title: Flow damping due to stochastization of the magnetic field.
abstract: The driving and damping mechanism of plasma flow is an important issue because flow shear has a significant impact on turbulence in a plasma, which determines the transport in the magnetized plasma. Here we report clear evidence of the flow damping due to stochastization of the magnetic field. Abrupt damping of the toroidal flow associated with a transition from a nested magnetic flux surface to a stochastic magnetic field is observed when the magnetic shear at the rational surface decreases to 0.5 in the large helical device. This flow damping and resulting profile flattening are much stronger than expected from the Rechester-Rosenbluth model. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. This observation suggests that the flow damping is due to the change in the non-diffusive term of momentum transport.
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ida
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yoshinuma
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Tsuchiya
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: C
authors.initials: C
authors.lastname: Suzuki
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yokoyama
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Shimizu
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nagaoka
authors.affiliation: Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Inagaki
authors.affiliation: National Institute for Fusion Science, Toki, Gifu 509-5292, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Itoh