Field Computation Program Research Articles

Description of the Coupling of two Loop Antennas using Electrical Equivalent Circuit Diagrams

Abstract. EMC measurements must be carried out in standardized and defined measuring environments. The frequency range between 9 kHz and 30 MHz is a major challenge for measurement technology. The established test sites are designed with an perfect elelctrically conducting ground. For the considered lower frequency range, the metrological validation is carried out with magnetic field antennas in this frequency range. The aim is therefore to take into account the ferromagnetic properties of the ground plane in such a measurement environment and to describe them analytically or numerically with an electrical equivalent circuit diagram. In this article we simplify the model to two loopantennas in Freespace without groundplane to check if the approache with the ECD will work. Therefore we use various numerical field calculation programs in the frequency range up to 30 MHz. The results from simulations are to be checked for correctness with describing them analytically or numerically. For this purpose, a model consisting of two loop antennas was created and simulated in a numerical simulation program. In order to validate the results from the simulation, two different approaches to creating an electrical equivalent circuit (ECD) are examined. The first approach is based on the real equivalent circuit diagram of a coil and the second approach forms a parallel resonant circuit of the first resonance of an antennas input impedance. The focus here is on the mutual inductance, which represents the coupling between the two antennas.

Mutual Coupling Effect in Unequally - Spaced Linear Antenna Array Performance

Unequally-spaced arrays can offer some advantages over equally-spaced arrays as follows: reducing the side-lobed level for the broadband array with an identical excitation coefficient. However, array design techniques do not take into account the mutual coupling effect among elements. In this article, the effect of mutual coupling on the array radiation pattern is investigated and discussed through studying the input impedance of the elements. Next, a technique for reducingmutual coupling based on radiation patterns of elements is presented. In this technique, the log-periodic dipole antenna with a frequency ranging from 900 MHz to 2500 MHz is selected as an array element. The results based on the FEKO magnetic field calculation program have shown that at 900 MHz, the proposed antenna array reaches a side-lobed level of -17.4 dB. At frequencies of 1500 MHz, 2000 MHz, 2500 MHz, the grating lobe levels of this antenna array are lower than 6.7 dB, 9.5 dBand 8.3 dB compared to those of the equally - spaced antenna array.

Automatic block dimensioning on GPU-accelerated programs through particle swarm optimization

Abstract Context Nowadays, the use of GPU to improve performance of computationally expensive systems are widely explored. On GPU-accelerated programs, performance is related to the partition of the problem into blocks of threads in such a way that the parallel tasks to be executed better fit the GPU architecture. Although there exists some general guidelines to help defining block dimensions, finding the optimum partition is still a complex and problem dependent task. In this work, it has been investigated the use of particle swarm optimization (PSO) to optimize blocks dimensions aiming to minimize programs execution time. The approach was evaluated on a GPU-accelerated wind field calculation program, in which block dimensioning was based on literature guidelines and empirical adjusts. Before PSO optimization, the program was about 25 times faster than the sequential program. After applying PSO, speedup increased to about 60 times. Unexpected optimized configurations were observed, ratifying that finding optimum dimensioning is a complex task. So the use of a robust optimization tool, such as PSO, demonstrated to be very profitable, allowing automatic optimization of blocks dimensions without necessity of a priori knowledge about problem, programs peculiarities and GPU architecture. Objective Improve speedup of GPU-accelerated programs by automatic defining optimized block dimensions using PSO. Method A GPU-accelerated wind field calculation problem has been focused. A PSO was interfaced to the program in order to find the block dimensions that leads to a minimum execution time. Results were compared to literature results. Results The speedup obtained with the proposed approach is more than 2 times the original speedup. Conclusion PSO, demonstrated to be very profitable, allowing automatic optimization of blocks dimensions without necessity of a priori knowledge about problem/programs peculiarities and/or GPU architecture.

Coupling Network Computing Applications in Air-cooled Turbine Blades Optimization

Abstract Through establishing control parameters from blade outside to inside, the parametric design of air-cooled turbine blade based on airfoil has been implemented. On the basis of fast updating structure features and generating solid model, a complex cooling system has been created. Different flow units are modeled into a complex network topology with parallel and serial connection. Applying one-dimensional flow theory, programs have been composed to get pipeline network physical quantities along flow path, including flow rate, pressure, temperature and other parameters. These inner units parameters set as inner boundary conditions for external flow field calculation program HIT-3D by interpolation, thus to achieve full field thermal coupling simulation. Referring the studies in literatures to verify the effectiveness of pipeline network program and coupling algorithm. After that, on the basis of a modified design, and with the help of iSIGHT-FD, an optimization platform had been established. Through MIGA mechanism, the target of enhancing cooling efficiency has been reached, and the thermal stress has been effectively reduced. Research work in this paper has significance for rapid deploying the cooling structure design.

