1,721,121 research outputs found
Development and Validation of a software for the Analysis of Antennas for Controlled Magnetically Confined Nuclear Fusion
No full textIon-Cyclotron Resonance Heating (ICRH) and Lower-Hybrid (LH)Resonance Heating are key parts of all present-day experiment toward the realization of controlled nuclear fusion with magnetic confinement.
Both auxiliary heating systems are essentially antennas made up of complex plasma facing components, charged with the difficult mission of delivering extremely high RF powers to the plasma with typically poor loadings (as compared to antennas in radar or broadcasting), and high near-field reactive energies that generate serious mismatches to the feeding power lines. Because of the impossibility of testing these antennas in plasmas outside the actual experiments for which they have to be designed, availability of accurate simulation tools is a key factor in assisting their design: this work is concerned with the numerical analysis of these plasma facing antennas, through the upgrade of an existing code called TOPICA and its recent extension named TOPLHA.
The antenna simulation code must be able to handle the actual geometry of both antennas (including their housing in the experiment, the protective screens, etc.), which have witnessed a constant increase in complexity. On the other hand, plasma loading on the antenna is extremely sensitive to the plasma profile, especially near the antenna itself: the antenna code must
therefore be able to correctly account for the plasma conditions,
which makes it necessary to include non-cold plasma terms (that
affect resonances).
More specifically, since the frequency range of the two heating
systems is quite different (below 100 MHz for ICRH and around few GHz for LH), the two antennas differ not only in the geometrical features (ICRH antennas are essentially metal loops while LH antennas are open-ended waveguide arrays), but also in the way the wave propagates in the plasma and the heating process happens.
The problem can be solved with a considerable numerical efficiency by formally separating it into two parts: the vacuum region around the antenna conductors and the plasma region. This approach leads to the problem formulation via a set of two coupled integral equations, further discretized via the Method of Moments (MoM). The MoM is used in a hybrid form: spatial-domain approach is employed for the antenna and other conductors (with high geometrical complexity), while a spectral-domain approach is used for the plasma region (as plasma description is naturally available in this domain).
Numerical tests have already been performed for simple ICRH launchers, and results compared with available experimental data both in vacuum and with real plasmas.
Eventually, this work has extended the existing capabilities of TOPICA in two directions: the efficient handling of IC antennas housed in near, but distinct recesses and the LH range. Both problems are multi-cavity, in the sense that the antennas are recessed in a modular way. Starting from the validated version of
TOPICA, a new approach has been developed to allow the code handle a much greater number of unknowns (from 10,000 to more than 150,000). In the IC range, this is dictated primarily by
geometrical complexity, while the overall electrical length of one
recess does not exceed one half free-space wavelength; in the LH
range, conversely, geometry is smoother, but electrical size is
larger.
The multi-cavity approach addressed in this work exploits the fact
that the inner parts of the individual cavities are coupled one to
each other only through the equivalent currents on their apertures, and accordingly solves the global MoM linear system
block-wise, with significant memory and time saving. Furthermore,
this modular approach led to a heavy parallelization of the code,
with an astonishing increase in the overall performances
Mitigation of parallel RF potentials by an appropriate antenna design using TOPICA
No full textA substantial effort has been devoted in recent years to the optimization of the ITER Ion Cyclotron (IC) launcher [1], above all with the aim of maximizing the coupling performances of the antenna; good improvements have been documented by using TOPICA code [2], a predictive tool for the design and optimization of RF launchers in front of a plasma region. Despite the progresses in the mentioned topic, this is not the only issue related to the design of IC antennas: a second crucial aspect is the impurities production, which is driven by the parallel RF potentials generated by the antenna itself and by the surrounding structures. The goal of this work is to analyze a set of innovative solutions that could be implemented in the next generation of IC antennas in order to mitigate the parallel RF potentials without reducing the power delivered to plasma. To achieve this challenging task, the TOPICA code has been adopted, taking advantage of recently