Dynamics of periodic ion holes in a forced beam-plasma experiment

Experimental observation of the propagation of periodic ion phase space vor tices is reported. Density fluctuation measurements in a double plasma devi ce show an apparently spontaneous acceleration of these periodic structures from ion thermal to ion acoustic velocity. A nonlinear kinetic description explains this as a transition from a new type of nonlinear electrostatic m ode (periodic ion holes) to an ion acoustic mode which is caused by trapped particle scattering. (C) 2001 American Institute of Physics.