Search

Deterioration of paper materials is mainly due to the degradation of cellulose caused by a lot of factors such as chemical attack due to acidic hydrolysis, oxidative agent, light, air pollution and biological attack due to presence of microorganisms like bacteria and fungi. Various technologies exist to limit the degradation of the paper materials but in a few cases are unsuited or produce no good results. Plasma technology is an innovative process which can be an alternative to the conventional methods. The plasma treatment produces a synergetic result of sterilization and coating of the paper. This technology is environmentally friendly and can be used for industrial applications. The aim of this project is the increasing of the paper tensile strength and paper conservation by means of several different plasma treatments.

Plasma technologies offer a wide spectrum of possible treatments of materials. In particular, in function of the peculiar physical characteristics of the plasma, produced by different ionisation systems, three types of processes on the materials can be activated: (1) Destruction of toxic/harmful materials; (2) Superficial modification of existing materials; (3) Creation of new materials. Thermal plasma can be used to destroy the solid, liquid and gaseous toxic halogenated and hazardous substances or to generate anticorrosion, thermal barriers, antiwear coatings, etc. Cold plasmas can be used for surface modifications of materials, ranging from the simple topographical changes to the creation of surface chemistries and coatings that are radically different with respect to the bulk material. Each of the three lines has a different weight with respect to an immediate industrial transferring. While the first two are ready for an immediate industrial utilisation of the processes, the third one is still under investigations. Some industrial processes will be described and, in the case of some treatments of toxic substances, a comparative cost analysis is presented.

The non-axisymmetric magnetic field, naturally present in every tokamak, constraints the machine operational space. A set of dedicated ‘Error Field Correction Coils’ (EFCC) is proposed for JET, which will replace the unreliable existing ‘saddle coils’. The new coils are specified to compensate the main harmonic contribution to error field induced modes. The EFCC structural design comprises a cable coil wound in a metallic casing supported on the JET iron magnetic circuit. Existing power supplies will drive the coils. The EFCC are expected to be installed in 2001 JET shutdown.

The degassing rates of the low activation martensitic steels BATMAN C and F82H were measured as a function of time and temperature. The electronic properties of F82H were measured using photoelectron spectroscopy and protium diffusion and trapping were modelled for MANET II which has hydrogen interaction properties similar to F82H. BATMAN C has superior degassing properties with respect to F82H and on cooling of MANET II, most of the hydrogen remains trapped.

In this paper, we present the results of an experiment wherein Zr[V 0.5 Fe 0.5 ] 2 alloy has been used for the conversion of light water vapour to hydrogen at a temperature of 400°C and partial pressure of ∼4 kPa through a series of batch processes nearly up to its full life. After ∼1960 cumulated hours of conversion, the oxygen uptake was found to be ∼2.24 moles of oxygen per an equivalent mole of alloy. Systematic investigations of the conversion process revealed a reduction in the hydrogen release capabilities as the oxidation of the alloy increased. The role and consequence of the hydrogen and oxygen atoms resulting from the cracking of water vapour molecules at the alloy surface are discussed from the observed dependences of the hydrogen release on the duration of conversion and the relaxation time between two successive conversions. The significance of the experimental results towards the usage and disposal of the alloy material, for the purpose of tritiated water conversion in a fusion reactor situation, is also discussed.

An experimental study of the release of hydrogen during the decomposition of water vapour by St 737 alloy [Zr(V0 .5 Fe0 .5)2] is presented and discussed. The hydrogen profile is discussed from the net effect of water vapour dissociation at the surface of the getter alloy and hydrogen sorption by the alloy. From the experiments performed at various initial concentrations of oxygen and hydrogen in the getter alloy, the effect of hydrogen and oxygen over alloy ratios on the hydrogen release is discussed.

