bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the aerodynamic trap for containerless laser materials processing in microgravity
Authors: Paradis Paul-François , Babin François , Gagné Jean-Marie
Published: July 2002

In the context of containerless laser processing of glasses in microgravity, a systematic study of the aerodynamic trap (ADT) has been done on the ground at both ambient and very high temperatures (≳2000 K). This work yielded a better understanding of the ADT and helped in improving its design. Experiments indicate that restoring force and sample stability depend upon the diffuser’s interior angle, flow rate, and ratio of sample to diffuser’s throat diameters. It was found that the trap’s potential energy curve versus position had a barrier height that increased with flow rate but decreased with increasing angle of the diffuser. Small angle diffusers show a greater spatial extent of the potential well, higher sphere-to-wall distances, and greater sample stability than larger angle diffusers. Low flow rates give quieter environments (smaller oscillations and perturbations due to the gas flow) than higher flow rates even though they are sufficient to trap the sample and damp external perturbations. Heat loss by forced air cooling is thus reduced, enabling the processing of larger samples for a given laser power. The research suggests that for dielectric samples of ≊3 mm diameter, at ambient, as well as at high temperature, where stability is a necessity, the ADT should be a small angle diffuser (30°–60°) operated at low flow rate (<4.4 l/min with a 1 mm throat diameter). These conditions allow stable positioning for ambient as well as for high-temperature containerless materials sciences experiments on the ground and in microgravity. The sample should stay positioned and contactless even during large acceleration variations (2 g–μg) with minimum perturbation allowing its use in a KC-135 aircraft environment. Also, a spherical sample whose size varies through evaporation can be continuously trapped in a unique conical diffuser as long as its diameter is greater than that of the throat.
Discharge characteristics of bucket source and its effects on very low energy beam
Authors: Ueda Yoshio , Yoshikawa Takafumi , Ito Yoshifumi , Nishikawa Masahiro , Goto Seiichi
Published: July 2002

The effects of source plasma parameters and space charge neutralization on energy spread of very low energy and high perveance ion beam have been studied experimentally. Plasma parameters of a bucket source were changed by shorting an arc chamber and a positive electrode (a plasma electrode) to deteriorate electron confinement. Although the change of plasma potential reflected the beam energy and the change of energy spread was observed, the relation between the plasma parameters and energy spread is unclear. Space charge neutralization of the ion beam by supplying thermal electron and increasing gas pressure in beam transport region showed reduction of the energy spread. This result suggests that the space charge effects of the ion beam plays an important role in energy broadening.
Improvements on the KSU-CRYEBIS: A facility for low-energy, highly charged ions
Authors: Stockli M. P. , Gibson P. E. , Cocke C. L. , DePaola B. D. , Fry D. , Kravis S. , Parks D. , Richard P. , Tipping T. N. , Walch B. , Winecki S.
Published: July 2002

The KSU-CRYEBIS, a cryogenic electron beam ion source, delivers ions over a wide range of ion energy per charge, ion mass, and charge state for atomic physics experiments. Lower charge states yield time-averaged currents in the nA range, whereas the highest charge states, such as Ar18+, Fe24+, Kr34+, and Xe47+, yield time-averaged currents in the pA range. The number of available species and isotopes has been substantially increased, and include metalorganics to produce stable, high-yield beams of metal ions. The high-voltage platform control system and the ion optics have been improved and allow for acceleration of the ions to 160 kV/q as well as for deceleration to a fraction of 1 kV/q. The diagnostics of the facility are continuously being upgraded.
Exact energy values of ‘‘low-energy ion beams’’
Authors: Sakudo N. , Hayashi K.
Published: July 2002

Ion beams with energies of several tens of electron volts are used for forming special films with excellent physical and chemical properties by ion-beam deposition. Although the ion energy values are considered very important for controlling physical and chemical characteristics of the deposited films, most reported values for such film formation have been considerably inaccurate since they have been given simply by multiplying the power supply voltages to the discharge chambers with electron charge e. In practice, the plasma potential at which ions are generated is several to several tens of volts higher than the discharge chamber, so that the real beam energy is that much higher. Although the excess energy originating from the plasma floating potential has been negligible for usual high-energy ion implantation, it cannot be neglected for ion-beam deposition where low-energy ion beams below 100 eV are used. In this article it is indicated that knowing electron temperatures of plasmas is necessary to get the exact energy values of low-energy ion beams. Thus, it is also clarified that ion energy spreads of usual ion beams may be caused by possible fluctuation of the electron temperatures as well as by thermal motion of ions in the plasma.
A new goniometer design for single-crystal nuclear magnetic resonance spectroscopy
Authors: Vosegaard Thomas , Langer Vagn , Daugaard Preben , Hald Eigil , Bildso/e Henrik , Jakobsen Hans J.
Published: July 2002

