Forces on a Small Grain in the Nonlinear Plasma Wake of Another

Abstract

The transverse force on a spherical charged grain lying in the plasma wake of another grain is analysed to assess the importance of ion-drag perturbation, in addition to the wake-potentialgradient. The ion-drag perturbation is intrinsically one order smaller than the wake-potential force in the ratio of grain size (rp) to Debye length (λDe). So ion-drag perturbation is important only in nonlinear wakes. Rigorous particle-in-cell calculations of the force are performed in the nonlinear regime with two interacting grains. It is found that even for quite large grains, rp/λDe = 0.1, the force is dominated by the wake-potential-gradient. The wake potential structure can then help explain the preferred alignment of floating dust grains.

Dynamic ion shadows behind finite-sized objects in collisionless magnetized plasma flows

“…The enhancement in ion density gives rise to a positive trailing peak in the potential distribution. The resulting oscillatory potentials in the wake correspond well to results obtained with the linear response (LR) theory [8] and can explain interactions between dust particle pairs in plasmas where collisions are negligible [17,22]. Analogous studies contribute to the interpretation of data from spacecrafts in various plasma environments [2,7,23,24].…”

Wake Formation and Wake Field Effects in Complex Plasmas

“…Extensive PIC-simulations by Patacchini et al [47] have shown that drag forces along the flow are positive for all relevant conditions. For sonic flows, drag forces are reported to be less important than the attractive wake field itself [48]. Lapenta [9] and recently Piel [35] discussed the stability of chains of grains perpendicular to the ion flow.…”

“…A regime where the ion focus and thus its attractive force on a downstream grain is still weak. For sonic flows, drag forces are reported to be less important than the attractive wake field itself [48].…”

Connecting the wakefield instabilities in dusty plasmas

“…As is usually donesee, e.g., [4,8,9,13,15,20,28,29]-the ion focus is modeled as a positive point charge q rigidly attached to a negative dust particle of charge Q at a distance d + below the dust (see Fig. 1).…”

“…The ion streaming motion in the plasma sheath where the dust particles are usually confined leads to the formation of an ion wake, or ion focus, which is a region of positive space charge downstream of the dust particle [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The influence of the ion focus on the structure formation has been studied in, e.g., [16][17][18][19].…”