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The ITER pre-compression ring system is based on two sets of 3 rings made in fibreglass-epoxy composite and is located on top and bottom of the inner straight leg region. These rings will provide a radial force of about 70 MN/coil (35 MN at the top and 35 MN at the bottom) under cryogenic conditions, pulling the TF coils into contact, reducing the gap between the poloidal shear keys and their keyways during operation and also reducing the toroidal tension in the four outer intercoil structures bands. The paper describes the stress relaxation test performed in ENEA Frascati laboratories on a reduced scale glass fibre-epoxy composite ring. The ring was manufactured with a diameter of 1 m (1/5 of the real scale one) by winding S2 glass fibres then impregnated with epoxy. The volumetric glass content was of 69% and no significant presence of defects was verified by an X-ray survey. The test has been carried out following as close as possible the ASTM standard E 328-86. The ring has been inserted into a dedicated hydraulic testing machine consisting of 18 radial pulling actuators and then loaded up to a ring membrane hoop stress of 800 MPa. The deformation has been maintained constant during the test by inserting a solid steel disk in the machine centre restraining the machine radial motion. Average hoop stress has been daily monitored measuring the force required to lift the ring just free of the constraints during the test period. The ring performed 125 testing days showing no significant stress relaxation and a small reduction of the ring stiffness that appeared mainly in the first days of the test.

The PERMCAT is a membrane reactor proposed for processing fusion reactor plasma exhaust gas: tritium removal is obtained by isotopic swamping operating in counter-current mode. In this work, a membrane reactor using a permeator tube of length about 500 mm produced via diffusion welding of Pd–Ag thin foils is described. An appropriate mechanical design of the membrane module has been developed in order to avoid any significant compressive and bending stresses on the very long and thin wall permeator tube: two expanded bellows have been applied to the Pd–Ag tube, so that it has been pre-tensioned before operating. The elongation of the metal permeator under hydrogenation has been theoretically estimated and experimentally verified for properly designing the membrane reactor.

A new method to measure volume capacities of vessels has been developed and tested. The method uses a simple apparatus consisting of a calibrated membrane, pressure gauges, thermocouples and a chronometer. The apparatus is connected to a vessel of unknown volume: the vessel filled with a test gas is then pressurized (or depressurized). The knowledge of the mass transfer mechanism of the test gas through the membrane allows evaluating in an original way the volume of the vessel by means of pressure measurements vs. time. Potential applications concern the determination of the volume of vessels with irregular shapes both in laboratory (i.e., metrology, experimental chambers) and industry (i.e., fine and pharmaceutical chemistry). The main advantages with respect to the alternative gravimetric methods used for volume measurements are the avoided contamination with liquids, the reduced costs, the ease of use, and a good accuracy.

The main design features and guidelines for the construction of the 8-T cryogenically cooled Frascati Tokamak Upgrade (FTU) are presented. The main features include the very compact toroidal magnets based on the concept of the 'Bitter' type of coil with wedge-shaped turns, utilized for the first time for the Alcator A and C magnets, and the original configuration of the vacuum vessel (VV) structure, which is fully welded in order to achieve the required high strength and electric resistivity. The present toroidal limiter has been installed following several years of operation, and this installation has required the development of specific remote-handling tools. The toroidal limiter consists of 12 independent sectors made of stainless steel carriers and molybdenum alloy (TZM) tiles. The main fabrication processes developed for the toroidal and poloidal coils as well as for the VV are described. It is to be noted that the assembly procedure has required very accurate machining of all the structures requiring several trials and steps. The machine has shown no problem in operating routinely at its maximum design values (8 T, 1.6 MA)

Cold-rolled and annealed Pd-Ag 25% at. foils of thickness 50 μm have been joined by diffusion bonding in order to obtain permeator tubes used in laboratory applications for hydrogen separation and purification. The tubes produced present a sound and effective joint along the generatrix line: particularly, this procedure has shown better performance than arc welding, responsible for formation of thermally stressed zones and embrittlement of permeators.

Three techniques were used to produce palladium–ceramic (Pd–ceramic) composite membranes for hydrogen separation and production. They are sputtering, electroless deposition and rolling of thin Pd alloy films over ceramic porous tubes. After studying and developing the three coating techniques, an extensive testing and characterizing work was carried out on these thin film composite membranes. The results show that in the sputtered (0.5–5 μm) and electroless (2.5–20 μm) composite membranes, the thermal cycling of the hydrogenated metallic layer produces membrane failures. Such failures are characterized by crack formation and metal film peeling. This fact has been explained by an evaluation of the shear stresses at the metal–ceramic interface due to the differential elongation between the palladium (Pd) coating and the ceramic support under thermal cycling and hydrogen loading. The rolled membranes (50–70 μm), however, because of the particular coating solution, have shown a complete hydrogen selectivity and good chemical and physical stability in long-term tests.

