Alfvén speed gradients in directions parallel and perpendicular to the ambient magnetic field in coronal holes are thought to aid dissipation of wave energy and thus contribute to coronal heating. We have studied Alfvén wave propagation under conditions similar to coronal holes in the Large Plasma Device located at University of California, Los Angeles. The energy of Alfvén waves propagating in the presence of an Alfvén speed gradient perpendicular to the ambient magnetic field is observed to spread to higher k⊥. This spreading of energy is more prominent for steeper gradients and larger z/λ∥, where z is the distance away from the antenna, and λ∥ is the wavelength parallel to the ambient magnetic field. Our initial analysis shows that spreading of wave energy to higher k⊥ may enhance the rate of dissipation of wave energy. However, additional experiments are necessary to confirm plasma heating. Alfvén waves propagating through an Alfvén speed gradient parallel to the ambient magnetic field are observed to lose five times more energy than they do when propagating through the same distance in the absence of a gradient. This reduction in wave energy is observed to increase monotonically with an increase in λ‖/LA,∥, where LA,∥ is the scale length of the Alfvén speed gradient parallel to the magnetic field. The cause of this reduction in energy is constrained by ruling out reflection, mode conversion and nonlinear effects. Since, the total energy must be conserved, it is possible that the reduced wave energy is deposited in the plasma. Further experiments are necessary to confirm if this wave energy contributes to plasma heating.
American Astronomical Society Meeting Abstracts #234
- Pub Date:
- June 2019