Estimation of soft X‐ray and EUV transition radiation power emitted from the MIRRORCLE‐type tabletop synchrotron

The tabletop synchrotron light sources MIRRORCLE‐6X and MIRRORCLE‐20SX, operating at electron energies E_el = 6 MeV and E_el = 20 MeV, respectively, can emit powerful transition radiation (TR) in the extreme ultraviolet (EUV) and the soft X‐ray regions. To clarify the applicability of these soft X‐ray and EUV sources, the total TR power has been determined. A TR experiment was performed using a 385 nm‐thick Al foil target in MIRRORCLE‐6X. The angular distribution of the emitted power was measured using a detector assembly based on an NE102 scintillator, an optical bundle and a photomultiplier. The maximal measured total TR power for MIRRORCLE‐6X is P_max? 2.95 mW at full power operation. Introduction of an analytical expression for the lifetime of the electron beam allows calculation of the emitted TR power by a tabletop synchrotron light source. Using the above measurement result, and the theoretically determined ratio between the TR power for MIRRORCLE‐6X and MIRRORCLE‐20SX, the total TR power for MIRRORCLE‐20SX can be obtained. The one‐foil TR target thickness is optimized for the 20 MeV electron energy. P_max? 810 mW for MIRRORCLE‐20SX is obtained with a single foil of 240 nm‐thick Be target. The emitted bremsstrahlung is negligible with respect to the emitted TR for optimized TR targets. From a theoretically known TR spectrum it is concluded that MIRRORCLE‐20SX can emit 150 mW of photons with E > 500 eV, which makes it applicable as a source for performing X‐ray lithography. The average wavelength, = 13.6 nm, of the TR emission of MIRRORCLE‐20SX, with a 200 nm Al target, could provide of the order of 1 W EUV.     

Correlation of Electron Beams and Hard X‐ray Emissions in ISTTOK Tokamak

The paper reports on experimental studies of electron beams in the ISTTOK tokamak, those were performed by means of an improved four‐channel detector. The Cherenkov‐type detector measuring head was equipped with four radiators made of two types of alumina‐nitrate (AlN) poly‐crystals: machinable and translucent ones, both of 10 mm in diameter and 2.5 mm in thickness. The movable support that enabled the whole detectors to be placed inside the tokamak vacuum chamber, at chosen positions along the ISTTOK minor radius. Since the electron energy distribution is one of the most important characteristics of tokamak plasmas, the main aim of the study was to perform estimations of an energy spectrum of the recorded electrons. For this purpose the radiators were coated with molybdenum (Mo) layers of different thickness. The technique based on the use of Cherenkov‐type detectors enabled the detection of fast electrons (of energy above 66 keV) and determination of their spatial and temporal characteristics in the ISTTOK experiment. Measurements of hard X‐rays (HXR), which were emitted during ISTTOK discharges, have also been performed. Particular attention was paid to the correlation measurements of HXR pulses with run‐away electron beams. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Large-angle channeling radiation from relativistic electrons in optically transparent crystals

In the work within the frame of quantum electrodynamics are obtained new formulae describing the large-angle photon emission from channeled electrons with taking into account of the dispersion of refractive index. Calculations based on these formulae show that the spectral and angular distributions of large-angle optical and ultraviolet radiation from planar channeled sub-GeV electrons in optically transparent crystal reflect the band structure of transverse energy levels of channeled electrons. Comparison with ordinary Cherenkov radiation spectrum reveals that channeling (depending on the beam energy) leads to sufficient change of the large-angle emission spectrum.     

