bluuebunny/crossref_metadata_2025 huggingface dataset:
Successful modeling, design, and test of electron cyclotron resonance ion sources
Authors: Heinen A. , Rüther M. , Ducrée J. , Leuker J. , Mrogenda J. , Ortjohann H. W. , Reckels E. , Vitt Ch. , Andrä H. J.
Published: July 2002

Plasmas in electron cyclotron resonance ion sources (ECRIS) are collisionless and can therefore be simulated by only following the motion of electrons in the confining static magnetic and oscillating microwave field of ECRIS. The experimental performance of three different ECRIS is successfully compared to calculated spatial electron (plasma) and electron energy density as well as to the energy spectrum and the average energy of the electrons. Further simulations suggest a new and better design of an ECRIS, the good experimental performance of which corresponds to the predictions.
Status report on a dc 130 mA, 75 keV proton injector (invited)
Authors: Sherman Joseph , Arvin Andrew , Hansborough Lash , Hodgkins David , Meyer Earl , Schneider J. David , Smith H. Vernon , Stettler Matthew , Stevens Ralph R. , Thuot Michael , Zaugg Thomas , Ferdinand Robin
Published: July 2002

A 110 mA, 75 keV dc proton injector is being developed at Los Alamos. A microwave proton source is coupled to a two solenoid, space-charge neutralized, low-energy beam transport (LEBT) system. The ion source produces 110 mA proton current at 75 keV using 600–800 W of 2.45 GHz discharge power. Typical proton fraction is 85%–90% of the total extracted ion current, and the rms normalized beam emittance after transport through a prototype 2.1 m LEBT is 0.20 (πmm mrad). Beam space-charge neutralization is measured to be >98% which enables the solenoid magnetic transport to successfully match the injector beam into a radio-frequency quadrupole. Beam simulations indicate small emittance growth in the proposed 2.8 m low-energy demonstration accelerator LEBT. The LEBT also contains beam diagnostics, steering, and a beam deflector for variable duty factor and accelerator fast protect functions. The injector beam availability status is also discussed.
Development of an in-vacuum minipole undulator array for National Synchrotron Light Source In-Vacuum UNdulator
Authors: Tanabe T. , Marechal X. , Tanaka T. , Kitamura H. , Stefan P. , Krinsky S. , Rakowsky G. , Solomon L.
Published: July 2002

An in-vacuum minipole (short period) insertion device has been developed in a collaboration between SPring-8 and the National Synchrotron Light Source (NSLS). The magnetic arrays were assembled, field measured, corrected, and vacuum tested by SPring-8 and were installed in an NSLS-developed chamber with mechanical parts in the NSLS X-Ray Ring (E=2.584 GeV) in May 1997 and a successful commissioning of the device was carried out in June 1997. The device is made of permanent magnets with 30.5 periods and a period length of 11 mm. It is designed to produce fundamental radiation at 4.6 keV, and with a modest value of deflection parameter (K=0.7 at 3.3& mm gap) enables higher harmonics to be used as well, for a variety of experiments. A detailed description of the mechanical support and vacuum chamber will be reported elsewhere. We describe technical challenges encountered in constructing this type of device, and present an outline of our collaboration.
A multidetection, multicoincidence spectrometer for (e,2e) and (e,3e) electron impact ionization measurements
Authors: Duguet A. , Lahmam-Bennani A. , Lecas M. , El Marji B.
Published: July 2002

A new spectrometer for the coincidence study of (e,2e) single ionization, and e,(3-1)e or (e,3e) double ionization by electron impact is described. The system is based on two double toroidal analyzers for the ejected electrons and a cylindrical electrostatic analyzer for the scattered electrons. It allows angular and energy distributions of the ejected electrons to be measured over almost the totality of the collision plane, using dual two-dimensional position sensitive detectors. The design and operation of the spectrometer is described with a special emphasis on the imaging properties of the system. The performance (energy and angular resolutions,…) and the calibration of the spectrometer are discussed and sample results for (e,2e), e,(3-1)e and (e,3e) experiments on the rare gases are presented.
Low-cost design of 35 mm drum camera for high-resolution, high-speed image analysis
Authors: Lawson N. J. , Liow J.-L.
Published: July 2002

A design for a continuous access high-speed 35 mm photographic imaging system with a maximum frame rate of 3000 frames/s is presented. The design is based on a readily available 35 mm camera body and other inexpensive components and can operate with f numbers of f5.6 and above. To demonstrate the system, results are recorded of a water drop impacting a free surface with a resolution per frame of 1200×2500 grayscale pixels and 152 third frame images per run.
Ultrahigh vacuum apparatus for x-ray powder diffraction in surface science
Authors: Peters K. F. , Chung Y.-W. , Cohen J. B.
Published: July 2002

A laboratory apparatus for surface science and in situ x-ray powder diffraction studies of highly dispersed particles has been constructed. The chamber incorporates standard sample preparation and characterization facilities into a high-flux x-ray diffraction setup, capable of two-circle goniometry with 0.1 nm−1 Q resolution from samples as thin as 1 nm average thickness (1 μg), at an elevated temperature under ultrahigh vacuum, in minutes.
Fiber-optic coupled probe for scanning optically active materials
Authors: Trost Peter K.
Published: July 2002

