Ballooning mode stabilization by moderate sheared rotation

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:489395

Hameiri, E ^[1]

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1. New York Univ., NY (United States)

Sheared toroidal plasma rotation has been known for some time to have a stabilizing effect on the ballooning modes. A recent calculation showed that a large flow shear, with d{Omega}/dq of the order of the Alfven toroidal frequency, can stabilize the ballooning modes. This latest result is, in fact, not so optimistic. For observed flows with Mach number of order unity one gets d{Omega}/dq smaller by a factor O({radical}{beta}) from the required level (if the flow shear length is of the same order as the magnetic shear length). Moreover, the calculation does not take into account a possibly large transient growth of the mode amplitude due to its Floquet structures We show here that, in fact, there is a general tendency of the ballooning mode to stabilize as soon as the flow shear d{Omega}/dq exceeds the (O{radical}{beta} smaller) {open_quotes}slow{close_quotes} magnetosonic wave frequency. Our analysis is perturbative, where the small parameter is related to the small coupling between the slow and Alfven waves-as is the case in a high aspect-ratio tokamak. (In the perturbation it is important to take the Hamiltonian nature of the governing equations into account.) Moreover, our results apply to the relevant transient growth of the mode amplitude.

• DOE Contract Number: FG02-86ER53223
• OSTI ID: 489395
• Report Number(s): CONF-960354--
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALFVEN WAVES
BALLOONING INSTABILITY
ROTATING PLASMA
SHEAR
TOKAMAK DEVICES