bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of the axial beam line for the injection of high intensity beams into the Laboratorio Nazionale del Sud superconducting cyclotron
Authors: Gammino S. , Ciavola G.
Published: July 2002

At Laboratorio Nazionale del Sud the superconducting electron cyclotron resonance source SERSE will be used as injector for the K-800 Superconducting Cyclotron which in the future will provide the intense light ion beams to be used as primary beams for the radioactive beam project EXCYT. The goal is to inject and accelerate a few pμA of fully stripped carbon and oxygen into the cyclotron with an emittance as close as possible to the typical acceptance of the cyclotron, which should be in the order of 50π mm mrad. The study of the beam line has been carried out by taking into account both the phase space growth due to space charge and the aberrations inside the magnets. The design has been based on the results of different codes (TRANSPORT, GIOSP, PARMILA). A few details on the diagnostics will also be given. The assembly of the beam line is scheduled for the summer of 1996, just before the transfer of the source SERSE from Grenoble to Catania.
A microwave plasma cathode for the high-current CHORDIS ion source
Authors: Cojocaru G. , Wolf B. H. , Emig H.
Published: July 2002

The microwave plasma cathodes (MPC) dedicated to high-current ion sources are characterized by long lifetime with reactive gases and a compact structure. An Ishikawa-type MPC developed at GSI Darmstadt coupled with the CHORDIS ion source is presented. The electron current of the MPC is extracted from a dense plasma generated under electron-cyclotron-resonance condition. The axial magnetic field is produced by permanent magnets and ferromagnetic components. The 2.45 GHz microwave power (some tens of watts) is introduced into the plasma chamber via a coaxial line ended with a helical antenna. Experiments with argon and oxygen gas are presented and discussed.
Recent developments for metallic ion production at the National Superconducting Cyclotron Laboratory
Authors: McNeely P. , Cole D. , Moskalik J. , Zeller A. F.
Published: July 2002

This article describes studies performed on the National Superconducting Cyclotron Laboratory’s Superconducting-ECR (electron cyclotron resonance) ion source for the production of metallic ion beams. The Room Temperature-ECR ion source as the workhorse for generating metallic ion beams using a solid feed system will be superceded in the future by the Superconducting-ECR ion source. A series of tests were carried out with a Langmuir probe introduced axially into the plasma chamber of the Superconducting-ECR ion source. These tests determined the location and shape of the plasma and its floating potential. The results presented show the effect of source bias and axial magnetic field on the plasma boundary. Some preliminary results for gold sputtering are also included. The use of a solid metal, saturated in deuterium, to produce deuterium beams in the Room Temperature-ECR ion source has also been studied.
A side extraction PIG negative ion source with a permanent magnet
Authors: Yu Jinxiang , Song Zhizhong , Ren Xiaotang
Published: July 2002

A side extraction PIG ion source with a permanent magnet is introduced, which can be used not only for producing miliampere positive ion beams, but also for direct extraction of negative ions of some elements with larger electron affinity. So far H, O, and F negative ions have been extracted from the source. At −15 kV extraction voltage, O− ion beams of 130 μA and a F− ion beam of 75 μA are extracted, and the discharge power consumption is 110 and 280 W, respectively.
Production of multiply charge-state ions in a multicusp ion source
Authors: Williams M. D. , deVries G. J. , Gough R. A. , Leung K. N. , Monroy M.
Published: July 2002

High charge state ion beams are commonly used in atomic and nuclear physics experiments. Multiply charged ions are normally produced in an ECR or in an EBIS. Multicusp generators can confine primary electrons very efficiently. Therefore, the electrical and gas efficiencies of these devices are high. Since the magnetic cusp fields are localized near the chamber wall, large volumes of uniform and high density plasmas can be obtained at low pressure, conditions favorable for the formation of multiply charged state ions. Attempts have been made at LBNL to generate multiply charged ion beams by employing a 25-cm diam by 25-cm long multicusp source. Experimental results demonstrated that charge states as high as 7+ can be obtained with argon or xenon plasmas. Multiply charged metallic ions such as tungsten and titanium have also been successfully formed in the multicusp source by evaporation and sputtering processes. In order to extend the charge state to higher values, a novel technique of injecting high energy electrons into the source plasma is proposed. If this is successful, the multicusp source will become very useful for radioactive beam accelerators, ion implantation, and nuclear physics applications.
Results and analysis of measurements on a proton-source beam for halo formation studies
Authors: Beauvais P.-Y. , Chamouard P.-A. , Ferdinand R. , Haouat G. , Lagniel J.-M. , Pichoff N. , Ruiz C.
Published: July 2002

An important experiment investigating halo formation is in progress at Laboratoire National Saturne (LNS). Its purpose is to detect and measure the halo developed by an intense proton beam in a long magnetic quadrupole FODO channel (58 quadrupoles). Two different arrangements of apparatus built to measure the emittance and the brightness of the beam entering the FODO channel are described. The first one, the LNS method, is made up of a sampling hole and a multiwire profile monitor whereas the second one, the Service Physique et Techniques Nucleaires method, is made up of a scintillating screen and a high performance charge-coupled device camera. Results and analysis of the measurements are presented.
TRIUMF injection line nonintercepting beam energy monitoring through phase measurement
Authors: Yin Y. , Laxdal R. E. , Ostroumov P.
Published: July 2002