A novel confocal microscope probe which uses fiber-optic coupling has been developed and applied to DNA sequencing. The probe consists of simple optical elements with a circular fiber optic bundle. In the optical head, spherical aberration and defocus are used to separate the two beam paths involved in the confocal geometry. This design provides a modular system which simplifies the design, manufacture, and maintenance of a commercial device. Presented are the results of using the probe in a DNA sequencing application where performance is determined to be at a comparable level with standard DNA sequencing machines.
Automatic compensation technique for alternating current metrology based on synchronous filtering
Authors: Callegaro Luca , D’Elia Vincenzo
Published: July 2002

In alternating current electrical metrology, the balancing procedure is the act of reduction to zero of a measured terminal-pair voltage (or current), accomplished via injection of a compensation voltage (current) in the circuit. An automatic compensation technique is described here: the terminal-pair voltage is continuously sensed, by means of vector synchronous detection, and the injected voltage is directly synthesized from the main circuit source. An implementation of the compensation technique, realized with analog electronics, permits compensation of audio frequency small voltages down to the nV range, with settling time in the order of milliseconds.
Polarization characteristics of longitudinally pumped pulsed dye laser
Authors: Tiwari S. K. , Mehendale S. C.
Published: July 2002

Experimental results on the polarization properties of the emission from a grating-tuned dye laser longitudinally pumped by 532 nm laser pulses are presented. Use of p-polarized pump emission was found to result in linearly polarized dye laser emission without an intracavity polarizer.
Fast photomultiplier tube gating system for photon counting applications
Authors: Creasey David J. , Halford-Maw Peter A. , Heard Dwayne E. , Spence John E. , Whitaker Benjamin J.
Published: July 2002

A normally “on” linear-focused 14-stage end-window photomultiplier tube (PMT) (Electron Tubes Limited 9893Q/100B), designed for fast photon counting, has been gated through control of the voltage applied to the first dynode. The gating circuit reduces the gain of the PMT during a laser pulse, in order to discriminate against the detection of scattered light, and then increases the gain promptly to observe extremely low levels of laser-induced fluorescence (LIF). An extinction factor for the laser scattered photons of >105 was observed, and has enabled count rates for photons due to LIF as low as 1 Hz to be measured for a laser pulse-repetition frequency of 7 kHz. The rise of the PMT gain is monitored directly by observation of the fluorescence using time-resolved photon counting, and the PMT turn-on time is 30 ns. No significant distortion of the temporal profile of the fluorescence was observed during PMT turn-on. The system, which can also be operated in ungated mode, is rugged and reliable, and has been employed outdoors during atmospheric field measurements of the hydroxyl radical using LIF. The gating circuit is suitable for the rejection of laser scattered light in applications with extremely low levels of fluorescence on the submicrosecond timescale.
The optimum dynamics of preset count digital rate meter algorithms
Authors: Arandjelović V. Dj. , Koturović A. M.
Published: July 2002

The concept of “quality of measurement,” Q, of the count rate digital measurement algorithm has been applied to the class of preset count digital rate meter algorithms. The best quality corresponds to the minimum of (τ×ε) product, where τ is the response time of the algorithm to a sudden change in the average count rate and ε is the fractional standard deviation of the steady-state measurement of a constant average count-rate pulse stream. Analytical expressions for τ and ε of digital rate meter algorithms are used to calculate maximum values of Q for both weighted moving average and exponential algorithms. The values of the basic algorithm parameters, k for the moving average, and a for the exponential algorithm to achieve these maximum values of Q are derived for both algorithms. A comparison of the present results with the corresponding results obtained for preset time algorithms of these types has been carried out.
Coulomb blockade thermometer: Tests and instrumentation
Authors: Kauppinen J. P. , Loberg K. T. , Manninen A. J. , Pekola J. P. , Voutilainen R. A.
Published: July 2002

Coulomb blockade thermometry (CBT) provides a simple method for absolute thermometry in every day laboratory use at cryogenic temperatures. CBT has been found insensitive to even high magnetic fields. We review the principles and the operation of CBT and the fabrication of the sensors, and present new data on radiation hardness and stability of the sensors. We describe the instrumentation of CBT in detail. We have developed two signal conditioning units for CBT measurements. One is a modified alternating current resistance bridge, a versatile laboratory instrument operating with a PC computer, and the other one is a simple stand-alone instrument for direct temperature reading. Test results on their performance are also presented. Both prototypes have a short-term reproducibility of 0.3% or better in temperature measurement.
New type of compact electrostatic energy analyzer adequate to measurement of charge exchange neutral particles with a low counting yield
Authors: Goto T. , Ishii K. , Katsuki Y. , Kikuno N. , Goi Y. , Nagasaki M. , Ishibashi N. , Ono Y. , Yamanashi M. , Ichimura M. , Tamano T. , Yatsu K.
Published: July 2002

A new type of compact electrostatic cylindrical energy analyzer originally providing a deflection angle of π/22 has been designed with the aim of measuring energy spectra of charge exchange neutral particles in the tandem mirror GAMMA10. The essential advantage of the use of this analyzer is that a large entrance aperture can be adopted with high energy resolution so that high incident current is analyzed, while the radius of the cylindrical electrodes remain compact. Characteristics of the analyzer are discussed using computer simulations of ion trajectories including an effect of fringing field obtained by finite-element method as well as small-angle scattering in stripping collisions of hydrogen atoms.
Operation of the TFTR pellet charge exchange diagnostic in the pulse counting mode during H+ radio frequency minority heating
Authors: Medley S. S. , Petrov M. P. , Roquemore A. L. , Fisher R. K.
Published: July 2002

