Compact X-ray Source Research Articles

ELI Gammatron Beamline: A Dawn of Ultrafast Hard X-ray Science

The realization of compact X-ray sources is one of the most intriguing applications of laser-plasma based electron acceleration. These sources based on the oscillation of short micron-sized bunches of relativistic electrons provide femtosecond X-ray pulses that are collimated, bright, and partially coherent. The state-of-the-art laser plasma X-ray sources can provide photon flux of over 1011 photons/shot. The photon flux can further be enhanced with the availability of high repetition rate, high-power lasers, providing capacities complementary to the large scale facilities such as synchrotrons and X-ray free-electron lasers. Even though the optimization of such sources has been underway for the last two decades, their applications in material and biological sciences are still emerging, which entail the necessity of a user-oriented X-ray beamlines. Based on this concept, a high-power-laser-based user-oriented X-ray source is being developed at ELI Beamlines. This article reports on the ELI Gammatron beamline and presents an overview of the research accessible with the ultrashort hard X-ray pulses at the ELI Gammatron beamline.

Compact high-flux X-ray source based on irradiation of solid targets by gigahertz and megahertz bursts of femtosecond laser pulses

In this study, we demonstrate the significant increase in the hard X-ray yield (more than 1011 photons/s in 4π solid angle in 6 - 40 keV range) that can be achieved in an ambient air environment when solid targets are irradiated by sequences of high average power (90 W) bursts of femtosecond laser pulses, generated in GHz burst laser amplifier operated at high repetition rate (100 kHz). The combination of the prepulse and ∼ 10 times greater driving pulse not only enhances X-ray generation efficiency (∼ 10−6) by more than two orders of magnitude compared to the single pulse regime but also protects a target allowing continuous operation for 3 hours with only 30% predictable and gradual drop of X-ray yield. In addition, we show that X-ray yield enhancement becomes around 6 times more pronounced at higher repetition rates (100 kHz compared to < 5 kHz). The simplicity and relative cost-effectiveness of the presented X-ray source makes it an attractive solution for future applications in ultrafast X-ray imaging and spectroscopy.

Transverse oscillating bubble enhanced laser-driven betatron X-ray radiation generation

Ultrafast high-brightness X-ray pulses have proven invaluable for a broad range of research. Such pulses are typically generated via synchrotron emission from relativistic electron bunches using large-scale facilities. Recently, significantly more compact X-ray sources based on laser-wakefield accelerated (LWFA) electron beams have been demonstrated. In particular, laser-driven sources, where the radiation is generated by transverse oscillations of electrons within the plasma accelerator structure (so-called betatron oscillations) can generate highly-brilliant ultrashort X-ray pulses using a comparably simple setup. Here, we experimentally demonstrate a method to markedly enhance the parameters of LWFA-driven betatron X-ray emission in a proof-of-principle experiment. We show a significant increase in the number of generated photons by specifically manipulating the amplitude of the betatron oscillations by using our novel Transverse Oscillating Bubble Enhanced Betatron Radiation scheme. We realize this through an orchestrated evolution of the temporal laser pulse shape and the accelerating plasma structure. This leads to controlled off-axis injection of electrons that perform large-amplitude collective transverse betatron oscillations, resulting in increased radiation emission. Our concept holds the promise for a method to optimize the X-ray parameters for specific applications, such as time-resolved investigations with spatial and temporal atomic resolution or advanced high-resolution imaging modalities, and the generation of X-ray beams with even higher peak and average brightness.

Applicability of Large-Area Single-Photon Counting Detectors Timepix for High-Resolution and High-Contrast X-Ray Imaging of Biological Samples

High-resolution X-ray imaging techniques, usually known as microradiography and micro-computed tomography (CT), have become highly required and frequently used tools for biology, biomedical and preclinical research. State-of-the-art micro-CT scanners are capable of achieving a spatial resolution of few micrometers or even less, thanks to the constant development of compact microfocus X-ray sources together with simultaneous progress in detector technologies. The current standard in X-ray detection is a digital imaging device containing read-out circuitry coupled with a scintillation sensor. Such detectors are available in a variety of different sizes, and are easy to use and relatively affordable. Nevertheless, the mentioned technology suffers from inherent limitations like, for example, undesirable generation of dark current, that compromise the quality of the provided data. This work demonstrates the applicability of Timepix large-area hybrid-pixel photon-counting detectors (PCDs) for high-resolution X-ray imaging in biology research. Photon-counting detection technology provides dark-current-free quantum-counting operation. Therefore, an enhanced contrast-to-noise ratio of the acquired data is achieved. Furthermore, the biased semiconductor sensor achieves almost ideal point-spread function (PSF) resulting in images with high spatial-resolution. Both above-mentioned features make PCDs to be excellent tools for high-resolution X-ray imaging especially for samples with low intrinsic absorption contrast. We evaluated the imaging performance of large-area Timepix detectors compared to a state-of-the-art flat-panel detector dedicated for high-resolution X-ray imaging. The presented data demonstrate the versatility of the used detectors as it covers a wide range of samples from laboratory animals to single-cell marine organisms.