A new goniometer for single-crystal nuclear magnetic resonance (NMR) spectroscopy has been constructed and built into a multinuclear X–1H double-tuned probe for cross-polarization and/or 1H decoupling. Improvements in the ease of mounting/remounting the crystal on the three rotational axes and in the accuracy of the stepwise rotation about these axes have been achieved compared to the usual cube goniometer. A similar improvement is achieved for the determination of the orientation of the crystal relative to the goniometer frame. The NMR goniometer has three dovetail mortises that enable rotation of the crystal about three orthogonal axes, all perpendicular to the magnetic field. The crystal is glued onto a tenon that fits precisely into the dovetails of the NMR goniometer and also into a slightly modified x-ray diffraction goniometer, thereby allowing a high-accuracy determination of the orientation for the tensorial NMR interactions with respect to the crystal frame. The performance of the goniometer is illustrated by single-crystal 23Na NMR spectra of NaNO3.
Absolute experimental and numerical calibration of the 14 MeV neutron source at the Frascati neutron generator
Authors: Angelone M. , Pillon M. , Batistoni P. , Martini M. , Martone M. , Rado V.
Published: July 2002

The absolute neutron yield of the 14 MeV Frascati neutron generator (FNG) is routinely measured by means of the associated alpha-particle method with a silicon surface barrier detector (SSD). This paper describes the work carried out to characterize the neutron source in terms of absolute intensity and angle-energy distribution of the emitted neutrons. The development of the measuring setup and the assessment of the measurement results are also reported. A complementary calibration procedure for validating the SSD results, based on the use of fission chambers and the activation technique, is also reported. An accurate analysis of the system has been performed via the Monte Carlo neutron and photon MCNP transport code. A detailed model of the neutron source that includes ion slowing down has been inserted into the MCNP code to permit a numerical calibration of the neutron source for comparison with the experimental results. The resulting agreement among the various methods is very good considering the uncertainties, and an accuracy of ±2% is achieved for the measurement of the 14 MeV neutron yield of the FNG.
A compact mass spectrometer for plasma discharge ion analysis
Authors: Tuszewski M.
Published: July 2002

A simple, compact, and inexpensive mass spectrometer for ion species analysis in plasma processing experiments has been successfully operated. The above attractive attributes are made possible by a single-step mass analysis rather than the usual two-step process of ion extraction followed by mass filtering. Theory and data show that the single-step process can be used without compromising the accuracy of ion species concentrations for sufficiently low applied voltages and large front aperture separations. The instrument is small enough to be introduced in most plasma discharges for in situ rather than for edge studies. The mass spectrometer has a moderate resolution that is adequate for many applications. The instrument can be afforded by all researchers, can be easily built, and can be operated in steady-state or pulsed plasma discharges.
Photodetachment diagnostics of plasma with a high n−/n
e ratio
Authors: Balghiti-Sube F. El , Baksht F. G. , Bacal M.
Published: July 2002

The method of determination of the electron and H− densities in the photodetachment experiment, particularly when performed in plasma with a high n−/ne ratio, is discussed. Some essential peculiarities of this method arise from the creation of a potential well in plasma after photodetachment. The well captures the excess electrons, generated by the laser beam, and supports the quasineutrality in the plasma. The method is applied to the diagnostics of the extraction region of the negative ion source ‘‘Camembert III.’’ The dependencies of the negative ion and electron densities, and of the electron temperature upon the plasma electrode voltage, are obtained and discussed.
Ultrafast two-dimensional x-ray imaging with x-ray streak cameras for laser fusion research (invited)
Authors: Shiraga H. , Miyanaga N. , Heya M. , Nakasuji M. , Aoki Y. , Azechi H. , Yamanaka T. , Mima K.
Published: July 2002

Ultrafast two-dimensional x-ray imaging is required for diagnosing laser-driven inertial confinement fusion plasmas. Image sampling technique with x-ray streak cameras can meet this requirement. Multi-imaging x-ray streak camera method (MIXS) with temporal and spatial resolutions of 10 ps and 15 μm, respectively, has been developed and successfully utilized for diagnosing the uniformity and heating process of the imploded core plasmas. The two-dimensional sampling-image x-ray streak camera method is also presented. Two types of spectroscopic applications of the MIXS have been developed recently. One is multichannel MIXS, which has three MIXS channels with various spectral responses for time-resolved two-dimensional temperature measurement of the plasmas. Another is monochromatic MIXS for temperature, density, and mixing measurement, in which monochromatic images with Bragg crystals are coupled to MIXS.
Multichannel millimeter wave interferometer for W7-AS
Authors: Geist T. , Würsching E. , Hartfuss H.-J.
Published: July 2002

A newly designed ten channel microwave interferometer for line integrated electron density measurements at the experiment W7-AS stellarator is described. The probing signals in the frequency range of 160–162 GHz are generated by Gunn oscillators with subsequent frequency doublers. Double conversion heterodyne receivers with 2 MHz bandwidth are used for detection. All oscillators involved are phase locked. Use of each Gunn oscillator is twofold: as a source for the probing signal and as a local oscillator for heterodyne detection. The dynamic range of the millimeter wave part is about 70 dB. The instrument operates up to a peak density of 7×1019 m−3 with a temporal resolution of 5 μs. This article gives a detailed technical description of the system and demonstrates its usefulness by means of an experimental example.
A quartz quasimonolith for absolute x-ray wavelength measurements
Authors: Klöpfel D. , Hölzer G. , Förster E. , Beiersdörfer P.
Published: July 2002

