The effect of drift length, beam radius, and perveance on klystron power conversion efficiency

Abstract

Current bunching calculations based on the disk electron model are used to determine the effect of drift length, beam radius, and beam perveance on the power conversion efficiency of a two-cavity klystron. In a 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> perveance klystron, a loss in power output exceeding one decibel results when a drift length shorter than 0.08λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</inf> is used. Power conversion efficiency is found to be reduced by 5 to 10 points in beams where normalized beam radius <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\gamma b</tex> lies in the range from 0.3 to 0.1. The loss of efficiency due to perveance in an optimum klystron design is found to be given approximately by the expression <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Delta_{\eta}=0.0606 \sqrt {\mu}{P}</tex> , where Δ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</inf> is expressed in percentage points, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu P</tex> is the microperveance of the beam. In a 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> perveance beam, the power conversion efficiency is reduced by ten percentage points from its ballistic value of 58.2 percent, indicating that previously published work is in error by a factor of two.