bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature mapping of compressed fusion pellets obtained by monochromatic imaging
Authors: Uschmann I. , Förster E. , Nishimura H. , Fujita K. , Kato Y. , Nakai S.
Published: July 2002

We report the first use of toroidally bent crystals to record two-dimensional, spatially resolved, monochromatic images of laser-produced fusion plasma. The electron temperature was determined by seeding the deuterium fuel with argon and evaluating the intensity ratio of the two monochromatic images in the Ar+ 17Ly β and the Ar+ 16He β lines. Silicon and germanium crystals were chosen to achieve high diffraction reflectivities. Spatial resolution better than 10 μm was achieved by bending the crystals toroidally to minimize the geometrical aberrations [E. Förster, K. Gäbel, and I. Uschmann, Laser Particle Beams 9, 135 (1991)]. Comparison of the two line intensities requires a calibrated imaging system. Monochromatic images of fusion pellets driven with the GEKKO XII glass laser system are presented.
Determination of Hα emissivities from line integrated brightness measurements on Alcator C-Mod
Authors: Kurz C. , Snipes J. A. , Terry J. L. , Labombard B. , Lipschultz B. , McCracken G. M.
Published: July 2002

Alcator C-Mod is equipped with a 227 chord visible light imaging system. Using a nonlinearly constrained least-squares algorithm, local emissivities have been obtained from the chordal brightness measurements without any assumptions about poloidal symmetry. The robustness of the inversion to noise and calibration errors as well as the spatial information (∼5-cm resolution) obtainable has been examined in detail. Some examples, demonstrating how results from the tomographic reconstruction of the Hα light can be used to calculate a particle confinement time and neutral density are given. Different interference filters in front of the arrays allow the same technique to be applied to other atomic species.
Direct determination of the band-gap states in hydrogenated amorphous silicon using surface photovoltage spectroscopy
Authors: Fefer E. , Shapira Y. , Balberg I.
Published: July 2002

Surface photovoltage spectroscopy (SPS) is used to determine the position of the deep defect state levels in undoped hydrogenated amorphous silicon (a-Si:H). The occupied and the empty levels, and their nature, are identified with a clear advantage over existing methods. The identification of the levels and the effect of light soaking on their concentration provides direct experimental confirmation of the main features predicted by thermal equilibrium models. The finding of other levels in a-Si:H materials of larger disorder further supports the recently proposed potential fluctuations model.
Numerical studies of the imaging properties of doubly focussing crystals and their application to ITER
Authors: Bitter M. , Fraenkel B. , Hill K. W. , Hsuan H. , von Goeler S.
Published: July 2002

Line brightness calculations for the parameters at the International Thermonuclear Experimental Reactor (ITER) and results from recent experiments on the Tokamak Fusion Test Reactor (TFTR) indicate that time-resolved measurements of the central ion temperature and other central plasma parameters should be feasible on ITER with nonperturbing amounts of krypton. Since the measurements will have to be performed in the presence of high fluxes of 14-MeV neutrons from DT-fusion reactions, the size of windows, apertures and x-ray detectors must be as small as possible. Under these conditions, the use of doubly focussing crystals can significantly enhance the signal-to-noise ratio. This paper describes numerical studies of the focussing properties of spherically bent crystals and their application to ITER.
X-ray diagnostic systems in the GAMMA 10 tandem mirror and new x-ray semiconductor-detector responses in the DIII–D tokamak
Authors: Cho T. , Hirata M. , Kohagura J. , Yatsu K. , Tamano T. , Snider R. T.
Published: July 2002

The energy response of a new semiconductor-detector array in the DIII–D tokamak for plasma x-ray diagnostics is characterized using synchrotron radiation at the Photon Factory (KEK) in Japan. This international cooperation research clarifies its good x-ray response ranging up to about 10 keV. The variations in detector-channel responses are also studied. Furthermore, new aluminum-coated x-ray semiconductor detectors are designed, fabricated, and characterized for the 10-keV-order DIII–D electron studies including the purpose of rf current-drive investigations; a flat response (the quantum efficiency η∼1) up to around 10-keV x rays, and a high efficiency (η≥0.3) even for the 20-keV x rays, are achieved. A wide variety of x-ray detection systems for the x-ray-energy range from a few tens eV to several hundreds keV in the GAMMA 10 tandem mirror is shown; that is, microchannel-plate tomography systems for the 0.01–60-keV x rays, a new ultra-low- energy-sensitive pure-Ge detector (0.2–50 keV), a Si(Li) detector (0.7–150 keV), a conventional pure-Ge detector (1.8–250 keV), and an NaI(Tl) detector (20–750 keV), silicon-surface-barrier detectors, and new semiconductor x-ray detectors for the purpose of the investigations of the effects of potentials on electron behavior in various tandem-mirror regions are represented.
An acoustically driven Kelvin probe for work-function measurements in gas ambient
Authors: Johnson Kendall B. , Hansen Wilford N.
Published: July 2002

