High Intensity Photon Research Articles

Study of Fabrication Process and Performance Analysis of the CDS/CDTE Based Photovoltaic Cell

Fabrication of CDS/CDTE based heterojunction photovoltaic cell has been undertaken to explore better light conversion efficiency. We have developed a photovoltaic cell using glass coated with Indium doped Tin Oxide (ITO) which works as transparent conducting oxide (TCO). ITO coated glass has promising prospects of enhancing the efficiency of the photovoltaic cell. ITO layers are known to be employed as anode terminal due to the negative polarity they possess compared to the whole PV cell; here, we have employed it for the same function as the front layer. During fabrication of the photovoltaic cell, the deposition of nanoparticles of CDS and CDTE layer is undertaken through doctor-blade method. We have employed pure CDS as window layer for its high band gap of 3.8 eV (particle size: 8 nm) and CDTE as absorber layer due to its high optical absorption coefficient with high mobility, good carrier lifetime and enhanced crystallographic properties. The CDS window layer and CDTE absorber layer together constitute a p-n junction where the CDS window layer captures high intensity photons and transmits the photo-excited electron to CDTE absorber layer, thereby leading to photo-current output, which serves as a base to explore and test its further applications. To obtain band gap of respective CDTE and CDS nanoparticles, optical characterization is used. Silver paste is used as rear contact to form anode terminal having good conductivity and providing better mechanical support to the photovoltaic cell.

Effect of intense x-ray free-electron laser transient gratings on the magnetic domain structure of Tm:YIG

In ferromagnets, domain patterns can be controlled globally using magnetic fields or spin-polarized currents. In contrast, the local control of the magnetization on the nanometer length scale remains challenging. Here, we demonstrate how magnetic domain patterns in a Tm-doped yttrium iron garnet (Tm:YIG) thin film with perpendicular magnetic anisotropy can be permanently and locally imprinted by high intensity photon pulses of a hard x-ray transient grating (XTG). Micromagnetic simulations provide a qualitative understanding of the observed changes in the orientation of magnetic domains in Tm:YIG and XTG-induced changes. The presented results offer a route for the local manipulation of the magnetic state using hard XTG.

Charge sharing simulations and measurements for digital algorithms aiming at subpixel resolution in photon counting pixel detectors

Hybrid pixel detectors are segmented devices used for X-ray detection that consist of a sensor attached to the readout electronics. Detectors working in single-photon counting mode process each incoming photon individually, have essentially infinite dynamic range, and by applying energy discrimination they provide noiseless imaging. To improve the resolution of the detector and allow operation with high-intensity photon fluxes, the pixel size is reduced. However, with decreasing pixel size, a charge sharing effect is more prominent. This leads to false event registration or omitting the event, and degradation of the energy resolution of the detector. Algorithms aiming at reducing the influence of charge sharing have already been implemented on-chip. However, the spatial resolution of the detector can be increased beyond the physical size of the pixel if the charge proportions collected by neighboring pixels are analyzed.The simulations show that charge cloud size referred to pixel size and noise are the key parameters that determine the accuracy of the subpixel algorithm. The article shows the concept of subpixel algorithm and the simulations for different detector parameters and approximation algorithms. The slanted-edge method was implemented to quantify the resolution of detectors consisting standard readout architecture. The chips were simulated and tested to verify the influence of different bias voltages, sensor materials, and thicknesses on charge sharing and as a consequence on the detector resolution. The simulated and measured edge spread functions were compared. The results show that the simulator can be used to describe the spatial resolution of the detectors, and can be used for further studies of the resolution of detectors with subpixel algorithm implemented.

FORMATION OF MIXED X,n-RADIATION FIELD AT AN ELECTRON ACCELERATOR

For conducting photonuclear programs with the use of a high-intensity photon source the latter is ordinary obtained by transformation of an electron beam into X-ray radiation. Such a process is performed using an intermediate target-converter maid from a high-Z material. The (γ,n) reactions take place in the converter under the action of high-energy bremsstrahlung photons. As a result, a quasi-isotropic neutron flux escapes the converter jointly with the photon beam directed forward. The parameters of the both types of radiation, as well as the ratio of their intensities play the important role depending on a program under way. In work, the spatial radiant characteristics of the mixed X,n-radiation generated with the electron beam in the converter located together with an isotopic target in the middle of a neutron moderator in the electron energy range 40…95 MeV and various size of the moderator are studied by computer simulations with the use of a GEANT4 transport code.

