Absolute and convective instabilities of parallel propagating circularly polarized Alfven waves: Beat instability

Journal Article · Wed Jun 15 04:00:00 EDT 2005 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.1919407· OSTI ID:20764285

Simpson, D; Ruderman, M S ^[1]

---

1. Department of Applied Mathematics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH (United Kingdom)

Ruderman and Simpson [Phys. Plasmas 11, 4178 (2004)] studied the absolute and convective decay instabilities of parallel propagating circularly polarized Alfven waves in plasmas where the sound speed c{sub S} is smaller than the Alfven speed {upsilon}{sub A}. We extend their analysis for the beat instability which occurs in plasmas with c{sub S}>{upsilon}{sub A}. We assume that the dimensionless amplitude of the circularly polarized Alfven wave (pump wave), a, is small. Applying Briggs' method we study the problem analytically using expansions in power series with respect to a. It is shown that the pump wave is absolutely unstable in a reference frame moving with the velocity U with respect to the rest plasma if U{sub l}<U<U{sub r}, where U{sub l}=-{upsilon}{sub A}+O(a) and U{sub r}={upsilon}{sub A}+O(a). When U<U{sub l} or U>U{sub r}, the instability is convective. The signaling problem is studied in a reference frame where the pump wave is convectively unstable. It is shown that the spatially amplifying waves exist only when the signaling frequency is in two narrow symmetric frequency bands with the widths of the order of a{sup 3}. These results enable us to extend for the case when c{sub S}>{upsilon}{sub A} the conclusions, previously made for the case when c{sub S}<{upsilon}{sub A}, that circularly polarized Alfven waves propagating in the solar wind are convectively unstable in a reference frame of any spacecraft moving with the velocity not exceeding a few tens of km/s in the solar reference frame. The characteristic scale of spatial amplification for these waves exceeds 1 a.u.

• OSTI ID: 20764285
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 6 Vol. 12; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ABSOLUTE INSTABILITIES
ALFVEN WAVES
CONVECTIVE INSTABILITIES
DECAY INSTABILITY
MAGNETOHYDRODYNAMICS
PLASMA
POWER SERIES
SOLAR WIND
WAVE PROPAGATION