ABSTRACT
T he term plasm a is o ften referred to as the fourth state o f m atter. A s tem pera tu re increases, m olecu les b ecom e m ore energetic and transform in the sequence: solid , liqu id , gas, and p lasm a. In the la tte r stages, m olecu les in the gas d issocia te to form a gas o f a tom s and then a gas o f freely m oving charged partic les, e lec trons, and positive ions. T h is state is ca lled the p lasm a state, a term a ttribu ted to L angm uir to describe the reg ion o f a d ischarge not influenced by w alls an d /o r e lec trodes. It is charac te rized by a m ix ture o f e lec trons, ions, and neutral partic les m oving in random d irec tions that, on average, is e lec trica lly neutral (nl, = «,) In add ition , p lasm as are e lec trica lly conducting due to the p resence o f these free-charge carriers and can attain e lec trica l conductiv ities la rger than those o f m etals such as gold and copper.
