The excitation of obliquely propagating fast Alfvén waves at fusion ion cyclotron harmonics

<p>Intrinsic Alfven waves (IAWs) exist pervasively in the solar-terrestrial plasma, which can preferentially heat newborn ions in the direction perpendicular to the ambient magnetic field via non-resonant interactions when the plasma beta is low. The anisotropized newborn ion populations can excite electromagnetic ion-cyclotron (EMIC) instability. Parametric calculations indicate that the lower the plasma beta is, the higher the growth rate, while the growth rate increases with the number density of newborn ions and the intensity of IAWs. The marginal stable surface in three-dimensional parameter space is also calculated, which provides a qualitative description of parametric conditions for instability. We propose that the coupled effects of non-resonant heating by IAWs and EMIC instability could be an effective mechanism for transferring the energy from low-frequency IAWs to EMIC waves with a frequency below the gyrofrequency of the corresponding ion species. Furthermore, the temperature anisotropy of background ions with the same sense has positive effects on the growth of EMIC waves excited by newborn ions.</p>

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Solar off-limb line widths with SUMER: revised value of the non-thermal velocity and new results

Annales Geophysicae ◽

10.5194/angeo-27-3551-2009 ◽

2009 ◽

Vol 27 (9) ◽

pp. 3551-3558 ◽

Cited By ~ 2

Author(s):

L. Dolla ◽

J. Solomon

Keyword(s):

Solar Wind ◽

Cyclotron Resonance ◽

Alfven Waves ◽

Stray Light ◽

Alfven Wave ◽

Alfvén Waves ◽

Thermal Velocity ◽

Line Profiles ◽

Lower Corona ◽

Ion Cyclotron

Abstract. Alfvén waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind and in the upper corona. In the lower corona, one can use the line profiles to infer the ion temperatures. But the value of the so-called "non-thermal" (or "unresolved") velocity, potentially related to the amplitude of Alfvén waves propagating in the corona, is critical in firmly identifying ion-cyclotron preferential heating. In a previous paper, we proposed a method to constrain both the Alfvén wave amplitude and the preferential heating, above a polar coronal hole observed with the SUMER/SOHO spectrometer. Taking into account the effect of instrumental stray light before analysing the line profiles, we ruled out any direct evidence of damping of the Alfvén waves and showed that ions with the lowest charge-to-mass ratios were preferentially heated. We re-analyse these data here to correct the derived non-thermal velocity, and we discuss the consequences on the main results. We also include a measure of the Fe VIII 1442.56 Å line width (second order), thus extending the charge-to-mass ratio domain towards ions more likely to experience cyclotron resonance.

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