Field Quality of MBH 11-T Dipoles for HL-LHC and Impact on Beam Dynamic Aperture

For the high-luminosity upgrade of the Large Hadron Collider (HL-LHC), the development of the 11-T Nb $_3$ Sn dipole (MBH) is progressing. At present, one double-aperture and five single-aperture short-model magnets have been built and tested. Magnetic measurements have been performed both at ambient and cryogenic temperatures. In addition, a double-aperture short model and the first full-length collared-coil assemblies have been produced and measured at ambient temperature. In this paper, the measurement results collected so far are presented and discussed. The geometrical field multipoles, the iron saturation effects, as well as the effects of persistent currents are summarized. Experimental data are compared with the magnetic calculations using the CERN field computation program ROXIE and discussed in view of the construction of the final magnets. In addition, based on the measured field errors, beam dynamics simulations have been carried out by taking into consideration different scenarios with and without MBH magnets installed in the accelerator.

Development of Simulation Program for Temperature Field of Mass Concrete Structures

Most existing temperature field calculation programs have relative defects. In the present paper, based on merits of ANSYS platform, a temperature field calculation program of mass concrete structure is developed and demonstrated. According to actual pouring progress and thermodynamic parameters, a roller-compacted concrete dam is simulated. The difference of maximum temperature between calculated and measured values of measuring points is less than 1.8°C. Furthermore, the relative difference is -5%–5%. This result shows that the calculation program developed based on ANSYS platform can simulate and calculate the temperature field of mass concrete structure.

Investigation on emission characteristics of metal-ceramic cathode applied to industrial X-ray diode.

The industrial x-ray diode with high impedance configuration is usually adopted to generate repetitive x-ray, but its performance would be worsened due to lower electric field on the cathode of diode when a voltage of several hundreds of kV is applied. To improve its performance, a novel metal-ceramic cathode is proposed in this paper. Key factors (width, relative permittivity of ceramic, and so on) affecting electric field distribution on triple points are analyzed by electrostatic field calculation program, so as to optimize the design of this novel cathode. Experiments are done to study the characteristics including emission current of cathode, diode voltage duration, diode mean dynamic impedance, and diode impedance drop velocity within diode power duration. The results show that metal-ceramic cathode could improve diode performance by enhancing emission current and stabling impedance; the impedance drop velocity of diode with spoke-shaped metal-ceramic cathode was reduced to -5 Ω ns(-1) within diode power duration, comparing to -15 Ω ns(-1) with metal foil cathode.

Magnetic Measurements and Analysis of the First 11-T Nb3Sn Dipole Models Developed at CERN for HL-LHC

The high-luminosity upgrade for the LHC (HL-LHC) envisages the replacement of some 15-m-long NbTi dipoles in the dispersion suppressor area by shorter Nb3Sn magnets with a nominal field of 11 T. The new magnets must be compatible with the lattice and other main systems of the LHC. The shorter length of new units will allow the installation of collimators. The successful use of the Nb3Sn technology requires an intense R&D program, and therefore, a CERN–Fermilab joint development program was established. This paper describes the magnetic measurement procedure and presents the analysis of the magnetic measurements on the first 2-m-long single-aperture demonstrators built and tested at CERN. The geometrical field multipoles, the iron saturation effects, and the effects of persistent currents are presented. The experimental data are compared with the magnetic calculations using the CERN field computation program ROXIE and are discussed in view of the requirements for machine operation.

Magnetic Measurements and Analysis of the First 11-T Nb3Sn 2-in-1 Model for HL-LHC

In the framework of the High-Luminosity upgrade of the Large Hadron Collider, the design and development of new magnets, relying on Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting cables, is progressing. In particular, a double-aperture dipole, with a bore diameter of 60 mm and a central field of 11 T, is required for the replacement of some Nb-Ti dipoles in the dispersion suppressor areas. The new magnets must comply with the specifications of the machine in terms of reliability and field quality. An intense short-model campaign was launched in order to validate the design choices. Various single-aperture models have been built and tested. Recently, the first 2-in-1 model has been produced by assembling the collared coils already tested in the single-aperture configuration. This paper presents the analysis of the magnetic measurements on the first 2-m-long, double-aperture demonstrator built and tested at CERN. The geometrical field multipoles, the iron saturation effects, the magnetic cross-talk as well as the effects of persistent currents are presented. The experimental data are compared with the magnetic calculations using the CERN field computation program ROXIE and are discussed in view of the construction of the full-length magnets.