We have constructed a quasimonolithic crystal consisting of two offset, parallel-mounted quartz (101̄0) crystals for determining the wavelengths of x-ray transitions on an absolute scale without the need for reference lines. The design and organization of the quasimonolith crystal device, as well as the determination of the relevant parameters and their corresponding uncertainties are discussed. A calibration chain is established that enables linking any wavelength measurement directly to optical wavelength standards and thus to SI units. Our analysis shows that absolute wavelength measurements with an uncertainty of one part per million are in principle possible with the device. Implementation of the quartz quasimonolith in a high-resolution vacuum spectrometer used to study x-ray line emission from an electron beam ion trap is described.
Comparison of calculated phase-sensitive recoverable signals using a Fabry–Perot cavity in reflection and transmission
Authors: Bava E. , Massari F.
Published: July 2002

This work is concerned with the analysis of the signals which can be recovered in a phase-sensitive detector after either transmission through or reflection from a Fabry–Perot interferometer of a phase-modulated light. The frequency responses are obtained and compared, the effects of amplitude modulation which result in offsets and line shape distortions are analyzed, the conditions to reduce the in-loop frequency noise are examined taking into account the electronic noise, when the source is locked to the cavity by means of a high gain control system.
Characterization of the helical undulator HELIOS I in the 520 to 930 eV range using a multilayer polarimeter
Authors: Drescher M. , Snell G. , Kleineberg U. , Stock H.-J. , Müller N. , Heinzmann U. , Brookes N. B.
Published: July 2002

A W/Si multilayer was used to determine the degree of circular polarization of the soft x-ray radiation of the European Synchrotron Radiation Facility helical undulator HELIOS I. The multilayer, manufactured by vapor deposition serves as a wideband tunable polarization analyzer in the photon energy range from 520 to 930 eV. The characterization of the multilayer’s analyzing power, varying from 0.82 to 0.25 for these energies, indicates that it operates close to its calculated specifications. The lack of phase-shifters applicable in this energy range was overcome by a detailed analysis of the unpolarized background identified as radiation from the magnetic lattice. In this way, the degree of circular polarization of HELIOS I was determined to exceed 0.85 for hν>685 eV.
Sulfur diffusion and the interstitial contribution to arsenic self-diffusion in GaAs
Authors: Uematsu Masashi , Werner Peter , Schultz Matthias , Tan Teh Y. , Gösele Ulrich M.
Published: July 2002

A quantitative determination of the contribution of As self-interstitials to the As self-diffusion coefficient in GaAs has been carried out. Values of the As self-interstitial contributions are deduced from sulfur indiffusion profiles in GaAs, which are simulated based on the kick-out mechanism. Furthermore, the relative contributions of As self-interstitials and of As vacancies are discussed.
Thermographic temperature determination of gray materials with an infrared camera in different environments
Authors: Kiwamoto Y. , Abe H. , Tatematsu Y. , Saito T. , Kurata M. , Kajiwara K. , Kikuchi Y. , Takahashi T. , Tamano T.
Published: July 2002

In conventional infrared (IR) thermographic cameras it is normally assumed that the ambient temperatures of optical objects are the same as the temperature determined at the camera head. In increasing cases of application of thermography, this assumption is not always satisfied, and often leads to erroneous results. In this article, we propose a determination scheme of the true temperature of such objects in an explicit form of equation to be solved by combining the readout temperature of the camera with a response function of the camera to a blackbody. The equation can be used to determine optical properties of components in an IR system. It also works to evaluate the contribution coming from each element along the optical path. Though the scheme is written in a form applicable to a specific camera among commercial products, it can be modified so that conventional IR cameras are conveniently used for thermographic determination of the temperature of gray objects in exotic environments.
Analog gain of microchannel plates for 1.5–154 keV/q Arq+(3⩽q⩽16)
Authors: Stockli M. P. , Fry D.
Published: July 2002

The gain of microchannel plates operated with low bias voltages in the analog mode has been measured for Arq+ ions (3⩽q⩽16) with energies in the range from 1.5 to 154 keV/q. The results show that the gain, most likely due to the varying number of secondary electrons emitted upon impact of the detected ions, depends substantially on the charge as well as the energy of the ions. The measured gain is shown as a function of the charge state for five different ion energies per charge to assist in the interpretation of the results from the ion sources. The measured gain is also shown as a function of ion impact velocity for all measured charge states, which indicates a rather complex dependence on the ion impact velocity. The interpolated gain is also shown as a function of charge states for four different ion impact velocities. For the lowest ion impact velocity, the gain seems to increase linearly with the ions’s potential energy with the gain measured for Ar16+ being roughly twice as large as the gain measured for low charge states. However, for higher ion velocities, the gain surprisingly decreases for the first few charge states before it increases for higher charges (q>8) forming a minimum for an intermediate charge state. For 1.4×106 m/s, the measured gain of Ar3+ roughly matches the gain measured for Ar16+, but is roughly 60% larger than the gain measured for Ar8+.
Simple method for measuring refractive index of supercritical fluids
Authors: Kirby C. F. , McHugh M. A.
Published: July 2002

