Progress in the Secondary Heating System for the HL-2A Tokamak

In 2006, the following work on secondary heating systems for HL-2A tokamak have been done： the development of an electron cyclotron resonance heating （ECRH） system, the improvement of lower hybrid resonance heating （LHCD） system and the fabrication on neutral beam injection （NBI） system.     

Scaling of the temperature-dependent resistivity in SrFe2−xNixAs2

We show that the zero-field normal-state resistivity of temperature-dependent resistivity ρ(T) of SrFe_2?xNi_xAs₂ can be reproduced by the expression ρ(T) = ρ₀ + c T exp(?2Δ/T). ρ(T) can be scaled using both this expression where the energy scale Δ, c and the residual resistivity ρ₀ are scaling parameters and a recently proposed model-independent scaling method (H.G. Luo, Y.H. Su, T. Xiang, Phys. Rev. B 77 (2008) 014529). The scaling parameters have been calculated and the compositional variation of 2Δ(x) has been determined. This dependence show almost a linear decreasing in the underdoped regime similar to that reported for cuprates. The existence of a universal metallic ρ(T) curve in a wide temperature range which, however, is restricted for the underdoped compounds to temperatures above a structural and anitiferromagnetic transition is interpreted as an indication of a single mechanism which dominates the scattering of the charge carriers in SrFe_2?xNi_xAs₂ (x = 0–0.3).     

Color centers in the ionized and in the triplet state —Z 2 centers in calcium doped KCl crystals

Optical absorption measurements ofZ ₂ andZ ₂ ⁺ centers in KCl:Ca are combined with electron spin resonance experiments in order to reveal the electronic and atomistic structure of these centers.Z ₂ ⁺ centers are alignable in the crystal by polarized optical irradiation at suitable temperatures. From orientedZ ₂ ⁺ centers equally orientedZ ₂ centers can be produced, both types of centers showing a (100) axial symmetry. ConcerningZ ₂ this is also confirmed by ESR measurements on their triplet state produced by optical excitation. Polarized excitations allow a determination of the ratio of oscillator strengths for transitions parallel and perpendicular to the center axis using the variations in ESR line intensities. ForZ ₂ f /f =1.6 is found in this way; decomposition of the dichroism ofZ ₂ ⁺ centers gives for this speciesf /f =1.8. It is shown that theZ ₂(Ca) center is a molecule made up of a Ca⁺⁺ ion and an anion vacancy in (100) nearest neighborhood, sharing two electrons with antiparallel spins in the ground state. Both, withZ ₂ andZ ₂ ⁺ , the absorption bands at lowest energies are best explained bys—d charge transfer transitions.     

Pellet Injection Experiments in the HL-2A Tokamak

The advantages of pellet injection as a competitive means of fuelling a tokamak are well known. They include： （ 1 ） deep deposition of fuel, （ 2 ） better fuelling efficiency, （ 3 ） purer plasma, and so on. Meanwhile, improving plasma performance by pellet injection has been proven in many tokamak experiments. The deposition of pellet particles following pellet injection causes a temporal change of the local plasma temperature and density gradients which affects the transport properties of the plasma, so pellet injection can be used as a method of studying the transport process as well.     

Two triple points in the H2O–H2 system

Using a volumetric technique, phase transitions in the H₂O–H₂ system were investigated in the vicinity of two points of an invariant equilibrium, L+I _h+sII and L+sII+C ₁, located at 1.07 kbar and?10 °C and at 3.6 kbar and 1 °C, respectively. Liquid water (L), low-pressure hexagonal ice (I _h) and high-pressure cubic (sII) and rhombohedral (C ₁) clathrate hydrates were in equilibrium with gaseous hydrogen taken in excess.     

“Superslow” processes in the Ge-GeO2 system

A study was made of the charged state on a natural or an oxidized germanium surface during heat-and-field treatment. This study dealt with the kinetics of charging and discharging of superslow surface states. The thermal activation energy of these charging and discharging processes has also been evaluated. Conclusions are drawn about the possible nature of superslow traps in the Ge-GeO₂ system.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.2, pp.79–86, February, 1976.In conclusion, the authors thank V. F. Kiselev for the useful discussion of this report and his valuable comments.     

