ABSTRACT
The improved magnetically insulated transmission line oscillator (MILO) is a gigawatt-class L-band high power microwave tube. It has allowed us to generate 3.1 GW pulse of 40 ns duration in the single-pulse operation and 500 MW pulse of 25 ns duration in the repetition rate operation. However, because of the severe impedance mismatch, the power conversion efficiency is only about 4% in the repetition rate operation. In order to eliminate the impedance mismatch and obtain repetitive long-pulse high-power microwave (HPM), a series of experiments are carried out and the recent progress is presented in this paper. In the single-pulse operation, when the diode voltage is 466 kV and current is 41.6 kA, the radiated microwave power is above 2.2 GW, the pulse duration is above 102 ns, the microwave frequency is about 1.74 GHz, and the power conversion efficiency is about 11.5%. In the repetition rate operation, under the condition of the diode voltage about 400 kV, beam current about 38 kA, the radiated microwave power is about 1.0 GW, the pulse duration is about 85 ns. Moreover, the radiated microwave power and the pulse duration decline little by little when the shot numbers increase gradually. The experimental results show that the impedance matching is a vital factor for HPM systems and one of the major technical challenges is to improve the cathode for the repetition rate operation MILO.
ABSTRACT
A radial-current aqueous resistive solution load was applied to characterize a laser triggered transformer-type accelerator. The current direction in the dummy load is radial and is different from the traditional load in the axial. Therefore, this type of dummy load has smaller inductance and fast response characteristic. The load was designed to accommodate both the resistance requirement of accelerator and to allow optical access for the laser. Theoretical and numerical calculations of the load's inductance and capacitance are given. The equivalent circuit of the dummy load is calculated in theory and analyzed with a PSPICE code. The simulation results agree well with the theoretical analysis. At last, experiments of the dummy load applied to the high power spiral pulse forming line were performed; a quasisquare pulse voltage is obtained at the dummy load.
ABSTRACT
An all solid-state and compact pulsed strip pulse forming line (PFL) is investigated both theoretically and experimentally. The electromagnetic field distribution and the pulse formation in the strip PFL are analyzed numerically. Based on the theoretical analysis and numerical results, a rolled strip PFL with output voltage of 20 kV, pulse duration of 230 ns, and characteristic impedance of 0.5 Omega was designed and manufactured. We use the Mylar film and copper as the dielectric and conductor of the strip PFL. The dimension of the strip line is 23,000 x 400 x 1.6 mm(3) in the case in which the strip line is unrolled, and the strip line is finally rolled into a cylinder of diameter of 311 mm for the experiment. The dimension and weight are about ten times smaller than those of traditional dielectric (oil or pure water) PFL with the same electrical parameters. Two experiments were performed using the strip line. One was for a transmission line experiment, and the other was for a PFL experiment. In the experiment of transmission line, the transmission time of the voltage signal was 115 ns, and the signal had almost no distortion, which verified the design. In the PFL experiment, results gave a 17.8 kV, 270 ns (full width at half maximum) voltage pulse which was a quasisquare wave on the water load of 0.5 Omega. The current going through the load is about 35.6 kA.
ABSTRACT
In order to reduce the effective area of the receiving antenna to receive microwave power in the high electric field regions, a 1.76 GHz shorted coaxial transmission line (SCTL) is investigated numerically and experimentally in this paper. When the frequency is 1.76 GHz, the simulation results show that the general gain and the effective area of the SCTL are -10.21 dBi and 2.19 cm(2), respectively, and the power capacity of the SCTL is about 41 kW. So the maximum power flow density, which can be measured by the SCTL, is 18.7 kW/cm(2). With the frequency varying from 1.70 to 1.80 GHz, the general gain increases from -11.19 to -9.42 dBi linearly. The general gain of the SCTL is calibrated with the Agilent E8363B network analyzer in an anechoic chamber, and the calibrated results agree with the simulation. The high-power tests are performed on an improved magnetically insulated transmission line oscillator. Compared to the cutoff free-field probe, the maximum power flow density, which can be measured by the SCTL, is higher.
ABSTRACT
The improved magnetically insulated transmission line oscillator (MILO) is a gigawatt-class L-band high power microwave tube driven by a 550 kV, 57 kA, 50 ns electron beam. It has allowed us to generate 2.4 GW pulse of 22 ns duration. The recent progress of the improved MILO is presented in this paper. First, a field shaper cathode is introduced into the improved MILO to avoid the cathode flares in the triple point region. The experimental results show that the cathode flares are avoided, so the lifetime of the velvet cathode is longer than that of the taper cathode. Furthermore, the shot-to-shot reproducibility is better than that of the taper cathode. Second, In order to prolong the pulse duration and increase the radiated microwave power, a self-built 600 kV, 10 Omega, 80 ns pulser: SPARK-03 is employed to drive the improved MILO. Simulation and experimental investigation are performed. In simulation, when the improved MILO is driven by a 600 kV, 57 kA electron beam, high-power microwave is generated with output power of 4.15 GW, frequency of 1.76 GHz, and relevant power conversion efficiency of 12.0%. In experiments, when the diode voltage is 550 kV and current is 54 kA, the measured results are that the radiated microwave power is above 3.1 GW, the pulse duration is above 40 ns, the microwave frequency is about 1.755 GHz, and the power conversion efficiency is about 10.4%.