A high pressure, optical system is presented for measuring the refractive index of a supercritical fluid solvent to within ±3×10−3 at pressures as high as 2500 bar and temperatures of 200 °C. The experimental technique used here is an adaptation of the laser beam displacement method for measuring the refractive index of liquids at ambient pressure. This optical system is used to measure the refractive index of supercritical ethane to pressures of 2000 bar and temperatures of 200 °C.
A transmission x-ray microscope based on secondary-electron imaging
Authors: Watts R. N. , Liang S. , Levine Z. H. , Lucatorto T. B. , Polack F. , Scheinfein M. R.
Published: July 2002

A design for a transmission x-ray microscope with 20 nm transverse spatial resolution is presented. The microscope, which is based on the electron-optical imaging of the photoemitted electrons from an x-ray shadowgraph, consists of a transmission x-ray photocathode coupled to a photoelectron emission microscope (PEEM—also called a PEM for photoelectron microscope). Unlike the conventional PEEM, which produces a surface map of photoelectron yield, this microscope can provide information on the subsurface properties of thin samples. The analysis of the microscope’s electron-optical performance is based on the evaluation of Gaussian focusing properties and third-order aberration coefficients computed using several complementary methods. The electron optical properties of the microscope are examined with an emphasis on issues affecting overall performance and achieving the best possible resolution. Preliminary experimental results using a cesium iodide photocathode are shown.
Temperature measurement of fine wires by photothermal radiometry
Authors: Borca-Tasciuc T. , Chen G.
Published: July 2002

This work reports temperature measurement of fine wires using the photothermal radiometry (PTR) technique. In this method, a laser is employed to create a small periodic temperature perturbation on the wire and thus a small modulation of the thermal emission signal from the wire. The temperature of the wire is derived from the ratio of the photothermal emission signals at two different wavelengths. Temperature measurement is performed on an electrically heated metallic wire of 127 μm in diameter. A calibration procedure is developed to account for the emissivity difference at the two signal wavelengths. The measured temperatures by the PTR technique are in good agreement with the thermocouple readings at different laser modulation frequencies. The possibility of extending the technique to optical fibers is discussed based on Mie scattering theory. Calculations suggest that the PTR technique can be used to measure temperature of optical fibers during the fiber drawing process by choosing an appropriate excitation laser and the signal wavelengths.
A filamentless ion source for materials processing
Authors: Anders André , MacGill Robert A. , Brown Ian G. , Vizir Alexey
Published: July 2002

A dual-stage, multiaperture gas ion source with 5 cm beam diameter has been built and characterized. The first discharge stage is a constricted glow discharge injecting a plasma stream into a discharge cavity supporting a Penning ion gauge discharge in the low pressure mode. Both discharge stages and ion extraction are fed by a single, grounded power supply. This simplifies the electrical setup and reduces costs. Various gases have been tested including nitrogen, oxygen, and argon. The ion beam current density is 250 μA/cm2, i.e., the beam current is about 5 mA, at an extraction voltage of 3.0 kV and a discharge current of 59 mA. Measurements of the ion beam current as a function of various parameters such as the discharge voltage and current, gas flow, and magnetic field are presented. The source is compact and can be easily adapted to various materials modification applications in which ion energies of a few keV are required.
Buried thermoplastic layer diagnostics by the use of combined frequency-domain and impulse response photo-thermo-mechanical radiometry
Authors: Munidasa Mahendra , Mandelis Andreas , Ball Mel
Published: July 2002

A photothermal approach to the problem of characterizing the thermoplastic layer thickness sandwiched between two metal foils used in heat-sealed food containers is described. Real-time signal acquisition instrumentation for the photothermal radiometric signal based on impulse-response fast Fourier transform (FFT) processing via chirped laser-beam modulation and cross-correlation spectral analysis, instead of the conventional point-by-point discrete frequency scans with a lock-in amplifier has been introduced. A theoretical frequency-domain model for the signal generation due to laser heating, which contains both a thermal component and a mechanical component due to the thermal expansion of the thermoplastic layer, is presented. The time domain impulse response theoretical data have been obtained by a numerical FFT of the frequency-domain theoretical data. The total signal was measured via radiometric detection in both domains and was fitted to the theory to obtain thermal transport properties of the three-layered system. The thickness of the thermoplastic layer has been extracted with better than 5% precision.
Ion source electrode biasing technique for microsecond beam pulse rise times
Authors: Perkins L. T. , Kwan J. W. , Leung K. N. , Rickard M. , Williams M. D.
Published: July 2002

Heavy ion fusion (HIF) induction accelerators require ion sources that can deliver intense heavy ion beams with low emittance. The typical pulse length is 20 μs with a rise time less than 1 μs and a repetition rate of 10 Hz. So far, the surface ionization sources have been used in most HIF induction linac designs. However, there are other ions of interest to HIF (e.g., Hg, Xe, Rb, Ar, and Ne) which cannot be produced by the surface ionization sources, but rather by volume ion sources. In this paper, we describe an experiment that uses a multicusp source with a magnetic filter to produce beam pulses that have a rise time in the order of 1 μs. By applying a positive biasing pulse on the plasma electrode with respect to the source body, the positive plasma ions can be temporarily repelled from the neighborhood of the extraction aperture, leading to a suppression of the ion beam. As the bias is removed, positive ions flow to the extraction region, enabling a fast-rising beam pulse. The beam current pulses show that there are two distinct groups of ions. An initial fast current rise time (<2 μs) corresponding to ions originating from within the magnetic filter region followed by a second group of ions with a longer rise time (10–20 μs) originating from the plasma bulk region. Proper positioning of the filament cathode and the magnetic filter field relative to the extraction aperture was found to be critical.
The virtual cathode: Key to the numerical simulation of negative ion extraction
Authors: Becker R. , Leung K. N. , Kunkel W.
Published: July 2002

