Electrostatic heat flux instabilities

The linear Vlasov dispersion relation for electrostatic waves in a homogeneous plasma is studied for instabilities driven by an electron heat flux. A two Maxwellian model of the electron distribution function gives rise to three unstable modes: the electron beam, ion-acoustic and ion cyclotron heat flux instabilities. At large T_e/T_i the ion-acoustic instability has the lowest threshold; at small T_e/T_i the electron beam instability is dominant; and at intermediate values of T_e/T_i the ion cyclotron mode is the first to go unstable. The presence of a high energy tail on the electron distribution function raises the value of the dimensionless heat flux q_e/(n_em_ev³_e) at the ion-acoustic threshold, but increasing atomic number of the ions decreases this value.