Magnetohydrodynamic Effects On Mixed Convection Flows In Channels And Ducts

This work focuses on magnetohydrodynamic (MHD) mixed convection flow of electrically conducting fluids enclosed in simple 1D and 2D geometries in steady periodic regime. In particular, in Chapter one a short overview is given about the history of MHD, with reference to papers available in literature, and a listing of some of its most common technological applications, whereas Chapter two deals with the analytical formulation of the MHD problem, starting from the fluid dynamic and energy equations and adding the effects of an external imposed magnetic field using the Ohm's law and the definition of the Lorentz force. Moreover a description of the various kinds of boundary conditions is given, with particular emphasis given to their practical realization. Chapter three, four and five describe the solution procedure of mixed convective flows with MHD effects. In all cases a uniform parallel magnetic field is supposed to be present in the whole fluid domain transverse with respect to the velocity field. The steady-periodic regime will be analyzed, where the periodicity is induced by wall temperature boundary conditions, which vary in time with a sinusoidal law. Local balance equations of momentum, energy and charge will be solved analytically and numerically using as parameters either geometrical ratios or material properties. In particular, in Chapter three the solution method for the mixed convective flow in a 1D vertical parallel channel with MHD effects is illustrated. The influence of a transverse magnetic field will be studied in the steady periodic regime induced by an oscillating wall temperature. Analytical and numerical solutions will be provided in terms of velocity and temperature profiles, wall friction factors and average heat fluxes for several values of the governing parameters. In Chapter four the 2D problem of the mixed convective flow in a vertical round pipe with MHD effects is analyzed. Again, a transverse magnetic field influences the steady periodic regime induced by the oscillating wall temperature of the wall. A numerical solution is presented, obtained using a finite element approach, and as a result velocity and temperature profiles, wall friction factors and average heat fluxes are derived for several values of the Hartmann and Prandtl numbers. In Chapter five the 2D problem of the mixed convective flow in a vertical rectangular duct with MHD effects is discussed. As seen in the previous chapters, a transverse magnetic field influences the steady periodic regime induced by the oscillating wall temperature of the four walls. The numerical solution obtained using a finite element approach is presented, and a collection of results, including velocity and temperature profiles, wall friction factors and average heat fluxes, is provided for several values of, among other parameters, the duct aspect ratio. A comparison with analytical solutions is also provided, as a proof of the validity of the numerical method. Chapter six is the concluding chapter, where some reflections on the MHD effects on mixed convection flow will be made, in agreement with the experience and the results gathered in the analyses presented in the previous chapters. In the appendices special auxiliary functions and FORTRAN program listings are reported, to support the formulations used in the solution chapters

Reshaping the DEMO Tokamak’s TF Coil with high fidelity Multiphysics CAE and advanced mesh morphing

The next phase in the EU’s ambitious nuclear fusion power generation project is the construction of a DEMOnstration powerplant. This represents the first step towards the creation of a commercial power plant and is drawing on the combined efforts of large teams of scientists and engineers across various research units. This article describes the Multiphysics optimization procedure undertaken to ensure the best compromise between electromagnetic and structural compliance for the Toroidal Field coils of the Advanced Divertor Configurations of the toroidal chamber, that holds the plasma in which the fusion reaction takes place. The TF coils are subjected to enormous Lorentz forces that are transferred to robust steel casings that hold the TF coils in place. It has been learnt that these casings should perform the dual function of shaping the super-conducting loops appropriately, and bearing the loads within a reasonable margin of safety. However, preliminary stress analyses revealed that their initial shape had structural deficiencies. FEM analyses and mesh morphing were used to optimize the shapes to the best compromise between the two functions

Structural optimisation of the DEMO alternative divertor configurations based on FE and RBF mesh morphing

The DEMO tokamak exhibits extraordinary complexity due to the constraints and requirements pertaining to different fields of physics and engineering. The multidisciplinary nature of the DEMO system makes its design phase extremely challenging since different and often opposite requirements need to be accounted for. Toroidal field (TF) coils generate the toroidal magnetic field required to magnetically confine the plasma particles and support at the same time the poloidal field coils. They must bear tremendous loads deriving from electromagnetic interactions between the coil currents and the generated magnetic field. An efficient tokamak design aims at minimizing the energy stored in its magnetic field and hence at reducing the toroidal volume within the TF coils whose shape would hence ideally mimic co-centrically the shape of the plasma. In order to bear the enormous forces a D-shape is most suitable for the TF coils as it allows them to resist the very large compression on the inner side and to carry the electro-magnetic (EM) pressure mainly by membrane stresses preventing large bending to occur on the outer side. At the same time the divertor structures must fit within the TF coils and this requires adaptations of the TF coil shape in the case of so-called advanced divertor configurations (ADCs), which require larger divertor structures. This article shows the TF coils adapted to ADCs using a structural optimisation procedure applied to the reference shape. The introduced strategy takes as structural optimum the iso-stress profile associated to each coil. A continuous transformation, based on radial basis functions mesh morphing, turns the baseline finite element (FE) model into its iso-stress counterpart, with a series of intermediate configurations available for electromagnetic and structural investigations as output. The adopted strategy allowed to determine, for each of the ADC cases, a candidate shape. Static membrane stress levels during magnetization could be reduced significantly from more than 700 MPa to below 450 MPa

