Cold Test Facility Research Articles

Design and Performance of a Linear Flux Pump for the Frascati Coil Cold Test Facility

Design and Performance of a Linear Flux Pump for the Frascati Coil Cold Test Facility

On the Thermal Contact Between Winding Packs and Casings of JT-60SA TF Coils in Self-Field and Tokamak Configurations

The present study aims at providing quantitative insight, extracted from experimental data, about the impact of Lorentz forces on the distribution of static heat load within JT-60SA Toroidal Field (TF) coils. More accurately, we assess the distribution of these loads over the winding packs (WP) and casings from Helium enthalpy balances when the TF current is either zero or nominal. This study is motivated by the impact of such loads and associated distribution on the quench margin in operation and on the cryogenics system. It is divided in two parts: the first one focuses on the distribution results obtained for the Cold Test Facility (CTF) tests (i.e., in self-field configuration) while the second one focuses on those obtained during JT-60SA integrated commissioning (i.e., in tokamak configuration). We then draw the main outcomes of these studies and discuss the consistency of the results obtained for the two configurations.

Factory Acceptance Test and Delivery of the First Two Poloidal Field Coils to ITER Fusion Facility

Fusion for Energy (F4E), the European Domestic Agency for the International Thermonuclear Experimental Reactor (ITER), is responsible for the supply of 5 out of the 6 Poloidal Field (PF) Coils: PF2-PF6. One coil, PF1, is being manufactured by the Russian Federation Domestic Agency (RFDA). While the 10 m diameter PF6 was manufactured by the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and tested in the cold test facility at Cadarache under a collaboration agreement with F4E; coils PF2-PF5 are currently being manufactured on site, close to the Tokamak building, their size ranging from 17 to 24 m diameter and weights from 200 to 400 T. This article describes the final acceptance tests performed on the coils PF5 and PF6, the testing setup, paying special attention to the tests performed before, after and during the cool-down at 80 K. The tests cover a wide range of aspects of the operation at cryogenic temperatures: ranging from the high voltage electrical insulation performance during the potential fault conditions during plasma operation, leak tightness under vacuum and pressure drop behavior of its hydraulic system during operation with forced flow helium. In addition, we will briefly introduce the results for the current center line (CCL) calculation obtained for PF5 and PF6.

Thermal Hydraulic Analysis of JT-60SA TFC02 Complementary Quench Tests in CTF

In the framework of JT-60SA tokamak commissioning (Japan, 2021), the 20 Toroidal Field Coils (TFC) were tested at the Cold Test Facility (CTF) at CEA-Saclay (France, 2018) and submitted to quench acceptance test (quench temperature up to 7.5 K at nominal current). Some complementary quench tests were performed on the spare coil TFC02, with different conditions, especially reduced current (at 75% and 50% of nominal current) and delayed quench detection (holding time of 0.5 s instead of 0.1 s). A numerical model was developed, with SuperMagnet (fortran, CryoSoft) coupling THEA (Thermohydraulic and electric 1-D physics of Cable In Conduit Conductor, CICC) and Flower (Thermohydraulic model of cryogenic network). The measurements are presented and compared to simulation results. The acceptance quench test of TFC02 depicted a maximal helium temperature of 27 K. During complementary quench tests, delayed quench detection induced higher helium temperature of 37 K. At 75% and 50% of nominal current, a so called “smooth” quench occurred. It is characterized by slow quench propagation and low resistive voltage which increase the quench propagation time required before triggering current discharge although it reduces the Joule energy dissipated by the coil.