Photon yield of superradiant inverse Compton scattering from microbunched electrons

Compact x-ray sources offering high-brightness radiation for advanced imaging applications are highly desired. We investigate, analytically and numerically, the photon yield of superradiant inverse Compton scattering from microbunched electrons in the linear Thomson regime, using a classical electrodynamics approach. We show that for low electron beam energy, which is generic to inverse Compton sources, the single electron radiation distribution does not match well to collective amplification pattern induced by a density modulated electron beam. Consequently, for head-on scattering from a visible laser, the superradiant yield is limited by the transverse size of typical electron bunches driving Compton sources. However, by simultaneously increasing the electron beam energy and introducing an oblique scattering geometry, the superradiant yield can be increased by orders of magnitude.

Low-energy X-ray irradiation: A novel non-thermal microbial inactivation technology.

Over the last several decades, food irradiation technology has been proven neither to reduce the nutritional value of foods more than other preservation technologies, nor to make foods radioactive or dangerous to eat. Furthermore, food irradiation is a non-thermal food processing technology that helps preserve more heat sensitive nutrients than those found in thermally processed foods. Conventional food irradiation technologies, including γ-ray, electron beam and high energy X-ray, have certain limitations and drawbacks, such as involving radioactive isotopes, low penetration ability, and economical unfeasibility, respectively. Owing to the recent developments in instrumentation technology, more compact and cheaper tabletop low-energy X-ray sources have become available. The generation of low-energy X-ray, unlike γ-ray, does not involve radioactive isotopes and the cost is lower than high energy X-ray. Furthermore, low-energy X-ray possesses unique advantages, i.e., high linear energy transfer (LET) value and high relative biological effect (RBE) value. The advantages allow low-energy X-ray irradiation to provide a higher microbial inactivation efficacy than γ-ray and high energy X-ray irradiation. In the last few years, various applications reported in the literature indicate that low-energy X-ray irradiation has a great potential to become an alternative food preservation technique. This chapter discusses the technical advances of low-energy X-ray irradiation, microbial inactivation mechanism, factors influencing its efficiency, current applications, consumer acceptance, and limitations.

Optimization of parameters of a compact soft X-ray source for operation in the wavelength range 2-5 nm

This paper presents a compact source of soft X-ray radiation for operation in the wavelength range of 2-5 nm with a pulse repetition frequency of more than 500 Hz. The source parameters were optimized to reduce the intensity of ablation of the discharge volume wall and obtain the maximum intensity of the spectral lines of multicharged ions C V --- 4 nm and Ar IX --- 4.87 nm. The obtained results can be used in the development of a microscope for the tasks of cell transmission microscopy with nanometer resolution. Keywords: High-voltage pulse generator, Capillary plasma, "Water-window" microscopy.

Transverse confinement of electron beams in a 2D optical lattice for compact coherent x-ray sources

Compact coherent x-ray sources have been the focus of extensive research efforts over the past decades. As a result, several novel schemes like optical and nano-undulators for generating x-ray emissions in ‘table-top’ setups are proposed, developed, and assessed. Despite the extensive efforts in the past decades, there exists no operational FEL based on optical or electromagnetic undulators. By combining the particle confinement capability of optical cavities with wiggling motion inside an optical undulator, this paper proposes a new concept for making a compact coherent x-ray source. The full-wave solution of first-principle equations based on finite-difference time-domain and particle-in-cell is performed to simulate inverse-Compton scattering (ICS) off both free and confined electrons. It is shown that the strong space-charge effect in a low-energy electron beam (5 MeV) is the main obstacle in acquiring coherent gain through the ICS mechanism with a 10 micrometer laser. Subsequently, it is shown that by confining the electron beam at the field nodes of an optical cavity, the space-charge effect is compensated, and additionally, the ultrahigh charge density enables high FEL-gain at confinement spots. The full-wave numerical simulations predict enhancement of about three orders of magnitude in the radiation efficiency when ICS is carried out with confined electrons compared to free electrons. These theoretical results show promising potential as a new scheme for implementing a compact coherent x-ray source.