Performance of the far‐IR beamline of the 6 MeV tabletop synchrotron light source

The performance of the far‐infrared (FIR) beamline of the 6 MeV tabletop synchrotron light source MIRRORCLE‐6FIR dedicated to far‐infrared spectroscopy is presented. MIRRORCLE‐6FIR is equipped with a perfectly circular optical system (PhSR) placed around the 1 m‐long circumference electron orbit. To illustrate the facility of this light source, the FIR output as well as its spectra were measured. The optimum optical system was designed by using the ray‐tracing simulation code ZEMAX. The measured FIR intensity with the PhSR in place is about five times higher than that without the PhSR, which is in good agreement with the simulation results. The MIRRORCLE‐6FIR spectral flux is compared with a standard thermal source and is found to be 1000 times greater than that from a typical thermal source at ～15 cm^?1. It is also observed that the MIRRORCLE‐6FIR radiation has a highly coherent nature. The broadband infrared allows the facility to reach the spectral range from 10 cm^?1 to 100 cm^?1. MIRRORCLE‐6FIR, owing to a large beam current, the PhSR mirror system, a large dynamic aperture and small ring energy, can deliver a bright flux of photons in the FIR/THz region useful for broadband spectroscopy.     

6 MeV storage ring dedicated to hard X-ray imaging and far-infrared spectroscopy

The tabletop storage ring, 6 MeV MIRRORCLE, is dedicated to hard X-ray imaging as well as far-infrared (FIR) spectroscopy. In spite of low electron energy, the 6 MeV MIRRORCLE generates hard X-rays ranging from 10 keV up to its electron energy and milliwatt order sub-millimetre range FIR rays. Bremsstrahlung is the mechanism for the hard X-ray generation. Images produced with 11× geometrical magnification display a sharply enhanced edge effect when generated using a 25 mm rod electron target. Bright far-infrared is generated in the same way using a conventional synchrotron light source, but with MIRRORCLE the spectral flux is found to be ∼1000 times greater than that of a standard thermal source. Partially coherent enhancement is observed in the case of FIR output.     

Intense Cherenkov-type terahertz electromagnetic radiation from ultrafast laser-plasma interaction

A Cherenkov-type terahertz electromagnetic radiation is revealed, which results efficiently from the collective effects in the time-domain of ultrafast pulsed electron current produced by ultrafast intense laser--plasma interaction. The emitted pulse waveform and spectrum, and the dependence of laser pulse parameters on the structure of the radiation field are investigated numerically. The condition of THz radiation generation in this regime and Cherenkov geometry of the radiation field are studied analytically.     

聚变反应随时间变化诊断装置辐射转换体设计

聚变反应随时间变化诊断装置是惯性约束聚变(ICF)研究中的一项重要诊断设备, 使用蒙特卡罗程序Geant4研究了基于气体切伦科夫探测器的聚变反应随时间变化诊断装置的时间分辨和辐射转换效率,给出了优化后的辐射转换体材料厚度,以及CO2气室压力与长度。模拟计算表明,优化后的系统时间分辨可达22 ps左右,伽马-切伦科夫光子转换效率可达4.710-3 Cherenkov photons/gamma。     

Compton scattering of 59.54 keV γ‐rays from Fe and p‐Si samples in an external magnetic field

We report on the Compton scattering of photons from samples whose surface charge density distributions are changed by an external magnetic field. We performed a Compton scattering experiment known to be particularly sensitive to the behavior of the relatively slower moving outer electrons (valence electrons) involved in bonding in condensed matter. The external magnetic field was used to change the surface charge density distributions of Fe and p‐Si samples. Samples were located in the external magnetic field of intensity 215 G and in a direction which was perpendicular both to the current and surface of the samples bombarded by 59.5 keV γ‐photons emitted from an Am‐241 point source. Currents in the ranges 0–8.5 A and 0–300 µA were applied to the Fe and p‐Si samples, respectively. The Compton scattered photons at an angle of 100° were detected by an Si(Li) detector. It was observed that the counts acquired under the Compton peaks tended to decrease linearly with increasing current in a magnetic field. The results show that positive charge carriers behave like negative charge carriers and electrons are more effective than holes in the Compton scattering of γ‐rays. Copyright © 2003 John Wiley & Sons, Ltd.     

