Dynamics of high- and low-pressure plasma remediation

Plasma remediation is an efficient and promising technology to destroy toxic and greenhouse gases. In this work we computationally study the dynamics of high-pressure dielectric barrier discharges (DBDs) and low-pressure plasma processing reactors. The high-pressure systems are examined in the context of volatile organic compound (VOC) and NOx remediation. The low-pressure systems are studied in the context of the consumption and generation of perfluorocompounds (PFCs) in an inductively coupled plasma (ICP) etching reactor and abatement of PFCs in a plasma burn box. The plasma kinetic processes are discussed with the goal of providing insight for optimizing efficiencies.;In electropositive gas mixtures, the expanding microdischarges in DBDs maintain a fairly uniform electron density as a function of radius. In electronegative gas mixtures, the electron density has a maximum value near the streamer edge due to dielectric charging and attachment at smaller radii at lower E/N (electric field/number density). The expansion and ultimate stalling of the microdischarge is largely determined by charging of the dielectric at larger radii than the core of the microdischarge.;The dynamics of adjacent microdischarges are similar to a single microdischarge, with the exception that the electron density peaks at the interface. The residual charge on the dielectric in DBDs from a preceding microdischarge can significantly change the dynamics of microdischarges produced by the next voltage pulse.;Remediation of carbon tetrachloride (CCl4) in DBDs progresses by chain chemistry. Though dissociative electron attachment is primarily responsible for initial dissociation of CCl4, dissociative excitation and charge transfers from Ar*, Ar**, Ar+, and O2+ to CCl4 play a significant role. Choosing the proper O2 to CCl4 ratio and preventing the presence of water vapor in gas mixtures can considerably increase the remediation efficiency of CCl 4.;C2F6 (or CF4) consumption in the plasma etching reactor increases with increasing ICP power deposition, and decreasing C2F6 (or CF4) mole fraction or total gas flow rate, but the efficiency of removal of C2F6 (eV/molecule) is only strongly dependent on the C2F6 mole fraction and total gas flow rate. All PFCs in the effluent can generally be remediated in the burn-box at high power deposition with a sufficiently large flow of additive gases (O2, H2, or H2O). In general, CF4 generation occurs during abatement of C2F6 using O2 as an additive, especially for high power with low O2 input. CF4 is not, however, substantially produced when H2 or H2O is used as additives.;The use of DBDs as excimer ultraviolet (UV) lighting sources was also studied. The mixture Xe/Cl2 ≈ 99/1 was found to be an optimum gas mixture for the generation of the XeCl*. Higher applied voltage improves both the intensity and efficiency of UV photon generations. The strong attachment at high Cl2 concentration (e.g., ≥5%) leads to electron shell propagation to smaller radii after the voltage pulse.