A nonintercepting beam velocity monitoring system has been installed in the 300 keV injection line of the TRIUMF cyclotron to reproduce the injection energy for different ion source beams and monitor any beam energy fluctuations. The monitor is tuned to resonate at 46 MHz and is 3.25 m downstream from the first 23 MHz buncher. The phase difference between the first buncher and the pickup is related to the average beam velocity, i.e., beam energy. The energy sensitivity of the measurement is 1×10−4. The dynamic range of the monitor with beam current is 60 dB, and the measured instantaneous beam intensity can go down to 100 nA. The theory behind the device and the results of beam tests will be described.
Characteristic x rays and electron energy distribution function in anisotropical hot plasmas
Authors: Friedlein R. , Tyrroff H. , Zippe C. , Zschornack G. , Barnitzke W.
Published: July 2002

Characteristic x-ray lines of heavy ions are used as threshold indicators for the number of plasma electrons with an energy higher than the orbital electron binding energy of the initial vacancy for the corresponding x-ray transition. For heavy ion plasmas the intensity ratio between x-ray lines of different series shows how the mean energy of the electron changes with the operating conditions of an electron cyclotron resonance ion source. With the combination of line intensity and bremsstrahlung measurements, information on the anisotropy of the electron energy distribution function is obtained. Characteristic and continuous radiation is recorded at the same time and with the same apparatus. Therefore, errors are extremely small.
An electron cyclotron resonance injector for the French proton therapy program ECRIPAC
Authors: Golovanivsky K. S. , Bruneteau J. , Bacal M. , Buzzi J. M. , Geller R. , Karetnikov M. D. , Schwartz L. H.
Published: July 2002

This paper deals with a new concept of the full scale ion plasma injector for ECRIPAC—a new supercompact collective action accelerator for ions. The injector has an electron cyclotron resonance (ECR) 10 GHz ‘‘min B’’ quadrupolar magnetic structure which, in contrast to the traditional ECR ion sources, allows the microwaves to penetrate on the periphery of the plasma, and also on the axis of the plasma in conditions close to the first and second Bernstein modes.
The TRIUMF optically pumped polarized H− ion source
Authors: Levy C. D. P. , Jayamanna K. , McDonald M. , Schmor P. W. , van Oers W. T. H. , Welz J. , Wight G. W. , Dutto G. , Zelenski A. N. , Sakae T.
Published: July 2002

The TRIUMF dc optically pumped polarized H− ion source (OPPIS) produces a 200 μA dc H− current at 85% polarization within a normalized emittance (90%) of 0.8 π mm mrad, for operation at the TRIUMF cyclotron. As a result of development of the electron cyclotron resonance primary proton source, a 1.6 mA dc polarized H− current is produced within a normalized emittance of 2 π mm mrad, suitable for high energy accelerators. The OPPIS has also been developed for use in a parity nonconservation experiment which has very severe limits on permissible helicity- correlated changes in beam current and energy.
First results on the warm EBIS source at Saclay
Authors: Gobin R. , Delferrière O. , Gros P. , Leaux P. , Visentin B. , Congretel G. , Faure J. , Harrault F. , Leroy P. A. , Courtois A. , Thuriez S. , Giardino G. , Briand J. P.
Published: July 2002

A large high current EBIS source, working at room temperature, and using a noncryogenic solenoid, has been completed in Saclay. This source, whose current density is lower (≊100 A cm−2) than the cryogenic EBIS, has been designed to be used at very low pressures with turbo and Ti sublimator pumping. An ultimate vacuum of 8×10−12 mbar has been reached and may be obtained in a few days after opening. This ultrahigh vacuum allows very long confinement times. The electron beam has been injected and large amounts of Ar16+ and Ar17+ ions have been obtained in July. These preliminary results are in good agreement with theoretical simulations. More details about the special dynamics of the warm EBIS are presented.
Enhanced production of multicharged boron ions by approaching a boride target to an ECR zone
Authors: Kato Y. , Fukukawa A. , Ishii S.
Published: July 2002

Multicharged boron ions have been produced by a sputtering boride target in a 2.45-GHz electron cyclotron resonance (ECR) source. The target material is immersed in an ECR argon plasma along the geometrical axis of the mirror field, and dc bias voltages are applied. Extracted boron ion currents increase as the target approaches the ECR zone formed at the bottom of mirror trap although the argon charge state deteriorates. The increase of boron ion current is coincident with that of the solid angle subtended by the target at the ECR zone. Measurement of the boron flux shows that the increase of boron atoms sputtered into the ECR zone causes this enhanced production. Ratio of total boron to argon ion current and that of B2+ to B+ current are about 10% and 10%–20%, respectively. The B3+ current can be detected at low microwave power (∼150 W). The isotopes of boron are clearly separated in natural abundance ratio.
Production of a Li− ion beam from a thermal contact–ionization plasma source
Authors: Fukuura Y. , Murakami K. , Masuoka T. , Katsumata I.
Published: July 2002

