ITER PF Research Articles

Pulsed Field Stability and AC Loss of ITER PF Joints by Detailed Quantitative Modeling

Pulsed Field Stability and AC Loss of ITER PF Joints by Detailed Quantitative Modeling

AC Losses Calculations for the ITER CS and PF Magnet Systems During Plasma Operation

While the ITER magnet system assembly is progressing, models are being developed to predict the performances of the coils in support of the preparation of commissioning and operation. In particular, the AC losses generated in the coils during a plasma scenario need to be estimated as input to thermo-hydraulic performance simulations. The largest AC losses during plasma operation are expected in the CS and PF coils. This paper discusses the results of simulations of AC losses in these coils during a representative ITER plasma pulse. These calculations also take into account the electromagnetic screening provided by the ITER passive structures, most importantly the vacuum vessel, discussing its impact on the conductor AC losses. The results will also be compared to earlier predictions. Finally, the CS and PF coil AC losses expected during commissioning will be briefly discussed.

Review of Experimental Results and Models for AC Losses in the ITER PF and CS Conductors

During the years of ITER conductors qualification and production, samples from all domestic agencies were tested. Some of these tests were focused on characterizing the AC losses properties of the ITER conductors. The data produced originate from various facilities (PSI, University of Twente, CERN), using different experimental and data reduction protocols, for a large number of samples. The result is thus a considerable database of results with a wide spread in the properties. The need for a reduced set of parameters describing the AC losses properties of the ITER conductors is now becoming urgent in order to permit consistent analysis of the coils heat loads in commissioning and operation. In particular, PF and CS are pulsed coils, cooled by supercritical helium 4.5 K, operating at nominal currents up to 50 kA while subject to time varying fields that can reach 2 T/s during the plasma scenario. This paper summarizes the reference conductor samples, the models and the parameters that emerge from the extensive experimental characterizations, hoping to give a strong baseline for analysts investigating AC losses in ITER CS and PF conductors.

Algorithm Research on the Conductor Eccentricity of a Circular Dot Matrix Hall High Current Sensor for ITER

To meet the high current measurement requirements of the international thermonuclear experimental reactor polar field (ITER PF) power supply, a noncontact dot matrix Hall high current sensor without a magnetic core is designed. Due to the existence of installation error, the measurement accuracy will be reduced due to conductor eccentricity in practical use. To solve this problem, this article will take the circular dot matrix Hall current sensor composed of eight Hall elements as an example and note the shortcomings of the two algorithms by analyzing the numerical integration algorithm and conductor positioning algorithm. Based on the two algorithms, a digital signal processing (DSP) conditioning algorithm is proposed. The DSP conditioning algorithm detects the output voltage of each Hall element after conductor offset and adjusts the output voltage of each Hall element by self-feedback, which simplifies the complexity of algorithm operation and eliminates conductor eccentricity error at the same time. Through simulation and field measurement verification, DSP self-feedback conditioning of the Hall element output voltage can eliminate the influence of conductor eccentricity error and improve the measurement accuracy of the sensor.

Circuit Controller for PF Converter System Based on CODAC Core System

The poloidal field converter system of the International Thermonuclear Experimental reactor, which is developed, assembled, and tested by the Institute of Plasma Physics of the Chinese Academy of Sciences, uses the CODAC core system provided by ITER organization to design its control system. This paper completes the design of the circuit control system as well as realizes the transmission, state transition, and real-time control of the operating status of the poloidal field converter system to meet specific requirements for the control cycle of the control system. This paper provides solutions to some key problems, such as the state transition, real-time transmission, and operating state display, and real-time control of the converter circuit control system. The system designed by this paper has been successfully tested in the ITER PF prototype and ITER PF test platform.

Remote monitoring system for ITER PF converter system based on EtherCAT

Abstract This paper describes ITER PF converter system architecture in details. According to its real-time and reliability characteristics, ITER PF converter system uses an industrial Ethernet fieldbus based on EtherCAT protocol with high real-time communication performance to develop its remote monitoring system. This system follows ITER design specification, it realize the real-time monitoring of thousands of analog and digital signals, and can realize remote operation of the switches in the field layer, real-time data and historical data query, event alarm and authority management functions. The system has achieved continuous and stable operation on the test platform of ITER PF converter system, meeting the requirements of high real-time performance and reliability of the remote monitoring system of ITER PF converter system.