A vibrating Kelvin probe has been developed for the measurement of work-function difference and outer potential difference measurements in gas ambient conditions. The Kelvin probe consists of a thin conducting diaphragm loosely stretched over the end of a tube. The conducting film is vibrated by an acoustic sound wave coming through the tube. This probe was especially developed for use over liquid as well as solid surfaces and is suited for dealing with problems encountered when making measurements in gas ambient and contaminating environments. The probe head, being aluminized Mylar, is cheap and disposable. Mercury and other liquids can easily destroy or contaminate other probes which are generally delicate and made of precious metal. This probe head also has a more stable work function than many precious metals normally used. Details are presented on construction, theory, operation, and performance. Conducting ionic solutions have been of interest and this probe also works well with them. A working definition of the work function of conducting ionic liquids is presented.
Light choppers: A new approach to the problem of heat load on samples and optical elements at ELETTRA beamlines
Authors: Lausi A. , Gambitta A. , Bernstorff S.
Published: July 2002

A high-vacuum compatible water-cooled rotating chopper has been designed and constructed for use at the electron storage ring ELETTRA in Trieste. By means of this device the time-integrated power load on downstream optical elements and the radiation doses on delicate samples can be greatly reduced, allowing to work with full source power during data acquisition times only, while the beam will be shut off during detector dead times.
Midplane Faraday rotation: A tokamak densitometer
Authors: Jobes F. C.
Published: July 2002

The density in a tokamak can be determined by measuring the Faraday rotation of a laser directed tangent to the toroidal field. If there is a horizontal array of such beams, then ne(R) can be readily obtained with a simple Abel inversion about the center line of the tokamak. For a large machine, such as ITER, TPX, or JT-60, a 10.6 μm laser would be appropriate. If the machine operated at a full field of 10–50 T m and a peak density of 2.5×1020/m3, the rotation angle would be quite large—about 15°–75° per pass. An elegant measurement system can be made up from a single laser beam diffracted off a moving grating to form a fan of ∼10 probe beams. With the addition of a few optical components to the system, the return beams can be recombined and sent to a single detector. In the detector there is a separate frequency component for both the right and left hand component of each ray. These can be separated electronically to provide a reference and probe signal for each ray; the difference in phase between the two signals is twice the Faraday rotation angle.
Temporal multiplexing of Thomson scattering for the study of laser-produced plasmas
Authors: Baldis H. A. , Labaune C.
Published: July 2002

We present a technique to obtain simultaneous recording of time-resolved Thomson scattering spectra at multiple locations in a laser-produced plasma. The multiplexing technique, although simple, makes possible for the first time the direct correlation of the behavior of plasma waves at different locations within the interaction region in a plasma. The application of this technique to the study of parametric instabilities in laser-produced plasmas is discussed, as well as the potential application to other diagnostics.
Creation of nanostructures on gold surfaces in nonconducting liquid
Authors: Chang T. C. , Chang C. S. , Lin H. N. , Tsong Tien T.
Published: July 2002

With the application of voltage pulses, mounds of 20 nm in diameter and 2 nm in height on the average can be created on a gold surface with very high efficiency in nonconducting liquid from a gold tip. The created mounds are similar to those produced in air. Tungsten and PtIr tips are also used in this study and the dominant shapes of created structures are craters and volcanolike mounds, respectively. Our data show that these nanometer structures are created by a mechanical contact between the tip and the sample.
A segmented Faraday cup for two-dimensional representation of the current distribution of an ion beam
Authors: Knolle D. , Ratschko D. , Gläser M.
Published: July 2002

A Faraday cup with 37 segments has been developed to measure the two-dimensional current distribution I=f(x,y) and the total beam current of an ion beam. With an overall cross-sectional area of about 3420 mm2, reproducible current measurements can be carried out down to some nanoamperes. The Faraday cup is used to measure ion beams in an energy range up to 25 keV and beam currents up to 10 mA. The current is determined on the basis of the voltage drop at selected metal film resistors. Initial results confirm good practical applicability in the analysis and adjustment of ion beams.
Electrochemical preparation of tungsten tips for a scanning tunneling microscope
Authors: Oliva A. I. , Romero G. A. , Peña J. L. , Anguiano E. , Aguilar M.
Published: July 2002

We present experimental results obtained during the electrochemical preparation of tungsten tips for a scanning tunneling microscope. Experiments were done with direct current and two kinds of electrolytes widely reported in the literature: KOH and NaOH. We report the effects of the applied voltage, time of etching, tip length, electrolyte concentration, wire diameter, and immersed portion as relevant parameters in the process. From the images obtained by a metallurgical microscope and a scanning electron microscope as well as from Auger and electron diffraction x-ray analysis the best conditions for W tip preparation were obtained. We found that KOH is better than NaOH as an electrolyte to prepare tips for scanning tunneling microscopy and that tip quality increases as the wire diameter and the immersed portion increases.
Analysis of scanning tunneling microscopy feedback system: Experimental determination of parameters
Authors: Anguiano E. , Oliva A. I. , Aguilar M. , Peña J. L.
Published: July 2002

We describe the experimental work necessary on a scanning tunneling microscopy (STM) system to obtain some important feedback parameters—to have stability and good imaging conditions—such as the mechanical resonance frequency ω0, the delay time τ, and the damping factor ζ. We study and analyze each one of the main components involved on the STM such as the feedback system, the piezoelectric elements, the rigidity of the mechanical structure (the mechanical resonance), and its relation with the scanning rate for imaging. We conclude that it is necessary to obtain these parameters with the STM in tunnel conditions, in order to consider the effects of the tip, surface contamination, and tip sample interaction. We also conclude that tripod based STM can be better than STM based on piezo tubes scanners.
A Fourier transform cavity ring down spectrometer
Authors: Engeln Richard , Meijer Gerard
Published: July 2002