The beam source is composed of a thermal contact–ionization plasma source and an accelerating lens system. The plasma source is made of a rhenium-foil cylinder 5 mm in diameter and it can be heated up to about 3000 K. A Li+ beam current over 500 μA has been obtained with this source. For the production of a Li− beam, an additional reservoir is attached to the source to supply Cs vapor into the plasma. The ion species can be examined by the time-of-flight (TOF) technique. In the case of Li+ production, ions of alkaline impurities, Na and K, in the Li metal have been observed in the TOF spectra. In the case of Li− ion production, the current intensity of negative ions also changes with the passage of operating time from K−, Na− to H− or H−2. This is also attributable to alkaline impurities in Li metal. A negative ion beam, which has been observed after the evaporation of impurities amounting to 200 nA, is very likely attributable to the Li− beam, though the corresponding TOF signal is very noisy.
Vacuum arc ion sources—Micro to macro
Authors: MacGill R. A. , Dickinson M. R. , Brown I. G.
Published: July 2002

Vacuum arc ion sources provide a convenient tool for the production of intense beams of metal ions. The sources are relatively easy to construct and they can produce beams from all of the solid metals as well as from compounds, alloys, and mixtures. We have made a number of different kinds of such sources over the course of our development work at LBL in the past decade, from very small ‘‘thumb-size’’ versions to a very large one with a 50 cm diameter extractor. Beam current ranges from a few milliamperes up to almost 10 A and extraction voltage from about 1 to 100 kV. Multicathode versions have been made so that one can switch between metal ion species simply and quickly. Most of the sources have been operated in a repetitively pulsed mode, and we’ve also tested a dc version. Here we outline some construction features of the array of vacuum arc ion sources that we’ve developed and used, and describe their performance and limitations.
Multi-sample negative ion source
Authors: Gelbart W. Z. , Johnson R. R. , Paul M. , Shahar Y. , Schubank R. B. , Cifarelli F.
Published: July 2002

A cesium sputter, negative ion source was developed and built at Triumf. While designed for accelerator mass spectrometry, it can be applied in any field requiring intensive negative ion beams covering the whole range from hydrogen to uranium. The source features an internal cesium oven and simplified target insulation. A pneumatically actuated target changer contains a 28-sample wheel but allows manual placing of single samples as well. In initial runs the source produced over 1 μA of 40CaH−3 and .25 μA of 27Al− beams. The construction of the source and the operation of the sample changer are discussed in this article.
Factors affecting the design of a single gap accelerating column
Authors: Abdelaziz M. E. , Zakhary S. G. , Ghanem A. A.
Published: July 2002

The transport of high intensity, high brightness beams without aberrations in low energy accelerators (50–100 keV) is the main objective of this work. An analytical approach is used for the design of a single gap accelerating column. The tracing of beam lines inside the accelerating gap shows a decrease of the beam radius with an increase of the accelerating voltage ratio up to the optimal value. Beyond this optimal value the beam line makes a crossover with the axis of the accelerating tube, which indicates the presence of beam aberration. Also the rate of beam emittance growth increases due to the presence of beam aberration. An estimation of the minimum value of the electric field required to contain the beam against space charge expansion is set forth for different gaseous ions.
Basic processes of negative hydrogen ion production and destruction in sources and beams (invited)
Authors: Bacal M. , Michaut C. , Elizarov L. I. , El Balghiti F.
Published: July 2002

This article contains the discussion of new discoveries and ideas relevant to volume H− ion sources and beams. Recent research in laser irradiated H2 by Pinnaduwage and Christophorou has shown that the rates of dissociative attachment are strongly dependent on electronic excitation involving superexcited states and possibly Rydberg states. The observation of anomalous attenuation of a 15 keV H− beam in a hydrogen gas target led us to consider the possibility of secondary H− stripping processes, related to low-energy interactions between primary H− ions and the secondary H+, H0, and electron beams produced by primary stripping. The results of the investigation by electrostatic probes and by photodetachment of the properties of a hydrogen/deuterium multicusp ion source plasma when seeded with cesium vapor are reported. We found that the negative ion/electron density ratio is enhanced by cesium seeding, particularly at low pressure (a factor of 4 at 1 mTorr), while both the electron temperature and the electron density are reduced.
Selection of targets and ion sources for radioactive ion beam generation at the Holifield Radioactive Ion Beam Facility (invited) (abstract)a),b)
Authors: Alton G. D.
Published: July 2002

