bluuebunny/crossref_metadata_2025 huggingface dataset:
Easy method to characterize a piezoelectric ceramic tube as a displacer
Authors: Locatelli M. , Lamboley G. , Michenaud J. P. , Bayot V.
Published: July 2002

We describe a useful method using a commercial linear variable differential transformer as a detector to characterize a piezoelectric ceramic tube as a displacer. Results show some inhomogeneity in the reduction of the voltage-to-displacement conversion of commercial piezoelectric tubes as a function of temperature from room to liquid-helium temperature.
Scanning x-ray microscope with 75-nm resolution
Authors: Rarback H. , Shu D. , Feng S. C. , Ade H. , Kirz J. , McNulty I. , Kern D. P. , Chang T. H. P. , Vladimirsky Y. , Iskander N. , Attwood D. , McQuaid K. , Rothman S.
Published: July 2002

A scanning soft x-ray microscope has been built and operated at the National Synchrotron Light Source. It makes use of a mini-undulator as a bright source of 3.2-nm photons. An electron beam fabricated Fresnel zone plate focuses the beam onto the specimen, which is scanned under computer control. The scanning stage can be moved by both piezoelectric transducers and stepping motors, and the location is monitored by a high-speed laser interferometer. X rays transmitted through the specimen are detected using a flow proportional counter. Images of biological specimens and of artificial microstructures have been made with resolution in the 75–100-nm range. Acquisition time for 256×256-pixel images is about 5 min.
Applications of point projection spectroscopy (invited) (abstract)
Authors: Foster J. M.
Published: July 2002

X-ray point projection spectroscopy is a powerful experimental technique in the investigation of laser driven plasma physics experiments. Projection backlighting using a near point x-ray backlighting source together with a Bragg crystal provides simultaneously spectral, temporal, and two dimensions of spatial resolution. We discuss two applications of point projection spectroscopy. In the first, the opacity of a hot, dense (T=40 eV, ρ=0.01 g/cc) aluminum plasma heated by the thermal radiation from a gold laser target has been investigated. In the second application, point projection spectroscopy has been used as a diagnostic of hydrodynamic mixing between two dissimilar (but spectroscopically identifiable) materials undergoing ablatively driven acceleration. Experimental results from these experiments carried out at the AWE Helen and LLNL Nova lasers will be shown. This work was performed in collaboration with S. J. Davidson, P. Fieldhouse, T. J. Goldsack, J. C. V. Hansom, and C. C. Smith at AWE and J. D. Kilkenny and D. Bach at LLNL.
Calibration of the TFTR neutron activation system
Authors: Nieschmidt E. B. , Saito T. , Barnes C. W. , Bosch H.-S. , Murphy T. J.
Published: July 2002

Neutron generators, both D–D and D–T, have been used to calibrate the TFTR neutron activation (NA) system for point sources located within the tokamak. The foils used were In for D–D neutrons and Cu, Al, and 238U for D–T neutrons. Delayed neutrons following fission were counted when using 238U foils, 336-keV γ rays from 115In(n,n′)115m In reactions, annihilation radiation from 62Cu following the 63Cu(n,2n)62Cu reaction, and 1368- and 2754-keV γ rays from the 27Al(n,α)24Na reaction. Large effects caused by source anisotropy and local machine structure were observed. These effects and the attempts to accommodate them in the data analysis will be described.
X-mode scattering for the measurement of density fluctuations on TFTR (invited)
Authors: Bretz N. , Efthimion P. , Doane J. , Kritz A.
Published: July 2002

Most microwave scattering measurements in tokamaks are done with the polarization of the incident radiation approximately parallel to the toroidal field (ordinary mode) and at a frequency which is sufficiently above the plasma frequency ωpe that refraction effects are small. However, as confinement devices get hotter, drift wave turbulence is expected to occur at longer wavelengths. In order to observe density fluctuations associated with these phenomena with good spatial resolution, the ideal probe wavelength λi is near or beyond the ordinary cutoff at λi=2πc/ωpe. As a result, we have considered the propagation and scattering of the extraordinary (X) mode where the incident polarization is nearly perpendicular to the confining fields and where the cutoff density is significantly higher than in the ordinary mode. We have modeled the propagation of the X mode in a tokamak field geometry and shown that the polarization typically remains perpendicular to the local field along the ray path, simplifying the interpretation of the scattering results. We have calculated the single-particle cross section and give a formula for X-to-X-mode scattering. An apparatus for carrying out these measurements on TFTR at λi=0.5 cm will be described. For BT=5.0 T, the X-mode cutoff density in this case is 1.5×1014 cm−3, so that a major part of the operating density range can be studied by this technique.
Performance comparison of a single-photon avalanche diode with a microchannel-plate photomultiplier in time-correlated single-photon counting
Authors: Louis T. , Schatz G. H. , Klein-Bölting P. , Holzwarth A. R. , Ripamonti G. , Cova S.
Published: July 2002