JT-60SA TF coil quench model and Analysis: Joule energy estimation with SuperMagnet and STREAM

In the framework of JT-60SA Tokamak commissioning (Japan, 2021), all coils have to be cooled with supercritical helium forced-flow at the temperature of 4.5 K in order to reach superconducting state before energization. An important issue is to predict the Joule energy dissipated in Cable-In-Conduit Conductors (CICC) and the maximal temperature reached in case of an incidental quench occurrence. Therefore, quench simulations were performed on the Toroidal Field Coil (TFC) with the STREAM (Superconductor Thermal hydraulic and Resistive Electrical Analytical Model) code and with the SuperMagnet code (CryoSoft), coupling THEA (thermal hydraulic and electrical 1-D CICC model) and Flower (thermal hydraulic network model). The quench event was simulated for one TFC at nominal conditions of tokamak operation. External energy deposition over each pancake’s first turn of the coil at the peak magnetic field location was applied for initiating the resistive transition. This way, the computed Joule energy dissipated by one TFC is conservatively evaluated to be 5.65 MJ. The Joule energy dissipation depends strongly on quench initiation conditions and on the number of fully and rapidly quenched pancakes (maximal quench propagation velocity of 19.5 m/s). Some further analyses were performed on the acceptance quench test realized at the Cold Test Facility (CEA Saclay, 2018) on TFC02. The different calculation results (helium temperature, mass flow rate in upstream and downstream manifolds, normal length propagation) are presented in the following study and are consistent with the measurements. This analysis brings information on the limits and the ability of STREAM code to model quench behaviour in CICC coils cooled by forced flow of supercritical helium. This tool could be useful for tokamak magnets protection during quench event and safe operation, notably thanks to its fast computing time.

Modeling of AC Losses and Simulation of Their Impact on JT-60SA TF Magnets During Commissioning

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.

OLYMPE, a multi-physic platform for fusion magnet design: Development status and first applications

In the framework of design studies for tokamak superconducting magnets a first step is usually required of pre-dimensioning that provides a rough magnets dimensioning, followed by detailed analyses. Such analyses aim at verifying that predefined design criteria are met in normal and in off-normal operation conditions, in order to ultimately progress step by step towards the most optimized configuration with respect to defined factors of merit of the tokamak. These studies involve several physics and thus several specific numerical codes modelling those physics. In order to handle these process analyses as efficiently and reliably as possible, the development of a multi-physic platform is underway at CEA. This platform, called OLYMPE, integrates different solvers under the supervision of a single actor for interfaces management. Furthermore, the availability of an integrated tool such as OLYMPE also aims at providing a possibility to easily run parametric studies in an automatic mode, to access to more efficient methods for confrontation with experimental data.In this paper, the structure of the platform is described, detailing the different codes and the coupling between the codes. The development status of these different codes included in OLYMPE workflow will also be exposed.Another part of the paper will present the application of the two most advanced OLYMPE modules (electromagnetic and thermal-thermohydraulic) on two projects. The first application is about the modelling of the experimental tests performed on the JT-60SA Toroidal Field coils tested in the Cold Test Facility. Parametric studies on some defined parameters are performed to fit the experimental data (e.g. impact on the thermal loads of the winding pack detachment from the casing, effect of pancakes friction factor variability…). The second application focuses on the CEA design proposal for EU-DEMO Toroidal Field (TF) magnets, where other parametric analyses will be provided.

Test Facility and Results of ITER PF4 Current Leads

The International Thermonuclear Experimental Reactor (ITER) high-temperature superconducting (HTS) current leads designed and manufactured by Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP), Hefei, China, are used to transmit current to the magnetic coil of the ITER device with lower heat conduction load. PF4 HTS current leads which supply pulse current for PF4 coil are the first pair of all 33 pairs series current leads, have finished its test recently. The cold test was performed in a new test facility in which the current leads were vertically installed, and a dedicated design was added to abate the gravitation produced between the two current leads. Besides the cold test facility, this article will also summarize the major test results, joint resistance, high current-sharing temperature, loss of flow accident (LOFA) time, overheating time, heat conduction loads to 5-K ends, and the consumption of 50-K mass flow.