In this report, we describe the performance characteristics for a selected number of target ion sources that will be employed for initial use at the Holifield Radioactive Ion Beam Facility as well as prototype ion sources that show promise for future use for radioactive ion beam applications. A brief review of present efforts to select target materials and to design composite target matrix/heat-sink systems that simultaneously incorporate the short diffusion lengths, high permeabilities, and controllable temperatures required to effect fast and efficient diffusion release of the short-lived species is also given.
Dubna electron cyclotron resonance ion source (DECRIS)-14-2: Results of the first operation
Authors: Efremov A. , Kutner V. B. , Lebedev A. N. , Loginov V. N. , Yazvitskiy N. , Zhao H.
Published: July 2002

The new electron cyclotron resonance (ECR) ion source, the Dubna electron cyclotron resonance ion source (DECRIS)-14-2, was designed and built for use with the isochronous cyclotron U-400M. The source assembly was completely finished by the end of 1994 and in January of 1995 the source was tested on the ECR-test bench. In February the source was installed in the cyclotron and in April the first physical experiment on the accelerated beam was carried out. Here we present some design aspects of this source and the results of the first operation on the cyclotron.
Computational studies for a multiple-frequency electron cyclotron resonance ion source (abstract)
Authors: Alton G. D.
Published: July 2002

The number density of electrons, the energy (electron temperature), and energy distribution are three of the fundamental properties which govern the performance of electron cyclotron resonance (ECR) ion sources in terms of their capability to produce high charge state ions. The maximum electron energy is affected by several processes including the ability of the plasma to absorb power. In principle, the performances of an ECR ion source can be realized by increasing the physical size of the ECR zone in relation to the total plasma volume. The ECR zones can be increased either in the spatial or frequency domains in any ECR ion source based on B-minimum plasma confinement principles. The former technique requires the design of a carefully tailored magnetic field geometry so that the central region of the plasma volume is a large, uniformly distributed plasma volume which surrounds the axis of symmetry, as proposed in Ref. . Present art forms of the ECR source utilize single frequency microwave power supplies to maintain the plasma discharge; because the magnetic field distribution continually changes in this source design, the ECR zones are relegated to thin ‘‘surfaces’’ which surround the axis of symmetry. As a consequence of the small ECR zone in relation to the total plasma volume, the probability for stochastic heating of the electrons is quite low, thereby compromising the source performance. This handicap can be overcome by use of broadband, multiple frequency microwave power as evidenced by the enhanced performances of the CAPRICE and AECR ion sources when two frequency microwave power was utilized. We have used particle-in-cell codes to simulate the magnetic field distributions in these sources and to demonstrate the advantages of using multiple, discrete frequencies over single frequencies to power conventional ECR ion sources. The electron heating rates are found to scale directly in proportion to the resonant plasma ‘‘volume.’’
Multicusp type machine for electron cyclotron resonance plasma with reduced dimensions
Authors: Amemiya H. , Maeda M.
Published: July 2002

Plasmas are created in a cusp type magnetic trap using electron cyclotron resonance heating. The magnetic field is generated with permanent magnets forming a 12-pole, whereby the polarity at the ends of the rods has been reversed in order to obtain end plugs and to improve the plasma confinement. In this way, the plasma volume could be reduced such that the cross section was close to or smaller than the cutoff width of a circular waveguide. This increases the microwave power absorbed and gives a high plasma density even above the cutoff value.
Wave form analysis of constant capacitance–voltage transient deep level transient spectroscopy using an iterative feedback system
Authors: Okamoto Y. , Yonekura H. , Morimoto J. , Miyakawa T.
Published: July 2002

We propose an improved version of the CCVT (constant capacitance–voltage transient) method to study the emission rate spectrum of deep impurity levels in semiconductors. The iterative feedback system is developed for this CCVT technique. The emission rate spectrum is analyzed from the feedback voltage transient wave form by using a nonlinear least-squares program. The feasibility of the method is shown for an Au-doped Si p+n diode. The method is expected to be effective in resolving the problem of closely spaced multiple deep levels, even if the sample has a high trap concentration and/or a nonabrupt junction profile.
Electronically tunable fiber laser for optical pumping of 3He and 4He
Authors: Stephens E. F. , Patrick H. , Gilbert S. L.
Published: July 2002

We present in this paper a low threshold, highly stable, integrated fiber laser cavity that uses an electronically tunable internal Bragg grating. The fiber laser produced over 5 mW with a spectral width of about 5 GHz at 1083 nm. The laser was used to achieve 30% polarization of the 2 3S1 metastable states of 4He in a weak rf discharge cell.
Measurement and calculation of the spatial and spectral distribution of wavelength shifter radiation at BESSY
Authors: Thornagel R. , Fliegauf R. , Klein R. , Scholze F. , Ulm G.
Published: July 2002

