Enhancement of the non-resonant streaming instability by particle collisions

Cosmic rays can power the growth of a seed magnetic field by exciting a non-resonant insta- bility, which can help confine and accelerate high energy particles in supernovae remnants and young stellar jets shocks. This work aims at elucidating the behaviour of the non-resonant cos- mic rays streaming instability in cold and denser environments, such as H II regions and molec- ular clouds, where particle collisions in the background plasma must be taken into account. We investigate theoretically and numerically their impact by including Monte-Carlo Coulomb and neutral collisions in the simulations. We find that in poorly ionized plasmas, where proton- hydrogen collisions dominate, the instability is rapidly suppressed, confirming quantitatively existing multi-fluid linear theory calculations. In contrast, we find that Coulomb collisions in fully ionized plasmas unexpectedly favour the development of the instability by reducing self- generated pressure anisotropies that would otherwise oppose its growth [1].

References

[1] A.Marretetal.,PhysicalReviewLetters128,115101(2022)