Influence of Irradiation-driven Winds on the Evolution of Intermediate-mass Black Hole X-ray Binaries

Abstract In young dense clusters, an intermediate-mass black hole (IMBH) may get a companion star via exchange encounters or tidal capture and then evolve toward the IMBH X-ray binary by the Roche lobe overflow. It is generally thought that IMBH X-ray binaries are potential ultraluminous X-ray sources (ULXs); hence, their evolution is very significant. However, the irradiation-driven winds by the strong X-ray flux from the accretion disks around the IMBHs play an important role in determining the evolution of IMBH X-ray binaries and should be considered in the detailed binary evolution simulation. Employing the models with the MESA code, we focus on the influence of irradiation-driven winds on the evolution of IMBH X-ray binaries. Our simulations indicate that a high wind-driving efficiency (f = 0.01 for Z = 0.02, and f = 0.002 for Z = 0.001) substantially shortens the duration in the ULX stage of IMBH X-ray binaries with an intermediate-mass (5 M ⊙) donor star. However, this effect can be ignored for high-mass (10 M ⊙) donor stars. The irradiation effect (f = 0.01 or 0.002) markedly shrinks the initial parameter space of IMBH binaries evolving toward ULXs with high luminosity (L X > 1040 erg s−1) and hyperluminous X-ray sources in the donor-star mass versus orbital period diagram. Furthermore, the irradiation effect results in an efficient angular momentum loss, yielding to IMBH X-ray binaries with relatively close orbits. In our simulated parameter space, about 1% of IMBH binaries would evolve toward compact X-ray sources owing to short initial orbital periods, some of which might be detected as low-frequency gravitational-wave sources.

Protein Dynamics and Time Resolved Protein Crystallography at Synchrotron Radiation Sources: Past, Present and Future

The ultrabright and ultrashort pulses produced at X-ray free electron lasers (XFELs) has enabled studies of crystallized molecular machines at work under ‘native’ conditions at room temperature by the so-called time-resolved serial femtosecond crystallography (TR-SFX) technique. Since early TR-SFX experiments were conducted at XFELs, it has been largely reported in the literature that time-resolved X-ray experiments at synchrotrons are no longer feasible or are impractical due to the severe technical limitations of these radiation sources. The transfer of the serial crystallography approach to newest synchrotrons upgraded for higher flux density and with beamlines using sophisticated focusing optics, submicron beam diameters and fast low-noise photon-counting detectors offers a way to overcome these difficulties opening new and exciting possibilities. In fact, there is an increasing amount of publications reporting new findings in structural dynamics of protein macromolecules by using time resolved crystallography from microcrystals at synchrotron sources. This review gathers information to provide an overview of the recent work and the advances made in this filed in the past years, as well as outlines future perspectives at the next generation of synchrotron sources and the upcoming compact pulsed X-ray sources.

The nuclear environment of NGC 2442: a Compton-thick low-luminosity AGN

ABSTRACT The detailed study of nuclear regions of galaxies is important because it can help understanding the active galactic nucleus (AGN) feedback mechanisms, the connections between the nuclei and their host galaxies, and ultimately the galaxy formation processes. We present the analysis of an optical data cube of the central region of the galaxy NGC 2442, obtained with the integral field unit (IFU) of the Gemini Multi-Object Spectrograph (GMOS). We also performed a multiwavelength analysis, with Chandra data, XMM–Newton and NuSTAR spectra, and Hubble Space Telescope (HST) images. The analysis revealed that the nuclear emission is consistent with a Low Ionization Nuclear Emission-line Region (LINER) associated with a highly obscured compact hard X-ray source, indicating a Compton-thick AGN. The HST image in the F658N filter (H α) reveals an arched structure corresponding to the walls of the ionization cone of the AGN. The gas kinematic pattern and the high gas velocity dispersion values in the same region of the ionization cone suggest an outflow emission. The stellar archaeology results indicate the presence of only old stellar populations (∼ 10 Gyr), with high metallicity (z = 0.02 and 0.05), and the absence of recent star formation in the central region of NGC 2442, which is possibly a consequence of the AGN feedback, associated with the detected outflow, shutting off star formation. NGC 2442 is a late-type galaxy similar to the Milky Way, and comparisons show that the main difference between them is the presence of a low-luminosity AGN.

