Methods Phys Research Articles

Theoretical and experimental investigations of electron emission inHe2++H2Ocollisions

Very recently, Ohsawa et al. have presented a new experimental apparatus for measuring doubly differential cross sections of electron emission from water vapor with fast heavy-ion impact (6-25 MeV). Successful measured energy and angular distributions of secondary electrons were produced for a collision of 6.0 MeV/u He{sup 2+} ions with vapor water [Nucl. Instrum. Methods Phys. Res. B 227, 431 (2005)] and for 10.0 MeV/u He{sup 2+} ions [Phys. Rev. A 72, 062710 (2005)]. The present theoretical work aims to reproduce these very recent measurements as well as more former existing data dedicated to low-energy alpha particles. Doubly, singly differential, and total ionization cross sections have then been studied.

Nano-fabrication utilizing point defects induced by ion-implantation

Nano-structure fabrication is performed using focused ion beam (FIB) based on the nano-fabrication technique [N. Nitta and Taniwaki, Nucl. Instrum. Methods Phys. Res., B Beam Interact. Mater. Atoms 206 (2003) 482] previously proposed by the authors and its validity is examined. An initial pattern consisting of the matrices of the irradiated dots at constant intervals is prepared by raster scanning mode and it is developed by irradiation using the imaging mode in FIB at room temperature. An ordered cellular structure develops when the cell interval is 100 nm or more, which demonstrates that the proposed technique is promising for future nano-device processing.

The Crystal and Solution Structures of Glyceraldehyde-3-phosphate Dehydrogenase Reveal Different Quaternary Structures

The presence of an isoform of glyceraldehyde-3-phosphate dehydrogenase (kmGAPDH1p) associated with the cell wall of a flocculent strain of Kluyveromyces marxianus was the first report of a non-cytosolic localization of a glycolytic enzyme, but the mechanism by which the protein is transported to the cell surface is not known. To identify structural features that could account for the multiple localizations of the protein, the three-dimensional structure of kmGAPDH1p was determined by x-ray crystallography and small angle x-ray scattering. The x-ray crystallographic structure of kmGAPDH1p revealed a dimer, although all GAPDH homologs studied thus far have a tetrameric structure with 222 symmetry. Interestingly, the structure of kmGAPDH1p in solution revealed a tetramer with a 70 degrees tilt angle between the dimers. Moreover, the separation between the centers of the dimers composing the kmGAPDH1p tetramer diminished from 34 to 30 A upon NAD(+) binding, this latter value being similar to the observed in the crystallographic models of GAPDH homologs. The less compact structure of apo-kmGAPDH1p could already be the first image of the transition intermediate between the tetramer observed in solution and the dimeric form found in the crystal structure, which we postulate to exist in vivo because of the protein's multiple subcellular localizations in this yeast species.

Design and characterization of a movable emittance meter for low-energy electron beams

In order to characterize and optimize the beam emittance compensation scheme [L. Serafini and J. B. Rosenzweig, Phys. Rev. E 55, 7565 (1997)] of the Sorgente Pulsata Autoamplificata di Radiazione Coerente project [D. Alesini et al., Nucl. Instrum. Methods Phys. Res. A 507, 345 (2003)] high brightness preinjector a system to accurately measure the beam rms emittance evolution downstream of the rf gun has been developed. Since in a space charge dominated beam the quadrupole-scan method is not applicable, a movable emittance measurement device has been built based on the pepper-pot technique. The device consists of a double system of horizontal and vertical slit arrays and a downstream screen, all installed on a longitudinally movable support equipped with bellows and spanning the ≈1.2m long drift space between gun and first accelerating section. The system allows the measuring of the beam rms emittance all along the spanned region so as to accurately reconstruct its evolution along the beam trajectory. More than a simple improvement over more conventional beam emittance measurement tools this device defines a new strategy for characterizing high performance photoinjectors as it allows a detailed analysis of the beam behavior over a section of the accelerator where crucial beam shaping takes place. Numerical simulations of the measurement, mainly based on PARMELA [J. Billen, PARMELA Report No. LA-UR 96-1835, 1996 (unpublished)], have been used to estimate the achievable accuracy and to optimize the experimental setup. Wake field effects induced by the beam propagation through the bellows have also been investigated with HOMDYN [M. Ferrario et al., LCLS Report No. SLAC-PUB 84000, 1999 (unpublished)]. A series of laboratory tests to evaluate its performance has been carried out at LNF in Frascati. The system was then moved to DESY Zeuthen and installed on the Photo Injector Test Facility PITZ, for further testing with beam. Design criteria and tests carried out to evaluate the device performance are discussed.

