Andrei Khodak

ITER Central Solenoid Insert Test Results

The ITER central solenoid (CS) is a highly stressed magnet that must provide 30 000 plasma cycles under the ITER prescribed maximum operating conditions. To verify the performance of the ITER CS conductor in conditions close to those for the ITER CS, the CS insert was built under a USA-Japan collaboration. The insert was tested in the aperture of the CSMC facility in Naka, Japan, during the first half of 2015. A magnetic field of up to 13 T and a transport current of up to 60 kA provided a wide range of parameters to characterize the conductor. The CS insert has been tested under direct and reverse charges, which allowed a wide range of strain variation and provided valuable data for characterization of the CS conductor performance at different strain levels. The CS insert test program had several important goals as follows. 1) Measure the temperature margin of the CS conductor at the relevant ITER CS operational conditions. 2) Study the effects of electromagnetic forces and strain in the cable on the CS conductor performance. 3) Study the effects of the warmup and cooldown cycles on the CS conductor performance. 4) Compare the conductor performance in the CS insert with the performance of the CS conductor in a straight hairpin configuration (hoop strain free) tested in the SULTAN facility. 5) Measure the maximum temperature rise of the cable as a result of quench. The main results of the CS insert testing are presented and discussed.

Thermal and structural analysis of the ITER ELM coils

A thermal and structural analysis of the ELM Coil design for ITER is presented. The ELM Coils are constructed using a jacketed mineral insulated conductor of CuCrZr, MgO and Inconel 625, rigidly mounted to the vacuum vessel inner shell, behind the Blanket Modules. Since the coils are not designed to be remotely maintained, a major issue is demonstrating the structural integrity against fatigue and crack propagation over an estimated 100 million cycles arising from operation at 5 hz in a high magnetic field. The temperature rises from ohmic and nuclear heating produce mean thermal stresses that further limit the allowable alternating stresses. Thermal growth also imparts large forces which must be reacted by the Vacuum Vessel. This paper presents the analysis and results with particular attention to the design criteria which is unique to the In-Vessel Coils.

Electromagnetic and Structural Analysis of ITER Central Solenoid Insert Coil

The United States ITER Project Office (USIPO) is responsible for fabrication of the Central Solenoid (CS) for International Thermonuclear Experimental Reactor (ITER). The CS Insert (CSI) project should provide verification of the conductor performance in relevant conditions of temperature, field, currents and mechanical strain. The USIPO will build the CSI that will be tested at the Central Solenoid Model Coil (CSMC) Test Facility at JAEA, Naka, Japan. This paper presents three-dimensional mathematical model of CSI based on the design. Simulations were performed in order to verify structural integrity and compliance with the Japanese High Gas Pressure Safety Law. Numerical simulations lead to the design of the CSI that produced a required strain levels during operation on the superconductor cable, while simultaneously satisfy the ITER magnet structural design criteria.

Numerical analysis and optimization of divertor cooling system

Novel divertor cooling system concept is currently under development at Princeton Plasma Physics Laboratory (PPPL). This concept utilizes supercritical carbon dioxide as a coolant for the liquid lithium filled porous divertor front plate. Coolant is flowing in closed loop in the T tube type channel. Application of CO2 eliminates safety concerns associated with water cooling of liquid lithium systems, and promises higher overall efficiency compared to systems using He as a coolant Numerical analysis of divertor system initial configuration was performed using ANSYS software. Initially conjugated heat transfer problem was solved involving computational fluid dynamics (CFD) simulation of the coolant flow, and heat transfer in the coolant and solid regions of the cooling system. Redlich Kwong real gas model was used for equation of state of supercritical CO2 together with temperature and pressure dependent transport properties. Porous region filled with liquid lithium was modeled as a solid body with liquid lithium properties. Evaporation of liquid lithium from the front face was included via special temperature dependent boundary condition. Results of CFD and heat transfer analysis were used as external conditions for structural analysis of the system components. Simulations were performed within ANSYS Workbench framework using ANSYS CFX for conjugated heat transfer and CFD analysis, and ANSYS Mechanical for structural analysis. Initial results were obtained using simplified 2D model of the cooling system. 2D model allowed direct comparison with previous cooling concepts which use He as a coolant. Optimization of the channel geometry in 2D allowed increase in efficiency of the cooling system by reducing the total pressure drop in the coolant flow. Optimized geometrical parameters were used to create a 3D model of the cooling system which eventually can be implemented and tested experimentally. 3D numerical simulation will be used to validate design variants of the divertor cooling system.

Analysis of TF Insert Coil

The United States ITER Project Office (USIPO) is responsible for the design of the oroidal Field (TF) insert coil, which will allow validation of the performance of significant lengths of the conductors to be used in the full scale TF coils in relevant conditions of field, current density and mechanical strain. The Japan Atomic Energy Agency (JAEA) will build the TF insert which will be tested at the central solenoid model coil (CSMC) test facility at JAEA, Naka, Japan. Three dimensional mathematical model of TF insert was created based on the initial design geometry data, and included the following features: orthotropic material properties of superconductor material and insulation; external magnetic field from CSMC, temperature dependent properties of the materials; precompression and plastic deformation in lap joint. Major geometrical characteristics of the design were preserved including cable jacket and insulation shape, mandrel outline, and support clamps and spacers. The model is capable of performing coupled structural, thermal, and electromagnetic analysis using ANSYS. Numerical simulations were performed for room temperature conditions; cool down to 4 K, and the operating regime with 68 kA current at 11.8 Tesla background field. Numerical simulations led to the final design of the coil producing the required strain levels on the cable, while simultaneously satisfying the ITER magnet structural design criteria.

Tensile strain mitigation during the NSTX-U Ohmic Heating (OH) coil cooldown

NSTX-U uses an inertially cooled OH coil that is cooled with water between shots. Cooling is fed from the bottom of the coil and a cooling wave propagates up the height of the coil. The finite height of the cooling “wave” causes a thermal gradient in the coil that causes a bending stress in the coil build. The larger radial build of the new NSTX Upgrade OH coil produces a shorter “wave” than the previous coil, and larger bending stress. The OH insulation system uses CTD 425 epoxy with interleaved glass and Kapton. This insulation is intended to provide some accommodation of tensile strains and delamination. Localized tensile strains, and shear stresses beyond recommended allowables have been a characteristic of many coil winding packs. Mechanical and electrical array testing is often used to qualify these winding packs. Mitigation of tensile strains via preloads is also often employed. For NSTX-U, only a small preload is practical. Strain controlled array testing has been performed. This has demonstrated a robustly acceptable electrical behavior after cyclic loading. This allows some relief in the requirement to control the cooling water “thermal shock”. To provide additional protection of the insulation, an active system that introduces cooling water with a more gradual thermal gradient and longer cooling wave height is being implemented to mitigate the tensile strains. This system employs an inline heater that supplies water at the post shot OH temperature that linearly decreases to the 12C supply chilled water temperature. Results of array testing, and design of the active system are presented. The final decisions regarding acceptance of the testing and implementation of the preheater are presented.