205 research outputs found
Complex unit lattice cell for low-emittance storage ring light source
To achieve the true diffraction-limited emittance of a storage ring light
source, such as ~10 pm.rad for medium-energy electron beams, within a limited
circumference, it is generally necessary to increase the number of bending
magnets in a multi-bend achromat (MBA) lattice, as in the future upgrade plan
of MAX IV with a 19BA replacing the current 7BA. However, this comes with
extremely strong quadrupole and sextupole magnets and very limited space. The
former can result in very small vacuum chambers, increasing the coupling
impedance and thus enhancing the beam instabilities, and the latter can pose
significant challenges in accommodating the necessary diagnostics and vacuum
components. Inspired by the hybrid MBA lattice concept, in this paper we
propose a new unit lattice concept called the complex unit lattice cell, which
can reduce the magnet strengths and also save space. The complex unit cell is
numerically studied using a simplified model. Then as an example, a 17BA
lattice based on the complex unit cell concept is designed for a 3 GeV storage
ring light source with a circumference of 537.6 m, which has a natural
emittance of 19.3 pm.rad. This 17BA lattice is also compared with the 17BA
lattice designed with conventional unit cells to showcase the benefits of the
complex unit cell concept. This 17BA lattice also suggests a new type of MBA
lattice, which we call the MBA lattice with semi-distributed chromatic
correction
Minimizing the fluctuation of resonance driving terms in dynamic aperture optimization
Dynamic aperture (DA) is an important nonlinear property of a storage ring
lattice, which has a dominant effect on beam injection efficiency and beam
lifetime. Generally, minimizing both resonance driving terms (RDTs) and
amplitude dependent tune shifts is an essential condition for enlarging the DA.
In this paper, we study the correlation between the fluctuation of RDTs along
the ring and the DA area with double- and multi-bend achromat lattices. It is
found that minimizing the RDT fluctuations is more effective than minimizing
RDTs themselves in enlarging the DA, and thus can serve as a very powerful
indicator in the DA optimization. Besides, it is found that minimizing
lower-order RDT fluctuations can also reduce higher-order RDTs, which are not
only more computationally complicated but also more numerous. The effectiveness
of controlling the RDT fluctuations in enlarging the DA confirms that the local
cancellation of nonlinear effects used in some diffraction-limited storage ring
lattices is more effective than the global cancellation
EMITTANCE OPTIMIZATION USING PARTICLE SWARM ALGORITHM*
Abstract In this paper we use a swarm intelligence algorithm, Particle Swarm Optimization (PSO), to optimize the emittance directly. Some constraint conditions such as beta functions, fractional tunes and dispersion function, are considered in the emittance optimization. We optimize the strengths of quadrupoles to search for low emittances. Here an FBA lattice studied in the design of the Hefei Advanced Light Source storage ring is used as the test lattice. The PSO is shown to be beneficial in the optimization
Design of Compact Dual-Polarized Antennas for MIMO Handsets
A design method of compact dual-polarized antennas has been proposed for multiple input and multiple output (MIMO) handset application. For the sake of high isolation in dual polarizations, a printed monopole and a hybrid slot antenna are combined using a coplanar waveguide (CPW) and microstrip hybrid feeding structure. The proposed topology will result in orthogonal current distribution modes for the different polarizations, which effectively reduces the mutual coupling of the two modes. The operation mechanism of the feeding structure is analyzed in principle and verified by simulation. Simulated and measured results show this compact dual-polarized antenna achieves isolation between the two ports of better than 25 dB, and the relative bandwidth is wider than 23.5%
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