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AC losses deposited in the magnets during JT-60SA commissioning and operation will both affect the local stability of the conductor and act as a load on the cryogenic system. Our objective is thus to establish a detailed modeling of AC losses generated in the magnets by different current scenarios. Since the TF coils have been tested in the Cold Test Facility (CTF) and will be the first ones to be fully energized during the commissioning, we have focused our work on the AC losses deposited in the TF; this enables us to assess the relevancy of our modeling against the CTF data. We also present thermohydraulic simulations conducted with TACTICS (a CEA tool coupling THEA and Cast3m) to both have a view on heat load propagation inside TF winding pack and estimate the impact on the helium temperature of the AC losses generated by the TF fast discharge during the cold tests and the commissioning. [ABSTRACT FROM AUTHOR]

The toroidal field system of the JT-60SA tokamak is composed of 18 NbTi superconducting coils. Each TF coil is composed of six cable-in-conduit conductor lengths, wound in doublepancakes, and carrying a nominal current of 25.7 kA. These coils are being tested in the single-coil configuration at the so-called cold test facility (CEA/IRFU, Saclay, France). The test program includes for all coils a quench test at nominal current obtained by a progressive increase of the operating temperature at helium inlet up to quench (around 7.5 K). Thanks to the accuracy of the voltage measurements, it has been possible to followthe very early development of the quench at the scale of a few millimeters normal length. The paper presents the evolution of the resistive voltages measured on eight coils before the safety discharge is triggered. In addition, this early quench development over one conductor length was also simulated using theTHEAcodewith relevant boundary conditions. Two different quenches, which occurred on two different coils, were analyzed, one starting on a central pancake (peak magnetic field) and the other starting on a side pancake (warmer conductor due to heat transfer from the casing). The simulations show good agreement with experiments, stressing particularly three phases in the quench development clearly identified in the measured resistive voltages of all coils. [ABSTRACT FROM AUTHOR]

The toroidal field (TF) system of JT-60SA tokamak comprises 18 NbTi superconducting coils. In each TF coil, 6 cablein-conduit conductor (CICC) lengths are wound into 6 doublepancakes and carry a nominal current of 25.7 kA at a temperature of 4.7 K. Each coil is tested in the cold test facility (CEA Saclay), up to quench. A SuperMagnet (CryoSoft) model has been developed, each of the 12 pancakes being modeled with THEA and cryogenic circuit being modeled with FLOWER. The experiments showed that helium inlet temperature increases until quench triggering at about 7.5 K on C11 and C13, with quench starting on a lateral and on a central pancake, respectively. Each test has been simulated, applying (or not) a realistic heat load from casing to winding pack that was estimated from experimental measurements. A parametric analysis has been performed, considering realistic or null heat flux deposition, variation of friction factor (in fabrication quality range), and CICC critical current density (in strand Jc performance range). This last parameter was found to have the largest impact on the localization of the first quenched pancake (central or lateral). [ABSTRACT FROM AUTHOR]

In the framework of the design activities conducted in the EU for dimensioning the future fusion demonstration reactor (DEMO), extensive analyses were carried out within the framework of the EUROfusion consortium, with the objective of defining the design of the DEMO magnets system. To this aim, CEA has developed ad-hoc predimensioning tools and associated methods in order to size the different magnets: toroidal field coils, central solenoid (CS) and poloidal field (PF) coils. Once predimensioned, the magnet concepts undergo a detailed evaluation procedure withmore complex tools and methods. As these detailed analyses are time consuming, the whole design process benefits from an accurate and robust predimensioning process. The predimensioning tools described herein address various aspects driving the operational limits of the magnets while energized in the tokamak, related to electromagnetic, thermal, and mechanic phenomena. In this paper, we expose the latest developments in the predimensioning tools and the methods employed for obtaining a rapid and reliable macroscopic semi-analytical representation of the magnets. The assessment of the predimensioning tools on reference configurations (e.g., ITER) is also described. The application of these design tools on the DEMO configuration issued by EUROfusion is presented, and the resulting magnet design proposals are summarized: First, the PF system, composed of six coils, with one PF selected for study here. Second, the CS, with a modular geometry (five modules) and pancake winding. The approach here assesses the resilience of the CS to a fast-transient (breakdown). The outcomes of a sensitivity study on parameters/criteria are discussed, and extended to some tentative recommendations on the design approach for the DEMO PF and CS magnets. For the PF, a design is obtained for the PF5 coil following a dimensioning methodology consistent with the ITER PF system design with the same level of definition of the plasma operating scenario. As for the CS, it is stressed that consideration of the internal field (from shielding) substantially affects temperature margin results. [ABSTRACT FROM AUTHOR]

In the framework of the European-Japanese project JT-60SA, the quench tests are performed for each of the 18 NbTi superconducting tokamak toroidal field coils (TFC) in the Cold Test Facility at the CEA Saclay, Gif-sur-Yvette, France. While launching these experimental quench tests, the conductor current sharing temperature (Tcs) is reached by progressively increasing the inlet helium temperature. The quite complex quench dynamics are then observed due to several coupled physical phenomena influencing the quench propagation. In order to better understand the experimental analyses on coils quench behavior, a numerical model has been used, combining the computation code thermal hydraulic and electric analysis of superconducting cables for the longitudinal quench transient modeling along the cable-in-conduit conductor, and an additional interturn thermal couplingmodel for transverse heat flux modeling. In this paper, several parametric studies will be done, thanks to simplified numerical simulations in order to identify the predominant physical phenomena driving the JT-60SA TFC quench propagation. The analysis focuses on the linear power impact on the quench initiation, the quench propagation dynamics, and the reverse flow effect. [ABSTRACT FROM AUTHOR]

In the framework of the EUROfusion DEMO project, design studies for the tokamak magnet systems are conducted across several European institutions. Superconducting magnets are required to generate the high magnetic fields needed for the plasma confinement and control. The reference conductor design is based on Cable-In-Conduit Conductors (CICC) cooled at cryogenic temperatures by forced circulation of supercritical helium. The proposed Toroidal Field (TF) coils Winding Pack (WP) design should satisfy the design/safety criteria during operation (e.g., minimal temperature margin) and in off-normal conditions (e.g., hotspot temperature). Quenches are studied to ensure that the proposed conductor design and associated quench protection system guarantee the integrity of the magnet; such events are a safety and investment protection issue, and as such deserve high levels of scrutiny. Quench propagation in a coil is a 3-dimensional (3D) problem. For this reason, a transient pseudo-3D modeling tool was developed for coupled thermal and thermo-hydraulic calculation in a tokamak superconducting coil. The coupling tool is based on a 1D model of the cable using the THEA code, considering current distribution, helium flow, thermal conduction in the strands and propagation of the quench along the conductor; the 2D transverse thermal diffusion across turns is modeled using the Cast3M code, considering the conductor jacket and insulation, on a selected set of cross-sections along the coil. The aim of the analysis is to assess the quench behavior of the CEA proposal for DEMO TF coil. The hotspot temperatures as well as the propagation of the normal zone along the conductor length are evaluated in a realistic quench scenario, taking into account the impact of transverse heat diffusion. [ABSTRACT FROM AUTHOR]