The pellet charge exchange technique on TFTR has been used primarily to obtain active charge exchange measurements using a high-energy (0.5–4.0 MeV) neutral particle analyzer (NPA) in conjunction with impurity pellet injection (Li and B) with the scintillator-photomultiplier detector system operated in the current mode. While passive measurements using pulse counting were also obtained using this instrumentation, operation in this mode was very restrictive with pulse counting rates limited to less than ∼10 kHz in the absence of any significant neutron and gamma induced background signal. An upgrade to a specialized pulse counting capability which was developed by the Ioffe Institute was implemented which consisted of CsI(Tl) scintillators having features designed to minimize signals induced by background neutron and gamma rays and 16-channel pulse height analysis electronics on each of the eight NPA energy channels. Passive measurements of rf-driven energetic hydrogen minority ions which served to verify operation of the pulse counting mode are reported. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at a rf power of 2 MW to 0.35 MeV at 6 MW.
Automated liquid helium transfer system
Authors: Cushman G. Mark , Gummer Richard M. , Buchanan Ernie , Jenkins Omar , Powers Tim
Published: July 2002

An optimized automated liquid helium transfer system diverts warm gas from entering the cryostat, saves on liquid helium consumption, reduces man hours, and enhances safety. Control electronics, cryogenic valves and a multipiped transfer line are also discussed.
The Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes
Authors: Weaver I. , Martin G. W. , Graham W. G. , Morrow T. , Lewis C. L. S.
Published: July 2002

A Langmuir probe has been used as a diagnostic of the temporally evolving electron component within a laser ablated Cu plasma expanding into vacuum, for an incident laser power density on target similar to that used for the pulsed laser deposition of thin films. Electron temperature data were obtained from the retarding region of the probe current/voltage (I/V) characteristic, which was also used to calculate an associated electron number density. Additionally, electron number density data were obtained from the saturation electron current region of the probe (I/V) characteristic. Electron number density data, extracted by the two different techniques, were observed to show the same temporal form, with measured absolute values agreeing to within a factor of 2. The Langmuir probe, in the saturation current region, has been shown for the first time to be a convenient diagnostic of the electron component within relatively low temperature laser ablated plasma plumes.
Switching device for the superconducting phase transition measurements of thin W films using a single superconducting quantum interference device
Authors: Sáfrán G. , Loidl M. , Meier O. , Angloher G. , Pröbst F. , Seidel W.
Published: July 2002

A simple superconducting switch has been developed for the measurements of the low temperature superconducting phase transitions of several thin W samples connected simultaneously to a single superconducting quantum interference device. The switch, based on a Ti thin film resistor, can be set to normal or to superconducting within the cryostat by adjusting its temperature above or below the transition temperature by means of a thin film heater. The experimental setup, circuit and device properties, are discussed in detail. As an example of its application the superconducting phase transitions of two thin W samples on sapphire connected in series were measured subsequently as a function of temperature by applying two switches connected parallel to the samples. The switches exhibited a resistance of 67 Ω–1 kΩ at 4 K depending on the thickness and geometry of the Ti film and on the substrate material. The deviation from the real electrical resistance value of the samples caused by the finite resistance of the switches was found to be a maximum of 6×10−6 Ω. This, compared to the resistances to be measured (about 2×10−2 Ω), we consider negligible. The application of several switches within a cryostat can multiply the number of specimens measured in the same cooling cycle, enabling a more efficient characterization of the cryogenic properties of superconducting specimens.
A simple technique using the diffraction pattern of a shadow region for the evaluation of a vertex of a wedge having an acute angle
Authors: Kanai N.
Published: July 2002

The dependence of the diffraction in the shadow on the finish of a vertex of a wedge having an acute angle is studied experimentally. The length of a rounded top can be obtained by analyzing the diffraction intensity along the vertical line from the vertex. This method is a valuable technique for evaluating the finish of a vertex of a small wedge having an acute angle. It is found that this technique makes the evaluating system simple.
Experimental studies on a compact electron cyclotron resonance plasma x-ray source
Authors: Baskaran R. , Selvakumaran T. S.
Published: July 2002

A compact electron cyclotron resonance plasma x-ray source, which has a potential use for medical imaging is presented in this article. In this article, the experimental system and the characterization studies on plasma and x ray are presented. Using a Langmuir probe, the plasma parameters are measured for different magnetic field profiles and gas pressures. The x-ray spectrum is obtained for various gas pressures and magnetic field profiles. In the x-ray spectrum, the Bremstrahlung radiation, peaking at 20–60 keV is observed and the final energy of the x ray is extended up to ∼200 keV. Thermo luminescence dosimeter (CaSO4 sample) is used for estimating the dose at the port and these results are presented for typical x-ray spectra. Using a teletector, the dose at the port for various coil current is measured and these are compared with the estimated dose obtained from the x-ray spectrum.
Characteristics of 63.6° cylindrical energy analyzer used as charge exchange neutral particle analyzer
Authors: Goto T. , Ishii K. , Nagao A. , Goi Y. , Katsuki Y. , Kikuno N. , Ishibashi N. , Ono Y. , Yamanashi M. , Nakashima Y. , Tamano T. , Yatsu K.
Published: July 2002

