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Here we discuss the radiative decays of excited states of transition elements located inside and outside of the subwavelength core-shell nanoparticles embedded in dielectric medium. Based on the quantum mechanics and quantum electrodynamics, the general analytical expressions are derived for the probability of the spontaneous transitions in the luminescent centers (emitter) inside and outside the subwavelength core-shell nanoparticle. Obtained expressions holds for arbitrary orientation of the dipole moment and the principal axes of the quadrupole moment of the emitter with respect to the radius-vector r connecting the center of the emitter with the center of the nanoparticle. They have simple form and show how the spontaneous emission in core-shell NPs can be controlled and engineered due to the dependence of the emission rates on core-shell sizes, radius-vector r and permittivities of the surrounding medium, shell, and core.

A novel series of substituted N-aminothioglycolurils was synthesized by tandem hydrazone formation – ring contraction reaction of 3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-6-ones with (E)-3-phenyl(furan-2-yl)acrylaldehyde derivatives. S-Alkyl substituted N-aminothioglycolurils were prepared through alkylation of corresponding thioglycolurils with iodoalkane or 4-chlorobenzylchloride. Methylthio group in S-methyl derivatives can be substituted with hydroxyl group in acid medium to give N-aminoglycolurils. Representative compounds were evaluated for their cytotoxic activity against RD, A549, HCT116 and MCF7 human cancer cell lines by MTT-assay and screened for their antifungal activity against phytopathogenic fungi using the mycelium growth inhibition method in vitro. Among the derivatives, 4-((E)-((E)-3-(2-Methoxyphenyl)allylidene)amino)-3-methyl-1-phenylthioglycoluril 8i was found to have the highest antiproliferative activity toward the RD and HCT116 cell lines (8i: IC50 = 0.02 and 0.012 μM, respectively), which exceeded cytotoxicity of reference drugs. 1,3-Diethyl-4-((E)-((E)-3-(2-methoxyphenyl)allylidene)amino)thioglycoluril 8l showed the most marked activity toward A549 cells (8l: IC50 = 0.61 μM) compared to reference drugs. The IC50 values of thioglycolurils 8i,l against normal human embryonic kidney cells HEK293 were 0.23 and 86.11 μM, respectively, exceeding the IC50 values of this compound toward the RD, HCT116 (8i) and A549 cells (8l) by one-two orders of magnitude. Experiments with annexin showed that compounds 8b,i,l induced apoptosis in Jurkat cells (acute T cell leukemia). Alkylthioderivatives 12a,13a displayed the strongest antifungal action against R. solani, F. oxysporum, and F. moniliforme exceeding those of triadimefon.

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world's first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ~12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected to sample the wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented., 7 pages, 7 figures, 2 tables

We present a new particle-merging algorithm for the particle-in-cell method. Based on the concept of the Voronoi diagram, the algorithm partitions the phase space into smaller subsets, which consist of only particles that are in close proximity in the phase space to each other. We show the performance of our algorithm in the case of the two-stream instability and the magnetic shower., 11 figures

Here we present a summary of the theoretical studies of the emission rates modifications of emitter placed inside or near the subwavelength nanoparticle that are embedded in a medium. The change in spontaneous emission rate as a function of the effective refractive index of the nanocomposite, as well as on the refractive indices of NPs and the substance filling the space between them is presented. Both naked and coated nanoparticles are considered.

AWAKE Run 2 aims to preserve the transverse normalised emittance of an externally injected electron beam throughout acceleration, requiring a new diagnostic to measure the beam emittance after the accelerating plasma stage. Spectroscopy of the betatron emission from the electron beam could be suitable for this case. The method of trace-space reconstruction from a measured betatron spectrum is described via a simplified analytical model in order to assess its suitability the AWAKE experiment. The expected betatron emission from witness electrons at AWAKE is characterised using 3D quasi-static PIC simulations, revealing a measurable quantity of UV to soft x-ray emission. Practical challenges for the measurement are discussed.

