[en] A modified cup-like TW accelerating structure for TESLA Positron Pre-Accelerator (PPA) is designed by optimizing the structure geometry and by changing the iris thickness cell by cell in a section . This structure has high shunt-impedance and a large iris radius to meet with the requirements of high gradient and large transverse acceptance. The beam dynamics in the structure with the optimum solenoid focus field are studied. A satisfactory positron beam transmission and the beam performance at the PPA output have been obtained. In this paper the accelerating structure design is described in detail and the results are presented

[en] The collinear load consists of few disk-loaded cavities coated with high-resistance material on the inside walls. The load terminates the accelerator section and forms a part of actual accelerating structure with collinear to the electron beam. Not only can it dissipate residual RF power of the accelerator section in the form of skin losses, but also the particles are still accelerated in the structure. In this paper, the design and technology of an X-band constant power-loss collinear load are described in detail and some results are presented

No abstract available

[en] The RF coupler is an important component for a Linac accelerating structure. It must be well matched to the feeding waveguide and has synchronous frequency for the proper phase advance in the structure so that the input power is fed into effectively and an excellent travelling wave is transmitted in the accelerating cavities train. In our project, S-Band Linac Radiation Facility R and D, a calculation means for RF coupler numerical simulation design was considered by computing the phase of scattering parameter S₁₁ and the good results are obtained in conjunction with microwave measurement. In this paper, the three-dimension time-domain S-parameters calculation for coupler design is described in detail. The results and analysis of computation and measurement are presented

[en] Charge-ordered La_0.5Ca_0.5MnO₃ film has been deposited on (100)-LaAlO₃ substrate using rf magnetron sputtering method. X-ray diffraction analysis shows that the bulk has orthorhombic structure and the film has the better epitaxial character. The charge-ordering transition temperature is about 280 K by fitting the resistance-temperature curve using the variable-range hopping model. The decrease in the resistance of the film irradiated by the laser is caused by the delocalization effect of the correlated electron system. The photoinduced relaxation exhibits different processes when the laser is on and off, which can be attributed to thermal fluctuation

[en] La_0.67Sr_0.33Mn_0.95Zn_0.05O₃ film has been deposited on LaAlO₃ (100) substrate by the magnetron sputtering method. The results concerning the photoinduced character of the film are reported. In the ferromagnetic metallic state, the increasing photoinduced resistance is caused by photoinduced demagnetization of the spin correlation system in manganites. The photoinduced relaxation character of the film indicates that the time constant increases with increasing temperature, which is attributed to the thermal fluctuation

[en] The quantum-size effects are shown to play a crucial role in defining the patterns of metal islands formed on surfaces. The energy in elongated needlelike islands oscillates with the width of the needle, clearly demonstrating the existence of preferred needle widths. The energy of the square or rectangular islands varies periodically with the side length, predicting preference for islands with specific sizes. copyright 1998 The American Physical Society

[en] The transport properties of the La_0.8Sr_0.2MnO₃/Co heterostructrue prepared by the sol-gel method were investigated. The results about the heterostructure in the current-perpendicular-to-plane geometry are reported. The sample exhibits the semiconductor-type conduction as the temperature is increased. The formed interface is the Schottky barrier and the dominant transport is the quasiparticle tunnelling via a pair of localized states due to the space-charge limits rule

[en] Phase stability of NiCoFeCr and Al_0.12NiCoFeCr single phase high entropy alloys (HEAs) was studied under 3 MeV Ni²⁺ irradiation at 500 ^°C to a fluence of 1 × 10¹⁷/cm² reaching a peak dose of ~100 displacements per atom (dpa). Transmission electron microscopy (TEM) diffraction pattern and scanning transmission electron microscopy-energy dispersive X-Ray spectroscopy (STEM-EDS) were utilized to detect any second phases that formed in the irradiated regions of the specimens. While the single phase of NiCoFeCr alloy has remained stable under the irradiation, the phase in Al_0.12NiCoFeCr alloy decomposed into FCC matrix phase, and Ni₃Al type nanoprecipitates with L1₂ ordered structure. On the other hand, in Al_0.12NiCoFeCr alloy, the non-irradiated region of the TEM specimen (annealed for 10 h at 500 ^°C) and the as-cast alloy annealed for 490 h at 500 ^°C exhibited no such precipitates similar to those observed in the irradiated region. Based upon the thermodynamic stability of these alloys, we propose that radiation-enhanced diffusion under the irradiation accelerated the formation of the Ni₃Al type equilibrium phase. Our study clearly demonstrates that the phase stability of HEAs under irradiation should be considered as one of the deciding factors in the materials design and selection for nuclear applications.

[en] NiCoCrFeMn and NiCoCrFe high-entropy alloys are formed by the method of arc melting and casting in a copper cell, followed by vacuum annealing at a temperature. Studies carried out by scanning electron microscopy and XRD analysis showed that the formed HEAs have a coarse-grained structure (80-100 μm) and are single-phase substitutional solid solutions with an fcc lattice. High-entropy alloys were irradiated at room temperature with He ions with the energy of 40 keV at fluences from 3×10¹⁷ to 5×10¹⁷ cm^-2 cm². It was found that irradiation with helium ions does not lead to erosion of the sample surface, as well as to the decomposition of NiCoCrFeMn and NiCoCrFe solid solutions. An increase in the root-mean-square deviation and tensile stresses in the samples under irradiation with helium ions is revealed. It was found that the most radiation-resistant system is NiCoCrFeMn. (authors)