A silicon single-photon avalanche diode (SPAD) detector and a proximity-focus-type microchannel-plate photomultiplier tube (MCP-PMT) are compared with respect to their performance in time-correlated single-photon counting (TCSPC) applications. A solution of pinacyanol (1,1′-diethyl–2,2′-carbocyanine) in ethanol, which is used as a test substance with short-lived fluorescence, is excited at 620 nm with a synchronously pumped, cavity-dumped rhodamine 6G dye laser. Deconvolution analysis of the fluorescence decay with a biexponential decay model gives excellent fits to the experimental data recorded with any one of the detectors. The fluorescence lifetimes for the dominating decay component are 13±2 and 11±2 ps as measured at 635 nm with the SPAD detector and the MCP-PMT, respectively. The excellent agreement of these values and the quality of the fits show that the SPAD detector as well as the MCP-PMT can resolve fluorescence decay time constants of the order of 10 ps. This is significantly better than what had been expected on the basis of the instrumental response widths of 70 ps (FWHM) with the SPAD detector and 50 ps (FWHM) with the MCP-PMT.
Control systems for scanning tunneling microscopes with tube scanners
Authors: DiLella D. P. , Wandass J. H. , Colton R. J. , Marrian C. R. K.
Published: July 2002

The design of the control system for a scanning tunneling microscope is described. The control system was optimized for a tube scanner instrument and for constant-current-mode operation. The optimization process included measurement of the transient and frequency responses of the instrument, design of the appropriate control electronics, and development of software consistent with the characteristics of the instrument and electronics. The limiting factor for tube scanner performance was found to be the transient settling time rather than the lowest mechanical resonant frequency of the tube. The settling time for the mechanical resonances of the tube scanner was reduced from 100 to 1 ms by potting the device with silicone rubber. After the potting procedure, the sensitivity of the tube scanner was essentially unchanged.
Structural parameter determination in fluorescence EXAFS of concentrated samples
Authors: Tan Zhengquan , Budnick Joseph I. , Heald Steve M.
Published: July 2002

Fluorescence detection is often used to obtain the extended x-ray absorption fine structure (EXAFS) of dilute samples and thin films. As the samples become concentrated and the films become thick, significant errors can be introduced in the EXAFS amplitudes. With detailed calculations we determine the reduction in the coordination numbers (N) and the deviation in the mean-squared relative displacements (σ2) as determined by fluorescence detection. Experimental results on Cu, Ni, Fe, and Nb samples support the predictions of the calculation. We suggest corrections to obtain the correct coordination numbers and σ2 values for studies of concentrated samples by fluorescence EXAFS detection when other methods are not feasible.
Calibration of a Mott detector using circularly polarized impact radiation from helium
Authors: Uhrig M. , Beck A. , Goeke J. , Eschen F. , Sohn M. , Hanne G. F. , Jost K. , Kessler J.
Published: July 2002

The conventional methods of determining the analyzing power of a Mott detector for electron-polarization measurement are not very accurate. That is why alternative methods have recently been discussed. The present paper shows how a Mott detector can be calibrated with an uncertainty of ±1% using the circular polarization of impact radiation from helium atoms that are excited by polarized electrons. The retarding-field-type Mott analyzer, its performance, and the calibration procedure are described in detail. Accurate data of the circular light polarization that may be used for absolute electron polarimetry are given at electron energies of 23.3 and 26 eV.
A simple technique for modulating the output of a cw e-beam evaporator
Authors: Bhatia M. S. , Joshi A. , Patel K. , Chatterjee U. K.
Published: July 2002

Modulation of evaporation rate is desirable as it significantly increases the signal detection capability by making it possible to use phase sensitive techniques. An easy method for achieving modulation of evaporation rate via control of focus coil current is described. This method avoids the expense as well as complexities involved in doing the same by switching the e-gun acceleration voltage (>10 kV) or switching the grid bias on the e-gun (>2 kV).
Development of x-ray imaging at the Daresbury SRS
Authors: Morrison G. R. , Bridgwater S. , Browne M. T. , Burge R. E. , Cave R. C. , Charalambous P. S. , Foster G. F. , Hare A. R. , Michette A. G. , Morris D. , Taguchi T. , Duke P. J.
Published: July 2002

A scanning transmission x-ray microscope has been used to form images with 380-eV x rays on the undulator beamline at the Daresbury synchrotron radiation source. A resolution of 80 nm has been achieved using Fresnel zone-plate focusing optics and images with reasonable signal-to-noise ratios can be acquired in less than 30 min.
Compact fluorescence x-ray detector for surface EXAFS and x-ray standing wave measurements
Authors: Funabashi M. , Ohta T. , Yokoyama T. , Kitajima Y. , Kuroda H.
Published: July 2002

The design and performance of a compact, ultrahigh vacuum (UHV) compatible x-ray detector is described which can be applied to measurements of surface EXAFS spectra and x-ray standing wave (SW) profiles. The detector is a type of gas flow proportional counter. Its compactness allows us to save space around the sample. A 25-μm-thick beryllium window separates UHV (<1×10−10 mbar) environment from atmospheric pressure and provides good efficiency to detect low energy x rays. Surface EXAFS spectra of less than 0.1 monolayer chlorine on a Ni substrate are successfully measured with high quality. Its high signal-to-background ratio allows us to measure SW profiles, which could hardly be obtained with any electron yield detection technique.
Variable focus crystal diffraction lens
Authors: Smither R. K.
Published: July 2002

