Abstract: Tuning, integrating, and operating an electron beam CT scanning system is simplified by using the fringe field from dipole magnets arranged as a chicane to focus the electron beam, thus replacing conventional quadrupole and solenoid coils. Preferably four "chicane" dipole magnets are series-coupled with the windings in the downstream deflection magnet, such that the chicane magnet X and Y coils are energized 90.degree. out of phase with the deflection magnet coils. The alternating current polarity in the chicane magnets creates an "S"-shaped electron beam trajectory that adequately uniformly focuses over the full cross-section of the electron beam. Winding the coils with a cosine distribution permits rotating the magnetic fields to change the azimuthal and deflecting planes of the electron beam, without disturbing the deflection angle and focusing properties.

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.

Abstract: A scanning electron beam CT system generates an electron beam along a beam source axis offset from the scanner axis, or axis of symmetry, thereby permitting the X-ray subject to pass completely through the stationary gantry. The electron beam is produced with the first drift tube region of an evacuated housing chamber, and is directed downstream toward a second region that includes a gantry. A scan target and a tuning target, each concentric with and defining a plane normal to the system axis of symmetry, are located in the gantry. A beam optics system, through which the electron beam passes, is located within the housing intermediate the electron gun and gantry. A control system focusses and scans the electron beam upon the scan target, maintaining a beam spot of desired quality. Upon impingement by the scanning beam spot, the scan target emits a fan beam of X-rays.

Abstract: An x-ray collimator is described which is useful in an electron beam (EB) computed tomography (CT) scanner of the type in which a rotating electron beam is directed to impinge upon a ring-shaped target and the x-rays generated in response thereto are directed to a ring shaped detector array spaced therefrom. The collimator consists of an x-ray blocking septum having an aperture therein, the septum being located in a fixed position substantially co-planer with the planes of the target and the detector, so as to block all x-rays directed from said target to said detector except those which pass through said aperture. Tomographic slice width is determined by the "view" from the spot where the electron beam impinges upon the target, through the aperture, to the detector, and is variable by adjusting the position where the electron beam impinges upon the width of the x-ray target, and in a preferred embodiment, the position of a movable ring.

Abstract: In a scanning electron beam CT system, the electron beam is focused by controlling the distribution of beam-generated ions electrostatically. The upstream (self-expanding, de-focusing) beam region and downstream (converging, self-focusing) beam region are distinguished by the absence or presence of beam-generated positive ions. The relative lengths of these two beam regions are electrostatically controlled such that beam de-focusing in the upstream region compensates for beam self-focusing in the downstream region. In this fashion, essentially zero external focusing strength is required, and the magnetic focus coil used in the prior art is eliminated. Located downstream from the electron gun, a positive ion electrode ("PIE") determines the position of the boundary between the two regions, and thus the relative length of each region. The PIE is a disk-like electrode, mounted coaxially to the beam optic axis within the drift tube, and coupled to a large positive potential.

Abstract: An electron beam scanning system producing an electron beam in a relatively short chamber includes an ion controlling electrode assembly located between the electron gun and system beam optics. The assembly includes a somewhat cone-shaped rotating field ion controlling electrode ("RICE") unit disposed between first and second ion controlling electrode units ("ICE"s). The RICE and ICEs each comprise element pairs symmetrically disposed on opposite sides of the chamber Z-axis, preferably forming regular polygons in cross-section. Preferably corresponding elements in each ICE are electrically coupled to each other and to an opposite element in the RICE. Preferably equal and opposite bias potentials, with respect to an average potential, are coupled to the RICE and ICE elements comprising an element pair. Because it is somewhat cone-shaped, the RICE and electron beam create a transverse electric field with no axial component.

Abstract: A scanning electron beam computed tomography scanner is disclosed herein and includes means defining a vacuum chamber, means for producing an electron beam at one location in the chamber and for directing it to a second location therein, a target located at a third position therein of the type which produces X-rays as a result of the impingement thereon by the electron beam, means for focusing the beam onto the target in the form of a beam spot and for scanning the beam spot across the target along a particular scan path in order to produce X-rays, and means for monitoring the profile, position, and orientation of the beam spot at a plurality of locations along the scan path. The specific scanner disclosed also includes an arrangement for determining from the signals produced by the monitoring devices if the beam spot conforms to as desired profile, position, and orientation and automatically adjusting the electron beam such that its profile, position, and orientation conform to desired values.

Abstract: An electron beam scanning system employing a relatively short housing chamber wherein an electron beam is produced includes an ion controlling electrode assembly. Located in the housing between the electron gun and system beam optics, the assembly includes a generally cone-shaped rotating field ion controlling electrode (or "RICE") unit comprising cylindrically symmetrical element pairs disposed on opposite sides of the housing Z-axis. Preferably equal and opposite potential sources coupled to elements comprising an element pair create a transverse electric field therebetween. The vector sum of the fields produced by all element pairs is the transverse field created by the RICE unit. The potentials are varied, rotating the overall RICE field to controllably remove most but not all positive ions. The remaining ions improve the electron beam space-charge density, resulting in a sharply focused scanning electron beam.