How the asymmetry of internal potential influences the shape of I-V characteristic of nanochannels

Ion transport in biological and synthetic nanochannels is characterized by such phenomena as ion current fluctuations, rectification, and pumping. Recently, it has been shown that the nanofabricated synthetic pores could be considered as analogous to biological channels with respect to their transport characteristics [P. Yu. Apel et al., Nucl. Instrum. Methods Phys. Res. B 184, 337 (2001); Z. Siwy et al., Europhys. Lett. 60, 349 (2002)]. The ion current rectification is analyzed. Ion transport through cylindrical nanopores is described by the Smoluchowski equation. The model is considering the symmetric nanopore with asymmetric charge distribution. In this model, the current rectification in asymmetrically charged nanochannels shows a diodelike shape of I-V characteristic. It is shown that this feature may be induced by the coupling between the degree of asymmetry and the depth of internal electric potential well. The role of concentration gradient is discussed.

Ion-beam induced transformations in nanoscale multilayers: Evolution of clusters with preferred length scales

Ion-irradiation-induced modifications of a periodic Pt∕C multilayer system containing a small amount of Fe have been analyzed by transmission electron microscopy and grazing incidence x-ray diffraction (GIXRD) studies. The multilayer stack with 16 Pt∕C layer pairs (period of 4.23nm) was fabricated on a glass substrate. A 2MeV Au2+ ion beam was rastered on the sample to obtain uniformly irradiated strips with fluences from 1×1014to1×1015ions∕cm2. Ion irradiation has been found to cause preferential migration of Fe towards Pt layers [Bera et al., Nucl. Instrum. Methods Phys. Res. B 212, 530 (2003)]. Cross-sectional transmission electron microscopy (XTEM) shows considerable atomic redistribution for irradiation at the highest ion fluence (1×1015ions∕cm2). This structure is composed of small clusters. Phase separation and cluster formation processes are discussed. Periodic multilayers have periodicity only in the direction normal to the multilayer surface. However, Fourier transform (FT) of the XTEM images of the sample irradiated at the highest fluence shows extra off-normal Fourier components of superlattice periodicities arising due to ion irradiation. These extra spots in the FT are due to preferential length scales in intercluster separation in three dimensions. With a proper understanding of this phenomenon it may be possible to fabricate useful three-dimensional self-assembled structures of nanoclusters. Our high resolution transmission electron microscopy and GIXRD results reveal the formation of an FePt alloy. As FePt is a magnetic alloy, our observation raises the possibility of fabrication of ion-beam induced magnetic nanocluster lattices.

Production of charged (singly and multiply) phosphorous beams with electron cyclotron resonance ion source

Within the framework of biological application linked to ion irradiation, the fabrication of radioactive stents by ion implantation provides a significant improvement of the recovery of arteries after a treatment of stenosed coronary arteries [P. Fehsenfeld et al., Semin Interv Cardiol. 3, 157 (1998); E. Huttel et al., Rev. Sci. Instrum. 73, 825 (2002); M.-A. Golombeck et al., Nucl. Instrum. Methods Phys. Res. B 206, 495 (2003)]. For this appliance, the suitable radioactive ion is P32. Obviously, in order to have a minimum loss of these radioactive ions through the ionization process, it is imperative to have high ionization efficiency. In this article, the production of such singly and multiply charged phosphorous beams is investigated using two different electron cyclotron resonance ion sources: MONO1000∕1001 [P. Jardin et al., Rev. Sci. Instrum. 73, 789 (2002)] and SUPERSHyPIE [J. Y. Pacquet et al., EP Patent No. 97 401294 (pending); R. Leroy et al., 14th International Workshop on ECR Ion Sources, May 1999 (unpublished)]. Spectra and above all efficiencies [J. Y. Pacquet et al., GANIL R 02 07; GANIL R 03 08] (31% of ionization efficiency for phosphorous atoms and compound with MONO1000∕1001 and 43% of ionization efficiency for phosphorous atoms with SUPERSHyPIE) of these beams will be presented as well as the intensities (227eμA for P+ with MONO1000∕1001 and 145eμA for P7+ with SUPERSHyPIE) of such beams.

