21 research outputs found
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Experimental Data on High Power Explosive Opening and Closing Switches at CEM-UT
The need for high power switching i n pulse power research has lead to the development of fast acting opening and closing switches with current capacity of more than 1 MA. Presented is the performance data of two switches developed for railgun experiments at the Center for Electromechanics at The University of Texas at Austin (CEM-UT). The first is a compact closing switch, explosively actuated, used as an isolation device for staging parallel inductors charged by homopolar generators (HPGs) and as a crowbar to shunt excess energy from railguns during projectile exit .The second i s an explosive opening switch which provides a low resistance path during inductor charging before quickly opening to transfer energy to the railgun.Center for Electromechanic
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Arc Initiation for the Electromagnetic Powder Deposition Gun
The instrumentation, interpretation of data, and subsequent decisions regarding the direction of system development are discussed. Important system parameters, their impact on system performance, and techniques to measure them are presented. The electromagnetic powder deposition system is based on railgun technology developed by the Department of Defense. The system drives an ionized plasma sheet down the length of a railgun, reaching a final plasma velocity of 4 km/sec. The high velocity plasma, in turn, snowplows a shock compressed gas column in front of it. This gas column sweeps through a powder cloud and accelerates it by viscous drag to a final velocity of 2 km/sec. Important system parameters include particle velocity, gas velocity, gas column pressure, and plasma propagation and velocity. Diagnostic tools include pressure transducers, a high speed digital framing camera, fiber optics and magnetic probes.Center for Electromechanic
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High Power Switches at the Center for Electromechanics at the University of Texas at Austin
Three high coulomb explosively actuated opening switches which have demonstrated reliability and fast switching in railgun experiments are presented. Two of these switches first provide a low conductivity path to transfer energy from homopolar generators to inductive energy stores and then open to commutate current to the railgun. One is a monolithic aluminum element with machined stress concentrations, and the other uses reloadable cartridges mechanically clamped. The third switch is designed to interrupt current in a compulsator powered railgun experiment. In the event of a short circuit fault, the switch automatically opens in order to prevent overheating of the compulsator armature windings. The design and excellent performance of these switches are reviewedCenter for Electromechanic
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Generation of High Toroidal Magnet Fields Using Single-Turn Magnet Technology
The production of very high magnetic fields in a toroidal configuration has been accomplished using single-turn magnet technology coupled with low voltage, high current homopolar generators (HPGs). Single-turn, toroidal field magnets are an attractive alternative to conventional multi-turn coils because of the elimination of turn-to-turn insulation and complicated case structures. A20 T, single-turn toroidal magnet has been designed, built, and tested to demonstrate the high-field technology necessary for a fullscale fusion ignition experiment (IGNITEX). Six, 10 MJ HPGs, operated in a parallel circuit configuration, have powered the 1/16 scale (9 cm major radius) toroidal magnet to an on-axis field density of 20 T. The nominal peak current in the magnet is 9 MA while the open circuit voltage of the generators for a full current test is only 57 V. Each generator drives a 60° section of magnet circuit consisting of multiple wedge-shaped conductor plates. Stresses and temperatures within the magnet are managed by the use of a high strength beryllium copper conductor precooled to liquid nitrogen temperature and axially preloaded to produce an isostatic stress condition at peak electromagnetic loading. The stresses and temperatures produced in the scale TF magnet are representative of those that would be produced in a full-scale device with a 5 s flat top. Generator synchronization is accomplished by one explosively driven closing switch per generator that experiences an action of 1.24 x 1011 A2s per switch. Magnet instrumentation includes magnetic field density, temperature and strain measurements. A description of the experiment, operation and test results are presented in this paper.Center for Electromechanic
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High Current Transmission and Switching System for a Prototype, 20 Tesla, Toroidal Magnet
The Ignition Technology Demonstration (ITD) is a 0.06 scale prototype toroidal field magnet of the proposed full-scale IGNITEX (Ignition Experiment) tokamak. The goal of ITD is to achieve an on-axis magnetic confinement field of 20 T while demonstrating the magnet's ability to withstand high magnetic and thermal stresses [1,2]. To accomplish this task, a peak current of 9 MA must be transferred from six balanced homopolar generator (HPG)/busbar circuits to the liquid nitrogen (LN2) cooled magnet. HPGs are well suited for operation of single-turn coils because they are inherently high current, low voltage machines which can inertially store the energy required for a pulsed discharge. To date the system has delivered pulses of up to 8.14 MA to the toroidal magnet, producing an onaxis field of 18.1 T. In order to properly synchronize current transfer, an explosive closing switch is employed for each of the six independent HPG/busbar circuits. The switches operate by explosively driving a scalloped copper ring into a tapered annular gap made up of two copper alloy rings. With a jitter time of 10 μs, parallel circuit synchronization is better than 0.03% relative to the current rise time. The excellent performance of the switches during discharges of up to 8.14 MA is attributed to several design features which assure proper current distribution. Busbar design considerations have included electromagnetic loading, thermal gradients and magnet preloading effects. The switches and busbars have successfully operated at 82% of their rated action of 1.24 x 1011A2s per switch. Description of the ITD busbar/switching system, design improvements, and operational experience are presented.Center for Electromechanic