A charge exchange neutral particle analyzer including a newly designed multichannel 63.6° cylindrical electrostatic energy analyzer was constructed. Since the energy analyzer can simultaneously adopt a small radius of cylindrical electrodes and a large width of an entrance slit, high incident current can be analyzed while the size of the analyzer remain compact. Characteristics of the analyzer were investigated using hydrogen beam with energies from about 0.5 to 5 keV. The experimental results are compared well with the numerical analysis.
Superconducting quantum interference device based resistance bridge for shot noise measurement on low impedance samples
Authors: Jehl X. , Payet-Burin P. , Baraduc C. , Calemczuk R. , Sanquer M.
Published: July 2002

We present a resistance bridge which uses a superconducting quantum interference device (SQUID) to measure the shot noise in low impedance samples (<1 Ω). The experimental requirements are high direct current (dc) bias currents (≲10 mA), in order to obtain sufficiently high bias voltages, together with high alternating current (ac) sensitivity (≈pA/Hz) to detect small changes of the noise away from the thermal noise ground level. These conditions are fulfilled by changing continuously the overall gain of the SQUID electronics and separating the dc and ac feedbacks. This system is used to investigate the shot noise in mesoscopic samples made with superconducting (S) and normal (N) metals (R4.2 K≈0.25 Ω). This value of source resistance is out of the range of classical noise measurement schemes. Because of its low intrinsic noise (≲5 pA/Hz), our system is dominated by the thermal noise of the resistors composing the bridge (∼24 pA/Hz at 4.2 K); therefore, this method greatly simplifies the analysis of shot noise results.
InAs/Al
0.2
Ga
0.8
Sb
quantum well Hall sensors with improved temperature stability
Authors: Bekaert J. , Moshchalkov V. V. , Bruynseraede Y. , Behet M. , De Boeck J. , Borghs G.
Published: July 2002

Cross-shaped Hall sensors with high sensitivity and excellent temperature stability were fabricated from quantum wells based on an InAs/Al0.2Ga0.8Sb heterostructure. The layers were grown on semi-insulating GaAs substrates by molecular beam epitaxy. Maximum Hall mobilities of 215 000 cm2/V s with sheet carrier concentrations of 9×1011 cm−2 were measured at 4.2 K for an undoped quantum well structure. These transport properties result in sensitivities as high as 3 T−1 (for voltage drive) and 650 Ω/T (for current drive). Additional Si δ doping in the middle of the InAs quantum well leads to a highly improved temperature stability of the sensitivities.
A simple, high sensitivity torquemeter
Authors: Flanders P. J. , Wu G.
Published: July 2002

A simple torquemeter has been developed with a sensitivity exceeding 10−13 Nm when using a 13-μm-diam glass fiber and a low-mass suspension. The maximum twist angle of the fiber is constrained by the choice of its diameter to ∼1°. This angle is measured using a light, mirror, and split silicon photodetector, and is proportional to the torque on a sample in a rotating dc magnetic field.
Manipulation force microscopy
Authors: Sagvolden G. , Giaever I. , Feder J.
Published: July 2002

The manipulation force microscope is a novel atomic force microscope adapted to measuring the force necessary to displace micron-size samples adhering to surfaces. It has successfully characterized the adhesion of both proteins and living cells to substrates. This instrument enables measurement of samples not previously accessible to atomic force microscopes. Here, we give a detailed account of this new method, and report on computer simulations and models to assist the interpretation of data.
Novel apparatus for the in situ study of hydrothermal crystallizations using time-resolved neutron diffraction
Authors: Walton Richard I. , Francis Robin J. , Halasyamani P. Shiv , O’ Hare Dermot , Smith Ronald I. , Done Robert , Humphreys Robin J.
Published: July 2002

The design and use of a pressure cell for the in situ study of hydrothermal crystallizations using time-resolved neutron diffraction are described. This novel apparatus allows the kinetics and mechanism of the crystallization of complex inorganic solids, such as zeolites and other microporous materials, to be investigated under laboratory conditions. Reactions can be studied over a wide range of temperatures (25–250 °C) under conditions of autogenous pressure (1–22 bar). The use of the cell is demonstrated by a study of the hydrothermal crystallization of the zeolite sodium hydroxosodalite with time-of-flight neutron diffraction data collected using the Polaris diffractometer of the United Kingdom’s pulsed spallation neutron source, ISIS.
Laser power build-up cavity for high-resolution laser spectroscopy
Authors: Barnes J. A. , Gough T. E. , Stoer M.
Published: July 2002

The design, construction, and operation of an optical build-up cavity (BUC) designed primarily for use in molecular beam laser spectroscopy where signal is proportional to laser power, is presented. The design is such that the cavity has no internal adjustment controls, needing only alignment with respect to the laser and molecular beams. When used with a single-mode titanium:sapphire laser, a circulating cw power of 900 W was achieved. The BUC increased the signal to noise of the experiment by a factor of 390 relative to a single crossing of laser and molecular beam without degrading resolution. Performance of the BUC is limited by heating of its mirrors by the high power densities incident upon them (∼3 MW cm−2).
Cylindrical compound refractive x-ray lenses using plastic substrates
Authors: Cremer J. T. , Piestrup M. A. , Beguiristain H. R. , Gary C. K. , Pantell R. H. , Tatchyn R.
Published: July 2002