Decaborane beam from ITEP Bernas ion source

A joint research and development program is under way to develop steady-state intense ion sources for the two energy extremes of MeV and hundreds of eV. The difficulties of extraction and transportation of low-energy boron beams are investigated using a decaborane compound [I. Yamada, W. L. Brown, J. A. Northby, and M. Sosnowski, Nucl. Instrum. Methods Phys. Res. B 79, 223 (1993)]. Presented here are the results from ITEP experiments using the Bernas ion source with an indirectly heated LaB6 cathode.

6.0–10.0−MeV∕uHe2+-ion-induced electron emission from water vapor

We discuss absolute doubly differential cross sections (DDCS's) for the energy and angular distributions (20\ifmmode^\circ\else\textdegree\fi{}--160\ifmmode^\circ\else\textdegree\fi{}) of secondary electrons produced in the collisions of 6.0- and $10.0\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{He}}^{2+}$ ions with water vapor. Details of our experiments were reported in our previous paper [D. Ohsawa et al., Nucl. Instrum. Methods Phys. Res. B 227, 431 (2005)], which mainly considered the total uncertainty $(\ifmmode\pm\else\textpm\fi{}13%)$, as well as absolute DDCS data $(7--10\phantom{\rule{0.2em}{0ex}}000\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ by $6.0\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{He}}^{2+}$ ions. All DDCS data, including the newly obtained data $(20--12\phantom{\rule{0.2em}{0ex}}000\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ by $10.0\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{He}}^{2+}$ ions, are compared with classical theories after being corrected for relativistic effects. Based on the Rudd model and the Rutherford cross section, the experimental results are discussed by taking account of the momentum spread of the bound electrons. This paper mainly describes the analysis of low-energy electrons and binary encounter peaks at high energies, as well as details of relativistic corrections.

Scaling and extended scaling in sediment registers of a paleolake perturbed by volcanic activity

We analyze a sequence of density variations of sedimentary material from an extinct paleolake of the state of Tlaxcala, Mexico, which we previously obtained by means of computer-aided tomography [J. Miranda, A. Oliver, G. Vilaclara, R. Rico-Montiel, V.M. Macias, J.L. Ruvalcava, M.A. Zenteno, Nucl. Instrum. Methods Phys. Res. B 85 (1994) 886]. In the stratified blocks chiselled out of mines at the lake bed, low-density sediments have a high concentration of diatomite, while high-density strata show a considerable amount of material external to the lake, mostly of volcanic origin. Two regions can be distinguished by visual inspection: a darker and older one which we attribute to a strongly externally perturbed regime, and a whiter more recent one which appears to have been subjected to less frequent volcanic perturbations. By means of a scaling analysis of the distribution function of density fluctuations, we show that for the most recent region there is a range of scales where these fluctuations present a self-similar behavior. We attribute this observation to a rare event response, namely, the onset of correlations in the lake relaxation processes to steady-state conditions following intense volcanic disturbances. Based on scaling properties of the structure function, we also show that the complete data series presents extended self-similarity as encountered in turbulence studies [R. Benzi, S. Ciliberto, R. Tripiccione, C. Baudet, F. Massoli, S. Succi, Phys. Rev. E 48 (1993) R29]. Our characterization of the statistical behavior of the density fluctuations contributes to our knowledge of the volcanic activity over a period of thousands of years, as well as aspects of ecological interest of the lake's response to these disturbances [G. Vilaclara, E. Ugalde, E. Cuna, G. Martinez-Mekler, Complex dynamics of the evolution of a Paleolake subjected to volcanic activity: geology meets ecology, submitted for publication]. Our approach can be implemented in general to other situations where a scaling characterization may be of interest.

