A major extension of the capabilities of nonvacuum electron-beam welding follows from the development of a machine with higher beam power. Tests with a new atmospheric electron gun operating at 60 kW have shown that the advantages of nonvacuum electron-beam welding must be reevaluated. Gas heating produced by the beam itself becomes very pronounced, so that electron scattering is reduced causing the high-power density of the beam to be retained over larger working distances. Single-pass butt welds with a depth-to-width ratio of 4 : 1 can be made in 3.8-cm-thick steel at a speed of 0.77 cm/sec, while the ultimate welding depth exceeds 5 cm. Medium thick material, e.g., 1.3-cm steel, can be welded at a 5-cm work distance, with a depth-to-width ratio of 3 : 1. The large work distance permits access to more complex structures and interior corners such at T sections, which can now be fabricated from a plate, 1.3 cm thick, at a speed of 2–3 cm/sec, making a full through weld from one side. Also, seam welds of two 3-mm-thick hot-rolled steel sheets can be produced at speeds of up to 15 cm/sec. High-power machines need not be significantly larger or costlier than low-power guns, and the present 60 kW does not represent any technical limit. Welding efficiency improves with higher power; when welding steel of 2 cm thickness or more the energy efficiency of the process at 60 kW is better than 50%, while at 40 kW it is merely 30%. In addition, the high power permits greater welding speed. These developments translate directly into improved cost justification for electron-beam welding and a broad expansion of its possible applications.
The Westinghouse team has extended the Lawrence Livermore National Laboratory advanced conceptual design for the TPX PF magnets through preliminary design. This is the first time superconducting PF magnets have been designed for application in a tokamak. Particular challenges were encountered and solved in developing the coil insulation system, welding the helium stubs, and winding the coil. We fabricated a coil using copper stranded CIC conductor, to surface manufacturability issues and demonstrate our solutions.In the paragraphs that follow, we describe aspects of the PF magnet system preliminary design, and discuss our solutions to some of the most challenging aspects of the preliminary design.
The absolute iC-photoionization cross section of helium has been measured in the region extending from 100 to 250 A to a precision of 5% or better. Above 250 A, where the present results overlap with earlier work performed in this laboratory, there is satisfactory agreement and the data have been combined so as to extend the range of measurements by about 8 Ry above the ionization threshold. It has been possible to join these results with a previous observation made at a higher energy (20.3 Ry) so that helium is the only gas other than Ne for which the cross section is known over a large energy range with comparable precision. This information, combined with the outcome of theoretical calculations and with estimates of discrete oscillator strengths, has led to the evaluation of four sum rules. The calculations attest to the reliability of the observations.
To study second harmonic generation in nonlinear crystals it is important to have a versatile laser driver which can produce high -power variable pulse widths at a single frequency which is adjustable over both the 9 pm and 10 /im laser bands. To satisfy these requirements, a nominal 5 J UV-preionized self -sustained discharge TEA laser has been designed to give 100 ns 9.6 /sm pulses at 2 Hz. The laser is a line -tunable oscillator -amplifier design with CO2 pulse width which is adjustable from "3 to 250 ns.
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