We present a pulsed multiplex absorption spectrometer in which the sensitivity of the cavity ring down absorption detection technique is combined with the multiplex advantage of a Fourier Transform spectrometer. A description of the Fourier transform cavity ring down (CRD) spectrometer—substantiated with first experimental results on the atmospheric band of molecular oxygen—is given. It is shown that as in the case of normal CRD spectroscopy, the measurement is independent of light intensity fluctuations provided the spectral intensity distribution of the light source is known and is constant during the measurement.
Comment on ‘‘Comments on the use of asymmetric monochromators for x-ray diffraction on a synchrotron source’’ [Rev. Sci. Instrum. 66, 2174 (1995)]
Authors: Sanchez del Rio M. , Cerrina F.
Published: July 2002

In the article ‘‘Comments on the use of asymmetric monochromators for x-ray diffraction on a synchrotron source,’’ by Colin Nave, Ana Gonzalez, Graham Clark, Sean McSweeney, Stewart Cummings, and Michael Hart, Rev. Sci. Instrum. 66, 2174 (1995), paragraph II, the authors’ unfamiliarity with our modeling codes leads them to claim that our approach to treat bent-asymmetrically cut crystals in ray tracing calculations is incorrect. Since SHADOW is a widely used code, it is important to correct any misunderstandings, and we give here arguments to demonstrate that our approach is perfectly valid, and the arguments used by the authors to criticize our method are based on an unwarranted conclusion extracted from one of our previous articles. We show that SHADOW, when properly run, treats the cases raised exactly. Indeed, their arguments provide a nice benchmark test for verifying the accuracy of SHADOW
Helium partial pressure measurement in a deuterium environment
Authors: Denner T. , Finken K. H. , Mank G.
Published: July 2002

To study the removal of helium ash in present day, medium sized tokamaks, experiments with deuterium plasmas and helium puffs are conducted. Because D2 and He have almost the same mass, a spectroscopic method had been developed at TEXTOR where the He partial pressure in the exhaust line was measured by exciting the neutral gas in a Penning gauge and observing the characteristic emission lines of helium and deuterium. This method was limited to low pressures and concentrations because broad spectral lines from the deuterium molecules superimpose the He lines. By using a spectrometer and an intensified charge coupled device camera instead of optical filters and photomultipliers, it is now possible to record the interesting part of the spectrum with a time resolution of 20 ms. By subtracting the molecular spectrum of deuterium, helium concentrations from 2% on can be detected over about three orders of magnitude in pressure down to 2×10−6 mbar. He and D2 pressures are measured simultaneously. By another method the 58 nm resonance line of helium is observed and the crosstalk of the deuterium gas could be eliminated. Pressure measurements as low as 5×10−8 mbar and 1% He concentration are possible. A detection system utilizing a vacuum ultraviolet monochromator in combination with a channeltron has been tested.
The magnetic trapping mode of an electron beam ion trap: New opportunities for highly charged ion research
Authors: Beiersdorfer P. , Schweikhard L. , López-Urrutia J. Crespo , Widmann K.
Published: July 2002

Using x-ray spectroscopic techniques, we have investigated the properties of an electron beam ion trap (EBIT) after the electron beam is switched off. In the absence of the electron beam, bare, and hydrogenlike Kr35+ and Kr36+ ions remain trapped due to externally applied magnetic and electric fields for at least 5 s; xenon ions with an open L shell, i.e., Xe45+–Xe52+, remain trapped at least as long as 20 s. The ion storage time in this ‘‘magnetic trapping mode’’ depends on the pressure of background atoms as well as on the value of the externally applied trapping potential, and even longer ion storage times appear possible. The magnetic trapping mode enables a variety of new opportunities for atomic physics research involving highly charged ions, which include the study of charge transfer reactions, Doppler-shift-free measurements of the Lamb shift, measurements of radiative lifetimes of long-lived metastable levels, or ion-ion collision studies, by x-ray or laser spectroscopy, and mass spectrometry. Because the trap is filled in situ during the electron trapping phase, transfer losses associated with filling the trap from an external source are avoided. We present spectra of the K-shell emission from heliumlike and hydrogenlike Kr34+ and Kr35+ as well as Xe52+ and Xe53+ that are produced by charge transfer reactions in collisions between ions and neutral atoms. Marked differences with K-shell spectra produced by electron-impact excitation are evident. We use the measurements to infer the Lamb shift contribution to the energy of the 1s1/2–2p3/2 transition in hydrogenlike Xe53+ and determine it to be 31 276(12) eV. The measurement technique can be applied to any ion produced in an EBIT so that Doppler-shift-free Lamb shift measurements of hydrogenlike U91+ are within reach. We also illustrate the utility of the magnetic mode for lifetime determinations by measuring the 3.92(13) ms radiative decay of the 1s2s 3S1 level in heliumlike N5+.
In-situ long trace profiler for measurement of mirror profiles at third-generation synchrotron facilities (abstract)
Authors: Qian Shinan , Jark Werner , Takacs Peter Z. , Randall Kevin J. , Xu Zhongde , Yun Wenbing
Published: July 2002

