We have conducted a detailed analysis of a set of events termed short large-arnphtude magnetic structures (SLAMS) observed at an encounter of the quasi-parallel bow shock by the AMPTE UKS and IBM satellites. Both the satellite configuration and the solar wind conditions are favorable for the case study presented here. We have identified isolated SLAMS, surrounded by solar wind conditions, and embedded SLAMS, which lie within or form the boundary with regions of significant heating and deceleration. The duration, polarization, and other characteristics of SLAMS are all consistent with their growth directly out of the ULF wave field, including the common occurrence of an attached whistler as found in ULF shocklets. The plasma rest iYmne propagation speeds, where they can be determined, and two-spacecraft time delays for all cases show that the SLAMS attempt to propagate upstream against the oncoming flow, but are convected back downstream. The speeds and delays vary systematically with SLAMS amphtude in the way anticipated from nonlinear wave theory, as do their polarization features. Inter-SLAMS regions, and boundary regions with the solar wind, contain hot deflected ions of lesser density than within the SLAMS. The amplitude of the SLAMS requires an active growth mechanism. Following earlier inferences about the limited transverse extent of SLAMS, we highlight the importance of determining the thickness of the transition zone over which SLAMS grow and the bulk heating and deceleration is effected. From this case study it appears that, at least under some circumstances, the quasi-parallel shock cannot be regarded as an undulating, cychcally re-forming simply connected surface. Instead, the transition zone is better represented as a set of ULF waves, some of which grow to become SLAMS which gradually decelerate and merge to form the downstream state. conditions and that these instabilities cause the shock to cyclically re-form. pulsations was dictated primarily by the Larmor radii of the backstreaming particles found in abundance upstream of the bow shock but downstream of the foreshock boundary. This boundary is defined by the upstream field line which is tangent to the curved bow shock, or by the trajectory of field-aligned ion beams of a given energy originating at the point of tangency. The turbulence associated with the shock apparently saturates some distance, typically 10 R•, downstream of this ion foreshock boundary [Bonifazi et al., 1983], downstream of which nearly isotropic distributions of "diffuse" energetic ions are found. The curved nature of the bow shock led early workers to suggest that the turbulent appearance of the quasi-parallel shock was due to debris which originated under more quasi-perpendicular configura-4209

Computer simulations and observations in laboratory and space plasmas have revealed that some incident ions are reflected at perpendicular and quasi‐perpendicular high Mach number (i.e., supercritical) shocks. Moreover, these studies have established that the gyration and subsequent thermalization of these ions play a dominant role in the the shock dissipation process. We use a hybrid kinetic simulation in order to study the selection of an incoming ion as either reflected‐gyrating or transmitted. We find that the reflected ions come from a limited region in the upstream velocity space distribution. None of the reflected ions come from the core of the distribution. Whether a particle becomes reflected depends on its energy in the upstream frame and its gyrophase as it encounters the shock. In the simulations we have carefully identified and separated the two subpopulations: transmitted and reflected. The transmitted ions do not heat appreciably in passing through the shock, although there may be wave‐particle effects neglected in the hybrid simulation. There is a contribution to the total downstream pressure due to the gyration of the two subpopulations about their common center of mass, in addition to the pressure associated with the reflected component relative to its own center of mass.

Focused ion beam induced deposition of platinum from a gas of (methylcyclopentadientyl) trimethyl platinum has been demonstrated and used for integrated circuit repair. Ga+ ions in the range of 30–40 keV have been used and line widths down to 0.3 μm with resistivities as low as 70 μΩ cm have been observed. The deposition yield as a function of angle of incidence has been measured by scanning the ion beam across a 2.6 μm diameter pyrex rod. The conductors on an actual integrated circuit have been modified by milling and filling a via to connect two Al lines in a sandwiched configuration as well as by milling two vias through passivation and connecting two adjacent Al lines.

