The Study Of Discharge Stability In Atmospheric Pressure Radio Frequency Glow Discharges

Atmospheric pressure glow discharge (APGD) is a type of non-equilibrium thermodynamics discharge. It provides a way to generates low temperature plasmas at atmospheric pressure without any vacuum system. These features suggest that APGDs have wide application scopes in future industries. Nowadays, radio-frequency (RF) APGD is one of the mostly ways to obtain APGD because it can provide high density plasma with low gas breakdown voltage. A key issue in APGDs is the discharge stability, especially at high discharge intensity. With increasing discharge current density, mode transition of RF APGD occurs, transiting from volumetric glow discharge in a mode to unstable constricted discharge column in y mode. Currently, most of studies focus on expanding the stable operation regime of a mode. In this study, the experimental studies are carried out by altering radio-frequency excitation frequency and applying pulse modulation on radio-frequency excitation. They are briefly introduced as following:1. The current-voltage characteristics of RF APGDs in argon are studies at excitation frequencies of 6.78 MHz and 13.56MHz, which indicates operation regime of a mode in each case and that the mode transition occurs at higher discharge current density with 13.56MHz than that with 6.78 MHz. The operation regime of a mode is furtherly investigated in excitation frequency range of 5-24MHz, which suggests that the stable operation regime of a mode can be expanded by applying higher excitation frequencies. The discharge reactivity in terms of optical emission intensity at 750 nm and gas temperature are studied at excitation frequencies of 6.78 MHz,13.56 MHz and 20.34 MHz, respectively. It shows that the discharge intensity and gas temperature grow with discharge current density and excitation frequency.2. Pulse-modulation of radio-frequency power is proposed to manipulate the discharge characteristics and stability. In experiments, RF APGD at 13.56 MHz is generated in atmospheric helium and RF power is modulated with pulses. The discharge characteristics are studies based on characteristics of modulation pulse in terms of repetition frequency and duty cycle. The discharge current and applied voltage when discharge is ignited were measured, from which the breakdown voltage, the stable operation range of discharge (a mode) in modulation pulse repetition frequency range of 100 kHz-900 kHz and duty cycle of 10%-90% are investigated. It is found that an increase of gas breakdown voltage and expansion of operation regime of a mode are achieved by reducing duty cycle and applying higher repetition frequency.