X-ray mirrors have the potential to be subjected to extremely high heat loads at third-generation synchrotron radiation sources. In many cases, sophisticated cooling methods will be required to prevent surface distortion that would otherwise degrade the intrinsic source brightness. As a diagnostic for such mirrors, we have previously proposed to modify the long trace optical profiler for use within a UHV mirror chamber [Shinan Qian et al., Optical Engineering 34, 396 (1995)], thereby making it feasible to take profile measurements of mirrors irradiated with high power x-ray beams. We present in detail the mechanical design of a complete in-situ measurement. The objective of developing an in-situ measurement system is to aid the development of reliable, low-cost, high-heat-load substrates for mirrors and multilayers. This will provide a firm basis on which to design new optical elements that will be necessary as a result of performance enhancements to current machines, as well as future generations of storage rings.
Summary of the workshop on ‘‘X-ray Optics and Ray Tracing: Status and Needs’’ (invited)
Authors: Cerrina F. , Hulbert S.L. , Sanchez del Rio M.
Published: July 2002

A workshop on x-ray optics and ray tracing was held on October 18, 1995, at the Synchrotron Radiation Instrumentation conference held at Argonne. The object of the workshop was to exchange experience in ray-tracing calculations between the largest synchrotron radiation facilities. The introduction was carried out by Franco Cerrina, who made a review presentation of SHADOW, the only ray-tracing code that can be used for almost all the synchrotron radiation applications and surely is the most wide-spread and complete one. Then a total of seven speakers presented in short talks (20 minutes) their experience in the use of SHADOW at their respective facilities, their developments, suggestions, wishes, and complaints about some points of the package. Some of the presentations are available as contributed papers to the SRI’95 proceedings. In general, the speakers (representing all the U.S. Department of Energy synchrotron radiation sources) felt that the program was an essential part of the facilities experimental development.
Performance analysis of the commissioning filter and window assembly for insertion device beamlines at the Advanced Photon Source
Authors: Kuzay T. M. , Nian H. L.Thomas , Wang Z. , Shu D.
Published: July 2002

Although the Advanced Photon Source (APS) undulator beamlines are designed for windowless operation, a special window assembly will be used during the commissioning phase of the beamlines until sufficient operational experience is gained with the powerful undulator A photon beam. This assembly is called a ‘‘commissioning window.’’ The commissioning window assembly as designed consists of a 300-μm-thick filter (made of graphite), a fixed mask (made of Glidcop), a multipurpose transmitting filter/BPM disk (made of 127-μm-thick CVD diamond), and set of a double windows (made of 250-μm-thick beryllium). Due to the high total power and power density, the filter/window assembly must be carefully designed to guarantee longevity and satisfactory performance throughout its service. Hence extensive analytical work has been conducted on various thermal and structural aspects of the commissioning window assembly. This paper summarizes the analytical results and presents the expected performance characteristics of the as-designed commissioning window.
Determination of TFTR far-field neutron detector efficiencies by local neutron flux spectrum measurement
Authors: Jassby D. L. , Ascione G. , Kugel H. W. , Roquemore A. L. , Barcelo T. W. , Kumar A.
Published: July 2002

Neutron detectors have often been located on the tokamak fusion test reactor (TFTR) test cell floor 3 m or more from the vacuum vessel for ease of detector access, to reduce radiation damage, minimize count saturation problems, and to avoid high magnetic fields. These detectors include Si surface-barrier diodes, fission chambers, natural diamond detectors, and T2 production in a moderated 3He cell. To evaluate the performance of these detectors during deuterium–tritium (D–T) operation, we determined the neutron flux spectrum incident on the principal detector enclosure using nuclide sample sets containing Al, Ti, Fe, Co, Cu, Zn, Ni, Zr, Nb, In, and Au activation foils. Foils were installed and then removed after ample exposure to TFTR D–T neutrons. High efficiency, high purity Ge detectors were used for gamma spectroscopy of the irradiated foils. The incident neutron fluence and spectral distribution were unfolded from the measured results, and used to derive absolute detector efficiencies.
A study of CR-39 track response to charged particles from NOVA implosions
Authors: Phillips T. W. , Cable M. D. , Hicks D. G. , Li C. K. , Petrasso R. D. , Seguin F. H.
Published: July 2002

We have exposed CR-39 track recording material to a number of NOVA implosions. Radiation from the implosion passed through an array of ranging filters, which aided identification of the incident particles and their energies. The etching procedure was calibrated by including a piece of track exposed to DD protons from a small accelerator. For the same shots, we quantitatively compare the DD neutron yield with the DD proton yield determined from the track. In DT implosions, tracks produced by neutron interactions prevent observation of charged-particle tracks that are produced by the processes of knock on, secondary, or tertiary fusion.
Exact forward scattering of a CO2 laser beam from a relativistic plasma wave by time resolved frequency mixing in AgGaS2
Authors: Lal Amit , Gordon Dan , Marsh Ken , Wharton Ken , Clayton Chris , Joshi Chan
Published: July 2002

