Calculation and Optimization of ITER Upper VS Feeder Under an Electromagnetic Load

The upper vertical stability (VS) feeder is a part connected to the upper VS coil by a welding joint.The function of the feeder is to transfer current and coolant water to the VS coil.A giant electroma...     

Mechanical Analysis and Optimization of ITER Upper ELM Coil & Feeder

International thermonuclear experimental reactor （ITER） edge localized mode （ELM） coils are used to mitigate or suppress ELMs. The location of the coils in the vacuum vessel and behind the blankets exposes them to high radiation levels and high temperatures. The feeders provide the power and cooling water for ELM coils. They are located in the chinmey ports and experience lower radiation and temperature levels. These coils and feeders work in a high magnetic field environment and are subjected to alternating electromagnetic force due to the interaction between high magnetic field and alternating current （AC） current in the coils. They are also subjected to thermal stresses due to thermal expansion. Using the ITER upper ELM coil and feeder as an example, mechanical analyses are performed to verify and optimize the updated design to enhance their structural performance. The results show that the conductor, jacket and bracket can meet the static, fatigue and crack threshold criteria. The optimization indicates that adding chamfers to the bracket can reduce the high stress of the bracket, and removing two rails can reduce the peak reaction force on the two rails arising from thermal expansion.     

Electromagnetic–thermal–structural coupling analysis of the ITER edge localized mode coil with fiexible supports

In a fusion reactor, the edge localized mode (ELM) coil has a mitigating effect on the ELMs of the plasma. The coil is placed close to the plasma between the vacuum vessel and the blanket to reduce its design power and improve its mitigating ability. The coil works in a high-temperature, high-nuclear-heat and high-magnetic-field environment. Due to the existence of outer superconducting coils, the coil is subjected to an alternating electromagnetic force induced by its own alternating current and the outer magnetic field. The design goal for the ELM coil is to maintain its structural integrity in the multi-physical field. Taking as an example the middle ELM coil (with flexible supports) of ITER (the International Thermonuclear Fusion Reactor),an electromagnetic–thermal–structural coupling analysis is carried out using ANSYS. The results show that the flexible supports help the three-layer casing meet the static and fatigue design requirements. The structural design of the middle ELM coil is reasonable and feasible. The work described in this paper provides the theoretical basis and method for ELM coil design.     

Electromagnetic–thermal–structural coupling analysis of the ITER edge localized mode coil with flexible supports

In a fusion reactor, the edge localized mode(ELM) coil has a mitigating effect on the ELMs of the plasma. The coil is placed close to the plasma between the vacuum vessel and the blanket to reduce its design power and improve its mitigating ability. The coil works in a high-temperature,high-nuclear-heat and high-magnetic-field environment. Due to the existence of outer superconducting coils, the coil is subjected to an alternating electromagnetic force induced by its own alternating current and the outer magnetic field. The design goal for the ELM coil is to maintain its structural integrity in the multi-physical field. Taking as an example the middle ELM coil(with flexible supports) of ITER(the International Thermonuclear Fusion Reactor), an electromagnetic–thermal–structural coupling analysis is carried out using ANSYS. The results show that the flexible supports help the three-layer casing meet the static and fatigue design requirements. The structural design of the middle ELM coil is reasonable and feasible. The work described in this paper provides the theoretical basis and method for ELM coil design.     

Physical design of a new set of high poloidal mode number coils in the EAST tokamak

An external resonant magnetic perturbation (RMP) field, which is an effective method to mitigate or suppress the edge localized mode (ELM), has been planned to be applied on the ELM control issue in ITER. A new set of magnetic perturbation coils, named as high m coils, has been developed for the EAST tokamak. The magnetic perturbation field of the high m coils is localized in the midplane of the low field side, with the spectral characteristic of high m and wide n, where m and n are the poloidal and toroidal mode numbers, respectively. The high m coils generate a strong localized perturbation field. Edge magnetic topology under the application of high m coils should have either a small or no stochastic region. With the combination of the high m coils and the current RMP coils in the EAST, flexible working scenarios of the magnetic perturbation field are available, which is beneficial for ELM control exploration on EAST. Numerical simulations have been carried out to characterize the high m coil system, including the magnetic spectrum and magnetic topology, which shows a great flexibility of magnetic perturbation variation as a tool to investigate the interaction between ELM and external magnetic perturbation.     

Structural analysis and optimization for ITER upper ELM coil

ITER ELM coils are used to mitigate or suppress Edge Localized Modes (ELM), which are located between the vacuum vessel (VV) and shielding blanket modules and subject to high radiation levels, high temperature and high magnetic field. These coils shall have high heat transfer performance to avoid high thermal stress, sufficient strength and excellent fatigue to transport and bear the alternating electromagnetic force due to the combination of the high magnetic field and the AC current in the coil. Therefore these coils should be designed and analyzed to confirm the temperature distribution, strength and fatigue performance in the case of conservative assumption. To verify the design structural feasibility of the upper ELM coil under EM and thermal loads, thermal, static and fatigue structural analysis have been performed in detail using ANSYS. In addition, design optimization has been done to enhance the structural performance of the upper ELM coil.     

