Design and comparison of hybrid multi-bend achromat lattices for HALF storage ring

The Hefei Advanced Light Facility(HALF)proposed by the National Synchrotron Radiation Laboratory is a green-field vacuum ultraviolet and soft X-ray diffraction-limited storage ring light source with a beam energy of 2.2 GeV and emittance goal of less than 100 pm rad.Inspired by the ESRF-EBS hybrid multi-bend achromat(HMBA),SLS-2,and Diamond-II lattices,we have proposed and designed a modified H6BA lattice as the baseline lattice of the HALF storage ring with 20 identical cells and a natural emittance of approximately 86 pm rad.In this paper,three other types of HMBA lattices including two H7BA lattices and a H6BA lattice are designed for HALF with the same number of cells.The main storage ring proper-ties of these four HMBA lattices are compared.Because the intra-beam scattering(IBS)effect is significant in the HALF storage ring,we calculate and compare the equilibrium emittances of the four lattices with IBS included.These comparisons show that the present modified H6BA lattice,which has a relatively low equilibrium emittance and more straight sections,is preferred for the HALF storage ring after a comprehensive consideration.

Monte Carlo simulation of incident electrons passing through thin metal layer

A Monte Carlo simulation using two schemes,the discrete energy loss approach and the continuous slowing down approximation,was implemented in C++ to calculate the energy transmission coefficient and average energy loss for low-energy(1–10 keV) incident electrons passing through a thin metal layer.The simulation model uses the Ashley model for electron inelastic scattering,the electron elastic scattering cross section taken from the NIST database,and the stopping power derived from the full Penn algorithm.The results of the two schemes agree well with each other and can be used to quantitatively evaluate the shielding effect of a thin coated metal layer on incident electrons for a diamond amplified photocathode.