Flow Damping Due to a Model of Fluctuation Induced Viscosity in DEBS

The global viscous damping rate in MST has been studied experimentally[1]. In these experiments a biased electrode was applied to a steady RFP plasma with Θ ∼ 1.8. This causes a radial electric field Er, which in turn induces an increased toroidal velocity in the discharge that reaches a steady value. When the electrode is removed, the toroidal flow is damped with a characteristic time τsd ∼ 0.5 msec. The effective viscous diffusion (flow damping) coefficient was then estimated as ν⊥ ∼ (∆r) 2/τsd ≃ 50m /sec, where ∆r = 0.37 m is the radial extent of the core region. This estimate is several orders of magnitude larger than that implied by the standard collisional perpendicular viscosity, so that the viscosity in MST is anomalous. It is stated in Ref. [1] that ν⊥ is consistent with a theoretically derived viscosity driven by magnetic fluctuations[2],