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Plasma, often referred to as the fourth state of matter, is ionized gas consisting of positive ions and free electrons. Specifically, a glow discharge is a glowing plasma formed by a voltage across a low pressure gas. The area of the glow discharge of interest in this study is the positive column, a relatively long column of pink, glowing plasma, and its bright and dark striated patterns.
The striated positive column resembles pattern phenomena caused by standing pressure waves. These pressure wave patterns are due to the length of the tube in which they are contained. However, in past plasma research, the relation between striations and plasma tube length has been a neglected parameter.
This study investigates how altering the spacing between electrodes, in effect altering the length of the tube, causes a change in the positive column. This parameter is changed by utilizing four tubes of different lengths and a movable cathode. Research was conducted in both air and argon gas.
It is found that changing electrode spacing does not alter the distance between striations, suggesting the analogy between standing pressure waves and the mechanisms of the positive column do not align along this parameter. Yet, a change in electrode spacing does alter the length of the entire positive column, falling along a clear linear relationship. This relationship is used to suggest the minimum spacing needed to achieve a positive column in both air and argon gas.
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Jackson, Loren Hamilton, "Plasma Striations in Vacuum Chambers" (2017). Senior Projects Spring 2017. 349.