The radial propagation of blobs generated from plasma instabilities is investigated in an open magnetic field line configuration. Blob cross-field velocities and sizes are obtained from internal probe measurements using pattern recognition. By varying the ion mass, the normalized vertical blob scale a approximate to is scanned from a approximate to < 1 to a approximate to > 1. An analytical expression for the blob velocity including cross-field ion polarization currents, parallel currents to the sheath, and ion-neutral collisions is derived and shows good quantitative agreement with the experimental data. In agreement with previous theoretical studies, this scaling shows that, for a approximate to < 1, the blob velocity is limited by cross-field ion polarization currents, while for a approximate to > 1 it is limited by parallel currents to the sheath.
Olivier Sauter, Basil Duval, Duccio Testa, Alexander Karpushov, Mario Ludovico Podesta, Antoine Pierre Emmanuel Alexis Merle, Marcelo Baquero Ruiz, Dmytry Mykytchuk, Matteo Vallar, Lorenzo Stipani
Javier García Hernández, Antonio José Pereira de Figueiredo, Matteo Vallar