Design of Tokamak ELM Coil Support in High Nuclear Heat Environment

In Tokomak, the support of the ELM coil, which is close to the plasma and subject to high radiation level, high temperature and high magnetic field, is used to transport and bear the thermal load due to thermal expansion and the alternating electromagnetic force generated by high magnetic field and AC current in the coil. According to the feature of ITER ELM coil, the mechanical performance of rigid and flexible supports under different high nuclear heat levels is studied. Results show that flexible supports have more excellent performance in high nuclear heat condition than rigid supports. Concerning thermal and electromagnetic （EM） loads, optimized results further prove that flexible supports have better mechanical performance than rigid ones. Through these studies, reasonable support design can be provided for the ELM coils or similar coils in Tokamak based on the nuclear heat level.     

Structural Design Study for ITER Upper ELM Coils

ITER ELM coils are important parts of in-vessel coils and they are mounted on the vacuum vessel and behind the blanket module. They consist of three sets of coils, referred to as the upper, mid, and lower coils. In order to verify the structural design feasibility and find the better structure for upper edge localized modes (ELM) coil, two different variants of coil support structures are studied under the electromagnetic load, thermal and other loads. Results show that besides the bracket of variant 2 does not meet the fatigue criteria, the conductor, jacket and bracket of the two structures can meet the static, fatigue and crack threshold criteria and both of them are valid and feasible. In addition, the better structure is chosen for upper ELM coil.     

Structural and Fracture Mechanics Analysis for the Bracket of ITER Upper ELM Coil

The brackets are the important components of ITER edge localized modes (ELM) coils to connect the coils and rails. In order to assure the structural integrity and security of the bracket, the maximum tresca stress and stress intensity factor are examined from the viewpoints of structural and fracture mechanics. Based on the finite element method, the global upper ELM coils with simplified and detailed bracket are investigated. Since it is difficult to perform in-service inspection due to inaccessibility of in-vessel coils, it is important to estimate the allowable initial defect. Assuming an initial crack in the maximum first principal stress region on the bracket, the fracture mechanics analyses under different loads are performed. Results show that the bracket design is valid and feasible and the calculation method of finite element for stress intensity factor is feasible and reliable. Assuming the initial crack of 7 mm depth, the bracket can meet the crack growth criteria. The stress intensity factor of the bracket is mainly caused by electromagnetic (EM) load and the thermal load can reduce the stress intensity factor under EM load. The thermal load can make the crack grow on the surface of the bracket and the EM load can cause the crack to extend in the inner of the bracket.     

Design finalization and start of construction of ITER vacuum vessel

The vacuum vessel (VV) design is being finalized including interface components, such as the support rails and feedthroughs of coils for mitigation of edge localized modes (ELM) and vertical stabilization (VS) of the plasma (ELM/VS coils). It was necessary to make adjustments in the locations of the blanket supports and manifolds to accommodate the design modifications in the ELM/VS coils. The lower port gussets were reinforced to keep a sufficient margin under the increased VV load conditions. The VV support design is being finalized as well, with an emphasis on structure simplification. The design of the in-wall shielding (IWS) has progressed, considering assembly and required tolerances. The layout of ferritic steel plates and borated steel plates will be optimized based on on-going toroidal field ripple analysis. The VV instrumentation was defined in detail. Strain gauges, thermocouples, displacement meters and accelerometers shall be installed to monitor the status of the VV in normal and off-normal conditions to confirm all safety functions are performed correctly. The ITER VV design was preliminarily approved, and the VV materials including 316L(N) IG were already qualified by the Agreed Notified Body (ANB) according to the procedure of Nuclear Pressure Equipment Order.     

Multiaxial fatigue analysis for IMIC of ITER upper ELM coil

Inconel Jacketed Mineral Insulated Conductor (IMIC) is a very important component of International Thermonuclear Experimental Reactor (ITER) Edge Localized Modes (ELM) coils, which are located between the vacuum vessel (VV) and blanket shield modules and subject to high radiation levels, high temperature and high magnetic field. These coils will experience thermal pulsed, cyclic electromagnetic (EM) load during operation. They are designed to sustain at 1.5e8 total stress cycles and shall have sufficient strength and excellent fatigue to transport and bear the high cyclic load. For IMIC, multiaxial fatigue analysis is used to evaluate failure. Two methods based on the alternating stress and mean stress in American Society of Mechanical Engineers (ASME) code provide the design codes for multiaxial fatigue evaluation: constant principal stress direction and variation of principal stress direction. Results show that using the two methods obtains basically the same equivalent alternating stress. Both of them can be recommended for the ELM coils and IMIC can meet the fatigue criteria.     