The results of the studies performed to investigate the saturation capacity of St 737 getter alloy (Zr[V 0.5 Fe 0.5 ] 2 ) in its application for conversion of water to hydrogen and the functional behaviour of the conversion reaction rate with large oxygen concentration in the alloy are reported. The experiment was performed with the getter alloy at a temperature of 400°C. The conversion process was monitored by two independent techniques — (i) by the hydrogen release, using a quadrupole mass spectrometer and (ii) by the quantity of water reduction in liquid phase. It was found that more than 100 mg of water was converted and 13 Pa m 3 of hydrogen was released by a gram of alloy. A chemical analysis of the alloy performed after the experiment showed that the oxygen content in the alloy was about 7% by weight. The post-experiment diffraction analysis of the alloy showed that the crystalline structure of the alloy is almost completely destroyed and that the oxides formed are essentially amorphous. A brief discussion of the significance of the results for the application to tritiated water handling in future fusion reactions is also given.

This work was carried out to determine the utility of using getter materials for tritium purification in glove box atmospheres. The main goal of this experiment was to reach a residual tritium concentration lower than 1 mCi/m3, as imposed by the international safety rules. Two groups of measurements were carried out simulating tritium with deuterium; the first group was performed under static conditions, in order to find the best working temperature for the getter, relative to the pumping speed. The second one was performed under dynamic conditions, in order to find the tritium residual partial pressure. The measurements provided a residual pressure three times higher than the pressure predicted by Sieverts’ law. The selected getter consisted of a Zr–V–Fe alloy; two types of getter configurations were tested: a getter cartridge pump and a getter purifier. The results showed that the diffusion of D2 in argon limited the sorption speed. The results of static tests did not change when the getter temperature was changed. The results of dynamic tests showed the need for lower getter temperatures to achieve lower deuterium partial pressures. Starting from the experimental results, a proposal for an economical tritium purification system for a glove box atmosphere is presented.

Ignitor is a compact high field fusion experiment under design in Italy. The vacuum system design for the experiment must take into account the complexity of the required plasma parameters, together with the introduction and recovery of the D-T gas mixture injected into the vessel. The design guidelines and the expected performances of the vacuum and tritium systems are described.

The degassing rates of the low activation martensitic steels BATMAN C and F82H were measured as a function of time and temperature. The electronic properties of F82H were measured using photoelectron spectroscopy and protium diffusion and trapping were modelled for MANET II which has hydrogen interaction properties similar to F82H. BATMAN C has superior degassing properties with respect to F82H and on cooling of MANET II, most of the hydrogen remains trapped. © 1997 Elsevier Science Ltd. All rights reserved.

Tritiated water production is a consequence of tritium gas handling. If tritium emission to the environment is to be minimized, then tritiated water must be processed so that the chemically bound tritium is recovered. For DT burning fusion machines, tritiated-water-processing systems are under development. These systems, however, are intended for large-scale applications and cannot be scaled down practically or economically. HTO vapour reduction to HT over hot metal getters offers a simple alternative. In such cases the metal getter selected should reduce HTO efficiently and retain negligible residual tritium inventory. HTO reduction over a ZrFeMn alloy is reported in this paper. Conversion efficiencies exceeding 90% are achievable for gas residence times above 0.7 s and alloy temperatures above 400 °C over the useful life of the alloy. HTO-to-HT conversion rates greater than 6 μmol min −1 per gram of alloy can be attained for oxygen-to-alloy mole ratios from 0 up to 2.6 without a significant reduction in the reaction rate.

__

__

__

The feasibility of reducing HTO over the alloy St737 has been studied for alloy temperatures ranging from 300 to 600°C, for bed residence times ranging from 0.36 to 2.4 seconds and for water partial pressures ranging from 28 to 312 mbar in an argon carrier at 101 kPa. Quasi-steady state HTO to HT conversion efficiencies on the order of 25% were routinely measured in many typical runs for alloy temperatures below 400°C.

An investigation of flow of gases and vapors in vacuum through a path of very small cross‐sectional area, namely that of a high vacuum gas leak valve, reveals the existence of a new flow behavior which is well behaved. The characteristics are different from that of the molecular flow or that of the sonic flow through a small aperture. The unambiguous nature of the flow has been observed by three independent flow measurement techniques. The conductance is found to decrease with the pressure upstream and depends on the geometry and specie. The effect of the residence time of the gas molecules during the collisions with the wall of the conducting path has been attributed as a possible mechanism to explain the observed flow phenomenon. The flow behavior has also been studied for two isotopic water vapors. Based on the defined characteristics of the flow, an application technique is proposed for finding the partial pressures of the component vapor and gases in a low‐vacuum system by making the measurements in a coupled high vacuum system using a quadrupole mass analyzer. The applicability and sensitivity of the technique are demonstrated by an example measurement of the compositions of hydrogen and oxygen gas mixture.

