Wenkang Zou

Current Transmission Efficiency for Conical Magnetically Insulated Transmission Line on a 1.0-MV Linear Transformer Driver System

Current transmission efficiency in a conical transition magnetically insulated transmission line (MITL) has been studied experimentally on a 1.0-MV linear transformer driver system, which has 10 identical cavities connected in series with MITL. Transmission efficiencies of anode current as high as 98.4% and 93.1% could be achieved when the MITL operates at load-limited and self-limited flows, respectively. As for the cathode current, because of the sufficient length of conical transition MITL, cathode current is also able to sustain high transmission efficiency. But as long as the diode gap is too large, many of the electrons will be launched into the anode-cathode gap and the cathode current near the diode drastically decreases. Particle-in-cell simulations were conducted to validate the conclusions. The simulation results agree with experiments.

PIC simulations of conical magnetically insulated transmission line with LTD generator: Transition from self-limited to load-limited flow

Based on the 3-dimensional Particle-In-Cell (PIC) code CHIPIC3D, with a new circuit boundary algorithm we developed, a conical magnetically insulated transmission line (MITL) with a 1.0-MV linear transformer driver (LTD) is explored numerically. The values of switch jitter time of LTD are critical parameters for the system, which are difficult to be measured experimentally. In this paper, these values are obtained by comparing the PIC results with experimental data of large diode-gap MITL. By decreasing the diode gap, we find that all PIC results agree well with experimental data only if MITL works on self-limited flow no matter how large the diode gap is. However, when the diode gap decreases to a threshold, the self-limited flow would transfer to a load-limited flow. In this situation, PIC results no longer agree with experimental data anymore due to the anode plasma expansion in the diode load. This disagreement is used to estimate the plasma expansion speed.

Investigation of surface evolution for stainless steel electrode under pulsed megagauss magnetic field

Surface evolution for a conductor electrode under pulsed megagauss (MG) magnetic field was investigated. Stainless steel rods with 3 mm diameter were driven by 8 MA, 130 ns (10%–90%) current pulse in a series of shots on the Primary Test Stand. Experimental data from two complementary diagnostic systems and simulation results from one-dimensional magneto-hydrodynamics code reveal a transition phase for instability development. The transition, which begins as the conductor surface starts to expand, lasts about 40 ns in the pulse. It ends after the thermal plasma is formed, and striation electrothermal instability growth stops but magneto-Rayleigh-Taylor instability (MRTI) starts to develop. An expanding velocity which grows to about 2.0 km/s during the transition phase was directly measured for the first time. The threshold magnetic field for thermal plasma formation on the stainless steel surface was inferred to be 3.3 MG under a rising rate of about 66 MG/μs, and after that MRTI becomes predominant for a...

PIC simulation of the anode plasma in a high-power hollow cathode diode

In this paper, the evolution and dynamics of anode plasmas in high-power hollow cathode diodes were studied by particle-in-cell (PIC) simulation. The simulation results show that the ion flow emitted by the anode plasma layer and the increase of the electron current caused by the ion flow will cause a significant decline in the diode impedance in a short time. In addition, the expansion of the anode plasma layer will cause the diode impedance to decrease. The PIC simulation technique is also applied to a high-power hollow cathode diode of a 1.0 MV-LTD generator for anode plasmas, and the PIC simulation results were compared with the experimental data.

PIC simulation of the vacuum power flow for a 5 terawatt, 5 MV, 1 MA pulsed power system

In this paper, a 5 Terawatt, 5 MV, 1 MA pulsed power system based on vacuum magnetic insulation is simulated by the particle-in-cell (PIC) simulation method. The system consists of 50 100-kV linear transformer drive (LTD) cavities in series, using magnetically insulated induction voltage adder (MIVA) technology for pulsed power addition and transmission. The pulsed power formation and the vacuum power flow are simulated when the system works in self-limited flow and load-limited flow. When the pulsed power system isn’t connected to the load, the downstream magnetically insulated transmission line (MITL) works in the self-limited flow, the maximum of output current is 1.14 MA and the amplitude of voltage is 4.63 MV. The ratio of the electron current to the total current is 67.5%, when the output current reached the peak value. When the impedance of the load is 3.0 Ω, the downstream MITL works in the self-limited flow, the maximums of output current and the amplitude of voltage are 1.28 MA and 3.96 MV, and the ratio of the electron current to the total current is 11.7% when the output current reached the peak value. In addition, when the switches are triggered in synchronism with the passage of the pulse power flow, it effectively reduces the rise time of the pulse current.In this paper, a 5 Terawatt, 5 MV, 1 MA pulsed power system based on vacuum magnetic insulation is simulated by the particle-in-cell (PIC) simulation method. The system consists of 50 100-kV linear transformer drive (LTD) cavities in series, using magnetically insulated induction voltage adder (MIVA) technology for pulsed power addition and transmission. The pulsed power formation and the vacuum power flow are simulated when the system works in self-limited flow and load-limited flow. When the pulsed power system isn’t connected to the load, the downstream magnetically insulated transmission line (MITL) works in the self-limited flow, the maximum of output current is 1.14 MA and the amplitude of voltage is 4.63 MV. The ratio of the electron current to the total current is 67.5%, when the output current reached the peak value. When the impedance of the load is 3.0 Ω, the downstream MITL works in the self-limited flow, the maximums of output current and the amplitude of voltage are 1.28 MA and 3.96 MV, and ...