of the void fraction and twist pitch variations is discussed in view of freezing the ITER conductor design and large series manufacture. A comparison with the former generation of conductors, using similar strands but based on the ITER Model Coil layout, is also carried out. The ITER specifications, in terms of current sharing temperature, are fulfilled by both samples, with outstanding results for the conductor with longer twist pitches.

Methods, Accuracy and Reliability of ITER Conductor Tests in SULTAN

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.

Design and Procurement of the European Dipole (EDIPO) Superconducting Magnet

A 12.5 T superconducting dipole magnet (European DIPOle, EDIPO) has been designed by EFDA and it is now being procured within the framework of the European Fusion Programme in order to be installed in CRPP-PSI. This saddle-shaped magnet is designed to reach 12.5 T in a 100 times 150 mm rectangular bore over a length of about 1.5 m in order to test full size conductor samples that shall be produced during the ITER magnets procurement. The magnet uses Cable In Conduit Conductor (CICC) technology and the cables are made of high Jc (about 2300 A/mm2 at 4.2 K, 12 T) superconducting strands. In this paper the main magnet parameters are given together with the key supporting electromagnetic, mechanical and thermal analyses. An update on the general status of the procurement of the strand, conductors, dipole magnet and facility is also given together with the key results of the on-going supporting R&D.

A signal-processing tool for non-destructive testing of inaccessible pipes

The design of Non-Destructive-Testing systems for fault detection in long and not accessible pipelines is an actual task in the industrial and civil environment. At this purpose, the diagnosis based on the propagation of guided ultrasonic waves along the pipes offers an attractive solution for the fault identification and classification. The authors studied this problem by means of suitable Artificial Neural Network models. Numerical techniques have been used to simulate the guided wave propagation in the pipes. In particular, the finite element method has been used to model different kinds of pipes and faults, and to obtain several returning echoes containing the faults information. Torsional wave modes have been used as excitation waves. The obtained signals have been processed in order to reduce the data dimensionality, and to extract suitable features. The features selected from the signals can be further processed in order to limit the size of the Neural Network models without loss of information. At this purpose, the principal component analysis has been investigated. Finally, the selected features have been used as input for the neural network models. In this paper, traditional feed-forward, multi-layer perceptron networks have been used to obtain the information on size and location of localized notches.

Status Report of the SULTAN Test Facility

One year of operation and test activity of the SULTAN test facility at CRPP-Villigen, from October 2008 to October 2009 is reviewed. The main improvements of the facility include a new control system for the cryo-plant and a new electric motor for the helium compressor. The range of operation for the SULTAN samples has been improved in terms of cyclic loading rate. The test campaigns from October 2008 to October 2009 include eight ITER TF conductor samples, two JT60SA samples and a number of other developmental samples. The highlights of the test campaign and the statistical data about cool-downs, warm-ups and test duration are reported. For the eight ITER TF samples, more detail is given about the joint development, the standard test program and the data reduction for the assessment of the results. Eventually, an outlook in the next operation period is also discussed.

Results of Thermal Strain and Conductor Elongation Upon Heat Treatment for

The change of length upon heat treatment of steel jacketed, Nb3Sn cable-in-conduit conductors (CICC) is driven by the difference of coefficient of thermal expansion between Nb3Sn and the other components. The cold work of the steel jacket also plays an important role. During the preparation of CICC samples for test in the SULTAN facility, the change in length has been systematically measured for 16 sections of CICC. The broad range of changes, from elongation to shrinkage, is a concern for the manufacture of the ITER toroidal field (TF) coils, where the shape/length of the conductor after heat treatment must be exactly predicted to fit into the radial plates. For a reliable assessment of the performance of Nb3Sn CICC, the axial, thermal strain in the Nb3Sn filaments is a key parameter. To gain information on the subject, the residual strain on the steel jacket is systematically measured by strain gauges on 28 ITER CICC sections tested in SULTAN. The range of results is very broad and no clear correlation is found with the conductor performance, i.e. with the thermal strain in the filaments. To gain more inside about the actual thermal strain in the Nb3Sn filaments embedded in a CICC, neutron diffraction techniques have been applied (with limited success) to deduce the thermal strain from the direct, in situ measurements of the lattice parameter.

{\rm Nb}_{3}{\rm Sn}

The EDIPO test facility is erected at CRPP Villigen with the aim of providing a flexible, high field test bed for high current force flow superconductors. The EDIPO main coil is a tilted-head race-track pair wound by a graded Nb3Sn cable-in-conduit conductor. The whole project, partly funded by the European Commission, started in 2004 and entered the commissioning phase in 2013. The final steps of instrumentation and installation of the main coil, delivered by industry in May 2011, lasted about 18 months. The first cool-down of the facility started in November 2012. The commissioning of the main coil, including the precise measurement of the generated magnetic field, was carried out in March 2013. At an operating current of 17.2 kA, a ± 1% homogenous field of 12.35 T was generated over a length of 900 mm in the center of the test well, 140 mm × 91 mm in cross section. Details about cool-down, flux jumps, forces and displacements, field map, and charging rate are presented in this paper.

Cable-in-Conduit Conductors

In this paper, different pattern recognition techniques have been tested in order to implement an automatic tool for disruption classification in a tokamak experiment. The methods considered refer to clustering and classification techniques. In particular, the investigated clustering techniques are self-organizing maps and K-means, while the classification techniques are multi-layer perceptrons, support vector machines, and k- nearest neighbours. Training and testing data have been collected selecting suitable diagnostic signals recorded over 4 years of EFDA-JET experiments. Multi-layer perceptron classifiers exhibited the best performance in classifying mode lock, density limit/high radiated power, H-mode/L-mode transition and internal transport barrier plasma disruptions. This classification performance can be increased using multiple classifiers. In particular the outputs of five multi-layer perceptron classifiers have been combined using multiple classifier techniques in order to obtain a more robust and reliable classification tool, that is presently implemented at JET.

Commissioning of the Main Coil of the EDIPO Test Facility

The design of non-destructive testing systems for fault detection in long and not accessible pipelines is an actual task in the industrial and civil environment. At this purpose the diagnosis based on the propagation of guided ultrasonic waves along the pipes offers an attractive solution for the fault identification and classification. The authors studied this problem by means of suitable artificial neural network models. Numerical techniques have been used to model different kinds of pipes and faults, and to obtain several returning echoes containing the fault information. These signals have been processed to filter the noise by using wavelets e blind separation methods and passed to a feature extractor system, whose purpose is to reduce the data dimensionality and to compute suitable features. The features selected from the signals have been further processed in order to limit the size of the neural network models without loss of information. At this purpose, the Garsons method and the principal component analysis have been investigated and compared. Finally, the extracted features have been used as input for the neural network models. In this paper, traditional feed-forward, multi layer perceptron networks have been used to classify position, width, and depth of the defects.

Automatic disruption classification at JET: comparison of different pattern recognition techniques

Since it is practically impossible to remove the Poloidal Field (PF) coils from the assembled ITER (International Thermonuclear Experimental Reactor) tokamak without major interruption in operation, the design of these coils shall provide their high reliability under high voltage operation. The design of the coil insulation relies on a separation of functions: mechanical function of the load transmission, performed by glass-fiber impregnated with epoxy resin on one side, and the independent electrical barrier made of polyimide tapes on the other side. Numerical simulation has shown that the maximum electrical field in the coil is lower than 4 kV/mm, which is taken as the design criterion for the PF insulator system. In case of a single insulation failure in a coil, its functionality can be recovered by installing a so-called jumper to by-pass the faulty double pancake. The design of the jumpers and their installation procedure are described.