The novel PIC/fluid hybrid plasma simulation code H-VLPL3D is introduced. In addition to the particle-in-cell algorithm, it uses a new numerical fluid scheme for wake field simulations. Specially designed for the accurate simulation of very long wake fields, this scheme is capable of simulating ∼1000 plasma oscillations of the wake. A comprehensive description of the discretization schemes is given, and we demonstrate the code's correctness and its order of accuracy. Also, its superior efficiency in the plasma wake field acceleration (PWFA) regime is shown.

micrOMEGAs is a code to compute dark matter observables in generic extensions of the standard model. This new version of micrOMEGAs is a major update which includes a generalization of the Boltzmann equations to accommodate models with asymmetric dark matter or with semi-annihilation and a first approach to a generalization of the thermodynamics of the Universe in the relic density computation. Furthermore a switch to include virtual vector bosons in the final states in the annihilation cross sections or relic density computations is added. Effective operators to describe loop-induced couplings of Higgses to two-photons or two-gluons are introduced and reduced couplings of the Higgs are provided allowing for a direct comparison with recent LHC results. A module that computes the signature of DM captured in celestial bodies in neutrino telescopes is also provided. Moreover the direct detection module has been improved as concerns the implementation of the strange “content” of the nucleon. New extensions of the standard model are included in the distribution. Program summary Title of program: micrOMEGAs3. Program obtainable from: http://lapth.cnrs.fr/micromegas Computers for which the program is designed and others on which it has been tested: PC, Mac Operating systems under which the program has been tested : UNIX (Linux, Darwin) Programming language used: C and Fortran Memory required to execute with typical data: 50 MB depending on the number of processes required. No. of processors used: 1 Has the code been vectorized or parallelized: no No. of bytes in distributed program, including test data: 70736 kB External routines/libraries used: no CPC Program Library subprograms used: CalcHEP, SuSpect, NMSSMTools, CPSuperH, LoopTools, HiggsBounds Catalogue identifier of previous version: ADQR_v1_3 Journal reference of previous version: Comput. Phys. Comm. 182 (2011) 842 Does the new version supersede the previous version: yes Nature of physical problem: Calculation of the relic density and direct and indirect detection rates of the lightest stable particle in a generic new model of particle physics. Method of solution: In numerically solving the evolution equation for the density of dark matter, relativistic formulae for the thermal average are used. All tree-level processes for annihilation and coannihilation of new particles in the model are included as well as some 3-body final states. The cross-sections for all processes are calculated exactly with CalcHEP after definition of a model file. The propagation of the charged cosmic rays is solved within a semi-analytical two-zone model. Reasons for the new version: There are many experiments that are currently searching for the remnants of dark matter annihilation and the relic density is determined precisely from cosmological measurements. In this version we add the computation of dark matter signals in neutrino telescopes, we generalize the Boltzmann equations so as to take into account a larger class of dark matter models and improve the precision in the prediction of the relic density for DM masses that are below the W mass. We compute the signal strength for Higgs production in different channels to compare with the results of the LHC. Summary of revisions: • Generalization of the Boltzmann equations to include asymmetric dark matter and semi-annihilations: the DM asymmetry is taken into account when computing direct/indirect detection rates. • Incorporating loop-induced decays of Higgs particles to two-photons and two-gluons, and computing the signal strength for Higgs production in various channels that can be compared to results from LHC searches. • New module for neutrino signature from DM capture in the Sun and the Earth • Annihilation cross sections for some selected 3-body processes in addition to the 2-body tree-level processes. The 3-body option can be included in the computation of the relic density and/or for annihilation of dark matter in the galaxy. • Possibility of using different tables for the effective degrees of freedom in the early Universe • Annihilation cross sections for the loop induced processes γ γ and γ Z 0 in the NMSSM and the CPVMSSM • New function for incorporating DM clumps • New function to define the strange quark content of the nucleon • The LanHEP source code for new models is included • New models with scalar DM are included (Inert doublet model and model with Z 3 symmetry) • New implementation of the NMSSM which uses the Higgs self-couplings and the particle spectrum calculated in NMSSMTools_4.1 • New versions of spectrum generators used in the MSSM (Suspect_2.4.1) and in the CPVMSSM (CPsuperH2.3) • Extended routines for flavor physics in the MSSM • New facilities to compute DM observables independently of the model • Update in interface tools to read files produced by other codes, this allows easy interface to other codes Typical running time: 4 s Unusual features of the program: Depending on the parameters of the model, the program generates additional new code, compiles it and loads it dynamically.

We propose a method for high-sensitivity subwavelength spectromicroscopy based on the usage of a spaser (plasmonic nanolaser) in the form of a scanning probe microscope tip. The high spatial resolution is defined by plasmon localization at the tip, as is the case for apertureless scanning near-field optical microscopy. In contrast to the latter method, we suggest using radiationless plasmon pumping with quantum dots instead of irradiation with an external laser beam. Due to absorption at the transition frequencies of neighboring nano-objects (molecules or clusters), dips appear in the plasmon generation spectrum. The highest sensitivity is achieved near the generation threshold.

