Experiments and analysis of thin tungsten slice and W/Cu brazing for primary collimator scraper in CSNS/RCS

According to the requirements for the beam collimation system of the rapid cycling synchrotron(RCS)of China Spallation Neutron Source(CSNS),the main structure of a scraper of primary collimator is made by W/Cu brazing,in which the thickness of tungsten slice is 0.17 mm.In order to get the best mechanical properties,the brazing temperature is suggested to be controlled under the recrystallization temperature of tungsten,while the recrystallization temperature is affected directly by the thickness of tungsten.Because of little research and application on the brazing of thin tungsten slice of 0.17 mm and copper,tensile tests are done to get the mechanical properties of tungsten slices which experience different brazing temperatures.In keeping the inner relationships between the mechanical properties and temperature,another experiment is done by using SEM to scan the microstructures including the size and distribution of crystals.Finally we determine the recrystallization temperature of tungsten slice of 0.17 mm,and get the best parameters of W/Cu brazing for scrapers of primary collimator in CSNS/RCS.     

Maximal possible accretion rates for slim disks

It was proved in the previous work that there must be a maximal possible accretion rate $ \dot M_{max} $ \dot M_{max} for a slim disk. Here we discuss how the value of $ \dot M_{max} $ \dot M_{max} depends on the two fundamental parameters of the disk, namely the mass of the central black hole M and the viscosity parameter α. It is shown that $ \dot M_{max} $ \dot M_{max} increases with decreasing α, but is almost independent of M if $ \dot M_{max} $ \dot M_{max} is measured by the Eddington accretion rate $ \dot M_{Edd} $ \dot M_{Edd} , which is in turn proportional to M.     

The CST bounce universe model——A parametric study

A bounce universe model with a scale-invariant and stable spectrum of primordial density perturbations was constructed using a consistent truncation of the D-brane dynamics from Type IIB string theory. A coupling was introduced between the tachyon field and the adjoint Higgs field on the D3-branes to lock the tachyon at the top of its potential hill and to model the bounce process,which is known as the Coupled Scalar and Tachyon Bounce(CSTB) Universe. The CSTB model has been shown to be ghost free,and it fulfils the null energy condition; in addition, it can also solve the Big Bang cosmic singularity problem. In this paper we conduct an extensive follow-up study of the parameter space of the CSTB model. In particular we are interested in the parameter values that can produce a single bounce to arrive at a radiation-dominated universe. We further establish that the CSTB universe is a viable alternative to inflation, as it can naturally produce a sufficient number of e-foldings in the locked inflation epoch and in the post-bounce expansion to overcome the four fundamental limitations of the Big Bang cosmology, which are flatness, horizon,homogeneity and singularity, resulting in a universe of the current size.     

Design and manufacturing of the antechamber for BEPCII storage rings

Antechamber which composes the arc vacuum chamber of storage rings is one of the key devices of BEPCII. It has the characteristic of various specifications, large size, complex structure, and high dimension accuracy. This paper gives a review on the structure features and the procedure of production, including the mechanical machining process, cleaning and welding process of high vacuum aluminum alloy, ultrahigh vacuum test and so on. In view of the occurrence of the concave deformation, the reasons are analyzed and the correction method developed is introduced too.