DC Breakdown Characteristics of C₄F₇N/CO₂ Mixtures With Particle-in-Cell Simulation

The breakdown characteristics of C
₄
F
₇
N/CO
₂
mixtures under dc condition are investigated with a particle-in-cell method. The processes of elastic, excitation, ionization, and attachment collisions are all considered. The elastic cross section of electron scattering from C
₄
F
₇
N is modeled through quantum mechanical spherical complex optical potential formalism. Based on the cross-sectional data, the dielectric strength of pure C
₄
F
₇
N is studied. The threshold of breakdown is in good agreement with the experiment. Besides, the dielectric strength of C
₄
F
₇
N/CO
₂
mixtures is also obtained. The threshold of breakdown in 80% C
₄
F
₇
N and 20% CO
₂
is larger than that of pure C
₄
F
₇
N when the gas pressure is larger than 1300 torr. The results show that the energy loss of electrons is mainly caused by excitation collision with CO
₂
when the energy of electrons
${T}_{e}$
is smaller than 5.5 eV. When
${E}/{P}$
is small, the proportion of low-energy electrons is large and
${T}_{e}$
increases with the ratio of C
₄
F
₇
N. Therefore, the effective ionization rate first decreases and then increases as the ratio of C
₄
F
₇
N increases.