The applicability of the concept of permittivity with Im ɛ gain N of elementary cells will sooner or later lead to lasing; (ii) if the frequency of the pump lies in the band gap, then lasing at band gap frequencies may occur in a sample with a low N before the band gap has been formed. Nevertheless, lasing will be necessarily suppressed by a further increase in N . In any case, for sufficiently large number of layers due to a finite line width of ɛ gain ( ω ), lasing appears in the pass band even if the pump frequency is in the band gap.

Here we present the results of our theoretical study of the optical characteristics (lifetimes, IR absorption coefficient, Raman gain coefficient) for small-radius optical centers in subwavelength spherical and ellipsoidal nanocrystals embedded in a dielectric medium.

We study new pumping and sensitization scheme of 3.9 μm mid-IR laser transition (5I5 → 5I6 of Ho3+) in the BaF2 low-phonon crystal doped by Ho3+ and co-doped by Tm3+. It includes direct energy transfer from Tm3+ to Ho3+ governing by the 3H4 → 3H6; 5I8 → 5I5 cross-relaxation that gives ninefold increase of absorption of pumping light. We measure and analyze the lifetimes of all participated levels of Ho3+ and Tm3+ at low impurity concentrations, as well as energy transfer kinetics of the 3H4 level of Tm3+ and the 5I6 level of Ho3+ vs. acceptor concentration. We analyze the drawback of sensitization scheme, i.e. a self-quenching of Tm3+ excitation governing by the 5H4 → 3F4; 3H6 → 3F4 cross-relaxation. Nevertheless, this drawback compensates by fast depletion of the 5I6 terminal laser level with energy transfer governing by the 5I6 → 5I8; 3H6 → 3H5 cross-relaxation. As a result 3.9 μm laser transition of Ho3+ in BaF2: Ho3+: Tm3+ is not self-terminated. Moreover, efficient depletion of Ho3+ terminal laser level with energy transfer to the initial level of 3.6 μm laser transition of Tm3+ may cause cascade lasing in the mid-IR spectral range at two wavelengths of two different ions (Ho3+ and Tm3+).

The equation was presented for the spontaneous emission rate Anano of the two-level optical centers in the subwavelength ellipsoidal nanocrystals embedded in a dielectric medium. An important result was that the ratio Anano/Abulk could be estimated without recourse to a particular local-field model. On the ground of this equation the expression was derived for linestrength of electric-dipole transition in trivalent rare-earth ions. The applicability of the Judd-Ofelt equation for nanoparticles was discussed.

Using Particle-in-Cell simulations as well as analytical theory we study electron acceleration in underdense plasmas both in the Bubble regime and in the weakly relativistic periodic wake fields. In the Bubble regime, electron trapping is taken as a function of the propagated distance. The number of trapped electrons depends on the effective phase velocity of the X-point at the rear of the Bubble. For the weakly relativistic periodic wakes, we show that the phase synchronism between the wake and the relativistic electrons can be maintained over very long distances when the plasma density is tapered properly. Moreover, one can use layered plasmas to control and improve the accelerated beam quality. To cite this article: A. Pukhov et al., C. R. Physique 10 (2009).

The spectroscopic characteristics of translucent oxysulfide optical ceramics doped by Nd3+, which can be perspective for 1-μm lasing with high quantum efficiency is considered. Analysis of multiphonon relaxation (MR) rate of the low 4I11/2 laser level in the ceramics is provided using nonlinear theory of MR for multifrequency model of lattice vibration. MR rate dependence for the transitions with equal number of phonons p=4 on the extent of the phonon spectrum and Nd3+ to the nearest ligands distance R0 is established experimentally and analyzed. For the initial 4F3/2 laser level in the Gd2O2S:Nd3+ and La2O2S:Nd3+ ceramic samples an analysis of the energy transfer kinetics is provided. Different stages of energy transfer—direct energy transfer and a stationary migration-controlled stage are observed and analyzed. Dipole–dipole mechanism of energy transfer is established and microparameters of energy transfer and migration are determined.

