Abstract:
The charged-particle beam system includes a non-axisymmetric diode forms a non-axisymmetric beam having an elliptic cross-section. A focusing element utilizes a magnetic field for focusing and transporting the non-axisymmetric beam, wherein the non-axisymmetric beam is approximately matched with the channel of the focusing element.
Abstract:
A means is provided for compensating for spherical aberration in charged particle beam devices. The means includes a sextupole (22) positioned between two focusing lenses (18, 24).
Abstract:
A variable spot size x-ray tube comprises a cathode having an electron emitting surface providing an electron beam that travels essentially along the tube axis of symmetry to an anode. The anode, spaced from the cathode, includes a target, the front surface of which is disposed at an oblique angle with respect to the axis of symmetry. The potential of the anode is generally positive with respect to that of the cathode. The cathode is heated to a temperature at which electrons are emitted by the thermionic emission process. Current from the cathode can be controlled by varying the cathode temperature if the cathode is operated in the temperature limited region. The incident electron beam forms a spot on the target surface (38) whereupon x-rays are produced in response to impingement of the electron beam on the target. The x-rays propagate outwardly from the target spot through a vacuum window (42) to form a beam of x-radiation outside the x-ray tube. An aperture grid (18) is disposed between the cathode and the anode, and has a central aperture permitting the electron beam to pass therethrough. The aperture grid further has a variable voltage applied to it which may be positive, negative, or equal to the potential of the cathode. The voltage on the control grid is used to control the diameter of the electron beam which impinges upon the target. Specifically, the electron beam diameter varies in correspondence with the variable aperture grid voltage, and selective variation of the electron beam diameter results in a corresponding variation in size of the x-ray imaging spot.
Abstract:
An electron beam device (10) has a cathode (34) that generates a fan-shaped electron beam. A first focusing lens (44, 46, 48, 50) includes first (48) and second (50) plates on opposed sides of a filament. The edges of the plates closest to a positively charged anode (20) are arcuate, so that as individual electrons are accelerated normal to the edge of the charged plates, the beam (60) increases in length with departure from the filament. A second focusing lens includes third (44) and fourth (46) plates on opposed sides of the first focusing lens. Each of the third and fourth plates has an arcuate edge proximate to the positively charged anode. The plates of the first and second focusing lenses provide focusing in a widthwise direction, while defining the increase in the lengthwise direction. The curvature of the plates of the first focusing lens defines a common radius with the plates of the second focusing lens.