ORIGINAL RESEARCH Ion Temperature Effect on Weakly Collisional DC Plasma Sheath Mansour Khoramabadi • Hamid Ghomi • Mahmoud Ghorannevis Published online: 3 April 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Using a collisional two-fluid model, we inves- tigate the ion temperature effect on the sheath formation criterion as well as the sheath structure in electropositive plasmas. In this work, temperature dependence of the characteristics of a weakly collisional DC plasma sheath is examined numerically. It will be shown in the constant cathode electric potential, the more the ion temperature, the low the thickness of sheath. Moreover, for a special set of physical parameters, the sheath formation criterion is not fulfilled for ion temperature under a minimum value. Keywords Ion temperature  DC plasma sheath  Collisional plasma Introduction A plasma sheath is the localized positive space charge that separates the plasma from its surrounding wall. When an electrode (conducting plane) is immersed in the plasma, an electrostatic sheath is formed around it and shields the plasma from the electrode. Difference between the mobil- ity of the positive and negative charged particles in the plasma is caused for the sheath formation. Many authors have been investigated the reasons of the sheath existence in the plasma-wall interface in more detailed [1, 2]. The Bohm criterion, the necessary condition for the sheath to be formed, has been assessed by them. Using the both fluid and kinetic models, Riemann [2, 3] analyzed the Bohm criterion and the influence of collisions on the sheath for- mation. Braithwaite et al. [4], Amemiya [5, 6] and Fer- nandez Palop et al. [7] have investigated the Bohm criterion in electronegative plasmas and they have shown that, how it can be used in plasma diagnostics by using Langmuir probes. Identifying plasma sheaths is one of the oldest problems in plasma physics. Many models have been used to study the sheath structure and the effects of different physical processes on it, and their results are often consistent with the experimental results [8–15]. Almost all of these models are on the basis of the plasma fluid approximation. It has been shown that ion temperature, strongly affects on the sheath parameters (such as ion energy and density). Ghomi et al. [16] deduced a Sagdeev potential by a thermal collisional two-fluid model and derived an upper limit for ion transition velocity in addition a lower limit. Effect of ion temperature on RF plasma sheath was described by Lei et al. [17]. Moreover, Das et al. [18] and Alterkop [19] studied the DC plasma sheath formation in thermal plasma. Hear on the basis of the two-fluid model, the specifi- cations of a DC plasma sheath are evaluated numerically by solving its nonlinear equations. This model is involved in ion-neutral collisions, in addition the effect of the ion pressure (temperature). We have restricted the analysis to the plasma sheath layer, and have not considered the pro- cesses in the bulk of the plasma and presheath. After the introduction, the sheath equations are formu- lated in ‘‘Basic Equations and Sheath Formulation’’ on a simple plasma sheath model basis. In ‘‘Computational Results and Discussion’’, numerical results and the corre- sponding discussions are presented showing the role of M. Khoramabadi (&)  M. Ghorannevis Plasma Physics Research Center, Science & Research Campus of Islamic Azad University, P.O. Box 14665-678, Tehran, Iran e-mail: makhoram1351@yahoo.com H. Ghomi Laser and Plasma Research Institute, Shahid Beheshti University, 1983963113 Evin, Tehran, Iran 123 J Fusion Energ (2010) 29:365–370 DOI 10.1007/s10894-010-9289-8