Calibrating X-Ray Binary Luminosity Functions via Optical Reconnaissance. I. The Case of M83

Abstract Building on recent work by Chandar et al., we construct X-ray luminosity functions (XLFs) for different classes of X-ray binary (XRB) donors in the nearby star-forming galaxy M83 through a novel methodology. Rather than classifying low- versus high-mass XRBs based on the scaling of the number of X-ray sources with stellar mass and star formation rate, respectively, we utilize multiband Hubble Space Telescope imaging data to classify each Chandra-detected compact X-ray source as a low-mass (i.e., donor mass ≲3 M ⊙), high-mass (donor mass ≳8M ⊙), or intermediate-mass XRB based on either the location of its candidate counterpart on optical color–magnitude diagrams or the age of its host star cluster. In addition to the standard (single and/or truncated) power-law functional shape, we approximate the resulting XLFs with a Schechter function. We identify a marginally significant (at the 1σ-to-2σ level) exponential downturn for the high-mass XRB XLF, at ℓ ≃ 38.48 − 0.33 + 0.52 (in log CGS units). In contrast, the low- and intermediate-mass XRB XLFs, as well as the total XLF of M83, are formally consistent with sampling statistics from a single power law. Our method suggests a non-negligible contribution from low- and possibly intermediate-mass XRBs to the total XRB XLF of M83, i.e., between 20% and 50%, in broad agreement with X-ray-based XLFs. More generally, we caution against considerable contamination from X-ray emitting supernova remnants to the published, X-ray-based XLFs of M83, and possibly all actively star-forming galaxies.

Validation of a laser driven plasma X-ray microfocus source for high resolution radiography imaging.

Hard X-ray radiation with high brightness and high fluxes is nowadays available on the fourth generation of synchrotrons and X-FELs, but the large size and complexity of these sources makes its use difficult for widespread applications. New table top X-ray sources driven by ultrashort high power lasers offer a compelling route to expand the availability of hard X-ray sources. They can be used for advanced imaging techniques, due to its small source size and spatial coherence. We present in this paper the validation of a compact laser-driven X-ray microfocus source for high-resolution radiography imaging. This novel device was built at the Laser Laboratory for Acceleration and Applications (L2A2) at the University of Santiago de Compostela. This paper describes the laser-plasma X-ray source with improved stability and characterize some of its properties. We demonstrate the high-contrast and resolution of the images obtained with this source by using masks with well known geometries, and detailed analysis by using the modulation transfer function. Finally, we discuss the properties of this source in comparison to other compact microfocus X-ray sources.

X-ray photons produced from a plasma-cathode electron beam for radiation biology applications

A compact low-energy and high-intensity x-ray source for radiation biology applications is presented. A laser-induced plasma moves inside a 30 kV diode and produces a beam of 1014 electrons at the anode location. An aluminum foil converts a part of the energy of these electrons into x-ray photons, which are characterized using filtered imaging plates. The dose that would be deposited by these x-ray photons in C. elegans larvae is calculated from Geant4 simulations. It can be set to a value ranging between 10 μGy and 10 mGy per laser shot by simply changing the aluminum foil thickness and the diode voltage. Therefore, this versatile and compact x-ray source opens a new path to explore the radiation effects induced by dose rates varying over several orders of magnitude.

On the Opportunity of Liquid Metal Rotated Anode for High Brightness X-Ray Source

The new generation compact X-ray source for semiconductor metrology requires a brilliance that is higher than existing technology can offer. In this article, we propose a new X-ray source anode where an electron beam is focused on a rotating liquid metal layer. We assume that high brilliance emission can be achieved with power densities in the range of 1–10 MW/mm2 in the focal spot. The liquid tin layer is formed on top of the rotating anode disk electrode which is partially immersed in liquid tin. This scheme has recently been implemented in the plasma-discharge-based 13.5-nm extreme UV source of the EBL-2 beamline system at TNO. The existing technology of liquid tin circulation can provide cooling of up to 10 kW of input power with peak power densities up to 5 MW/mm2. An opportunity to use a liquid metal layer with the thickness of several tens of micrometers on the fast-rotating metal disk is discussed.

Compact high-flux hard X-ray source driven by femtosecond mid-infrared pulses at a 1 kHz repetition rate.