A new method has been developed to control the shape of the surface of a diffracting crystal that will allow it to function as a variable focus crystal diffraction lens for focusing photon beams from a synchrotron source. The new method uses thermal gradients in the crystal to control the shape of the surface of the crystal in two dimensions and allows one to generate both spherical and ellipsoidal surface shapes. In this work the thermal gradient was generated by core drilling two sets of cooling channels in a silicon crystal so that cooling or heating fluids could be circulated through the crystal at two different levels. The first set of channels is close to the surface of the crystal where the photon beam strikes it. The second set of channels is equidistant from the back surface. If a concave surface is desired, the fluid in the channels just below the surface exposed to the beam is cooler than the fluid circulating through the channels near the back surface. If a convex surface is desired, then the cooling fluid in the upper channels near the surface exposed to the incident photon beam is warmer than the fluid in the lower channels. The focal length of the crystal lens is varied by varying the thermal gradient in the crystal. This approach can also be applied to the first crystal in a high power synchrotron beamline to eliminate the bowing and other thermal distortions of the crystal caused by the high heat load.
New multipole wiggler/undulator beamline (BL-16) at the Photon Factory
Authors: Matsushita T. , Maezawa H. , Ishikawa T. , Nomura M. , Nakagawa A. , Mikuni A. , Muramatsu Y. , Satow Y. , Kosuge T. , Sato S. , Koide T. , Kanaya N. , Asaoka S. , Nagakura I.
Published: July 2002

Design and experience of the initial operation of a new beamline (BL-16) for a 3.6-m-long, 53-pole wiggler/undulator constructed at the Photon Factory are described. The insertion device has hybrid permanent magnets with a period of 12 cm and a maximum magnetic field of 1.47 T. In the undulator mode, the energy of the fundamental peak can be varied from 40 to 400 eV. In the wiggler mode, an x-ray beam (critical energy of 6 keV) 50–100 times more intense than that from the bending magnets is obtained. The beamline consists of two time-shared branch lines: a side beamline for soft x-rays in the undulator operation, to which photon beams are deflected sideways by a cylindrical SiC mirror, and a straight line for hard x rays under the wiggler operation. On the hard x-ray line, a fixed-exit sagittal-focusing double-crystal monochromator has been installed and commissioned. Collimating and refocusing mirrors will be installed in 1989. On the undulator beamline, a soft x-ray monochromator utilizing sophisticatedly devised aberration correction optics is commissioned.
Status of insertion device and beamline design for ELETTRA
Authors: Rosei R. , Walker R. P.
Published: July 2002

ELETTRA is a new ultrahigh-brightness VUV/soft x-ray synchrotron radiation facility under construction by Sincrotrone Trieste in Italy. The main features of the project and its status are described. Details of the expected properties of the different types of radiation source are presented, and initial studies of insertion device and beamline components are summarized.
Bubbling characterization in gas-solid fluidized beds using optical fiber probes and transitional analysis
Authors: Cavalier H. , Thioye M. , Darrigo R.
Published: July 2002

In order to study the size and velocity of bubbles in a gas-solid fluidized bed, we have developed a device using an optical fiber probe, an optoelectronic converter, special acquisition and interface board and software, and a PC-compatible microcomputer. Transitional analysis has been our guideline in this realization. Experiment is described, and software-programmable duration filters are detailed, including timing diagrams. Important points of the software are given, which are parameter values input and interrupt subroutines organization.
On the design of a high-speed combined high-resolution powder diffractometer and small-angle scattering system with time-resolution capability based on the use of imaging plates and CCCC monochromators
Authors: Barnea Z. , Clapp R. , Creagh D. C. , Sabine T. M. , Stevenson A. W. , White J. W. , Wilkins S. W. , Harada J. , Hashizume H. , Kashihara Y. , Sakata M. , Ohsumi K. , Zemb T.
Published: July 2002

Design features of a proposed high-resolution, high-speed powder diffractometer for operation at a synchrotron source are described. A key feature of the design is the use of imaging plates to record an almost complete range of data including both the high-angle and the small-angle scattering regime. The x-ray optics involve the use of a condensing-collimating channel-cut monochromator (CCCC) to achieve narrow parallel beams with cross sections of the order of 50 μm in the plane of diffraction, so that geometrical aberrations are very low and the beam cross section is well matched to the spatial resolution of the imaging plate detector. Angular resolution in 2θ of the diffractometer is easily variable, and designed to range from 0.01° upwards. Optional translation of the detector perpendicular to the incident-beam direction makes it possible to obtain time-resolved data. Applications of the instrument include high-resolution powder data collection for Rietveld analysis, studies of dynamic phenomena such as chemical reactions and phase transformations, particle-size determination, texture analysis, residual-stress measurements, single-crystal studies of the truncation-rod effect and surface scattering, microdiffraction, combined high-angle and small-angle scattering measurements, and studies of multilayer structures. As an illustration of the sort of results attainable with the proposed system, we present an oscillation photograph of the crystal-truncation rod effect for a Si wafer which was recorded at a synchrotron source using an imaging plate as the detector.
Measurement of physical adsorption of gases at high pressure
Authors: Vidal D. , Malbrunot P. , Guengant L. , Vermesse J. , Bose T. K. , Chahine R.
Published: July 2002

A dielectric method is described for the measurement of physisorption of gases at pressures up to 200 MPa. The adsorption measurements of methane on activated carbon obtained at moderate pressures are in good agreement with precedent results but reveal unexpected negative values at higher pressures.
Two-wavelength infrared heterodyne transceiver with a continuous phase tracking system
Authors: Bartolini L. , Fornetti G. , Collibus M. Ferri De , Occhionero G. , Papetti F.
Published: July 2002