Magnetohydrodynamic flows entering the region of a flow channel insert in a duct

In this study, three-dimensional developing liquid-metal (LM) magnetohydrodynamic (MHD) flows entering the region of the flow channel insert (FCI) under a uniform magnetic field are numerically analyzed. The features of the LM MHD flows in a square duct near the leading edge of the FCI are examined in terms of flow velocity, pressure, current, electric potential, and Lorentz force. Because near the leading edge of the FCI the current moves obliquely in the inner flow region, the pressure gradient along the main flow direction near the slit of FCI's leading edge is smaller, yielding a region of velocity recirculation with lower electric potential therein. The interdependency of current, fluid velocity, pressure, electric potential gradient, and Lorentz force is examined in order to describe the electromagnetic features of the current flows.     

Investigation and analysis on ITER in-vessel coils’ raw-materials

The ITER in-vessel coils (IVCs) consist of 27 coils edge localized modes (ELM) and 2 coils vertical stabilization (VS) which are all mounted on the vacuum vessel wall behind the shield modules. The IVCs design and manufacturing work is being conducted in between Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and Princeton Plasma Physics Laboratory (PPPL). Because the position of ELM and VS coils is close and face to the plasma, the IVCs must undergo a severe environment, such as the high dose of radiation and high operation temperature, thus the conventional electrical insulation materials cannot be used. And the technology of “Stainless Steel Jacketed Mineral Insulated Conductor” (SSMIC) is deemed as the best choice to provide the necessary radiation resistance and compatibility strength in ITER's vacuum vessel. While mineral insulated conductor technology is not new, and is similar to the mineral insulated cable used in industrial. Some difficulties still need to be solved, such as searching for the proper raw-materials to make sure that the conductor have the properties of high current carrying capability, the necessary radiation resistance, the proper strength, at the same time, it must be come true in manufacture technology. This paper described the analysis of the materials for VS and ELM coil conductor.     

Analysis of edge magnetic field line structure in ITER due to in-vessel ELM control coils

In this work we evaluated the ITER ELM coils design based on two metrics: the Chirikov vacuum magnetic island overlap parameter, and the vacuum Field Line Loss Fraction. The study was performed for a range of current amplitudes for three different n = 4 waveforms: square, cosine and sine. The results indicated that ITER ELM coils are designed with a high level of flexibility to accommodate different operation scenarios (H-mode and Steady State) with different values of q₉₅ and q-profiles. The magnetic island overlap analysis showed that ITER ELM coils are capable of matching the DIII-D I-coil spectrum. The Field Line Loss analysis showed that edge vacuum stochastization might be achieved that is similar or greater than in DIII-D. Fault analysis of the coils indicated that ITER ELM coils are robust and show good characteristics even with 11% of dead coils.     

Quench detection of fast plasma events for the JT-60SA central solenoid

The JT-60 is planned to be modified to a full-superconducting tokamak referred to as the JT-60 Super Advanced (JT-60SA). The maximum temperature of the magnet during its quench might reach the temperature of higher than several hundreds Kelvin that will damage the superconducting magnet itself. The high precision quench detection system, therefore, is one of the key technologies in the superconducting magnet protection system.The pick-up coil method, which is using voltage taps to detect the normal voltage, is used for the quench detection of the JT-60SA superconducting magnet system. The disk-shaped pick-up coils are inserted in the central solenoid (CS) module to compensate the inductive voltage. In the previous study, the quench detection system requires a large number of pick-up coils. The reliability of quench detection system would be higher by simplifying the detection system such as reducing the number of pick-up coils. Simplifying the quench detection system is also important to reduce the total cost of the protection system. Hence the design method is improved by increasing optimizing parameters. The improved design method can reduce the number of pick-up coils without reducing the sensitivity of detection; consequently the protection system can be designed with higher reliability and lower cost. The applicability of the disk-shaped pick-up coil for quench detection system is evaluated by the two dimensional analysis. In the previous study, however, the analysis model only took into account the CS, EF (equilibrium field) coils and plasma. Therefore, applicability of the disk-shaped pick-up coil for the quench detection system remains open question because the fast plasma events, such as disruption, mini collapse and ELM (edge localized mode), directly influences on the voltage of pick-up coil making the quench signal undetectable. Consequently, a new analysis model proposed in the present paper was designed to avoid this difficulty by introducing the passive coil series such as vacuum vessel and stabilizer. The influence of fast plasma events is absorbed by passive coil series like real system, and the evaluation of applicability can be examined in detail. The analysis results show that the disk-shaped pick-up coil is applicable whenever the standard operation, disruption, mini collapse and ELM.     

