Coherent Diffraction Radiation experiment at CTF3—Simulation studies

A two-target model was developed for the simulations of Coherent Diffraction Radiation (CDR) phenomenon for the experiment at the CLIC Test Facility 3 (CTF3 at CERN). The model is based on a classical DR theory. The radiation distribution from the targets, as a function of the angle and the frequency, was calculated for the first and the second target separately in order to understand how the final radiation distribution from the two targets, working as a system, is formed. The final radiation distribution of destructive interference between the two targets was obtained as well. The distributions were calculated for the working parameters of both the CTF3 and the experimental setup and were used for a single-electron spectrum calculation, required for the bunch profile reconstruction

Diffractive shadowing of coherent polarization radiation

We report on the study of shadowing of electromagnetic fields radiated in the Terahertz (THz) region from two consecutive sources of coherent diffraction and transition radiation. In these conditions, the formation length is predicted to be $\leq$ 100 m, and shadowing effects should result in an almost complete suppression of radiated fields within distances of the order of tens of centimeters. We experimentally measured that shadowing effects disappear for distances significantly shorter than those predicted. We propose a new model that explains our experimental observations by taking into account 3D diffraction effects. These findings will have a positive impact on the beneficial use of consecutive radiators both for the generation of intense electromagnetic radiation and for beam diagnostics using coherent polarization radiation from ultra-relativistic charged particles

Monochromaticity of coherent Smith-Purcell radiation from finite size grating

Investigation of coherent Smith-Purcell Radiation (SPR) spectral characteristics was performed both experimentally and by numerical simulation. The measurement of SPR spectral line shapes of different diffraction orders was carried out at KEK LUCX facility. A pair of room-temperature Schottky barrier diode (SBD) detectors with sensitivity bands of $60-90$~GHz and $320-460$~GHz was used in the measurements. Reasonable agreement of experimental results and simulations performed with CST Studio Suite justifies the use of different narrow-band SBD detectors to investigate different SPR diffraction orders. It was shown that monochromaticity of the SPR spectral lines increases with diffraction order. The comparison of coherent transition radiation and coherent SPR intensities in sub-THz frequency range showed that the brightnesses of both radiation mechanisms were comparable. A fine tuning feasibility of the SPR spectral lines is discussed.Comment: 7 pages, 7 figures, 3 table

Selectivity of stop codon recognition in translation termination is modulated by multiple conformations of GTS loop in eRF1

Translation termination in eukaryotes is catalyzed by two release factors eRF1 and eRF3 in a cooperative manner. The precise mechanism of stop codon discrimination by eRF1 remains obscure, hindering drug development targeting aberrations at translation termination. By solving the solution structures of the wild-type N-domain of human eRF1 exhibited omnipotent specificity, i.e. recognition of all three stop codons, and its unipotent mutant with UGA-only specificity, we found the conserved GTS loop adopting alternate conformations. We propose that structural variability in the GTS loop may underline the switching between omnipotency and unipotency of eRF1, implying the direct access of the GTS loop to the stop codon. To explore such feasibility, we positioned N-domain in a pre-termination ribosomal complex using the binding interface between N-domain and model RNA oligonucleotides mimicking Helix 44 of 18S rRNA. NMR analysis revealed that those duplex RNA containing 2-nt internal loops interact specifically with helix α1 of N-domain, and displace C-domain from a non-covalent complex of N-domain and C-domain, suggesting domain rearrangement in eRF1 that accompanies N-domain accommodation into the ribosomal A site

Investigation of Coherent Diffraction Radiation from a dual target system at CTF3 and its application for longitudinal bunch profile diagnostics

A coherent Diffraction Radiation (CDR) originating from a dual-target system was investigated theoretically and experimentally. Diffraction Radiation is emitted when a bunch of charged particles moves in the vicinity of an optical obstacle. The coherency of the effect is achieved when electrons in the bunch radiate in phase, i.e. the wavelength of the radiation is comparable to or larger than the bunch length. An experimental setup at the CLIC Test Facility 3 (CTF3) at CERN was modified by installation of a second target. In the experiment two targets are positioned to one side of the beam and the radiation originating from them is translated towards a Michelson interferometer. The ultimate goal of the experiment is to reconstruct the longitudinal parameters of the beam from the CDR spectrum. A precise knowledge of the bunch time profile is particularly important in the context of a luminosity challenge in the future linear colliders and therefore the development of a non-invasive and robust longitudinal beam diagnostic technique is very important. A theoretical model based on the classical Diffraction Radiation theory was devel- oped to calculate the spatial distributions of the CDR from the dual-target system and based on this knowledge to calculate a single electron spectrum which is used in a bunch shape reconstruction. The Kramers-Kronig analysis as a tool for the bunch profile reconstruction was studied theoretically. The CDR spatial distributions were measured at the experimental setup and compared with the theory. The ability of the two-target system to cut-off the backgrounds originating upstream of the experimental setup was tested.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Investigation of Coherent Diffraction Radiation from a dual target system at CTF3 and its application for longitudinal bunch profile diagnostics

A coherent Diffraction Radiation (CDR) originating from a dual-target system was investigated theoretically and experimentally. Diffraction Radiation is emitted when a bunch of charged particles moves in the vicinity of an optical obstacle. The coherency of the effect is achieved when electrons in the bunch radiate in phase, i.e. the wavelength of the radiation is comparable to or larger than the bunch length. An experimental setup at the CLIC Test Facility 3 (CTF3) at CERN was modified by installation of a second target. In the experiment two targets are positioned to one side of the beam and the radiation originating from them is translated towards a Michelson interferometer. The ultimate goal of the experiment is to reconstruct the longitudinal parameters of the beam from the CDR spectrum. A precise knowledge of the bunch time profile is particularly important in the context of a luminosity challenge in the future linear colliders and therefore the development of a non-invasive and robust longitudinal beam diagnostic technique is very important. A theoretical model based on the classical Diffraction Radiation theory was devel- oped to calculate the spatial distributions of the CDR from the dual-target system and based on this knowledge to calculate a single electron spectrum which is used in a bunch shape reconstruction. The Kramers-Kronig analysis as a tool for the bunch profile reconstruction was studied theoretically. The CDR spatial distributions were measured at the experimental setup and compared with the theory. The ability of the two-target system to cut-off the backgrounds originating upstream of the experimental setup was tested.EThOS - Electronic Theses Online ServiceGBUnited Kingdo