Inductively Coupled Plasmas

Self organization in Torr pressure ICP plasma sources have recently  been observed and studied in the literature [1,2]. Reproduction of this phenomenon in N2 gas in the lab exhibits much of the well-known behavior, including the transition to successively higher azimuthal mode number with increasing power, the eventual transition from a discrete number of azimuthal modes to a continuous mode, and the rotation of these striations in the plasma. New observations also indicate the importance of the coupling between the plasma, excitation of electronic states, and their transport and loss governed by the gas residence time. To date, theoretical and experimental efforts neglect the role of multi-step ionization and how these threshold-reducing molecular excited states couple to the large scale gas transport. Existing experimental evidence points to the importance of these effects: (1) At fixed pressure, the apparent increase in power required to shift between mode number increases with increasing flow rate. (2) The power at which continuous mode is achieved is significantly reduced at low flow. (3) Rotation is only present at low flow conditions. In this study, we explore the effect of gas flow on the observed boundaries between mode number in Gas Flow – Power parameter space. The understanding of these observations is aided by the use of a 0D model to capture the effect of species loss in high flow systems.

[1] V. Désangles, J.-L. Raimbault, A. Poyé, P. Chabert, and N. Plihon, PRL 123, 265001 (2019)

[2] Alsaeed et al “Thermoelectric instability trends in inductively coupled plasmas”  [in preparation for submission to Journal]