Abstract
A shear Alfvén wave parametric instability is observed for the first time in the laboratory. When a single finite ω/Ωi kinetic Alfvén wave (KAW) is launched in the Large Plasma Device above a threshold amplitude, three daughter modes are produced. These daughter modes have frequencies and parallel wave numbers that are consistent with copropagating KAW sidebands and a low frequency nonresonant mode. The observed process is parametric in nature, with the frequency of the daughter modes varying as a function of pump wave amplitude. The daughter modes are spatially localized on a gradient of the pump wave magnetic field amplitude in the plane perpendicular to the background field, suggesting that perpendicular nonlinear forces (and therefore k⊥ of the pump wave) play an important role in the instability process. Despite this, modulational instability theory with k⊥=0 has several features in common with the observed nonresonant mode and Alfvén wave sidebands.
| Original language | English |
|---|---|
| Article number | 195002 |
| Journal | Physical Review Letters |
| Volume | 116 |
| Issue number | 19 |
| DOIs | |
| State | Published - May 11 2016 |
| Externally published | Yes |
Funding
The authors thank Y. Lin, R. Sydora, G. Morales, and J. Maggs for insightful discussions; S. Vincena, P. Pribyl, S. K. P. Tripathi, and B. Van Compernolle, for insightful discussions and assistance with the experiment; and Z. Lucky, M. Drandell, and T. Ly for their excellent technical support. S. D. was supported by a NASA Jack Eddy Fellowship. This work was performed at the UCLA Basic Plasma Science Facility which is supported by DOE and NSF.
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