Compact Synchrotron Radiation Research Articles

Experimental Demonstration of Laser Guiding and Wakefield Acceleration in a Curved Plasma Channel.

Curved plasma channels have been proposed to guide intense lasers for various applications, such as x-ray laser emission, compact synchrotron radiation, and multistage laser wakefield acceleration [e.g. J. Luo etal., Phys. Rev. Lett. 120, 154801 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.154801]. Here, a carefully designed experiment shows evidences of intense laser guidance and wakefield acceleration in a centimeter-scale curved plasma channel. Both experiments and simulations indicate that when the channel curvature radius is gradually increased and the laser incidence offset is optimized, the transverse oscillation of the laser beam can be mitigated, and the stably guided laser pulse excites wakefields and accelerates electrons along the curved plasma channel to a maximum energy of 0.7GeV. Our results also show that such a channel exhibits good potential for seamless multistage laser wakefield acceleration.

Generation of straight and curved hollow plasma channels by laser-generated nonlinear wakefields and studies of ultra-intense laser pulse guiding

We report on a study of highly controllable, quasi-static hollow plasma channels generated by ion motion following a laser–plasma interaction via numerical simulations. These channels are generated by ion motion in a nonlinear wakefield, which has an asymmetry between focusing and defocusing periods. Such plasma channels, driven by a fs duration, 100 TW level laser pulse, have the capability to guide more powerful laser pulses. Moreover, we show that curved plasma channels can be generated in a transverse density gradient plasma and all-optical guiding of a second, significantly more powerful laser pulse in such a curved plasma channel. This mechanism may be useful for creating plasma optics for multi-stage TeV laser plasma accelerators and compact synchrotron radiation sources.

The versatile X-ray beamline of the Munich Compact Light Source: design, instrumentation and applications.

Inverse Compton scattering provides means to generate low-divergence partially coherent quasi-monochromatic, i.e. synchrotron-like, X-ray radiation on a laboratory scale. This enables the transfer of synchrotron techniques into university or industrial environments. Here, the Munich Compact Light Source is presented, which is such a compact synchrotron radiation facility based on an inverse Compton X-ray source (ICS). The recent improvements of the ICS are reported first and then the various experimental techniques which are most suited to the ICS installed at the Technical University of Munich are reviewed. For the latter, a multipurpose X-ray application beamline with two end-stations was designed. The beamline's design and geometry are presented in detail including the different set-ups as well as the available detector options. Application examples of the classes of experiments that can be performed are summarized afterwards. Among them are dynamic in vivo respiratory imaging, propagation-based phase-contrast imaging, grating-based phase-contrast imaging, X-ray microtomography, K-edge subtraction imaging and X-ray spectroscopy. Finally, plans to upgrade the beamline in order to enhance its capabilities are discussed.

Short-period high-strength helical undulator by laser-driven bifilar capacitor coil.

Laser wakefield accelerators have emerged as a promising candidate for compact synchrotron radiation and even x-ray free electron lasers. Today, to make the electrons emit electromagnetic radiation, the trajectories of laser wakefield accelerated electrons are deflected by transverse wakefield, counter-propagating laser field or external permanent magnet insertion device. Here, we propose a novel type of undulator that has a period of a few hundred microns and a magnetic field of tens of Tesla. The undulator consists of a bifilar capacitor-coil target that sustains a strong discharge current that generates a helical magnetic field around the coil axis when irradiated by a high-energy laser. Coupling this undulator with state-of-the-art laser wakefield accelerators can, simultaneously, produce ultra-bright quasi-monochromatic x-rays with tunable energy ranging 5-250 keV and optimize the free electron laser parameter and gain length compared with a permanent magnet-based undulator. This concept may pave a path toward ultra-compact synchrotron radiation and even x-ray free electron lasers.