introduced features. In particular, the code permits to compute the electric field distribution everywhere inside the antenna enclosure and in the plasma column, allowing to determine not only the magnitude and shape of the fields in front of the antenna, but also to evaluate their radial decay. Provided the electric field map, it is then possible to determine the parallel RF potentials and, even more important, to directly verify the impact of geometrical modifications of the front elements of the antenna on the RF potentials themselves. Furthermore, the capability to simulate the full 3D antenna with a high geometrical accuracy (as the one provided by commercial codes) and to account for an accurate plasma model indicates in TOPICA code a perfect candidate for this specific task. To lower the parallel RF potentials, two complementary approaches are outlined in the paper: the first one acts on the reduction of the electric field values, the second works on the minimization of the geometrical asymmetries. Pros and cons of the adopted solutions are discussed in detail. Two realistic cases have been taken into account in this work. Firstly, an ITER‐like IC launcher has been adopted as a reference and optimized, then few solutions have been proposed for the ASDEX Upgrade experiment, with the final goal of testing the most promising concept for the machine in the coming years. This second activity has been carried out in collaboration with IPP‐Garching and ENEA‐Frascat
Mitigation of parallel RF potentials using TOPICA code
No full textThe design of an Ion Cyclotron (IC) launcher is not only driven by its coupling properties, but also by its capability of maintaining low parallel electric fields, in order first to provide good power transfer to plasma and then to reduce the impurities production. However, due to the impossibility to verify the antenna performances before the starting of the operations, advanced numerical simulation tools are the only alternative to carry out reliable design. With this in mind, it should be clear that the adoption of a code, such as TOPICA [1], able to precisely take into account a realistic antenna geometry and an accurate plasma description, is extremely important to achieve these goals. Because of the recently introduced features that allow to compute the electric field and RF potential distribution everywhere inside the antenna enclosure and in the plasma column, the TOPICA code appears to be the best candidate in helping to understand which elements may have a not negligible impact on the antenna design. The present work reports a detailed analysis of antenna concepts and their further optimization in order to mitigate RF potentials; the evaluation of the effect of different plasma loadings is included as well
Advanced electric field computation for RF sheaths prediction with TOPICA
No full textThe design of an Ion Cyclotron (IC) launcher is not only driven by its coupling properties, but also by its capability of maintaining low parallel electric fields in front of it, in order to provide good power transfer to plasma and to reduce the impurities production. However, due to the impossibility to verify the antenna performances before the starting of the operations, advanced numerical simulation tools are the only alternative to carry out a proper antenna design. With this in mind, it should be clear that the adoption of a code, such as TOPICA [1], able to precisely take into account a realistic antenna geometry and an accurate plasma description, is extremely important to achieve these goals. Because of the recently introduced features that allow to compute the electric field distribution everywhere inside the antenna enclosure and in the plasma column, the TOPICA code appears to be the only alternative to understand which elements may have a not negligible impact on the antenna design and then to suggest further optimizations in order to mitigate RF potentials. The present work documents the evaluation of the electric field map from actual antennas, like the Tore Supra Q5 and the JET A2 launchers, and the foreseen ITER IC antenna
JET ITER-Like Antenna Simulation Using the TOPICA Code
No full textIn this work, we carried out the analysis of the recently installed JET ITER-Like antenna with TOPICA code. Comparisons between TOPICA simulations and measurements taken during the actual experiment are presented. As routinely done for all simulated antennas, TOPICA inputs are the technical drawings of the launcher and the accurate density and temperature profiles, which, in this case, have been provided by the JET team. The standard outputs are the input parameters of the antenna, namely the impedance matrix, the electric current distribution and the electric field pattern at the interface between the antenna region and the plasma column. This work provides an additional proof that the code can be adopted to predict the behavior of the ITER antenna, and to confidently use TOPICA for the challenging task of optimizing the complex design of the actual ITER antenna. More generally viewed, the possibility to reliably simulate the detailed geometry of an ICRF antenna, given a realistic plasma description, and to obtain the actual antenna input parameters, is of paramount importance to evaluate and predict the system performances, and to assist in system operation
