Marshall N. Rosenbluth Doctoral Thesis Award: When do waves drive plasma flows?*

When waves damp or amplify on resonant particles in a plasma, the resonant particles absorb “plasmon” momentum proportional to the wave action. If this absorbed momentum points perpendicularly to a background magnetic field, the particles can be pushed across field lines, driving ExB rotation. However, resonant particles alone do not tell the whole story. In fact, the forces on the nonresonant particles play a critical role, ensuring that the entire particle + field system conserves momentum. In some cases, these forces take the form of a “ponderomotive recoil,” which completely negates current drive [1, 2] and rotation drive [3] mechanisms predicted on the basis of only the resonant particles. This negation of ExB rotation drive is fundamentally related to ambipolarity in classical transport [4], flux freezing, and MHD torques, which govern the behavior of many physical systems, including Z pinches [5-8]. Recently, the electrostatic theory [9-11] of the ponderomotive recoil has been extended to electromagnetic waves [12]. This extension provides physical insight into the nature of the plasmon momentum of geometrical optics, which corresponds to the momentum gained by the field and nonresonant particles as the wave is self-consistently ramped up from zero amplitude. 

1]  I. E. Ochs and N. J. Fisch, PoP, 27, 062109, (2020). 

[2]  I. E. Ochs and N. J. Fisch, ApJ, 905, 13 (2020). 

[3]  I. E. Ochs and N. J. Fisch, PRL, 127, 025003 (2021). 

[4] E. J. Kolmes et al., PoP, vol. 26, 082309 (2019).

[5] I. E. Ochs and N. J. Fisch, PRL, 121, 235002 (2018).

[6] I. E. Ochs et al., PoP, 26, 122706 (2019).

[7] C. Stollberg et al., PRL, 130, 205101 (2023).

[8] M. Cvejić et al., PRL, 128, 015001 (2022).

[9]  I. E. Ochs and N. J. Fisch, PoP, 28, 102506 (2021). 

[10]  I. E. Ochs, PhD thesis, Princeton University (2022). 

[11]  I. E. Ochs and N. J. Fisch, PoP, 20, 062106 (2022). 

[12]  I. E. Ochs and N. J. Fisch, PoP, 30, 022102 (2023).