Space charge formation and Bohm’s criterion in the edge of thermal electronegative plasma

The collisional electronegative plasma spacecharge is investigated in the presence of the thermal positiveions. The Boltzmann distribution is assumed for electrons andnegative ions and fluid equations are used to treat the acceleratedpositive ion through the sheath region. The influence ofthe positive ion temperature on the profile of the space charge isobtained for different negative ion concentration and negativeion temperature for collisionless and collisional cases. It isshown that the position of the space charge peak is independentof positive ion temperature while its amplitude depends on thepositive ion temperature. The presence of the negative ionleads to damping of the space charge amplitude. In addition thethermal effect of the positive ion on the kinetic energy of theion extracted from an ion source is studied in difference ofcollisionality and electronegativity. It is shown that, in thepresence of thermal positive ion, the influence of the negativeion temperature on the sheath characteristics disappears. It isobserved that in the presence of the hot positive ion, the twofoldfeature of the space charge starts at higher values ofnegative ion temperature which is more pronounced in collisionalcase. Finally, the influences of the positive and negativeion temperature, as well as the electronegativity and collisionalityon the net electric current are studied.