Resonant electron firehose instability: Particle-in-cell simulations

Abstract

Consider a collisionless, homogeneous plasma in which the electron velocity distribution is a bi-Maxwellian with T⊥<T∥, where the subscripts refer to directions relative to the background magnetic field B0. If this anisotropy is sufficiently large and the electron β∥ is sufficiently greater than one, linear dispersion theory predicts that a cyclotron resonant electron firehose instability is excited at propagation oblique to B0 with growth rates less than the electron cyclotron frequency |Ωe| and zero real frequency. This theory at constant maximum growth rate yields threshold conditions for this growing mode of the form 1−T⊥e/T∥e=Se′/β∥eαe′, where the two fitting parameters satisfy 1≲Se′≲2 and αe′≲1.0 over 2.0⩽β∥e⩽25.0. The first particle-in-cell computer simulations of the resonant electron firehose instability are described here. These simulations show that enhanced magnetic field fluctuations reach a maximum value of |δB|2/B02 which increases with β∥e. These enhanced fields scatter the electrons, reducing their anisotropy approximately to a linear theory threshold condition and yielding a dimensionless scattering rate which increases as β∥e increases. These results are consistent with the general principle that, for a given plasma species, scattering by enhanced fluctuations from anisotropy-driven electromagnetic instabilities acts to make the velocity distribution more nearly isotropic as the β∥ of that species increases.

Effects of Electrons on the Solar Wind Proton Temperature Anisotropy

“…The instability driven by excessive proton parallel temperature is called the proton firehose instability (PFHI) by many authors (Kennel & Scarf 1968;Gary & Feldman 1978;Yoon et al 1993;Gary et al 1998). Soon thereafter, a second instability driven by anisotropic electrons was identified (Hollweg & Völk 1970), which is known as the electron firehose instability (EFHI; Pilipp & Völk 1971;Gary & Madland 1985;Gary & Nishimura 2003;Paesold & Benz 1999Messmer 2002;Camporeale & Burgess 2008). Due to the kinetic effects of plasma particles both instabilities have finite wave-frequencies and maximum growth at propagation parallel to the magnetic field.…”

Firehose instability in space plasmas with bi-kappa distributions

“…The ions, however, are resonant and they can gain energy making the firehose instability responsible for the transfer of the electron energy to the ions. The first simulations of the electron firehose instability have also shown that the generated magnetic field fluctuations scatter the electrons, reducing their anisotropy (Gary & Nishimura 2003;Paesold & Benz 2003).…”

Kinetic instabilities in the solar wind driven by temperature anisotropies

“…Later, however, with applications to the solar wind and other astrophysical situations in mind, further simulations were carried out by Califano et al (2008), Camporeale andBurgess (2008, 2010), Génot et al (2009, Porazik and Johnson (2013b), and Ahmadi et al (2016). Firehose instability driven by excessive parallel temperature anisotropy was also simulated (Gary and Nishimura 2003). Gary et al (1993aGary et al ( , 1995Gary et al ( , 1997 compared the theory, simulation, and observation made in the magnetosheath in order to establish the role of anisotropy-driven instabilities in regulating the thermal anisotropies.…”