ALBA Synchrotron Facility

ALBA is the Spanish synchrotron facility located in the area of Barcelona. It is a low-emittance, 3 GeV machine having, at present, seven state-of-the-art operating beamlines covering soft and hard X-rays. The hard X-ray beamlines comprise macromolecular crystallography, non-crystalline diffraction (SAXS and WAXS), high-resolution powder diffraction, and absorption spectroscopy. The soft X-ray beamlines include a photoemission beamline with two endstations—one devoted to photoelectron microscopy (PEEM) and the second to near ambient pressure photoemission (NAPP)—and another beamline devoted to XMCD and soft X-ray scattering. Both beamlines allow full control of the polarization of the beam, since they are equipped with helical undulators. An additional soft X-ray beamline, installed on a bending magnet port, is equipped with a full-field transmission X-ray microscope. Additional information may be found at http://www.albasynchrotron.es/en/beamlines.     

The rms-flux relation of Cyg X-2 in the horizontal branch

We have investigated the relation between the root mean square (rms) variability and the X-ray flux (rms-flux relation) of the Z source Cyg X-2, and as well the energy dependence based on the Rossi X-ray Timing Explorer (RXTE) observations. We currently focus on the horizontal branch (HB), due to the negative correlation in flux of the soft and the hard X-rays. The rms-flux correlation has energy dependence as follows: positive at hard X-rays (above 10 keV) but negative at soft X-rays (below 10 keV). This provides a feature different from the previous one, and may be suggestive of different origins of X-rays below and above 10 keV. Nevertheless, the overall spectrum can be well fitted with a model consisting of a blackbody and Comptonization components, but the fitting results do not reveal any features around 10 keV that could account for such a change in the rms-flux relation.     

Resonant X-ray magnetic scattering has gone soft

The Linac Coherent Light Source [1] (LCLS) at SLAC National Accelerator Laboratory is preparing for the arrival of its first scientific users in the fall of 2009. LCLS is the world's first free-electron in the spectral range 800?8,000?eV, producing intense, sub-picosecond pulses of Xrays with very high spatial coherence. The accelerator facility has been commissioned in stages, beginning in April 2007 [2] with the injector linac and culminating in December 2008 [3] with the first transport of electrons through the complete beam path. On April 10, 2009, the LCLS Project team was rewarded for years of planning, design, construction, and checkout with a dream-come-true: as undulators were placed on the beam path one-by-one, the laser simply turned on without drama in the course of one hour [4]. First visible evidence of light amplification at 8,000?eV was observed on a fluorescent screen with ten undulators in place, at which point a highly collimated spot of X-rays could be discerned in the center of the spontaneous radiation pattern. After just four days of further checkout, the intensity of this spot increased smoothly and exponentially to the threshold of “saturation” at full power with just 20 of 33 undulators in place. The commissioning team was faced with a mixture of shock and euphoria. The Project team has spent years focused on everything that could possibly go wrong, and what to do about each concern. Speaking for myself, I found I was mentally unprepared for the special case of NOTHING going wrong! In fact, a critical aspect of the FEL performance was significantly better than design goals—the gain length (the distance the electron beam must travel in undulators to increase X-ray power by a factor e) proved to be just 3.5 meters. With this gain length, and room for 33 undulators in the tunnel, we find we have ten more spares! The shutter was closed at about midnight, temporarily preventing the electron beam entering the undulator. At 8:00 A.M. the next morning, the shutter was retracted to reveal the FEL producing an 8,000?eV laser beam without need for operator intervention.     

All-laser-driven Thomson X-ray sources

We discuss the development of a new generation of accelerator-based hard X-ray sources driven exclusively by laser light. High-intensity laser pulses serve the dual roles: first, accelerating electrons by laser-driven plasma wakefields, and second, generating X-rays by inverse Compton scattering. Such all-laser-driven X-rays have recently been demonstrated to be energetic, tunable, relatively narrow in bandwidth, short pulsed and well collimated. Such characteristics, especially from a compact source, are highly advantageous for numerous advanced X-ray applications – in metrology, biomedicine, materials, ultrafast phenomena, radiology and fundamental physics.     

Preliminary experiment of the Thomson scattering X-ray source at Tsinghua University

The X-ray source based on Thomson scattering of ultrashort laser pulse with a relativistic electron beam is a means of generating a tunable, narrow bandwidth and ultrashort pulse of hard X-rays. Such a sub-picosecond hard X-ray source is proposed at Tsinghua University, and a preliminary experiment with a 16 MeV Backward Traveling electron linac and a 1.5 J, 6 ns Q-switched Nd:YAG laser is carried out first. A 6 ns pulse X-ray with a peak energy of 4.6 keV and an intensity of 1.7×104 per pulse is generated successfully in the experiment. The experimental setup, result and discussion are reported in this paper.     