Detailed calculations have been performed of multiphonon relaxation rates of optical excitations in Nd-doped LiYF 4 and Pr-doped CsCdBr 3 crystals in the frameworks of the exchange charge model of the crystal fields and rigid ion harmonic models of lattice dynamics. It is shown that the empirical energy gap low emerges from the exponential diminishing of spectral densities of n -phonon correlation functions with the increase of an order n . Calculated transition probabilities for 2-, 3-phonon processes agree with experimental data. However, for energy gaps exceeding the maximum phonon energy more than twice, the existing theory which neglects the lattice anharmonicity brings about underestimated relaxation rates.

Mid-IR Nd 3+ transitions perspective for laser oscillation were analyzed in the CaGa2S4, PbGa2S4, and PbCl2 crystals and compared with low phonon fluoride crystals. Fluorescence kinetics decay of the high-lying 4 G7/2 and 4 G5/2; 2 G7/2 and low-lying 4 IJ levels and its temperature dependence in the range of 13–295 K were measured. For 5 lm mid-IR transitions of Nd 3+ the radiative relaxation rates are found to be several times higher and multiphonon relaxation (MR) rates are several times lower in lead and calcium thiogallate crystals compared to low phonon fluoride crystals. MR rate dependence on the Nd 3+ to the nearest ligand distance R0 is established experimentally and analyzed in the frame of point-charge model of nonlinear theory of multiphonon relaxation. Mid-IR Nd 3+ 4–5.5 lm fluorescence spectra of 4 Ii– 4 Ij transitions perspective for laser oscillation were measured for the first time in the studied crystals.

We present the theory of vibronic sideband spectra due to coherent phonon modes using the conventional model of linear electron–phonon coupling and displaced equilibrium positions of the oscillators in the exited and final electronic states. Unlike in the conventional theory the initial state of the oscillator is taken as a coherent phonon state and not as a thermalized one. Under these conditions we got an exact analytical solution for the lineshape of the vibronic sideband. The sideband is determined by two parameters, the Huang–Rhys parameter S and the coherence parameter α of the phonon state. For α=0 the lineshape converts into the standard Pekarian form for T=0.

The cooperative energy transfer from a donor ion to two-particle acceptors is recently experimentally observed in many optically pumped rare-earth doped crystals and may appear in excitation quenching processes, as well as in down-conversion and sensitization energy transfer. Our theoretical study and computer simulation of cooperative three-body interaction for an ensemble of particles with different dimensions d , concentrations c , and multipolarity S have shown that donor fluorescence decay due to cooperative quenching corresponds to the asymptotic law I ( t ) ∼ exp[−( Wt ) d /2 S − d ] at the long-time stage. The power dependence of the cooperative quenching rate on the acceptor particle concentration was deduced to be W ∼ c 2 S / d .

The process of low temperature laser excitation of neodymium ion M pair centers in CaF2 crystals at the 4I9/2–4G5/2 optical transition is analyzed. It is shown that maximally entangled Bell’s vacuum–single exciton and vacuum–biexciton states are experimentally prepared when irradiating these crystals by nanosecond laser pulses.

We present results of the theoretical study of optical characteristics for the small-radius optical centers in the subwavelength ellipsoidal nanocrystals embedded in a medium. Analytical expressions are obtained for the electric-dipole and magnetic-dipole decay rates of excitations of optical centers in a magnetodielectric nanocomposite.

Conductivity of thin (∼200 nm) Indium Tin Oxide (TTO) films with pore size ∼2-3 nm demonstrates anomalous temperature behavior. After every heating-cooling cycle conductivity of the films reduced nearly irreversible. After exposing to the air conductivity increased to no more than 10 percent. We explain the effect by combination of water and oxygen adsorption and desorption from the surface and diffusion in the pores. Under heating electron-donor H2O molecules desorb and concentration of charge careers decreases respectively. Histeresis of temperature of conductivity can be related with electron-acceptor oxygen occupying adsorption sites of desorbed water molecules. These effects were never observed previously and result from the porous structure of the films.

Vibronic sidebands may originate from two main classes of processes which have been called Δ- and M-processes. We will consider multiphonon transitions in the M-process case; vibronics are induced by the joint action of the electromagnetic field and the high-order optical anharmonicity. The contributions to multiphonon sidebands due to point-charge, inhomogeneous-dielectric and polarized-ligand mechanisms are considered. As a result, all mechanisms considered by Judd for the one photon–one phonon transitions are extended to the multiphonon case.

