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Ph.D. Thesis Proposal
by
Connie Liu
(Advisor: Prof. Mitchell Walker)
“Investigating Physics of Nanosecond Pulsed Argon Plasma Discharges for VLF Plasma Antenna”
3 p.m., Thursday, August 23
Montgomery Knight Building, Room 317
Abstract:
Very low frequency (VLF) waves (3-30 kHz) are useful in communication and navigation, can deeply penetrate the ground and ocean surface, and help with satellite protection by removing energetic charged particles in the Van Allen radiation belts that damage satellite electronics. However, current VLF antenna array take 1000s of acres because they are efficiency-limited – the signal propagates down the antenna and reflects back faster than the signal period, which interferes with and cancels the outgoing signal. A top-hat loaded antenna is a solution that radiates more efficiently but is constrained to a small bandwidth. Replacing the metal conductor in a conventional antenna with a series of individually-controlled plasma cells in a plasma antenna could overcome both efficiency and bandwidth limitations. Modulating the plasma conductivity in each segment would turn a portion of the antenna on or off and suppress reflected waves in the time-domain by removing the necessary electrically conducting pathway.
The two main research goals are to further understand the physics of pulsed plasmas by investigating what processes are necessary for both ionization and recombination of pulsed plasmas to happen on the nanosecond timescale and what effects electrode geometry and operating conditions have on the conductivity of a pulsed plasma. A single plasma cell was investigated by generating a pulsed, 1 kV argon plasma at various pulse frequencies, widths, and pressures. Argon emission lines were analyzed with a spectrometer, and relative intensities of strong argon neutral and ion lines were used in line-ratio calculations. These experimentally-determined ratios were compared to theoretical ratios generated from PrismSPECT, a collisional-radiative spectral analysis software. Electron temperature and electron number density were calculated and compared to direct Langmuir probe measurements. Next steps involve nanosecond, time-resolved measurements using an ultra-fast ICCD camera and spectrograph. Those electron density and temperature values will be compared to PrismSPECT and VSim (a plasma simulation software) results to extract a set of plasma parameters for the rapid plasma generation and quenching needed for a multi-celled plasma antenna demonstration.
Committee:
