Anomalous evolution of Ar metastable density with electron density in high density Ar discharge

Abstract

Recently, an anomalous evolution of argon metastable density with plasma discharge power (electron density) was reported [A

Normal and abnormal evolution of argon metastable density in high-density plasmas

“…This is a quite interesting result for the following reason: According to a previous report that has been considered the final conclusion for metastable evolution until now, the evolution of the metastable density can be comprehensively understood as a part of abnormal evolution occurring at low-and high-density regimes, respectively, and thus the normal and abnormal evolutions of the metastable density take place depending on their electron density regimes. 5,7 In our results, however, in spite of having the same electron density regime, the metastable density exhibited both normal and abnormal evolution depending on the measurement position. It seems, therefore, that there is still a missing factor influencing the evolution of metastable-state density in the plasma.…”

“…7,13 At the steady-state condition, the density of the metastable state can be expressed as follows: 7,13 n m ¼ k gm n g þ k rm n r þ k pm n p ð Þ n e k mg þ k mr þ k mp þ k mi ð Þ n e þ D ef f K 2 þ A pm;eff n p k mg þ k mr þ k mp þ k mi ð Þ n e þ D ef f K 2…”

“…This model showed that the main mechanism of the population and depopulation of the Argon metastable atoms can be significantly changed depending on the electron density and that the anomalous evolution can result from the competition between the mechanisms. Therefore, the physics behind the metastable evolution has seemed to be clearly disclosed, 7 and recent discovering of the decreasing metastable trend has been understood based on this analysis as well.…”

“…[4][5][6][7][8][9][10][11][12][13][14][15] However, the results have been controversial: Some groups have reported that the Ar metastable density increases or is almost constant with increasing electron density, 9,11,13 whereas other groups have reported that the Ar metastable density decreases with the electron density. 8,10 This controversial problem was resolved by discovering the anomalous evolution of argon metastable density with electron density (discharge power) included both trends.…”

“…(1), related to the population of the metastable state from the 4p state by radiative decay. 7 Thus, the two different trends (increasing and decreasing) can occur as a result of the competition of the two processes [the two terms in Eq. (1)].…”