US 6,208,711 B1 · Method and apparatus for clearing ions in a scanning electron beam computed tomographic system using a single potential power source

Abstract

In a scanning electron beam CT system, a positive ion clearing electrode system is disposed within the CT system solenoid coil, and is operated from a single power source. Mounted coaxially about the electron beam, preferably the electrode system includes three sections, each having two electrode elements, one element being coupled to about −800 V to about −2 kV and the other element being grounded. Within the electrode system, the ratio between element diameter and electron beam diameter is substantially constant. Preferably elements are helically twisted about the beam axis. The electrode configuration cancels net quadrupole (focusing) and octopole (aberration-producing) fields. In the presence of electric discharge, essentially zero electron beam displacement and deflections occurs, and changes in focusing strength remain zero.

Claims20

Dependent claims

A single potential ion clearing electrode system useable with an electron beam computed tomographic scanning system including a solenoid coil coaxially mounted about an axis of said scanning system, the electrode system positioned substantially within said solenoid coil and comprising:

an array of at least three first elements, each of said first elements disposed along said axis and coaxial therewith and coupleable to a first node of an electrical power source;
and
an array of at least three second elements, each of said second elements disposed along said axis oppositely from a corresponding one of said first elements and coupleable to a second node of said electrical power source;
wherein in cross-section, each of said first elements and of said second elements define complementary arc length and have an element dimension that increases with position along said axis such that a ratio between element radius and electron beam radius is substantially constant.

1 more element

at least three first elements disposed along said axis and coaxial therewith and coupleable to a first node of an electrical power source, each of said first elements having a shape selected from a group consisting of cylindrical and conical;
at least three second elements disposed along said axis oppositely from a corresponding one of said first elements and coupleable to a second node of said electrical power source, each of said second elements having a shape corresponding to a shape of an associated one of said first elements;
wherein in cross-section, each of said first elements and of said second elements have an element dimension that increases with position along said axis such that a ratio between element radius and electron beam radius is substantially constant;
wherein said electrode system is positioned substantially within said solenoid coil.

1 more element

A method of extracting positive ions from an electron beam generated by a computed tomographic scanning system that has a solenoid coil coaxially mounted about an axis of said scanning system, while ensuring safe focusing regimes, the method comprising the following steps:

(a) disposing within a length of said solenoid coil at least three first elements along said axis and coaxial therewith, said first elements having a substantially constant ratio between element radius and electron beam radius;
(b) coupling said first elements to a single power-source generated potential whose absolute magnitude ranges from about 800 V to about 2 kV;
(c) disposing within said length of said solenoid coil at least three second elements along said axis and coaxial therewith oppositely from a corresponding one of said first elements, said second elements sized to have said substantially constant ratio between element radius and electron beam radius;
and
(d) coupling said second elements to ground.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for clearing ions in a scanning electron beam computed tomographic system using a single potential power source

Life of this patent

Method and apparatus for clearing ions in a scanning electron beam computed tomographic system using a single potential power source

Life of this patent

Abstract

Claims20