(Invited) Characterization of Semiconductor Materials Using Syncrotron Radiation, XAFS and X-Ray CTR Scattering

Synchrotron radiation (SR) is a very powerful tool for the material science. However some of the characterization techniques using the SR are not so popular for the researchers studying on the semiconductors. At the PRiME 2016 meeting, I would like to provide three topics relating to the SR. Two of them are topics on the measurement techniques, which must be interesting for the researchers of semiconductors. The third one is to introduce a compact SR facility recently built in Japan, which is successfully operating for the academic and industrial researchers. X-ray absorption fine structure (XAFS) measurement might be one of the minor techniques for the researchers studying on semiconductors, although it is a very powerful technique to investigate atomic scale structure. For example, by the XAFS measurement, a local structure around a target element in a semiconductor crystal can be revealed. In other words, if impurity atoms in a crystal locate at interstitial site or are substituting matrix can be discussed and the distortion of the lattice around the impurity atoms can also be estimated. Further, if the impurity atoms are ionized or not, is able to be determined by the XAFS measurement. Because the XAFS measurement is a kind of absorption measurement in the energy range of X-ray, the SR is essentially important to scan the energy of the incident X-ray and it is very difficult to conduct the measurement at laboratory using ordinal X-ray sources like X-ray tubes. That might be one of the reasons why the XAFS measurement is not so popular. At the PRiME 2016 meeting, I would like to introduce what the XAFS measurement is, why we can obtain such atomic scale information from the spectra, and for what kind of studies the measurement is useful. X-ray CTR scattering measurement is an important technique to study on layer structures like semiconductor films so precisely in an atomic scale and it is another measurement which essentially needs the SR. In order to measure the so week CTR scattering signal, the intensity of the SR is very important. When the measurement is conducted properly and obtained spectra are analyzed carefully, the results show us the interface structures of semiconductor hetero layers in an atomic scale. I would like to show some of the examples at the meeting. Finally, I am going to introduce a recently built compact SR facility in Aichi, Japan. The facility is named Aichi SR, of which acceleration energy and current are 1.2 GeV and 300mA. By using super conducting bending magnets of 5 T as light source, the facility can provide X-rays in the energy range of hard X-ray, more than 5 keV and up to 20 keV or higher as easy as those in the range of soft X-ray. The specs of the light source are not on cutting edge, however, the general design is so useful and stable for the users who would like to use the SR as a daily tool to characterize their samples. Such a facility must be very important to bottom up the level of the researches.

Comparison ofin vitrobreast cancer visibility in analyser-based computed tomography with histopathology, mammography, computed tomography and magnetic resonance imaging

High-resolution analyser-based X-ray imaging computed tomography (HR ABI-CT) findings on in vitro human breast cancer are compared with histopathology, mammography, computed tomography (CT) and magnetic resonance imaging. The HR ABI-CT images provided significantly better low-contrast visibility compared with the standard radiological images. Fine cancer structures indistinguishable and superimposed in mammograms were seen, and could be matched with the histopathological results. The mean glandular dose was less than 1 mGy in mammography and 12-13 mGy in CT and ABI-CT. The excellent visibility of in vitro breast cancer suggests that HR ABI-CT may have a valuable role in the future as an adjunct or even alternative to current breast diagnostics, when radiation dose is further decreased, and compact synchrotron radiation sources become available.

Low-dose x-ray phase-contrast and absorption CT using equally sloped tomography

Tomographic reconstruction from undersampled and noisy projections is often desirable in transmission CT modalities for purposes of low-dose tomography and fast acquisition imaging. However under such conditions, due to the violation of the Nyquist sampling criteria and the presence of noise, reconstructions with acceptable accuracy may not be possible. Recent experiments in transmission electron tomography and coherent diffraction microscopy have shown that the technique of equally sloped tomography (EST), an exact tomographic method utilizing an oversampling iterative Fourier-based reconstruction, provides more accurate image reconstructions when the number of projections is significantly undersampled relative to filtered back projection and algebraic iterative methods. Here we extend this technique by developing new reconstruction algorithms which allow for the incorporation of advanced mathematical regularization constraints, such as the nonlocal means total variational model, in a manner that is consistent with experimental projections. We then evaluate the resulting image quality of the developed algorithm through simulations and experiments at the European Synchrotron Radiation Facility on image quality phantoms using the x-ray absorption and phase contrast CT modalities. Both our simulation and experimental results have indicated that the method can reduce the number of projections by 60–75% in parallel beam modalities, while achieving comparable or better image quality than the conventional reconstructions. As large-scale and compact synchrotron radiation facilities are currently under rapid development worldwide, the implementation of low-dose x-ray absorption and phase-contrast CT can find broad applications in biology and medicine using these advanced x-ray sources.