We describe the performance of an optical heterodyne sensor with a two-wavelength coherent infrared beam, which is used to detect the motion of remote targets in a real environment with an unambiguous sensing of the instantaneous direction along the line-of-sight propagation path. The initial phase condition of maximum sensitivity of the transceiver is stabilized and held by an active feedback system which drives the phase of the optical field of the local oscillator. The experimental results show that this feedback is particularly useful in reducing the noise generated by low-frequency environmental disturbances, leaving the signal unaffected when the respective frequency ranges are separated. Under certain circumstances, the signal can be recovered from the noise by the linearizing properties of the phase tracking on the interferometer response. The measurements reported show that the two-wavelength infrared heterodyne transceiver generates signals which replicate the target vibration exactly up to amplitudes at a multiwavelength level. This allows measurements of displacements on targets with submicron accuracy at distances of several meters.
Energy spectra of ions and electrons of a duoplasmatron
Authors: Volk K. , Sarstedt M. , Klein H. , Schempp A.
Published: July 2002

The energy distributions of ions and electrons extracted from a duoplasmatron ion source have been measured by a 127° cylinder spectrometer, providing information on the axial potential distribution in the source. The energy resolution of the spectrometer was about ±1 eV. Compared to measurements with Langmuir probes, this method has the advantage that the plasma potential is not disturbed. The energy spectrum of the extracted ions shows up to three peaks, which are related to different places of ionization in the source. The total energy spread is up to 100 eV. This energy spread can be influenced (down to 6 eV) by the potential of the expansion cup. Surprisingly, 90% of the extracted electrons are not created at the cathode but in the plasma of the intermediate electrode. This knowedge allows a better optimization of the source by independent regulation of gas pressure, intermediate electrode potential, and cathode potential. For optimum ionization of the working gas the potential of the intermediate electrode can be regulated so that the electron energy reaches the optimum value for the ionization in front of the anode and the energy and the intensity of the electron current is regulated by means of the potential of the expansion cup. These parameters strongly influence the beam quality.
A 14 cm×36 cm volume negative ion source producing multi-ampere H− ion beams
Authors: Hanada M. , Inoue T. , Kojima H. , Matsuda Y. , Ohara Y. , Okumura Y. , Watanabe K. , Seki M.
Published: July 2002

A large volume negative ion source, which has a newly devised magnetic filter called a PG filter, was designed and tested. The PG filter produces a uniform magnetic filter field over a large extraction area of 14×36 cm2 by flowing a high current through the plasma grid itself. By optimizing the filter strength, we succeeded to produce 3.4-A 75-keV negative hydrogen ion beams for 50 ms from 253 apertures of 11.3 mm diam with an average current H− density of 13 mA/cm2.
A tandem four-element lens system for surface electron spectroscopy
Authors: Sellidj A. , Erskine J. L.
Published: July 2002

Electron ray tracing studies and experimental tests of a tandem four-element lens system are presented. The lens system operates over a 0–400-eV energy range and is suited for applications such as angle-resolved photoemission spectroscopy and inelastic electron scattering spectroscopy requiring high energy and angular resolution. Each four-element lens of the tandem lens system can be operated in a zoom lens mode in which both the position and linear magnification of the image remain constant over a wide range of deceleration ratios. Performance characteristics including lens transmission, angular acceptance properties as a function of deceleration ratio, and operating voltages for the lens elements are evaluated analytically and by electron ray tracing analysis. Empirical tests of the lens system incorporated into an inelastic electron scattering spectrometer are compared with predicted performance. Comparison of four-element lens properties with corresponding properties of three-element lenses are also presented.
A tandem microwave-driven negative ion source: Experimental results
Authors: Marinak M. M. , Morse E. C.
Published: July 2002

A tandem microwave-driven plasma source for the production of H− ions has been developed and tested. The source has a microwave-driven primary chamber with a thermionic cathode-driven secondary plasma. This source was used to experimentally verify certain aspects of a theoretical model of H− production by Hiskes. A general agreement with the theory was found for the dependence of produced H− current with the plasma electron temperature. In addition, it appears that a surface production mechanism on the BaO-impregnated cathode enhanced the H− current production. Experimental results are given and compared to present theoretical understanding.
Ion production on the PI-110A accelerator
Authors: McKay P. F. , Bieg K. W. , Olson R. E. , Pregenzer A. L. , Wiemann D. K.
Published: July 2002

Lithium ion and proton source experiments have been performed using an extraction geometry applied-B ion diode on the 0.02-TW PI-110A accelerator. These sources are being developed for use in inertial confinement fusion (ICF). The proton source relies on surface flashover to form an anode plasma from which the protons are drawn. The lithium sources seem to depend upon the local electric field for operation. The applied electric field was enhanced in the experiment by the geometry of the anode surface. For the proton source, ion generation was reduced when the applied magnetic field was increased. By contrast, lithium ion generation continued to increase as the applied magnetic field was increased. The effect of anode temperature was investigated for two lithium sources and was found not to be a factor in ion generation. Measurements of the turn-on characteristics of the various ion sources show shorter turn-on delays with higher diode voltage.
Extraction-induced emittance growth for negative-ion sources
Authors: Whealton J. H. , Meszaros P. S. , Raridon R. J. , Rothe K. E.
Published: July 2002