Parity nonconservation in the circular polarization of primary photons of the radiation accompanying electron conversion in the 5/2− → 5/2+ nuclear transition in the 229Pa91 nucleus

The ground state of ²²⁹Pa₉₁ is a 5/2^± doublet, with the splitting energy being 220+-50 eV. A direct observation of P-odd effects in this system is of great interest, since this may furnish information about the parity-nonconserving effective one-nucleon potential. Since a transition between two oppositeparity doublet states is accompanied by a strong conversion, it is possible to study P-odd mixing by exploring the conversion-electron helicity and the circular polarization P _γ of the lines of atomic radiation that arises upon the filling of a hole in the 6s _1/2, 6p _1/2, and 6p _3/2 shells of the ²²⁹Pa₉₁ atom. Since P _γ is about 3–5% for individual atomic transitions, experiments aimed at observing parity-nonconservation effects on this basis are feasible.     

Angular distributions of electrons in the (γ, 2e) reaction andee-correlations in the atom

The cross sectionsd ³ σ/dE ₁ d n ₁ d n ₂ for the Ar (γ, 2e) Ar⁺⁺ process are calculated on the basis of the diagram approach within the energy intervalω=400–650 eV as functions of the angleθ ₁₂ between final electrons with equal energiesE ₁=E ₂ for several levels of the final Ar⁺⁺ ion. It has been elucidated that the interference of amplitudes corresponding to the interaction in the final and initial states is of prime importance. The angular distributions over the angleθ ₁₂ are very sensitive to the term of the final ion. There are numerous data for the experimental verification of the theory, in particular, for the selection of leading diagrams. The (e, 3e) experiment is also desirable.     

Studying parity-nonconservation effect in the conversion transition between the levels of the (5/2)± doublet in the 229Pa nucleus

Effects of weak nucleon interaction are calculated for the ground-state doublet of 5/2^± levels of the strongly deformed nucleus ²²⁹Pa₉₁. A parity-nonconservation effect in the doublet states can be observed in the conversion spectrum for the isomeric transition between the doublet levels. By using a generalized model of the nucleus, the matrix element of the effective one-nucleon weak-interaction potential, which determines the weight of the opposite parity admixture in the doublet components is estimated in the single-particle approximation. The reduced probabilities of the E1 and M1 nuclear transitions between the doublet states are calculated within various models of the deformed nuclear potential. The effect of Coriolis forces on the dipole electric transition in question is considered. The lifetime of the upper doublet state is estimated.     

Parity violation in the 17/2−–17/2+ doublet in93Tc

The parity-violating mixing of the 17/2^– and 17/2⁺ levels in⁹³Tc nuclei, polarized by the tilted multifoil interaction, was measured by the observation of the forward-backward-ray asymmetry. The nuclear polarization, induced by the tilted multifoils, was measured directly for the neighboring^88,90Zr isomers. The forward to backward asymmetry was determined to be A=(2.5±2.1) 10^–3 which implies a parity violating matrix element ¦H _PV )¦=(4.0±3.7)meV.     

Entanglement in the supermolecular dimer [Mn4]2

This paper investigates the entanglement in the supermolecular dimer [Mn4]2 consisting of a pair of single molecular magnets with antiferromagnetic exchange-coupllng J. The conventional yon Neumann entropy as a function of the exchange-coupling is calculated explicitly for all eigenstates with the quantum number range from M = M1 ＋ M2 = -9 to 0. It is shown that the yon Neumann entropy is not a monotonic function of the coupling strength. However, it is significant that the entropy of entanglement has the maximum values and the minimum values for most eigenstates, which is extremely useful in the quantum computing. It also presents the time-evolution of entanglement from various initial states. The results are useful in the design of devices based on the entanglement of two molecular magnets.     

Siliconization for Wall Conditioning in the HL-2A Tokamak

The sputtering of impurities is caused by the interactions between plasma and the first wall, and the recycling of the gas affects the particle and energy transport of plasmas with a complicated mechanism in plasma operation. It is important for present tokarnaks to achieve a good confinement and high performance plasmas by means of controls of the vacuum condition, usage of low Z materials, control of the recycling of neutral particles and suppressions of the appearances and yield of impurities. For higher plasma parameters, some of the first wall of HL-2A is covered with graphite materials and carbon fiber tiles. Hence the studies on the in-situ coating application and development, and the interactions between the coating film and plasma are needed to effectively control the impurity, improve plasma confinement and achieve high performance plasma.     