The simulation of volume produced negative ions from a plasma is by far more complicated than the extraction of positive ions, while in experiments the only difficulty seemes to be connected with the power of the electrons, which are extracted at the same time. The reason for this complication in simple minded simulations is the infinite space charge, which builds up in the turning point of the positive ions in the extraction aperture for the negative ions. Smearing out the energy of the positive ions seems to help, however, this is mostly not justified by experiments, showing a low ion energy, especially in the region between the magnetic filter and the extraction hole. This difficulty may be overcome by using experience from virtual cathode formation in magnetically focused, decelerated electron beams. The decelerated electrons behave similarly to the reflected positive ions and are forming a virtual cathode in the reflection zone. From the analysis of the electron deceleration experiment, a simple power law is deduced to describe the decreasing electron current by the local potential. In turn, this power law may also be applied to the positive ion current, resulting in simulations without space charge singularity, even in the case of monoenergetic ions. As a first step towards the numerical simulation of negative ion extraction, a linear model has been made, using this power law. The transition from a Boltzmann distribution for the plasma electrons to a truncated one for the extracted beam electrons is considered as well, parallel to Langmuir’s treatment of a thermal diode for electrons.
Novel array antenna for mobile and satellite communications with an omnidirectional radiation pattern
Authors: Singh Ranjit
Published: July 2002

A novel array antenna is proposed for obtaining omnidirectional radiation pattern and is suitable for satellite and mobile communication applications. The method is based on application of the Bessel function to derive a new family of array current distribution to achieve omnidirectional pattern. The array provides a microstrip implementation of an omnidirectional antenna that is simple to design and inexpensive to fabricate. Simulated results for the rectangular microstrip patch array validate the present design technique.
Acceleration-field calculation for a structure-based laser-driven linear accelerator
Authors: Huang Y. C. , Byer R. L.
Published: July 2002

A laser-driven particle accelerator, scaled to optical wavelengths, has a feature size many orders of magnitude smaller than a radio-frequency accelerator. However, similar to a radio-frequency accelerator, a laser-driven accelerator cell may have apertures to transmit electrons. We numerically calculate the acceleration field for a cylindrically focused, crossed-laser-beam linear accelerator with the presence of electron transit apertures. A 4-μm-width electron aperture decreases electron energy gain by 17%, and a 6-μm-width aperture decreases energy gain by 34% relative to a structure without apertures.
Lobster-eye all-sky monitors: A comparison of one- and two-dimensional designs
Authors: Peele A. , Zhang W.
Published: July 2002

X-ray all-sky monitors (ASMs) have played a vital role in the development of x-ray astronomy. In order for them to continue to do so ASMs with high sensitivity, broad energy band coverage, and large sky coverage will be required. The best way to achieve these goals is for the next generation of ASMs to have focusing capability. Lobster-eye optics offer a way to construct a focusing ASM and a design is presented for a lobster-eye ASM that offers an order of magnitude increase in sensitivity over previous nonfocusing instruments. Simpler versions of the lobster-eye telescope, based on arrays of flat reflectors in one dimension only, have also been suggested in the past. In this article we compare the one- and two-dimensional (lobster-eye) configurations and conclude that, for intense short-lived phenomena, where the background is negligible, the one-dimensional configuration is optimal, whereas for ultimate sensitivity of background-limited faint sources the two-dimensional configuration is preferred.
On the gain media uniformity in controlled expansion cooled high gain recombination x-ray lasers
Authors: Li Ruxin , Zhang Zhengquan , Fan Pinzhong , Zhang Lingqing , Xu Zhizhan
Published: July 2002

We investigate the uniformity of the plasma column produced on a multifin target which is designed for implementing a high gain recombination x-ray laser based on the controlled adiabatic expansion cooling scheme. It is shown that a plasma column, which is as uniform as that produced on a flat slab target, can be generated on a segmented target under an appropriate laser irradiation condition, and an enhancement of the on-axis emission of lasing lines is observed simultaneously, which can be attributed to an increase in laser gain. For the Li-like Al 4f-3d laser system, an increase of gain from 1.8 to 2.4 cm−1 was evaluated by comparing the on-axis emission from the multifin target with that from the flat-slab target. However, a large nonuniformity is also observed when the laser condition is so changed that strong ion collisions between the neighboring plasmas appear. The extension of this target design to the shorter wavelength laser regime appears to be promising provided that both the target parameter and the driving laser condition are optimized.
Inexpensive substrate heater for oxidizing environments
Authors: Paturi P. , Huhtinen H. , Laiho R.
Published: July 2002

