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Ein Aluminiummatrixverbundwerkstoff (AMC), der aus einer mit 25 Vol.-% SiC Partikeln verstarkten AA2124 Matrix bestand, wurde in Extrusionsrichtung zu artgleichen AMC+AMC und artverschiedenen AMC+2024-T3 Verbindungen reibruhrgeschweist. Wenn das partikelverstarkte Aluminium bei artverschiedenen Verbindungen auf der „retreating side“ positioniert wurde, war der Materialaustausch weniger intensiv. Aufgrund eines Verhakungseffekts waren Festigkeit und Duktilitat trotzdem hoher als bei der umgekehrten Anordnung der Fugepartner. Das Verhalten bei monotoner und zyklischer Belastung wurde sowohl fur den partikelverstarkten Grundwerkstoff als auch fur die Schweisverbindungen von einer ausgepragten Richtungsabhangigkeit bestimmt. Ursache ist die Orientierung von SiC-Partikelzeilen in Extrusionsrichtung. Bei artverschiedenen Verbindungen sind die longitudinalen Zugeigenspannungen auf der partikelverstarkten Seite der Schweisnaht geringer als auf der Seite des unverstarkten Materials, was wahrscheinlich mit der Ausbildung von SiC-Partikelclustern an der Grenzflache zwischen den beiden Materialien zusammenhangt. Die fur artgleiche Verbindungen ermittelten da/dN-ΔK Kurven wurden mit den gemessenen Eigenspannungen korreliert.

The influence of sintering temperature on the pore morphology, microstructure, and fatigue behaviour of a MoNiCu alloy is presented. Besides pore area, shape factors for bulkiness, elongation, and roughness of the pores were determined. Energy dispersive spectroscopy X-ray analyses were used to examine the distribution of alloying elements in the bulk of the material. Cyclic stress-strain, cyclic stress-temperature, and cyclic stress-electrical resistance responses were studied simultaneously to obtain a more comprehensive description of the fatigue behaviour. With increasing sintering temperature the pores are larger and more regular and, owing to a more homogeneous distribution of alloying elements, the solid solution hardening is more pronounced. Nevertheless, there is only a slight increase in the endurance limit. The higher sintering temperature leads to lower plastic strain amplitudes, temperature, and electrical resistance changes. This corresponds to less pronounced slip features at a low...

—The influence of sintering temperature on the fatigue behaviour of a NiCuMo alloy was determined. It is common practice to characterize the cyclic deformation behaviour by means of plastic strain amplitudes. For sintered materials the quantity of the plastic strain amplitudes is influenced by microstructural changes as well as crack opening and crack growth effects and does not allow any distinction between these mechanisms. In the present work cyclic stress-strain, cyclic stress-temperature and cyclic stress-electrical resistance measurements were studied simultaneously to get a more comprehensive description of the fatigue behaviour of sintered steels. The temperature is essentially sensitive to the work of plastic deformation during cyclic loading. The electrical resistance responds to microstructural changes, e.g. dislocation rearrangements and void formation as well as to crack initiation and propagation. Beyond that it is shown that continuous stress-increase tests are a suitable short term testing method to determine cyclic stress-strain curves which are in a very good agreement with those from single step tests.

We make use of the generation‐regeneration or “light shining through a wall” technique in searches for optical‐wavelength photons mixing with hypothetical hidden‐sector paraphotons in the mass range between 10−5 and 10−2 electron volts for a mixing parameter greater than 10−7 and in sensitive searches for scalar and pseudoscalar coupling of photons to light neutral bosons in the mass range of approximately 1.0 milli‐electron volts and coupling strength greater than 10−6 GeV−1. Additionally, there is an effort underway to use photons in the microwave region using this same technique to make a more sensitive measurement in the mass range of approximately 0.1 milli‐electron volts. The equipment in the latter effort will be used to search for galactic halo axions in this same mass range.

DC high voltage photoemission electron guns with GaAs photocathodes have been used to produce polarized electron beams for nuclear physics experiments for about 3 decades with great success. In the late 1990s, Jefferson Lab adopted this gun technology for a free electron laser (FEL), but to assist with high bunch charge operation, considerably higher bias voltage is required compared to the photoguns used at the Jefferson Lab Continuous Electron Beam Accelerator Facility. The FEL gun has been conditioned above 400 kV several times, albeit encountering non‐trivial challenges with ceramic insulators and field emission from electrodes. Recently, high voltage processing with krypton gas was employed to process very stubborn field emitters. This work presents a summary of the high voltage techniques used to high voltage condition the Jefferson Lab FEL photoemission gun.

PM1000 is an oxide dispersion strengthened (ODS) nickel based superalloy with applications in the aerospace and glass processing industries. It contains about 0.6 weight percent of incoherent finely dispersed yttria particles. Earlier work has addressed the high- temperature isothermal low-cycle fatigue (LCF) [1, 2], creep [3] and oxidation [4] behaviour of PM1000. However, no known work has been done to characterize the thermomechanical fatigue (TMF) performance of this superalloy. The present work therefore involved a study of the high-temperature cyclic stress-strain response of PM1000 under isothermal fatigue (IF) and TMF loading conditions. Both IF and TMF tests were conducted in the temperature range from 450 to 950°C, with mechanical strain amplitudes varying from 0.35 to 0.5% in laboratory air conditions. The maximum mechanical strain and maximum temperature occurs simultaneously in in-phase (IP) TMF, while out-of-phase (OP) TMF has the maximum strain coinciding with minimum temperature.