Fundamental Concepts of Electron Spin Resonance Technique in the Determination of the Crystal Field Structure of O− 2 Ions in TiO2

Abstract

The basic principles of Electron Spin Resonance (ESR) as applicable in crystal field characterization of paramagnetic species has been outlined. Fundamental concepts of the precessional motion of electrons and their magnetic moments at resonance were developed. The theory of ESR based on the response of unpaired electron(s) as they undergo spin-spin or spin-lattice relaxation when subjected to strong external magnetic fields was examined. Ions of the O^? ₂ group adsorbed on TiO₂ were studied using a Varian Spectrometer. The resulting spectral diagrams obtained were used in calculating the g-factors which gave results for orthorhombic crystal symmetry for O^? ₂ ions in TiO₂.     

Reading the patterns in living cells —the physics of ca2+ signaling

Ca²⁺ is one of the most important messengers. It transmits signals inside living cells and takes part in intercellular coordination. The dynamics of the Ca²⁺ concentration shows a transition from elemental, stochastic events to global events like waves and oscillations. This transition renders it an ideal tool for studying basic concepts of pattern formation, especially since access to the most important experimental parameters is given. Ca²⁺ dynamics in living cells has been a major topic of biophysical modelling in the last 15 years. Modelling has reached the level of predictive power. The theoretical analysis of waves provided new insight into the mechanisms of Ca²⁺ signaling and led to new concepts of analysis of wave equations with concentration dependent diffusion and novel wave bifurcations. Modelling of oscillations provided understanding especially of complex oscillations and allowed to extract information about the underlying cellular parameters and mechanisms. The investigation of the stochastic aspects of intracellular Ca²⁺ dynamics demonstrated the fundamental role of fluctuations arising from the control of the release channel by Ca²⁺ and IP₃. This review presents an overview of current theoretical research on Ca²⁺ dynamics in living cells driven by the inositol 1,4,5-trisphosphate receptor channel.     

Contributions of the Two Nuclei to the Harmonic Generation in H2＋ Molecules

The separate contributions of the two nuclei in H2＋ to the harmonic generation are investigated by numerically solving the time-dependent Schroedinger equation. The results show that the diverse electron distributions around the two nuclei under the effect of a laser field lead to different contributions of the two nuclei to the harmonic generation in different times, i.e., the contribution mainly comes from nucleus A around the （n ＋ 0.5） optical cycle while from nucleus B around the n optical cycle. By means of the time-frequency distributions and the coupled electron nuclear wave-packet density distributions, the physical mechanism is discussed in detail.     

Changes in the phonon spectra of Bi 2212 superconductors connected with the metal-semiconductor transition in the series of Bi2Sr2(Ca1−xYx)Cu2O8 compounds

By means of inelastic neutron scattering the phonon density of states (PDOS) has been measured for compounds Bi₂Sr₂(Ca_1–xY_x)Cu₂O₈₊ for different values ofx. The transition from a superconducting to a semiconducting material is paralleled by characteristic changes in the PDOS as it was observed before for other HTC ceramics. The results are discussed on the basis of a model calculation and it can be shown that high frequency oxygen vibrations in the Cu–O sublattice are stongly renormalized in the superconducting compound.     

g-factors in the ground state and in the γ-bands in 160,162,164Dy

The g-factors of some members of the ground state band and of the 2⁺ state in the %-vibrational band have been measured in ^160,162,164Dy using the Coulomb Excitation Transient Field technique, induced by ⁵⁸Ni projectiles at 230, 210 and 217 MeV, respectively. The g-factors in the ground state band are consistent with a constant value, while that of the 2⁺_% states is about 20% larger in average than those in the ground state band. Results are discussed in the frame of the systematics in this nuclear region.     

Asymmetric local displacements in the Bi2Sr2CaCu2O8+β superconductor

Instantaneous in-plane Cu-O bond distribution in the Bi₂Sr₂CaCu₂O_8+β (Bi2212) superconductor has been investigated by high k-resolution Cu K-edge extended X-ray absorption fine structure (EXAFS) measured with polarized vector parallel to the two orthogonal Cu-O-Cu bonds of the CuO₂ square plane. The results show an anisotropic Cu-O distribution in the two directions and provide further information on the local atomic displacements in the lattice-charge stripes. Received 5 June 2000