[en] The emission processes of electron beams from Cs₂Te photocathodes have been experimentally studied at the photoinjector test facility at Zeuthen (PITZ) and the results have been compared with simulations. Low charge electron beams have been generated in order to minimize the space charge influence. Drive-laser pulses with a short length have been used to generate the bunches in order to maximize the emission phase sensitivity. As a function of emission phase and rf gradient, the Schottky effect, the thermal emittance variation, and the secondary electron emission processes have been investigated. The results for the low charge beams have been extended to analyze the beam dynamics for typical operating conditions of PITZ. Characteristic field emission sources for dark current and its dynamics with respect to the rf gradients and the solenoid field configurations have been studied. Electron multipacting occurring at the photocathode has been measured systematically and the multiplication process has been numerically modeled. Finally, the thermal emittance of the beam, dark current and multipacting for the X-ray free electron laser (XFEL) gun have been estimated. (orig.)

[en] Microstructural evolution during equal channel angular rolling (ECAR) is investigated in a 7050 Al alloy sheet that includes two types of precipitates, large plate-type MgZn₂ and fine spherical Al₃Zr. With increasing number of ECAR passes, gradual fragmentation of MgZn₂ precipitates and subsequent grain refinement are revealed by transmission electron microscopy. After 6 passes of ECAR, the sheet's grain size decreases to ∼600 nm and most large plate-type MgZn₂ precipitates are fragmented into fine spherical particles. Roles of the two types of precipitates on the evolution of fine-grained structure are discussed

[en] A magnetoinductive (Darwin) particle simulation model developed for examining low frequency plasma behavior with large time steps is presented. Electron motion perpendicular to the magnetic field is treated as massless keeping only the guiding center motion. Electron motion parallel to the magnetic field retains full inertial effects as does the ion motion. This model has been implemented in two and three dimensions. Computational tests of the equilibrium properties of the code are compared with linear theory and the fluctuation dissipation theorem. This code has been applied to the problems of Alfven wave resonance heating and twist-kink modes

[en] The authors have cloned a full-length putative rat pancreatic lysophospholipase cDNA by an improved mRNA isolation method and cDNA cloning strategy using [³²P]-labelled nucleotides. These new methods allow the construction of a cDNA library from the adult rat pancreas in which the majority of recombinant clones contained complete sequences for the corresponding mRNAs. A previously recognized but unidentified long and relatively rare cDNA clone containing the entire sequence from the cap site at the 5' end to the poly(A) tail at the 3' end of the mRNA was isolated by single-step screening of the library. The size, amino acid composition, and the activity of the protein expressed in heterologous cells strongly suggest this mRNA codes for lysophospholipase

[en] The planned Korea Superconducting Tokamak Advanced Research (KSTAR) divertor has been designed to provide reliable power handling and particle control with enough shaping flexibility to accommodate a wide range of plasma operation. The physics basis for the current configuration of the KSTAR divertor through analyses of the heat flux at the target, particle control, and plasma-facting component is reported. A simple zero-dimensional model based on the power balance assumptions and two-dimensional codes is utilized to estimate the heat flux to the divertor plate. The limit for the peak heat flux on the divertor plate, 3.5 MW/m², requires advanced operating modes such as the radiative divertor and radiative mantle, which are considered to overcome the weakness of a high-recycling divertor. A simple particle balance model could estimate the pumping rate with total leakage fraction assuming particle sources. A Monte Carlo neutral transport calculation determines the dimension of a gap between the center and outer divertor targets. It also determines the number and best position of the pumps, as well as the geometry for conductance. For the initial 20-s discharges, a bolted-tile carbon-fiber-composite design is relied upon for the upper and lower divertor targets. The design of the supporting structure for the divertors will allow for future modifications to accommodate thermal steady-state 300-s operation or to optimize divertor performance based on new understanding gained during initial tokamak operation

[en] A mathematical model of fluid flow and turbulent characteristics in continuous casting tundishes has been develpoed with the use of 2-D computational scheme together with adequate modelling of turbulent viscosity. Computations for a various flow control in a tundish are presented via full scale molten steel system. Similary, the behavior of non-metallic inclusions is modelled by establishing a particle force balance in a moving fluid system. The results obtained from these studies are expected to be used semi-quantitatively in the conventional metallurgical processes governed by transport phenomena. (Author)

[en] Destructive analysis on three pulled tubes from a Korean nuclear power plant was carried out. The microstructure was analyzed using an optical microscope and a transmission electron microscope (TEM). Information on the crack length and depth was obtained by metallography, and crack detection and evolution were evaluated by analyzing the eddy current data obtained from each In-Service-Inspection (ISI). A shape of cracks was identical to that of the other plants kiss rolled at the top of tube sheet. The carbon content in the pulled tubes was higher than that of Alloy 600 tubing used in other operating nuclear power plants. Most carbides in the pulled tubing were distributed in the grains rather than along the grain boundaries. The poor microstructure might come from high carbon contents, low temperature annealing, or high residual stress during tube straightening. Mill annealing temperature should be high to dissolve all carbon in order to decorate the grain boundary with semi-continuous carbide during 700 C thermal treatment. Shot peening seemed to suppress the growth of the axial cracks, while it was analyzed to play a role in increasing crack growth in the wall thickness direction. (authors)

[en] Streaming cold ions due to the potential drop along the magnetic field lines in the high latitude Auroral zone is the main free energy source of the instabilities occurring in this region. Both linear and nonlinear behavior of these streaming instabilities are studied concentrating on parallel subsonic ions of H⁺ and O⁺ with relative streaming velocity Δv < C_s(H⁺). Linear analysis shows that for Δv > v_th(H⁺) there exists a critical k_c in wave number space with unstable modes for k < k_c and stable modes above k_c for given free energy m_HΔv²/2. Particle simulation using a 1-D quasi-neutral code having massless electrons with full nonlinear adiabatic response are carried out. It is shown that the most unstable short wave length mode in the linear stage breaks and coalesces into long wave length modes with scale length order of several electron debye length in the saturated state. Power spectrum analysis shows that the phase velocities of this long wave length modes are order of the thermal velocities of ion species but rather close to heavy ion species and thus induces significant heavy ion heating. Dynamics of the phase space vortices coalescence is discussed

[en] We have developed a hybrid particle-fluid computer model for quasineutral microinstabilities in magnetically confined plasmas. The ions are treated in the fluid approximation. The electrons are taken as guiding-center macroparticles. The model has been extensively tested for frequency and fluctuation spectra. Linear and nonlinear studies of drift waves, η_i modes, interchange modes, and trapped electron modes have also been carried out. 4 refs., 3 figs

[en] Particle simulation using a nonlinear adiabatic electron response with two streaming ion species and nonlinear theory are used to study the collisionless thermalization of ion beams in a hot electron plasma. The slow beam or subsonic regime is investigated and the criterion for the transition from predominantly light ion to predominantly heavy ion heating is developed. Long-lived ion hole structures a-re observed in the final state