MHD Ballooning Instability in the Plasma Sheet

Technical Report · Mon Oct 20 04:00:00 EDT 2003

DOI:https://doi.org/10.2172/820113· OSTI ID:820113

Cheng, C Z ^[1]; Zaharia, S

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1. Princeton Plasma Physics Laboratory

Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD beq threshold is too low in comparison with observations by AMPTE/CCE at X = -(8 - 9)R(sub)E, which show that a low-frequency instability is excited only when beq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyrorad ii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the beta(sub)eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum.

• Research Organization: Princeton Plasma Physics Lab., NJ (US)
• Sponsoring Organization: USDOE Office of Science (SC) (US)
• DOE Contract Number: AC02-76CH03073
• OSTI ID: 820113
• Report Number(s): PPPL-3890
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
BALLOONING INSTABILITIES
BALLOONING INSTABILITY
COMPRESSIBILITY
FREE ENERGY
INSTABILITY
IONOSPHERE
KINETICS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS (MHD)
PLASMA
PLASMA PRESSURE
PLASMA SHEET
SPACE PLASMA PHYSICS
STABILITY
SUBSTORM
TRAPPED ELECTRONS