Effect of ITER CS and PF magnets on EM loads outside vacuum vessel at plasma disruption events

One of the most crucial issues in the design of the ITER machine is the electromagnetic (EM) loads associated with eddy currents induced in the conducting structures during plasma disruptions. The ITER database contains tens of calculation scenarios for possible plasma disruption events. The duration of these scenarios is usually limited by the end of the plasma current quench when the toroidal plasma current decreases to zero. For further EM analysis, the currents in the poloidal field coils are conventionally assumed constant after the end of the current quench. Such approach is not good for estimation of electromagnetic loads acting on the tokamak components located outside vacuum vessel. A possible way to solve this problem is to employ pre-determined coil current variations over the entire period of observation including time interval after the current quench. This paper describes an approach to such electromagnetic calculations and comparative results for selected cases with/out an extended current-time specification.

Electrical performance characterization of helium inlet of the ITER PF6 coil double pancakes

The helium inlet is one of the most important components of the ITER Poloidal Field (PF) coils. The insulation structure of the helium inlet is critical to provide sufficient electrical and mechanical properties for a practical application. In this paper, an ITER PF6 coil double pancake helium inlet trial mock-up was designed and manufactured by simulating the actual manufacturing process. A thermal cycling test on the sample was carried out from 280 K to77 K, also before and after the thermal cycling, a turn-to-turn DC HV test and Paschen test were performed. The test results satisfied the ITER requirements. It has therefore been verified that the PF6 coil double pancake helium inlet insulation has good electrical properties, and can be applied to the formal production of the PF6 coil double pancakes.

ITER PF6 double pancakes stacking

The Poloidal Field (PF) coils are one of the main sub-systems of the ITER magnets. The PF6 coil is being manufactured by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) as per the Poloidal Field coils cooperation agreement signed between ASIPP and Fusion for Energy (F4E). ITER PF6 winding pack (WP) is composed by 9 double pancakes (DPs). After the vacuum pressure impregnation (VPI) of each DP, the 9 DPs were stacked together and inter-pancake joints were manufactured to form the WP.This paper focus on the main process of ITER PF6 DPs stacking. During stacking, the DP being stacked was firstly been placed in position by means of vacuum pads lifting system, laser tracker and stacking guiding tooling. To eliminate the thermal stress, the DP being stacked was then lifted up to 80–90% of its weight to allow free rotating and moving while inter-pancake joints copper sole soldering. At the end, the DP being stacked was released, followed by welding of lateral plates and wedges. The DPs stacking has been finished with an overall concentricity of less than 1 mm and toroidal positioning of less than 5 mm for each DP, which well met the technical requirements.

Design, manufacturing, acceptance testing and quality control of ITER PF AC/DC converters

ITER PF converter system is the largest converter system in the world. This special converter has the mutual superconductive coils as load, and requires large scale and rapid response. The institute of plasma physics Chinese academy of sciences (ASIPP) is responsible for this converter’s preliminary design, final design, and manufacture. To meet these special requirements, during design and manufacture phase, quality assurance (QA) and quality control (QC) actions are worked out and strictly performed to ensure the validity of the product.

Performance of the insulation mock-ups for the ITER PF6 coil

The ITER PF6 coil is manufactured by winding, insulating the superconducting conductors, and further connecting them electrically and hydraulically. To qualify the insulation design and manufacturing process to be applied to the ITER PF6 coil, two beam-shaped mock-ups taking the form of a 3 × 3 array of conductors combined with the same insulation as in the production coil have been tested in simulated Tokamak operating conditions. All the results of the electrical and mechanical tests, including DC and AC high-voltage withstanding at both room and cryogenic temperature, AC partial discharge, Paschen tests, cryogenic compressive fatigue, push-out, and thermal cycling, met the ITER requirements. Performance of the mock-ups confirmed that the insulation design and manufacturing process are suitable for the ITER PF6 coil, based on that the qualification of the insulation manufacturing process for the double pancake can be started.