We describe a substrate heater constructed for use in an oxidizing environment in the temperature range of T⩽900 °C. The heating element is an ordinary projection lamp working in ambient near the end of a quartz tube fixed with a flange to a vacuum chamber. On the vacuum (outer) side of the tube is a smooth fitting stainless steel cylinder that conducts the heat to the region of the substrate. For fixing or removing the substrate the cylinder can be simply pulled off its position on the quartz tube. The heater that is described has been used, for example, for laser ablation of YBa2Cu3O6+x superconducting films.
Development of millimeter-wave two-dimensional imaging array
Authors: Oyama N. , Mase A. , Negishi H. , Tokuzawa T. , Itakura A. , Tamano T. , Yatsu K. , Watabe K. , Mizuno K. , Nagayama Y. , Kawahata K. , Matsuura H. , Uchida K. , Miura A.
Published: July 2002

A millimeter-wave two-dimensional imaging array has been developed for diagnostics of magnetically confined plasmas. It is applied to the plug cell of the GAMMA 10 tandem mirror, and measures time evolution of radial and axial line-density and electron cyclotron emission (ECE) profiles in one plasma shot. The monolithic-type GaAs Schottky diode detector having an antenna and built-in amplifier on a GaAs substrate is newly fabricated using monolithic microwave integrated circuit (MMIC) technology. This novel detector is developed to attain high frequency response up to submillimeter-wave region and wideband heterodyne characteristics, and is expected to be applied to ECE imaging in a large helical device. The response of the detector is compared with that of the hybrid-type detector using beam-lead Schottky barrier diodes. The first experimental result of the ECE measurement is reported using a heterodyne radiometer with the MMIC detector.
Charge-exchange recombination spectroscopy and beam-emission spectroscopy for C-Mod
Authors: Rowan William L. , Bravenec R. V. , Eisner E. C. , Ross D. W. , Wootton A. J. , Bretz N. , Marmar E. S. , Terry J. L.
Published: July 2002

The design of two beam-based diagnostic systems for C-Mod, charge-exchange recombination spectroscopy (CXRS) and beam-emission spectroscopy (BES) will be presented. A 50-keV diagnostic neutral beam (DNB) will be installed on C-Mod for these and other diagnostics. By adding BES and CXRS to the set of C-Mod diagnostics, it will be possible to test theory-based models of turbulent transport, which are typically based on marginal stability and the existence/dominance of ion temperature gradient (ITG) modes. Tests that coordinate turbulence measurements with transport measurements are largely unavailable at present.
A diagnostic neutral beam system for the MST reversed-field pinch: Charge-exchange recombination spectroscopy and Rutherford scattering (abstract)
Authors: Den Hartog D. J. , Fiksel G. , Davydenko V. , Ivanov A. , Mishagin V.
Published: July 2002

A diagnostic neutral beam system is being purchased for the MST reversed-field pinch. Initially, this beam will be used for charge-exchange recombination spectroscopy (CHERS) to measure impurity ion velocity and temperature, both equilibrium and fluctuating. This work is an extension of an existing MST spectroscopic diagnostic which has successfully measured chord-averaged flow with 10 μs time resolution [D. J. Den Hartog and R. J. Fonck, Rev. Sci. Instrum. 65, 3238 (1994)]. CHERS will provide high spatial resolution, critically needed for the investigation of fluctuations associated with the dynamo and transport. This beam will also be applied to Rutherford scattering for local measurements of majority ion velocity and temperature. Ion velocity is determined by the shift of the energy spectrum of the scattered neutral beam; ion temperature by the width of the energy spectrum. The scattered spectrum will be detected by two multichannel neutral particle analyzers. In order to achieve a time resolution of about 10 μs, the neutral beam equivalent current density and current must be high; both of these characteristics are hallmarks of the DINA beam design.
Hyper-Rayleigh scattering using 1907 nm laser excitation
Authors: Pauley M. A. , Wang C. H.
Published: July 2002

The experimental setup used to perform hyper-Rayleigh scattering at the near infrared wavelength of 1907 nm is described. The setup described is employed to measure the first molecular hyperpolarizabilities, β, of three new thiophene-based nonlinear optical chromophores. Although scattering at this wavelength is weak and the experiment requires great care, use of it allows one to obtain near dispersion-free first hyperpolarizability. Comparing the results with those obtained on the same chromophores using the 1064 nm excitation, we show that the two state model, which is commonly used to relate the β values at different wavelengths, fails to correlate the results at these two excitation wavelengths.
Effect of a metal–dielectric structure introduced in the plasma chamber of the Frankfurt 14 GHz electron cyclotron resonance ion source
Authors: Schächter L. , Stiebing K. E. , Dobrescu S. , Badescu-Singureanu Al. I. , Schmidt L. , Hohn O. , Runkel S.
Published: July 2002