Electrical field computation of polymeric insulator using reduced dimension modeling

In recent years, electrical field distribution is the area of major concern in the service life of Polymeric Insulators. Several methodologies are proposed to analyze the electrical field along the insulators both experimentally and numerically of which the former might be very time consuming requiring a number of trial-error tests to determine the optimum dimensions. The advent of super computers makes numerical analyses feasible on any complex geometry modeled in 3-D and the overall optimization techniques to control the electrical field become quite easier. However, the main drawbacks in 3-D analyses are the more computation time and memory, making it desirable to simplify the structure. Hence a methodology based on relationship between electrical field profiles of 2-D (axi-symmetry model of insulator with corona ring) and 3-D model (insulator with corona ring, tower, 3 phase hardware fittings and conductors) for a dimension and location of corona/grading rings is proposed. Based on the relationship, electrical field profiles of 3-D models are predicted for different dimension and location of rings using its equivalent 2-D model electrical field profile. Commercially available 2-D and 3-D finite element based electrostatic field computation program is used. A 220 kV suspension type I string assembly is used for this study. Later, the approach is validated for 132 kV and 400 kV insulators. The type of tower, string configuration is kept constant throughout the analyses.

Development of a magnetic field calculation program for air-core solenoids which can control the precision of a magnetic field

A numerical method of magnetic field calculation for the air-core solenoid is presented in this paper. In application of the Biot- Savart law, the magnetic field induced from the source current can be obtained by a double integration ormula. The numerical method named composite Simpson’s rule for the integration is applied to the program and the adaptive quadrature method is used to adjust the step size in the calculation according to the precision we need. When the target point is in the solenoid and the tegrand’s denominator may be zero in the process of calculation, the method still can provide an appropriate result. We have developed a program which calculates the magnetic field with at least 1ppm precision and named it as rzBI() to implement this method. The method has been used in the design of an MRI magnet, and the result show it is very flexible and convenient.

Design Challenges for a Wide-Aperture Insertion Quadrupole Magnet

The design and development of a superconducting (Nb-Ti) quadrupole with 120-mm aperture, for an upgrade of the LHC insertion region, faces challenges arising from the LHC beam optics requirements and the heat-deposition. The first triggered extensive studies of coil alternatives with four and six coil-blocks in view of field quality and operation margins. The latter requires more porous insulation schemes for both the cables and the ground-plane. This in turn necessitates extensive heat propagation and quench-velocity studies, as well as more efficient quench heaters. The engineering design of the magnet includes innovative features such as self-locking collars, which will enable the collaring to be performed with the coils on a horizontal assembly bench, a spring-loaded and collapsible assembly mandrel, tuning-shims for field quality, porous collaring-shoes, and coil end-spacer design based on differential geometry methods. The project also initiated code extensions in the quench-simulation and CAD/CAM modules of the CERN field computation program ROXIE.

Proposal for Emitter Shape to Obtain Higher Ion Current of Gas Field Ion Source

The emitter shape dependence of the ion current from a gas field ion source (GFIS) was examined using numerical simulations. The simulator is constructed by an electric field calculation program and the spread sheets which were developed by authors based on the gas supply model. The gas supply for Ar was examined in this article, and was compared with that for He. As a result, when using the same emitter, it demonstrated that the effective capture area of Ar gas is 6.8-8.0 times larger than that of He. For a gas temperature of 300K, the effective capture area of Ar and He were estimated to be 0.0814 and 0.0107 μm2, respectively. It was also estimated that the ion current of Ar was 2-2.3 times larger than that of He. Through an actual experiment, a similar tendency was confirmed. For Ar, the influence of the shank taper angle to the ion current was confirmed and that influence is more effective than He. The emitter of small shank angle is capable of higher ion current. Therefore, it was concluded that the ion current can be increased through optimization of the emitter configuration. [DOI: 10.1380/ejssnt.2010.174]

Numerical Study of Quench Protection for Fast-Ramping Accelerator Magnets

The quench module of the ROXIE field computation program has been presented at previous conferences. In this paper we discuss recently implemented features that allow quench simulation of fast-ramping superconducting magnets. As the reliability of quench detection during the ramps depends on the signal to noise ratio, we simulate the influence of detection thresholds and the propagation of undetected quenches during the ramps. We also study the effect of an increased copper content and the feasibility of a self-protected magnet surviving a powering cycle with an undetected quench and without quench heater firing or energy-extraction system.

