The present invention relates to pulsed-power technology and, in particular, to a high-voltage, low-inductance gas switch that can be used in linear-transformer-driver cavities.
Linear transformer drivers (LTDs) are a relatively new technology being developed because of their potential to provide high performance and greater versatility of applications at a significantly reduced cost. LTDs can potentially achieve compactness and low cost by going directly from DC-charged capacitors to a 100-ns pulse propagating on a vacuum or water transmission line, without any of the pulse-compression sections normally associated with large pulsed-power drivers. See E. A. Weinbrecht et al., Proc. 15th IEEE Pulsed Power Conf., 170 (2005); D. Johnson et al., Proc. 15th IEEE Pulsed Power Conf., 314 (2005); I. D. Smith et al., IEEE Trans. Plasma Sci. 28, 1653 (2000); J. J. Ramirez et al., Proc. 7th IEEE Pulsed Power Conf., 26 (1989); K. R. Lechien et al., Phys. Rev. ST Accel. Beams 11, 060401 (2009); J. R. Woodworth et al., IEEE Trans. Plasma Sci. 32, 1778 (2004); and P. Sincerny et al., Proc. 11th IEEE Pulsed Power Conf., 698 (1997). However, in order to induce a voltage pulse in a magnetically insulated vacuum transmission line with a ˜70 ns or less rise time, the inductance of the capacitors, switch, and the transmission line leading to the vacuum section of the LTD must be minimized.
Therefore, the switches required to power LTDs must be reliable and perform within precise parameters that include low inductance, low jitter, and high longevity. In particular, LTDs require gas switches that can be DC charged to ˜200 kV, triggered with ˜5-10 ns one sigma jitter, be low inductance, have very low prefire and no-fire rates, and have lifetimes of at least several thousand shots. See J. R. Woodworth et al., Phys. Rev. ST Accel. Beams 12, 060401 (2009), which is incorporated herein by reference.
Since the discharge normally occurs from one electrode to a trigger pin and then from the trigger pin to the other electrode, this switch effectively has two 0.5-cm spark gaps.
Therefore, a need remains for a high-voltage, low-inductance gas switch that can be used with LTDs and other pulsed-power systems.
The present invention is directed to a high-voltage, low-inductance gas switch, comprising a hollow housing pressurized with a gas; a pair of axially symmetric opposing high voltage electrodes spaced apart and located on a centerline within the pressurized housing; and an annular trigger ring disposed on a midplane between the opposing high voltage electrodes, wherein the surfaces of the trigger ring and the opposing high voltage electrodes are shaped to provide a uniform electric field in the gap formed therebetween. The surfaces of the high voltage electrodes can have a modified Rogowski profile and the annular trigger ring can have a double concave (de-enhanced) inner surface to provide the uniform electric field. For example, the pressurized gas can comprise dry air, nitrogen, hydrogen, or sulfur hexafluoride. The housing is preferably cylindrically symmetric about the centerline with internal threads on each end and each high voltage electrode can be mounted on an externally threaded insulating end piece that can be rotatably inserted into opposing ends of the housing, thereby enabling adjustment of the spacing of the electrodes therebetween. The annular trigger ring can be mounted on the inside wall of an insulating tubular liner and the outside wall of the tubular liner can be compressibly sealed to the inner wall of the housing when the housing is pressurized. At least one spark plug can be provided at the midplane to provide a spark to pre-ionize the pressurized gas.
The gas switch can be air-insulated, DC chargeable to 200 kilovolts or more, triggerable, have a low jitter (5 ns or less), have pre-fire and no-fire rates of no more than one in 10,000 shots, and have a lifetime of greater than 100,000 shots. Importantly, the switch also has a low inductance (less than 60 nH) and the ability to conduct currents with less than 100 ns rise times.
The detailed description will refer to the following drawings, wherein like elements are referred to by like numbers.
For reliable triggering and self-break voltage scalability, a de-enhanced (concave) gap can be used on the annular trigger ring in which a uniform field can be created to lower the total inductance. See M. E. Savage and B. S. Stoltzfus, Phys. Rev. ST Accel. Beams 12, 080401 (2009), which is incorporated herein by reference. The switch can also be made to eliminate electric field hot spots, thereby enabling it to perform better and prevent tracking of the insulator. The electric field intensity projected for the switch can be iterated to optimize the trigger ring profile for the electric fields. For example,
A switch test apparatus was constructed that uses the capacitors and brick design of an LTD.
An exemplary gas switch was tested using the test apparatus. The specifications for the gas switch tested are shown in Table 2. The tested gas switch was designed to use different gasses including hydrogen, which operates at much higher pressures. Because of this, the switch is very robust and can survive arcs in any area surrounding the switch including the failure of capacitors. Finite element analysis determined that the minimum safety factor at 250 psi was 5.43. The switch was operated at 200 psi for these tests. No leaks or mechanical failures occurred during testing.
The above data was typical up until after 50,000 shots at which point the switch started to prefire.
A summary of the test results is shown in Table 3.
The present invention has been described as a high-voltage, low-inductance gas switch. It will be understood that the above description is merely illustrative of the applications of the principles of the present invention, the scope of which is to be determined by the claims viewed in light of the specification. Other variants and modifications of the invention will be apparent to those of skill in the art.
This application claims the benefit of U.S. Provisional Application No. 61/752,259, filed Jan. 14, 2013, which is incorporated herein by reference.
This invention was made with Government support under contract no. DE-AC04-94AL85000 awarded by the U. S. Department of Energy to Sandia Corporation. The Government has certain rights in the invention.
Number | Name | Date | Kind |
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3408527 | Michel | Oct 1968 | A |
3592988 | Pucher | Jul 1971 | A |
5146141 | Rohde | Sep 1992 | A |
6026099 | Young | Feb 2000 | A |
20070205001 | Shuster | Sep 2007 | A1 |
Entry |
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J.R. Woodworth et al., Low-Inductance Gas Switches for Linear Transformer Drivers, Phys. Rev. STAB, vol. 12, 060401 (2009). |
M.E. Savage et al., High Reliability Low Jitter 80 kV Pulse Generator, Phys. Rev. STAB, vol. 12, 080401 (2009). |
Number | Date | Country | |
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61752259 | Jan 2013 | US |