A critical aspect of modern fusion research is the open question of how to efficiently couple energy into fusion plasmas. In magnetically confined schemes, particularly high-density spherical aspect tokamaks, it is difficult to reach plasma resonances with injected microwave beams, as the usual targets, like the first or second harmonic of the electron cyclotron resonance and lower hybrid are cut off due to the high plasma frequencies. In inertial confinement schemes non-linear wave-plasma interactions at optical frequencies cause fast electrons that preheat the fuel (SRS) and reduce implosion performance or cause back-scattered signals (SBS) that can damage laser systems. These environments are either difficult to access or too harsh for detailed probe diagnostics. Thus, a large, low density, low temperature plasma source in the form of a helicon has been developed to enable the study of parametric and other beat-wave type interactions at microwave frequencies. In this parameter space experiments can be conducted on longer length and timescales in a long-lived continuous operation plasma that will not destroy probe diagnostics. This thesis presents the design and commissioning of the apparatus, including characterisation measurements and the development of a numerical model of the plasma source. The device operated in the HF band at powers up to 200 W. Noble gas plasmas in either helium or argon can be generated, with neutral gas pressures ranging from 0.8 Pa to 6.8 Pa. Peak ne ≈ 3 × 10¹⁵ m−3 and Te 1 - 2 eV have been measured for helium in the inductively coupled mode while argon plasmas with ne ≈ 1× 10¹⁵ m−3 and Te between 0.5 eV and 1 eV have been achieved. The device has been successfully operated in the helicon mode in helium at an RF power of 200 W at 14 MHz, with evidence of enhanced confinement and altered radial profile. A fluid numerical model of the source has also been developed that has low computation cost. The model over-estimates the densities by a factor of 3 - 4 and the temperatures by a factor of 2. This model is lacking the capacitive coupling that may be present in the apparatus and should provide better predictive capability in future high-power operation. The model looks capable of calculating the helicon mode, showing wave structures that match the dispersion relation and profiles predicted by helicon wave theory in the literature.
| Date of Award | 1 Mar 2024 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | University of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council) |
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| Supervisor | Kevin Ronald (Supervisor) & Bengt Eliasson (Supervisor) |
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