Challenges in the Thermal Modeling of Quenches With ROXIE

The simulation of thermal processes in a superconducting coil during resistive transition is an intricate problem. A detailed thermo-hydraulic modeling comes at a high computational cost and suffers from the large number of empirical parameters. We present a macroscopical approach, covering the most relevant features while providing enough flexibility to gauge the material parameters with measurements. By combining the thermal model with numerical field computation, effects can be simulated that are otherwise difficult to measure, e.g., turn-to-turn voltages, quench propagation and recovery. The thermal model recently implemented in the CERN field computation program ROXIE is validated by means of measurements on model and prototype magnets, as well as data taken during the hardware commissioning of the LHC.

New ideas for long Josephson junctions realistic devices simulation

In the paper, we consider the problem of numerical simulation of long Josephson Junction (JJ) devices. Our interest to the problem is motivated by need of erective parameters calculation of Flux Flow Oscillator (FFO). Practical FFOs have complicated structures and traditional model in form of simple perturbed sine-Gordon equation is inadequate because it doesn't capture important physical details. In this work, we evaluate variable coeficient 1D sine-Gordon equation and boundary conditions for this 1D equation starting from full 2D model of junction and 3D magnetic field problem for bias and control line currents. Then this 1D problem is solved numerically using implicit time stepping numerical procedure. As result program FFOSIM was developed. It is a general tool that allow calculations of critical current, I-V curves and other values. We present results of calculations of junctions inside microstrips where boundary conditions were evaluated using 3D magnetic field calculation program 3DMLSI.

Eddy Current Effects of the J-PARC RCS Sextupole Magnets

Sextupole magnets for the chromaticity correction of the rapid-cycling synchrotron of the Japan Proton Accelerator Research Complex have a large bore of 330 mm and a relatively short length of 320 mm. The end effect, therefore, was not negligible and a three-dimensional magnetic field calculation was necessary to achieve the required field quality of inside the radius of 141.2 mm for the designed maximum field gradient of 18.6 T/m. Eddy current effect on the field quality and temperature rise was considered because the magnets were to be excited with a current pattern of a frequency of 25 Hz. Measurement using harmonic coils confirmed that the required field quality was achieved. Measurement results of the sextupole component and 18-pole component field were reproduced with the magnetic field calculation program OPERA3d/ELEKTRA.

Calculation of Field Quality in Fast-Ramping Superconducting Magnets

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Fast-ramping superconducting (SC) accelerator magnets are the subject of R&amp;D efforts at various laboratories. The simulation of field quality in fast-ramping magnets requires modifications of magnet design tools such as the CERN field computation program ROXIE. In this paper we present the efforts towards dynamic 2-D simulations of fast-ramping SC magnets. Models for persistent currents, inter-strand coupling currents, inter-filament coupling currents, and for eddy-currents in conducting coil-wedges are described and validated. </para>

Discrete Differential Geometry Applied to the Coil-End Design of Superconducting Magnets

Coil-end design for superconducting accelerator magnets, based on the continuous strip theory of differential geometry, has been introduced by Cook in 1991. A similar method has later been coupled to numerical field calculation and used in an integrated design process for LHC magnets within the CERN field computation program ROXIE. In this paper we present a discrete analog on to the continuous theory of strips. Its inherent simplicity enhances the computational performance, while reproducing the accuracy of the continuous model. The method has been applied to the design of coil ends for the SIS300 dipole magnets of the FAIR project.

Positive streamer discharges along liquid dielectric surfaces: effect of dielectric constant and surface properties

This paper presents investigations on positive streamer discharges propagating in air along the surface of two nonmixing dielectric liquids. By measuring the currents associated with the streamer discharge propagating along the surface of the two nonmixing liquids for varying ratio of their volume, we analyzed the effect of the dielectric constant (the capacitive effect) and the surface properties. Especially, we separated and quantified the magnitude of each contribution. Two different combinations were studied: silicone oil together with glycerol and transformer oil together with glycerol. For these material combinations, we found that the influence of the dielectric constant is about 3 times larger than the effect of the surface properties. Further, by using a simple model of the streamer discharge, we determined with a 3D field calculation program the capacitive behavior of the two nonmixing dielectric materials for varying ratio of their volume. We found that, in order to obtain the observed capacitive dependence, the streamer must propagate literally on the insulator surface.