A Simple Model for Induction Core Voltage Distributions

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In fall 2003 T. Hughes of MRC used a full EM simulation code (LSP) to show that the electric field stress distribution near the outer radius of the longitudinal gaps between the four Metglas induction cores is very nonuniform in the original design of the DARHT-2 accelerator cells. In this note we derive a simple model of the electric field distribution in the induction core region to provide physical insights into this result. The starting point in formulating our model is to recognize that the electromagnetic fields in the induction core region of the DARHT-2 accelerator cells should be accurately ... continued below

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20 pages

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Briggs, Richard J. & Fawley, William M. July 1, 2004.

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In fall 2003 T. Hughes of MRC used a full EM simulation code (LSP) to show that the electric field stress distribution near the outer radius of the longitudinal gaps between the four Metglas induction cores is very nonuniform in the original design of the DARHT-2 accelerator cells. In this note we derive a simple model of the electric field distribution in the induction core region to provide physical insights into this result. The starting point in formulating our model is to recognize that the electromagnetic fields in the induction core region of the DARHT-2 accelerator cells should be accurately represented within a quasi-static approximation because the timescale for the fields to change is much longer than the EM wave propagation time. The difficulty one faces is the fact that the electric field is a mixture of both a ''quasi-magnetostatic field'' (having a nonzero curl, with Bdot the source) and a ''quasi-electrostatic field'' (the source being electric charges on the various metal surfaces). We first discuss the EM field structure on the ''micro-scale'' of individual tape windings in Section 2. The insights from that discussion are then used to formulate a ''macroscopic'' description of the fields inside an ''equivalent homogeneous tape wound core region'' in Section 3. This formulation explicitly separates the nonlinear core magnetics from the quasi-electrostatic components of the electric field. In Section 4 a physical interpretation of the radial dependence of the electrostatic component of the electric field derived from this model is presented in terms of distributed capacitances, and the voltage distribution from gap to gap is related to various ''equivalent'' lumped capacitances. Analytic solutions of several simple multi-core cases are presented in Sections 5 and 6 to help provide physical insight into the effect of various proposed changes in the geometrical parameters of the DARHT-2 accelerator cell. Our results show that over most of the gap between adjacent cores there will be near equipartition of the voltages but there will be a region near the outer radius of each core where the voltages (and more importantly, the electric field stress) can deviate significantly from equipartition. In Section 7 we apply our results to some multicore measurements form the LBNL test stand and make some predictions for the general DARHT-2 accelerator cell configuration.

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20 pages

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INIS; OSTI as DE00827575

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  • Other Information: PBD: 1 Jul 2004

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  • Report No.: LBNL--55079
  • Grant Number: AC03-76SF00098
  • DOI: 10.2172/827575 | External Link
  • Office of Scientific & Technical Information Report Number: 827575
  • Archival Resource Key: ark:/67531/metadc780121

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  • July 1, 2004

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

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  • Sept. 21, 2017, 3:11 p.m.

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Briggs, Richard J. & Fawley, William M. A Simple Model for Induction Core Voltage Distributions, report, July 1, 2004; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc780121/: accessed June 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.