In the UCLA plasma beat wave accelerator, a high intensity two frequency CO2 laser (λ1=10.6 μm, λ2=10.3 μm) is used to drive a large amplitude relativistic plasma wave. The plasma wave acts as a moving phase grating and scatters the incident pump waves into Stokes and anti-Stokes sidebands (ω1−ωp, ω2+ωp). The observation of these sidebands in the forward direction confirms the presence of the relativistic plasmon, and also gives an estimate of the amplitude–length product (n1/n0×L) of the wave. Since the Stokes and anti-Stokes signals are picosecond pulses at 10.9 and 10.0 μm, respectively, this light cannot be time resolved directly on a conventional detector or streak camera. The forward scattered light can be analyzed, however, by mixing the 10 μm light with visible light from a laser diode (670 nm) in a nonlinear crystal (AgGaS2) to produce frequency shifted light at 630 nm. The intensity of the 630 nm light is proportional to the product of the intensities of the two incident laser pulses, and can be time resolved on a streak camera. Experimental results for the plasma wave amplitude, spatial length, and temporal length are shown.
Electrodynamic trapping and manipulation of particle clouds
Authors: Vehring R. , Aardahl C. L. , Davis E. J. , Schweiger G. , Covert D. S.
Published: July 2002

Apparatus and techniques were developed to electrodynamically trap and manipulate groups of microparticles. The equipment consists of a vibrating orifice aerosol generator, an inductive particle charger, a plenum chamber, and a double-ring electrodynamic balance. Salt particles (NaNO3) of controllable and measurable mass and charge were produced and introduced into the balance in nitrogen at flow rates up to 25 cm3/min. Ordered arrays of any number of particles up to 26 were assembled and manipulated. Methods for compressing the arrays are presented, and controlled ejection of single particles from a trapped array is demonstrated. Particles of opposite polarity were successfully levitated and kept apart, and aggregation of these particles was then induced by changing the electric field. Raman spectra were recorded for multiple salt particles, each having a diameter of 3.5 μm, by aligning them in a laser beam. The enhanced Raman signal is compared with that from a single particle isolated from the array. From the results, a detection limit of 0.4 pg per particle was estimated.
New optical methods for short wavelength hot plasma diagnostics
Authors: Kantsyrev V. , Bruch R.
Published: July 2002

We have developed new types of experimental methods for high-temperature plasma diagnostics based on both glass capillary converters (GCCs) and multilayer mirrors (MLMs), where the optical GCC device provides guiding, focusing, and polarization analysis of short wavelength radiation with a large bandwidth, and the MLM elements are used for dispersing, focusing, and polarization sensitive studies of radiation within a narrow bandwidth. In particular, we report here for the first time, to the best of our knowledge, the development and testing of such new optical diagnostic devices for: (i) pinhole chamber with GCC, (ii) GCC converter for time-resolved x-ray measurements, (iii) polarimeters–spectrometers with GCC and MLM for measurements of polarization and spectral characteristics of short wavelength radiation, and (iv) high sensitivity extreme ultraviolet spectrometers.
One- and two-dimensional fast x-ray imaging of laser-driven implosion dynamics with x-ray streak cameras
Authors: Shiraga H. , Heya M. , Nakasuji M. , Miyanaga N. , Azechi H. , Takabe H. , Yamanaka T. , Mima K.
Published: July 2002

One- (1D) and two-dimensional (2D) x-ray imaging techniques with x-ray streak cameras have been developed and utilized for investigating implosion dynamics of laser fusion targets. Conventional streaked 1D images of the shell motion of the imploding target was recorded together with the time-resolved 2D multi-imaging x-ray streak images of the core shapes on the same x-ray streak camera. Precise comparison of the core dynamics between the experimental and simulation results was performed with an accuracy of 30 ps by fitting the trajectories of the x-ray emission from the imploding shell.
Investigation of the response of superconducting quantum interference devices to temperature variation
Authors: Schöne S. , Mück M. , Thummes G. , Heiden C.
Published: July 2002

We have measured the temperature dependent change ∂Φ/∂T in the flux signal of a superconducting quantum interference device (SQUID) operating in a flux locked loop. Thin film niobium dc SQUIDs were used for these investigations. One and the same device could be operated either as dc or rf SQUID allowing one to compare the effect of temperature variation in both modes of operation. We have found that relaxation of trapped flux appears to be the dominant result of temperature variation. The asymmetry of the two critical junction currents in dc SQUID operation could be seen, as well as an influence of an external magnetic field on ∂Φ/∂T. This influence was an order of magnitude smaller when the device was operated as an rf SQUID, compared to dc SQUID operation. By the use of a high frequency demagnetization process, ∂Φ/∂T could be reduced from typical values of about 0.3 Φ0/K to less than 0.05Φ0/K in certain cases.
A novel method for diagnosing the growth of subresolution-scale perturbations
Authors: Budil K. S. , Remington B. A. , Perry T. S. , Rubenchik A. M. , Berning M. , Peyser T. A. , Louis H. , Demiris T. , Wallace R.
Published: July 2002

We have demonstrated a technique for diagnosing the growth of subresolution-scale perturbations by the appearance of longer-wavelength, coupled modes once the growth has proceeded into the nonlinear regime. Comparison of the growth rate of this larger scale feature with numerical simulations can then be used to infer the growth rates of the initial perturbations. This experiment was conceived as an analog of large-scale computer simulations where the large eddy approximation is applied. There a subgrid-scale model is used to represent the effects of small scales on large-scale motion, which is directly numerically simulated.
Soft x-ray and Auger electron spectroscopy of single and double electron capture processes in slow Ne8++He collisions
Authors: Bliman S. , Cornille M. , Langereis A. , Nordgren J. , Bruch R. , Phaneuf R. , Swenson J. , Schneider D.
Published: July 2002