A novel, to the best of our knowledge, table-top hard X-ray source driven by femtosecond mid-infrared pulses provides 8 keV pulses at a 1 kHz repetition rate with an unprecedented flux of up to 1.5×1012 X-ray photons/s. Sub-100 fs pulses at a center wavelength of 5 µm and multi-millijoule energy are generated in a four-stage optical parametric chirped-pulse amplifier and focused onto a thin Cu tape target. Electrons are extracted from the target and accelerated in a vacuum up to 100 keV kinetic energy during the optical cycle; the electrons generate a highly stable K α photon flux from the target in a transmission geometry.

The ThomX ICS source

ThomX is a new generation Compact Compton Source. It is currently commissioned by and at the IJCLab (Laboratoire de physique des 2 infinis - Irène Joliot-Curie (UMR9012)) at Orsay. The first beam is expected at the begining of 2021. The aim of ThomX is to demonstrate the characteristics of an intense and Compact (lab-size) X-ray source based on Compton Scattering. The performances are mostly driven by the laser optical system which is above the state of the art of stored laser power. Proof of principle of various X-ray techniques will be performed thanks to the versatile ThomX beamline. Firstly, this article presents the machine description. Secondly, the issues and limits of the laser system are discussed. Then, the ThomX beamline is described and the machine status conclude the ThomX presentation. Finally, the expected performances for the next years and the possible experiments that can be made with this new machine are detailed.

Evaluation of a compact multicontrast and multiresolution X-ray phase contrast edge illumination system for small animal imaging.

In this work the performance of a compact multiresolution and multicontrast x-ray phase system based on edge illumination is investigated. It has been designed for small animal imaging and with a limited footprint for ease of deployment in laboratories. The presented edge illumination system is based on a compact microfocus tungsten x-ray source combined with a flat panel detector. The source has a maximum output of 10W when the minimum spot size of about 15μm is used. The system has an overall length of 70cm. A new double sample mask design, obtained by arranging both skipped and nonskipped configurations on the same structure, provides dual resolution capability. To test the system, we carried out computed tomography (CT) scans of a plastic phantom with different source settings using both single-image and multi-image acquisition schemes at different spatial resolutions. In addition, CT scans of an ex-vivo mouse specimen were acquired at the best identified working conditions to demonstrate the application of the presented system to small animal imaging. We found this system delivers good image quality, allowing for an efficient material separation and improving detail visibility in small animals thanks to the higher signal-to-noise ratio (SNR) of phase contrast with respect to conventional attenuation contrast. The system offers high versatility in terms of spatial resolution thanks to the double sample mask design integrated into a single scanner. The availability of both multi- and single-image acquisition schemes coupled with their dedicated retrieval algorithms, allows different working modes which can be selected based on user preference. Multi-image acquisition provides quantitative separation of the real and imaginary part of the refractive index, however, it requires a long scanning time. On the other hand, the single image approach delivers the best material separation and image quality at all the investigated source settings with a shorter scanning time but at the cost of quantitativeness. Finally, we also observed that the single image approach combined with a high-power x-ray source may result in a fast acquisition protocol compatible with in-vivo imaging.

Spectroscopic imaging at compact inverse Compton X-ray sources.

While K-edge subtraction (KES) imaging is a commonly applied technique at synchrotron sources, the application of this imaging method in clinical imaging is limited although results have shown its superiority to conventional clinical subtraction imaging. Over the past decades, compact synchrotron X-ray sources, based on inverse Compton scattering, have been developed to fill the gap between conventional X-ray tubes and synchrotron facilities. These so called inverse Compton sources (ICSs) provide a tunable, quasi-monochromatic X-ray beam in a laboratory setting with reduced spatial and financial requirements. This allows for the transfer of imaging techniques that have been limited to synchrotrons until now, like KES imaging, into a laboratory environment. This review article presents the first studies that have successfully performed KES at ICSs. These have shown that KES provides improved image quality in comparison to conventional X-ray imaging. The results indicate that medical imaging could benefit from monochromatic imaging and KES techniques. Currently, the clinical application of KES is limited by the low K-edge energy of available iodine contrast agents. However, several ICSs are under development or already in commissioning which will provide monochromatic X-ray beams with higher X-ray energies and will enable KES using high-Z elements as contrast media. With these developments, KES at an ICS has the ability to become an important tool in pre-clinical research and potentially advancing existing clinical imaging techniques.

PO-1416: Dose calculation algorithm for a compact xray source in Microbeam Radiation Therapy

PO-1416: Dose calculation algorithm for a compact xray source in Microbeam Radiation Therapy