Theoretical study of helium insertion and diffusion in 3C-SiC

Insertion and diffusion of helium in cubic silicon carbide have been investigated by means of density functional theory. The method was assessed by calculating relevant properties for the perfect crystal along with point defect formation energies. Results are consistent with available theoretical and experimental data. Helium insertion energies were calculated to be lower for divacancy and silicon vacancy defects compared to the other mono-vacancies and interstitial sites considered. Migration barriers for helium were determined by using the nudged elastic band method. Calculated activation energies for migration in and around vacancies (silicon vacancy, carbon vacancy or divacancy) range from 0.6 to 1.0 eV. Activation energy for interstitial migration is calculated to be 2.5 eV. Those values are discussed and related to recent experimental activation energies for migration that range from 1.1 [P. Jung, J. Nucl. Mater. 191–194 (1992) 377] to 3.2 eV [E. Oliviero, A. van Veen, A.V. Fedorov, M.F. Beaufort, J.F. Bardot, Nucl. Instrum. Methods Phys. Res. B 186 (2002) 223; E. Oliviero, M.F. Beaufort, J.F. Bardot, A. van Veen, A.V. Fedorov, J. Appl. Phys. 93 (2003) 231], depending on the SiC samples used and on helium implantation conditions.

Laser ion source for ITEP–TWAC project

Laser ion source (LIS) is the only type of source capable of generating 10–30 mA beams of highly charged ions for the ITEP–TeraWatt (TWAC) accelerator/accumulator facility [B.Yu. Sharkov et al., Nucl. Instrum. Methods Phys. Res. A 415 20 (1998).]. The assembling stage of the new LIS based on 100 J/1 Hz master oscillator–power amplifier CO2-laser system [Yu. Satov, et al., J. Russ. Laser Res. 25(3) 205 (2004).] is in progress at ITEP now. In the first phase, the ion beam parameters (charge state distribution, current, pulse length and emittance) will be specified for different elements and target irradiation conditions. According to the planning, the new LIS and the new high-current injector [D. Kashinsky, et al., Proceedings of the Heavy Ion Fusion Conference, Moskow (2002).] will be used to deliver the beams of highly charged ions for the ITEP–TWAC accelerator/accumulator facility.

Simulation and analysis of using deflecting cavities to produce short x-ray pulses with the Advanced Photon Source

We present detailed simulations and analysis of Zholents’s [A. Zholents, P. Heimann, M. Zolotorev, and J. Byrd, Nucl. Instrum. Methods Phys. Res., Sect. A 425, 385 (1999).] concept for using deflecting cavities in a synchrotron light source storage ring for the purpose of producing short x-ray pulses. In particular, we look at the optimization and performance of such a system for the Advanced Photon Source. We find the concept is practical and that x-ray pulse durations of about 1.5 ps FWHM should be achievable with more than 15% of the original intensity retained. Issues covered include lattice design, emittance degradation, lifetime, photon beam modeling, errors, and optimum choice of rf parameters.

Lipid imaging by gold cluster time-of-flight secondary ion mass spectrometry: application to Duchenne muscular dystrophy

Imaging with time-of-flight secondary ion mass spectrometry (TOF-SIMS) has expanded very rapidly with the development of gold cluster ion sources (Au(3+)). It is now possible to acquire ion density maps (ion images) on a tissue section without any treatment and with a lateral resolution of few micrometers. In this article, we have taken advantage of this technique to study the degeneration/regeneration process in muscles of a Duchenne muscular dystrophy model mouse. Specific distribution of different lipid classes (fatty acids, triglycerides, phospholipids, tocopherol, coenzyme Q9, and cholesterol) allows us to distinguish three different regions on a mouse leg section: one is destroyed, another is degenerating (oxidative stress and deregulation of the phosphoinositol cycle), and the last one is stable. TOF-SIMS imaging shows the ability to localize directly on a tissue section a great number of lipid compounds that reflect the state of the cellular metabolism.

Time dependent models of field-assisted photoemission

A time-dependent model of photoemission, developed to analyze current from and laser heating of metals and dispenser photocathodes, is here applied to examine the impact of geometrical field enhancement and the contribution of tunneling to the photocurrent from a tungsten needle in terms of temporal response, quantum efficiency, and cathode performance. First, a review is given of an updated Fowler–Dubridge model of quantum efficiency including quantum mechanical effects. Second, a prolate spheroidal model of a tungsten needle is given to determine applied fields and incident angles necessary to evaluate emitted current and laser heating effects. Third, a time-dependent model of laser heating of an electron distribution is given which affects the photoemitted current and (if conditions are right) gives field and thermal components as well. Finally, the methodology is related to the experimental findings of Garcia and Brau [Nucl. Instrum. Methods Phys. Res. A 483, 273 (2002)], in which an intense laser illuminates a tungsten needle under sufficiently high fields that the photoemitted current contains field and thermal emission components and effects.

