Progress in Plasma Diagnostics and Physics Experiment

The development of eight new diagnostic systems and the improvement of the laser Thomson scattering system contributed to the experimental campaign on HL-2A in 2006. Besides, the accuracy and flexibility of the molecular beam injection （MBI） system was improved greatly by using the special driver and controller, it is more convenient for studies such as particle transport. In the field of plasma physics experiment, the features of 3-D GAM zonal flows were further studied and some signs of low frequency zonal flows were observed. In the ECRH experiments, the effects of ECRH on sawtooth activities and m/n= 1/1 mode were studied under different plasma discharge conditions. The effect of MBI during ECRH on plasma behavior, such as non-local heat transport, was also studied.     

Hyperfine interactions of neutron-activated β emitters in insulators and metals

The general features of hyperfine interaction measurements using neutron-activated emitters are described and the applications of this technique are reviewed: nuclear magnetic resonance and transients of the nuclear polarization give informations on nuclear moments, interactions in undisturbed lattices, radiation induced and thermal defects in insulators and metals.Most of the experiments reported here were performed at the High Flux Reactor Grenoble and at the FR 2 reactor Karlsruhe in collaboration with K. Dörr, D. Dubbers, F. Fujara, H. Grupp, M. Grupp, P. Heitjans, A. Koerblein, P. von Blanckenhagen, H.-J. Stoeckmann and A. Winnacker.     

Hyperfine fields and Fe magnetic moments in Fe−Ni invar alloys

Mössbauer spectra of Fe_1?x Ni _x withx=0.40, 0.35 and 0.32 were taken at various temperatures and fitted withB _hf distributions. TheP(B _hf) curves generally show a peak and a low-field tail. The peakB ^* and the average \(\bar B\) were obtained in theT→0 limit. Fe moments were deduced from these data with help of a semiempirical equation. While the average \(\bar \mu _{Fe} \) decreases withx (invar anomaly), a large fraction of Fe atoms retain the strong moment (≈ 2.7 μ_B) typical of Ni-rich alloys. This result is consistent with a two-states model for invar.     

Hyperfine Field and Isomer Shift Evolution in Hydrogenated Nd–Fe–B Alloy

RE₂Fe₁₄B (RE=rare earth) materials are capable of absorbing hydrogen to form a stable solid solution at room temperature. Hydrogenation produces a number of significant changes in the hyperfine interactions. In this work, ⁵⁷Fe Mössbauer effect spectroscopy and X-ray diffraction measurements were performed on Nd_14.01Hf_0.08Fe_78.91B_7.00 alloys submitted to thermal treatment in hydrogen atmosphere. A non-linear increase of the hyperfine fields and isomer shifts with hydrogen concentration was observed. The hyperfine parameters of the 8j₁ site exhibit a rather different evolution than those experienced by the other major sites (8j₂, 16k₁, 16k₂). The origin of the hyperfine field enhancement is analyzed in terms of volume expansion and H nearest neighbors to the Fe sites. A linear expression on these two effects to give account of isomer shift evolution for 8j₁ site is given.