We have measured the intensity profile of x rays focused by compound refractive lenses (CRLs) fabricated using acrylic (Lucite) and polyethylene plastics. A linear array of closely spaced holes acts as multiple cylindrical lenses. The important parameters for this type of focusing are the focal length and absorption, and, for wavelengths shorter than 3 Å, low atomic number plastics are suitable. We have experimentally demonstrated that we can achieve one-dimensional focusing for photon energies between 9 and 19.5 keV with focal lengths between 20 and 100 cm. For example, using 12 keV x rays we have achieved focal full width at half maximum linewidths down to 21 μm at a distance of only 20 cm from the CRL. The x-ray source was a synchrotron emitter whose source size in the vertical dimension was 445 μm.
High precision free spectral range measurement using a phase modulated laser beam
Authors: Manson P. J.
Published: July 2002

A simple, new technique for high precision measurement of the free spectral range of an optical cavity is presented. The technique uses a laser beam which is phase modulated at a frequency near an integer multiple of the cavity free spectral range. When the modulation frequency is equal to the integer multiple of the free spectral range, a sharp dip in the component at the modulation frequency of the photocurrent generated by the transmitted beam is observed. Experimental measurements with a precision of 1.5 parts in 107 and theoretical discussion of the mechanism are given.
Multipoint velocity interferometer system for any reflector
Authors: Li Zeren , Ma Ruchao , Chen Guanghua , Liu Jun , Yao Jianquan
Published: July 2002

A multipoint velocity interferometer system for any reflector (VISAR) has been developed which can simultaneously measure velocity versus time histories of two to six points on a target or different objects during dynamic compression. A single-frequency laser beam is divided into two to six individual beams that are transmitted into an experimental device by incident fibers to illuminate measured points. Diffusely reflected laser beams from different measured points are separately collected by fiber detectors and guided by signal fibers into a common “push and pull” interfering cavity with the same delay etalon to interfere. This not only simplifies the system structure and the experimental operation, but also eliminates the system error among measured points and makes the system almost as small in volume as that of a single-point VISAR. The multipoint VISAR possesses all the advantages of the traditional single-point VISAR as well as the temporal and the space resolution ability. We have used it to monitor velocity histories of several points on a target in a few explosion experiments, and good experimental results were obtained.
Steady state operation of an ampere-class hydrogen negative ion source
Authors: Miyamoto Naoki , Fujiwara Yukio , Miyamoto Kenji , Okumura Yoshikazu
Published: July 2002

A cesium-seeded volume negative ion source producing H− ion beams of 800 mA has been operated continuously at a high current density of 20 mA/cm2. The ion source consists of a magnetically filtered multicusp plasma generator and a multiaperture extractor. The ion source has a frame-cooling-type plasma grid, which is continuously able to keep the temperature at optimum using radiation from filaments and arc discharge. The ion source produces about 150 mA of H− in operation without cesium (pure volume operation). The negative ion yield is enhanced by more than a factor of four by injecting 600 mg of cesium. It is important to keep the plasma grid surface temperature at about 300 °C, where the negative ion yield has the maximum. The plasma generator has six tungsten filament cathodes of 1.2 mm in diameter. To estimate a lifetime of the filaments, weight and diameter of the filaments were measured after continuous operation. It was found that evaporation is the dominant wearing-out process, and no significant sputtering effect such as the self-sputtering, cesium sputtering, and chemical sputtering was observed.
ATLAS 10 GHz electron cyclotron resonance ion source upgrade project
Authors: Moehs D. P. , Vondrasek R. , Pardo R. C. , Xie D.
Published: July 2002

A major upgrade of the first ATLAS 10 GHz electron cyclotron resonance (ECR) ion source, which began operations in 1987, is in the planning and procurement phase. The new design will convert the old two-stage source into a single-stage source with an electron donor disk and high gradient magnetic field that preserves radial access for solid material feeds and pumping of the plasma chamber. The new magnetic-field profile allows for the possibility of a second ECR zone at a frequency of 14 GHz. An open hexapole configuration, using a high-energy-product Nd–Fe–B magnet material, having an inner diameter of 8.8 cm and pole gaps of 2.4 cm, has been adopted. Models indicate that the field strengths at the chamber wall, 4 cm in radius, will be 9.3 kG along the magnet poles and 5.6 kG along the pole gaps. The individual magnet bars will be housed in austenitic stainless steel, allowing the magnet housing within the aluminum plasma chamber to be used as a water channel for direct cooling of the magnets. Eight solenoid coils from the existing ECR will be enclosed in an iron yoke to produce the axial mirror. Based on a current of 500 A, the final model predicts a minimum B field of 3 kG with injection and extraction mirror ratios of 4.4 and 2.9, respectively.
Multicomponent consideration of electron fraction of electron-cyclotron resonance source plasma
Authors: Shirkov G.
Published: July 2002

The development of a model of electron and ion accumulation and production in the electron-cyclotron resonance (ECR) ion source is presented. Any kind of experimental or analytical electron distribution function can be approximated with a series of Maxwellian distributions with different temperatures and partial weights. A main positive plasma potential with negative potential dip is introduced into consideration. The first test of a new model and code with recent experimental data of the RIKEN 18 GHz ECR source has shown some new opportunities for investigators to study the ECR ion sources.
Influence of the secondary electrons emitted by a cylindrical metal-dielectric structure on the Frankfurt 14 GHz electron cyclotron resonance ion source performances
Authors: Schächter L. , Stiebing K. E. , Dobrescu S. , Badescu-Singureanu Al. I. , Runkel S. , Hohn O. , Schmidt L. , Schempp A. , Schmidt-Böcking H.
Published: July 2002

