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Predicting the Current-Voltage Sweeps of PINQUED for a Cylindrical Langmuir Probe
Burns, Russell A
Burns, Russell A
Abstract
The William & Mary physics department built the PINQUED vacuum chamber to measure the electric field of a low-temperature, low-density Argon plasma with non-perturbative coherent spectroscopy. Readings from a Langmuir probe serve as a ground truth for the plasma parameters. This thesis presents BRLPy, a predictive Python model for PINQUED that generates theoretical cylindrical Langmuir probe current-voltage (IV) sweeps over existing IV sweeps and estimates the parameters. BRLPy fitted seven PINQUED sweeps for two probe lengths, accurately modeling their transition regions. The results supported existing estimates of plasma potential ΦP and electron temperature Te, yielding Te,avg = 0.8717 ± 0.0468 eV. However, none of the floating potential ΦF or electron density ne predictions fell in range, with ne,avg = 6.993*1013± 1.762*1013 m-3---an order of magnitude below expected. Additional results suggest that improved saturation could be achieved for a new probe by using the lab’s 1.0mm diameter copper filament cut to 8.13mm. The computational routine of BRLPy is thorough: it parametrizes the electron current results of Laframboise’s Fortran II programs, with R2 values ranging from 0.956 to 1.000 for ξ < 21.316 and an exact edge case for ξ ≥ 21.316, and it recodes a high-accuracy ion current formula from Chen’s Excel97 electrostatic probe analysis program.
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Date
2025-04-01
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Physics