Cryogenic effect on dust grain charging in a plasma

Charging mechanism of dust particles in a nonuniform discharge plasma under cryogenic environment is studied theoretically. The plasma density and temperature effects on dust grain charging are investigated with characteristic time scales of density variation and temperature relaxation in consideration. The charge of a dust grain, initially placed in a discharge plasma and cooled to cryogenic temperature, is governed by the time-dependent ion temperature and ion-neutral collisions. The magnitude of a dust charge decreases with the decrease of ion temperature. The charge at a cryogenic temperature is found to be much smaller than that at the room temperature, in agreement with experimental observation reported earlier. It is suggested that charged dust grains at cryogenic temperature make the formation of a strongly coupled system of dust particles.