Rarefaction Shock Waves in Collisionless Plasma with Electronic Beam
  We show that an electronic beam passing through the collisionless plasma of the "cold" ions and the "hot" Boltzmann electrons can give rise to the propagation of the supersonic ion-acoustic rarefaction shock waves. These waves are analogous to those predicted by Zeldovich [5] in gasodynamics and complementary to the ion-acoustic compression shock waves in collisionless plasma described by Sagdeev [3]. 
Victor Ts. Gurovich and Leonid G. Fel
physics.plasm-ph