Radiative Thermal Memory (Orale)

International audienc

Characterization of the ``guided light/photonic crystal'' coupling by absorbance

International audienceConsidering luminescent TiO2 films whose surface was imprinted with a 2D square shaped photonic crystal with different pattern depths (from 20 to 61 nm), we demonstrate the possibility to use simple absorption measurements to evaluate the efficiency of light extraction. Absorption spectra of the patterned systems show absorption peaks, evidencing the coupling between the photonic crystal structure and light guided within the film, in good agreement with 2D-RCWA simulations. The deeper the pattern depth, the stronger the coupling between the guided light and the photonic crystal. Using RCWA simulations, we show that it is possible to evaluate the extraction length, characteristic of the efficiency of light extraction, from the absorption spectra, in good agreement with direct measurements reported elsewhere

Commissioning of the ThomX Storage Ring

International audienceWe will report on the ongoing ThomX ring commissioning, its status, its main challenges, our results and our planning.ThomX is a compact Compton-based X-ray source under commissioning at IJCLab in Orsay (France). This facility is composed of a 50-70 MeV linac, a transfer line and a storage ring whose closed orbit is 18 m long. Compton scattering between the 50 MeV electron bunch of 1 nC and the 30 mJ laser pulses stacked in a Fabry-Perot cavity results in the production of X-rays with energy ranging between 45 keV and 90 keV. We aim at a total flux of about 10^13 X-rays per second. The injector commissioning started in the spring of 2021. The ongoing storage ring commissioning faces many challenges due to the ring’s low energy, its compactness, its non-linear beam dynamics, the time-limited beam storage and the need to achieve a very accurate and stable geometry of the collision region between the laser pulses and the electron bunch. The commissioning and operational experience is of great importance for the future Compton sources

Characterization of photonic crystal coupling to and from guided light by absorbance

International audienceWe considered luminescent TiO2 films whose surface was imprinted with a two-dimensional (2-D) square shaped photonic crystal with different pattern depths (from 20 to 61 nm). The aim of this work is to develop a straightforward method to characterize the PhC efficiency on light extraction. Transmission spectra of the patterned areas as obtained using a routine spectrometer exhibit peaks evidencing the coupling by the photonic crystal structure of free-space light with guided modes within the film, in good agreement with 2-D rigorous-coupled wave analysis (RCWA) simulations. As expected, the deeper the pattern depth, the stronger the coupling between the guided light and the photonic crystal. RCWA simulations allow evaluating quantitatively the extraction length, characteristic of the efficiency of light extraction, from the transmission spectra, in good agreement with direct measurements

Theoretical investigations on the Adiabatic Matching Device-based positron capture system

The positrons produced with the electron beam impinging on a conversion target, possess wide energy spectrum and large sweep of the angle of trajectories to the system axis. Accommodation of the positron bunch to the acceptance of an ajacent accelerator, mandates the reduction of angular spread. One of the most appropriate devices for transforming the phase portrait of a positron bunch is Adiabatic Matching Device (AMD). The paper presents an abridge theory of AMD. It is shown that the transformation of the transverse phase phase volume aimed at decrease the angular spread causes prolonging the bunch. Both the longitudinal and the transversal probability density functions are derived. The analytical results are validated with numerical simulations

Early Phase 2 Results of LumiBelle2 for the SuperKEKB Electron Ring

International audienceWe report on the early SuperKEKB Phase 2 operations of the fast luminosity monitor (LumiBelle2 project). Fast luminosity monitoring is required by the dithering feedback system, which is used to stabilize the beam in the presence of horizontal vibrations. In this report, we focus on the operations related to the electron side of LumiBelle2. Diamond sensors are located 30 meters downstream of the IP, just above, beside, and below the electron beam pipe. During early Phase 2, the sensors are used to measure the background, arising from beam-gas scattering. We present the hardware design, the detection algorithm, and the analysis of the background measurements taken up-to-date. The results are then compared with a detailed simulation of the background, in order to well understand the physical processes involved. The simulation is performed using SAD for generation and tracking purposes, while Geant4 is used to calculate the energy deposition in the diamond sensors

Preparation of CVD Diamond Detector for fast Luminosity Monitoring of SuperKEKB

International audienceThe SuperKEKB e⁺-e⁻ collider aims to reach a very high luminosity of 8×10 ³⁵ cm'2s'1, using highly focused ultra-low emittance bunches colliding every 4ns. To meet the requirement of the dithering feedback system used to stabilize the horizontal orbit at the IP (interaction point), a relative precision of 10 '3 in 1ms is specified for the fast luminosity monitoring, which can be in principle achieved thanks to the large cross section of the radiative Bhabha process. This paper firstly presents the fraction of detected Bhabha scattering positrons with a new beam pipe arrangement coupled with a Tungsten radiator to be installed in the Low Energy Ring; Then the characteristics of signals from a sCVD diamond detector with thickness of 140'm coupled with a broadband current amplifier were studied based on tests with a Sr-90 source; Finally, simulated results for the reconstructed luminosity and the relative precision with different assumed luminosities are also reported

Lens Calibration for Beam Size Monitors at ThomX

International audienceThomX is a novel compact X-ray light source, utilising a laser and 50 MeV electron storage ring to produce X-ray photons via Compton scattering. Screens, observed by zoom lenses and optical cameras, can be used to monitor the transverse beam profile at various points. An issue with the implementation of this system is that after adjusting the zoom one needs to recalibrate the the optical system, measuring the resolution of the optical system and deducing the transformation from pixel space observed on the camera to geometrical space in the laboratory. To calibrate and measure the resolution limit of the cameras a USAF 1951 resolution chart that can be moved into or out of the screen position is used. We will report on and demonstrate the use of open source computer vision libraries to compute this calibration, and the affine transformation between the camera image plane and the screens can be deduced. We will also comment on how consumer available Canon EF mount lenses may be used as a remote controllable optical system