Diagnostic measurements on explosive emission cathodes operating at high current densities and UHV pressures

C. Lynnx, J. Walter, A. Neuber, M. Kristiansen

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Scopus citations

Abstract

Vacuum diodes utilizing explosive emission cathodes generally suffer from non-uniform emission, gap closure by anode and cathode plasma expansion, and outgassing. Also, the Child-Langmuir relation does not apply at the edge of the emission area. This results in a high current density sheath at the edge of the emission area. Each of these phenomena presents its own technical challenge in HPM source design and optimization. Diagnostic techniques and particle in cell simulations for a vacuum diode, to be operated as a greater than 100 MW class vircator, have been used in order to compare the characteristics of the electron beam produced by various cathode materials and geometries. Uniform current density plays a key role in vircator performance and efficiency, as well as in the lifetime of the diode. The diode under investigation has an emission area of 20.3 cm 2, and operates at a current density on the order of 300 A/cm 2 at 200 kV. The background vacuum level and the associated adsorbed and absorbed gases at the surface play a major role in the behavior of an explosive emission cathode. This vircator source is operated as a sealed tube, requiring no vacuum pumping until the device is repetitively operated. The small amount of gas generated during operation is pumped down in between shots, if needed, utilizing an integrated small sputter-ion pump. The background pressure in the diode is in the ultra-high vacuum (UHV) range, on the order of 10 -9 Torr to 10 -8 Torr. Particle in cell simulations were performed to investigate current density distributions at the surface of both the anode and cathode due to various field shaping profiles. Additionally, scintillator images were taken to compare the beam profile of a machined aluminum cathode with a CsI coated carbon fiber cathode.

Original languageEnglish
Title of host publicationIEEE Conference Record - PPC 2011, Pulsed Power Conference 2011
Subtitle of host publicationThe 18th IEEE International Pulsed Power Conference
Pages1142-1145
Number of pages4
DOIs
StatePublished - 2011
Event18th IEEE International Pulsed Power Conference, PPC 2011 - Chicago, IL, United States
Duration: Jun 19 2011Jun 23 2011

Publication series

NameDigest of Technical Papers-IEEE International Pulsed Power Conference

Conference

Conference18th IEEE International Pulsed Power Conference, PPC 2011
CountryUnited States
CityChicago, IL
Period06/19/1106/23/11

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