71 research outputs found

    On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

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    A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

    Overview of the JET results in support to ITER

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    Enhanced magnetic entropy in GdNi2

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    Measurements of the specific heat have been performed on Gd1-x Yx Ni2 (x=0,0.2) compounds and their nonmagnetic analogs Lu1-y Yy Ni2, which have similar molar masses. It is found that the difference between the entropies of magnetic and nonmagnetic compounds with identical molar masses surpasses substantially (by 14-19%) the theoretical limit for the magnetic contribution Sm = (1-x) R ln (8) calculated assuming that only Gd ions possess a magnetic moment. This observed enhancement of the magnetic entropy in Gd1-x Yx Ni2 is believed to result from spin fluctuations induced by f-d exchange in the 3d electron subsystem of Ni. © 2007 The American Physical Society.This work was supported by the Russian Foundation for Basic Research (Grant No. 04-02-96060), by the Program 2.1.1.6945 of the Russian Ministry for Education and Science, and by the Swiss National Science Foundation (SCOPES, Project No. IB7420-110849)

    Magnetic lock-in phase transition in Tb0.95Er0.05Ni5 driven by low magnetic fields

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    AbstractThe magnetic properties of a mixed inter-metallic compound, Tb0.95Er0.05Ni5, were investigated using a neutron diffraction method at low temperatures. These compounds were known to have a successive magnetic phase transition from the paramagnetic state at high temperature to a lock-in phase at low temperature through intermediate phases, i.e., PM(paramagnetic)–FM(ferromagnetic)–IC(incommensurate)–L(lock-in) in reverse order of temperature. A meta-magnetic phase transition between an IC phase and a FM phase at 9K was observed with the critical field, HMT~200mT. A new magnetic phase between the new phase (lock-in phase) and an IC phase has been observed. From the field dependence of the Bragg reflections and their satellite peaks at low temperatures (3–12K), weak field driven first-order magnetic phase transitions were recorded at six fixed temperatures. The critical magnetic field decreases exponentially with the temperature. From these experimental results, we obtained a magnetic phase diagram of Tb0.95Er0.05Ni5 at a low temperature region for the first time
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