上海光源硬X射线相干衍射成像实验方法初探

相干X射线衍射成像方法是一种先进的成像技术,分辨率可达纳米量级.国际上大多数的同步辐射装置和自由电子激光装置都建立了该成像方法,并有将其作为主要成像技术的趋势.上海光源作为目前国内唯一的一台第三代同步辐射光源,尚未建立基于硬X射线的相干衍射成像实验平台.随着一批以波荡器为光源的光束线站投入使用,使得该方法的建立成为了可能.本文基于上海光源BL19U2生物小角散射线站,通过有效的光路设计,搭建了相干衍射实验平台,在12 keV和13.5 keV能量点均获得了硬X射线相干光束,并基于小孔衍射测量了入射光束的空间相干长度.该平台支持常规和扫描相干衍射实验模式,对小孔衍射图样及波带片扫描衍射图样实现了正确的相位重建,证明了该平台初步具备开展硬X射线相干衍射成像实验的能力.硬X射线相干衍射成像实验平台为国内首次建立,将为国内该实验方法的发展和应用提供有效的软硬件支持.     

Surface roughness-aided hard X-ray emission from carbon nanotubes

Efficient low debris hard X-ray source based on multiwalled carbon nanotubes (MWNT) irradiated by intense, femtosecond laser over an intensity range of 10¹⁵–10¹⁷ W cm⁻² μm² is reported. The MWNT targets yield two orders of magnitude higher X-rays (indicating significant enhancement of laser coupling) and three orders of magnitude lower debris compared to conventional metallic targets under identical experimental conditions. The simple analytical model explains the basic experimental observations and also serves as a guide to design efficient targets to achieve low-debris laser plasma-based hard X-ray sources at low laser intensities suitable for multi-kHz operation.     

High resolution hard X-ray photoemission using synchrotron radiation as an essential tool for characterization of thin solid films

Recently, we have shown that hard X-ray photoemission spectroscopy using undulator X-rays at SPring-8 is quite feasible with both high resolution and high throughput. Here we report an application of hard X-ray photoemission spectroscopy to the characterization of electronic and chemical states of thin solid films, for which conventional PES is not applicable. As a typical example, we focus on the problem of the scatter in the reported band-gap values for InN. We show that oxygen incorporation into the InN film strongly modifies the valence and plays a crucial role in the band gap problem. The present results demonstrate the powerful applicability of high resolution photoemission spectroscopy with hard X-rays from a synchrotron source.     

Fabrication of multi-scale structures with multiple X-ray masks and synchrotron hard X-ray irradiations

Synchrotron hard X-ray irradiation can be utilized in lithography processes to manufacture precise structures. Due to the difficulty of precise X-ray mask fabrication in hard X-ray lithography, this X-ray process has been used mainly to fabricate precise microstructures. In this study, a technology is proposed for fabricating novel multi-scale patterns that include submicron-scale structures using hard X-rays. The required X-ray masks for submicron-sized patterning are fabricated by a simple UV lithography process and sidewall metal deposition. Above all, thanks to the high penetration capability of hard X-rays with sub-nanometer wavelengths, it is possible to employ multiple masks to fabricate a variety of patterns. By combining each sub-micron X-ray mask with typical micro-sized X-ray masks, a unique X-ray lithography is performed, and various multi-scale structures are fabricated. The usefulness of the proposed technology is demonstrated by the realization of these structures.     

Photon Sources at DESY

During the past 10 years, photon science activities at DESY in Hamburg, Germany, have expanded significantly and this development is expected to continue in the coming years. The soft X-ray free-electron laser (FEL) FLASH has been in user operation for over 10 years and the high-brilliance hard X-ray synchrotron radiation source PETRA III started serving the user community five years ago. Access to both light sources has since been highly demanded by scientists not only from Germany and Europe, but from all over the world. The request for beamtime far exceeded the capacity of available experimental infrastructure at both facilities and, for this reason, it was necessary to add further beamlines and also to broaden the portfolio of techniques. Therefore, new facilities have recently been built to almost double the existing capacity for user beamtime at both sources (Figure 1).     

Studying the Dynamics of Hybrid X-Pinches

Since the first experiments with hybrid X-pinches (HXP), it has been shown that a short wire between two conical tungsten electrodes produces the same radiation as a standard X-pinch. Since HXP has a simple construction, it is commonly used in many laboratories instead of standard pinches. Although details of the HXP dynamics remain poorly studied, the main factors governing HXP formation are investigated experimentally in this work. It is shown that the process of the electrode plasma formation is one of the main factors that lead to single hot spot bursts. Experimental results allow the fitting of HXP parameters and determination of the size of the source of X-ray radiation. It is also shown the radiation of HXP can be used as a source for point projection radiography in the wavelength range of soft to hard X-rays. Such sources can be also used for absorption spectroscopy and even electron beams.     