We have performed high resolution extreme ultraviolet (EUV) photon and Auger electron measurements to elucidate single and double capture processes in Ne8++He single collisions at 80 keV impact energy. Numerous new transitions both in the Auger and the EUV spectra have been identified by means of extensive theoretical calculations and correlation diagrams. These data are of importance for the modeling of impurities in plasma and for future plasma diagnostics.
An investigation of the opacity of high-Z mixture and implications for inertial confinement fusion hohlraum design
Authors: Wang P. , MacFarlane J. J. , Orzechowski T. J.
Published: July 2002

We use an unresolved transition array model to investigate the opacities of high-Z materials and their mixtures which are of interest to indirect-drive inertial confinement fusion hohlraum design. In particular, we report on calculated opacities for pure Au, Gd, and Sm, as well as Au–Sm and Au–Gd mixtures. Our results indicate that mixtures of Au–Gd and Au–Sm can produce a significant enhancement in the Rosseland mean opacity. Radiation hydrodynamics simulations of Au radiation burnthrough are also presented, and compared with NOVA experimental data.
Improved multistage wide band laser frequency stabilization
Authors: Kawamura Seiji , Abramovici Alex , Zucker Michael E.
Published: July 2002

Suppression of laser frequency fluctuations is an essential technology for planned interferometric detectors for astrophysical gravitational waves. Because of the low degree of residual frequency noise which is ultimately required, control topologies comprising two or more cascaded loops are favored. One such topology, used in the Laser Interferometer Gravitational-Wave Observatory 40 m interferometer, relied on electro-optic Pockels cell phase correction as a fast actuator for the final stage. This actuation method proved susceptible to spurious amplitude modulation effects, which provided an unintended parasitic feedback path. An alternate arrangement, which achieves comparably effective frequency stabilization without using a phase correcting Pockels cell, was introduced and successfully tested.
E∥B energy-mass spectrograph for measurement of ions and neutral atoms
Authors: Funsten H. O. , McComas D. J. , Scime E. E.
Published: July 2002

Real-time measurement of plasma composition and energy is an important diagnostic in fusion experiments. The Thomson parabola spectrograph described here utilizes an electric field parallel to a magnetic field (E∥B) and a two-dimensional imaging detector to uniquely identify the energy-per-charge and mass-per-charge distributions of plasma ions. An ultrathin foil can be inserted in front of the E∥B filter to convert neutral atoms to ions, which are subsequently analyzed using the E∥B filter. Since helium exiting an ultrathin foil does not form a negative ion and hydrogen isotopes do, this spectrograph allows unique identification of tritium ions and neutrals even in the presence of a large background of 3He.
A study for the installation of the TEXT heavy-ion beam probe on DIII-D
Authors: Edmonds P. H. , Solano E. R. , Bravenec R. V. , Wootton A. J. , Schoch P. M. , Crowley T. P. , Hickok R. L. , West W. P. , Leuer J. , Anderson P.
Published: July 2002

An assessment of the feasibility of installing the TEXT 2 MeV heavy-ion beam probe on the DIII-D tokamak has been completed. Detailed drawings of the machine cross section were imported into the CAD application AutoCAD. A set of programs written in AutoLisp were used to generate trajectories. Displays of the accessible cross section of the plasma, scan lines for the entire range of primary beam energy and injection angle ranges, and sample–volume dimensions can be rapidly generated. Because of the large deflection between the primary input beam and the emergent secondary beam, either the analyzer needs to be tracked over a ±20° angle or secondary poloidal deflector plates need to be installed at the exit port. Toroidal deflector plates will be installed at both the injection and exit ports to compensate for toroidal displacements and deflections. The sample volumes generated by this procedure are within a few centimeters of the locations derived from a full three-dimensional calculation.
Progress toward a microsecond duration, repetitively pulsed, intense-ion beam for active spectroscopic measurements on ITER
Authors: Davis H. A. , Olson J. C. , Reass W. A. , Barnes Cris W. , Bartsch R. R. , Coates D. M. , Hunt J. W. , Schleinitz H. M. , Lovberg R. H. , Greenly J. B.
Published: July 2002

We describe the design of an intense, pulsed, repetitive, neutral beam based on magnetically insulated diode technology for injection into ITER for spectroscopic measurements of thermalizing alpha particle and thermal helium density profiles, ion temperature, plasma rotation, and low Z impurity concentrations throughout the confinement region. The beam is being developed to enhance low signal-to-noise ratios expected with conventional steady-state ion beams because of severe beam attenuation and intense bremsstrahlung emission. A 5 GW (e.g., 100 keV, 50 kA) 1 μs duration beam would increase the charge exchange recombination signal by 103 compared to a conventional 5 MW beam.
Measurement of hydrogen and lithium ion energy densities on PBFA II using direct nuclear activation diagnostics
Authors: Ruiz C. L. , Cooper G. W. , Chambers G. , Schmidlapp F. A.
Published: July 2002

In the light-ion-beam fusion program at Sandia National Laboratories an intense lithium beam is being developed to drive inertial confinement fusion targets. An important issue is the purity of the beam. To assess this concern, direct nuclear activation diagnostics based on the reactions Li7(p,n)7Be, B10(p,α)7Be, and F19(7Li,d)24Na were fielded to measure the energy densities of hydrogen and lithium in the beam. The hydrogen beam energy density was measured to be less than 2% of the lithium beam energy density on a majority (10) of the 19 LiF anode shots taken and was always less than 10%. The total hydrogen energy in the beam ranged from only 0.5–10 kJ. Over this shot series increasing efforts were made to clean the anode prior to each shot. In general, there was a modest reduction in the hydrogen energy fraction with improved cleaning, but no corresponding increase in the lithium energy density was seen. The lithium energy density as a function of location was also measured and found to typically vary by factors of 1.5–4 over the diode.
How to beat the low resolution of multilayer mirror spectra (invited)
Authors: Regan S. P. , Fournier K. B. , May M. J. , Soukhanovskii V. , Finkenthal M. , Moos H. W.
Published: July 2002

