Design and evaluation of the XBT diode

This paper describes the design and experimental results achieved with the 440 kV, microperveance 1.9, XBT (X-band Beam Tester) diode. The Pierce gun was developed for the 100 MW X-band klystron; the high power RF source to be used on the NLC (Next Linear Collider). The gun is electrostatically focused (no magnetic compression) to a beam diameter of 6.35 mm, with an area convergence of 110:1. Maximum cathode loading is approximately 25 A/cm², with a beam power density of 770 MW/cm². The measured beam current was within 2% of the value predicted by simulation with egun. Transmission through the highly instrumented beam tester was 99.98%. Some novel techniques were used to achieve near perfect beam transmission, which include the use of a reentrant-floating input pole piece.