Thin palladium and palladium alloy membrane tubes with thickness up to 50 μm have been produced. These metal membranes, used as tube permeators in catalytic membrane reactors for the water gas shift reaction, are thinner than the commercial ones (100–150 μm) and have both complete selectivity to hydrogen and good durability. A manufacturing procedure consisting of several steps of cold-rolling and annealing the metal foils coupled with a simple welding technique of the tubes has been carried out in order to produce the prototype thin palladium permeators. The procedure of rolling and annealing the palladium and palladium alloy foils is described in detail: the work hardening upon rolling of the palladium and palladium alloy foils has been controlled by means of hardness measurements. Model studies and tests on the membranes and the CMRs for the water gas shift reaction have demonstrated the possibility to separate and recover highly pure hydrogen in energy applications such as nuclear fusion fuel cycle and fuel cells fuelling.

The JET Toroidal Field (TF) coils were originally designed for operation at 3.4 tesla. In order to upgrade the field to 4 tesla and thus improve the performance of the JET machine, new mechanical tests and analysis were carried out on the insulation of TF coil samples. They are aimed at investigating the mechanical properties and the status of the insulation in order to set allowable stresses and force limits. In particular since the shear stress in the insulation is strongly affected by the shear modulus of elasticity G, it is important to measure this parameter. A method for the measurement of G in glass-resin fibres, the V-notched beam method (Iosipescu method) , was applied. The particular shape of the rectangular Iosipescu V- notched sample and the particular modality of force application produce pure shear stress for a reliable measurement of the G value and of the shear strength of the insulation. The effect of temperature on these mechanical properties was also investigated. Results show higher average shear strength with lower scatter compared with previous tests on conventional rectangular samples, thus confirming the reliability of the method. Micrographic analysis of the insulation and comparison between the straight and curved regions of the magnet, where the highest stress occurs, confirm the good quality of the impregnation of the coil. Glass-resin content, void content, micros and TG measurements have been performed on different samples and correlation between the different properties of the insulation investigated. Moreover fatigue tests at different temperatures were performed and data analyzed with the cumulative damage technique, which allows for an extrapolation of the fatigue curve with less samples than the standard method. (6 refs).

Fasteners are generally considered a matter of a mature technology with a variety of solutions ready to meet a wide range of applications, but their use in remote handling needs accurate considerations. The fastening system has a substantial effect on the total time to perform maintenance operations, and therefore care should be taken from the beginning of the project to its standardization. The set of requirements to be satisfied by a qualification activity on fasteners to be remotely handled within the environmental conditions relevant to the NET—ITER machine (high temperature, radiation, vacuum, cryogenic temperature) deals with shape and dimensions, materials properties, surface finish of mating parts, lubricant compatibility, precautions against galling and seizure, provisions of remedial actions from an emergency situation, fabrication process specification, methods of preload application and control of its persistence under machine operation. The qualification of high strength bolts at cryogenic temperature (4 K) and relevant fracture mechanics tests, and the qualification of suitable coatings and lubricants has been extensively investigated on both specimens and full size components. In this paper we report final results of a three-year development programme on fastener technology.

In the paper we report the salient results of the test activities performed to measure the tensile and thermal-elastic properties of a number of materials whose use is envisaged for the manufacturing of NET mechanical fasteners, together with the outcomes of the test on the antiseizure performance of coatings and lubricants under high vacuum operation.

The FTU tokamak will have to operate steadily at high magnetic fields in order to reach the expected performance. Its magnet and vacuum chamber, due to thermal and electromagnetic loads, will undergo very high stresses for a large number of shots. In order to assess the feasibility of the components, numerical codes to compute current, magnetic field and temperature distributions, and extensive three dimensional finite element stress analysis have been developed. The main results obtained are illustrated.

This paper deals with the work done to define, construct and test a detailed critical part, spatially limited at about 10 cm3, reproducing the essential configuration of the FT-U magnet coil. The tests were performed at room and LN 2 temperatures in order to study the degradation of the insulating materials after repeated mechanical stresses. We describe criteria required to design a practical model with the possibility to simulate the thermo- -mechanical behaviour of the coil and allowing the measurement of the electrical insulation properties. The experimental set-up is described, as well as the operations for test analysis, optical observations and measurements on the components. Finally some results and typical microphotographs are reported.

In order to reduce the energy consumption and improve the mechanical characteristics of the structural materials, the FTU (Frascati Tokamak Upgrade) machine operates at -196°C. In the following, the cryogenic system of the FTU machine is described.

Raising the JET maximum toroidal field from 3.45 to 4.0 T results in increased forces and stresses in the key machine components during normal operations and disruptions. These forces and stresses have been predicted for 4.0 T operation and compared with allowable values derived from tests on used and spare JET coils. In this assessment significant lessons related to the design, manufacture and operation of key Tokamak components have also been learnt. (C) 2001 The European Commission. Published by Elsevier Science Ltd. All rights reserved.

Full details are given for the realization of a windowless image converter for low energy particle or soft x−ray spectroscopy, based on the use of new microchannelplate mountings in which the electrical contacts are secured by small spring load pin−contacts. Among other improvements, this kind of mounting can match any microchannelplate thicknesses and can easily be extrapolated to the case of tandem microchannelplate mounting.