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We discuss Peter Gary’s contributions to the understanding of the origin and properties of ultra-low frequency (ULF) waves in the Earth’s foreshock during the period when the International Sun Earth Explorer spacecraft (ISEE-1 and -2) provided unique data about the plasma and wave environment in this region. Peter’s work concerning the linear theory of electromagnetic ion beam instabilities is contained in five journal articles and then summarized in a review article, all of which are discussed here. Brief summaries of observations and theory prior to ISEE as well as to later work are also included.

In the decade from the mid 80's to the mid 90's there was considerable interest in the generation of diamagnetic cavities produced by the sub-Alfvenic expansion of heavy ions across a background magnetic field. Examples included the AMPTE and CRRES barium releases in the magnetotail and magnetosphere as well as laser experiments at various laboratories in the United States and the Soviet Union. In all of these experiments field-aligned striations and other small-scale structures were produced as the cavities formed. Local and non-local linear theory as well as full particle (PIC), hybrid, and Hall-MHD simulations (mostly 2-D) were developed and used to understand at least qualitatively the features of these experiments. Much of this review is a summary of this work, with the addition of some new 3-D PIC and Hall-MHD simulations that clarify old issues associated with the origin and evolution of cavities and their surface features. In the last part of this review we discuss recent extensions of the earlier efforts: new space observations of cavity-like structures as well as new laboratory experiments and calculations with greatly improved diagnostics of cavities formed by expansions of laser-produced ions at super-Alfvenic speeds both across and along the background magnetic field.

The electromagnetic proton cyclotron anisotropy instability is excited if the hot proton temperature anisotropy, T⊥h/Tmidmid h, is sufficiently large compared to unity, where the subscript h denotes the hot protons and the perpendicular and parallel symbols denote directions relative to the background magnetic field. This instability is important in the outer magnetosphere because it has been shown to lead to an upper bound on T⊥h/Tmidmid h and to cool iron heating. Here one-dimensional initial-value hybrid simulations with spatial variations in the direction of the background magnetic field are used to study this instability in a homogeneous plasma model which represents three ionic constituents of the outer magnetosphere: hot anisotropic protons, cool, initially isotropic protons, and cool, initially isotropic singly ionized helium. These simulations show that the presence of a tenuous helium component does not significantly change the scalings of either the hot proton anisotropy upper bound or the heating of the cool protons. The simulations also show that the helium ion heating rate increases with βmidmidh in contrast to the cool proton energization which decreases with this parameter. The prediction of this homogeneous plasma model, therefore, for cool ions subject to heating by the proton cyclotron instability is that the observed ratio of cool helium temperature to cool proton temperature should increase as βmidmidh increases.

Motivated by recent advances in laboratory experiments on parallel ion-beam instabilities, we present a theoretical framework for—and simulations of—their evolution toward shock formation and Fermi acceleration. After reviewing the linear theory of beam instabilities, with an emphasis on how magnetic helicity and polarization depend on properties of the beam, we compare the evolution and saturation of three distinct parameter regimes: (I) the left-handed “non-resonant” regime; (II) the right-handed beam-gyroresonant regime; (III) the balanced, mixed-turbulence regime. [ABSTRACT FROM AUTHOR]

We show that the Bell instability, which is widely considered potentially important for cosmic-ray (CR) acceleration, is the low-frequency limit of a gyroresonant interaction between the protons of the interstellar medium and shear-Alfvén waves. At large CR current densities, its growth rate is therefore limited by the proton gyrofrequency, and two modes emerge from the cold-beam dispersion relation. A third mode driven by electron gyroresonance is only weakly unstable at low current densities. We discuss implications for magnetic field amplification and its saturation in the vicinity of supernova remnants. [ABSTRACT FROM AUTHOR]