Nonlinear emittance growth produced by ion extraction is considered by a 3-D analysis in a Vlasov–Poisson–Boltzmann formulation. Phenomena considered include (1) presheath effects, including electron depletion, (2) electron sheath accumulation (for large transverse magnetic fields), (3) nonlinear sheath fields (obtained by a self-consistent solution with an assumed quasiequilibrium positive-ion distribution and at least one Vlasov distribution), (4) nonlinear fringe fields produced by the accelerator-extractor itself [obtained self-consistently with item (3) above], (5) nonlinear space charge of the beam itself, and (6) beam in conjunction with extracted electrons. For specific volume negative-ion source configurations, an investigation of the contribution of aberrations caused by an electron trap and electron accumulation in the extraction sheath are studied. Either of these effects can contribute significantly to the beam emittance, possibly dominating the contribution of the negative-ion temperature in the source.
Experiments on a reflex-type sheet plasma negative-ion source
Authors: Ando A. , Kuroda T. , Oka Y. , Kaneko O. , Karita A. , Kawamoto T.
Published: July 2002

Negative hydrogen ions are extracted from a reflex-type sheet plasma. Electron density and temperature profiles are measured with changing the filling gas pressure, and they are optimized to the H− production at the optimum gas pressure. The optimum gas pressure is 5 mTorr for the discharge current Id =2 A. As the discharge current Id increases, H− current increases linearly corresponding to the density increase in the center region, but saturates above Id =40 A. The maximum extracted H− current density of 4 mA/cm2 is obtained at Id=100 A.
High-current deuteron ion source
Authors: Sethi R. C. , Thakur N. M.
Published: July 2002

A duoplasmatron ion source capable of delivering 20 mA of deuteron beam at an energy of 20 keV has been designed. This ion source will inject the beam into an RFQ accelerator, which is intended to be used as a 14-MeV neutron generator. In this design the emphasis is laid on the design of the plasma expansion cup and the extraction geometry. The space-charge beam dynamics through the ion source and the einzel lens is investigated with the help of a computer code iora developed by us. Almost all the components of the ion source have been made. The solenoid magnet and the intermediate electrode have been tested. The full assembly and the testing of the various parts is underway.
50-A ion source IK-50 for AMBAL-M device
Authors: Dimov G. I. , Morozov I. I.
Published: July 2002

In this paper an ion source design is described. An ion beam with a current of 50 A, an energy of 30 keV, and a pulse duration of 0.1 s is extracted from a rectangular plasma emitter with dimensions of 24×12 cm. A new way is used for creating a uniform plasma current density at the emission surface. The source is distinguished from the typical bucket sources by its high degree of monatomic ions, the absence of heating cathodes, and an original ion-optic system design.
Enhanced performance of the LBL/SNLL leaky EBIS: Evidence for cooling of trapped heavy ions
Authors: Schmieder Robert W. , Bisson Charles L.
Published: July 2002

The LBL/SNLL EBIS has been operated as a leaky electron beam ion source (EBIS), i.e., with continuous gas leaks and continuous extraction of the ions. Under normal conditions the charge-state distributions are determined by the extraction from the trap; recombination with the residual gas is negligible. A simple rate equation model of the charge-state distributions shows clear evidence that heavy ions (Xe) reach higher charge states than expected, while light residual gas ions (C,N,O) reach lower charge states. This is taken as evidence that ion-ion collisional cooling and heating of these ions results in enhanced trapping of the heavy ions, due to the presence of the residual gas.
Single-stage electron cyclotron resonance ion source for efficient low-charge-state production
Authors: Decrock P. , Van Duppen P. , Baeten F. , Dom C. , Jongen Y.
Published: July 2002

A single-stage electron cyclotron resonance source was developed for the Radioactive Ion Beam project. The layout of the source and results obtained with an off-line test separator are presented. Maximum ionization efficiencies obtained for Ne+1, Ne+2, and Ne+3 using He as support gas equal 52%, 15%, and 3%, respectively.
A device for performing surface-plasmon-polariton-assisted Raman scattering from adsorbates on single-crystal silver surfaces
Authors: Byahut S. , Furtak T. E.
Published: July 2002

We describe the theory, design, and performance of a new surface-plasmon-polariton-(SPP) assisted Raman scattering instrument that exploits the Kretschmann geometry. In contrast to previous methods, our device allows the entire SPP emission cone to be collected, thus optimizing the detected Raman intensity. This advantage makes surface Raman scattering from adsorbates on relatively smooth or single-crystal silver films possible with routine optics and electronics in the rest of the system. We demonstrate the concept with data acquired from a monolayer of paranitrosodimethylanaline (pNDMA) on nearly smooth polycrystalline Ag and single-crystal Ag(111) with air or liquid as the ambient medium.
A compact, resonant cavity, five centimeter, multicusp, ECR broad-beam ion source
Authors: Mahoney L. , Asmussen J.
Published: July 2002