__

__

__

__

Thermonuclear fusion machines (which will be operated with D-T mixtures) should provide the tritium storage and supply systems with safety conditions. In order to prevent possible accidents, with a large release of tritium, it must be trapped in solid and reversible solution forms by absorption beds. Moreover, residual gaseous form tritium in the pipelines, and permeation through the primary containment system, must be minimized. For storage, transfer, injection and recovery, a suitable system can be designed which uses metallic getter beds. Reversible solid solutions by tritium sorption are formed with low residual partial pressure, and re-emission by heating at low temperatures, which results in the reduction of permeation. This work shows the possibility of the use of a combination of two ZrVFe getter beds with different alloy compositions as an alternative to the usual uranium beds. In particular, the characterization of the new St737 getter alloy is carried out. Advantages of the combination of the new getter with the well-known St707 getter alloy are presented. presented.

_

_

RFX is a large fusion experiment under construction in Padova (Italy). The toroidal vacuum vessel, having a major radius of 2 m and a minor radius of 0.475 m, is built in Inconel 625, and its inner surface is completely covered by 2016 graphite tiles. The residual final pressure should be in the range of 10 −9 mbar; to reach the required vacuum conditions, 12 uhv pumping groups are provided, each of them including one turbo pump (1000l s −1 ) and one cryogenic pump (1500l s −1 ). Six forevacuum pump systems, each including one roots pump (double stage) and one rotary pump, assure the regeneration of the cryogenic pumps and the forevacuum conditions for the turbo pumps. The gas inlet system is designed to supply H 2 and D 2 to the vessel in very high purity conditions or in a pre-defined mixture with impurities. The plant control system can work either in manual or automatic mode: in manual mode the system is handled from ‘local operation panels’, whereas in automatic mode it is controlled by a ‘Programmable Logic Controller’ (PLC) which is part of the overall control and monitoring system of the RFX experiment. The paper describes the design of the systems and evidences the main technical solutions that have been adopted.

In the present work design solutions for the vacuum system of the Ignitor Tokamak experiment are presented. We describe performance of the vacuum system. The material treatments and the cleaning discharge processes are briefly discussed. The D-T mixture envisaged as the gas filler of the vessel must be considered another problem for the vacuum system, related to the tritium β− emission and to the safety protection.

Resonant and non-resonant parametric decay instabilities in the region near the lower hybrid resonance have been investigated in a mirror linear device. The identification of the two processes was possible by comparing with theory the experimental value of the ratio omega 0/ omega LH between the pump frequency and the maximum lower hybrid frequency. In connection with the appearance of decay into quasi-modes, electron and ion heating was found. The propagation of the pump and of the decay waves has been also studied. A pattern of trajectories following a 'resonant cone' was found both for the pump and the decay waves. The measured values of the resonant angles show a reasonable agreement with the theory.

The main characteristics of the plasma produced in Thor tokamak discharges are described. The machine performances are outlined and the experimental results relevant to the equilibrium, the stability and the control of the discharge regimes are discussed in detail.

The conditioning of the walls of Thor container by means of cleaning hydrogen discharges allowed a reduction of the influence of light impurities as oxygen and carbon on the plasma; as a consequenceZeff was also reduced. The experimental results seem to confirm the correlation between the cleaning and the amount of water and methane in the discharge. The build-up of these compounds is explained by supposing low-energy chemical reactions induced by hydrogen ion and atom bombardment. In particular water production is related to metal oxide layers on the walls. The cleaning discharge efficiency has been found to depend on the plasma temperature. High-energy cleaning discharges are not convenient as they increase the dissociation of water molecules and the container wall activation.

The collaboration of the toroidal magnet in the containment of the stresses imposes to adopt restricted spatial solutions for the vacuum vessel design of the Ignitor Tokamak. The material choice criteria regarding the vacuum technique, the working cryogenic temperature (77°K) and the toroidal electric resistance are presented. AISI 304 L and Carpenter 18–18 Plus stainless steels are considered as building materials of the vessel. Calculations show that the designed structure is able to support the mechanical stresses, the neutron and particle radiations and the thermic cycles.

