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PEARL Report Summary

Project ID: 690991
Funded under: H2020-EU.1.3.3.

Periodic Reporting for period 1 - PEARL (Periodically bent crystals for crystalline undulators)

Reporting period: 2016-01-01 to 2017-12-31

Summary of the context and overall objectives of the project

The PEARL project aims at advancing the technologies for manufacturing high quality Periodically Bent Crystals (PBCr). The PBCr developed in the course of this project will be utilised for the construction of novel light sources of high-energy monochromatic electromagnetic radiation by means of a Crystalline Undulator (CU). Such radiation will find broad use in fundamental science as well as in technological and medical applications, and thus will contribute towards the EU’s global aims such as increase of the quality of life, creation of new high technological working places, etc. In addition it should be emphasized that PEARL impact targets not only developing a new light source, but it is also aimed at improving of the quality of super lattice synthesis. It is expected that in the project, the technology for production of the key elements of CU, viz. periodically structured crystalline materials, will be developed. Besides the realization of CUs, the development of the techniques for bending crystals will benefit the performance of other channelling experiments. Such novel technology will enable bending of crystals without the use of external fixtures. Aside from channelling experiments, bent crystals may find applications in X-ray optics, medical X-ray imaging, as accelerator components (collimators, extraction devices), in the measurement of fundamental physical quantities. Crystals that are bent without the use of external holders may also find application in shielding of spacecrafts from cosmic radiation, an essential requirement for long term human space flight (e.g. human mission to Mars). The members of the PEARL Consortium are world leaders in their research areas. Their main specializations and expertise are complementary to one another, thus maximizing the participant’s interactions within PEARL and helping to reach the project objectives.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

(I) Modelling of PBCr structure, beam dynamics and radiation emission in CU
(1) Structure deformation of ideal silicon crystal due to doping with germanium atoms was stud-ied at atomistic level by carrying out classical molecular dynamics (MD) simulations by means of the MBN Explorer osftware package.
(2) Channeling and radiation were also studied for the sub-GeV relativistic electrons and positrons passing through a Si1-xGex superlattice periodically bent with a Small Amplitude and a Short Peri-od SASP). Comprehensive analysis of the channeling process for various bending amplitudes was presented on the grounds of numerical simulations carried out by means of MBN Explorer.
(3) Channeling properties and radiation spectra were simulated for 855 MeV electrons in a period-ically bent diamond crystal. It was demonstrated for the first time that periodicity in the crystal-line profiles results in strong enhancement of the re-channeling of the projectiles.
(4) Emission spectra were calculated for 270 MeV electrons channeled in diamond-based CU. The crystal geometry, and the parameters of the periodic bending considered correspond to those in the boron doped diamond crystal produced by the ESRF team. Some of the samples have been already used in the experiments carried by the Uni-Mainz, ESRF and UAAR
(II) Manufacture and characterisation of PBCr, experimental studies of the beam propaga-tion and photon emission
(1) PBCr were designed and fabricated at UNIFE/INFN, UAAR and ESRF by means of different technologies.
(a) UNIFE/INFN teams used the superficial grooving and the sandblasting methods to fabri-cate silicon-based CUs. All together five CUs were fabricated by means of these methods. The period of bending varied from hundred microns up to the millimetre range.
(b) Two sets of the SASP periodically bent Si1−xGex crystal were produced by using Molecular Beam Epitaxy (UAAR). The crystals from the first set were used in the experiments at MAMI (together with the Uni-Mainz team).
(c) The ESRF team in collaboration with UJ have fabricated several diamond-based SASP CUs each containing 4 periods of bending varied from 5.3 to 5.9 microns. The CU structure was formed by an overgrown epitaxial CVD diamond layer with periodic boron doping pro-file. The characterization of the fabricated samples carried out at ESRF has demonstrated good quality of the crystalline quality of the overgrown layer.
(2) Experimental studies of the beam propagation and the photon emission
(a) The observation of steering of 855 eV electrons by both germanium and silicon (111) bent crystals (15 μm of length) at the MAMI were reported. Experimental results, in agreement numerical simulations, demonstrated that maximum channeling efficiency were about 40% and 8% for Si and Ge, respectively. For silicon such efficiency is a record for negatively charged particles. For germanium this is the first evidence of negative beam steering by pla-nar channeling.
(b) Experiments aimed at the measurements of the dechanneling length measurements as function of the electron beam energy E were carried out at the Mainz Microtron MAMI with silicon single crystals in the beam energy range E=180-855 MeV.
(c) The SASP PBCr Si1−xGex containing 120 periods along the (110) planar direction (beam period 0.44 μm and amplitude 0.12 Å) were used in the experiments with 855 MeV electrons at MAMI where the emission spectra were measured. The observed sensitivity of the CU radi-ation intensity on the emission collimation was in accordance with theoretical predictions.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The PEARL Project operates successfully progressing towards to the expected impacts described in the GA.The important goal of the project is the practical realization of a novel light source of high-energy electromagnetic radiation with narrow spectral-angular distribution based on a CU. Such radiation will find broad use in fundamental science as well as in technological and medical applications, and thus will contribute towards the EU’s global aims such as increase of the quality of life, creation of new high technological working places, etc. The innovative Crystalline Undulator Light Source which is under development in the project is in complementary advances on: (i) Manufacture of an exceptional lattice quality periodically bent crystals (PBC), (ii) Precise characterisation of the PBC quality, (iii) Characterisation of the CU radiation in experiments with beams of ultra-relativistic electrons and positrons, (iv) Highly-predictive of CUs by means of advanced software developed. The other Innovation that has been developed and being exploited in the project is MBN-PEARL computational tool. MBN RC offers computational tools integrated into the MBN Explorer & MBN Studio software packages. The tools allow the atomistic level modelling (simulation, visualisation, analysis) of the whole suite of phenomena related to exposure of oriented periodically bent crystals to beams of ultra-relativistic particles. These innovative tools will be sufficiently accurate and predictive thus enabling better experimental planning, interpretation of the experiments and minimisation of experimental costs.
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