Abstract: A rotating x-ray tube includes an electron-beam accelerator assembly having an indirectly heated cathode structure. The cathode structure includes an electron-emitting region mounted at the center of a rotationally symmetric Pierce-cathode configuration. An electron beam travels along a selected path as the tube rotates so that the electron beam strikes selected portions of a target mounted within the tube as it rotates. Two magnetic coils and a ferromagnetic mirror plate are arranged to function as a single quadrupole electromagnet, which has its axis parallel to and offset from the electron beam and which elongates the electron beam in a radial direction.

Abstract: X-ray tube includes a rotatable envelope in which is mounted an electron gun at one end and a target anode at the other end. A fixed means for deflecting the electron beam from the electron gun is provided to deflect the electron beam on a fixed path as the envelope of the x-ray tube rotates about an axis. The electron beam being confined to a fixed path results in the electron beam striking various positions of the target anode to provide for improved heat dissipation. The electron beam is deflected along the fixed path using magnetic deflection means including magnetic deflection coils positioned external of the envelope to provide a deflection field transverse to the electron beam. The target anode is cooled by directing a cooling fluid on an external side of the target anode.

Abstract: A deflecting magnet assembly for scanning an incident beam of charged particles in a scanning electron beam computed tomography scanner. The configuration (including angular orientation and coil end connection geometry) of the coils which comprise the magnet is selected to approximate the field of a pure dipole. In addition, a magnetic shield is used which equalizes the effective radii of the constituent coils and thereby simplifies construction of the assembly.

Abstract: A scanning beam computed tomography scanner is disclosed herein and includes means defining a vacuum chamber, means for producing an electron beam at one location in the chamber and for directing it to a second location therein, a target of the type which produces X-rays as a result of the impingement thereon by the electron beam, and means for focusing the beam onto the target in the form of a beam spot and for scanning the beam spot across the target along a particular scan path in order to produce X-rays. The specific scanner disclosed also includes an arrangement for monitoring the profile, position and orientation of the beam spot at a plurality of different points along the scan path.

Abstract: An improved ion clearing electrode assembly for use in an electron beam production and control assembly which is especially suitable for use in a scanning electron beam computed tomography X-ray scanning system. The assembly uses a vacuum sealed housing chamber which is evacuated of internal gases and in which the electron beam is generated and propagated. Normally residual gas within the chamber interacts with the electrons of the beam to produce positive ions which have the affect of neutralizing the space charge of the electron beam and thereby causing focusing difficulties and destabilization of the beam. The ion collecting electrodes herein are an improvement of those disclosed in the co-pending Rand U.S. patent application Ser. No. 434,252, now U.S. Pat. No. 4,521,900. The electrodes are designed to extract the ions and reduce their neutralizing effect while maintaining a precisely uniform electric field and therefore beam optical aberrations are minimized.

Abstract: An electron gun which can be easily disassembled to replace a defective cathode assembly and which can be easily and quickly reassembled and realigned.

Abstract: A scanning electron beam computed tomography scanner is disclosed herein and includes means defining a vacuum chamber, means for producing an electron beam at a first location in the chamber and for directing the beam to a second location therein along a particular desired path. A target of a type which produces X-rays as a result of the impingement thereon by the electron beam is positioned at a third location and means at the second location are provided to cause the beam to impinge on the target in a scanning fashion for producing X-rays. The scanner also includes a system for maintaining the electron beam on the desired path between the first and second locations. To this end, the system includes first means acting on the beam between these locations so as to detect for deviations, if any, between the actual path taken by the beam and the desired path and means responsive to these deviations, again if any, for adjusting the position of the electron beam in order to eliminate the deviations.

Abstract: An electron beam production and control assembly especially suitable for use in producing X-rays in a computed tomography X-ray scanning system is disclosed herein. In this system, an electron beam is ultimately directed onto an X-ray producing target in a converging manner using electromagnetic components to accomplish this. The system also includes an arrangement for neutralizing the converging beam in a controlled manner sufficient to cause it to converge to a greater extent than it otherwise would in the absence of controlled neutralization, whereby to provide ion aided focusing.

Abstract: An electron beam production and control assembly especially suitable for use in producing X-rays in a computed tomography (CT) X-ray scanning system is disclosed herein along with its method of operation. This assembly produces its electron beam within a vacuum-sealed housing chamber which is evacuated of internal gases, except inevitably for small amounts of residual gas. The electron beam is produced by suitable means within the chamber and directed along a path therethrough from the chamber's rearwardmost end to its forwardmost end whereby to impinge on a suitable target for producing the necessary X-rays. Since there is residual gas within the chamber, the electrons of the beam will interact with it and thereby produce positive ions which have the effect of neutralizing the space charge of the electron beam.