Researchers in many industrial and scientific activities desire a physically compact, long-life ion source that can produce high-current density broad-beams in chemically reactive gases such as CF4 and O2. Earlier studies of a multicusp-ECR microwave-cavity ion source concept have demonstrated that a 5-cm-diam discharge can produce high beam current densities for broad-beam applications. More recently, this ion source concept has been redesigned to compact its size and to improve its operation and lifetime. In particular the physical size of the cylindrical microwave-cavity has been reduced to an outer diameter of 3.75 in. and an inner diameter of 3.5 in. Improved water and air cooling and permanent magnet arrangement allows the instrument to be operated continuously with powers greater than 200 W. The microwave cavity operates in the TE111 mode at 2.45 GHz and is self-starting in Ar, O2, and N2 gases at discharge pressures necessary for beam extraction (<5 mTorr). Ion densities of 1011/cm3–1012/cm3 have been achieved with input powers less than 200 W. These ion densities produce ion current densities in excess of 10 mA/cm2 which may be extracted by either single- or multiple-grid extraction optics. The operation, diagnostics and performance of this new ion source is reviewed.
Experimental study of the beam divergence from a broad-beam electron cyclotron resonance ion source
Authors: Ghanbari E. , Nguyen T. , Lindstrom R.
Published: July 2002

Various factors affecting divergence of an ion beam extracted from a broad-beam electron cyclotron resonance ion source are studied. The source has three graphite grid extraction optics providing an 18-cm ion beam. A simple apparatus and method is used to investigate the beam divergence as a function of source pressure, magnetic field, microwave power, beam energy, and suppression voltage. We discovered that the beam divergence ranges from ±4° to ±8°. We also noticed that, considering a 10% experimental error, suppression voltage does not strongly affect the beam divergence.
Apparatus for measurement of surface resistance versus rf magnetic field of high-T
c superconductors
Authors: Delayen J. R. , Bohn C. L. , Roche C. T.
Published: July 2002

A coaxial niobium quarter-wave resonant cavity has been fabricated and used for measurement of the surface resistance of disk-shaped samples of high-Tc superconductors at 820 MHz and 4.2 K, and at surface rf magnetic fields ranging to 300 G. The cavity can accommodate samples as large as 36 mm in diameter. A measurement procedure has been developed with which rf surface resistances less than 20 μΩ can be resolved for a 24-mm-diam sample at 820 MHz. This cavity is useful in determining the suitability of high-Tc superconductors for high-power rf applications.
Frequency-stabilized LNA laser for application in He(23S) optical pumping
Authors: Lynn J. G. , Dunning F. B.
Published: July 2002

A single-mode, standing-wave lanthanum neodymium magnesium hexaaluminate laser is described that is suitable for application in He(23S) optical pumping. The laser is frequency stabilized by reference to an external temperature-controlled Fabry–Perot étalon using simple control circuitry. Tests show that the laser can provide stable, efficient optical pumping of a collimated beam of He(23S) atoms resulting in polarizations approaching 100%.
Improved sample cell design for optical studies of glass-forming liquids in the 0–530 K range
Authors: Halalay Ion C. , Nelson Keith A.
Published: July 2002

An improved design is described for a cell which holds glass-forming liquid samples for optical spectroscopy experiments in the 0–530 K temperature range. The optical quality of the sample remains high throughout the liquid to glass transformation.
Gated neutron streak camera with a uranium cathode
Authors: Miyanaga N. , Oida H. , Yamanaka M. , Yamanaka T. , Nakai S. , Yamamoto T. , Iida T. , Araki T. , Ohga T. , Miyake C.
Published: July 2002

A gated neutron streak camera with a uranium oxide cathode has been developed for laser fusion experiments. The energy spectrum of secondary electrons was improved by coating the uranium oxide cathode with thin cesium iodine. The tube design was carried out by computer calculation of electron trajectories. The newly developed streak tube showed a temporal resolution of about 70 ps. This streak camera can be applicable to a neutron yield greater than 1012 with a reasonable signal-to-noise ratio by gating a microchannel plate electron multiplier.
Elimination of instrumental asymmetries in electron polarization analysis
Authors: Gellrich A. , Jost K. , Kessler J.
Published: July 2002

Recent advances in polarized-electron sources had the consequence that the accuracy of many experiments with polarized electrons is no longer limited by statistics, but rather by the uncertainty in polarization analysis by Mott scattering. One of the reasons for this uncertainty is spurious asymmetries that are caused by a small misalignment of the polarized beam. This article discusses how spurious asymmetries can be corrected for by proper use of monitor counters. It is shown that such a correction requires proper positioning of the monitor counters. A method of finding and checking the correct analyzer arrangement is given. The result is a polarization measurement with high reproducibility and accuracy.
Neutron penumbral imaging at Gekko XII (abstract)
Authors: Miyanaga N. , Chen Y.-W. , Unemoto M. , Yamanaka M. , Yamanaka T. , Nakai S. , Iida T. , Iguchi T. , Nakazawa M.
Published: July 2002

14 MeV DT neutrons emitted from a laser-imploded target have been imaged by using a penumbral aperture camera. This system consists of a 6-cm-thick tungsten toroidal aperture, an array of plastic scintillators, an optical fiber coupled two-stage image intensifier, and a cooled CCD camera. A burn region has been observed with a spatial resolution of ∼35 μm at a neutron yield of 5×1011. The spatial resolution was determined by a pixel resolution, the accuracy of the aperture fabrication, the alignment accuracy of the aperture, the signal-to-noise ratio of an encoded image, and the statistical fluctuation in detecting neutrons.
Fast Pb-glass neutron-to-light converter for ICF target burn history measurements
Authors: Lerche R. A. , Cable M. D. , Phillion D. W.
Published: July 2002