[1] The heating of directly transmitted ions at low Mach number, quasi-perpendicular collisionless shocks is rapid, greater than adiabatic, and exhibits a distinct T ? > T k anisotropy. In this paper we present a theoretical study of the evolution of the ion velocity distribution across a stationary one-dimensional perpendicular model shock profile. A Lagrangian/Hamiltonian formulation of the ion equations of motion is introduced. We argue that the classical statistical physics solution of Liouville's equation in terms of the energy (Hamiltonian) is not applicable to the case of a laminar perpendicular shock. Assuming a Maxwellian incident ion velocity distribution, it is possible to obtain the analytical form for the distribution through the shock in terms of functions of upstream parameters that are independent of the incident temperature. Unlike the classical Hamiltonian solution, we show that contours of equal phase space probability do not correspond to contours of equal energy. It is this property of the velocity distribution that makes anisotropic heating possible. We recover the observed results that the distribution is stretched across the magnetic field direction as it passes through the shock and that it rotates as a whole around the field in the downstream region. We are able to show that in the low-temperature limit, the shape of the distribution remains Gaussian but that this is not the case for higher temperatures. For this Gaussian approximation, lower and upper bounds for the variance of the downstream velocity and therefore the heating are obtained. An efficient method for the numerical computation of the distribution through the shock is proposed and evaluated for typical shock parameter combinations. The downstream behaviour of the distribution is also elucidated.

Observations of some low Mach number collisionless shocks in space have revealed that their associated ion heating is greater than adiabatic, is very rapid, is primarily in the direction perpendicular to the magnetic field, and takes place in the bulk of the distribution. These features are very different from those encountered at crossings of supercritical shocks and not yet fully understood. In this paper we use a one-dimensional hybrid kinetic simulation to study the details of the evolution of the incoming ions across a set of low Mach shocks. We find that the bulk of the ion velocity distribution becomes elongated along the direction perpendicular to the shock front as the ions traverse the shock ramp. The subsequent gyration of the ions in the steady field downstream gives rise to a temperature signature with features that correspond closely to those enumerated above. This suggests that these features may originate primarily from the kinetic behavior of the ions at the shock rather than from the operation of some instability. We also investigate the dependence of our results on a number of physical and numerical parameters in the simulation. Hugoniot conservation relations across the shock [Sckopke et al., 105a]. This equality has been used in analytical studies of the dependence of the fraction of ions reflected at the shock upon various upstream parameters [e.g., Paschmann and Sckopke, 105a; Wilkinson and Schwartz, 1990]. The ion velocity distribution immediately downstream of the ramp is therefore highly non-Maxwellian, with true thermalization occurring only gradually with time [Sckopke et al., 1983] through the action of waves driven by a number of instabilities, the most important of which is thought to be the Alfv6n ion cyclotron instability [ Tanaka et al., 1983; Thomas arid Brecht, 1986; Winskeand Quest, 1988]. It should be noted that the contribution of the directly transmitted (as opposed to reflected) ions to the overall downstream heating is small but nonnegligible and results from the mutual gyration of directly transmitted and reflected ion populations about their common center of mass (their gyration about the magnetic field in the frame of reference determined by the bulk ion velocity) [Burgess et al., 1989]. The various characteristic structural elements in the magnetic field profile of supercritical quasi-perpendicular shocks are also linked to the kinetic behavior of ions at these shocks. Thus, the extended "foot" preceding the main shock ramp is caused by the reflected ions [e.g., Paul et al., 1965; .Wong, 1968; Woods, 1969; Phillips and Robson, 1972], and the overshoot that follows the ramp results from the gyrational motion of the directly transmitted ion population about the total ion center of mass [Goodrich, 1985; Burgess et al., 1989]. Many references on the subject of ion reflection and dissipation at supercritical quasi-perpendicular shocks can be found, for example, in the review article by Gosling and Robson [1985]. We now turn our attention to low Mach number quasiperpendicul...

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The heating of the bulk of the incident ions at low Mach number quasi‐perpendicular collisionless shocks is observed to take place very rapidly, within the shock ramp. In this paper we show that the trajectories of ions passing through the shock ramp lead to a dispersion in phase space resulting in an effective increase in ion temperature. The main heating is predicted to take place in the second half of the ramp. We present results of self‐consistent computer simulations which confirm this prediction.