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The stabilization of a hot‐electron plasma in a simple mirror geometry is investigated. Controlled quantities of neutral gas generate a cold plasma through hot‐electron ionization. Increasing stability is found with increasing gas pressure. The pressure required for stabilization is found to be inversely proportional to the ionization cross section of the type of neutral gas, indicating that the number of cold electrons is the key stabilizing quantity. The stabilization requires the cold electron density to be at least the same order of magnitude as the hot electron density. Line tying to external surfaces does not play a role in the stabilization. A theory in which the electrons, but not the ions, can be treated in the drift approximation is most closely applicable to the experiment. Reasonable agreement between theory and experiment has been obtained.

Tormac (Toroidal Magnetic Cusp) is a plasma confinement concept combining the favorable MHD stability properties of a cusp geometry with the good particle confinement inherent to closed field geometry, A Tormac plasma has two regions: an interior region in which a toroidal bias or studding field is embedded, and an exterior or surface region confined by mirror trapping along open field lines. The combination of these two regions is expected to lead to a configuration having confinement substantially superior to that of a mirror. and to allow the plasma to be stable at high {beta}. The Tormac V experiment is an attempt to establish such a configuration and to investigate characteristic behavior of the Tormac plasma. In this paper we describe the Tormac concept. the Tormac V experimental set-up. and the results obtained.

The perpendicular ion temperature of a barium plasma contained in a double‐ended Q machine has been measured by a spectroscopic technique. When the plasma is “ion‐rich”, good agreement is found between the measured ion temperature and the hot‐plate temperature, while in the “electron‐rich” regime, the ion temperature is elevated above the hot‐plate temperature. The increased ion temperature can be well accounted for by the energy input through the acceleration of ions through the electron sheath and their consequent thermalization.

A comparison was made of plasma density measurements obtained using cylindrical Langmuir probes and a high‐sensitivity microwave interferometer in magnetic fields between 1 and 7 kG. The experiment was carried out in a current‐free stream of ionized hydrogen with electron densities ranging from 3×109 to 4×1011 cm−3. A set of probes of different sizes was used so that the ratio of probe diameter to ion gyroradius 2rp/ρi covered the critical range from 0.2 to 5 or more. It was found that (1) the shape of the probe characteristics was not affected very much by the presence of the strong magnetic field; (2) the electron temperature derived from the slope seemed to be the true temperature; but (3) the apparent ion density inferred from the characteristic using Laframboise's calculation, which applies in the absence of magnetic fields, was consistently low by a factor which depended primarily on the ratio rp/ρi and seemed nearly independent of the Debye length. This reduction factor was considerably larger in the streaming plasma than in a stationary one, presumably because of the wake or “shadow” cast by the probe when rp/ρi is not negligible.

A multiple mirror experiment confirms the predictions of the theory that the axial confinement time exceeds that of a single mirror of the same length, and that the confinement scales as L2, where L is the system length. The experiment indicates that the improved confinement occurs in an intermediate mean free path regime in which the mean free path for scattering out of a loss cone is of the order of a cell length. The absolute value of the axial confinement is smaller than the optimum confinement predicted from the theory by a factor between two and three, which is accounted for by the deviation of experimental parameters from optimum conditions. The scaling of the confinement time with mirror ratio is also investigated. A reactor calculation using the multiple mirror confinement time gives QE = 2 for a 400‐m system with 3000‐MW(e) output.

ACE, Submitted to Surface and Coating Technology; International audience; In the perspective of long term geological storage, high level nuclear wastes will be overpacked in low carbon steel containers. In that context, we have studied the influence of oxygen dissolved in water on iron corrosion. Therefore, leaching experiments were performed in desaerated D$_2$O and in aerated H$_2$O and a kinetic study of iron corrosion under proton irradiation was lead in aqueous media with two different dissolved oxygen concentrations. The leaching experiments underline the major role of dissolved oxygen in oxydoreduction reactions which take place as far as iron is in contact with water. But the kinetic study of iron corrosion under irradiation put in evidence the balance between the oxydoreduction reactions and the corrosion rate induced by radicals species generated by water radiolysis. In addition, to check if, in the atomic % concentration range, hydrogen diffuse from the air/Fe interface through the foil an irradiation experiment was performed in argon. It proved that no hydrogen permeation occurs at a concentration level of the atomic percent.

VI ÖZET 316 L kalite Paslnmaz Çelik üzerinde, Ian G. BROWN tarafından geliştirilen; yeni yüzey işlemi gerçekleştiren MEWA teknolojisi kullanılarak, Oksijen ve Zirkonyum iyonları ile implantasyon yapılmış ve bu implant malzemenin yüzey sertliği, sürtünme ve aşınma gibi tiribolojik özellikleri incelenmiştir. Zirkonyum ve Oksijen iyonları ile implante edilmiş 316 L kalite Paslanmaz Çeliğin aşınma direncinin oldukça arttığı bulunmuştur. 316 L Paslanmaz Çeliğin yüzey mikrosertiğindeki artma ve sürtünme katsayısındaki düşme aşınma direncini artırmakta önemli bir rol oynar ve relatif aşınma hacmi ile relatif mikrosertlik arasındaki münasebet Zirkonyum ve Oksijen implantasyonu ile doğrudan alakalıdır. V ABSTRACT The tribological properties such as surface hardness, friction and wear have been studied for 316 L Stainless Steel substrates which were co - ion implanted with Zirconium and Oxygen ions by I. G. BROWN using new modified version of MEWA technology (Developed by BROWN et. al.). It is found that the wear resistance for 316 L Stainless Steel substrates implanted with Zirconium and Oxygen ions increased quite alot. It is concluded that the increase in surface microhardness and the decrease in friction coefficent of 316 L Stainless Steel substrates play an important role in improving the wear resistance, and the relationship between relative wear volume and relative microhardness is correlated for Zr and Oxygen co - ion implantation. 43