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Title: Constraints for the aperiodic O-mode streaming instability

In plasmas, where the thermal energy density exceeds the magnetic energy density (β{sub ∥} > 1), the aperiodic ordinary mode (O-mode) instability is driven by an excess of parallel temperature A = T{sub ⊥}/T{sub ∥} < 1 (where ∥ and ⊥ denote directions relative to the uniform magnetic field). When stimulated by parallel plasma streams, the instability conditions extend to low beta states, i.e., β{sub ∥} < 1, and recent studies have proven the existence of a new regime, where the anisotropy threshold decreases steeply with lowering β{sub ∥} → 0 if the streaming velocity is sufficiently high. However, the occurrence of this instability is questionable especially in the low-beta plasmas, where the electrostatic two-stream instabilities are expected to develop much faster in the process of relaxation of the counterstreams. It is therefore proposed here to identify the instability conditions for the O-mode below those required for the onset of the electrostatic instability. A hierarchy of these two instabilities is established for both the low β{sub ∥} < 1 and large β{sub ∥} > 1 plasmas. The conditions where the O-mode instability can operate efficiently are markedly constrained by the electrostatic instabilities especially in the low-beta plasmas.
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [1] ; ;  [3]
  1. Centre for Mathematical Plasma Astrophysics (CmPA), Celestijnenlaan 200B, 3001 Leuven (Belgium)
  2. (Germany)
  3. Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum (Germany)
Publication Date:
OSTI Identifier:
22407980
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 1; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANISOTROPY; ENERGY DENSITY; LIMITING VALUES; LOW-BETA PLASMA; MAGNETIC FIELDS; RELAXATION; TWO-STREAM INSTABILITY; VELOCITY