a1 Department of Physics, Indian Institute of Technology, New Dethi
Waves, propagating transverse to the direction of the streaming of a plasma in the presence of a uniform external magnetic field, are unstable if the streaming exceeds a certain minimum value. The magnetic field reduces the growth rate of this instability, and also increases the value of the minimum streaming velocity, above which the system is unstable. The thermal motions in the plasma, however, tend to stabilize the system if the magnetic field is weak (i.e. , Ω being the electron cyclotron frequency, k the characteristic wave-number, and Vt the thermal velocity); but, in case of strong magnetic field (i.e. ), they increase the growth rate, provided (ωp being the electron plasma frequency).
† The referee has drawn our attention to Bornatici & Lee (1970), who use the Vlasov equation to describe the behaviour of an anisotropic-temperature plasma. They find that the perpendicular temperature T is stabilizing, whereas the parallel temperature T is destabilizing, and that hence the conclusion of Lee (1969), that temperature is stabilizing, is valid only if T T. However, they do not explore the isotropic case; for this case, we find that the temperature can be destabilizing in some regions.