PRESENT STATUS AND FUTURE PLAN OF COMPACT SR RING HiSOR

Hiroshima Synchrotron Radiation Center (HSRC) is a common facility for research and education in the field of synchrotron radiation science in Japan. The major role of the facility is to promote nationwide SR research activities in materials science, especially in solid state physics, and education in the related fields simultaneously. HiSOR is a compact synchrotron radiation source of HSRC constructed in 1996 as a typical VUV — soft X-ray source (0.87 keV critical photon energy) similar to Helios in Singapore. Because of a compact racetrack-type ring, its natural emittance 400π nm · rad is not so small as the other standard-sized rings. There are two undulators, one linear for 26–300 eV range and the other helical/linear for 4–40 eV. The most outstanding feature of the facility lies in the good combination with beamlines to attain high-resolution (below 1 meV) for photoemission spectroscopy. It is routinely operated from 09:00 to 20:00 on weekdays at the stored current starting from 350 mA with 8 h lifetime at 300 mA. HiSOR has been running over 10 years, thus, it is time to think about the future improvements of the facility. The motivation is to pursue the leading position in the field of materials science (solid state physics) using SR for high-resolution photoemission spectroscopy. Some candidates for the upgraded HiSOR are presented.

Compact hard X-ray synchrotron radiation source based on superconducting bending magnets

The unique properties of synchrotron radiation (SR) account for its wide usage into fundamental, applied and technological investigations. Large growth of the number of SR applications in technological processes and medical diagnostics has been observed recently, which makes the problem of developing compact and relatively cheap SR sources very actual. A good progress of Budker Institute of Nuclear Physics (BINP) in the field of fabrication of different superconductive devices for SR generation may give rise to a new tendency in the design of compact SR sources. Indeed, the 9 T superconducting bending magnet fabricated at BINP for the BESSY-2 storage ring is a good candidate for the main element of the magnetic structure of a compact SR machine. The development of compact hard X-ray SR source started at BINP. This work involves analysis of possible implementation of compact SR sources in industry, medicine and education. Main SR parameters meet the requirements of most popular research application methods. These parameters became a basis for determination of main parameters of storage ring and allowed us to propose a possible scheme of storage ring.

Application of a compact synchrotron radiation facility to studies on the structure of solvated chloride and iodide ions in various solvents

Abstract A beamline equipped on the compact superconductive synchrotron radiation (SR) facility at Ritsumeikan University was designed for performing extended X-ray absorption fine structure (EXAFS) analyses of solutions and solids. The introduction of three different crystals, Si(220), Ge(220), and InSb(111), as the monochromator of the EXAFS spectrometer covers the K-edge absorption energy range of elements with low atomic numbers from silicon (atomic number 14) through zinc (30). The LIII-edge of the iodide ion could be measured by Si(220) and Ge(220). It is, however, not possible to measure the absorption of the bromide ion with this equipment. Using this spectrometer, the solvation structure of Cl- and I- ions was investigated in water, methanol, and ethanol under atmospheric pressure.

