The Braginskii fluid stability of Reversed Field Pinches
Numerical results are presented concerning the linear stability of the current and future generations of Reversed Field Pinches (RFPs). Resistive MHD indicates that finite beta RFP equilibria are unstable to resistive-g modes, and that these may be responsible for confinement degradation. However, as RFPs become more collisionless, terms that are neglected in resistive MHD become significant and should be included in any stability analysis. A linear initial value code was used to examine the effect of additional terms in the Braginskii equations on the stability of a tearing mode stable equilibrium. In order to make contact with analytical work, the additional physics is introduced term by term. The Hall terms alone are shown to stabilise resistive-g modes, but also to destabilise a variant of the eta(i)-mode. When electron thermal conductivities are also included, the eta(i)-mode remains largely unaffected but the resistive-g mode is no longer stabilised; instead, it evolves into a drift-tearing mode that is driven by the electron temperature gradient. Thus, in the cold ion limit there are two identificable branches of instability. The growth rate of the drift-tearing mode is slowed by finite Larmor radius effects, but both it and the eta(i)-mode remain unstable throughout the collisional ion regime for which the fluid equations are valid.
Bibliographic Reference: Report: AEA FUS 75 EN (1990) 45 pp.
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon. OX14 3DB (GB)
Record Number: 199110034 / Last updated on: 1994-12-02
Original language: en
Available languages: en