Qualification of ITER PF6 helium inlet

The Poloidal Field (PF) coils are one of the main sub-systems of the ITER magnets. The PF6 coil is being manufactured by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) as per the Poloidal Field coils cooperation agreement signed between ASIPP and Fusion for Energy (F4E). As one of the critical components, helium inlet locates on the innermost turn and supplies the coil with supercritical helium. During Tokamak operation, the helium inlet will undergo huge cyclic electromagnetic loads and thermal cycling during cooling down and warming up.This paper focus on the main steps of ITER PF6 helium inlet qualification. Helium inlet hole drilling and stainless steel wrapping removal were firstly been carried out. Helium inlet welding with full penetration by automatic welding machine was then performed, followed by leak proof test, non-destructive test, fatigue test and tomography test. At the end, the samples were sectioned for micro and macro inspection. The results show ITER PF6 helium inlet qualification has successfully met the requirements of PF procurement agreement(PA) and was approved by ITER IO.

ITER PF6 Dummy Double Pancake Winding

The poloidal field (PF) coils are one main subsystem of the ITER magnets. The PF6 coil is being manufactured by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) as per the PF coils cooperation agreement between ASIPP and Fusion for Energy. The ITER PF6 winding pack is composed by stacking nine double pancakes. Dummy double pancake fabrication aims to fully qualify the critical fabrication processes, before series production. This paper describes ITER PF6 dummy double pancake winding process and results, which was performed with a “two-in hand” configuration. Conductors were wound sequentially in the following steps: despooling, straightening, ultrasonic cleaning, sandblasting, bending, and turn insulation wrapping until deposition on the winding table. Joggle bending, helium inlet manufacturing, and tail assembly were also carried out during winding. The dummy double pancake winding was finally completed with the qualification requirements well met, which demonstrated good synchronization of the control system, fine conductor positioning accuracy, tight radial buildup, and so on.

ITER PF6 winding line multi-axis automatic controlling system

This paper focuses on the application of a multi-axis automatic control system for the “two-in-hand” configuration ITER PF6 winding line for the PF6 coil. The automatic control system is based on a Siemens Simotion D platform, which houses 16 servo motors and 68 interlocks. Tests are performed after the establishment of the hardware and debugging of the program. High precision and reliability are achieved, which demonstrated that the automatic control system satisfied the requirements of the PF6 coil double pancake winding.

ITER PF6 double pancakes winding line

The Poloidal Field (PF) coils are one of the main sub-systems of the ITER magnets. The PF6 coil is being manufactured by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) as per the Poloidal Field coils cooperation agreement signed between ASIPP and Fusion for Energy (F4E).The ITER PF6 winding pack is composed by stacking of 9 double pancakes. Each double pancake is wound with a “two-in-hand” configuration.This paper describes the ITER PF6 double pancakes winding line, including layout and main parameters of the winding line, features of main units and the commissioning trial with PF5 empty jacket conductor.

ITER Side Correction Coil Quench model and analysis

Previous thermohydraulic studies performed for the ITER TF, CS and PF magnet systems have brought some important information on the detection and consequences of a quench as a function of the initial conditions (deposited energy, heated length). Even if the temperature margin of the Correction Coils is high, their behavior during a quench should also be studied since a quench is likely to be triggered by potential anomalies in joints, ground fault on the instrumentation wires, etc. A model has been developed with the SuperMagnet Code (Bagnasco et al., 2010) for a Side Correction Coil (SCC2) with four pancakes cooled in parallel, each of them represented by a Thea module (with the proper Cable In Conduit Conductor characteristics). All the other coils of the PF cooling loop are hydraulically connected in parallel (top/bottom correction coils and six Poloidal Field Coils) are modeled by Flower modules with equivalent hydraulics properties. The model and the analysis results are presented for five quench initiation cases with/without fast discharge: two quenches initiated by a heat input to the innermost turn of one pancake (case 1 and case 2) and two other quenches initiated at the innermost turns of four pancakes (case 3 and case 4). In the 5th case, the quench is initiated at the middle turn of one pancake. The impact on the cooling circuit, e.g. the exceedance of the opening pressure of the quench relief valves, is detailed in case of an undetected quench (i.e. no discharge of the magnet). Particular attention is also paid to a possible secondary quench detection system based on measured thermohydraulic signals (pressure, temperature and/or helium mass flow rate). The maximum cable temperature achieved in case of a fast current discharge (primary detection by voltage) is compared to the design hot spot criterion of 150K, which includes the contribution of helium and jacket.

