Method for correcting spherical aberration of the electron beam

Details Method for correcting spherical aberration of the electron beam Method for correcting spherical aberration of the electron beam

1995-11-13

1998-02-17

Church, Craig E.

X-ray or gamma ray systems or devices

Specific application

Computerized tomography

378 10, G01N 2300

Patent

active

057199140

ABSTRACT:
In a scanning electron beam CT system, spherical aberration of the electron self-forces produces a deleterious halo around the final electron beam spot, causing loss of definition in the image rendered by the system. The spherical aberration is caused by non-uniform electron beam current density, and by non-uniform distribution of positive ions in the transition region of the beam-optical systems. The non-uniform electron beam current density depends upon the axial position of the electron gun cathode, while the transition region ion distribution depends upon the potential coupled to the washer-shaped positive ion electrode ("PIE") used to segregate the upstream and downstream portions of the electron beam. In the present invention, the beam spot halo is minimized (if not eliminated), and image definition is maximized by selecting the electron gun cathode axial position and the PIE potential such that their contributions to spherical aberrations at the final beam spot cancel.

REFERENCES:
patent: 5386445 (1995-01-01), Rand et al.

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