Influence of the Cathode Material Properties in Reducing the Back-Bombardment Effect in Thermionic RF Gun

Abstract

Abstract-The effect of back bombardment (BB) electrons is considered one of the main obstacles for extensive use of thermionic RF guns. Ten hexaboride materials named (Ca, Sr, Ba, La, Ce, Pr, Nd, Sm, Eu, and Gd) B6 are investigated in this work to survey the effect of the cathode material on reducing BB electrons and compare them with LaB6 (which is widely used as a thermionic cathode). A numerical model was used to conduct this study. Besides the numerical calculations; an experiment has been performed to determine the work functions of CeB6 and LaB6. The results from the numerical calculations revealed that (Ba, Ca, and Nd) B6 are less affected by BB electrons: 42, 50, and 59 % respectively, compared with LaB6, for low beam current applications. In contrast, for high beam current duties, (Nd, Ce, and Sm) B6 have minimum influence by BB electrons compared with other hexaborides. The study concluded that BB electrons are strongly affected by the properties of the cathode material, especially thermionic emission and material density. Moreover, the study suggests that it is worthwhile to prepare BaB6, CaB6, NdB6, and SmB6 as cathode materials, then to subject them to a real experimental test using thermionic RF gun to compare their performance and BB effect against LaB6.

Pushing the Capture Limit of Thermionic Gun Linacs

“…BB shortens the cathode lifetime by heating it up so it is poisoned easily and degrades faster [15][16][17]. Some work has been done to reduce the BB effect by external magnetic fields [7,9]; hollow cathodes [9,12]; cooling [11]; and improvements to the cathode material [18]. These methods would add extra cost and complicate the system.…”