Previous research allowed us to develop highly efficient electron emissive metal-dielectric (MD) structures, which are suitable to be used as sources of secondary electrons in electron cyclotron resonance ion sources (ECRIS). First tests have been performed replacing the stainless steel disk of the Frankfurt 14 GHz ECRIS by a MD structure. This method was recently extended by inserting a MD cylinder (150 mm long and 58 mm in diameter) into this source. The experiments were performed with pure argon as source gas and with gas mixing (argon+oxygen). In this contribution, the performance with MD cylinder is compared to that of the standard source (stainless steel plasma chamber) and to the case, where a cylinder of technical aluminum was installed. With the MD cylinder the yield of highly charged ions from the ECRIS are significantly enhanced. For Ar16+ ion current enhancement factors of up to 50 were obtained.
Status of the HIMAC pulsed Penning source
Authors: Miyata T. , Sakamoto H. , Yamamoto M. , Okada T. , Kobayasi C. , Honda Y. , Fujimoto T. , Takasugi W. , Yokoyama T. , Kageyama Y. , Fukusima T. , Ogawa H. , Fujiwara H. , Muramatsu M. , Kitagawa A. , Murakami T. , Yamada S. , Sato Y.
Published: July 2002

Since 1994 at the National Institute of Radiological Sciences HIMAC, the NIRS Penning ionized-gauge ion source (PIGIS) has so far been used for radiotherapy with carbon beams and for basic research with several ion species. The source can produce beams from H2 to Fe with a charge-to-mass ratio of between 1/7 and 1/2. It is a hot-cathode type with a filament, of which the lifetime is on the order of a week and the cathode on the order of 1 month, under a low-duty pulsed operation (⩽0.5%) synchronized to the ring operation. This PIGIS can produce highly charged ions: for example, 1 e mA of Ar7+ or 500 eμ A of Si5+ ions (by sputtering) under the typical arc power of 5 kW in peak. This article describes the present status of the NIRS-PIGIS.
Development of the compact electron cyclotron resonance ion source for heavy-ion therapy
Authors: Muramatsu M. , Kitagawa A. , Sato S. , Sato Y. , Yamada S. , Hattori T. , Shibuya S.
Published: July 2002

Carbon–ion cancer treatment is successfully being made at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Design philosophy for the ion sources for medical facilities are as follows: (1) sufficient beam intensity, a few hundred e μA; (2) long lifetime with good stability; (3) easy operation and easy maintenance; and (4) compactness. In order to develop such source for future heavy-ion facilities, we have tested compact electron cyclotron resonance (ECR) ion sources using permanent magnets both for axial and radial confinement of hot electrons. Since the yield of C2+ ion in the first developed source (2.45 GHz ECR) was 15 e μA and far below the medical requirement (∼150 e μA for the HIMAC), a new source has been proposed, having a frequency of 10 GHz. The extracted intensity of C4+ (and C2+) ions is expected to be higher than 200 e μA.
Measurements on H− sources for spallation neutron source application
Authors: Thomae R. , Gough R. , Keller R. , Leitner M. , Leung K. , Meyer D. , Williams M.
Published: July 2002

Lawrence Berkeley National Laboratory is engaged in the development of H− ion sources for the upgrade of the Los Alamos Neutron Science Center (LANSCE) facility and the spallation neutron source (SNS) to be built in the U.S. For the upgrade of the LANSCE facility, the H− ion generator has to deliver an output current of 40 mA. The repetition rate must be 120 Hz at a pulse length of 1 ms (12% duty factor). Furthermore, the normalized emittance must be less than 0.1π mm mrad. During the last years, the Ion Beam Technology Group of the LBNL improved the so-called surface conversion source for the generation of higher H− currents. In the first part of this article, we discuss the operation conditions of the source at the required 40 mA output current. The ion source for the 1 MW spallation neutron source is required to provide 35 mA of H− beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of less than 0.2π mm mrad. The H− beam will be accelerated to 65 keV and matched into a 2.5 MeV RFQ. The ion source is expected to ultimately produce 70 mA of H− at 6% duty factor when the SNS is upgraded to 2 MW of power. For this application, a radio-frequency driven, magnetically filtered multicusp source is being developed at LBNL. Experimental results (including emittance measurements) on the performance of the prototype ion source operated at the demanded beam parameters will be presented in this article.
Nondestructive electroluminescence characterization of as-grown semiconductor optoelectronic device structures using indium–tin–oxide coated electrodes
Authors: Ghosh Sandip , Hosea Thomas J. C.
Published: July 2002

We describe an arrangement for nondestructive electroluminescence measurements to characterize as-grown semiconductor optoelectronic device structures using indium–tin–oxide film coated on glass as a separate transparent electrode. The usefulness of this technique, and its applicability over a range of temperatures, are demonstrated by measurements on pieces of bare as-grown wafers of two different laser structures.
Status report of the accelerator for multiply charged ions in Grenoble
Authors: Biquard X. , Brenac A. , Gustavo F. , Hitz D.
Published: July 2002