Fluorescence kinetics decay of the 4 I 9/2 initial level for the 4.6 μm laser transition of erbium in the fluoride crystals with fluorite structure (CaF 2 , SrF 2 , CdF 2 , BaF 2 , and PbF 2 ) with short phonon spectra was measured at room temperature and 77 K. It was found that in the row of these crystals doped with erbium, the governing factor that influenced multiphonon relaxation (MR) rates is the number of phonons n , which is determined by the frequency of effective longitudinal optical phonon. A decrease of effective phonon frequency raises the number of phonons n . This decreases the MR rate and increases the fluorescence lifetimes for PbF 2 and BaF 2 . The latter fact could be favorable in laser generation in the 4–5 μm spectral region where multiphonon relaxation usually dominates. Influence of the unit dimension of crystal lattice (rare-earth ion to ligand distance R 0 ) on the MR rate is discussed.

An analytical expression and results of Monte-Carlo computer simulations are proposed for the kinetics of cooperative static quenching decay in crystals with arbitrary acceptor concentration and arbitrary multipolarity of interaction process S =6, 8, 10, which at a long decay time can be approximated by the nonexponential law I ( t )exp[−( wt ) k ], where k =0.41, 0.3, 0.25 for multipolarities S =6, 8, 10, respectively. The phenomenon of cooperative energy transfer from single Nd 3+ , Tm 3+ or Ho 3+ ion simultaneously to the pair of Ce 3+ ions and from single Er 3+ ion to three Ce 3+ ions with, respectively, two and three times smaller transition energy each in highly concentrated La 1− x Ce x F 3 crystals is presented. The influence of overlap integral (between donor ion and cooperative pair and triple Ce 3+ acceptor) and electronic matrix elements of donor transitions on the cooperative energy transfer rate for a set of donor ions is discussed.

We identified energy levels, and their corresponding symmetries, of F3+ and F2 color centers in LiF crystals, using the Feofilov method of polarized luminescence as applied to two-photon excitation. For this purpose, we measured the azimuthal dependencies of the polarization degree, P(ϕ), and the intensity, I(ϕ), of the F3+ and F2 color center luminescence in LiF crystals under two-photon excitation. To increase the reliability of the results we measured the polarization dependencies of three LiF crystal plates cut parallel to the three main crystallographic planes (1 0 0), (1 1 0) and (1 1 1), respectively. The measured polarization dependencies were seen to be in good agreement with the theoretical polarization dependencies derived for P(ϕ) and I(ϕ). We established that the new energy level of the F2 center has the same parity as the ground state. Consequently, the one-photon electric-dipole transitions are forbidden between the states. The symmetry of the new electronic state of the F3+center was found to be 1A1.

Excited Kramers fine level splittings of Nd 3+ pair (M) and quartet (N) clusters in CaF 2 crystal have been found and investigated by using absorption spectroscopy and accumulated photon echo (APE) techniques. Absorption spectra on the 4 I 9/2 → 4 G 5/2 transition between Kramers states split into four lines with overall splitting ∼5 cm −1 ( T =9 K, NdF 3 concentration 0.1, 0.3 and 1 wt%). At the picosecond laser excitation of the M- and N-centers on the same transition the APE kinetics was observed to be strongly modulated with multiple coherent beatings on pico- and nano-second time scale. Fast Fourier Transform (FFT) of the APE kinetics decay shows that nearest-neighbour absorption lines splittings 0.9, 1.5 and 2.1 cm −1 (M-center) are clearly defined in FFT spectrum. Theoretical study revealed that in general case the electrostatic interionic coupling lifts completely the eightfold degeneracy of the excited level of a pair of similar ions. The selection rules for the forced electric-dipole, magnetic dipole and quadrupole intermultiplet transitions are stated. It is suggested that in the case of Nd 3+ –Nd 3+ pair in CaF 2 (M-center), the strong quadrupole–quadrupole coupling is responsible for the fine splitting of the excited 4 I 9/2 × 4 G 5/2 levels and leads to delocalization of the optical electrons within ion pair.

The thermal instability development in a high Tc superconducting thin film carrying a transport current is studied both experimentally and theoretically. The normal phase propagation velocity ν is measured by means of both direct current and pulse current methods in a wide range of the transport currents I. It is shown that to explain the measured dependence ν(I) a non-linear heating over the thickness of a substrate, of which the reverse side is stabilized at a temperature T0, should be taken into account. The corresponding theory based on the solution of the non-stationary two-dimensional heat balance equation is developed and compared with experimental data. The results obtained may be of importance in the study of superconducting switching devices.

