Design of a low-emittance 2.5-GeV pohang light source lattice
The Pohang Light Source (PLS) storage ring is a synchrotron light source with the emittance of 18.9 nm at 2.5 GeV. We designed a new lattice with an achromat of the emittance of 13 nm that may provide more brilliant synchrotron radiation. We investigated dependence of the dynamic aperture on the betatron tune to search for large dynamic aperture in the low-emittance lattice by a simulation method. We examined the dynamic apertures by a tune survey within a specified tune space without and with machine errors. It is also shown that how large is the dynamic aperture in the storage ring after correction of a closed orbit distortion. The operating tune for the low-emittance lattice can be chosen on the view point of dynamic apertures obtained from a tune survey. The low-emittance lattice with the achromat shows the reduced horizontal and vertical beam sizes by 10% and 29% in the positions of insertion devices and by 31% and 52% in the bending magnets than the present lattice, respectively. It is also shown that the low-emittance lattice with 13 nm may provide sufficient dynamic aperture without changing of configuration of magnets in the storage ring.
Status of the Swiss Light Source Project SLS
The status of the SLS project is reviewed. This light source is based on a 270 m circumference electron storage ring with a reference energy of 2.1 GeV and a minimum emittance of 2.3 nm·rad. The lattice has been optimised introducing phase trombones to provide a large dynamic aperture with an energy acceptance of ±4% over a wide tuning range. Preliminary design of the quadrupole and sextupole magnets indicate that a maximum energy of 2.4 GeV is feasible. The full energy injector is based on a low emittance booster synchrotron in the storage ring tunnel. A test stand for the RF gun is in the comissioning stage. Figure 1: Layout of the SLS facility with linac, booster and storage ring. Shown are the possible photon beamlines from insertion devices and the possible twin beamlines from the six superconducting bending magnets. 1 STORAGE RING DESIGN 1.1 Layout. The design as previously described [1] was further elaborated, increasing the flexibility and performance of the lattice. The layout of the storage ring (Fig.1) consists of six achromatic arcs, two very long (15.7 m) and four 8 m long straight sections, one of them reserved for injection. Each arc contains a superconducting bending magnet for hard X-ray production. The circumference was increased from 252 m to 270 m introducing four phase trombones. They allow tuning of the lattice down to a minimum emittance of 2.3 nm·rad at the reference energy of 2.1 GeV with zero dispersion in all straight sections and ±4% energy acceptance. The straights sections may be tuned to meet individual user requirements. However standard mode of operation is with the lattice tuned to an emittance of 3.6 nm·rad at 2.1 GeV, providing dynamic acceptances of approx. 40 μm·rad horizontally, 60 μm·rad vertically and ±5% longitudinally for the ideal lattice. Table 1 displays the most important lattice parameters in the standard mode, and Figure 2 shows the optical functions of one quarter of the lattice. Table 1: SLS storage ring main parameters Maximum energy GeV 2.4 Circumference m 270 Harmonic number 450 = 15·30 RF frequency MHz 500 Lattice parameters in standard mode: Tunes (x,y) 21.21 6.10 Chromaticities (x,y) -52 -21 Momentum compaction factor 0.0006 Equilibrium values at 2.1 GeV: Emittance nm·rad 3.6 Radiation loss keV 480 Energy spread r.m.s. 0.12 % Figure 2: Beta functions and dispersion of one quarter of the SLS storage ring. Four single 500 MHz RF cavitities with independent power sources are distributed around the ring for reliability, flexibility and in order to avoid coupled higher order modes. The cavities with their tapers will be accomodated in four dispersion free 2 m straight sections of the phase trombones. 1.2 Sextupole scheme The nine terms of the map in first order of sextupole strength b3, – four chromatic and five geometric modes, – are eliminated in one step. They are given by
In search of optimum chest radiography techniques.
A nation-wide study of chest radiography in Sweden had previously revealed a large variation in the physical and technical factors involved, in particular the radiation dose. In this study the image quality could not be assessed unambiguously. The aim of the present study was to try to establish a correlation between visual grading of radiographs and physical and technical factors in order to find the optimum chest X-ray system. The physical and technical performance of 24 chest units was evaluated. Radiographs were taken of an anthropomorphic chest phantom supplied with test structures simulating various pathologies. Image quality was assessed by visual grading analysis of the radiographs. The physical and technical parameters of the units rated best were used to exemplify good radiographic practice. The results were in agreement with the recommendations issued by the Commission of the European Communities (CEC). It was also shown that low radiation dose is compatible with high-quality radiographic imaging of the chest.