2-D Beam Focusing Control Based on Passive Frequency Selective Surface (FSS)

In this paper, the novel design methodology of 2-D beam focusing control based on passive frequency selective surface (FSS) is proposed and described. The beam focusing antenna is composed of 1-D array source and 2-D FSS having a good transmittance and a full transmission phase variation of 360°. The 2-D FSS is designed to make the phase of wave radiated by one source be in-phase, so the transmission phase of the 2-D FSS is concave in itself. Then, the designed 2-D FSS is integrated to the 1-D array source and the longitudinal and the transverse beam focusing controls can be achieved by changing the phase shape of the array source. The relation between the focusing point and the phase combination of the sources is analyzed by a parabolic formula, and the performance of the beam focusing control system is confirmed by both simulation and measurement. From both results, it is concluded that the focusing spot can be tuned longitudinally and transversely by the proposed methodology at 5.8 GHz. In addition, the electric field intensity of 1-D array source with 2-D FSS increases by about 35% compared to that of only 1-D array source.

Shear Resistance Contribution of Constituent Elements Consisting RCS Joint

In this study, constituent elements affecting the shear strength of RCS joints were investigated through experiment and analysis study. A series of five interior RCS beam-column joint specimens, which were classified as JH-type and CP-type, was tested to investigate the contribution of each shear resisting element such as JH (Joint Hoop), CP (Cover Plate), FBP (Face Bearing Plate), E-FBP (Extended Face Bearing Plate), TB (Transverse Beam), and BP (Band Plate). Comparison between experiment and analysis results showed that the stiffness and strength of the RCS joint were reasonably assessed from the analysis. As a result of the analysis, it was found that TB, E-FBP, and CP increased the shear strength by about 15%, 14%, and 26%, respectively. For the JH-type specimen, 70% of the shear strength of the RCS joint is supported by the inner element and 30% of the shear strength is supported by the outer element. Shear strength contribution ratio of the outer element of CP-type specimen is larger than that of the JH-type specimen. For all specimens except for SNI-1, around 10% of total shear strength is supported by FBP. The shear strength equation of the RCS joint proposed by ASCE underestimates the contribution of the outer element, while that of M-Kanno tends to overestimate it.

Feasibility of X-ray beam nanofocusing with compound refractive lenses

A more general analytical theory of X-ray beam propagation through compound refractive lenses (CRLs) than the earlier study by Kohn [(2003). JETP, 97, 204–215] is presented. The problem of nanofocusing with CRLs is examined in detail. For a CRL with a relatively large aperture the focusing efficiency is limited by the radiation absorption in the lens material. The aperture does not affect the focusing process and it is replaced by the effective aperture. The X-ray transverse beam size at the focus is then by a factor of γ = β/δ times smaller than the transverse beam size just behind the CRL. Here, δ and β are the real and imaginary parts of the CRL material refractive index n = 1 − δ + iβ. In this instance, to improve focusing efficiency, it is advantageous to decrease the CRL aperture and increase the photon energy E. However, with increasing photon energy, the material absorption decreases, which results in the CRL aperture impact on the transverse beam size. The latter leads to the fact that with a proper CRL length the beam size is independent of both the aperture and photon energy but depends only on the CRL material electron density and is approximately equal to w c = λ/(8δ)1/2, where λ denotes the radiation wavelength, as predicted by Bergemann et al. [(2003). Phys. Rev. Lett, 91, 204801].

Virtual Diagnostic Suite for Electron Beam Prediction and Control at FACET-II

We discuss the implementation of a suite of virtual diagnostics at the FACET-II facility currently under commissioning at SLAC National Accelerator Laboratory. The diagnostics will be used for the prediction of the longitudinal phase space along the linac, spectral reconstruction of the bunch profile, and non-destructive inference of transverse beam quality (emittance) while using edge radiation at the injector dogleg and bunch compressor locations. These measurements will be folded into adaptive feedbacks and Machine Learning (ML)-based reinforcement learning controls to improve the stability and optimize the performance of the machine for different experimental configurations. In this paper we describe each of these diagnostics with expected measurement results that are based on simulation data and discuss progress towards implementation in regular operations.