Simulation of Plasma-facing Antennas for RF Ion-cyclotron Heating PDF Download
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Author: Fabio Paro
Publisher:
ISBN:
Category :
Languages : en
Pages : 214
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Author: Fabio Paro
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ISBN:
Category :
Languages : en
Pages : 214
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Author: Lorenzo Mazzilli
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Category :
Languages : en
Pages : 150
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Author: Walid Helou
Publisher:
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Category :
Languages : en
Pages : 0
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The thesis provides at first a brief introduction to magnetic nuclear fusion and tokamaks. It explains the need for auxiliary plasma heating and current-drive electromagnetic systems at the Ion Cyclotron and Lower Hybrid Range of Frequencies (ICRF and LHRF). The thesis then sets antenna specifications that allow satisfying proper plasma wave propagation and proper wave-particle resonance. The Radio Frequency (RF) network solver SIDON developed for this thesis is then presented. The thesis then discusses the different types of ICRF antennas and details the challenges of the impedance matching in ICRF arrays of straps. WEST ICRF launchers are discussed in great detail and simulations of impedance matching scenarios for these launchers using SIDON are reported. The thesis reports on the low-power (milliwatt range) testbed that has been developed for WEST ICRF launchers, as well as the low-power tests of the first one among them. Furthermore, high power (megawatt range) experiments on plasma with the JET ICRF ITER-Like Antenna are reported. The thesis then provides an overview about existing LHRF antennas and discusses the numerical modeling of the coupling of waveguide phased arrays to the plasma. The RF design of ASTARTE-LP and its feeding circuit is discussed. ASTARTE-LP is a low-power (milliwatt range) prototype LHRF antenna based on the Slotted Waveguide Antenna concept that has been designed and built to perform proof of principle experiments on the COMPASS tokamak. The experimental validation of ASTARTE-LP and its feeding circuit before the experiments on COMPASS, as well as the experiments performed on COMPASS plasmas are reported.
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Category :
Languages : en
Pages : 203
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SAIC has undergone a three year research and development program in support of the DOE Office of Fusion Energy's (OFE) program in Ion Cyclotron Range of Frequencies (ICRF) heating of present, next generation, and future plasma fusion devices. The effort entailed advancing theoretical models and numerical simulation technology of ICRF physics and engineering issues associated predominately with, but not limited to, tokamak Ion Cyclotron Heating (ICH) and fast wave current drive (FWCD). Ion cyclotron heating and current drive is a central element in all current and planned large fusion experiments. In recent years, the variety of uses for ICRF systems has expanded, and includes the following: (1) Heating sufficient to drive plasma to ignition. (a) Second-harmonic T heating. (b) He3 minority heating. (2) Second-harmonic He4 heating in H plasma (for non-activated phase). (3) Detailed equilibrium profile control minority heating. (a) Ion minority (He3) CD (for profile control on inside of plasma). (b) Ion minority (He3) CD (for profile control on outside of plasma). (4) Ion-ion hybrid regime majority ion heating. (5) Electron current drive. (6) Mode conversion to drive current. (7) Deuterium minority heating. (8) Sawtooth instability stabilization. (9) Alpha particle parameter enhancement. (10) The generation of minority tails by ICRF to simulate D-T plasma particle physics in a deuterium plasma. Optimization of ICRF antenna performance for either heating or current drive depends critically on the complex balance and interplay between the plasma physics and the electromechanical system requirements. For example, ITER IC rf designs call for an IC. system frequency range from 20 MHz to 100 MHz. Additionally, antenna designs and operational modes that minimize impurity production and induced sheath formation may degrade current drive efficiency. Such effects have been observed in experiments involving it versus zero antenna phasing.
Author:
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Category :
Languages : en
Pages : 16
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The edge plasma interactions of the actively cooled radio-frequency heating launchers in Tore Supra- ion-cyclotron range-of-frequencies (ICRF) antennas and lower-hybrid (LH) grills-are studied using infrared video imaging. On the two-strap ICRF antennas, operated in fast-wave electron heating or current drive mode, hot spots with temperatures of 500-900° C are observed by the end of 2-s power pulses of 2 MW per antenna. The distribution and maximum values of temperature are determined principally by the relative phase of the two antenna straps: dipole (heating) phasing results in significantly less antenna heating than does 90' (current drive) phasing. Transient heat fluxes of 1-20 MW/m2 are measured on the lateral protection bumpers at ICRF turn-on; these fluxes are primarily a function of plasma and radio frequency (rf) control, and are not simply correlated with the strap phasing or the final surface temperature distributions. The remarkable feature of the lower hybrid edge interaction is the production of beams of heat flux in front of the grills; these beams propagate along the helical magnetic field lines and can deliver fluxes of 5-10 MW/m2 over areas of several cm2 to plasma-facing components such as the grill or antenna lateral bumpers. Both the ICRF and LH phenomena appear to result from the acceleration of particles by the near fields of the launchers. Modeling of the heat flux deposition on components and its relation to sputtering processes is presented, and possibilities for controlling these interactions are discussed.
Author: Stephen J. Wukitch
Publisher: American Institute of Physics
ISBN:
Category : Science
Languages : en
Pages : 480
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In these proceedings of the April 2005 conference participants describe their current research in the theories, computations, and applications of radio frequency power in plasmas for fusion, space propulsion and material processing. Many of the papers describe solutions in tokamak geometries where phenomena to be modeled ranged from mm to tens of centimeters and self-consistent models of energetic particles and waves, with about half the papers describing work in ion cyclotron range of frequencies (ICRF). Other topics include lower hybrid ranges of frequencies, electron Bernstein ranges of frequencies, electron cyclotron ranges of frequencies and RF plasma applications. Annotation :2005 Book News, Inc., Portland, OR (booknews.com).
