My Contribution and Project Overview
Using the standard nanosecond pulse generators we sell at EHT, I surveyed the way in which populations of reactive species in a plasma change with respect to the pulse parameters: pulse width, frequency, and voltage. The result showed that, particularly in varying pulse width, spectral lines could be altered in intensity relative to other lines. While a null result would have shown all lines changing in intensity in the same way with pulse width, the result of our investigation showed the ability to discriminate between different populations. An example of this can be seen in the plot below, which shows the He1 line as constant through all pulse widths. The O1 line, however, is highly pulse width dependent, and the ratio between these two lines changes w.r.t. pulse width.
This idea was developed with my mentors at EHT. Afterwards I took the lead in designing the experimental setup, testing plan, and data analysis . I investigated a number of different DBD styles (High-pressure Xe lamp, plasma jet, etc) and a variety of data-gathering methods using a standard off-the-shelf Thorlabs spectrometer. While I had long been involved in investigative research at both the UW and EHT, this was one of the first projects where I had a great deal of freedom during the entire process - and enough background knowledge to make use of that freedom. My understanding of the functionality of the power supplies, and an ability to tweak them to enable particular types of performance during the testing, allowed me to explore regions that wouldn't have otherwise been available.
This work was enabled by, and meant to demonstrate, the variable nature of EHT's pulse generators. Most nanosecond pulse generators operate at one fixed voltage, one pulse width, and often a low pulse repetition frequency. This is because most generators create pulses using some sort of reactive component - a diode/thyristor, or some other device with in which similar style of "breakdown" condition creates a pulse. This can be very important in applications that that are either fixed, or are not pulse-width dependent. The supplies that I have designed and built with EHT use solid state switching technology, which allows for variable pulse width, voltage, and frequencies up to hundreds of kilohertz. For highly time-dependent phenomena such as plasma chemistry, the ability to vary these parameters is important during research. While for commercialization efficiency and single-use optimization may be the goal, research often benefits from a broader functionality.
Skills Demonstrated / Gained
- General research experience - managing project from conception to completion
- Spectroscopic measurement and analysis, processing of spectra
- Plasma Jet Design / Electrode Design
- High Voltage I*V Power Measurements on Nanosecond Timescales
- Poster Design
Varying pulse width changes the intensity of the O1 line while the Helium lines remain dominantly the same, indicating that the population ratio of reactive species can be changed by varying pulse width.
Plasma Jet-Style DBD with purple plume visible. Spectrometer, located on the right, measures the spectrum axially.