等离子体填充金属光子晶体Cherenkov辐射源模拟研究

等离子体填充能够明显提高真空电子器件的效率和功率, 研究等离子体填充器件具有重要的科学价值. 本文基于对等离子体填充金属光子晶体慢波结构色散特性的分析, 利用粒子模拟方法展示了等离子体填充慢波结构中的注波互作用过程. 重点研究了慢波结构中场分布特性、等离子体密度和外部工作条件对频率及输出功率的影响. 研究发现, 填充一定密度等离子体后, 慢波结构内纵向和横向电场强度明显增大, 注波互作用增强, 输出频率受等离子体影响不大. 金属光子晶体结构具有的频率选择特性使器件工作于TM₀₁模态. 阴极电压增加使输出功率增大, 频率略有增加. 引导磁场增加使输出功率先增大后减小, 而频率基本不受影响. 等离子体填充后器件的输出功率上升, 当增加压强至100 mTorr(1 mTorr=0.133 Pa) 时, 输出功率提高约20%, 但只有适当密度下才有较好的角向场分布. 通过理论与模拟相结合, 发现填充一定密度的等离子体能够提高器件输出功率和效率, 为发展新型高功率毫米波振荡辐射源奠定了理论和仿真基础.     

Geometry and optics calibration of WFCTA prototype telescopes using star light

The Large High Altitude Air Shower Observatory (LHAASO) project is proposed to study high energy gamma ray astronomy (40 GeV-1 PeV) and cosmic ray physics (20 TeV-1 EeV). The wide field of view Cherenkov telescope array, as a component of the LHAASO project, will be used to study the energy spectrum and composition of cosmic rays by measuring the total Cherenkov light generated by air showers and the shower maximum depth. Two prototype telescopes have been in operation since 2008. The pointing accuracy of each telescope is crucial for the direction reconstruction of the primary particles. On the other hand, the primary energy reconstruction relies on the shape of the Cherenkov image on the camera and the unrecorded photons due to the imperfect connections between the photomultiplier tubes. UV bright stars are used as point-like objects to calibrate the pointing and to study the optical properties of the camera, the spot size and the fractions of unrecorded photons in the insensitive areas of the camera.     

Linear Theory of Plasma-Filled Coaxial Cylindrical Cherenkov Maser

Injection of background plasma into the beam-wave interaction region can greatly enhance the beam-wave interaction efficiency and the microwave output power of the device. In this paper, a new type of plasma-filled slow-wave structure, i.e., plasma-filled, dielectric-loaded coaxial cylindrical waveguide with a dielectric ring enclosing tightly the inner conductor, is developed. The Cherenkov radiation excited by the beam-wave interaction in the slow-wave structure is examined by use of the self-consistent linear field theory. The dispersion equation and the synchronized condition of the beam-wave interaction are derived. It's clearly shown that the Cherenkov radiation excited by the beam-wave interaction results from the coupling between the slow electromagnetic wave, TM-modes, propagated along the slow-wave structure and the negative-energy space-charge wave propagated along the relativistic electron beam. And the wave growth rate is solved, and the beam-wave energy exchange in the presence of the background plasma is discussed. Finally, the effects of the background plasma density on the dispersion characteristics, the distribution of the longitudinal fluctuating electric field, the wave growth rate and the beam-wave energy exchange are calculated and discussed.     

The EIGER detector for low‐energy electron microscopy and photoemission electron microscopy

EIGER is a single‐photon‐counting hybrid pixel detector developed at the Paul Scherrer Institut, Switzerland. It is designed for applications at synchrotron light sources with photon energies above 5 keV. Features of EIGER include a small pixel size (75 µm × 75 µm), a high frame rate (up to 23 kHz), a small dead‐time between frames (down to 3 µs) and a dynamic range up to 32‐bit. In this article, the use of EIGER as a detector for electrons in low‐energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) is reported. It is demonstrated that, with only a minimal modification to the sensitive part of the detector, EIGER is able to detect electrons emitted or reflected by the sample and accelerated to 8–20 keV. The imaging capabilities are shown to be superior to the standard microchannel plate detector for these types of applications. This is due to the much higher signal‐to‐noise ratio, better homogeneity and improved dynamic range. In addition, the operation of the EIGER detector is not affected by radiation damage from electrons in the present energy range and guarantees more stable performance over time. To benchmark the detector capabilities, LEEM experiments are performed on selected surfaces and the magnetic and electronic properties of individual iron nanoparticles with sizes ranging from 8 to 22 nm are detected using the PEEM endstation at the Surface/Interface Microscopy (SIM) beamline of the Swiss Light Source.     