Investigation of gas‒solids flow hydrodynamics in a cold model of a dual fluidised bed gasifier using electrical capacitance tomography sensors

The flow characteristics of a dual fluidised bed gasifier (DFBG) are more complex than those of a single fluidised bed gasifier. For stable operation and appropriate control, a cold DFBG test facility with both an upper and a lower U-valve was built, and electrical capacitance tomography (ECT) sensors were installed with pressure transducers to investigate the effects of operating conditions on gas‒solids flow hydrodynamics. The operating parameters included gas velocities in the riser and in the bubbling fluidised bed, aeration velocity in the lower U-valve, bed material inventory, and particle size. This is the first time that ECT was applied in different flow zones of a dual fluidised bed gasifier system. The experimental results indicated that ECT in the recycle chamber could monitor the performance of the lower U-valve under different operating conditions for early detection of gas shortcut from the riser to the bubbling bed. Three main flow regimes in the riser and the differences between the reactors were identified by two sets of ECT sensors with pressure transducers. Finally, the effects of the operating conditions on the pressure drop in different parts of the DFBG was investigated.

JT-60SA TF Coils Tests: Critical Properties Analyses and First Extrapolations to Tokamak Operation

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

Cold Roll Cladding of Carbon Steels

Cladding of steel is mainly carried out by hot rolling. This process is very labor-intensive and, therefore, expensive. Cold plating has been used successfully to produce bimetals and could also be an alternative manufacturing process for cladded carbon steel composites. So far, however, only thin narrow IF-steels sheets were successfully cold plated. Different pretreatments and process windows have been used to successfully produce a cold roll-cladded composite of various steel grades on a cold rolling test facility. While joining two similar steels was relatively easy, the combination of different steel alloy compositions was more difficult. Higher necessary forces and edge cracks complicated the experiments. A slight warming of the sheets before joining had a positive effect on the production of the composite. From today's perspective, the required high rolling forces do not allow scaling up to large-scale production.

JT-60SA toroidal field coils procured by ENEA: A final review

Within the Broader Approach Program between Europe and Japan for the early realization of fusion with the construction of the JT-60SA tokamak, ENEA, the Italian Agency for New Technologies, Energy and Sustainable Economic Development, was in charge, among others, to supply ten superconducting Toroidal Field (TF) coils for the JT-60SA magnet system. The related procurement started in 2011 and was concluded in 2018 with the delivery of the tenth coil to the Cold Test Facility in France. The construction of each TF coil module consisted of two main phases: manufacturing of the superconducting winding pack and integration in the corresponding casing structure. With all the foreseen modules already completed, this paper provides a critical review of the contract for the manufacturing of the coils highlighting the main difficulties occurred in the different manufacturing steps and evaluating the performances obtained from the measurements taken at the acceptance tests.

Progress of the JT-60 SA Toroidal Field Coils Tests in the Cold Test Facility

JT-60 SA is a fusion experiment which is jointly constructed by Japan and Europe and which shall contribute to the early realization of fusion energy, by providing support to the operation of ITER, and by addressing key physics issues for ITER and DEMO. In order to achieve these goals, the existing JT-60 U experiment will be upgraded to JT-60 SA by using superconducting coils. The 18 Toroidal Field Coils (TFC) of the JT-60 SA device are provided by European industry and tested in a Cold Test Facility (CTF) at CEA Saclay. At the summer 2017, 14 TFCs will have been tested at the nominal current of 25.7 kA and at a temperature between 5 and 7.5 K. The main objective of these tests is to check the TF coils performances and hence mitigate the fabrication risks. These tests allowed checking a certain number of performances of the TFCs: DC/AC insulation, cooling down characterization, RRR of the conductor, pressure drop in the winding pack, and temperature margin against a quench. This paper will show the testing program progress and give an overview of the main experimental results obtained during these tests. The main performances of each coil will be summarized, analyzed, and discussed in the light of the expected TFCs performances.

Numerical Modeling of the Quench Propagation Phase in the JT-60SA TF Coils

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 ( $T_{cs}$ ) 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 coupling model 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.

Analysis of the Early Quench Development in JT-60SA Toroidal Field Coils Tested in the Cold Test Facility

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 double-pancakes, 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 follow the 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 the THEA code with 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.

