Magnetic field geometries

Ya.B. proved (1956, 7) that a two-dimensional flow, vx(x,y), vy(x,y), is not capable of generating a kinematic dynamo (for the special case of axisymmetric flow and magnetic field geometry this had been noted by the English scientist T. G. Cowling in 1934). 

Optical experiments have been done in both magnetic field geometries. With the field normal to the planes, thin-film transmission experiments probe the influence of the static magnetic field on the ah-plane transport. The conductivity can be obtained from the power transmission by KranTers-ICronig transformations or amplitude transmission by terahertz spectroscopy which yields the real and imaginary parts of the transmission... 

To reduce the parallel losses, closed configurations were developed. In these, the magnetic field lines close onto themselves at least in some finite plasma volume (the confined region). Concerning this closed magnetic field geometry, one point needs to be specially emphasized ... 

In closed-ended machines the plasma is twisted back on itself to form a torus, eliminating the end-loss problem. Since simple toroidal magnetic fields do not confine plasma against radial outward drift, more complex magnetic field geometries are required in closed systems. Of the eight concepts, two, EBT and the Reversed-Field-Pinch, are closed systems, the others are open. 

TRIFOU is a combined Finite Elements/Boundary Integral formulation code. The BIM formulation in vacuum is suitable for NDT simulation where the probe moves in the air around the test block. The FEM formulation needs more calculation time, but tetrahedral elements enable a large variety of specimens and defect geometries to be modelled. TRIFOU uses a formulation of Maxwell Equations using magnetic field vector h, where h is decomposed as h = hs + hr (hj source field, and hr reaction field). 

The sensibility to defects and other testing parameters of pieces can be modified by the geometry of the piece to be controlled and the conception of the probe. It is sufficient to set the direction of circulation of eddy currents, regulate the magnetic field intensity and choose the coil of the appropriate size. 

The starting point of imaging is the modelisation of the physical process implied when using the sensor once known the exci-tator geometry and the conductivity in any point of the tube, one must be able to compute the magnetic field at any point in the measurement area ... 

Special probe geometries and combinations of different types of magnetic field sensors make an important contribution to the further improvement of the eddy-current testing method and results in new applications. 

The shapes, disposition of a magnet relatively to the each other and relatively to the pattern are defined in calculation of magnetic field topography [4]. The geometry like magnets has the fields of identical configuration. It gives the possibility to carry out the calculations as for ferrets so for rare-earth materials. 

Thus from Equation 2-215 we see that for a given dynamo geometry, the developed torque only depends on the interaction between two magnetic fields and their orientation with respect to each other. One or both of the magnetic fields may be induced by a current. If one of the fields is the field of a magnet, then it may be either in the rotor or the stator. If the rotation results from the imposition of mechanical power on the rotor, the device is called a generator. If the rotation is caused by the flow of current, the device is called a motor, i.e., converts electric power to mechanical power. 

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