Extensive work was carried out to define the working conditions and the reference design of the first wall for the IGNITOR machine: graphite covered modular elements attached to the vacuum vessel by a locking key for remote handling are proposed. The work includes a transient thermostructural analysis of the graphite tiles to evaluate temperatures and thermal stresses in normal and fault conditions. A full scale prototype of the element was manufactured.

The present work has the purpose to evaluate experimentally the ablation threshold fluences of copper, silver, and their alloys in order to induce a safety laser cleaning of the metal artifacts avoiding damages to the bulk. We used two different pulsed lasers: a KrF excimer laser operating at 248 nm, 23 ns pulse duration and a Nd:YAG laser operating at 532 nm (second harmonic), 3 ns pulse. Preliminary experimental results about the laser cleaning of bronze coins will be reported. The laser cleaning consists on the reduction of the chlorine concentration from the surface of the coins. The laser cleaning, carried out by the KrF laser, provides a safe way of removing the chlorine concentration as the Energy Dispersive X-Ray Fluorescence analyses will demonstrate.

This work has the purpose to characterize the plasma produced by solid target ablation. The experiment was performed by using a KrF laser with an irradiance of 108 W/cm2 and different solid targets, i. e., Si, Ge, Pd, and Pb. A very suitable Faraday cup has been utilized to study the angular distribution of the plasma plume as well as to perform measurements of the ion charge carried by the plasma during its free expansion into the vacuum. Particular attention was done to estimate the charge losses ascribed to the recombination processes during the plasma expansion.

Advanced high brightness photo-injectors require photo-cathodes with fast response time, long lifetime and relatively high quantum efficiency. Metallic cathodes could satisfy these proprieties and in order to control the emitting material and its surface we produced an yttrium thin film, prepared by PLD (Pulsed Laser Deposition).

Light emission from porous silicon is known since several years. Recently, the ability of silicon nanocrystals (NCs) or nanoclusters embedded in a suitable dielectric (usually silicon oxide - SiO2) matrix to efficiently emit photons in the visible spectral region has been demonstrated; potential applications of these nanostructures are in the field of monolithically integrated Si-based photonic devices. Si NCs have been fabricated by a variety of methods, including co-sputtering, chemical vapour deposition, molecular beam epitaxy, gas evaporation, laser ablation, and ion implantation (at ion energies from 100 keV up to a few MeV) followed by high temperature annealing. The latter methodology has the advantage that a controllable dose of ions can be placed at a given depth and distribution into the dielectric medium. High temperature annealing of implanted samples leads to Si atoms precipitation and NC nucleation. In this work we present preliminary results on the synthesis of Si NCs by low (10-40 keV) energy implantation of Si ions into SiO2 films and their subsequent high temperature annealing.

The goal of this work is the modification of bio-medical materials. UHMWPE polyethylene was processed and analyzed. A UV pulsed lasers was employed to produce C and Ti ions of different charge with current densities of the order of 10 mA/cm2. The ions were accelerated by the application of a 30 kV to increase energy and to implant the polyethylene surfaces up to a depth of about 200 nm. Preliminary results about surface properties indicate that implanted surfaces have higher wetting and micro-hardness with respect to un-implanted ones.

In this work the photoemission performance of rough and smooth cathodes is presented.

Ultra-high-molecular weight (UHMWPE) is a versatile polymer employed in many fields for its good chemical-physics characteristics. In this work the laser irradiation has been utilized to modify the morphology of the polymer in order to improve the polymer hydrophilicity. Contact angle measurements have been performed on the processed samples to study the water wettability changing before and after laser treatment. Two different laser lights have been used: a pulsed KrF excimer laser of 248 nm wavelength and a pulsed XeCl excimer laser of 308 nm wavelength. The sample processing was performed applying different laser shots in atmosphere and approximately the same laser fluence for the both laser wavelengths. Interesting results have been found about the samples treated by the XeCl laser, i.e a linearly decreasing of the water drop contact angle with the increasing of the number of laser shots.