Effectiveness of the Chebyshev Approximation in Magnetic Field Line Tracking

The tracking of magnetic field lines can be very expensive, in terms of computational burden, when the field sources are numerous and have complex geometries, especially when accuracy is a priority, because an evaluation of the field is required in many situations. In some important applications, the computational cost can be significantly reduced by using a suitable approximation of the field in the integrated regions. This paper shows how Chebyshev polynomials are well-suited for field interpolation in magnetic field-line tracking, then discusses the conditions in which they are most appropriate, and quantifies the effectiveness of parallel computing in the approximation procedures

A Fast Matrix Compression Method for Large Scale Numerical Modelling of Rotationally Symmetric 3D Passive Structures in Fusion Devices

This paper illustrates the development of a recursive QR technique for the analysis of transient events, such as disruptions or scenario evolution, in fusion devices with three-dimensional conducting structures using an integral eddy current formulation. An integral formulation involves the solution, at each time step, of a large full linear system. For this reason, a direct solution is impractical in terms of time and memory consumption. Moreover, typical fusion devices show a symmetric/periodic structure. This can be properly exploited when the plasma and other sources possess the same symmetry/periodicity of the structure. Indeed, in this case, the computation can be reduced to only a single sector of the overall structure. In this work the periodicity and the symmetries are merged in the recursive QR technique, exhibiting a huge decrease in the computational cost. Finally, the proposed technique is applied to a realistic large-scale problem related to the International Thermonuclear Experimental Reactor (ITER)

Efficient Inclusion of Layered Media Green’s Functions in Full-wave Analysis of Microstrips

Inclusion of planar layered media Green's Functions (GFs) is a major issue in the computational efficiency of full-wave models derived from integral formulations. These GFs may be decomposed into quasi-dynamic and dynamic terms. In a wide range of practical applications, the quasi-dynamic terms may be given in closed form. This paper proposes two criteria to establish when the complete GFs may be approximated by the quasi-dynamic terms. These criteria are based on simple relations between frequency, line length, dielectric thickness and permittivity. If these criteria are satisfied, the inclusion of the GFs into full-wave integral models is straightforward and the overall computational cost is strongly reduced. The proposed criteria are verified through a benchmark test case. The model is then used to perform a full-wave analysis of the power lost in a microstrip, as a consequence of the excitation of parasitic modes, such as surface and leaky waves

Multiphysics approach to plasma neutron source modelling at the JET tokamak

A novel multiphysics methodology for the computation of realistic plasma neutron sources has been developed. The method is based on state-of-the-art plasma transport and neutron spectrum calculations, coupled with a Monte Carlo neutron transport code, bridging the gap between plasma physics and neutronics. In the paper two JET neutronics tokamak models are used to demonstrate the application of the developed plasma neutron sources and validate them. Diagnostic data for the record JET D discharge 92436 are used as input for the TRANSP code, modelling neutron emission in two external plasma heating scenarios, namely using only neutral beam injection and a combination of the latter and ion cyclotron resonance heating. Neutron spectra, based on plasma transport results, are computed using the DRESS code. The developed PLANET code package is employed to generate plasma neutron source descriptions and couple them with the MCNP code. The effects of using the developed sources in neutron transport calculations on the response of JET neutron diagnostic systems is studied and compared to the results obtained with a generic plasma neutron source. It is shown that, although there are significant differences in the emissivity profiles, spectra shape and anisotropy between the neutron sources, the integral response of the time-resolved ex-vessel neutron detectors is largely insensitive to source changes, with major relative deviations of up to several percent. However it is calculated that, due to the broadening of neutron spectra as a consequence of external plasma heating, larger differences may occur in activation of materials which have threshold reactions located at DD neutron peak energies. The PLANET plasma neutron source computational methodology is demonstrated to be suitable for detailed neutron source effect studies on JET during DT experiments and can be applied to ITER analyses

A method to compute the impact of iron parts and external fields on the low frequency magnetic sensors in smart devices

Many devices for the smart mobility make use of low frequency magnetic sensors to determine the alignment of the device with respect to the earth field. In highly manned areas, the presence of meaningful disturbance fields must be expected and as much as possible counteracted. Typical sources of disturbances are metallic parts or AC power lines, possibly carrying spurious current harmonics induced by rectifiers. Numerical analysis is hard also when the environment is known since the numerical computation requires meshing of complex 3D structures and non-linear problems resolution. In this paper, a numerical model able to treat, in a fast but accurate way, such complex 3D nonlinear problems is applied to estimate the impact of disturbing fields on the magnetic measurement of the device alignment