We are developing a streak-camera-based instrument to diagnose the fusion reaction rate (burn history) in laser-driven ICF targets filled with D-T fuel. Recently, we attempted measurements using the 16.7 MeV gamma ray emitted in the T(d,γ)5He fusion reaction. Pb glass acts as a gamma-ray-to-light converter. Gamma rays interact in the glass to form electron-position pairs that produce large amounts (1000 photons/gamma ray) of prompt (<10 ps) Cerenkov light as they slow down. In our experimental instrument, an f/10 Cassegrain telescope optically couples light produced in the converter to a streak camera having 20 ps resolution. Experiments using high-yield (1013 D-T neutrons), direct-drive targets at Nova produced good signals with widths of 200 ps. Time-of-flight measurements show the signals to be induced by neutrons rather than by gamma rays. The Pb glass appears to act as a fast neutron-to-light converter. We continue to study the interaction process and the possibility of using the 16.7 MeV gamma rays for burn time measurements.
Beam emission spectroscopy diagnostic for the study of turbulence in Phaedrus-T tokamak plasmas
Authors: Kim Y. J. , Breun R. A. , Brouchous D. A. , Fonck R. J.
Published: July 2002

A flexible beam emission spectroscopy diagnostic system is being installed on the Phaedrus-T tokamak. It consists of a low-power diagnostic neutral beam (H0 or He0) coupled with visible and vacuum UV collection optics to study low-amplitude, high-frequency fluctuations in local plasma density in ohmically and rf-heated plasmas. Neutral beam geometry and optical sightlines are chosen to optimize localization and radial resolution (<1 cm) over the whole plasma region. The ability to inject either a H or He neutral beam and observe in both the vacuum UV and the visible spectral ranges allows a wide choice of atomic transitions (e.g., Hα, Lα, He singlet or triplet lines, etc.) to be compared and optimized for a given experimental condition.
Application of diffraction tomography to plasma density measurements (invited)
Authors: Howard John , Peebles W. A. , Brower D. L. , Kim S. K. , Luhmann N. C.
Published: July 2002

Diffraction from plasma density irregularities can have significant consequences for the tomographic inversion of line-of-sight integrated measurements of the phase disturbance suffered by a probing beam. A new tomographic approach which takes account of diffraction from high-K refractive index structures is described. The relevance for multichannel interferometry measurements is demonstrated numerically and the technique is applied to the inversion of multichannel TEXT interferometer data.
A compact, low cost, seven channel polychromator for Thomson scattering measurements
Authors: Carlstrom T. N. , DeBoo J. C. , Evanko R. , Greenfield C. M. , Hsieh C.-L. , Snider R. T. , Trost P.
Published: July 2002

A seven channel polychromator, utilizing high performance interference filters (transmission ≳80%, rejection at laser wavelength>105), has been tested for use in the multi-Nd:YAG laser Thomson scattering system for the DIII-D tokamak. Unique features of this polychromator are the combination of high throughput, easy alignment, flexibility, compact size, and low cost when compared with other alternatives. Light is introduced to the polychromator (f/1.75) via a fiber optic bundle which permits the use of small (3.0 cm diam) optics and leads to a compact (44×24×8 cm) design, an important design consideration for multiple polychromator systems. The light is cascaded through a series of different bandpass interference filters and relay lenses which are mounted on two precision parallel rails in such a way that alignment is trivial. The relay lenses are positioned directly in front of the filters so that light reflected from the filter passes through the lens twice. This leads to an efficient, compact design and reduces the angle of incidence (4 °) and the cone angle of light (4.5 °) seen by the filter, an important factor for narrowband (3.0 nm) filters. The transmission (average 70%) was optimized for 700–1100 nm by using broadband coatings throughout. The output images of each channel (2.3 mm. diam) can be directly coupled to large format (3 mm diam) RCA silicon avalanche photodiode detectors, avoiding the losses caused by fiber optic coupling.
High temperature infrared cell for i
n s
i
t
u sample monitoring
Authors: Karpowicz Richard J.
Published: July 2002

A purgable, heatable, easy to construct, infrared cell was built to study in situ cure behavior of high-temperature stable polymers via Fourier transform infrared spectroscopy. Several advantages over existing designs are mentioned. Construction details are discussed.
Preventing rapid decomposition of rhodamine dyes in excimer-pumped pulsed dye lasers
Authors: Arias Paul D. , Dai Hai-Lung
Published: July 2002

A simple and effective method of preventing rapid decomposition of rhodamine dyes in Lambda-Physik excimer-pumped pulsed dye lasers is presented. Teflon coating the internal metal surfaces of the dye cell greatly increases the useful lifetime of the dye solution.
Capacitance measurement of semiconductor electrodes by means of the HP-4274A LCR meter
Authors: St. Popkirov George
Published: July 2002

It is suggested how a Hewlett-Packard LCR meter HP4274A can easily be used for capacitance-voltage measurements of semiconductor electrodes in an electrochemical cell. Two measurement schemes are presented. In the first, the electrode potential of the sample is controlled by means of an electronic potentiostat connected between the LCR meter and the electrochemical cell. In the lower-frequency range (100 Hz–4 kHz) the measurement error is less than 1%. Due to parasitic impedance and phase shift in the potentiostat electronic circuit it is within 4% at 10 kHz and greater for higher frequencies. In the second scheme the LCR meter bias supply is computer controled and performs the potentiostat functions. In this case the cell impedance could be measured accurately in the whole frequency range of the HP4274A.
Development of ionized cluster beam source for practical use
Authors: Ito H. , Minowa Y. , Ina T. , Yamanishi K. , Yasunaga S.
Published: July 2002