Mitigation of RF potentials by an appropriate antenna design using TOPICA
No full textThe final goal of this work is to set a list of rules to design a new Ion Cyclotron (IC) launcher with the aim to mitigate the RF potential generated by the antenna and its surroundings; to achieve this challenging task, we will adopt as our main tool the TOPICA code [1]. One peculiarity of the code is the capability to compute the accurate electric field map everywhere inside the antenna and the plasma regions; in fact, in this specific task, we are interested in finding a geometrical solution that mitigates the RF potentials and the precise knowledge of the electric field distribution close to conductors is essential to properly optimize the antenna geometry. The tasks of this work consist of the analysis of alternative innovative solutions taking advantage of all the crucial features of the TOPICA analysis tool namely the possibility to simulate the full 3D antenna geometry and the possibility to account for an accurate plasma model in front of the antenna. These solutions will exploit all the possible features in order to minimize the generated RF potentials
Analysis of LH Launcher Arrays (Like the ITER One) Using the TOPLHA Code
No full textTOPLHA (Torino Polytechnic Lower Hybrid Antenna) code is an innovative tool for the 3D∕1D simulation of Lower Hybrid (LH) antennas, i.e. accounting for realistic 3D waveguides geometry and for accurate 1D plasma models, and without restrictions on waveguide shape, including curvature. This tool provides a detailed performances prediction of any LH launcher, by computing the antenna scattering parameters, the current distribution, electric field maps and power spectra for any user‐specified waveguide excitation. In addition, a fully parallelized and multi‐cavity version of TOPLHA permits the analysis of large and complex waveguide arrays in a reasonable simulation time. A detailed analysis of the performances of the proposed ITER LH antenna geometry has been carried out, underlining the strong dependence of the antenna input parameters with respect to plasma conditions. A preliminary optimization of the antenna dimensions has also been accomplished. Electric current distribution on conductors, electric field distribution at the interface with plasma, and power spectra have been calculated as well. The analysis shows the strong capabilities of the TOPLHA code as a predictive tool and its usefulness to LH launcher arrays detailed desig
A Novel Approach to Ion Cyclotron Antennas for Nuclear Fusion Experiments
Full text linkIn nuclear fusion experiments, one of the most assessed methods for heating plasma is via transfer of electromagnetic energy in the Ion Cyclotron Resonance Frequency (ICRF) range. However, space constraints for the plasma-facing antennas result in poor impedance matching and high electric fields; for these reasons current antennas cannot efficiently couple high power to the plasma and require complex matching circuits. This preliminary study presents a new perspective on designing tunable resonant antennas, based on quarter-wavelength resonances
Analysis of a flat, dielectric-loaded, ion cyclotron, test antenna by using three electromagnetic codes
No full textThe present work compares the results coming out from the following three Ion Cyclotron antenna tools: HFSS, COMSOL Multiphysics and the TOPICA code. A simplified flat antenna geometry, working at 30 MHz, is used as benchmark. The comparison is carried out with respect to the scattering matrix and the RF potentials, i.e., the line integrals of the electric field along the flux tubes of the equilibrium magnetic field. Various operational configurations characterized by different antenna load clearance are considered. Very good agreement can be observed among the codes for all the simulated configurations in terms of scattering parameters. RF potentials also match as
regards to patterns, trends as well as absolute values
The Lower Hybrid resonance effect in the simulation of Ion-Cyclotron plasma heating
Full text linkThe TOPICA (TOrino Polytechnic Ion Cyclotron Antenna) code is an advanced tool for simulating ion-cyclotron (IC) radio frequency antennas. This document presents a study based on simulations of the lower hybrid (LH) resonance effect in the TOPICA code. The document briefly explains the lower hybrid resonance problem, describes the simulation setup, and presents the results in terms of electric field distribution. Additionally, we propose a possible approach to identifying the problem
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