Temperature-dependent relative self-absorption measurements in 27Al

Nuclear resonance fluorescence measurements provide direct sensitivity to ground-state transition widths by probing the photoexcitation process of nuclear resonances. A technique in Relative Self-Absorption (RSA) measurements, in which measurements are done at multiple absorber temperatures, was developed and tested with 27Al at the Darmstadt High Intensity Photon Setup of the Superconducting Darmstadt Linear Accelerator. The advantage of this technique, over the regular RSA, is the possibility to overcome the need for theory input on the effective temperatures and the uncertainties that they introduce in the measured level widths. The technique and the preliminary results of the first test-measurements are presented in this proceedings.

ALP searches at the LHC: FASER as a light-shining-through-walls experiment

We propose the use of FASER as a light-shining-through-walls experiment to search for axions and axion-like particles (ALPs). LHC collisions generate a high intensity and high energy photon flux in the forward direction which can oscillate into ALPs in the magnetic fields that are used to confine the beam. These ALPs then pass through about 100~m of rock before reaching the magnetic fields of FASER, where they can convert back into photons and be detected by an electromagnetic calorimeter. In the next years, FASER and its successor FASER2 at the Forward Physics Facility will be able to explore regions of the ALPs parameter space inaccessible by other laboratory-based experiments.

High-intensity laser experiments with highly charged ions in a Penning trap

We have conceived and built the HILITE (High-Intensity Laser-Ion Trap Experiment) Penning-trap setup for the production, confinement and preparation of pure ensembles of highly charged ions in a defined quantum state as a target for various high-intensity lasers. This enables a broad suite of laser-ion interaction studies at high photon energies and/or intensities, such as non-linear photo-ionisation studies. The setup has now been used to perform experiments at one such laser facility, namely the FLASH Free-Electron Laser at DESY in Hamburg, Germany. We describe the experimental possibilities of the apparatus, the results of the first measurements and future experiments at other laser facilities.

Therapeutic Strategies and Metal-Induced Oxidative Stress: Application of Synchrotron Radiation Microbeam to Amyotrophic Lateral Sclerosis in the Kii Peninsula of Japan.

A series of extensive gene-environment studies on amyotrophic lateral sclerosis (ALS) and Parkinsonism–dementia complex (PDC) in Guam Island, USA, and the Kii Peninsula of Japan, including Auyu Jakai, West New Guinea, have led us to hypothesize that a prolonged low calcium (Ca) and magnesium (Mg) intake, especially over generation, may cause oxidative stress to motor and nigral neurons by an increased uptake of environment metallic elements, i.e., aluminum (Al), manganese (Mn), and iron (Fe). Otherwise, 5–10% of total ALS cases are familial ALS (fALS), of which 20% of the fALS cases linked to a point mutation of Cu/Zn superoxide dismutase (SOD1). In the vicinity of the Kii Peninsula, about 7% of the ALS cases are also linked to the SOD1 mutation. Using synchrotron radiation (SR) microbeam, conglomerate inclusion (SOD1 aggregates) within a spinal motor neuron of the fALS case in the vicinity revealed a loss of copper (Cu) in contrast to extremely high contents of Zinc (Zn) and Ca. That means an exceptionally low Cu/Zn ratio with an increased Ca content, indicating the abnormalities of the active site of SOD1 protein of the fALS. Furthermore, sALS in the southernmost high incidence areas of the Kii Peninsula showed a low Cu/Zn ratio within a motor neuron, suggesting a fragility of SOD1 proteins. From the perspective of gene–environment interactions, the above two research trends may show a common oxidative stress underlying the neuronal degenerative process of ALS/PDC in the Kii Peninsula of Japan. Therefore, it is a crucial point for the prospect of therapeutic strategy to clarify a role of transition metals in the oxidative process in both ALS/PDC, including ALS elsewhere in the world. This paper reviews a history of the genetic epidemiological studies, especially from the aspect of gene–environment interaction, on ALS/PDC in the Kii and Guam high incidence foci and the results of a series of analytical research on trace metallic elements within neurons of both sALS and fALS cases, especially using a synchrotron radiation (SR) microbeam of Spring-8 and Photon Factory of Japan. The SR microbeam is an ideal X-ray source, which supplies an extremely high brilliance (high-intensity photon) and tunability (energy variability) to investigate trace metallic elements contained in biological specimens at the cellular level, even more without any damages. This research will provide a valuable information about the mechanism of oxidative stress involved in neuronal cell death in ALS and related neurodegenerative disorders. To elucidate the physicochemical mechanism of the oxidative process in neuronal degeneration, it will shed a new light on the therapeutic strategies for ALS/PDC in near future.

Multiphoton Absorption Simulation of Sapphire Substrate under the Action of Femtosecond Laser for Larger Density of Pattern-Related Process Windows.