X-ray absorption fine structure spectrometer using a compact superconducting synchrotron radiation source

We have constructed an x-ray absorption fine structure (XAFS) spectrometer at BL-4 using the compact superconducting synchrotron radiation (SR) source at Ritsumeikan University. BL-4 is simply designed and consists of a slit, a double-crystal monochromator, and two detectors. The mechanical movement of the monochromator is in the range from 15° to 75°. By using Si(220), Ge(220), and InSb(111) crystals, the XAFS spectrometer covers the K-edge absorption energies of elements from silicon to zinc under atmospheric pressure. The incident x-ray intensity is measured by an ionization chamber with a path length of 4.5 cm. The transmitted x-ray intensity after passing through a sample is monitored by either an ionization chamber with a path length of 31 cm or a scintillation counter. The steep decrease of x-ray intensities above 5 keV is characteristic of the spectrum of photons emitted from the compact SR source and the photon flux at 10 keV is two to three orders of magnitude smaller than that at 5 keV. Hence, the contamination of higher-order harmonics is negligible above 5 keV. The double-crystal monochromator should be detuned only in measuring K-edge XAFS spectra of K, Ca, and Sc by using Si(220) or Ge(220). Suitable gases for two ionization chambers are easily selected only based on the detection efficiency of He(100%), N2(100%), N2(85%)+Ar(15%), N2(50%)+Ar(50%), and Ar(100%) gases. The photon flux passing through a 2 mm×9 mm aperture is estimated from the ion current of the ionization chamber. Though the values normalized to 1 mm2 are a few orders of magnitude smaller than those of BL7C at the Photon Factory, it turned out that measurements of XAFS spectra of good quality are very easy to obtain from 1.7 to 10.5 keV by using the spectrometer at BL-4.

LIGA process – micromachining technique using synchrotron radiation lithography – and some industrial applications

We developed the LIGA (Lithographie or lithography/Galvanoformung or electroforming/Abformung or molding) process using a compact synchrotron radiation (SR) source. To make a compact SR source applicable for the LIGA process, we developed a highly sensitive resist and highly transparent mask for deep SR lithography. We commercialized two devices, a piezoelectric composite and a microprobe for IC testing. A microconnector and optical switch were also developed.

Compact synchrotron radiation lithography system for 70 nm device manufacturing

We report on the performance and reliability of our synchrotron radiation (SR) based x-ray lithography (XRL) system installed in Tanashi Works of Sumitomo Heavy Industries, Ltd. Our XRL facilities include a compact racetrack-type SR light source “AURORA-2S” (A2S), the injector microtron, a 3-m-long beamline, and the second version x-ray aligner. In 2000, A2S proved the beam lifetime of 16 h in regular operation at the designed beam current 500 mA. The XRL beamline offers a high-dose exposure rate of over 43 mW/cm2 on a wafer at beam current 500 mA. The x-ray aligner achieved an overlay accuracy better than 16 nm (3σ) using a video-based scattered-light alignment (SLA) system. In the SLA, edge scattering on matrix array patterns provides multispot video images for mask to wafer alignment. A 70 nm line and space (L/S) pattern was replicated with a gap of 15 μm. In resolution enhancement exposure, we replicated a 100 nm L/S and 1 100 nm hole pattern using a 200 nm L/S and a 200 nm hole pattern of x-ray mask, respectively.

Li K-edge spectra of lithium halides

We measured the Li K-edge spectra of lithium halides by means of total electron yield method (TEY), using the soft x-ray Beam Line 2 (BL2) of the compact synchrotron radiation facility at Ritsmeikan University in Japan. In lithium halides, the spectra have a sharp peak at about 60eV and a broad peak at the higher energy side. Various peak structures that appear in the absorption spectra are assigned to the corresponding Li-1s to valence band free orbitals transitions, which have been calculated by the Discrete Variational (DV)-Xalpha molecular orbital calculation method.

Light Source for X-ray Lithography.

Synchrotron-based proximity x-ray lithography (PXL) has been developed for more than 20 years. The lightsource for high-throughput PXL manufacturing is a synchrotron radiation (SR) ring with multiple x-ray steppers. From the late 1980 's to early 1990 's, many compact SR rings for PXL adopted superconducting magnetsfor achieving their compactness were built in the USA and Japan. The Association of Super-Advanced Electronics Technologies (ASET) was established in Japan in 1996 and ASET had several programs to promote PXL in NTT at Atsugi-shi. An e-beam X-ray mask writer “EB-X3” was developed by NTT and ASET fabricated PXL masks for 4Gbit DRAMs by the writer with 100nm design rules. Sumitomo Heavy Industries (SHI) has developed a new normal-conducting compact SR ring “AURORA-2S” with a beam current 500mA usinga novel idea to increase the field strength of normal-conducting magnets to 2.7 Tesla. In this paper, SR rings for PXL are introduced.