The status report of the Multiply Charged Ion Accelerator of the CEA-Grenoble is presented. This facility is devoted to the production of multiply charged ions (up to Xe31+) in the low energy domain (1–20 q keV). A new 14.5 GHz high magnetic field electron cyclotron resonance ion source of the Caprice type has been installed, the transmission of the beam line increased, resulting in a large enhancement of the available beam intensity. Ion selection and deceleration are simplified. Emittances as low as before are achieved. Performances for various beams are presented, together with updated beam emittance measurements. The intensity enhancement is especially large for highly charged ion beams like Ar17+ (100 times more intensity), and enables routine delivery to experiments of more than 10 μA of Xe25+ at 20 q keV in 20 π mm mrad. The range of available charge states was extended to Xe31+ (with a reasonable intensity of 180 nA). Future prospects include the extension of the energy range down to a few q eV.
A simple high-resolution on-line x-ray imaging crystal spectrograph for laser–plasma interaction studies
Authors: Arora V. , Kumbhare S. R. , Naik P. A. , Gupta P. D.
Published: July 2002

A simple, high-resolution x-ray imaging crystal spectrograph is described for on-line measurements and analysis of x-ray emission from laser-produced plasmas in the wavelength range of ∼5–12 Å. The spectrograph uses a planar TAP crystal for dispersion and a phosphor-coated optical fiber plate followed by an image intensifier and a charge-coupled device camera for detection. The spectrograph covers a wavelength range of ∼1.4 Å in a single shot about a desired wavelength setting with a spectral resolution of ∼0.012 Å. It also has a design flexibility to cover the full spectral range of 5–12 Å in a single shot with a spectral resolution of ∼0.040 Å. The spectrograph is particularly suited for studies involving low vacuum environment, e.g., plasma interaction with a background gas, laser interaction with a gas jet, etc., which preclude the use of other on-line detectors such as open-ended microchannel plates. An example of space resolved x-ray emission from laser-produced magnesium plasma expanding in a helium gas is also presented.
Arrays of normal metal tunnel junctions in weak Coulomb blockade regime
Authors: Hirvi K. P. , Kauppinen J. P. , Korotkov A. N. , Paalanen M. A. , Pekola J. P.
Published: July 2002

Universal features of I–V characteristics of one-dimensional arrays of normal metal tunnel junctions have been tested against inhomogenities in the junction parameters, number of junctions in the array, and magnetic field. We find that the differential conductance versus bias voltage obeys the analytic form to within 1% if the fabrication errors are smaller than 10% in junction areas, and if the array has more than ten junctions. Furthermore, the universal relation is insensitive to magnetic field at least up to 8 T.
Effect of beam thickness in a Cherenkov laser
Authors: Ueda T. , Shiozawa T.
Published: July 2002

The effect of beam thickness in a two-dimensional Cherenkov laser is investigated on the basis of the fluid model for the electron beam. In the analysis, the transverse variation of the drift velocity for the electron beam is taken into account. The numerical simulation shows that there exists an optimum beam thickness for an efficient use of the electron beam in the Cherenkov laser.
A compensating donor with a binding energy of 57 meV in nitrogen-doped ZnSe
Authors: Zhu Ziqiang , Brownlie Glen D. , Thompson Paul J. , Prior Kevin A. , Cavenett Brian C.
Published: July 2002

A compensating deep donor with a binding energy of 57 meV in ZnSe:N epilayers has been studied by means of photoluminescence and selectively excited photoluminescence (SPL) spectroscopy. The emission of 2.766 eV due to transitions between the deep donors and free holes (DdF) was observed at 4 K under strong excitation conditions. The emission at 2.681 eV due to transitions between deep donors and nitrogen acceptors (DdAP) is attributed to the same deep donor as that of the DdF emission through a detailed SPL study. It is also demonstrated that the SPL technique is important for studying the deep levels in ZnSe:N.
Measurement of the refractive index of thin SiO2 films using tunneling current oscillations and ellipsometry
Authors: Hebert K. J. , Zafar S. , Irene E. A. , Kuehn R. , McCarthy T. E. , Demirlioglu E. K.
Published: July 2002

We use Fowler–Nordheim tunneling current oscillations to accurately determine the thicknesses of ultrathin SiO2 films, and with the thicknesses as input, we employ precision single wavelength ellipsometry to determine the real part of the refractive index for thin SiO2 films in the range of 4–6 nm. An average value for this refractive index was found to be 1.894±0.110. This value is shown to yield SiO2 thicknesses to an accuracy of ±0.1 nm. A SiO2 thickness-refractive index interpolation formula for the thin film regime is given.
Stability of a low-temperature grown GaAs surface layer following air exposure using tunneling microscopy
Authors: Hong S. , Reifenberger R. , Janes D. B. , McInturff D. , Woodall J. M.
Published: July 2002

The stability of a GaAs layer structure consisting of a thin (10 nm) layer of low-temperature-grown GaAs on a heavily n-doped GaAs layer, both grown by molecular beam epitaxy, has been studied using a scanning tunneling microscope. The sample was exposed to the atmosphere between the layer growth and STM characterization. Tunneling spectroscopy shows both the GaAs band edges and a band of midgap states associated with the excess As in the surface layer. The observation of midgap states following atmospheric exposure indicates that the low-temperature-grown GaAs layer does not oxidize rapidly. The spectroscopy results are used to confirm a model for conduction in low resistance, nonalloyed contacts employing comparable layer structures.
Metalorganic chemical vapor deposition of tungsten nitride for advanced metallization
Authors: Tsai M. H. , Sun S. C. , Chiu H. T. , Chuang S. H.
Published: July 2002