Calculable synchrotron radiation (SR) from BESSY dipole magnets has been used by PTB for radiometry from the visible to the soft x-ray region with very low uncertainties for many years. The use of wavelength shifter (WLS) radiation bears the potential of extending the usable spectral range for radiometry with calculable SR to higher photon energies. Initial investigations on the feasibility of this approach have been performed: an energy dispersive high-purity germanium detector (HPGe) was used to characterize the radiation of the new BESSY WLS with a magnetic field of B=3.2 T. The HPGe detector has previously been calibrated and so the absolute spectral photon flux could be determined. The measured spectral photon flux was then compared to calculations and good agreement was found in the order of ±5%. Although this is to our knowledge the best agreement demonstrated so far for an absolute comparison of measured WLS radiation to calculations, further improvements are needed for a future radiometric use of WLS radiation. This will be discussed.
The experimental apparatus for electrical resistivity measurements of liquid metals and alloys under microgravity due to the launch of a rocket
Authors: Masaki T. , Itami T. , Kuribayashi K. , Hinada M. , Kawasaki K.
Published: July 2002

The experimental apparatus was developed for electrical resistivity measurements of liquid metals and alloys under microgravity due to the launch of rocket; whole assembly, contained in the small space of 360 mm(length)×360 mm(width)×97 mm(height), was composed of the cell box, the electronic circuit box, and the battery box. The cell for electrical resistivity measurements due to the dc four probe method was made of Ti metal because of its strength and no reaction to corrosive liquid alloys at high temperatures. The application of this method was made successfully to the measurement of electrical resistivity for liquid Bi–Ga alloys with critical mixing both under gravity condition and under microgravity condition due to the launch of the rocket. The far larger temperature coefficients of resistivity were observed near the critical point. This may indicate the appearance of larger concentration fluctuations under microgravity.
Differentially evacuated ion energy analyzer for cathodic arc plasma
Authors: Sakaki Mamoru , Sakakibara Tateki
Published: July 2002

A new type of retarding grid ion energy analyzer with a differential evacuation unit has been developed for the measurement of the ion energy distribution of a medium vacuum arc. The ion energy distribution in a cathodic arc plasma of 5 Pa pressure was measured. The experimental results indicate that the ion energy distribution measured with differential evacuation is more accurate than that measured without differential evacuation.
Following the dyeing of wool in real time using fluorescence microscopy
Authors: Bradley Grant , Collins Stephen , Davidson R. Stephen
Published: July 2002

The novel design of a heated stage (miniature dye bath) for use with an inverted fluorescence microscope is described. The heated stage allows investigation of wool dyeings to be followed in situ in real time. The photometer attachment of the microscope allows for quantitative analysis. The progress of the dyeing of wool with a fluorescent whitening agent and a fluorescent dye have been monitored in real time.
Instrument for the in situ measurement of haze in aircraft windscreens
Authors: Gallagher Frank W. , Brock Fred V.
Published: July 2002

Current instruments for the measurement of haze in aircraft windscreens generally require the removal, and possible destruction, of the windscreen to conduct the test. Most instruments available for haze measurement of samples taken from a windscreen cannot be used in situ. This is because the standard definition of haze requires measurement of light scattered in transmission through the sample so the instrument must have a light source and a light detector on opposite sides of the sample. One portable instrument has been reported in the literature; however, it is not readily available and, in the reported form, is subject to errors due to orientation of the instrument with respect to the sample under test, and due to background light. The orientation error arises from the typically more or less parallel orientation of scratches in the windscreen. If haze is measured in just one orientation through the sample, the haze value will depend upon whether the measurement plane is parallel to scratches or not. Background light will also affect the reading if the instrument has not been designed to eliminate most ambient light and to compensate for the remaining illumination. We report on the development of a new prototype instrument that is portable, easy to use, is relatively insensitive to ambient light, and will be less influenced by scratch orientation.
Current–voltage characteristics of the end loss ion flux from a tandem mirror collected on a gridded energy analyzer
Authors: Saito T. , Kiwamoto Y. , Tatematsu Y. , Yoshimura Y. , Sakakibara M. , Kajiwara K. , Kurata M. , Ichimura M. , Tamano T.
Published: July 2002

Examination is made of the relation between the distribution function of the ions confined in a tandem mirror and the current–voltage (I–V) characteristics of the end loss ions collected on a gridded energy analyzer. To do this, a model ion distribution function characterized by two parameters, an anisotropy parameter χ and a decay parameter Y is used. The decay parameter represents depletion of ion distribution in the loss cone. A Maxwellian distribution as the limit of Y=∞ is shown not to reproduce the measured I–V curve as an energy spectrum of the ions lost from the central cell of the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)]. The ions in the central cell are subject to strong ICRH and have a highly anisotropic velocity distribution. These ions are deeply trapped in the central cell and the loss cone is not fully occupied. The model distribution with a small value of Y represents such features of the ion distribution. From comparison between a measured loss current and calculated one, the decay parameter of the model distribution function is roughly determined. The model distribution with this parameter yields I–V characteristics similar to the measured one. The present article gives the relation between the apparent ion temperature Ti simply determined from the slope of the log plot of the measured I–V curve and the real parallel ion temperature Ti∥. When the ion distribution is of a loss cone type, Ti is almost equal to Ti∥. On the other hand, Ti can be more than two times as high as Ti∥ if the ion distribution is Maxwellian-like.
A new force controlled atomic force microscope for use in ultrahigh vacuum
Authors: Jarvis S. P. , Yamada H. , Yamamoto S.-I. , Tokumoto H.
Published: July 2002

