A Repetitive Gigawatt Pulse Generator With A Compact Tesla Transformer

Defense and industrial applications have stimulated intense interest in pulsed power technology towards high average power and compact structure. A repetitive pulsed power generator with a compact Tesla transformer, as an important pulsed power source, has attracted extensive attention nowadays. In this dissertation, a repetitive gigawatt pulse generator is developed based on the theoretical analyses, engineering designs and experimental investigations of the three key subsystems, a compact Tesla transformer, a spark gap with a gas blowing system and a primary energy source. These efforts set a good foundation for the development of a compact rep-rate pulse generator and show a promising application for the future. The detailed contents and innovative work include the followings.1. A systematic method and workflow to design a compact, repetitive Tesla transformer is presented.Three theories of the Tesla transformer are analyzed, indicating that high-couple-coefficient approximation theory is suitable for design. Based on the approximation, the effective method and workflow is presented to design parameters of electrical and geometrical for the compact Tesla transformer from output requirement. The designed Tesla transformer has a couple coefficient of about 0.9. Then the voltage distribution across the conic secondary winding is analyzed with electromagnetic field theory and electric network model. Results show that it is approximately linear with the turn radius of the secondary winding and almost the same as that for a coaxial pulse forming line (PFL).Then the electrical parameters of the developed Tesla transformer are experimentally measured, with the results in good agreement with design. The PFL charging experiments of the Tesla transformer are investigated in single shot and rep-rate (50 pps) modes. The maximum PFL charging voltages for the two cases are 380 kV and 300 kV, respectively. Particularly, the charging limitations are explored, allowing a conclusion that the PFL breakdown is recoverable under occasional breakdown for individual pulse, without the effects on the operations of subsequent pulses.In addition, the pressure effect of the oil PFL is experimentally investigated. It is found that the breakdown strength of oil-dielectric increases with hydrostatic pressure approximately to the one eighth power. Inhibitting the formation of the bubbles by pressurization is a probably explanation for increasing breakdown strength for pressurized liquid.2. The effects of gas pressure and gas flow velocity on the operation performance of the spark gap switch in the rep-rate mode are experimentally investigated.Using the designed spark gap switch with a gas blowing system, the rep-rate operation of spark gap switch is experimentally investigated in the case of pressurization. The results indicate for gas pressure in the range of 2.0 MPa, both the breakdown voltage and its pulse-to-pulse instability (RMS) decrease with the pulse number, and reach the steady operation when the pulses exceed 50. At the same time, the instability increases with the pulse rep-rate. Particularly, the instability is less than 5% in the range of less than 50 pps, so it is possible to avoid a gas blowing system, reducing the volume and weight of the system. Once the pulse repetition rate exceeds 100 pps, the instability will exceed 10%, resulting that it is necessary to adopt a gas blowing system.The effect of the gas flow velocity in the rep-rate operation for the spark gap switch is investigated. The conclusions on the gas flow velocity are shown as follows. There exists an optimal gas flow velocity with given rep-rate, which is linear with the rep-rate and can be experimentally determined. At the optimal gas flow velocity, the instability is less than 3% for gas pressures ranging from 0.7 to 1.5 MPa. The spark gap switch with the gas blowing system can steadily operate at the breakdown voltages up to 400 kV with a maximum rep-rate of 300 pps for gas pressure less than 2.0 MPa.3. The voltage stability for the repetitive primary energy source is theoretically analyzed and experimentally verified.In rep-rate mode, the recurrence relations between the adjacent pulses on the initial voltages across the primary capacitor are derived. Then the equation for the initial voltage across the primary capacitor in stable state is obtained. The method of calculating the transition time or the number of transition pulses from the unstable state to the stable state is presented. The condition of the charging thyristor switch's turn-on time independent of the spark gap switch's breakdown voltage is theoretically discussed. Base on the theory analyses, the primary energy source with a rep-rate up to 1000 pps is developed and experimentally investigated. Results show that the primary energy source can operate stably from the first pulse by choosing appropriate thyristor switch's turn-on time.4. The compact rep-rate pulse generator is developed.Based on the three subsystems, the pulse generator is developed with a 0.2 m diameter, a 1.0 m length, and a 90 kg mass. Across a 100Ωresistive load, it can generate the output pulses with voltage amplitude up to 330 kV, duration (FWHM) of 7 ns and risetime down to 2 ns in the single shot mode. In the rep-rate mode, it can steadily operate at a 310 kV output voltage with the instability of 5% for 300 pulses in 40 pps rep-rate and 300 kV with 10% in 100 pps. Moreover, the gas blowing system can be unadopted for rep-rate less than 100 pps. For the pulse generator, the output peaking power is ~1 GW, the average power ~0.7 kW, and the average power density ~22 kW/m3. By far, this type of pulse generators with such performance has not been reported at home country.