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Periodically bent crystals for crystalline undulators

Periodic Reporting for period 2 - PEARL (Periodically bent crystals for crystalline undulators)

Reporting period: 2018-01-01 to 2019-12-31

The PEARL project aimed at a technological advance towards realisation of a novel light source (LS) by means of a Crystalline Undulator (CU), a periodically bent crystal together with a beam of relativistic positrons or electrons which move in through the crystal along its planes (such a motion is called ‘channeling’) following the periodic bending of the planes. Periodicity of the trajectory gives rise to a powerful CU radiation (CUR). Its wavelength, energy and intensity can be varied by changing the beam energy, the bending amplitude and period. CU can provide electromagnetic radiation in the photon energy range 1−10 MeV (gamma-rays) of the intensity which is inaccessible to conventional LSs such as synchrotrons, magnetic undulators and X-ray Free Electron Lasers (XFEL). The development of LS is a challenging goal of modern physics. Once constructed and become operational, the radiation from these LSs will have many applications in the basic sciences, technology and medicine. They may have a revolutionary impact on nuclear and solid-state physics, as well as on the life sciences. Accordingly, the practical realisation of functional CU devices requires well elaborated novel technologies for the precise manufacturing and characterisation of periodically bent crystalline structures, and the validation of the device operational capacities with high quality accelerated particle beam experiments. Construction of novel CLSs is an extremely challenging task which constitutes a highly interdisciplinary field. To accomplish this task, a broad collaboration is needed of research groups with different but mutually complementary expertise, such as material science, nanotechnology, parti-cle beam and accelerator physics, radiation physics, X-ray diffraction imaging, acoustics, solid state physics, structure determination, advanced computational modeling methods and algorithms, high-performance computing as well as industries specializing in manufacturing of crystalline structures and in design and construction of complete accelerator systems.
Within the PEARL project the following activities towards the practical realisation of the CU-based LS have been accomplished:
Improvement in the technologies for manufacturing periodically bent crystals (PBC) of exceptional quality;
Developing techniques for high precision characterization of periodical bending by means of the highest quality X-ray diffraction imaging apparatus and beam;
Channelling experiments with CUs and the radiation detection;
Advanced algorithms and computer codes for crystalline structure modelling and optimization, in order to simulate particle propagation through media, calculate the spectral-angular distribution of the emitted radiation.
Within the PEARL project a series of CUs were manufactured at the Ferrara lab, Italy and their structural properties were characterized at the European Synchrotron Radiation Facility (ESRF) x-ray light source. A number of experiments aimed at accurate characterisation of the quality of the periodic bending in the PBCs produced by means of different technologies has been carried out at the ESRF. The bent and periodically bent crystalline samples were exposed to intensive beams of ultra-relativistic electrons and positrons at different accelerator facilities (at MAMI, SLAC, CERN). During these experiments the channeling properties of the projectiles were analysed and the radiation emitted was measured. Within the project, computational support of various experimental activities has been carried out by means of the MBN Explorer package. Channeling phenomenon and radiation emission has been studied computationally for ultra-relativistic electrons and positrons passing through Si1-xGex superlattices, periodically bent diamond crystals and in a heavier tungsten crystal. The features of the channeling process have been highlighted, the radiation spectra have been computed, discussed and the recommendation for the experimental observation of the predicted features have been formulated.
Within the PEARL project the first step towards achieving the major breakthrough in the field has been achieved though elaborating the key theoretical, experimental and technological aspects towards setting up the standards for construction of the CU-based LSs. It has become clear that further broad range of correlated and entangles activities is needed to finally construct the operational device. These activities should include (i) Fabrication of linear, bent and periodically bent crystalline structures with lattice quality necessary for delivering pre-defined bending parameters; (ii) Advanced control of the lattice quality by means of the highest quality non-destructive X-ray diffraction techniques, (iii) Validation of functionality of the manufactured structures through experiments with high-quality beams of ultra-relativistic electrons and positrons; (iv) Advance in computational and numerical methods for multiscale modeling of nanostructured materials with extremely high, reliable levels of prediction. The knowledge from the studies (i)-(iv) will provide CLSs prototypes and a roadmap for practical implementation by CLS system manufacturers and accelerator laboratories/users worldwide. Sub-angstrom wavelength powerful and tunable CU-based LS will have a broad range of exciting potential applications. A micron-sized narrow photon beam may be used in cancer therapy to improve the precision and effectiveness of the therapy for the destruction of tumour by collimated radiation as well as allowing delicate operations to be performed in close vicinity of vital organs. By varying the CU parameters one can tune the energy of CUR to values needed to induce the transmutation process in various isotopes. This opens the possibility for a novel technology for disposing of nuclear waste or production of medical isotopes. Another possible application of the CU-LSs concerns photo-induced nuclear fission. This process can be used in a new type of nuclear reactor– the photo-nuclear reactor. The production of Positron Emission Tomography (PET) isotopes which can be used directly for medial PET will be very favourable application. Powerful monochromatic radiation within the MeV range can be used as an alternative source for producing beams of MeV protons by focusing a photon pulse on to a solid target. Such protons can induce nuclear reactions in materials producing. Irradiation by hard X-ray strongly decreases the effects of natural surface tension of water. The possibility to tune the surface tension by the irradiation can be exploited to study many phenomena affected by this parameter in physics, chemistry, and biology. To quantify the scale of the impact within Europe and worldwide which the development of radically novel CU-LSs might have, we can draw historical parallels with synchrotrons, optical lasers and FELs. In each of these technologies there was a significant time lag between the formulation of a pioneering idea, its practical realization and follow-up industrial exploitation. However, each of these inventions has subsequently launched multi-billion dollar industries. The implementation of the novel LSs operating in the photon energy range up to hundreds of MeV, is expected to lead to a similar advance so that they have the potential to become the new synchrotrons and lasers of the mid to late 21st century, stimulating many applications in basic sciences, technology and medicine.
Schematic representation of a crystalline undulator