In this paper, we present the radio-frequency design of the DECA S-band accelerating structure, operating at 2.856 GHz in the Ï€-mode. RadiaBeam Technologies is developing a Doubled Energy Compact Accelerator (DECA) structure: an S-band standing wave electron linac designed to operate at accelerating gradients of up to 50 MV/m. Yakimenko, V.Ī strong demand for high gradient structures arises from the limited real estate available for linear accelerators. Ultra-High Gradient S-band Linac for Laboratory and Industrial Applicationsįaillace, L. Recent experimental results of near field gradient effects on HV-TERS were summarized, following the section of the theoretical analysis. Theoretical calculations also revealed that with the increase in gap distance between tip and substrate, the decrease in the plasmon gradient was more significant than the decrease in plasmon intensity, which is the reason that the gradient Raman can be only observed in the near field. The intensity ratio of the plasmon gradient term over the linear plasmon term can reach values greater than 1. Theoretical calculations using electromagnetic field theory firmly supported experimental observation. Furthermore, the molecular overtone modes and combinational modes can also be experimentally measured, where the Fermi resonance and Darling-Dennison resonance were successfully observed in HV-TERS. HV-TERS can not only be used to detect ultra-sensitive Raman spectra enhanced by surface plasmon, but also to detect clear molecular IR-active modes enhanced by strongly plasmonic gradient. Near field gradient effects in high vacuum tip-enhanced Raman spectroscopy (HV-TERS) are a recent developing ultra-sensitive optical and spectral analysis technology on the nanoscale, based on the plasmons and plasmonic gradient enhancement in the near field and under high vacuum.
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Near field plasmonic gradient effects on high vacuum tip-enhanced Raman spectroscopy.įang, Yurui Zhang, Zhenglong Chen, Li Sun, Mengtao
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We successfully combined this two-dimensional (2D) NMR experiment with methods for the application of ultra-high pulsed field gradients of up to 35 T/m, resulting in observation times and mixing times as short as 2 ms and 2.8 ms, respectively. Investigation of Molecular Exchange Using DEXSY with Ultra-High Pulsed Field Gradientsĭiffusion exchange spectroscopy has been employed for the investigation of water exchange between different regions of a cosmetic lotion as well as for the exchange of n-pentane between the inter- and intra-crystalline space in zeolite NaX. Several promising UHF-relevant gradient concepts are described, including insertable gradient coils aimed at higher performance neuroimaging. In particular, Lorentz forces, vibroacoustics, eddy currents, and peripheral nerve stimulation are discussed. This review summarizes the basics of gradient and shim technologies, and outlines a number of UHF-related challenges and solutions. Both the more challenging UHF environment by itself, as well as the higher currents used in high performance coils, require a deeper understanding combined with sophisticated engineering modeling and construction, to optimize gradient and shim hardware for safe operation and for highest image quality. Ultra High Field (UHF) MRI requires improved gradient and shim performance to fully realize the promised gains (SNR as well as spatial, spectral, diffusion resolution) that higher main magnetic fields offer.
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Schmitt, Franz Landes, Hermann DeBever, Josh Wade, Trevor Alejski, Andrew Gradient and shim technologies for ultra high field MRI