Author: Gurleen Kaur Bal
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Ion cyclotron range of frequencies (ICRF) heating in fusion plasmas is significantly hampered by the phenomenon of RF sheath rectification. Addressing RF sheaths and their related effects, such as impurity generation and convective cell formation, is important to make ICRF an effective heating option for future fusion devices. Experiments were performed on the Large Plasma Device (LAPD) using a single strap ICRF antenna to better understand how to mitigate RF sheath formation and its subsequent effects. The initial set of experiments explored the effects of electrically insulating antenna enclosures on RF-rectified sheaths. A single-strap RF antenna was powered using a high-power amplifier and matching network. Although the high-power amplifier and matching network were constructed during prior work, some improvements and changes were incorporated for this thesis work. For example, the amplifier, the matching network, and the antenna were modeled using the software LT-spice and simulations helped guide the changes made to the matching network. Additionally, the antenna design was updated to better shield against RF noise otherwise broadcasted into the lab, contaminating several data signals and electronics. Data from three experiments were compared where the enclosure material was made of copper, MACOR (electrically insulating), and MACOR over copper, respectively. The non-conductive MACOR material was exposed to the bulk plasma in the case of the MACOR-copper side walls, but a layer of copper was placed below to let image currents flow. All three experiments were carried out in a helium plasma with a background magnetic field of 1kG. In each of these three experiments, a single-strap, high-power (100kW) RF (2.4MHz) antenna was used to launch fast waves into the dense core of the magnetized helium plasma. The core density of the plasma was $n_e \approx 5 \times 10^{12} \ \mbox{cm}^{-3}$ to $8 \times 10^{12} \ \mbox{cm}^{-3}$ during each experiment. No Faraday screens were used on the front face of the antenna enclosure for all three experiments. In the case of the copper enclosure, RF rectified potentials, many times the local electron temperature, and associated formation of convective cells were observed and reported \cite{Martin2017}. The experiments with MACOR and MACOR-copper enclosures showed a considerable reduction in RF rectification. Furthermore, neither of these last two experiments indicated convective cell development. Although the results from the MACOR experiment are reminiscent of the results obtained in ASDEX-U with a 3-strap antenna optimized to reduce image currents on the antenna limiters \cite{bobkov2016first}, the MACOR-copper experiment seems to suggest that insulating plasma-facing materials have at least an equally strong impact on reducing potential rectification. To further explore the DC RF sheath mitigation seen in MACOR and MACOR-copper experiments, another set of experiments were executed with different thickness MACOR enclosures. A 1D voltage divider model by Myra and others has been presented to predict mitigation behavior depending on the insulator material and plasma properties. A series of experiments were conducted to investigate the effect of insulator material qualities and plasma properties on the degree of sheath mitigation. These experiments were conducted using enclosure walls made of copper, 1mm, 2mm, and 5mm MACOR. Also, each experiment was carried out under various plasma conditions by varying the time during discharge when the experiment was performed. RF rectified potentials in the copper enclosure experiment were used as a benchmark to determine the degree of mitigation in the MACOR studies. Findings from the various MACOR thickness and plasma parameters demonstrate that, with a few exceptions, sheath mitigation often follows the indicated trend of the voltage divider model. Moreover, the model's projected mitigation quantities and the measured sheath potentials do not agree well. To more accurately predict sheath mitigation in these experiments, the voltage divider sheath model will need to consider the 2D impacts of evolving density and plasma potential. In addition to the sheath mitigation work outlined above, additional work was done to document the parasitic lower hybrid (slow) wave in the LAPD edge. Most fusion experiments where coupling to the slow wave is a concern often have plasma densities and temperatures that are far too harsh for in-vessel diagnostics to be placed in the plasma volume. This work is unique because a fast-wave RF antenna was used to launch fast-wave, typically used for heating, in the core while simultaneously launching the unwanted slow-wave in the edge. Furthermore, this simultaneous coupling of waves was documented using electric dipole probes. Two new dipole probes were developed for this work to allow for better wave propagation mapping along the LAPD's length. One of the big challenges with this work has been achieving a range of densities in the LAPD that span the propagation region of the slow wave and fast wave. With the newly upgraded large $LaB_6$ source, several different plasma configurations were explored using annular limiters, different species plasmas, and a range of accessible frequencies. After the work done for documenting slow-wave propagation with the new $LaB_6$ source, we are better equipped to run high-power slow-wave experiments for future work.
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Languages : en
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A resonant double loop radio frequency (rf) antenna for radiating high-power rf energy into a magnetically confined plasma. An inductive element in the form of a large current strap, forming the radiating element, is connected between two variable capacitors to form a resonant circuit. A real input impedance results from tapping into the resonant circuit along the inductive element, generally near the midpoint thereof. The impedance can be matched to the source impedance by adjusting the separate capacitors for a given tap arrangement or by keeping the two capacitances fixed and adjustng the tap position. This results in a substantial reduction in the voltage and current in the transmission system to the antenna compared to unmatched antennas. Because the complete circuit loop consisting of the two capacitors and the inductive element is resonant, current flows in the same direction along the entire length of the radiating element and is approximately equal in each branch of the circuit. Unidirectional current flow permits excitation of low order poloidal modes which penetrate more deeply into the plasma.
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Category :
Languages : en
Pages : 0
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Author: Paola Demartini
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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