A NEW CROWBAR SYSTEM FOR THE PROTECTION OF HIGH POWER GRIDDED TUBES AND MICROWAVE DEVICES

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As part of the electron cyclotron heating (ECH) facility upgrade at the DIII-D National Fusion Facility, two 8.4 MW modulator/regulator power systems were designed and constructed (Ref. 1). Each power system uses a high power tetrode to modulate and regulate the cathode voltage for two 1 MW-class 110 GHz gyrotrons (Ref. 2). A critical element in the power system is the fault energy divertor, or crowbar switch, that protects the tetrode and the gyrotrons in the event of an arc fault. Traditionally, mercury filled ignitron switches are used for this application, but it was desired to eliminate hazardous materials and ... continued below

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Pronko, S. G. E. & Harris, T. E. April 2001.

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As part of the electron cyclotron heating (ECH) facility upgrade at the DIII-D National Fusion Facility, two 8.4 MW modulator/regulator power systems were designed and constructed (Ref. 1). Each power system uses a high power tetrode to modulate and regulate the cathode voltage for two 1 MW-class 110 GHz gyrotrons (Ref. 2). A critical element in the power system is the fault energy divertor, or crowbar switch, that protects the tetrode and the gyrotrons in the event of an arc fault. Traditionally, mercury filled ignitron switches are used for this application, but it was desired to eliminate hazardous materials and improve overall switching performance. The new crowbar switch system was required to meet the following requirements: Operating voltage: -105 kVdc; Peak current (750 ms e-fold): 1.6 kA; Follow-on current: <1 kA (25 ms); Charge transfer per shot: <15 Cb; and Turn-on time: <1 {micro}s. The switch that was chosen for the new design is a low pressure deuterium filled device, called a metal-arc thyratron, manufactured by Marconi Applied Technologies (Ref. 3). In addition to the new crowbar switch assembly, improved fault signal processing circuitry was developed. This new circuitry uses fiber-optics for signal and trigger transmission and a complex programmable logic device for high speed signal and logic processing. Two generations of metal-arc thyratrons have been commissioned in the two ECH power systems constructed at DIII-D. In the first, the crowbar system performed extremely well, meeting all of the operating requirements and demonstrating its ability to protect a 36 gauge copper wire from fusing (energy let-through <10 J). However, after accumulating over 500 shots, the metal-arc thyratrons lost their ability to reliably hold-off voltage. This problem was solved by Marconi with a design modification of the thyratron electrodes. The second generation tubes were installed in the second ECH power system. The crowbar system was fully commissioned and all of the performance requirements were satisfactorily achieved. The design of the crowbar switch and the fault signal processing system and their performance will be presented in this paper.

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Medium: X; Size: 9 pages

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Oakland Operations Office, Oakland, CA (US); INIS

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  • 2nd IEEE International Vacuum Electronics Conference, Noordwijk (NL), 04/02/2001--04/04/2001; Other Information: This is a preprint of a paper to be presented at the 2nd IEEE International Vacuum Electronics Conference, Noordwijk, The Netherlands, April 2-4, 2001 and to be published in the Proceedings.

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  • Report No.: NONE
  • Grant Number: AC03-99ER54463
  • Office of Scientific & Technical Information Report Number: 806774
  • Archival Resource Key: ark:/67531/metadc734093

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • April 2001

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  • Oct. 18, 2015, 6:40 p.m.

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  • April 19, 2016, 12:48 p.m.

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Pronko, S. G. E. & Harris, T. E. A NEW CROWBAR SYSTEM FOR THE PROTECTION OF HIGH POWER GRIDDED TUBES AND MICROWAVE DEVICES, article, April 2001; United States. (digital.library.unt.edu/ark:/67531/metadc734093/: accessed June 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.