A new small‐angle X‐ray scattering set‐up on the crystallography beamline I711 at MAX‐lab

A small‐angle X‐ray scattering (SAXS) set‐up has recently been developed at beamline I711 at the MAX II storage ring in Lund (Sweden). An overview of the required modifications is presented here together with a number of application examples. The accessible q range in a SAXS experiment is 0.009–0.3 Å^?1 for the standard set‐up but depends on the sample‐to‐detector distance, detector offset, beamstop size and wavelength. The SAXS camera has been designed to have a low background and has three collinear slit sets for collimating the incident beam. The standard beam size is about 0.37 mm × 0.37 mm (full width at half‐maximum) at the sample position, with a flux of 4 × 10¹⁰ photons s^?1 and λ = 1.1 Å. The vacuum is of the order of 0.05 mbar in the unbroken beam path from the first slits until the exit window in front of the detector. A large sample chamber with a number of lead‐throughs allows different sample environments to be mounted. This station is used for measurements on weakly scattering proteins in solutions and also for colloids, polymers and other nanoscale structures. A special application supported by the beamline is the effort to establish a micro‐fluidic sample environment for structural analysis of samples that are only available in limited quantities. Overall, this work demonstrates how a cost‐effective SAXS station can be constructed on a multipurpose beamline.     

Tachyonic Cherenkov emission from Jupiterʼs radio electrons

Tachyonic Cherenkov radiation from inertial relativistic electrons in the Jovian radiation belts is studied. The tachyonic modes are coupled to a frequency-dependent permeability tensor and admit a negative mass-square, rendering them superluminal and dispersive. The superluminal radiation field can be cast into Maxwellian form, using 3D field strengths and inductions, and the spectral densities of tachyonic Cherenkov radiation are derived. The negative mass-square gives rise to a longitudinal flux component. A spectral fit to Jupiter?s radio spectrum, inferred from ground-based observations and the Cassini 2001 fly-by, is performed with tachyonic Cherenkov flux densities averaged over a thermal electron population.     

The first microbeam synchrotron X‐ray fluorescence beamline at the Siam Photon Laboratory

The first microbeam synchrotron X‐ray fluorescence (µ‐SXRF) beamline using continuous synchrotron radiation from Siam Photon Source has been constructed and commissioned as of August 2011. Utilizing an X‐ray capillary half‐lens allows synchrotron radiation from a 1.4 T bending magnet of the 1.2 GeV electron storage ring to be focused from a few millimeters‐sized beam to a micrometer‐sized beam. This beamline was originally designed for deep X‐ray lithography (DXL) and was one of the first two operational beamlines at this facility. A modification has been carried out to the beamline in order to additionally enable µ‐SXRF and synchrotron X‐ray powder diffraction (SXPD). Modifications included the installation of a new chamber housing a Si(111) crystal to extract 8 keV synchrotron radiation from the white X‐ray beam (for SXPD), a fixed aperture and three gate valves. Two end‐stations incorporating optics and detectors for µ‐SXRF and SXPD have then been installed immediately upstream of the DXL station, with the three techniques sharing available beam time. The µ‐SXRF station utilizes a polycapillary half‐lens for X‐ray focusing. This optic focuses X‐ray white beam from 5 mm × 2 mm (H × V) at the entrance of the lens down to a diameter of 100 µm FWHM measured at a sample position 22 mm (lens focal point) downstream of the lens exit. The end‐station also incorporates an XYZ motorized sample holder with 25 mm travel per axis, a 5× ZEISS microscope objective with 5 mm × 5 mm field of view coupled to a CCD camera looking to the sample, and an AMPTEK single‐element Si (PIN) solid‐state detector for fluorescence detection. A graphic user interface data acquisition program using the LabVIEW platform has also been developed in‐house to generate a series of single‐column data which are compatible with available XRF data‐processing software. Finally, to test the performance of the µ‐SXRF beamline, an elemental surface profile has been obtained for a piece of ancient pottery from the Ban Chiang archaeological site, a UNESCO heritage site. It was found that the newly constructed µ‐SXRF technique was able to clearly distinguish the distribution of different elements on the specimen.     

