Date of Graduation
Eberly College of Arts and Sciences
Physics and Astronomy
Earl E. Scime.
The principle objective of this work is to determine if short wavelength fluctuations capable of heating ions are excited in helicon sources at the same plasma parameters for which anomalous ion heating has been observed in helicon sources. A portable 300 GHz based, coherent Thomson scattering (CTS) diagnostic, employing both quasioptical propagation and a homodyne detection scheme, was designed and installed on the HELIX source to measure fluctuations with wavelengths on the order of 1 mm. While testing a new antenna designed to directly excite finite k⊥ electrostatic waves in conjunction with a new electrostatic double probe, spontaneously occurring excited waves with wave numbers measurable with the scattering diagnostic were found. For plasma conditions shown to produce the largest amplitude, radially localized fluctuations, as measured with an electrostatic double probe, the CTS diagnostic observed a statistically significant scattered wave power at a frequency of f ∼ 100 kHz and a perpendicular wave number of k⊥ ∼ 89 rad/cm. While the wave frequency found with the CTS diagnostic is lower than expected for the fluctuations given the electrostatic probe measurements, the phase velocity of the waves is small enough that the waves can interact with the bulk of the ion distribution.
Hardin, Robert Aaron, "Measurement of short-wavelength electrostatic fluctuations in a helicon plasma source" (2008). Graduate Theses, Dissertations, and Problem Reports. 2723.