Parallel Ion Beam Instability In E-p-? Plasma

Streaming proton and alpha particles are permeating in the solar wind and solar atmosphere.These particles considerably affect the normal waves in electron-proton-alpha plasmas,especially inducing electrostatic and electromagnetic ion beam instabilities.This study gives a comprehensive investigation on stable and unstable parallel-propagating wave modes in plasmas with streaming proton and alpha particles.We give a complete analytic expression of the dispersion equation for plasma waves in e-p-alpha plasmas with isotropy temperature.We then derive the general dispersion equation of the plasma waves in an anisotropic e-p-alpha plasma.Based on above two dispersion equations,we analyze the properties of both electromagnetic and electrostatic instabilities resulted from streaming protons and alpha particles.Main results are listed as follows:(1)As the proton and/or alpha particle beam velocity increases,the backward propagating fast-magnetosonic/whistler wave(Alfven/proton-beam or Alfven/alpha-beam mode wave)turns to forward propagation in the core proton rest frame,and couple with forward propagating Alfv e n/alpha-cyclotron and alpha-cyclotron/proton-cyclotron waves(fast-magnetosonic/whistler wave),triggering Alfven/proton-cyclotron instability(fast-magnetosonic/whistler instability).(2)Besides Alfv e n/proton-cyclotron instability and fast-magnetosonic/whistler instabilities,there are other three electromagnetic instabilities in anisotropic e-p-a plasmas.(3)There are four kinds of electrostatic instabilities in isotropic e-p-alpha plasmas.(4)Based on the typical plasma parameters in solar coronal holes,it finds that both alfven/proton-cyclotron instability and fast-magnetosonic/whistler instabilities can be triggered,which would give a constraint on the ion differential drift velocity therein.