Observation of oscillatory radial electric field relaxation in a helical   plasma
  Measurements of the relaxation of a zonal electrostatic potential perturbation in a non-axisymmetric magnetically confined plasma are presented. A sudden perturbation of the plasma equilibrium is induced by the injection of a cryogenic hydrogen pellet in the TJ-II stellarator, which is observed to be followed by a damped oscillation in the electrostatic potential. The waveform of the relaxation is consistent with theoretical calculations of zonal potential relaxation in a non-axisymmetric magnetic geometry. The turbulent transport properties of a magnetic confinement configuration are expected to depend on the features of the collisionless damping of zonal flows, of which the present letter is the first direct observation. 
J. A. Alonso, E. Sanchez, I. Calvo, J. L. Velasco, S. Perfilov, A.   Chmyga, L. G. Eliseev, L. I. Krupnik, T. Estrada, R. Kl...
physics.plasm-ph