Broadband Anisotropic Optical Properties of the Terahertz Generator HMQ-TMS Organic Crystal

HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet. Here, from polarized reflectance and transmittance measurements along the x1 and x3 axes of a HMQ-TMS single-crystal, we extract both the refraction index n and the extinction coefficient k between 50 and 35,000 cm −1 . We further measure the THz radiation generated by optical rectification at different infrared (IR) wavelengths and along the two x1 and x3 axes. These data highlight the remarkable anisotropic linear and nonlinear optical behavior of HMQ-TMS crystals, expanding the knowledge of its properties and applications from the THz to the UV region

JT-60SA TF magnet assembly

JT-60SA will be the world’s largest superconducting tokamak when it is assembled in 2020 in Naka, Japan(R = 3 m, a = 1.2 m). It is being constructed jointly by institutions in the EU and Japan under the BroaderApproach agreement. The assembly of its 400-tonne toroidalfield (TF) magnet, designed for an on-axisfield of2.25 T, was completed in July 2018. Consideration of its assembly throughout the design process, with asso-ciated consultation and testing, allowed high positional accuracy and hence respect for magneticfield tolerancesto be achieve

Manufacturing and installation of the JT-60SA helium storage vessels for the cryogenic plant

The JT-60SA Tokamak is provided with a cryogenic system with a refrigeration capacity of 9 kW (eqv.) at 4.5 K. Before commissioning and during occasional warm-up periods the total 3.6 t helium inventory (at ∼1.5 Mpa(g)) is stored in six pressure vessels. Each vessel is 22 m long, has a diameter of 4 m, 250 m3 volume, and weighs about 73 t. As the vessels will store pure helium, the tightness and cleanliness require- ments were quite demanding. One of the vessels is also used to receive the cold helium (20 K) from the cryogenic system quench line, following a fast discharge of the superconducting coils. A special 18 m long helium diffuser system and a thermal barrier connector at the quench line flange have been designed and manufactured to avoid local chilling of the vessel wall below the minimum allowed temperature of the material

Achievement of Precise Assembly of the JT-60SA Superconducting Tokamak

The JT-60 Super Advanced (JT-60SA) tokamak construction has been achieved respecting the requirements of very tight tolerance for the assembly and by handling very heavy components in a very close space environment. The construction of this large superconducting tokamak represents a big step forward in the world nuclear fusion history, opening the road for ITER and DEMO. Precise assembly is required, not only to avoid mechanical interference, but also to obtain good plasma performance by less magnetic error field. To complete this work, unique and well-considered procedures were introduced. In this paper, the developed technologies and their results are reported, focusing on the assembly of the final sector of vacuum vessel, central solenoid and in-vessel components.28th IAEAFusion Energy Conferenc

Construction and commissioning of the JT-60SA tokamak system

The construction of the JT-60 Super Advanced (JT-60SA) tokamak has been completed after seven years. In parallel to the tokamak construction, peripheral devices such as vacuum pumping system, gas baking system, wall cleaning system, and so on, that are indispensable for tokamak operation, have been modified for reuse or newly developed. In the JT-60SA, an ultra-high vacuum up to ~10-6Pa is to be realized by eight turbomolecular pumps with a total pumping speed of 6m3/sec for a vacuum vessel. To achieve an ultra-high vacuum condition, a baking operation with 200 ℃ is planned for desorbing water by Nitrogen gas circulation into a double shell of the vacuum vessel. The gas circulation system has a high flow rate of ~18,000 Nm3/h for 200 ℃ baking with four blowers and a heater. Since a radiant heat from the vacuum vessel will be absorbed by an 80 K thermal shield, the system is also utilized to keep vacuum vessel temperature 50 ℃.Moreover, a glow discharge system has been developed for wall conditioning. The system contains three electrodes installed into the vacuum vessel and power supplies with ~3A/600V. The system makes Helium glow discharge where impurities such as Oxygen could be effectively spattered from graphite first wall. In this paper, the completion of JT-60SA construction and the peripheral devices will be reported, focusing on the results of commissioning before the initial operation.31st Symposium of Fusion Technology (SOFT2020