It is essential to develop pattern-related process windows on substrate surface for reducing the dislocation density of wide bandgap semiconductor film growth. For extremely high instantaneous intensity and excellent photon absorption rate, femtosecond lasers are currently being increasingly adopted. However, the mechanism of the femtosecond laser developing pattern-related process windows on the substrate remains to be further revealed. In this paper, a model is established based on the Fokker–Planck equation and the two-temperature model (TTM) equation to simulate the ablation of a sapphire substrate under the action of a femtosecond laser. The transient nonlinear evolutions such as free electron density, absorption coefficient, and electron–lattice temperature are obtained. This paper focuses on simulating the multiphoton absorption of sapphire under femtosecond lasers of different wavelengths. The results show that within the range of 400 to 1030 nm, when the wavelength is large, the number of multiphoton required for ionization is larger, and wider and shallower ablation pits can be obtained. When the wavelength is smaller, the number of multiphoton is smaller, narrower and deeper ablation pits can be obtained. Under the simulation conditions presented in this paper, the minimum ablation pit depth can reach 0.11 μm and the minimum radius can reach 0.6 μm. In the range of 400 to 1030 nm, selecting a laser with a shorter wavelength can achieve pattern-related process windows with a smaller diameter, which is beneficial to increase the density of pattern-related process windows on the substrate surface. The simulation is consistent with existing theories and experimental results, and further reveals the transient nonlinear mechanism of the femtosecond laser developing the pattern-related process windows on the sapphire substrate.

Acoustically induced transparency for synchrotron hard x-ray photons

The induced transparency of opaque medium for resonant electromagnetic radiation is a powerful tool for manipulating the field-matter interaction. Various techniques to make different physical systems transparent for radiation from microwaves to x-rays were implemented. Most of them are based on the modification of the quantum-optical properties of the medium under the action of an external coherent electromagnetic field. Recently, an observation of acoustically induced transparency (AIT) of the 57Fe absorber for resonant 14.4-keV photons from the radioactive 57Co source was reported. About 150-fold suppression of the resonant absorption of photons due to collective acoustic oscillations of the nuclei was demonstrated. In this paper, we extend the AIT phenomenon to a novel phase-locked regime, when the transmitted photons are synchronized with the absorber vibration. We show that the advantages of synchrotron Mössbauer sources such as the deterministic periodic emission of radiation and controlled spectral-temporal characteristics of the emitted photons along with high-intensity photon flux in a tightly focused beam, make it possible to efficiently implement this regime, paving the way for the development of the acoustically controlled interface between hard x-ray photons and nuclear ensembles.

Photoconductive gain in single crystal diamond detectors

Diamond crystals equipped with two metal electrodes can be operated as solid state ionization chambers for the detection of energetic radiation. Under irradiation with single α particles, the generated free electrons and holes are collected with a maximum efficiency close to 100%. When the same detectors are used for dosimetry in high intensity and high energy photon or particle beams, photoconductive gain G with values up to ≈106 is frequently observed as described in the literature. In this work, we studied theoretically the irradiation induced conductivity of perfect diamond single crystals with ohmic contacts containing nitrogen and boron with concentrations NN and NB, respectively, as only chemical impurities. Based on four rate equations, two considering the charge states of N and B and two the concentrations of free carriers n and p, and, additionally, the neutrality condition, we could derive analytical solutions for the gain G as a function of impurity concentrations, crystal thickness, and excitation density. It turned out that G varies systematically with the compensation ratio R=(NN−NB)/NB over five orders of magnitude. For R≈103, the gain G is close to unity. With decreasing R, the gain increases ∝1/R until saturation is reached for R≪1 and G≈104–105. Our theoretical data yield plausible explanations for the major trends that have been found experimentally in previous studies. They provide a valuable guideline for the future synthesis of diamond crystals to be used for manufacturing UV and radiation detectors.

Collimation of partially stripped ions in the CERN Large Hadron Collider

In the scope of the Physics Beyond Colliders studies, the Gamma-Factory initiative proposes the use of partially stripped ions as a driver of a new type of high-intensity photon source in CERN Large Hadron Collider (LHC). In 2018, the LHC accelerated and stored partially stripped $^{208}\text{Pb}^{81+}$ ions for the first time. The collimation system efficiency recorded during this test was found to be prohibitively low, so that only a very low-intensity beam could be stored without the risk of triggering a beam dump when regular, minor beam losses occur. The worst losses were localised in the dispersion suppressor of the betatron-cleaning insertion. This article presents an analysis to understand in detail the source of these losses. Based on this understanding, possible mitigation measures that could significantly improve the cleaning efficiency and enable regular operation with partially-stripped ions in the future are developed.

