Alonso, J. A., Sanchez, E., Calvo, I., Velasco, J. L., McCarthy, K. ., Chmyga, A., et al. (2017). Observation of Oscillatory Radial Electric Field Relaxation in a Helical Plasma. Physical Review Letters, 118: 185002. doi:10.1103/PhysRevLett.118.185002.