A new approach of the possibility to significantly increase the high charge state ion beams delivered by electron cyclotron resonance (ECR) ion sources by using metal–dielectric (MD) structures characterized by high secondary electron emission properties is presented. The intensities of argon ion beams extracted from the 14 GHz electron cyclotron resonance ion source of the Institut für Kernphysik (IKF) der Johann Wolfgang Goethe-Universität in Frankfurt/Main were measured when a 26 mm diam disk of a specially treated MD structure (Al–Al2O3) was introduced axially close to the ECR plasma. The Ar beam intensities and charge-state distributions obtained with this disk are compared to measurements with disks of iron and pure aluminum at the same position relative to the plasma. All measurements were performed with the disk at the plasma chamber potential. The results with the MD structure show a net shift of the beam intensity towards higher charge states as compared with the other disk materials. Enhancement factors of the beam current of up to 10 (for Ar12+) when using a MD disk compared to the output when using an aluminum disk and up to 40 (for Ar11+) when using an iron disk were measured.
Nanometer focusing of hard x rays by phase zone plates
Authors: Yun W. , Lai B. , Cai Z. , Maser J. , Legnini D. , Gluskin E. , Chen Z. , Krasnoperova A. A. , Vladimirsky Y. , Cerrina F. , Di Fabrizio E. , Gentili M.
Published: July 2002

Focusing of 8 keV x rays to a spot size of 150 and 90 nm full width at half maximum have been demonstrated at the first- and third-order foci, respectively, of a phase zone plate (PZP). The PZP has a numerical aperture of 1.5 mrad and focusing efficiency of 13% for 8 keV x rays. A flux density gain of 121 000 was obtained at the first-order focus. In this article, the fabrication of the PZP and its experimental characterization are presented and some special applications are discussed.
Rotating analyzer–fixed analyzer ellipsometer based on null type ellipsometer
Authors: Russev Stoyan C. , Arguirov Tzanimir Vl.
Published: July 2002

The theory and design of an inexpensive rotating analyzer unit is presented, which allows a conventional null type ellipsometer to work as rotating analyzer–fixed analyzer automatic ellipsometer, without sacrificing the possibility to work in null mode. The mode switching is performed simply by adding or removing the rotating analyzer from its holder. It is shown that the rotating analyzer phase shift in rotating analyzer–fixed analyzer mode can be run-time determined from the measured Fourier coefficients. This avoids any need of recalibration procedure after mode switching and makes unnecessary plane of incidence synchronization, which further simplifies the needed hardware and reduces the errors connected with the phase shift instability of the output signal. The run-time phase shift calibration procedure and subsequent ellipsometric angles determination do not involve normalization of the output signal Fourier coefficients to the zeroth harmonic, eliminating in this way the influence of the dc component time drift.
Automated, low-temperature dielectric relaxation apparatus for measurement of air-sensitive, corrosive, hygroscopic, powdered samples
Authors: Bessonette Paul W. R. , White Mary Anne
Published: July 2002

An automated apparatus for dielectric determinations on solid samples was designed to allow cryogenic measurements on air-sensitive, corrosive, hygroscopic, powdered samples, without determination of sample thickness, provided that it is uniform. A three-terminal design enabled measurements that were not affected by errors due to dimensional changes of the sample or the electrodes with changes in temperature. Meaningful dielectric data could be taken over the frequency range from 20 Hz to 1 MHz and the temperature range from 12 to 360 K. Tests with Teflon and with powdered NH4Cl gave results that were accurate within a few percent when compared with literature values.
Wide-band low-noise tunnel current measurements in laser assisted experiments
Authors: Jersch J. , Demming F. , Fedotov I. , Dickmann K.
Published: July 2002

A composite current-to-voltage converter that shows a superior bandwidth and signal-to-noise ratio (bandwidth ∼50 MHz at 410 kΩ transimpedance) was designed. Two options for the input stage were tested: a high input impedance wide-band operational amplifier (OP) OPA655 (Burr–Brown) and a differential cascade which is based on the junction field effect transistors SST440 (Siliconics). By using a wideband current feedback OPA658 in the second stage the achieved bandwidth gain product is ∼10 GHz. A method for testing the performance of the preamplifier by using laser induced electron emission is described. The technique’s possibility for measurements of laser induced acoustic waves with high sensitivity and nanometer local resolution is demonstrated. For further applications the design of a wide-bandwidth, low-noise, single tunneling electron counting capable preamplifier is discussed.
Source of potential systematic error in retarding-potential Mott polarimeters
Authors: Lancaster J. C. , Kontur F. J. , Walters G. K. , Dunning F. B.
Published: July 2002

Studies using a compact retarding-potential Mott polarimeter have revealed an unanticipated source of potential systematic error that can introduce significant error in the measured polarizations. The origin of this is discussed together with a simple procedure that can be used to test for its presence.
Suspension last stages for the mirrors of the Virgo interferometric gravitational wave antenna
Authors: Bernardini A. , Majorana E. , Puppo P. , Rapagnani P. , Ricci F. , Testi G.
Published: July 2002

We describe the design of the last stage suspension for the mirrors of the Virgo gravitational wave detector and, in particular, its key mechanical elements: the marionette and the reaction mass. Since the whole suspension system is an electromechanical device, we present both its mechanical and electromagnetic components. The main features of the fully assembled prototype and those worked out for the Virgo final design are discussed.
Nonlinear field effects in quadrupole mass filters
Authors: Schulte J. , Shevchenko P. V. , Radchik A. V.
Published: July 2002