Low-energy ion bombardment during film growth can significantly modify film properties. The practical advantages of using an ionized cluster beam (ICB) include reduced damages and high deposition rates at low temperature. The design and the characteristics of the ICB source are described. The ionized cluster trajectories and the potential profiles were numerically calculated in order to optimize the design. The ionization chamber has restrictive electrodes to enhance the ionization probability in the low cluster density region near the anode. With these electrodes, the source provides uniform ion current densities up to 30 μA/cm2 at voltages ranging from 200 to 8000 V over a 127 mm diam substrate at a distance of 300 mm from the source. The ICB source can operate over a wide temperature range up to 2000 °C. Deposition rates up to 120 nm/min are obtained for Ti, Si, and Cu. The source has successfully operated for more than 100 h in several industrial applications.
A compact injector for a small triton accelerator
Authors: Schlindwein R. , Seki S. , Korschinek G.
Published: July 2002

We have constructed a very compact 350-keV injector for a triton accelerator. Because of restrictive boundaries, the whole system has been optimized: for example, a disktron for the high-voltage power supply, a highly efficient gas recycling system on a platform, and an insulating cooling system. In the first step, the injector was operated with a duoplasmatron ion source. In test runs, the injector was charged up to 330 kV without any problems. To date, the injector has been used to accelerate hydrogen beam currents of ∼0.2 to 0.4 mA.
BNL intense polarized H− source progress
Authors: Alessi J. G. , DeVito B. , Hershcovitch A. , Kponou A. , Meitzler C. R.
Published: July 2002

Components are being developed which will eventually be part of a high-current polarized H− source. An atomic beam has been cooled to 6 K, resulting in a most probable velocity of approximately 680 m/s and a forward flux of about 3×1020 H0/sr/s. Focusing of this beam with a superconducting solenoid was unsuccessful at high H0 densities due to H0-H0 scattering. A permanent magnet sextupole is now being tested. An ionizer based on the charge exchange of the polarized H0 with ≊150-eV D− has also been studied.
Step-scan Fourier-transform infrared spectrometer
Authors: Manning Christopher J. , Palmer Richard A. , Chao James L.
Published: July 2002

This article describes the modification of a commercial Fourier-transform infrared (FT-IR) spectrometer for step-scan operation. Step-scan operation decouples the FT-IR spectral multiplexing from time and is therefore applicable to a variety of time-dependent spectroscopic experiments, including, particularly, photoacoustic and photothermal spectroscopy. The step-scan instrument described controls the retardation (moving mirror position) with a feedback loop. The loop uses path difference, or phase, modulation of the reference laser intensity, together with lock-in amplifiers to detect the mirror position. Since the interferogram can be sampled at intervals as small as 1/4 λHeNe, the maximum free-spectral range is 31 600 cm−1. For initial positioning of the mirror, stepping can be as rapid as 100 Hz. The current software will allow data collection at ∼1.6 Hz, although the mirror settling time of ≤20 ms would allow data to be collected at 20–30 Hz stepping frequency with more efficient software. The mirror control phase modulation (PM) can also be used for efficient modulation of the infrared beam by use of a PM amplitude on the order of 1–2 λHeNe. The stability of the retardation, which imposes an upper limit on the SNR of the measured spectra, is ∼±15 nm. Data collection times on the order of 20 min are typical for 8 cm−1 resolution. Examples of dynamic spectroscopic data obtained using the step-scan mode of operation are presented. Future improvements to the instrument are briefly discussed.
Optimum amplification of microchannel-plate photomultiplier pulses for picosecond photon timing
Authors: Cova S. , Ghioni M. , Zappa F.
Published: July 2002

Ultrafast microchannel-plate photomultipliers offer picosecond resolution in time-correlated photon counting, provided all additional causes of timing jitter be minimized. Here we analyze the contribution of the electronic circuit noise, mainly dependent on the fast preamplifier and no more negligible at picosecond level. Criteria are derived for minimizing this contribution by proper design or selection of the amplifier. We highlight that it does not make sense to select amplifiers with bandwidths of 3 GHz or more, looking mainly to the rise time of the fast microchannel-plate pulse and paying minor attention to the noise. We demonstrate that (i) the noise spectral amplitude has chief importance, (ii) the bandwidth providing minimum jitter is around 1 GHz, and (iii) satisfactory results are obtained with lower bandwidths, in some cases down to about 500 MHz.
Simple, fast, puff valve
Authors: Kriesel J. , Prohaska R. , Fisher A.
Published: July 2002

A simple, fast, reliable diamagnetically driven gas puff valve is described. It offers an extremely quick rise time (∼100 μs) and a large pressure rise rate (∼270 Pa/μs at a distance of 13.5 cm) with an input energy of only 90 J (600 V on a 500 μF capacitor). Because the valve can be operated with such a small input energy, solid-state switching devices are adequate and the operation of the valve will not produce the amount of electrical noise that other valves needing higher energy often do. Our valve achieves high-density puffs at relatively low plenum pressure (380 kPa, 3.8 atm), permitting it to be extremely simple in design and easy to operate. The entire package (valve plus driving circuit) is small in size; it can fit in a volume 4 in. in diameter by 8 in. long. The valve holds about 60 cm3 of gas and has an outlet opening of 1/4 in. in diameter.