CALIBRATION OF A SHOWER LEAD-SCINTILLATION SPECTROMETER BY COSMIC RADIATION

The results of calibration by cosmic muons of a shower lead-scintillation spectrometer of the sandwich type designed to work in high-intensity photon and electron beams with an energy of 0.1 - 1.0 GeV are presented. It was found that the relative energy resolution of the spectrometer depends on the angle of entry of cosmic muons into the spectrometer in the vertical plane and does not depend on the angle of entry in the horizontal plane. The relative energy resolution of the spectrometer was 16%. Placing an additional lead-scintillation assembly in front of the spectrometer improved the relative energy resolution of the spectrometer to 9%.

Production of 100-TW single attosecond x-ray pulse

Attosecond light sources have provided insight into the fastest atomic-scale electronic dynamics. True attosecond-pump–attosecond-probe experiments require a single attosecond pulse at high intensity and large photon energy, a challenge that has yet to be conquered. Here we show 100-TW single attosecond x-ray pulses with unprecedented intensity of 10 21 W / c m 2 and duration 8.0 as can be produced by intense laser irradiation of a capacitor-nanofoil target composed of two separate nanofoils. In the interaction, a strong electrostatic potential develops between the two foils, which drags electrons out of the second foil and piles them up in vacuum, forming an ultradense relativistic electron nanobunch. This nanobunch reaches both high density and high energy in only half a laser cycle and smears out in others, resulting in coherent synchrotron emission of a single, intense attosecond pulse. Such a pulse enables the capture and control of electron motion at the picometer–attosecond scale.

Charge sharing simulations for new digital algorithms achieving subpixel resolution in hybrid pixel detectors

Hybrid pixel detectors are segmented devices used for particles detection, consisting of a sensor and readout electronics. To improve the resolution of the detector and allow operation with high-intensity photon fluxes, the pixel size is reduced. However, with decreasing pixel size, a charge sharing effect is more significant. To detect a photon irrespectively of charge sharing effect, the total photon energy should be reconstructed from fractional signals. Therefore, the algorithms dealing with charge sharing are developed [1–4]. The resolution of such detectors is limited by the pixel size, which must be large enough to fit all the functionality required by the complex algorithms. However, there are known methods that can improve the spatial resolution of a detector applied for high energy physics [5], or astronomy [6–8], and both photon counting detectors [9–11] and integrating detectors [12–14] are used. An alternative digital solution that can be implemented on-chip dedicated to hybrid pixel detectors working in a single photon counting mode is presented in this work. In this approach, charge sharing becomes the desired effect, since the information on the proportions of charge collected by the pixels can be used to estimate the photon interaction position with subpixel resolution. In the work analytical approach towards detector and readout channel modeling is used to state the requirements for the algorithm. The concept of the new digital on-chip algorithm is presented.

The Gamma Factory Project at CERN: a New Generation of Research Tools Made of Light

The Gamma Factory project offers the possibility of creating novel re- search tools by producing relativistic beams of highly ionised atoms in CERN’s accelerator complex and exciting their atomic degrees of freedom by lasers to produce strongly collimated high-energy photon beams. Inten- sity of such beams would exceed by several orders of magnitude the ones offered by the presently operating light sources, in the particularly interest- ing energy domain from about 100 keV to above 400 MeV. In this energy regime, the high-intensity photon beams can be used to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neu- trinos, neutrons and radioactive ions. New research opportunities in many domains of physics, from particle physics through nuclear physics to atomic physics, can be opened by the Gamma Factory scientific programme based on the above primary and secondary beams. Except for basic research, it offers also a possibility for various application studies, e.g. in medical physics and nuclear power.

Photocathode study of the CompactLight Collaboration for a novel XFEL development

The latest generation of light sources, the Free Electron Lasers that are capable of delivering high-intensity photon beams of unprecedented brilliance and quality, provide a substantially novel way to probe matter with a very high, largely unexplored potential for science and innovation. The CompactLight Collaboration intends to design a hard X-ray FEL facility beyond today’s state of the art using the latest concepts for bright electron photoinjectors, very high-gradient X-band structures at 12 GHz, and innovative compact short-period undulators. When compared to existing facilities, the proposed facility will benefit from a lower electron beam energy, due to the enhanced undulator performance, will be significantly more compact with a smaller footprint, as a consequence of both the lower energy and the high-gradient X-band structures, and will have a much lower electrical power demand. This paper gives an overview of different candidate photocathode materials for use in conjunction with a laser and presents the proposed design of the photocathode and the related laser. Also presented are the e-gun with solenoid selection and design, together with relevant simulation results.