Fabrication of sub-micron structures for MEMS using deep X-ray lithography

Fabrication techniques of microstructures with high resolution and high aspect ratio are necessary for practical microelectromechanical systems (MEMS) that have high performance and integration. In order to fabricate microstructures with sub-micron resolution and high aspect ratio, deep X-ray lithography has been investigated using the compact synchrotron radiation (SR) light source called “AURORA”. An X-ray mask for sub-micron deep X-ray lithography, which is composed of 1 μm thick Au as absorbers, 2 μm thick SiC as a membrane and 625 μm thick Si as a frame, was designed. In preliminary experiments, the following results were achieved: EB resist microstructures with an aspect ratio of 22 corresponding with 0.07 μm width and 1.3 μm height were formed; a 10 μm thick PMMA resist containing no warp was formed by direct polymerization, enabling more precise gap control.

A superconducting magnet for a compact synchrotron radiation ring

A 180-degree superconducting bending magnet for a synchrotron radiation source has been designed and constructed based on three-dimensional electromagnetic analysis. The magnet is covered by an iron shield to prevent the leakage of magnetic fields. The liquid helium consumption of the equipment is very small in the persistent current mode. The results of the analysis are in good agreement with measured results. This magnet operates as a synchrotron radiation source at a beam energy of 600 MeV. The radiation source can be used for several applications, such as X-ray lithography, in the semiconductor industry. © 1998 Scripta Technica, Electr Eng Jpn, 126(1): 61–69, 1999

Study on fabrication of high aspect ratio MEMS microparts using a compact SR beamline

A compact beamline dedicated to hard x-ray deep lithography for fabrication of high aspect ratio MEMS microparts has been developed. The exposure stage was only 3 meters away from the synchrotron radiation (SR) source so that a relatively high photon flux could be achieved with a compact super-conducting SR source. The deep lithography using PMMA resist could be as deep as 1000 μm and the maximum aspect ratio achieved was about 50. The throughout for the 200 μm-deep lithography was found to be on the order of 5 cm2/h using the membrane-free mask under the routine SR conditions. Templates with the high aspect ratio microstructures have been made of the PMMA resist based on conducting substrates and applied further to electroforming to create metallic microstructures. In order to fabricate microparts for the MEMS applications, we have concentrated on development of masks for the hard x-ray deep lithography. The masks now can be made to have the 8 μm-thick gold absorber on the 2 μm-thick SiC membrane.

A Superconducting Magnet for Compact Synchrotron Radiation Ring

A 180 degree superconducting bending magnet for a synchrotron radiation source has been designed and constructed based on 3-dimensional electromagnetic analysis. The magnet is covered by iron shield to prevent the leakage of magnetic fields. The liquid helium consumption of the equipment is very small in the persistent current mode. The measurement results are in good agreement with the analysed ones. This magnet is under operation as a synchrotron radiation source at a beam energy of 600MeV. The radiation can be used for several applications, such as, X-ray lithography in semiconductor industries.

Solid phase epitaxy with x-ray irradiation using a compact synchrotron radiation source AURORA

Solid phase epitaxy from the 0.2-μm-thick amorphous Si films, which were made by As ion implantation, was achieved by exposure to synchrotron radiation at a distance of 0.75 m from a compact synchrotron radiation source AURORA. The substrate temperature during this process was below 430 °C, not enough for thermal crystallization. We found the photon flux threshold for this x-ray assisted crystallization to be 5×1015 photons/s mm2. The threshold may be due to the transition from the diffusion-limited rate to the reaction-limited rate for the annihilation of the vacancies to form the crystal. The L-shell excitation may play a more important role than the K-shell excitation in this case.