Research Of Radio Frequency Excitation Source For High Power Fast Axial Flow CO₂ Laser

The Fast Axial Flow ?FAF? CO₂ laser is widely applied because of its excellent performance in the area of the high power laser process.The radio frequency excited characteristics of high power FAF CO₂ laser is important both in the theoretical studies and in the engineering design. In order to study the radio frequency exciting Characteristics in the RF FAF CO₂ laser, the RF excited gas discharge characteristics,the solid state RF power supply and the impedance matching, the feed-through style RF power-measuring method, the rectangular grooved microchannel heat sink for the solid state RF power supply are analyzed theoretically and experimentally. The main contents of this paper are classified as follows:Based on one-dimensional plasma fluid model, the effect of the drive frequency on RF CO₂/He/N2 mixture discharge in laser discharge tube has been further investigated. The numerical results show that through modulating the driven frequency, the discharge can obtain higher plasma density. Moreover, as the driven frequency increasing, the electric-field in sheath increases, the length of the plasma increases, the thickness of sheath decreases; the electron production rate is across the whole tube and has peak value in sheath. The discharge is in a mode.According to the requirement of RF discharge in fast axial flow CO₂ Laser, RF power supplyhas been investigation,which frequency is 13.56MHz. Oscillator-Pre-Drivers circuit of power amplifier was designed in this paper. The Oscillator-Pre-Drivers circuit have two independent driver signal. The function of adjustable duty ratio is available for Oscillator-Pre-Drivers circuit. The topology of Class D is used for RF power supply design. The special setting of dead-time is used to match power d. The purpose of this setting is to reduce the switching loss. The impedance matching parameters have been calculated for RF power supply. The RF power supply prototype has been produced, and some experiments have been done.According to the thermal requirements for the power device, three-dimensional CFD simulations of laminar flow and heat transfer in rectangular grooved microchannel heat sink with different operation, geometry parameters and two different nanofluids have been performed under constant wall heat flux at substrate. The results obtained indicated that the thermal performance of rectangular grooved microchannel heat sink had increment with an optimum groove pitch. It is also found that using of nanofluid instead of pure fluid as a coolant leads to enhanced heat transfer performance by increasing the amount of heat dissipated but it also leads to increased pressure drop.In order to measure the incident power and reflection power between solid state power supply and discharge load, a kind of feed-through style RF power-measuring circuit have been designed in this paper. Directional coupler, analog multiplier, low-pass filter, amplifying circuit, rectifying circuit have been analyzed in the design of RF power-measuring circuit. Simulation software was used to verify the design results. The experimental investigation is also conducted for the RF power-measuring circuit.