Cherenkov Radiation of Gravitational Waves

<p align="justify">If the velocity of gravitational waves is less than the speed of light, the velocity of mass motion may exceed the velocity of gravitational waves. This will cause Cherenkov-like radiation similar to electromagnetic interaction. The Cherenkov-like radiation of gravitational waves will produce a relatively specific observable effect. Due to the concentrated release of energy, the easiest to observe is that a large number of photons are radiated from the Cherenkov-like radiation source to form optical effects of high intensity and relatively special shapes. The speed of gravitational waves is less than the speed of light, because the compression of space and time by very large masses causes the gravitational waves to travel less in the masses than the speed of light. The mass of the material itself is not affected by this space-time compression. Thus, under certain conditions, the velocity of the mass of matter exceeds the velocity of the gravitational wave, forming a Cherenkov-like effect. A typical example is the aura of special structures formed by the supernova explosion. Among them, the supernova 1987A has been in existence for more than 30 years. After several years of the explosion, through the observation of the high-resolution Hubble telescope, it was found that the supernova 1987A showed two distinct auras in its explosion direction. There are many explanations for how these halos are formed. This paper points out that the formation of the two halos of the supernova 1987A is related to the propagation of gravitational waves in the mass of matter. Due to the very high mass density of the supernova explosion area, the space-time compression effect is very obvious, which will cause the gravitational wave to have a wave speed less than the speed of light. The material ejected by the supernova after exploding is close to the speed of light, and it is easy to exceed the velocity of gravitational waves propagating in the cosmic fluid around the supernova explosion, which will form the shock wave effect of gravitational waves. The Cherenkov effect of gravitational waves can also be used to explain the origin of high-intensity photon radiation in some galaxy centers. When the black hole in the center of the galaxy attracts the outer mass, the closer it is to the central black hole, the faster it moves. In the right position, the mass moves faster than the gravitational wave. The Cherenkov-like radiation of gravitational waves will be product. In addition, if there is a white hole, the energy is continuously released from the source of the white hole, which will also cause the mass ejection speed to exceed the speed of the gravitational wave, and thus produces the Cherenkov-like effect. Since the dynamic mechanism of the black hole and the white hole are different, by observing the Cherenkov-like effect of the center of the galaxy, it can effectively distinguish whether the center of the galaxy is a white hole or a black hole.</p>

First partially stripped ions in the LHC (208Pb81+)

The Gamma Factory initiative proposes to use partially stripped ion (PSI) beams as drivers of a new type of high intensity photon source. As part of the ongoing Physics Beyond Collider studies, initial beam tests with PSI beams have been executed at CERN. On 25 July 2018 lead ions with one remaining electron (208Pb81+) were injected and accelerated in the LHC for the first time. After establishing the injection and circulation of a few 208Pb81+ bunches, beam lifetimes of about 50 hours could be established at 6.5 TeV proton equivalent energy. This paper describes the setup of the beam tests and observations made.

Do all the linear accelerators comply with the ICRU 91's constraints for stereotactic body radiation therapy treatments?

Recent technological developments in linear accelerators (linacs) and their imaging systems have made it possible to routinely perform stereotactic radiotherapy (SRT) treatments. To ensure the security and quality of the treatments, national and international recommendations have been written. This review focuses on the recommendations of the report 91 of the International Commission on Radiation Units (ICRU) on stereotactic treatments with small photon beams and proposes to answer the question of the eligibility of the commercially available accelerators for the treatment of extra-cranial SRT (SBRT). The ICRU 91 report outlines important features needed to respect the constraints, which are high intensity photon beam, integrated image-guidance, high mechanical accuracy of the linac, multileaf collimator with reduced leaf width, bundled motion management and bundled 6 Dimensional “robotic” couch tabletop. Most of the contemporary linacs meet these recommendations, in particular, stereotactic dedicated linacs, or modern gantry-based linacs equipped with 3 dimensional cone-beam CT imaging and 2D-stereoscopic planar imaging. Commercially available ring-based linacs have some limitations: they offer only coplanar treatments, and couch movements are limited to translations and, some have limited imaging equipment and no ability to manage intrafraction motion. However, for performing SBRT, non-coplanar irradiations are not mandatory, contrarily to intracranial stereotactic irradiations. Furthermore, patients’ rotations can be corrected, thanks to real-time adaptive radiotherapy available on MRI-linacs. Finally, significant improvements are expected in the short term to compensate the weaknesses of the current devices.