Jefferson Lab is in the process of building an upgrade to our Free-Electron Laser Facility with broad wavelength range and timing flexibility. The facility will have two cw free-electron lasers, one in the infrared operating from 1 to 14 microns and one in the infrared operating from 0.25 to 1 micron [1]. In addition, there will be beamlines for Thompson-backscattered femtosecond X-rays, and broadband THz radiation. The average power levels for each of these devices will exceed any other available sources by at least 2 orders of magnitude. Timing of the available laser pulses can be continuously mode-locked at least 4 different (MHz) repetition rates or in macropulse mode with pulses of a few microseconds in duration with a repetition rate of many kHz. The status of the construction of this facility and a review of its capabilities will be presented.

An important technique used for the suppression of surface flashover on high voltage DC ceramic insulators as well as for RF windows is that of providing some surface conduction to bleed off accumulated surface charge. We have used metal ion implantation to modify the surface of high voltage ceramic vacuum insulators to provide a uniform surface resistivity of approximately 5/spl times/10/sup 10/ /spl Omega//square. A vacuum arc ion source based implanter was used to implant Pt at an energy of about 135 keV to doses of up to more than 5/spl times/10/sup 16/ ions/cm/sup 2/ into small ceramic test coupons and also into the inside surface of several ceramic accelerator columns 25 cm I.D. by 28 cm long. Here we describe the experimental set-up used to do the ion implantation and summarize the results of our exploratory work on implantation into test coupons as well as the implantations of the actual ceramic columns.

During the last few months, several full size prototype dipole magnets for the Fermilab Energy Doubler were successfully tested. This was the result of several concurrent programs in conductor development as well as magnet construction, production, and testing. The present magnets have achieved their design goal. Progress to this point has solved many pitfalls. A description is given of the present technology as well as some of the decisions that led to the present design.

The design and fabrication of the cavity enclosure and calculation to support the 2°K operating temperature, and techniques for minimizing operating heat loads and cryostat loads are discussed: The integrating of the cryogen fluid distribution system into the cavity cryostat will be presented. Integration of the cavity design into cavity fabrication and maintenance program, with emphasis on system reliability and flexibility, is included.

A thermally optimized input waveguide for the CEBAF Superconducting Linac Cavity, to operate at 2.0K, has been designed. Calculations leading to thermal optimization including conduction, specularly reflected radiation and RF power dissipation are presented. An economic comparison between a thermal intercept and continuous counter flow cooling has been made. Calculations and techniques for reducing specularly reflected radiation are discussed.

The task is to measure the center line of the beam detector with respect to the magnetic centerline with a precision of +-0.2 mm; the measurement must be made on 250 magnets (they come in 6 lengths, from 25'' to 99'') by a technician. Optical, mechanical, and electrical techniques for carrying out this procedure were considered. An RF device operating at 53 MHZ was adopted for the following reasons: (a) it provides complete electrical checkout of the hardware at operating frequency, including the bidirectional operation of the pickup, (b) no mechanical contact with the strip lines is required, and (c) the demands of production measurements and maintenance of calibration are better matched to the skills of an average technician. We describe the conceptual design, fabrication, and performance of this device.

A special type of cryogenic current lead is described and its thermal evaluation is presented. This high voltage insulated lead was designed for heavy electrical conduction only during the quench of a superconducting magnet and for minimal heat leak.

A lithium lens focusing device will be used for the collection of 8 GeV antiprotons in the Fermilab Tevatron I Project. The details of the mechanical and electrical design of the Fermilab lens and its associated toroidal transformer are discussed. The lens, with a radius of 1 cm and length 15 cm, is expected to achieve gradients of 1000 T/m for a focal distance of 0.225 m. The gradient requires a current on the order of 5x105A, resulting in large electromagnetic and thermal stresses. The power supply discharge current and the effect of the inductance of the power leads and connections are minimized by the use of a toroidal matching transformer surrounding the lens itself.

The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.

This paper describes the support design, and mass production engineering of the Energy Doubler Dipole Cryostats. The coils, which are surrounded by a warm iron yoke, must be supported against high magnetic forces resulting from errors in the concentricity between the coil and iron yoke. The whole support system must be further contained within a one inch radial distance. The support system developed to meet these criteria which is a combination of heat-sunk G-11 blocks, meets the requirement of total helium heat leak of 5W per magnet. Data will be presented on both mechanical and thermal performance. The unique quality assurance system used by both industrial and Fermilab fabricators will be discussed.

A prototpye Lithium Lens to be used for the collection of antiprotons in the Fermilab Tevatron I project has been constructed. Some of the fabrication details, the procedure for lithium filling and the results of the initial operation are discussed.

The feasibility of using superconducting magnets in the beam interaction regions of particle accelerators is discussed. These higher field magnets can be shorter, leaving more room for detectors, but also must have a large aperture and magnetic shielding. The ''kissing geometry'' was investigated, and design and scaling considerations are given. A rough estimate of the cost of such superconducting magnets is given as an aid to the selection of interaction geometry. (PMA)

International audience; In this paper, an unified elasto-viscoplastic behaviour model based on internal states variables, is investigated in order to describe the thermo-mechanical stress-strain fatigue response of tempered martensitic steels. This model includes an isotropic part (drag stress) describing the cyclic softening of martensitic steels. The memory effect is introduced to take into account the influence of the plastic strain range on the amount of the cyclic softening. The kinematic part (back stress) of the model allows the description of complex load conditions to which tool steels are subjected. Thus, strain recovery (Baushinger effect) and time recovery terms (cyclic behaviour including tensile and compressive dwell time and ratcheting) are considered. Moreover, the identification methodology of the model parameters from only two sets of experimental data is presented; the coefficients of the kinematic and isotropic parts are determined successively. The main difficulty consists in reaching a good description both of the cyclic behaviour for different strain rates and the ratcheting effect.