Electricity: measuring and testing – Determining nonelectric properties by measuring electric... – Beam of atomic particles
Reexamination Certificate
1999-05-26
2001-10-09
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
Beam of atomic particles
C324S464000, C324S466000
Reexamination Certificate
active
06300755
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the measurement of the current density distribution in electron and ion beams, particularly to a modified Faraday cup having radial slits therein to create an image of the current density of such beams, and more particularly to an enhanced modified Faraday cup utilizing two spaced slit disks, one disk having one slit wider than the other slits, and a ring to help minimize the amount of secondary electrons and ions from being produced.
Electron beams are considered to be the most precise and clean method available for welding thick sections of materials. Unfortunately, electron beams suffer one critical deficiency, namely the repeatability of focusing the beam to a known power density. Without the ability to reliably reproduce the power distribution in an electron beam, weld quality cannot be guaranteed. This problem is exacerbated by the fact the many welds are made over a period of time and with different welding operators. Further complications arise when welds are developed on one machine than transferred to a different machine for production. An electron beam diagnostic method has been developed that enables the precise characterization of the power density distribution in high power electron beams. Such diagnostic method, which utilizes a modified Faraday cup, is exemplified by U.S. Pat. No. 5,382,895, U.S. Pat. No. 5,468,966, U.S. Pat. No. 5,554,926 and U.S. Pat. No. 5,583,427. This electron beam diagnostic method has been utilized, for example, to certify changes in electron beam welders, and is further described in J. W. Elmer et al, “Tomographic Imaging of Non-Circular and Irregular Electron Beam Power Density Distributions,” Welding Journal 72 (ii), p. 493-s, 1993; A. T. Teruya et al, “A System for the Tomographic Determination of the Power Distribution in Electron Beams”, The Laser and Electron Beam in Welding, Cutting, and Surface Treatment State-of-the-Art 1991, Bakish Materials Corp., p. 125, 1991; and J. W. Elmer et al, “Beam Profile Analysis for the C&MS B231 Electron Beam Welding Machines”, LLNL UCRL-ID-127549, Jun. 12, 1997.
The present invention provides an enhancement of the modified Faraday cup (MFC) diagnostic device utilized in the above-referenced patents, and specifically provides an improvement over the MFC of above-referenced U.S. Pat. No. 5,583,427. The enhanced MFC of the present invention improves the quality of the signal that is measured by the MFC, and thus improves the accuracy of the power density distribution measurements. In the MFC of U.S. Pat. No. 5,583,427, the electron beam is oscillated around a tungsten slit disk which samples the beam. The sampled beam current is then measured with an MFC. The MFC of the patent suffers from two problems. First, a substantial percentage of the electron current passing into the Faraday cup could be transported as secondary electrons and/or ions back up to the tungsten slit disk, and therefore would not be properly accounted for. Second, with repeated use, the electrical contact between the tungsten slit disk and the copper heat sink body would degrade. Also, when measuring non-circular beams with the prior MFC, there was no method to orient the measured beam profile with respect to the welding chamber.
The present invention overcomes the above-mentioned electron capture problems by the inclusion of several significant additions to the MFC, of which includes a second slit disk located inside the Faraday cup, a ring added in the Faraday cup below the second slit disk, a beam trap added within the Faraday cup, an improved ground arrangement for the tungsten slit disk, and modifying the tungsten slit disk to orient the beam profile with respect to the welding chamber.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved tomographic determination of the power distribution in electron or ion beams.
A further object of the invention is to provide an enhanced modified Faraday cup for fast determination of the power density distribution in non-circular and irregular electron beams.
Another object of the invention is to provide an enhanced modified Faraday cup which includes a shield to eliminate the majority of secondary electrons and ions from leaving the Faraday cup.
Another object of the invention is to provide an enhanced modified Faraday cup which includes means to help minimize the amount of secondary electrons and ions produced.
Another object of the invention is to provide a modified Faraday cup with a beam trap to provide greater containment of an electron beam when the full beam current is being examined through the center hole of the modified Faraday cup.
Another object of the invention is to provide an enhanced modified Faraday cup with improved grounding of the tungsten slit disk.
Another object of the invention is to provide an enhanced modified Faraday cup, wherein the tungsten slit disk is modified to orient properly the beam profile with respect to the welding chamber.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention involves an enhanced modified Faraday cup (MFC) for fast determination of the power density distribution in non-circular and irregular electron beams. The enhanced MFC utilizes a modified refractory metal slit disk which enables proper orientation of the beam profile with respect to the welding, provides improved grounding of the refractory metal slit disk, utilizes a second slit disk made of copper, for example, and located inside the MFC, utilizes means, such as a graphite ring, below the second slit disk, and utilizes a beam trap in the MFC. Thus, the modification of the prior known MFC which utilizes a refractory metal slit disk, as made in accordance with the present invention, provides an MFC diagnostic device with improved quality of the signal that is measured by the MFC, and thus improves the accuracy of the power density distribution measurements. The enhanced MFC of the present invention may be used for quality control and diagnostic measurements on existing electron beam welding and melting equipment, as well as to assist designers of electron welding and melting equipment to produce better machines.
REFERENCES:
patent: 5483036 (1996-01-01), Giedt
patent: 5583427 (1996-12-01), Teruya et al.
patent: 53-009566 (1978-01-01), None
J.W. Elmer et al, “Fast Method for Measuring Power Density Distribution of Non-circular and Irregular Electron Beams”, Science & Technology of Welding and Joining, 1998, vol. 3, No. 2, 51-58 (month unavailable).
J.W. Elmer et al, “Tomographic Imaging of Noncircular and Irregular Electron Beam Current Density Distributions”, Welding Research Supplement, Nov. 1993, pp 493-505.
Elmer John W.
Teruya Alan T.
Brown Glenn W.
Regents of the University of California
LandOfFree
Enhanced modified faraday cup for determination of power... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Enhanced modified faraday cup for determination of power..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Enhanced modified faraday cup for determination of power... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2596916