Cherenkov terahertz radiation from Dirac semimetals surface plasmon polaritons excited by an electron beam

We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band.     

产生切连科夫辐射的康普顿电子在介质中的临界散射角

讨论了γ光子在同一种介质中连续产生康普顿散射和切连科夫辐射的条件。这一条件可用产生切连科夫辐射的康普顿电子在介质中的临界散射角的大小来表示。     

Pair Events in Superluminal Optics

When an object moves faster than emissions it creates, it may appear at two positions simultaneously. The appearance or disappearance of this bifurcation is referred to as a pair event. Inherently convolved with superluminal motion, pair events have no subluminal counterparts. Common examples of superluminal motions that exhibit pair events include Cherenkov radiation, sonic booms, illumination fronts from variable light sources, and rotating beams. The minimally simple case of pair events from a single massive object is explored here: uniform linear motion. A pair event is perceived when the radial component of the object's speed toward the observer drops from superluminal to subluminal. Emission from the pair creation event will reach the observer before emission from either of the two images created. Potentially observable image pair events are described for sonic booms and Cherenkov light. To date, no detection of discrete images following a projectile pair event have ever been reported, and so the pair event nature of sonic booms and Cherenkov radiation, for example, remains unconfirmed. Recent advances in modern technology have made such pair event tracking feasible. If measured, pair events could provide important information about object distance and history.     

Image processing pipeline for synchrotron‐radiation‐based tomographic microscopy

With synchrotron‐radiation‐based tomographic microscopy, three‐dimensional structures down to the micrometer level can be visualized. Tomographic data sets typically consist of 1000 to 1500 projections of 1024 × 1024 to 2048 × 2048 pixels and are acquired in 5–15 min. A processing pipeline has been developed to handle this large amount of data efficiently and to reconstruct the tomographic volume within a few minutes after the end of a scan. Just a few seconds after the raw data have been acquired, a selection of reconstructed slices is accessible through a web interface for preview and to fine tune the reconstruction parameters. The same interface allows initiation and control of the reconstruction process on the computer cluster. By integrating all programs and tools, required for tomographic reconstruction into the pipeline, the necessary user interaction is reduced to a minimum. The modularity of the pipeline allows functionality for new scan protocols to be added, such as an extended field of view, or new physical signals such as phase‐contrast or dark‐field imaging etc.     

Fast X‐ray microfluorescence imaging with submicrometer‐resolution integrating a Maia detector at beamline P06 at PETRA III

The high brilliance of third‐generation synchrotron sources increases the demand for faster detectors to utilize the available flux. The Maia detector is an advanced imaging scheme for energy‐dispersive detection realising dwell times per image‐pixel as low as 50 µs and count rates higher than 10 × 10⁶ s^?1. In this article the integration of such a Maia detector in the Microprobe setup of beamline P06 at the storage ring PETRA III at the Deutsches Elektronen‐Synchrotron (DESY) in Hamburg, Germany, is described. The analytical performance of the complete system in terms of rate‐dependent energy resolution, scanning‐speed‐dependent spatial resolution and lower limits of detection is characterized. The potential of the Maia‐based setup is demonstrated by key applications from materials science and chemistry, as well as environmental science with geological applications and biological questions that have been investigated at the P06 beamline.