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Theses

Caliste-MM : a new spectro-polarimeter for soft X-ray astrophysics

Abstract : Performing X-ray polarimetry of astrophysical sources could provide precious insight into the properties of the emitting objects, for example the geometry of pulsars accretion disks, magnetic field inside the core of supernovae remnants or measurement of black holes spin. These fundamental observations are today impossible due to the missing performance of X-ray polarimeters.The use of the photo-electric effect to perform spectro-polarimetry in the energy band of 1 keV to 15 keV appears to be like a much better approach than the use of Bragg diffraction or Thomson scattering. Performing polarimetry with the photo-electric effect relies on the measurement of the ejection direction of the photo-electron, which is modulated by the polarization direction of the incoming light. In order to reconstruct the photo-electron track, a detector allowing the photo electrons to recoil far enough is needed. Gaseous detectors are naturally perfect candidates. This PhD thesis focusses on the development and the characterization of a soft X-ray spectro- polarimeter of a completely new design : Caliste-MM. It consists of a gaseous detector called piggyback Micromegas associated with a miniature 3D readout electronics baptized Caliste. The main innovation of this detector comes from the fact that its readout electronics is located outside the gaseous medium. The charges created inside the piggyback diffuse in a resistive layer spread on a solid ceramic plate that closes the detector. The Caliste records the signal of the charges in the resistive layer through the ceramic and a small air layer by capacitive induction. The detector is composed of two completely independent parts : the piggyback where the X-ray conversion and amplification takes place, and the Caliste for the recording of the signal. These two parts can then be developed independently. Moreover the electronics are protected from sparks thanks to the resistive layer of the piggyback.The detailed characteristics of the detector are studied such as the shape of the events, the gain and the energy resolution. Analytical models are compared to the obtained results in order to explain the physical phenomena responsible for the topology of the recorded events. Different strategies to improve the reconstruction of the photo-electrons are explored including for example finer pitched readout electronics, low pressure and the use of lighter gases such as Neon or Helium.Finally, thanks to the measurements performed on the 100% linearly polarized beam of the Mtrologie line of the SOLEIL synchrotron facility, the modulation factor of the detector has been measured at different energies ranging from 6 keV to 12 keV. A measurement of the modulation factor of 92% at 8 keV proves the high potential of this new spectro-polarimeter and the interest into its innovative design.
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https://tel.archives-ouvertes.fr/tel-01723432
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Submitted on : Monday, March 5, 2018 - 3:06:09 PM
Last modification on : Friday, April 10, 2020 - 5:14:44 PM
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  • HAL Id : tel-01723432, version 1

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Paul Serrano. Caliste-MM : a new spectro-polarimeter for soft X-ray astrophysics. Instrumentation and Methods for Astrophysic [astro-ph.IM]. Université Paris-Saclay, 2017. English. ⟨NNT : 2017SACLS594⟩. ⟨tel-01723432⟩

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