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High Coulomb Single Stage Opening Switches
Homopolar generators (HPGs) are modern day energy stores capable of producing large currents (megamps). The generators are typically low voltage, high-capacitance devices with correspondingly slow rise times, and so are unable to directly drive loads requiring fast rise times. A switch must be provided to first transfer energy from the HPG to an inductive energy store and then open to commutate the current to the load. Charging an inductive energy store with large currents for long times requires a massive switch to provide low charging resistance, yet the switch must open and commutate the current to the load in tens of microseconds, typically a feature of a light, fast-acting device. The use of explosives allows the integration of both features in single-stage switch. The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has developed two high coulomb, single stage opening switches for rai lgun applications. The first switch is a monolithic aluminum element with machined stress concentrations actuated by 100 gr/ft detonating cord; the second uses reloadable cartridges mechanically clamped and explosively actuated with 15 gr/ft detonating cord. Both switches develop in excess of 1 kV/gap with comparable long term holdoff. This paper reviews the development and excellent performance of these switches.Center for Electromechanic
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Demonstration of a Prototype, High Field, Single Turn, Toroidal-Magnet System
Very high toroidal magnetic fields have been produced using a single-turn magnet powered by homopolar generators (HPGs). A design goal of a 20 tesla confinement field has been met by the combination of a low impedance toroidal magnet, a high current, low voltage power supply, and the use of a high strength, high conductivity copper alloy. The Ignition Technology Demonstration (ITD) is a 1/16 scale prototype of the proposed full-scale IGNITEX (Ignition Experiment) toroidal field (TF) magnet. Stresses and temperatures reached in the prototype TF magnet are representative of those that would be experienced in a 1.5-m major radius magnet with a 5 s flat top current profile. Synchronized, parallel operation of multiple homopolar generators into a single-turn toroidal magnet has been realized. The prototype TF magnet has produced toroidal magnetic fields up to 18.1 T on-axis with liquid nitrogen (LN2) precooling and axial preloading of the magnet. Room temperature operation of the magnet has produced on-axis fields up to 11.5 T and with LN2 precooling only, up to 15.4 T. Peak current from the HPG system for the 18.1 T test was 8.14 MA with an open circuit voltage of only 49 V. Generator synchronization is achieved by six, 1.5 MA rated, closing switches with a maximum jitter of 10 μs. A peak current density in the inner leg region of the TF magnet of 750 MA/m2 was experienced during the 18.1 T test. Peak temperature in the inner leg region for this test was measured to be 135°C. The description of the ITD experiment, operational experience, and test results are presented.Center for Electromechanic
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Electromagnetic Powder Deposition Experiments
The US Department of Defense (DoD) and commercial entities are dependent on chemical plating and coating processes to replace worn or eroded material on damaged parts. Logistics Centers have been forced to consider replacement materials for repair operations due to the tightening of government regulations on the use of toxic and hazardous materials. This paper describes a new process capable of fulfilling many of these requirements. Existing state-of-the-art thermal spray processes (HVOF, D-gun, plasma spray) are limited to powder velocities of about 1 km/s because they rely on the thermodynamic expansion of gases. A new thermal spray process using electromagnetic forces can accelerate powder particles to a final velocity in excess of 2 km/s. At this velocity, powder particles have sufficient kinetic energy to melt their own mass and an equivalent substrate mass on impact. The energetics of the process allow fusion bonding of greater strength than that created by low velocity processes as well as improved coating density. This paper describes the laboratory system designed and constructed to conduct proof of principle experiments. Results of the experiments are presented along with high speed photographs of powder particles confirming system modeling and performance. The paper concludes with a discussion of the future direction of the programCenter for Electromechanic
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A New Electromagnetic Powder Deposition System
Existing state of the art thermal spray processes (HVOF, D-Gun, Plasma Spraying) are limited to powder velocities of about 1 km/sec because they rely on the thermodynamic expansion of gases. A new thermal spray process using electromagnetic forces can accelerate powder particles to a final velocity of up to 2 km/sec. At this velocity powder particles have sufficient kinetic energy to melt their own mass and an equivalent substrate mass on impact. The process is based on railgun technology developed by the Department of Defense. A railgun is filled with argon gas and a high energy electrical pulse, provided by a capacitor bank, drives the gas down the railgun to a final velocity of up to 4 km/sec. This gas passes over a powder cloud and accelerates the powder through drag forces. The electrical and powder discharge frequency can be adjusted so that the deposition rate and thermal input to the substrate can be controlled.Center for Electromechanic
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The Diagnostic History of a New Electromagnetic Powder Deposition System
This paper describes the diagnostic tools used in the development of a new electromagnetic powder deposition system.Center for Electromechanic