Linear transformer driver (LTD) technology is actively developed at the Institute of High Current Electronics in Tomsk, Russia. This technology is being examined for use in high current high voltage pulsed accelerators. Recent development of high voltage low inductance capacitors and low inductance switches enabled to achieve ~100 ns rise time of the LTD output pulse. This technique allows one to eliminate intermediate pulse forming sections, used in the present accelerator technology, which would keep the footprint of an LTD accelerator small. LTD based drivers are currently considered for many applications, including future very high current Z-pinch drivers for inertial confinement fusion, medium current drivers with adjustable pulse length for isentropic compression experiments, and finally relatively low current accelerators for radiography and X-pinches. In this article, we present the design and test results for a new LTD stage, that operates at 100 kV charging voltage. Current amplitude up to 850 kA with ~140 ns rise time was obtained on a 0.05 Ω load. Stack of the LTD stages can be easily assembled in series or in parallel, thus providing voltage or current multiplication, respectively. Design of multi-mega-volt and multi-mega-ampere generators becomes straightforward with the LTD technology.
High voltage, high current, and high Coulomb transfer closing switches are required for many high power pulsed systems. There are a few alternatives for closing switches, for example, ignitrons, vacuum switches, solid-state switches, high pressure gas switches (spark gaps), and some others. The most popular closing switches up to date are spark gaps due to relatively simple design, robustness, easily field maintenance, and repair. Main drawback of spark gaps is limited lifetime, which is related directly or indirectly to erosion of the electrodes. Multichannel switches and switches with moving arc have been proposed to prevent the electrodes erosion. This study investigates switches, where a spark channel is initiated in a three-electrode layout and then the spark accelerates due to electrodynamic force and moves along the extended electrodes. At a given current amplitude, the diameter of the extended electrodes allows to control the spark velocity and hence, the erosion of the electrodes providing the required lifetime. The first switch is designed for 24 kV charging voltage and approximately 4 C total charge transfer. This spark gap was tested at 25 kA peak current in 40 000 shots in a single polarity discharge and in 20 000 shots in bipolar discharge. Second spark gap is designed for 24 kV charging voltage and approximately 70 C total charge transfer. It was tested in 22 000 shots, at a current of 250 kA with a pulse length of 360 mus. In this paper, we present design of these spark gaps and trigger generator, describe the test bed, and present the results of the tests.
High-energy switches and trigger generators are required for MJ-level capacitor banks. We have developed a compact gas switch and a matched series injection trigger generator. A series inductance is required for isolation of the trigger pulse from the surrounded circuit. A saturable inductor is employed here because low inductance is needed after the switch breakdown. The switch is of coaxial two-electrode design with electrodynamic acceleration of a spark channel. The switch operates at atmospheric pressure. The spark gap can be triggered reliably down to zero voltage (at 50 kV self-breakdown voltage) with less than 35 ns timing jitter. Energy losses in this spark gap have been accurately investigated. The main results are as follows: energy losses in the switch do not exceed 4% at voltages higher than 15 kV, i.e., when operation voltage exceeds ∼36% of the self-breakdown voltage. The spark gap is designed for 24 kV charging voltage, at a current up to 250 kA, and ∼70 C charge transfer. In this paper, we present a design for the spark gap, inductor and trigger generator. Test bed schematics and results of the tests are also described.
High voltage, high current inductors are required for many high pulsed power systems, incorporating capacitor banks. Those inductors simultaneously serve both as a pulse shaping and protection element in R-L-C circuits. A 25 kV/ 70 kA protection inductor on inductance of 1 mH with low stray field was designed, manufactured, and tested. It was designed as a quasi-toroidal system, consisting of four coils (with 0.25 mH inductance each) evenly distributed in the perimeter of a square. The structure of coils was optimized to withstand a huge electromagnetic force produced by a 70 kA current. The 0.25 mH coil is made as multi-layer solenoid (six layers) from a copper wire (6 × 4 mm 2 net crosssection) with fiberglass insulation. Layers are connected in parallel in order to decrease active resistance of the coil. This 0.25 mH coil was tested at 70 kA peak current with a pulse length of about 20 ms, which corresponds to the action integral at about 32 × 10 6 A 2 s. Maximum magnetic field inside the coil is about 12 T. A finite element analysis with the ELCUT software was used to calculate the magnetic field, temperature rise, and stresses in the protection inductor. The typical maximum stresses in our design are 100 MPa in copper coils and 140 MPa in fiberglass body tubes; these are both below the yield strength for these materials. Simulations results are compared with the experimental tests and good agreement is observed.
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