Development of a predictive self-consistent fluid model for optimizing inductive RF coupling of powerful negative hydrogen ion sources

  • Magnetized confinement fusion devices such as ITER will be heated and fueled by large and powerful neutral beam injection systems, where neutralized negative hydrogen and deuterium ions are used. The negative ions are produced in an ion source plasma, which is sustained by powerful radio-frequency (RF) generators at 1 MHz. The power is transferred by a coil wrapped around a cylinder (called driver) via inductive coupling to the low pressure (up to 0.3 Pa) low temperature plasma. In ion sources used at the ITER neutral beam injection system there will be eight drivers, each powered with up to 100 kW. Voltages of several kilovolts are applied, wherefore electrical breakdowns are likely. Only a certain fraction η of the generator power is absorbed by the plasma, whereas the rest is lost by Joule heating of the coil and metallic components. By maximizing η, lower generator powers and coil voltages become possible. However, various parameters such as magnetic field, pressure, power, drivingMagnetized confinement fusion devices such as ITER will be heated and fueled by large and powerful neutral beam injection systems, where neutralized negative hydrogen and deuterium ions are used. The negative ions are produced in an ion source plasma, which is sustained by powerful radio-frequency (RF) generators at 1 MHz. The power is transferred by a coil wrapped around a cylinder (called driver) via inductive coupling to the low pressure (up to 0.3 Pa) low temperature plasma. In ion sources used at the ITER neutral beam injection system there will be eight drivers, each powered with up to 100 kW. Voltages of several kilovolts are applied, wherefore electrical breakdowns are likely. Only a certain fraction η of the generator power is absorbed by the plasma, whereas the rest is lost by Joule heating of the coil and metallic components. By maximizing η, lower generator powers and coil voltages become possible. However, various parameters such as magnetic field, pressure, power, driving frequency, as well as driver and coil geometry influence η. To get insight into the power coupling mechanism and to optimize η, a predictive self-consistent fluid model is established. No predictive model existed hitherto due to the complexity of the power coupling at low driving frequencies and the dynamics of the plasma and neutral species at low pressures and high powers. It is shown that the nonlinear RF Lorentz force and the electron viscosity are crucial for describing power coupling in this regime. Model validation is accomplished by systematic comparison with measurements of the plasma and electrical parameters that are performed for the first time at the ITER prototype RF ion source. Here η is around 0.5. The capability of the model to scan the broad parameter space and disentangle the various nonlinear effects provides a valuable guideline for experimental efforts towards optimizing the RF power coupling in ion sources. By optimizing the two parameters with maximum impact, driving frequency and driver length, η is increased from 0.5 to 0.9.show moreshow less

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Metadaten
Author:Dominikus ZielkeORCiD
URN:urn:nbn:de:bvb:384-opus4-894170
Frontdoor URLhttps://opus.bibliothek.uni-augsburg.de/opus4/89417
Advisor:Ursel Fantz
Type:Doctoral Thesis
Language:English
Year of first Publication:2021
Publishing Institution:Universität Augsburg
Granting Institution:Universität Augsburg, Mathematisch-Naturwissenschaftlich-Technische Fakultät
Date of final exam:2021/09/14
Release Date:2021/10/27
Tag:negative hydrogen ion sources; optimizing RF power coupling; predictive self-consistent fluid model; electron heating regimes; RF Lorentz force
GND-Keyword:Injektion; Ionenquelle; Plasma; ICP; Numerisches Modell; ITER; Neutrales Teilchen
Pagenumber:135
Institutes:Mathematisch-Naturwissenschaftlich-Technische Fakultät
Mathematisch-Naturwissenschaftlich-Technische Fakultät / Institut für Physik
Mathematisch-Naturwissenschaftlich-Technische Fakultät / Institut für Physik / AG Experimentelle Plasmaphysik (EPP)
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
Licence (German):Deutsches Urheberrecht mit Print on Demand