Lunar Sheath

Plasma sheath with two dust species

Here we focus on the formation of space charge limited (SCL) sheath over the dayside lunar surface, especially in the terminator region.

As it is a transitional sheath, it has the typical physical conditions. In this case, there are two regions as a potential dip comes into existence due to the existence of four populations of electrons namely — free plasma electrons, free photoelectrons, captured plasma electrons and captured photoelectrons. A potential minimum is created at a distance where the photoelectrons are trapped which shows no contribution of trapped photoelectrons to the bulk plasma. It is further assumed that the plasma model consists of a dusty plasma with two kinds of dust-particles — nano-dust and micron sized dust particles. While the nano-dusts are considered as constituent particles of plasma, the micro-sized dust particles behave as suspended impurities in the plasma without affecting the plasma dynamics.

Rinku Deka and Madhurjya P Bora, Physics of Plasmas 27, 043701 (2020)

Dust levitation in an inverse sheath

We consider the lunar plasma sheath in the dayside lunar surface. Due to the photoemission, the surface charges to a positive potential and an inverse sheath is formed. Also for the possibility of existence of negatively charged dust particles, a new charging model called “Patched Charged Model” is introduced here for the first time for sheath calculation, which was validated through experiments (by other authors).

For the levitation of negatively charged dust particles within the inverse sheath, the electrostatic and the gravitational forces are not enough as both the forces act along the same direction, whereas another force — ion-drag force is found to be responsible for the levitation of the dust particles. The results of this levitation indicate formation of dust bands as dust particles of dierent sizes found to be levitated at the same height due to the act of these forces.

Rinku Deka and Madhurjya P Bora, Physics of Plasmas 25, 103704 (2018)

Dust in plasma sheath - a revisit

We revisit the age-old problem of formation of plasma sheath on the nightside of the moon.

We have here self-consistently calculated the surface potential through a 1-D collissionless plasma model which results the formation of a classical sheath. As the sheath is assumed to be stationary, the total current on the dust particles is calculated and the dust-charge is self-consistently calculated by demanding the current balance on the dust particles.

After entering into the sheath, the micron sized dust particles, which are assumed to be negatively charged, experience dierent forces acting on it. The dierent levitation heights for dierent sized dust particles are obtained.

GC Das, R Deka, and MP Bora, Physics of Plasmas 23, 042308 (2016)