Bohm's Criterion and Sheath Formation, Theory & Experiment
| things found out about plasma sheaths (ion sheaths), experimentally and theoretically | reference or doi | comments |
| First enunciation of Bohm's Criterion (1949) | Ref 1 | theory–there have of course been many, many derivations of Bohm's Criterion in the literature, even long standing arguments between camps that have tried to understand Bohm a little differently than others. Riemann's '91 paper certainly is an important contribution and captures more or less the consensus view by the time the 20th C. came to a close. |
| Generalization of Bohm's Criterion to electronegative plasma (1988) | https://doi.org/10.1088/0022-3727/21/12/011 | theory - it's critical to note that there is no experimental benchmark for this theory yet! We are working on it at USD |
| Review of theories of sheath formation, K-U Riemann (1991) | https://doi.org/10.1088/0022-3727/24/4/001 | theory |
| Generalization of Bohm's Criterion to multiple ion species plasma (1995) | https://doi.org/10.1109/27.467993 | theory |
| First demonstration that Bohm's Criterion for single ion species, weakly collisional is satisfied (2001) | https://doi.org/10.1103/PhysRevLett.90.145001 | experiment, but not the first, Goree (Iowa-early to mid 90's) and Doviel (Marseille, France, early to mid 90's), and their groups were the first to show with LIF (dye laser based LIF, 611nm line in Ar II for excitation) that ions exceed Bohm speed inside of the sheath..lacking only localization of sheath edge with emissive probe diagnostic |
| First demonstration that Generalized Bohm Criterion (GBC) for weakly collisional multiple ion species (2) is satisfied (2007) | https://doi.org/10.1063/1.2760149 | experiment - which was a culmination of many experiments establishing the validity of the surpising discovery (ions generally DON'T reach the sheath edge at their individual Bohm speeds in a 2 ion species plasma) first written about in the PRL of 2001 |
| Theoretical explanation of Instability Enhanced Collision Friction (IEF), Baalrud, Hegna, Callen (2009-2012) | https://doi.org/10.1063/1.3555533 | theory - there were of course a series of papers, beginning first with an attempt to capture the idea in a fluid theory, but which required a kinetic theory to achieve agreement with experiment (which was the thesis work of Chi-Shung Yip) |
| Experiments that IEF theory of Baalrud agreed with, Noah's invited paper and one of Chi-Shung Yip's papers | https://doi.org/10.1063/1.3555533 and https://doi.org/10.1103/PhysRevLett.104.225003 | experiment |
| First experiments in multiple ion species (3) that attempt an IEF theory comparison | https://doi.org/10.1088/1361-6595/aa6776 | experiment and theory - it's critical to note that we still don't have a good deconvolution scheme for Kr II LIF, result: no test of the generalized Bohm Criterion has been done yet! We are working on it at USD |
| Sheaths surrounding Langmuir probes are disturbed, expanded, WE THINK, by ion flow in the presheath | https://doi.org/10.1088/1361-6595/ab69e5 | experiment-this is important because all the experiments were performed by undergraduates, first at USD (Eugene) and then by Peter who helped us finish the paper after he started graduate school as Noah's last student. We just surmised that the work of Armstrong, Weber, Armstrong, Skoelv, and Truleson at Tromso in Norway (See p. 134, part III C. in Noah's book chapter "How Langmuir Probes Work", Ref 2 |
Footnotes:
1
D. Bohm, “Minimum ionic kinetic energy for a stable sheath” in The Characteristics of Electrical Discharges in Magnetic Fields, A. Guthry and R. K. Wakerling, Eds. New York McGraw-Hill, 1949, ch. 3, p. 77.
2
Hershkowitz, Noah. "How Langmuir probes work." Plasma diagnostics 1, D.L. Flamm, O. Auciello, Eds. ACADEMIC PRESS, INC. Harcourt Brace Jovanovich, San Diego, 1989, p. 113-183.