Optimization of the operating condition of the accelerating tube for the high voltage electron microscope equipped with the field emission gun

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 363; no. 1; pp. 291 - 294
• Main Authors: Morita, Chiaki, Ohye, Toshimi, Shimoyama, Hiroshi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-09-1995
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/0168-9002(95)00263-4

Numerical calculations have been conducted on the electron optical characteristics of the accelerating tube (AT) for the high voltage electron microscope (HVEM) equipped with the field emission gun (FEG). The emitted electrons are firstly accelerated to
V
0 by the FEG and finally to
V
a by the AT which consists of 34 stages of accelerating electrodes with an inner diameter of 33 mm and has an overall length of 1423 mm. The AT is treated as a thick electrostatic accelerating lens. Several electron optical problems arising from a combination of the AT with the FEG are studied. In order to reduce an unfavorable aberration effect of the AT-lens, the beam crossover must be brought to a position near the entrance plane of the AT. This can be done by a transfer lens which is placed between the FEG and the AT. The introduction of a partial retarding field in the AT is also very effective for a flexible operation of the FEG system without serious aberration effects of the AT-lens.