Secondary threshold laws for multiple ionization of atoms

We propose a physical mechanism that leads to the emergence of secondary threshold laws in processes of multiple ionization of atoms. We argue that the removal of $n$ electrons $(n>2)$ from a many-electron atom may proceed via intermediate resonant states of the corresponding doubly charged ion. For atoms such as rare gases, the density of such resonances in the vicinity of subsequent ionization thresholds is high. As a result, the appearance energies for multiply charged ions are close to these thresholds, while the effective power indices $\ensuremath{\mu}$ in the near-threshold energy dependence of the cross section, $\ensuremath{\sigma}\ensuremath{\propto}{E}^{\ensuremath{\mu}}$, are lower compared to those from the Wannier theory. This provides a possible explanation of the recent experimental results of B. Gstir et al. [Nucl. Instrum. Methods Phys. Res. B 205, 413 (2003)].

Photoinduced free radical polymerization using self-initiating monomers

Historically, a number of self photo-initiating carbon-carbon double bond (C C) containing monomers have examined during a fairly long period of time with respect to their relative efficiencies in initiating free radical polymerization and these findings are well documented in the literature [ S.E. Jönsson, P.E. Sundell, J. Hultgren, D. Sheng, C.E. Hoyle, Prog. Org. Coat. 27 (1996) 107–122; S.E. Jönsson, M. Shimose, S. Clark, C.E. Hoyle, Polymer Communications, 38 (22) (1997) 5695–5697; S. Katogi, C.W. Miller, S.E. Jönsson, C.E. Hoyle, Polymer 39 (13) (1997) 2709; C.E. Hoyle, S.E. Jönsson, P.E. Sundell, M. Shimose, S.C. Clark, C. Miller, J. Owens, F. Morel, C. Decker Nucl. Instrum. Methods Phys. Res., B2 (1997)]. Traditional monomer systems involve maleimides and α,β-substituted maleimides and maleates/fumarates mostly in vinyl ether combinations [F. Morel, C. Decker, S.E. Jönsson, S.C. Clark, C.E. Hoyle, Polymer 40 (1999) 2447; C.E. Hoyle, S.E. Jönsson, C. Miller, K. Viswanathan, F. Morel, C. Decker, S.C. Clark, Nucl. Instrum. Methods Phys. Res. B, 151 (1999) 268; S.E. Jönsson, K. Viswanathan, C.E. Hoyle, S.C. Clark, C. Miller, C. Nguyen, W. Shao, L. Shao, F. Morel, C. Decker, J. Photopolym. Sci. Technol. 13 (1) (2000) 125–143; C. Decker, C. Bianchi, F. Morel, S.E. Jönsson, C.E. Hoyle, Macromol. Chem. Phys. 201 (2000) 1493–1503]. In this paper, a comprehensive study has been undertaken in investigating the initiating efficiencies of α,β-substituted alkenyl acrylates (X 1 C C(Y 1)COO(X 2 C C Y 2)). In order to evaluate the photochemistry involved in the excitation process, focus has been emphasized on vinyl acrylate (VA) as a model compound. VA exhibits fast rates of polymerization and high degrees of conversion are obtained. Real Time Infra Red analysis (RTIR) was used throughout the investigation in recording the kinetics of the homo and co-polymerization of VA and in combinations with various co-monomers in the presence and absence of PhI. In the homopolymerization of VA, the acrylate C C was found to polymerize much faster than the vinyl ester C C. The enhanced reactivity of the acrylate C C in VA is mainly due to the very close proximity of the two C C bonds exhibiting large differences in electron densities over the two C C bonds within the same molecule. Modeling studies are compared to real time recorded kinetics, showing good correlation. Furthermore, a mechanistic investigation of the nature of the excited state conformation in VA also indicates fundamental differences in the “efficiencies of initiation”, which can be caused by a biradical versus a conventional “monoradical” pathway of initiation seen by the use of commercially available PHI's. Finally, useful future implications in the use of VA and derivatives thereof as initiating monomers in practical acrylate based formulations will be discussed in the paper.