X-pinch source of subnanosecond soft X-ray pulses based on small-sized low-inductance current generator

For the first time, the regime of a micrometer-size hot spot formation is impemented for an X-pinch in a plasma, which is fed from a current generator based on low-inductance capacitors and rapid current switches. The configurations of X-pinches, which can be used effectively as point sources of soft X-rays with this type of current generator, are determined. A prototype of a small-size radiation source for high-resolution point projection X-ray radiography has been constructed. The main parameters of X-pinch as a radiation source are analyzed and compared with X-pinch parameters in high-voltage setups with shaping lines. An analysis of the data on the operation of X-pinches in generators with different parameters has led to simple relations that can be used to select optimal initial X-pinch parameters.     

X射线皮秒分幅相机在强X射线情况下的应用研究

扫描型变象管Ｘ射线皮秒分幅相机在强Ｘ射线情况下，由于空间电荷效应，像质变坏，甚至无法工作。本文简述了ＭｇＦ光阴极材料的性能。首次在Ｘ射线皮秒变象管分幅相机上的应用结果：降低了强Ｘ射线源情况下分幅管内空间电荷效应的影响，并获得了清晰的物理图像。     

Practical application of cross correlation technique to measure jitter of master-oscillator-power-amplifier (MOPA) laser system

The Linac coherent light source (LCLS) at the SLAC National Accelerator Laboratory (SLAC) is the world’s first hard X-ray free electron laser (XFEL) and is capable of producing high-energy, femtosecond duration X-ray pulses. A common technique to study fast timescale physical phenomena, various “pump/probe” techniques are used. In these techniques there are two lasers, one optical and one X-ray, that work as a pump and as a probe to study dynamic processes in atoms and molecules. In order to resolve phenomena that occur on femtosecond timescales, it is imperative to have very precise timing between the optical lasers and X-rays (on the order of ～20 fs or better). The lasers are synchronized to the same RF source that drives the accelerator and produces the X-ray laser. However, elements in the lasers cause some drift and time jitter, thereby de-synchronizing the system. This paper considers cross-correlation technique as a way to quantify the drift and jitter caused by the regenerative amplifier of the ultrafast optical laser.     

Special-purpose radiation sources based on the Siberia-2 storage ring

Synchrotron radiation (SR) generated by homogeneous magnetic fields of bending magnets is now employed at the Siberia-2 electron storage ring. It is planned that, in the near future, most of the storage ring’s free straight sections will be equipped with insertion devices (undulators and wigglers). Two projects of specialized radiation sources based on the Siberia-2 stor age ring are discussed. The first source is a vacuum milliundulator intended for generation of extremely bright X-ray beams. An X-ray source with vertically limited diffraction is shown to be feasible when the vertical emittance of an electron beam is equal to the diffraction emittance of photons with an energy of 2 keV. The second source uses edge radiation (ER) generated at the ends of bending magnets of the storage ring. Calculations show that, in the infrared and ultraviolet spectral regions, the ER intensity must exceed the intensity of standard SR formed by the homogeneous field of a bending magnet.     

Energy recovery LINAC: A next generation source for inelastic X-ray scattering

The Energy Recovery LINAC (ERL) being developed at Cornell should be an excellent source for Inelastic X-ray Scattering (IXS) because it will permit long undulators to operate at high efficiency generating unprecedented spectral flux (photons/second/meV) and brilliance. We discuss several advantages of the ERL for IXS experimentation.     

News and Views

ALBA is a low-emittance, 3 GeV synchrotron light source located near Barcelona. It is funded equally by the Spanish central and the Catalan autonomous governments. Seven state-of-the-art beamlines (BL), comprising soft and hard X-rays, are in operation to satisfy the requirements of the user community. This paper updates the status of the facility, focusing on its transition from commissioning to user operation, which has taken place during the last two years.     

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.     

Temporal and spatial structure of the X-ray emission in alow-energy vacuum spark

Two distinct phases of X-ray emission in a small vacuum spark with a plasma trigger have been identified. The first phase of emission is associated with the trigger plasma and originates from beam-target X-rays issued from the pointed anode. The source of electrons at this period is from the trigger plasma. The second phase of emission is associated with the breakdown of the main gap. The source of X-rays is a combination of beam-target and beam-plasma X-rays. It is observed that the angular distribution is constant. The X-ray energies vary regularly with the applied voltage, and the triggered vacuum spark as a high brightness     

X‐ray microscopy at the advanced photon source

In modern third generation synchrotron sources, undulators have become the principal source of X-rays and today a brilliance close to 10²¹ photons/sec?mm²?mrad?0.1%BW is routinely attained for photon energies of 10 keV. However, generating brilliant beams of photons with energies of 50 keV and above leads to conflicting choices for the undulator parameters as the following analysis shows.