Electron Beam Analyzer Using a Piezoelectric Scanner

Abstract

The electron beam analyzer reported here is intended to investigate the current density distribution of a high current-density electron beam for use with a klystron or a traveling-wave tube. A pair of piezo-electric elements of barium titanate ceramic is used to drive a vibrating, pinholed target for the purpose of sampling the beam to be investigated. This enables direct observation of the current density distribution on a cathode ray oscilloscope screen at any part of the electron beam under investigation, including the part very close to the anode aperture of the electron gun. This is one of the most important parts in our present investigation and yet it is inherently impossible to observe the entire picture of the distribution in this vicinity when a conventional method as, for example, that described by Ashkin is used. Both PPI and A presentations are possible. Only qualitative measurements can be made by the former type of presentation which, however, is indispensable for the purpose of observing the entire picture of the distribution at a glance. The latter, on the other hand, is suitable for quantitative measurements of the distribution along a straight line on a cross section of the beam. The analyzer is so designed and built that either one of these two types of presentation can be selected simply by turning a switch for rapid and accurate measurements. Utmost care is paid in the design and construction of the vacuum and mechanical systems as well as of the associated electrical circuitry with the intention of assuring satisfactory over-all performance and for the convenience of the experimenters. As the result, for example, the pressure in the useful part of the vacuum chamber, with all the complications of the entire setup, could be made to as low as 10−6∼10−7 mm Hg under typical operating conditions. The merits and demerits of the new analyzer are fully discussed with particular reference to the resolving power of the observed pattern. Possible causes of errors which might be introduced to the observed results are also considered.