AC and Mechanical Loss Analysis of the ITER PF RF SULTAN Samples

Analysis of the ac and mechanical losses of PF RF ITER SULTAN sample test results has been performed. Measurements were provided by the gas flow colorimetric method before and after cyclic mechanical loads. The mechanical loss investigation was carried out for the virgin sample and after 10, 400, and 1000 cycles. Mechanical loss, as it was expected, significantly decreased after the first ten cycles but remained almost the same after the subsequent cycling. The value of mechanical loss even of the virgin sample does not strongly affect the workability of a magnet. AC loss measurements were carried out at different operating currents in conductor, at background magnetic field of 2 and 4.5 T before and after cycling. The ac loss measurements of all tested samples were practically the same before and after cycling, but strongly depended on a background magnetic field. As an example, at zero operating current in conductor and variable magnet field frequency of 6 Hz, the ac loss decreased by ∼1.4 times at background magnetic field of 4.5 T compared with the loss at 2.0 T. An attempt to explain the phenomena has been done. The results of the calculation and experimental investigation are presented.

Thermal Analysis of Power Thyristor Used in ITER Poloidal Field Converter

As a key component of ITER PF converter module, thyristor conducting large current produces a lot of power loss, therefore it is meaningful to study its heat transfer characteristic for improving the performance of PF converter. This paper presents the thermal analysis of the thyristor. A 3D finite-element model with multi material layers is built and simulated in steady state operation. A special temperature rise test scheme is designed and done to verify the analysis result. The simulation is well in compliance with the test result. The modeling method presented in this paper is proved to be practical in thyristor thermal analysis. The proposed measurement method in temperature rise test is also of valuable reference for thermal testing of power semiconductor devices.

Wavelet Filter for Signals De-noising in ITER PF Converter I&C System

The wavelet transform has been proved to be an efficient tool for de-noising the signal due to its capability to stand out inhomogeneous and localized signal features. This paper presents a wavelet filter in ITER PF converter I&C system for signals de-noising and processing using the discrete wavelet transform. Daubechies 4 which is an orthogonal wavelet has been selected. The wavelet filter was realized by transforming the signal into the wavelet domain and then reconstructing the signal after eliminating the noise by compulsory de-noising method. The wavelet filter eliminates the noise effectively and accurately, proved by the simulation and experimental results.

Residual Resistances Ratio in NbTi Strands Extracted From the ITER PF1/6 Conductor Sample After SULTAN Tests

The residual resistance ratio (RRR) is an important parameter affecting the stability of superconductors and the quench protection properties of magnets. During the manufacture and testing of cable-in-conduit-conductors, RRR may change noticeably. Recently the RRR changes of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands for conductors of the ITER toroidal coils have been studied during the manufacturing process, heat treatment and SULTAN testing. Here we present the similar study of RRR of Nb-Ti strands used for conductors of the ITER poloidal coils. RRRs of the strands were measured in as-received condition and at different stages of the PF conductor manufacturing. RRR of strands extracted from ITER PF conductor sample after electromagnetic and thermal cycling in the SULTAN test facility was also measured. For this purpose the strand samples were extracted from different locations in the cross-section of the PF conductor and from different positions along the axis after testing in the SULTAN. The results about the RRR change during the manufacturing process and after the SULTAN tests and also the details of experiments are presented and discussed.