A seven-bend-achromat lattice option for the HALF storage ring

The Hefei Advanced Light Facility (HALF) is a soft X-ray diffraction-limited storage ring being designed with an energy of about 2.2 GeV and an emittance goal of less than 100 pm·rad. The present HALF lattice is a modified hybrid six-bend-achromat (6BA) lattice with a long and a short straight section in each cell. In this paper, a 7BA lattice is designed for HALF as a promising option, which follows the main feature of hybrid 7BA lattice, but to have a compact configuration and lower emittance, all bends in this lattice are combined-function bends and reverse bends. The designed HALF storage ring has a circumference of 388.8 m and 20 identical cells. Two solutions with different betatron tunes are studied for this lattice. One with smaller tunes has better nonlinear dynamics performance allowing for off-axis injection, which has a natural emittance of 67 pm·rad. The other with larger tunes has very small beta functions at the straight section as well as lower natural emittance of 59 pm·rad, which can enhance the brightness of insertion device (ID) radiation. The intra-beam scattering effect and ID radiation properties are also presented in this paper.

Scattering of generalized Bessel beams simulated with the discrete dipole approximation

We consider the simulation of scattering of the high-order vector Bessel beams in the discrete dipole approximation framework (DDA). For this purpose, a new general classification of all existing Bessel beam types was developed based on the superposition of transverse Hertz vector potentials. Next, we implemented these beams in ADDA code – an open-source parallel implementation of the DDA. The code enables easy and efficient simulation of Bessel beams scattering by arbitrary-shaped particles. Moreover, these results pave the way for the following research related to the Bessel beam scattering near a substrate and optical forces.