Computational analysis of direct current breakdown process in SF6 at low pressure

Abstract

The breakdown of SF6 gas at low pressure is of vital importance to both aerospace and microelectronics industries. However, the breakdown characteristics of SF6 in direct current at low pressure are still seldom studied. In this work, one-dimensional implicit particle-in-cell/Monte-Carlo collision algorithm is used to study the entire direct current breakdown process of low-pressure SF6. The ion-molecule collision, recombination, and external circuit are considered in the model. According to the results, the breakdown process can be divided into three stages: pre-breakdown stage, breakdown stage, and post-breakdown stage. In the pre-breakdown stage, the cathode sheath is not yet formed so the constant electric field exists in the entire area. In the breakdown stage, the formation mechanism of the cathode sheath is analyzed and the electrodes as a whole changes from capacitive to resistive, sharing the voltage with the external resistance. In the post-breakdown stage, the continued growth of positive ions leads to the formation of a thin anode sheath, which further causes the negative plasma potential, different from electropositive gas. The energy production terms including heating power and secondary electron emission (SEE) power are equal to the energy loss terms including collision loss power and boundary loss power, where collision loss power and boundary loss power are almost equal, while SEE power is negligible. In the final, plasma parameters gradually evolve to the last steady-state.