Seismic analysis of ITER fourth PF (Poloidal Field Coil) feeder

The ITER feeder systems connect the ITER magnet systems located inside the main cryostat to the cryo-plant, power-supply and control system interfaces outside the cryostat. The main purpose of the feeders is to convey the cryogenic supply and electrical power to the coils as well as house the instrumentation wiring. The PF busbar which carries 52 kA current will suffer from high Lorentz force due to the background magnetic field inspired by the coils and the self-field between every pair of busbars. Except their mechanical strength and thermal insulation performance must be achieved, the dynamic mechanism on PF structure should be assessed. This paper presents the simulation and seismic analysis on ITER 4th PF feeder including the Coil Terminal Box and S-bend Box (CTB and SBB), the Cryostat Feed-through (CFT), the In-Cryostat-Feeder (ICF), especially for the ground supports and main outer-tube firstly. This analysis aims to study seismic resistance on system design under local seismograms with floor response spectrum, the structural response vibration mode and response duration results of displacement, membrane stress, and bending stress on structure under different directions actuating signals were obtained by using the single-seismic spectrum analysis and Dead Weight analysis respectively. Based on the simulative and analytical results, the system seismic resistance and the integrity of the support structure in the 4th PF feeder have been studied and the detail design confirmed.     

Actuator and diagnostic requirements of the ITER Plasma Control System

The ITER Plasma Control System (PCS) requires an extensive set of about 50 diagnostic systems to measure the plasma response and about 20 actuators to act on the plasma to carry out its control functions. The specifications and real limitations of the actuators and diagnostics are being assessed as part of the ongoing conceptual design of the PCS to understand the potential impact on plasma control. The actuators include magnetic coils (central solenoid (CS), poloidal field (PF), vertical stability (VS), edge localized mode (ELM), correction coils (CC)), heating and current drive (electron cyclotron (EC), ion cyclotron (IC), neutral beam injection (NBI), and possibly lower hybrid (LH)), glow discharge cleaning, fueling and impurity gas and pellet injection, vacuum pumping, and disruption mitigation systems. Diagnostic systems are prioritized according to their role in machine protection (MP), basic control (BC), advanced control (AC), and physics studies (PS). At the conceptual design phase, detailed control algorithms do not yet need to be specified, but conceptual solutions must be chosen that satisfy the PCS requirements for control within the real constraints of the diagnostics and actuators. The feasibility of the chosen solutions must be proven either through established control schemes on existing machines or through an R&D program to develop them before they will be required on ITER. The diagnostic and actuator requirements of the PCS will evolve from first plasma through the high performance DT phase. A comparison is made of the expected requirements to control vertical stability, sawteeth, neoclassical tearing modes (NTMs), edge localized modes (ELMs), error fields, resistive wall modes (RWMs), Alfvén eigenmodes, and disruptions with the ITER baseline actuator and diagnostic specifications.     

A Tangentially Visible Fast Imaging System on EAST

A tangentially visible imaging system has been developed on the Experimental Advanced Superconducting Tokamak(EAST) to record the full cross-section plasma visible radiation with speed up to 7500 frames per second at full resolution or much faster for a limited number of pixels.The edge localized mode(ELM) filaments during ELM eruptions in H-modes are captured.Using these pictures,the current in the filament is estimated.     

Magnet design considerations for Tokamak fusion reactors

Design problems for superconducting ohmic heating and toroidal field coils for large Tokamak fusion reactors are discussed. The necessity for making these coils superconducting is explained, together with the functions of these coils in a Tokamak reactor. Major problem areas include materials related aspects and mechanical design and cryogenic considerations. Projections and comparisons are made based on existing superconducting magnet technology. The mechanical design of large-scale coils, which can contain the severe electromagnetic loading and stress generated in the winding, are emphasized. Additional major tasks include the development of high current conductors for pulsed applications to be used in fabricating the ohmic heating coils. It is important to note, however, that no insurmountable technical barriers are expected in the course of developing superconducting coils for Tokamak fusion reactors.     

Q-Band X-Mode Reflectometry and Density Profile Reconstruction

By installing an X-mode polarized Q-band(32-56 GHz) reflectometry at the low field side on EAST,the zero density cutoff layer was determined and the edge density profile was measured in normally operating plasmas.A Monte Carlo procedure has been developed to analyze the density profiles by considering the error of time delay measured by reflectometry.By combining this Q-band and previously developed V- and W-band reflectometries,the density profiles from edge to core can be measured in most EAST experiments.The line integrated densities deduced from density profiles measured by reflectometry are consistent with those directly measured by a horizontal interferometer.The density pedestal measured by reflectometry shows a clear crash during an ELM(edge localized mode) event,after which the pedestal gradually increases and recovers in 10 ms and then remains little changed up to the next ELM.