Charging of spinning insulating objects by plasma and photoemission

Abstract

[1] The charging of spinning insulating objects by plasma and photoemission is studied in two spatial dimensions with the particle-in-cell method. Unidirectional photon flux, different angular velocities of the object, and different plasma flow speeds are considered. Photoemission can lead to a positive total charge and electric dipole moment on the object. The spinning of the object redistributes the surface charge and leads to asymmetric potential barriers near the object. The total charge on the object oscillates in time with the period matching the period of the object rotation. The plasma potential and density in the vicinity of the object oscillate with the same frequency. For flowing plasmas, the wake in the ion density is conspicuous behind a positively charged object. The time averaged charge on the object depends on its angular velocity.

Electron Wing‐Like Structures Formed at a Negatively Charged Spacecraft Moving in a Magnetized Plasma

“…Since electrons are much more mobile than ions, if only electron and ion currents are taken into account, the floating potential will be negative (Spitzer, ; Hastings, ). In caseswhere photoemission and secondary emission currents give a significant contribution to the net current, the floating potential can also reach positive values (Roussel & Berthelier, ; Engwall et al, ; Miloch & Vladimirov, ; Miloch et al, ; Yaroshenko et al, ).…”

Shielding of absorbing objects in collisionless flowing plasma

“…Note that in deriving (10) we assumed that electrons are hotter than ions, so that k De ≪ k Di and hence…”

“…is the ion sound velocity) can be relevant, e.g., to dust grains suspended against gravity in a collisionless sheath region of the discharge (see, e.g., [12,17,18]), or to satellites in the upper ionosphere [10]. In this limit, we can approximate the unperturbed ion distribution function with a shifted delta-function: Neglecting the electron response (i.e., assuming that electrons are much hotter than ions so that electrons do not contribute significantly to the screening [12]), the dielectric function (9) becomes in this limit:…”

“…However, in reality the plasmas in which dust grains are immersed are usually anisotropic, e.g., due to ion fluxes from bulk plasma to the plasma boundaries (these can be dust-plasma boundaries such as in dust voids [8,9]), or due to the motion of dust grains relative to the plasma (we note that the latter situation is equally relevant for satellites moving in the plasma environment of upper ionosphere [10]). It is therefore necessary to investigate how absorption of plasma particles by a collecting body (e.g., a dust grain), either immersed in a flowing plasma, or moving in an isotropic plasma, affects the shielding of the body by the plasma.…”

“…Appendix B: On derivation of Eqs (15) and (16) To evaluate the integrals on k appearing after substituting (10) and (14) into (5), we expand exp(ik · r) following Cooper [11]:…”