We introduce a magnetic force controlled atomic force microscope (AFM) and point contact probe for use in ultrahigh vacuum and describe how our technique can significantly enhance the current capabilities of scanning probe microscopes. The instrument is specially designed to provide quantitative information on the nature of the tip-surface interaction. Forces are applied directly to magnetic material deposited behind the AFM tip via a current carrying coil. Oscillating the applied force and measuring the resulting displacement amplitude gives a continuous measurement of the absolute force gradient or contact stiffness. From this measurement the contact area or effective interaction area can be calculated for clean surfaces, thus eliminating the problems of unknown resolution and also facilitating the study of conduction and mechanical properties of small volumes.
Production of high-brightness continuous wave proton beams with very high proton fractions (abstract)a)
Authors: Spence D. , McMichael G. , Lykke K. R. , Schneider J. D. , Sherman J. , Stevens R. , Hodgkins D.
Published: July 2002

This article demonstrates a new technique to significantly enhance the proton fraction of an ion beam extracted from a plasma ion source. We employ a magnetically confined microwave driven source, though the technique is not source specific and can probably be applied equally effectively to other plasma sources such as Penning and multicusp types. Specifically, we dope the plasma with about 1% H2O, which increases the proton fraction of a 45 keV 45 mA beam from 75% to 90% with 375 W 2.45 GHz power to the source and from 84% to 92% for 500 W when the source is operated under nonresonant conditions. Much of the remaining fraction of the beam comprises a heavy mass ion we believe to be N+ impurity ions resulting from the conditions under which the experiments were performed. If so, this impurity can easily be removed and much higher proton fractions could be expected. Preliminary measurements show the additive has no adverse effect on the emittance of the extracted beam, and source stability is greatly improved.
Sectional and projectional emittance measurements (abstract)a)
Authors: Sarstedt M.
Published: July 2002

For many applications of ion sources the quality of the generated ion beam plays an increasingly important role. Ion sources consist of the plasma generator and the extraction system. Both parts can, due to high ion temperature or various aberrations, contribute to a degrading of the beam quality. Though the beam quality is determined by many more factors, the transverse motion of the particles certainly is one of the important parameters. Knowledge of it can be obtained by an emittance measurement. This is best done in a four-dimensional phase space, yielding a density distribution as function of the transverse spatial and momentum coordinates. Often, however, due to practical considerations, only two dimensions of the four-dimensional ‘‘trace space’’ are being measured. This two-dimensional data can be obtained as a section or as a projection of the four-dimensional trace space, where both methods have their merits. Projectional emittance measurements can usually be performed much easier and quicker, but by the projection of the four-dimensional space onto a two-dimensional plane information is lost. And although not all the particles of the beam are represented in a section of trace space, here aberrative distortions of the emittance can be seen most clearly and allow an easier comparison to numerically obtained data. The advantages and disadvantages of both methods are discussed. Numerical and experimental examples are presented.
Seventh symposium on EBIS/T and their applications combined with a workshop on ion sources for hadron colliders, a satellite meeting to ICIS’97 (invited)
Authors: Becker R.
Published: July 2002

The 7th symposium on EBIS and EBIT and their applications has been organized by M. Kleinod and R. Becker in Gelnhausen, Germany the week before ICIS’97. It was combined with a workshop on ion sources for hadron colliders being reported on by J. Alessi. Former EBIS symposia which have taken place are: 1977 at GSI, Darmstadt, Germany; 1981 in Saclay and Orsay, France; 1985 at Cornell University, Ithaca, New York; 1988 at Brookhaven National Lab (BNL), Brookhaven, New York; 1991 at JINR, Dubna, Russia; and 1994 at MSI, Stockholm, Sweden. The next one will be organized in the year 2000 by Krsto Prelec, BNL and Martin Stöckli, Manhattan, Kansas.
Three-dimensional analysis of ion beam deflection by the magnetic field at H− ion sources for the negative-ion-based neutral beam injection
Authors: Tanaka M. , Ose Y. , Koizumi M. , Yamashita Y. , Kawakami H. , Takeiri Y. , Kaneko O. , Oka Y. , Tsumori K. , Osakabe M.
Published: July 2002

In negative-ion-based neutral beam injection (NBI) systems for the large helical device (LHD), beams must be transported over 13 m from the H− ion source to the injection port. In order to clarify beam deflection by the electron deflection magnets set in a beam extraction grid (EG) and to control beam transport direction, we analyzed beam trajectories. The physics of the beam deflection was studied with theoretical calculations and the deflection angle was estimated by 3D beam trajectory simulation. The evaluated deflection angle was 10 mrad in the opposite direction of the electron deflection when the maximum magnetic field on the beam axis was 480 G and the beam energy was 83.2 keV. The electrostatic lens effect on the beam deflection at the EG exit was estimated to be larger than the magnetic field effect. This deflection was reduced to 2 mrad by a 1.3 mm displacement of the grounded grid (GG) aperture, a result in agreement with experimental results of a 1/3-scale model for the LHD ion source. The maximum GG aperture displacement of the LHD ion source was designed as 3.4 mm to reduce the deflection and to focus multibeamlets using the simulation. We have developed the ion source with this design. The targeted performance is a production of H− beams of 40 A (40 mA/cm2), 180 keV.
Time-of-flight analysis of neutral cluster beams through detection of charged particles produced by cluster impact on a channeltron
Authors: Piseri P. , Li Bassi A. , Milani P.
Published: July 2002