The performance of a quadrupole mass filter (QMF) generally degrades when using electrodes of circular cross section in place of mathematical ideal hyperbolic electrodes. The circular cross section of electrodes produces nonlinear resonances resulting in distortion and peak splitting in mass spectra. In addition, resonances reduce the actual working cross section, resulting in limited ion yield. In this article we study nonlinear resonances and intensities of resonance lines passing through the tip of the stability diagram of the QMF. We have found that balancing of multipole terms, rather than eliminating individual multipole terms, improves the sensitivity of the QMF considerably. The theory for assessing intensities of nonlinear resonances is presented in detail along with rescaling laws to adjust current QMF parameter settings. A general formula is presented from which the location and intensity of nonlinear can be derived, which then may be used for the design of special purpose QMFs.
Multipurpose high vacuum laser ablation/thin film deposition system
Authors: Gomlak Geoff , Kelly Michael C. , Panayotov Valentin G. , Koplitz Brent
Published: July 2002

An instrumental system is described that combines an apparatus for pulsed laser deposition (PLD) with a vacuum “suitcase” for transport of air-sensitive compounds. Laser ablation, plume diagnostics, and thin-film deposition are readily accomplished through a flexible design. The PLD apparatus consists of two cubes coupled via a bellows assembly and whose distance is easily changed pneumatically. For both the PLD apparatus and the vacuum suitcase, compact-design considerations have been implemented. Consequently, the footprint of the PLD apparatus is relatively small, and the vacuum suitcase can be transported easily between sites.
Inductive method for investigation of ferromagnetic properties of materials under pressure
Authors: Timofeev Yuri A. , Mao Ho-kwang , Struzhkin Viktor V. , Hemley Russell J.
Published: July 2002

A magnetic inductive method for investigating the magnetic properties of ferromagnetic substances over a broad range of temperatures under pressure in diamond-anvil cells is described. The proposed method exploits the fact that ferromagnetic substances change their dynamic magnetic susceptibility during magnetization by a constant external magnetic field up to the point of saturation. With increasing magnetic field, however, the magnetic properties of components of the high-pressure cell are essentially invariant. Therefore, the signal from the sample can be distinguished from that of the background caused asymmetries in the inductance system and the disposition of metal parts in the diamond-anvil cell. Measurements on CdCr2Se4 and iron demonstrate the feasibility of the method.
High current injectors for heavy ion driven inertial fusion
Authors: Kwan J. W.
Published: July 2002

Conceptual heavy ion driven inertial fusion (HIF) drivers typically have an array of up to 100 parallel beams each supplying a beam current of ≈0.25 A. According to space-charge limitations in beam extraction and in the low energy beam transport section, there are two options in building injectors for HIF drivers. The traditional way is to use low current density, large aperture, contact ionization sources. The major disadvantage of this approach is the very large size of the injector and matching section. The other option is to use high current density, multiple beamlet ion sources. From various scaling rules, it is found that the multiple beamlet approach is the more attractive one because it can be smaller, and more efficient, although the requirements on the ion source are more demanding.
The Frankfurt 200 mA proton source
Authors: Hollinger R. , Beller P. , Volk K. , Weber M. , Klein H.
Published: July 2002

For the International Fusion Materials Irradiation Facility (IFMIF) scenario, a 140 mA deuterium beam in continuous wave (cw) mode with an atomic yield of above 85% is required. The normalized root-mean-square emittance should be less than 0.2 π mm mrad at the entrance of a RFQ. As part of a conceptual design for IFMIF, a new ion source has been developed and is tested at the Institut für Angewandte Physik in Frankfurt. The ion source is of the volume type with a tungsten cathode driving the discharge. Both cw and pulsed mode are possible and were studied. First experiments were carried out with deuterium. 80 mA deuterons with a D+ fraction of above 90% were extracted [A. Maser et al., Rev. Sci. Instrum. 67, 1054 (1996)]. In order to avoid neutron generation by the d–d reaction, hydrogen was used instead of deuterium later on. As far as the ion source and plasma production processes are concerned, the use of hydrogen instead of deuterium is equivalent because of their similar atomic shells. Recently, a 200 mA proton beam at 55 kV was extracted in cw mode (according to Child–Langmuir, 200 mA H+ corresponds to 140 mA D+) with a H+ fraction of 93%. This article will give a detailed description of the ion source and the essential experimental results. Especially, the influence of important physical parameters (such as discharge current and strength of the filter field) on the H+ fraction was studied. By using different kinds of auxiliary gases, the influence on the H+ fraction and the noise level were investigated, too.
Beam instability excited by the magnetic filter
Authors: Naitou Hiroshi , Ohi Kazuo , Fukumasa Osamu
Published: July 2002

By the one-dimensional electrostatic particle simulation, the ion beam instability is observed in the plasma divided by the magnetic filter (MF). The strength of the MF is selected to influence only electron dynamics; ions move freely across the MF. There are grounded walls at the left and right ends of the system. Particles hitting the walls are absorbed there. The high temperature and high density plasma (main plasma) faces the low temperature and low density plasma (subplasma) across the MF located at the center of the system. The averaged space potential of the main plasma is higher than that of the subplasma. Due to the potential gap at the MF, ions in the main plasma are accelerated into the subplasma. Depending on the extent of the asymmetry of the system, steady or the periodic (dynamic) state manifests. For the periodic state, high density clumps get into the subplasma and excite the strong ion beam instability. The new clump comes into the subplasma when the old clump reaches the wall.