Study of Phase Reconstruction Techniques applied to Smith-Purcell Radiation Measurements

Measurements of coherent radiation at accelerators typically give the absolute value of the beam profile Fourier transform but not its phase. Phase reconstruction techniques such as Hilbert transform or Kramers Kronig reconstruction are used to recover such phase. We report a study of the performances of these methods and how to optimize the reconstructed profiles.Comment: Presented at IPAC'14 - THPME08

Proceedings of the third French-Ukrainian workshop on the instrumentation developments for HEP

The reports collected in these proceedings have been presented in the third French-Ukrainian workshop on the instrumentation developments for high-energy physics held at LAL, Orsay on October 15-16. The workshop was conducted in the scope of the IDEATE International Associated Laboratory (LIA). Joint developments between French and Ukrainian laboratories and universities as well as new proposals have been discussed. The main topics of the papers presented in the Proceedings are developments for accelerator and beam monitoring, detector developments, joint developments for large-scale high-energy and astroparticle physics projects, medical applications.Comment: 3rd French-Ukrainian workshop on the instrumentation developments for High Energy Physics, October 15-16, 2015, LAL, Orsay, France, 94 page

Comparison of Coherent Smith-Purcell Radiation and Coherent Transition Radiation

International audienceSmith-Purcell radiation and Transition Radiation are two radiative phenomenon that occur in charged particles accelerators. For both the emission can be significantly enhanced with sufficiently short pulses and both can be used to measure the form factor of the pulse. We compare the yield of these phenomenon in different configurations and look at their application as bunch length monitors, including background filtering and rejection. We apply these calculations to the specific case of the CLIO Free Electron laser

Stray light estimates due to micrometeoroid damage in space optics, application to the LISA telescope

International audienceThe impact on an optical surface by a micrometeoroid gives rise to a specific type of stray light inherent only in the space optical instruments. This causes a double source of light scattering: the impact crater and the ejected contamination. We propose a method of stray light estimation and apply it to the case of the Laser Interferometer Space Antenna telescope. We estimate the backscattering fraction for nominal (4 years) and extended (10 years) mission durations

First Measurements of Coherent Smith-Purcell Radiation in the SOLEIL Linac

International audienceAn experiment to measure the Coherent Smith-Purcell radiation has been installed in the SOLEIL Linac. Its aim is to produce a map of Smith-Purcell radiation emissions in several planes and compare it with theoretical predictions. Coherent Smith Purcell radiation is produced when a grating is brought close from a sufficiently short charged particles beam. The experiment consist of two detectors with 5 degrees of freedom. These two detectors can be moved around the emission point to measure the intensity of the radiation at different locations. Radiation maps are recorded parasitically by moving the detectors around during normal linac operations

Study of Short Bunches at the Free Electron Laser CLIO

International audienceCLIO is a Free Electron Laser based on a thermionic electron gun. In its normal operating mode it delivers electron 8 pulses but studies are ongoing to shorten the pulses to about 1 ps. We report on simulations showing how the pulse can be shortened and the expected signal yield from several bunchlength diagnostics (Coherent Transition Radiation, Coherent Smith Purcell Radiation)

Stray light in the LISA mission: perturbation of an interferometer due to back-scattered light

International audienceLISA is a constellation of three spacecraft exchanging laser beams on a 2.5 Mkm triangle. The GW measurement exploits heterodyne interferometric phase measurements of the distance between distant optical benches, with additional interferometers measuring the test mass to optical bench movement, and the optical phase difference of the two lasers onboard the same spacecraft. Stray light (SL) can affect the operations in various ways, but the most obvious perturbation comes from coherent SL being recoupled into one of the interferometers.We present activities aiming at- characterizing the re-coupling of SL scattered from a mirror, back into a Michelson interferometer where a collimated beam hits the mirror under test. Back-scatter (BS) from the mirror is measured down to 10^-13 in power- providing a simple and approximate, yet analytic method to estimate the fraction of BS recoupled into an interferometer: when a complex optics, such as a telescope, is involved, considering only BS rays in the solid angle corresponding to an overlap with the beam waist provides a reasonably precise value of coupled SL- measuring Rayleigh BS from the "back-link" optical fibre. The back-link allows to prepare the beating of one laser with the other laser on the same spacecraft. We use a heterodyne Mach-Zehnder interferometer to measure BS power in the ppm-level. We also characterize the fibers' reaction to stress and ionizing radiation. Mitigation strategies are presented

Study of Short Bunches at the Free Electron Laser CLIO

International audienceCLIO is a Free Electron Laser based on a thermionic electron gun. In its normal operating mode it delivers electron 8 pulses but studies are ongoing to shorten the pulses to about 1 ps. We report on simulations showing how the pulse can be shortened and the expected signal yield from several bunchlength diagnostics (Coherent Transition Radiation, Coherent Smith Purcell Radiation)

Stray light in the LISA instrument: characterization and modelling of the coherent perturbation of a homodyne interference

International audienceIn the LISA mission, the presence of stray light is a concern since a perturbation of the heterodyne phase measurement at the level of several µradian can give rise to significant noise in the LISA gravitational wave measurement. The perturbation scales as the square root of the stray light to nominal beam optical power ratio. Reaching very low deviation of the phase measurement may require a very strong rejection of coherent stray light. Apart from coherent interference in the heterodyne phase measurements, stray light can also shift measurements through an incoherent contribution. Various detectors, such as the CAS (constellation acquisition sensors) could receive light due to backscattering in the telescope optics, or from stars or planets, with a non-negligible power. We present work undertaken to set-up experiments for characterizing stray light at component and system level, including calibrated measurements of coherent back-scatter (BS) from a target with surface roughness, and interpretation of the data by a model description of the BS amplitude. The latter displays speckle-type variations when the sample is translated in front of the incident beam and fast variations when the sample orientation changes with respect the laser beam. These observations are interpreted using an electromagnetic model of the fields scattered by the surface, taking into account the measured surface topography and the design (thicknesses & optical indexes) of the coating constitutive of the mirror

РОЗРАХУНОК ДЕФОРМАЦІЙ РУСЕЛ ПРИ НЕСТАЦІОНАРНОМУ РУСІ ПОТОКУ

Розглянуто систему рівнянь Сен-Венана, яка дозволяє в рамках теорії мілкої води вести розрахунки нестаціонарного режиму потоку у річкових руслах. Побудовано алгоритм числового розв’язку, який дозволяє визначити глибини і швидкості потоку як функції часу. На основі запропонованої раніше масообмінної концепції дається спрощений розрахунок інтенсивності глибинних і планових деформацій русел