Abstract: A method is provided for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, the method comprising the steps of: providing at least one electron beam source emitting an electron beam for at least one of heating or fusing the powder material, where the electron beam source comprises a cathode, an anode, and a Wehnelt cup between the cathode and anode; providing a guard ring between the Wehnelt cup and the anode and in close proximity to the Wehnelt cup, where the guard ring is having an aperture which is larger than an aperture of the Wehnelt cup; protecting the cathode and/or the Wehnelt cup against vacuum arc discharge energy currents when forming the three-dimensional article by providing the guard ring with a higher negative potential than the Wehnelt cup and cathode.

Abstract: A logging tool is for determining a property of a subsurface formation having a borehole therein and includes a housing to fit within the borehole. An x-ray generator is carried by the housing and includes at least three extractor electrodes, an electron emitter to emit electrons toward the extractor electrodes, and a target downstream of the extractor electrodes. The extractor electrodes have independently selectable potentials so as to allow direction of an electron beam, formed from the electrons emitted by the electron emitter, toward different longitudinal and lateral regions of the target, the target to emit x-rays into the subsurface formation when struck by the electron beam. A radiation detector is carried by the housing to detect incoming radiation resulting from interactions between the x-rays and the subsurface formation. Processing circuitry is coupled to the radiation detector to determine the property of the subsurface formation based upon detected incoming radiation.

Abstract: A particle beam, segmented electron gun, segmented electron beam and electron collector system and method to achieve low power loss, segmented current control, and segmented energy control in electron beams, including a vacuum chamber to provide a region substantially free of background gas and allow for electron transport, an electron supply device including a segmented cathode to generate the segmented electron beam, an electrode with a grid conducting structure located in front of the segmented cathode and biased with respect to the segmented cathode in order to accelerate electrons away from the segmented cathode and control the current and energy of each electron beam segment, magnetic field production devices such as solenoidal and torroidal wire windings and permanent magnet material to produce magnetic fields to guide the segmented electron beam and to contain neutralizing-background-ions and an electron collector device including electrodes with a grid conducting structure and outer conducting shell

Abstract: A television camera tube with spurious image black-out screen is disclosed. Especially in image pick-up tubes where the electron beam, scanning a photosensitive target, is oriented by a system of electrostatic deflection, it has been observed that spurious images appear in the output video signal of the tube. These images are apparently due to a return beam that comes back from the target and strikes the accelerating electrode of the electron gun. To black out these spurious images, it is proposed to mask the accelerating electrode with a masking screen carried, in principle, to the same potential as the electrode, this screen being characterized by its rounded edges, with their convexity pointed towards the target. It is perforated with a central aperture, also provided with rounded edges.

Abstract: An ion trap for an electron beam generator consists of at least two electrically conductive elements which are in the form of a sector of a cylinder the elements being spaced apart from each other and together form a cylindrical form. Each element has end plates and a number of fins extending inwardly to the center of the cylindrical form. A recess in the form of a sector of a circle is located in each end plate and each fin adjacent to the center of the cylindrical form. These recesses form a central bore through which an electron beam from an electron gun travels, the electron beam and central bore being essentially of the same diameter. Each elements is attached to an outer envelope by an insulating element and a conductive lead is electrically connected to each element to maintain that element at a predetermined potential which deflects positive ions travelling along the beam path.

Abstract: A vacuum arc ion device having a plasma-emissive cathode and an anode, each being energized with suitable potentials, and having the further structure for eliminating micro drops of molten material which micro drops are emitted for certain materials during plasma formation.

Abstract: A flat thin display device is obtained by means of cold cathodes (10) in which each cathode provides the electron emission (14) for a (part of a) column of pixels. The emissive surface is preferably chosen to be parallel to the front and rear walls (3, 4) of the display device so that the cathodes cannot degrade due to an ion bombardment.

Abstract: Positive ions generated in a vacuum tube (1) which may detrimentally influence the electron emission of a cathode (3) are trapped by a plate (35). The plate is present in an aperture (36) in a grid (37) to which it is connected via bars (40). The aperture (36) is sufficiently large to pass the generated beam (6), while the bars (40) hardly influence the beam intensity.

Abstract: Positive ions which are generated in a vacuum tube (1) and can adversely affect the electron emission of a cathode (3) are collected for the major part by a screen grid or diaphragm (5), which forms part of a positive electron lens (4,5). In the case of a semiconductor cathode having a circular emission region (13) having a diameter larger than that of the opening in the screen grid (5), this emission region (13) is struck only by positive ions generated in a small region between the cathode (3) and a first grid (4). These ions moreover have a comparatively low energy so that the emission behavior is to only a limited extent adversely affected by sputtering by positive ions which would remove cathode material (33), such as cesium.

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 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.

Abstract: For reducing as much as possible the dimension of converging electron beams, at their point of minimum section, the invention provides in this zone an ionic charge counterbalancing the space charge of the beam, by means of an equipotential electrode disposed about this point. Said electrode is the tube in the figure. When further modulation is applied to the beam, the electrode which ensures it is placed after it in the path thereof.

Abstract: An electrostatic beam deflection system is provided for use in electron beam devices. In the present system several grids and an accelerating electrode are geometrically configured to direct positive ions away from an electron emitter surface. These positive ions are typically formed by interaction of the electrons emitted from the emitter surface with a gas ambient or with species adsorbed on the various grids and electrodes. Degradation of the electron emitter surface is thereby reduced, and the lifetime of the emitter concomitantly extended.

Abstract: An electron beam forming structure includes an anode having first and second sections spaced from each other with the first section being closest to the cathode and having a beam-admitting aperture and being connected to a positive potential and the second section having a beam-limiting aperture and being connected to ground relative to the first section. The first section will repel positive ions created in an area adjacent the beam-limiting aperture and deflect them away from the source of the electron beam so they can be collected at the second section.