The paper discusses both the linear and nonlinear mechanisms of multiphonon relaxation (MR) transitions in trivalent rare-earth (RE) ions in crystals. In the first well-known case, the linear terms of electron-phonon interaction (EPI) with respect to vibronic coordinates are responsible for MR transitions. In the last case, the nonlinear part of EPI induces the multiphonon relaxation. The expression for total rate of the MR transition due to both mechanisms taken into account was obtained.

The results of measurements of fast nonradiative relaxation rates from the strongly quenched 4 G 5/2 ; 2 G 7/2 multiplet of the Nd 3+ ion in the LiYF 4 crystal and in the fluorite-type crystals (CaF 2 :NdF 3 (0.6%), CaF 2 :NdF 3 (0.25%) : LaF 3 (0.25%) and CaF 2 :NdF 3 (0.25%) : CeF 3 (0.25%)) with different Nd 3+ optical centers by direct laser-selective-excitation and selective fluorescence kinetics decay measurements are presented. The multiphonon relaxation time of 4 G 5/2 + 2G 7/2 multiplet of the Nd 3+ ion in the single-site LiYF 4 crystal (τ = 4.5 ns); and in a multi-site CaF 2 crystal for a tetragonal symmetry the L-center (τ L < 2.0 ns), for a rhombic symmetry pair (the M- and M'-centers) (τ M = 5.2 ns and τ M = 7.1 ns, respectively), and the cross-relaxational energy transfer rate inside the Nd*-Nd pair in CaF 2 (τ tr -1 = (τ M -1 - τ M' -1 ) -1 = 5.2 × 10 7 s -1 ) were measured. Comparison of the experimental multiphonon relaxation rates with the calculated ones by the nonlinear theory of multiphonon relaxation was done. The dependence of multiphonon relaxation rates on crystal matrix parameters is discussed. Comparison of the quenched energy transfer rate between two Nd 3+ ions at minimal distance for the 4 G 5/2 ; 2 G 7/2 multiplet in fluoride crystals was done. The fastest rate in CaF 2 (W = 5.2 × 10 7 s -1 with R min = 0.386 nm and the slowest in LaF 3 (W = 4.35 × 10 7 s -1 ) with R min = 0.410 nm were found. The analysis of the dominant mechanisms and possible channels of cross relaxation was made.

The quench process in a superconductor with changing transport current /(t) or placed into a varying magnetic field B(t) is studied. It is shown that to describe the quench process in this case the Stekly parameter α is insufficient, and it is necessary to introduce additional parameters β, γ and δ. Parameter β determines a range of current rates where the quench can be described by means of normal zone propagation. A fast current variation results in normal zone nucleation within ‘weak’ spots of a superconductor. The following quench development depends on the value of parameter γ defining a characteristic region where the ‘weak’ spot can affect normal zone nucleation and propagation. Normal zone nucleation in one strand of a multi-strand superconducting cable gives rise to a fast current redistribution among strands. Parameter δ determines a range of currents where the local quench in one strand does not result in the quench of the whole cable. The considered hierarchy of dimensionless parameters may be of importance in the study of a.c. superconductors stability. © 1997 Elsevier Science Limited

The fluorescence kinetics decay from 3F3, 3H5, 3H4, 3F4 multiplets of Tm3+ and 5F5, 5I5, 5S2 + 5F4, 5I6, 5I7 multiplets of Ho3+ ions in Y3Al5O12, Lu3Al5O12 and LiYF4 crystals was directly measured. On the basis of these measurements the multiphonon relaxation (MPR) rates of the transitions were determined. The theoretical dependence of multiphonon relaxation rates on the rare-earth ionic radii was derived using the non-linear (NL) theory of multiphonon relaxation. A good qualitative agreement of this dependence with new and earlier measured MPR rates in rare-earth ions in the row from Tm3+ to Pr3+ in YAG, YLF, and LaF3 crystals was obtained. The dependence of multiphonon relaxation rates on the crystal type is also considered.

The influence of current redistribution between strands on the quench process in a superconducting cable is studied. A theoretical model is developed which accounts for non-uniformities in strands. In agreement with experimental data, the model predicts that three different current redistribution modes may be observed in the cable, depending on the initial current; namely the current sharing mode, and slow and fast quench modes. It is shown that fast current redistribution can initiate multiple normal zone nucleation in strands. This phenomenon is responsible for an abnormally large normal zone propagation velocity. The results obtained are of importance for understanding the quench process in multistrand superconducting cables.