Electromagnetic Proton Beam Instabilities in the Inner Heliosphere: Energy Transfer Rate, Radial Distribution, and Effective Excitation. (arXiv:2107.12883v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Liu_W/0/1/0/all/0/1">Wen Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhao_J/0/1/0/all/0/1">Jinsong Zhao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Xie_H/0/1/0/all/0/1">Huasheng Xie</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yao_Y/0/1/0/all/0/1">Yuhang Yao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wu_D/0/1/0/all/0/1">Dejin Wu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_L/0/1/0/all/0/1">L. C. Lee</a>

Differential flows among different ion species are often observed in the
solar wind, and such ion differential flows can provide the free energy to
drive Alfv’en/ion-cyclotron and fast-magnetosonic/whistler instabilities.
Previous works mainly focused on the ion beam instability under the parameters
representative of the solar wind nearby 1 au. In this paper we further study
the proton beam instability using the radial models of the magnetic field and
plasma parameters in the inner heliosphere. We explore a comprehensive
distribution of the proton beam instability as functions of the heliocentric
distance and the beam speed. We also perform a detailed analysis of the energy
transfer between unstable waves and particles and quantify how much the free
energy of the proton beam flows into unstable waves and other kinds of particle
species (i.e., proton core, alpha particle and electron). This work clarifies
that both parallel and perpendicular electric field are responsible for the
excitation of oblique Alfv’en/ion-cyclotron and oblique
fast-magnetosonic/whistler instabilities. Moreover, this work proposes an
effective growth length to estimate whether the instability is efficiently
excited or not. It shows that the oblique Alfv’en/ion-cyclotron instability,
oblique fast-magnetosonic/whistler instability and oblique Alfv’en/ion-beam
instability can be efficiently driven by proton beams drifting at the speed
$sim 600-1300$ km/s in the solar atmosphere. In particular, oblique
Alfv’en/ion-cyclotron waves driven in the solar atmosphere can be
significantly damped therein, leading to the solar corona heating. These
results are helpful for understanding the proton beam dynamics in the inner
heliosphere and can be verified through in situ satellite measurements.

Differential flows among different ion species are often observed in the
solar wind, and such ion differential flows can provide the free energy to
drive Alfv’en/ion-cyclotron and fast-magnetosonic/whistler instabilities.
Previous works mainly focused on the ion beam instability under the parameters
representative of the solar wind nearby 1 au. In this paper we further study
the proton beam instability using the radial models of the magnetic field and
plasma parameters in the inner heliosphere. We explore a comprehensive
distribution of the proton beam instability as functions of the heliocentric
distance and the beam speed. We also perform a detailed analysis of the energy
transfer between unstable waves and particles and quantify how much the free
energy of the proton beam flows into unstable waves and other kinds of particle
species (i.e., proton core, alpha particle and electron). This work clarifies
that both parallel and perpendicular electric field are responsible for the
excitation of oblique Alfv’en/ion-cyclotron and oblique
fast-magnetosonic/whistler instabilities. Moreover, this work proposes an
effective growth length to estimate whether the instability is efficiently
excited or not. It shows that the oblique Alfv’en/ion-cyclotron instability,
oblique fast-magnetosonic/whistler instability and oblique Alfv’en/ion-beam
instability can be efficiently driven by proton beams drifting at the speed
$sim 600-1300$ km/s in the solar atmosphere. In particular, oblique
Alfv’en/ion-cyclotron waves driven in the solar atmosphere can be
significantly damped therein, leading to the solar corona heating. These
results are helpful for understanding the proton beam dynamics in the inner
heliosphere and can be verified through in situ satellite measurements.

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