title: Electron Weibel instability in relativistic counterstreaming plasmas with flow-aligned external magnetic fields.
abstract: The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.
authors.affiliation: LULI, UPMC Université Paris 06: Sorbonne Universités, CNRS, Ecole Polytechnique, CEA, Université Paris-Saclay, F-75252 Paris Cedex 05, France.|Dipartimento di Fisica Enrico Fermi, Università di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy.|Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (CNR/INO), u.o.s. Adriano Gozzini, I-56127 Pisa, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Grassi
authors.affiliation: LULI, CNRS, Ecole Polytechnique, CEA, Université Paris-Saclay, UPMC Université Paris 06: Sorbonne Universités, F-91128 Palaiseau Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Grech
authors.affiliation: LULI, CNRS, Ecole Polytechnique, CEA, Université Paris-Saclay, UPMC Université Paris 06: Sorbonne Universités, F-91128 Palaiseau Cedex, France.
authors.forename: F
authors.initials: F
authors.lastname: Amiranoff
authors.affiliation: Dipartimento di Fisica Enrico Fermi, Università di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy.|Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (CNR/INO), u.o.s. Adriano Gozzini, I-56127 Pisa, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Pegoraro
authors.affiliation: Dipartimento di Fisica Enrico Fermi, Università di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy.|Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (CNR/INO), u.o.s. Adriano Gozzini, I-56127 Pisa, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Macchi
authors.affiliation: LULI, UPMC Université Paris 06: Sorbonne Universités, CNRS, Ecole Polytechnique, CEA, Université Paris-Saclay, F-75252 Paris Cedex 05, France.
authors.forename: C
authors.initials: C
authors.lastname: Riconda