Parametric Analyses of JT-60SA TF Coils in the Cold Test Facility With SuperMagnet Code

The toroidal field (TF) system of JT-60SA tokamak comprises 18 NbTi superconducting coils. In each TF coil, 6 cable-in-conduit conductor (CICC) lengths are wound into 6 double-pancakes 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).

Manufacturing and acceptance by CEA of the first JT-60SA TF coils

In the frame of the Broader Approach, CEA provides 9 Toroidal Field (TF) coils+1 spare for the JT-60SA tokamak. Mid 2011, a manufacturing contract was awarded to Alstom, Belfort, and now General Electric (GE). The first years were dedicated to the manufacturing process definition, the critical processes qualification through a set of 12 mockups, the manufacturing Quality Assurance (QA) definition and the procurement and commissioning of the tooling. Then, the production started early 2014.The manufacturing workshop was organized in 12 workstations. The production started with the preparation of the conductors provided by F4E and the winding in a stack of 6 Double Pancakes (DPs) which constitutes one Winding Pack (WP). The joints to connect electrically the DPs and the impregnations finalized the first WP. End 2014, acceptance tests related to geometry, tightness and electrical insulation validated the first WP for the following integration operations.The coil casings made under F4E to ENEA contract, were delivered as a set of components, including the U shaped straight and curved legs forming the D shape of the coil and the inner covers. After preparation, the WP was inserted vertically inside the casing straight leg lying horizontally. The curved leg and covers were then added to close the coil. The WP geometry and location in the casing were carefully controlled. The casing elements enclosing the WP were then welded either manually or by robots before performing the blocking impregnation. A final machining adjusted then the coil interfaces to the precise WP references. End 2015, after insulated piping integration, the final coil acceptance in terms of geometry, tightness and insulation allowed the delivery of the first coil at the Cold Test Facility (CTF), where the coils were tested at full current before final acceptance.This paper describes the first TF coils manufacturing process, the status of the production and provides first insights into the manufacturing feedback and the first coils performance results.

JT-60SA TF coils procured by ENEA: An intermediate assessment

ENEA, in the framework of Broader Approach program for the early realization of fusion with the construction of JT-60SA tokamak, is procuring 9 of the 18 TF coils of JT-60SA magnet system. Within 2016 five coils will be completed and delivered to the cold test facility in Saclay, France, for the final acceptance tests before their shipment to Naka site for the assembly. Manufacturing has been divided in two main production steps: winding pack (WP) manufacturing and integration into casing. All the nine WPs have been already completed on September 2015 and the final integration phase has started in 2015 for the first coil. The integration, in its turn, is composed of six sub-steps: insertion, welding, embedding impregnation, final machining of interface areas, He piping assembly and final acceptance tests. Each of these steps has been already accomplished and two coils have been delivered to Saclay and undergone the cryogenic acceptance tests. This paper provides an overview and intermediate assessment of the contract that ENEA signed with ASG Superconductors for this supply.

Quench tests analysis of the first JT-60SA Toroidal Field coils

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

Results of the first JT-60 SA toroidal field coils tests in the cold test facility

JT-60SA is a fusion experiment which is jointly constructed by Japan and Europe and which shall contribute to the early realization of fusion energy, by providing support to the operation of ITER, and by addressing key physics issues for ITER and DEMO. In order to achieve these goals, the existing JT-60U experiment will be upgraded to JT-60SA by using superconducting coils. The 18 TF coils of the JT-60SA device are provided by European industry and tested in a Cold Test Facility (CTF) at CEA Saclay. The first coils were tested at the nominal current of 25.7kA and at a temperature between 5K and 7.5K. The main objective of these tests is to check the TF coils performances and hence mitigate the fabrication risks. These first tests allowed checking a certain number of performances of the first TF coils: DC/AC insulation, cooling down characterization, RRR of the conductor, pressure drop in the winding pack and temperature margin against a quench. This paper will give an overview of the main experimental results obtained during these tests. These results will be analyzed and discussed in the light of the expected TF coils performances.