Wave-Particle Resonance in Magnetized Plasma

We report the first observation of the wave-particle resonance line in a magnetized and weakly collisional plasma. The linear resonance satisfies the relation $\omega -n{\Omega }_{\mathrm{ci}}{=k}_{\Vert }{\upsilon }_{\Vert }$ and has a width which is related to the wave-particle coherence time. Both the in-phase (real) and quadrature (imaginary) parts of the resonant response are directly determined by a phased-lock laser induced fluorescence diagnostic. The wave-particle coherence time obtained by fitting the resonance line shape to a one-dimensional Poisson-Fokker-Planck model does not agree with a simple model of ion collisionality.