3D Thermal and CFD Simulations of the Divertor Magnetic Coils for ITER

Magnetic diagnostics for the new generation fusion reactor “ITER” are required to be extremely reliable since they provide measurements essential for reactor operation and protection, plasma control and for measurement of several parameters fundamental to the plasma operation, such as plasma current and shape, disruptions and high frequency macro instabilities. ITER magnetic diagnostics consist of various sets of inductive coils and loops mounted on the inner wall, outside the vacuum vessel and in some of the divertor cassettes [1]. All these probes measure magnetic field or flux variations with respect to time, requiring a precise integration of the signals to recover the absolute values of the field components. They operate in a harsh reactor environment, subjected to nuclear heat loads mainly due to the neutron radiation, generated by the burning plasma. Difficult or impossible access after assembly requires reliability, especially in the area of wiring, connections and vacuum feed-throughs and in choosing margin against radiation damage and extreme transient electrical loads. Additional disturbing effects can arise when both a strong transient magnetic field and thermal gradient occur within the coil structure. All these aspects set a serial of strict design requirements and imply a serious technical challenge. This paper is focused on the design, simulation and optimization of the ITER divertor magnetic tangential coils. The divertor is one of the components exposed to the highest heat load in a fusion reactor, with a surface thermal peak load of 20 MW/m2. About 15 % of the energy produced by fusion reactions is absorbed in the divertor region. The radially-oriented divertor cassettes are exposed to inhomogeneous and time-dependent neutron flux. Six similar divertor cassettes are instrumented for magnetic measurements. Six pairs of equilibrium coils (normal and tangential to the mounting surface) are mounted within each of these cassettes. Of those, pairs near the top region of divertor dome will be exposed to the highest nuclear heating of all magnetic sensors, 2.5 MW/m3. The most critical issue for the divertor coils is to minimise Radiation Induced Thermo-Electric Sensitivity (RITES) [2] and Thermally Induced Electromagnetic Force (TIEMF) [3] by combining a proper choice of conductor with low temperature variation in the coil. Instead of Mineral Insulated Cable (MIC), which was foreseen as the preferred winding for the magnetic coils, a winding made of ceramic-coated steel wire was recently proposed [4]. It is thought that, for this wire, maintaining a temperature variation in the wiring below 10K will be sufficient to allow long-pulse operation. Variations of the divertor coil design have been investigated and simulated with the help of ANSYS programme. The aim was to keep the temperature variation in the winding pack within this limit. The optimisation of the coil, based only on a cooling by conduction was not sufficient to meet the 10 K target. Therefore, an actively water cooled coil was designed and simulated by the CFD code – ANSYS CFX

Waveguide Bandpass Filters for Millimeter-Wave Radiometers

A fundamental requirement for most mm-wave heterodyne receivers is the rejection of the input image signal which is located close to the local oscillator frequency. For this purpose we use a bandpass filter, which for heterodyne receivers is also called an image rejection filter. In this paper we present a systematic approach to the design of a waveguide bandpass filter with a passband from 100 to 110 GHz and upper rejection bandwidth in the range from 113 to 145 GHz. We consider two non-tunable filter configurations: the first one is relatively selective with 11 sections (poles) whereas the second one is simpler with 5 sections. We used established design equations to propose an initial guess for the geometries of the filters, optimized the geometries, constructed the filters using two different milling methods, measured their transmission and reflection characteristics, and compared the measurements with numerical simulations. Measurements of both filters agree well with simulations in frequency response and rejection bandwidth. The insertion loss of the 11-pole filter is better than 10 dB and that of the 5-pole filter is better than 5 dB. The 11-pole filter has a sharper attenuation roll-off compared with the 5-pole filter. The upper out-of-band rejection is better than 40 dB up to 145 GHz for the 11-pole filter and up to 155 GHz for the 5-pole filter

Baseline System Design And Prototyping For The Iter High-Frequency Magnetic Diagnostics Set

This paper reports the mechanical and electrical tests performed for the prototyping of the ITER high-frequency magnetic sensor and the analysis of the measurement performance of this diagnostic. The current design for the sensor is not suitable for manufacturing for ITER due to the high likelihood of breakages of the un-guided tungsten wire during the winding. A number of alternative designs and manufacturing processes have been investigated, with the Low Temperature Co-fired Ceramic technology giving the best results. The measurement performance of the baseline system design for the high-frequency magnetic diagnostic cannot meet the intended ITER requirements due to its intrinsic spatial periodicities

Diagnostic Components in Harsh Radiation Environments: Possible Overlap in R&D Requirements of IC and MF Systems

The next generation of large scale fusion devices--ITER/LMJ/NIF--will require diagnostic components to operate in environments far more severe than those encountered in present facilities. This harsh environment will be induced by fluxes of neutrons, gamma rays, energetic ions, electromagnetic radiation, and in some cases debris and shrapnel, at levels several orders of magnitude higher than those experienced in today's devices. For several years the question of possible synergy between inertial and the magnetic confinement research has been pursued by members of the respective communities. A first joint workshop specifically devoted to the identification and promotion of these synergies was organized in France, at Aix-en-Provence from June 27th to 29th, 2007. The workshop was attended by about 50 invited specialists. The participants identified a number of subject areas where common overlapping interests could benefit from additional interactions and meetings: windows, optical fibers, mirrors, cables, electronic components and 14 MeV neutron sources. In this paper we summarize the findings of these working groups. We put the discussion into context by including a brief description of the environments and the physical effects that have to be handled