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Title: Ion gyroradius effects on particle trapping in kinetic Alfven waves along auroral field lines

In this study, a 2-D self-consistent hybrid gyrofluid-kinetic electron model is used to investigate Alfven wave propagation along dipolar magnetic field lines for a range of ion to electron temperature ratios. The focus of the investigation is on understanding the role of these effects on electron trapping in kinetic Alfven waves sourced in the plasma sheet and the role of this trapping in contributing to the overall electron energization at the ionosphere. This work also builds on our previous effort by considering a similar system in the limit of fixed initial parallel current, rather than fixed initial perpendicular electric field. It is found that the effects of particle trapping are strongest in the cold ion limit and the kinetic Alfven wave is able to carry trapped electrons a large distance along the field line yielding a relatively large net energization of the trapped electron population as the phase speed of the wave is increased. However, as the ion temperature is increased, the ability of the kinetic Alfven wave to carry and energize trapped electrons is reduced by more significant wave energy dispersion perpendicular to the ambient magnetic field which reduces the amplitude of the wave. This reduction of wave amplitudemore » in turn reduces both the parallel current and the extent of the high-energy tails evident in the energized electron populations at the ionospheric boundary (which may serve to explain the limited extent of the broadband electron energization seen in observations). Here, even in the cold ion limit, trapping effects in kinetic Alfven waves lead to only modest electron energization for the parameters considered (on the order of tens of eV) and the primary energization of electrons to keV levels coincides with the arrival of the wave at the ionospheric boundary.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3]
  1. Princeton Univ., Princeton, NJ (United States)
  2. Princeton Univ., Princeton, NJ (United States); Andrews Univ., Berrien Springs, MI (United States)
  3. Univ. of California, Berkeley, CA (United States); Univ. of Sydney, Sydney, NSW (Australia)
Publication Date:
Report Number(s):
52-83
Journal ID: ISSN 2169-9380; TRN: US1701270
Grant/Contract Number:
AGS1203299; NNH16AC43; NNH15AZ95I; NNH14AY11I; NNH14AY20I; NNX15AJ01G; NNX13AE12G; NNX16AR10G; NNX16AQ87G; FT110100316; UPR10002; AC02-09CH11466
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 11; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; plasma sheet; electron acceleration; energization; magnetopause; dispersion; region; polar; model
OSTI Identifier:
1340072
Alternate Identifier(s):
OSTI ID: 1373991