A method for time-of-flight analysis of neutral cluster beams is presented. It is based on the use of a channeltron as a fast flux-sensitive detector of high-speed neutral particles in a beam. The impact of neutral clusters on the channeltron surface causes the emission of charged particles, which can be detected by the channeltron itself. We show that a channeltron can be used for the characterization of velocity distributions in analogy with fast ion gauges but without requiring any ionization device. This method has also the advantage of being selectively sensitive to the cluster component of seeded supersonic beams.
Low-energy, electron-spin-polarized He+4 ion source
Authors: Bixler D. L. , Lancaster J. C. , Popple R. A. , Dunning F. B. , Walters G. K.
Published: July 2002

A source of low-energy, electron-spin-polarized He+4 ions based on an optically pumped, rf-excited helium discharge is described. Ion polarizations P+ of ∼0.13 are achieved at beam currents of ∼0.1 nA, decreasing to ∼0.09 at currents of ∼0.5 nA. Ion beam energies as low as 10 eV have been realized, with an energy spread of ≲3 eV full width half maximum. The ion polarization can be reversed (P+→−P+) simply by changing the sense of circular polarization of the optical pumping radiation. The source is suitable for use in a wide variety of applications including surface physics studies.
Role of oxygen on the dangling bond configuration of low oxygen content SiNx:H films deposited at room temperature
Authors: Garcia S. , Bravo D. , Fernandez M. , Martil I. , López F. J.
Published: July 2002

SiNx:H films with a wide composition range and, some of them, with low oxygen content are deposited at room temperature. The defects observed in the films are attributed to Si-dangling bonds, with a structure depending on film composition. For the N-rich films they are of the form ⋅Si≡(N3), whereas for the films with similar [N]/[Si] ratio but containing oxygen, the predominant defect is proposed to be ⋅Si≡(Si2O), despite of the high N content and the low O content of these films. The spin density of the films has been related to the bonds that hydrogen establishes (either Si–H or N–H), with the maximum value corresponding to the minimum hydrogen content. Both maximum and minimum values, respectively, are obtained at the silicon percolation limit of the Si–Si bonds into the SiNx:H network, x∼1.10.
An alternative approach to vector vibrating sample magnetometer detection coil setup
Authors: Samwel E. O. , Bolhuis T. , Lodder J. C.
Published: July 2002

Vector vibrating sample magnetometers (VSMs) can present problems with respect to angular dependent calibration and positional dependency when they are used for measurements on thin film samples, which have dimensions comparable to or larger than the sample–coil distances. The problems are due to the fact that in conventional VSMs the sample is rotating with respect to the coils, when performing angular dependent measurements. In this article a solution is presented based on a setup of VSM detection coils, whose position is linked to that of the sample. Together with a newly designed sample holder, the above mentioned problems are prevented or reduced. The vector detection coil system shows a relatively small error in the determination of the magnetization vector (±1% in the absolute value and ±0.6° in the angle). Furthermore, it has a relatively small positional dependency (1% per mm) combined with a sufficient sensitivity (1 nA m2 or 1 μemu at 10 s time constant) and a capability of using samples up to 10×10 mm2. The improved sample holder for thin film measurements reduces positional problems while, at the same time, reducing the background signals of the holder (to 10 pA m2 per kA/m or 7.958×10−10 emu/Oe).
Control circuit for a scanning tunneling microscope
Authors: Munoz Raúl C. , Villagra Paolo , Kremer Germán , Moraga Luis , Vidal Guillermo
Published: July 2002