Effect of beam premodulation on gain and efficiency in a free electron laser

Beam premodulation on free electron laser (FEL) offers considerable enhancement in gain and efficiency when the phase of the premodulated beam is −π/2 (i.e., when the premodulated beam is in the decelerating zone) and the beam is highly modulated implying the maximum beam oscillatory velocity due to wiggler. The growth rate of the FEL instability increases with the modulation index and reaches maximum when the modulation index Δ∼1.0, and when the frequency and wave number of the modulation are comparable to that of the radiation wave ω0∼ω1, k0∼k1, i.e., when the phase velocity of the radiation is comparable to the premodulated beam velocity. The trends of our gain versus frequency plot seem to be consistent with the experimental observations of Cohen et al. The growth rate of the FEL instability scales as one-third power of the beam density in Compton regime and one-fourth power in the Raman regime. The frequency of radiation increases with the beam energy. In the present calculation, beam energy fluctuation is negligible. Numerical calculations of the growth rate, efficiency, and gain have been carried out for the parameters of the experiment of Cohen et al. [Phys. Rev. Lett. 74, 3812 (1995); Nucl. Instrum. Methods Phys. Res. A 358, 82 (1995)].

Phase measurement of reflection of EUV multilayer mirror using EUV standing waves

Projection optics of an EUV lithography system consists of multilayer mirrors. Phase of the incident beam is shifted on reflection at the multilayer mirror [Y. Watanabe et al., Jpn. J. Appl. Phys. 30, 3053 (1991)]. If the phase shift at reflection of a multilayer is not well controlled, it becomes the cause of wavefront aberration. The phase shift depends on the incident angle and the wavelength of the beam. The phase shift is also dependent on the structure of the multilayer. Certain kinds of structural change cause non-negligible variation of the phase shift with very little change of wavelength dependency of reflectivity. Therefore, not only reflectivity measurement but also measurement of phase shift is essential to manufacture multilayer mirrors for projection optics. X-ray standing wave technique has been used to characterize multilayer structure [B. Lai et al., Nucl. Instrum. Methods Phys. Res. A 266, 684 (1988); T. Kawamura and H. Takenaka, J. Appl. Phys. 75, 3806 (1996)]. Intensity of electric field, which generates photoelectrons, near a multilayer surface depends not only on the intensity of incident beam but also on the phase shift and the reflectivity. EUV reflectivity and photo-yield of Mo∕Si multilayer samples were measured using a laser produced plasma source (LPP) based EUV reflectometer [A. Miyake, Proc. SPIE 5037, 647 (2003)]. Thickness ratio Γ is the ratio of the thickness of molybdenum layer to the multilayer period. Γ of each sample is changed by 2% step. According to a simulation, it corresponds to variation of phase shift by 0.02πstep, in other words, variation of wavefront by 10mλstep. Measured wavelength dependencies of photo-yield for each sample are clearly separated. From the results of this experiment, it is shown that phase shift on multilayer reflection can be detected at a resolution of 0.02πrad.

String formulation of space charge forces in a deflecting bunch

The force between two moving point charges, because of its inverse square law singularity, cannot be applied directly in the numerical simulation of bunch dynamics; radiative effects make this especially true for short bunches being deflected by magnets. This paper describes a formalism circumventing this restriction in which the basic ingredient is the total force on a point charge comoving with a longitudinally aligned, uniformly charged string. Bunch evolution can then be treated using direct particle-to-particle, intrabeam scattering, with no need for an intermediate, particle-in-cell, step. Electric and magnetic fields do not appear individually in the theory. Since the basic formulas are both exact (in paraxial approximation) and fully relativistic, they are applicable to beams of all particle types and all energies. But the theory is expected to be especially useful for calculating the emittance growth of the ultrashort electron bunches of current interest for energy recovery linacs and free-electron lasers. The theory subsumes coherent synchrotron radiation and centrifugal space charge force. Renormalized, on-axis, longitudinal field components are in excellent agreement with values from Saldin et al. [DESY Report No. DESY-TESLA-FEL-96-14, 1995; Nucl. Instrum. Methods Phys. Res., Sect. A 417, 158 (1998).]