The soft x-ray and extreme ultraviolet (XUV) impurity emissions from tokamaks (10 Å<λ<304 Å) have been extensively studied with high-resolution grazing incidence spectrographs, and atomic physics models predicting spectral line brightnesses have been benchmarked against these experimental data. This, together with the ability to perform large amounts of accurate atomic physics computations, enables the relaxation on the requirement for high resolution spectra. The multilayer mirror (MLM) is a low resolving power (λ/δ λ<100) XUV dispersive/reflective optical element that obeys the Bragg law of reflection. MLM based monitors are compact, high-photon-throughput diagnostics capable of extracting XUV emissions of impurities from the harsh environment of large fusion reactor-type devices. We will show how atomic physics modeling can be used to extract the XUV spectral line brightnesses measured with low-resolution, high-photon-throughput, MLM-based devices. The Plasma Spectroscopy Group at The Johns Hopkins University has investigated the application of MLM based diagnostics for magnetically confined fusion plasmas: MLM based monitors have been constructed for and extensively used on DIII–D, Alcator C-Mod, TEXT, Phaedrus-T, and CDX-U to study the impurity behavior of elements ranging from He to Mo. Experiments were also performed in which MLMs were irradiated to a fast neutron fluence of 1.1×1019 n cm−2 at 270–300 °C, and the preliminary results indicate that MLMs would be a good first wall reflector for fusion plasmas. Future applications of MLM based devices to study divertor coolants (Ne, Ar, and Kr emissions) and “killer pellet” (W emissions) experiments will also be discussed.
A modified molecular beam instrument for the imaging of radicals interacting with surfaces during plasma processing
Authors: McCurdy Patrick R. , Bogart K. H. A. , Dalleska N. F. , Fisher Ellen R.
Published: July 2002

A new instrument employing molecular beam techniques and laser induced fluorescence (LIF) for measuring the reactivity of gas phase radicals at the surface of a depositing film has been designed and characterized. The instrument uses an inductively coupled plasma source to create a molecular beam containing essentially all plasma species. A tunable excimer pumped dye laser is used to excite a single species in this complex molecular beam. LIF signals are imaged onto a gated, intensified charge coupled device (ICCD) to provide spatial resolution. ICCD images depict the fluorescence from molecules both in the molecular beam and scattering from the surface of a depositing film. Data collected with and without a substrate in the path of the molecular beam provide information about the surface reactivity of the species of interest. Here, we report the first measurements using the third generation imaging of radicals interacting with surfaces apparatus. We have measured the surface reactivity of SiH molecules formed in a 100% SiH4 plasma during deposition of an amorphous hydrogenated silicon film. On a 300 K Si (100) substrate, the reactivity of SiH is near unity. The substrate temperature dependence (300–673 K) of the reactivity is also reported. In addition, reactivity measurements for OH molecules formed in a water plasma are presented. In contrast to the SiH molecule, the reactivity of OH radicals is 0.55±0.05 on the surface of a Si (100) substrate.
New spectrometer for grazing exit x-ray fluorescence
Authors: Pérez Roberto D. , Sánchez Héctor Jorge
Published: July 2002

Among the x-ray fluorescence techniques using energy dispersive systems, the excitation in the total reflection regime is becoming widespread. This technique may be applied to surface analysis if the fluorescent radiation emitted by the sample is measured as a function of the grazing incidence angle. The main limitation in performing this sort of analysis is the need to use a monochromator, which notably reduces the incident flux of radiation. Besides, the method requires the radiated surface to be perfectly smooth and polished and to have a total length of some centimeters. A similar technique known as grazing exit x-ray fluorescence presents certain advantages and is easier to implement. By this method, fluorescent photons in terms of the grazing exit angle are detected. In this work, a spectrometer for performing surface analysis at grazing exit is described, the different experimental situations are analyzed, and some measurements performed with this device are shown.
Effects of air damping in noncontact resonant force microscopy
Authors: Lévêque G. , Girard P. , Belaidi S. , Cohen Solal G.
Published: July 2002

The action of viscous forces on the motion of an atomic force microscope cantilever operating in resonant mode in air is modelized. We demonstrate that for most applications, the vibration of a V shaped cantilever in the air can be approximated to a simple damped oscillator. The damping factor is distance dependent and includes terms issued of the interaction of both cantilever and tip with the sample. Expressions for the various damping forces have been derived and related to the geometry of the tip-cantilever system. They lead to an expression which quantifies the variations in oscillation amplitude versus tip sample distance.
A new compact 60 kV Mott polarimeter for spin polarized electron spectroscopy
Authors: Petrov V. N. , Landolt M. , Galaktionov M. S. , Yushenkov B. V.
Published: July 2002