We have successfully built and tested a circuit designed to control a piezoelectric tube scanner having the standard single inner-electrode quartered outer-electrode configuration, using digital-to-analog (D/A) converters commercially available. To avoid noise associated with the PC, the signals transmitted by the D/A channels to the control electronics are received by instrumentation amplifiers INA 105 at the control circuit, providing 86 dB common mode rejection, thereby over four orders of magnitude of immunity to common mode noise. To prevent ground loops in the communication between the control electronics and the analog-to-digital (A/D) converters, a novel approach was used. The signals sent by the control electronics to the A/D converters were transmitted via isolation amplifiers ISO 122 followed by a 10 kHz Sallen–Key low pass filter incorporated at each output of the control circuit, providing galvanic isolation between the control electronics and the PC, thereby eliminating ground loops. The control circuit was designed to allow analog as well as digital feedback, selectable via a toggle switch. The design also incorporates the possibility of using two independent external signals to modulate the polarization of the sample and two independent external signals to modulate the piezoelectric transducer drive along the Z direction. It also incorporates the possibility of electronically canceling the slope that might occur while scanning due to the sample being tilted along the X axis (fast scan direction) and/or along the Y axis (slow scan direction). The circuit was tested using two 12 bit A/D–D/A converters DAS 1602 to control the scanner of a scanning tunneling microscope, with a home-built scanning head, electrometer, and preamplifier. With the complete system in operation but in the absence of tunneling current, the electrometer exhibits a current noise under 3 pA rms and a response time of 30 μs to a step input current, a performance that compares well with that of bulkier and more expensive commercial low noise current amplifiers. To calibrate the instrument and verify proper control operation, we obtained images of a commercial holographic grating covered with gold running the instrument in the digital feedback mode, using the algorithm described by Piner and Reifenberger [Rev. Sci. Instrum. 60, 3123 (1989)]. The control circuit and the electrometer turn out to be about one order of magnitude less expensive than commercially available control circuits and low noise current amplifiers of similar performance.
Optimized dipole antennas on photonic band gap crystals
Authors: Cheng S. D. , Biswas R. , Ozbay E. , McCalmont S. , Tuttle G. , Ho K.-M.
Published: July 2002

Photonic band gap crystals have been used as a perfectly reflecting substrate for planar dipole antennas in the 12–15 GHz regime. The position, orientation, and driving frequency of the dipole antenna on the photonic band gap crystal surface, have been optimized for antenna performance and directionality. Virtually no radiated power is lost to the photonic crystal resulting in gains and radiation efficiencies larger than antennas on other conventional dielectric substrates.
Background correction in electron-ion coincidence experiments using a self-optimizing, pseudorandom count generator
Authors: Powis Ivan , Downie Peter
Published: July 2002

A technique is described whereby an estimate of the false coincidence signal, suitable for background correction of data acquired in a coincidence experiment, is obtained by using a pseudorandom pulser to generate a stream of “false” start events. The statistical properties of this simulated source are adjusted to mimic those of the real source of electron start events. False ion coincidences with the simulated starts are measured concurrently with the real coincidence signal, with the mean count rate of the pseudorandom pulse source automatically tracking that of the true electron start events. In this manner any long term instrumental drifts during the course of an extended experimental measurement will similarly affect both the real and simulated coincidence data. Subtraction of the simulated background of false coincidences from the real coincidence data then yields an improved estimate of the true coincidence signal.
Parameters of the discharge plasma of surface-plasma H− ion sources
Authors: Antsiferov V. V.
Published: July 2002

The plasma of a high-current hydrogen–cesium glow discharge of planotron and Penning H− ion sources was studied with the use of spectroscopic methods. The elemental and charge compositions of the plasma were determined. The temperature of hydrogen atoms was determined and the electron density was estimated. The density variation of hydrogen atoms, cesium atoms, and molybdenum atoms (electrode material) and cesium ions during the discharge pulse with the space resolution along two coordinates was observed. Blocking up of cesium atoms and ions and molybdenum atoms near the cathode surface was found. The radiation energy of the discharge plasma was measured within the visible spectral range.
Measurement of thin liquid film drainage using a novel high-speed impedance analyzer
Authors: Hool Kevin O. , Saunders Robert C. , Ploehn Harry J.
Published: July 2002

This work describes the design and implementation of a new instrument, called the thin film impedance analyzer, which measures the rate of drainage of thin oil films. The instrument forms an oil film by elevating a planar oil–water interface into a water drop hanging from a stainless steel capillary tube immersed in the oil. The instrument measures the magnitude of the impedance of the matter between the capillary tube and a screen electrode immersed in the lower water phase. Under appropriate conditions, the capacitance of the oil film dominates the impedance. The instrument records the increase in the magnitude of the admittance associated with the draining and thinning of the oil film. The features of the drainage curves vary considerably with the type, amount, and location of surfactants in the oil and water phases, as well as with user-specified values of drop volume, drop equilibration time, and extent of drop compression. For this reason, the instrument has utility as a screening tool for selecting surfactants for emulsion formulations. Potential future uses include accelerated prediction of emulsion stability and extraction of oil–water interfacial rheological parameters.
Lubricant film thickness mapping using a capacitance technique on magnetic thin-film rigid disks
Authors: Hahm Chris D. , Bhushan Bharat
Published: July 2002

We describe a novel capacitance measurement technique which is used to determine lubricant film thickness on magnetic thin-film rigid disks. Using this technique, variations in lubricant thickness as small as 0.1 nm can be measured quickly and nondestructively. Film thickness measurements made with an ellipsometer are found to be comparable to the capacitance measurements. We compare the uniformity in film thickness of disks lubricated with a dip-coating process with that of disks lubricated with a drain-coating process and find that the drain coated disks have better film uniformity than those that are dip coated. Also, wear tracks in fully bonded and partially bonded perfluoropolyether lubricants are profiled. We find that lubricant depletion occurs more rapidly in fully bonded lubricant than in partially bonded lubricant and that some recovery of the partially bonded lubricant occurs while none is observed in fully bonded lubricant.