In this study, the physical and electrical properties of tungsten nitride thin films deposited by thermal decomposition of bis(tertbutylimido)bis(tertbutylamido)tungsten have been investigated. The films have an excellent step coverage over high aspect-ratio contact holes as well as a low carbon concentration. Strong W–N double bonds in the precursor preserved the nitrogen atoms during the pyrolysis process. This method subsequently yielded low-resistivity films. A decrease in film resistivity from 4300 to 620 μΩ cm corresponded to an increase in the deposition temperature from 500 to 650 °C. X-ray diffraction (XRD) and wavelength dispersive spectroscopy (WDS) results indicated that the as-deposited films have face centered cubic (fcc) phase polycrystalline structures with excessive nitrogen atoms.
Dry oxidation mechanisms of thin dielectric films formed under N2O using isotopic tracing methods
Authors: Ganem J.-J. , Rigo S. , Trimaille I. , Baumvol I. J. R. , Stedile F. C.
Published: July 2002

We investigated the mechanisms of thermal reoxidation in dry O2 of silicon oxynitride films prepared by processing Si(100) wafers in a rapid thermal furnace in a pure nitrous oxide (N2O) ambient, using isotopic tracing of oxygen and nitrogen. Standard nuclear reaction analyses for the measurement of the total amounts of the different isotopes, and very narrow resonant nuclear reactions for high resolution (1 nm) depth profiling of these elements were used. The silicon oxynitride films grown in pure 15N216O were 8-nm thick, with a small amount of nitrogen localized near the interfacial region. Under reoxidation in dry 18O2, the thickness of the dielectric film increased while a pronounced isotopic exchange took place between the 18O from the gas and the 16O from the film, as well as a significant loss of 15N. This is in contrast with the reoxidation in dry O2 of pure SiO2 films, where the oxygen exchange is rather small as compared to that observed in the present case.
Kinetics of thermal oxidation of AlAs in water vapor
Authors: Ochiai M. , Giudice G. E. , Temkin H. , Scott J. W. , Cockerill T. M.
Published: July 2002

We have investigated the lateral thermal oxidation of AlAs in water vapor in vertical cavity surface emitting laser structures. At low temperatures and short oxidation times, oxide growth was found to be reaction rate limited. Conversely, diffusion across the oxide was the rate controlling mechanism at higher temperatures and longer oxidation times. Lasers are typically processed at intermediate values of temperatures and time. The observed growth can be modeled by rate equations by which the two component growth mechanisms can be separated. Activation energies of 1.6 and 0.8 eV were determined for the reaction rate and diffusion limited mechanisms, respectively.
Influence of surface morphology on ordered GaInP structures
Authors: Nasi L. , Salviati G. , Mazzer M. , Zanotti-Fregonara C.
Published: July 2002

Ga0.51In0.49P layers, grown by organometallic chemical vapor deposition on differently misoriented (001) GaAs substrates exhibit CuPtB-type domains. The increase in structural homogeneity of the ordered domains, with increasing substrate misorientation, results in a very sharp distribution of the degree of ordering. The correlation between cathodoluminescence emission from ordered regions and changes in surface step distribution direction confirm the influence of the surface morphology on the distribution of ordered regions and their antiphase boundaries.
Superconductor-normal-superconductor behavior of Josephson junctions scribed in Y1Ba2Cu3O7−δ by a high-brightness electron source
Authors: Davidson B. A. , Nordman J. E. , Hinaus B. M. , Rzchowski M. S. , Siangchaew K. , Libera M.
Published: July 2002

We report a substantial improvement in the behavior of Josephson junctions scribed in Y1Ba2Cu3O7−δ films using a high-brightness field-emission electron gun source instead of a lower-brightness thermionic source. These junctions exhibit resistively shunted junction behavior over the entire temperature range from the coupling temperature to at least 4 K, a temperature window which can be larger than 55 K. Superconductor-normal-superconductor character is indicated by the exponential dependence of the critical current on temperature for all temperatures below 90 K. The data demonstrate that electron irradiation under these conditions produces a modified region which is completely normal above 4 K and is narrower in width than previously obtained.
Highly coercive Sm2Fe15Ga2C2 magnets made by intense ball milling
Authors: Cao L. , Handstein A. , Grünberger W. , Edelman J. , Schultz L. , Müller K.-H.
Published: July 2002

Thermodynamically stable nanocrystalline Sm2Fe15Ga2C2 powders were prepared by intense ball milling of homogenized and coarsely ground ingots, and a subsequent annealing of the powders in an argon atmosphere. Such processing results in magnetically isotropic material with a room-temperature coercivity μ0JHc of up to 1.2 T. Scanning electron microscopy observations suggest a homogeneous microstructure, and combined with Scherrer formula estimations, an average grain size of <100 nm has been determined. The coercivity can be preserved at high annealing temperatures when the process is performed at an argon pressure of about 800 mbar. The attempt of a hot-pressing procedure resulted in a magnet with a density of 86% (6.7 g/cm3) of the theoretical density (7.8 g/cm3) and a coercivity of 1.3 T.
Fast wavelength switching of semiconductor laser pulses by self-seeding
Authors: Huhse D. , Schell M. , Utz W. , Bimberg D. , Williams J. A. R. , Zhang L. , Bennion I.
Published: July 2002

Electrically wavelength tunable single-mode laser pulses with a width (FWHM) of about 30 ps were achieved by gain-switching and self-seeding of a 1.5 μm Fabry-Perot laser diode. Using a novel setup with a short, wavelength depending cavity length, switching between different wavelengths is demonstrated here at a frequency of 10 kHz. The buildup of stable single mode emission takes less than 7 roundtrips thus showing the potential of this approach for fast electrical wavelength switching in the tens-of-MHz range.