A compact 60 kV Mott polarimeter has been constructed, tested, and calibrated especially for the local analysis of surface and two-dimension magnetism by means of electron spectroscopy with spin resolution. The use of construction combining spherical accelerating field with the absence of retarding potential after electron scattering provides low sensitivity of the polarimeter to movements of the analyzed electron beam and changes in its diameter. Special silicon surface-barrier detectors with large electron-optical acceptance provide efficiency ∈(≡Seff2×I/I0) about ≈2.5×10−4. The unique fast electronics allow to work with maximum count rate of detected electrons up to 5×106 counts/s. As a result, there is the possibility to calibrate the polarimeter (to calculate the effective Sherman function Seff) by extrapolation of the measured asymmetry to the high level of discrimination. This instrument is compact, fully UHV compatible and may be used in other fields of solid state physics, atomic physics, and physics of high energies.
Electron-impact dissociation of molecular nitrogen in atmospheric-pressure nonthermal plasma reactors
Authors: Penetrante B. M. , Hsiao M. C. , Merritt B. T. , Vogtlin G. E. , Wallman P. H. , Kuthi A. , Burkhart C. P. , Bayless J. R.
Published: July 2002

This letter presents measurements of the specific energy consumption (eV per molecule) for electron-impact dissociation of N2 (e+N2→e+N+N) in a pulsed corona and an electron beam reactor. Measurements were done using 100 pm of NO in N2. In this mixture the removal of NO is dominated by the reduction reaction N+NO→N2+O. By measuring the specific energy consumption for reduction of NO, these experiments provide a good measure of the specific energy consumption for electron-impact dissociation of N2. The specific energy consumption using pulsed corona processing is 480 eV per dissociated N2 molecule. For electron beam processing, the specific energy consumption is 80 eV per dissociated N2 molecule.
A sensitive broadband high-frequency electron spin resonance/electron nuclear double resonance spectrometer operating at 5–7.5 mm wavelength
Authors: Seck M. , Wyder P.
Published: July 2002

A novel high-frequency electron spin resonance (ESR) spectrometer is described. The features are high sensitivity, a continuously tunable operating frequency of 40–60 GHz, a cylindrical cavity with a novel coupling scheme, and simultaneous detection of absorption and dispersion. A radio frequency coil can be integrated into the cavity for electron nuclear double resonance (ENDOR) experiments. ESR and ENDOR spectra of a test sample are presented in order to demonstrate in particular the scientific potential of a variable-frequency spectrometer.
Increased x-ray production efficiency from transition radiators utilizing a multiple-pass electron beam
Authors: Piestrup M. A. , Lombardo L. W. , Cremer J. T. , Retzlaff G. A. , Silzer R. M. , Skopik D. M. , Kaplin V. V.
Published: July 2002

We have observed x-ray emission from transition radiators placed inside an electron storage ring. The radiators were thin (0.18–9 μm) and the electrons were of sufficient energy (118–252 MeV) so that the electrons passed through the radiators many times. This effectively increased the efficiency of the radiators (photons/electron). The electron-beam lifetime in the storage ring was measured, and used to determine the number of passes through each radiator. Multiple passes between 5 and 385 were observed, thus giving a corresponding increase in radiator efficiency. Five electron-beam energies (118, 151, 181, 213, and 252 MeV) were used on a variety of radiators consisting of both single and multiple foils and different materials (C, Al, Cu, Ta). The total output power and the spatial distribution of the x rays were measured. The emission pattern was the typical annular cone of transition radiation. Single-foil transition radiation was observed whose total output power was comparable to that of multiple-foil radiators composed of the same material. Thus, for this range of parameters, the product of the number of foils times the number of passes was a constant.
A combined high-pressure reaction cell-ultrahigh vacuum chamber with sample transfer system
Authors: Jachimowski T. A. , Lauterbach J.
Published: July 2002

We have designed a high-pressure reaction cell and sample transfer system as an addition to an existing ultrahigh vacuum chamber. The system enables us to study catalytic reactions on both single crystals and polycrystalline foils over a large range of pressures from 10−4 Torr to 1 atm. The key advantage of the setup is that the thermocouple is in direct contact with the sample, providing exact measurement of the sample temperature, while allowing transfer between two different manipulators. We demonstrate the utility of the experimental setup by monitoring oscillations in the rate of carbon monoxide oxidation over a platinum catalyst.
Development of the third generation electron cyclotron resonance ion source
Authors: Lyneis C. M. , Xie Z. Q. , Taylor C. E.
Published: July 2002

The LBNL third generation electron cyclotron resonance (ECR) ion source has progressed from a concept to the fabrication of a full scale prototype superconducting magnet structure. This new ECR ion source will combine the recent ECR ion source techniques that significantly enhance the production of high charge state ions. The design includes a plasma chamber made from aluminum to provide additional cold electrons, three separate microwave feeds to allow multiple-frequency plasma heating (at 10, 14, and 18 GHz or at 6, 10, and 14 GHz) and very high magnetic mirror fields. The design calls for mirror fields of 4 T at injection and 3 T at extraction and for a radial field strength at the wall of 2.4 T. The prototype superconducting magnet structure which consists of three solenoid coils and six race track coils with iron poles forming the sextupole has been tested in a vertical Dewar. After training, the sextupole magnet reached 105% of its design current with the solenoids off. With the solenoids operating at approximately 70% of their full design field, the sextupole coils operated at 95% of the design value which corresponds to a sextupole field strength at the plasma wall of more than 2.1 T.