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Feb 2000

Volume 71, Issue 2, pp. 335-1239

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back to top FUNDAMENTAL PHENOMENA FOR ION SOURCES

Investigation of different oven types for sample evaporation in the CAPRICE electron cyclotron resonance ion source

R. Lang, J. Bossler, H. Schulte, and K. Tinschert

Rev. Sci. Instrum. 71, 651 (2000); http://dx.doi.org/10.1063/1.1150338 (3 pages) | Cited 5 times

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The operation of the CAPRICE-type electron cyclotron resonance ion source (ECRIS) at the high charge state injector of GSI requires a great variety of different ion species (between Z = 3 and Z = 92) to be delivered to the accelerator. As most of the elements have to be produced from nongaseous materials, oven evaporation has become an elaborate and routinely used technique at GSI. Besides an evaporator for high vapor pressure materials (T ⩽ 300 °C) a standard oven system is used for temperatures between 600 °C and 1500 °C. Several modifications of this standard oven have been developed to adapt it to the operating conditions for different materials. The respective characteristics are described and operational experiences are reported. In order to extend the available temperature regime up to 2000 °C, a new type of oven is being developed which completely avoids any ceramics in its high temperature zone. Thus the number of materials accessible for evaporation is considerably extended. First experiences obtained with this high temperature oven are presented. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
07.20.Hy Furnaces; heaters
29.27.Ac Beam injection and extraction

Selective minority-ion heating in the afterglow of an electron cyclotron resonance ion source

A. Nadzeyka, D. Meyer, F. Barzangy, A. G. Drentje, and K. Wiesemann

Rev. Sci. Instrum. 71, 654 (2000); http://dx.doi.org/10.1063/1.1150339 (3 pages)

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We report first experimental results on selective minority-ion heating in the afterglow mode of electron cyclotron resonance ion sources in Bochum and at the KVI (Groningen) in mixtures of Ar/O/He and in pure nitrogen. In addition we measured time resolved vacuum ultraviolet-line intensities of different ion species and compared them to the extracted ion currents in the afterglow. In contrast to our model calculations, selective ion heating of medium and high charge states of, e.g., oxygen results in an instantaneous destruction of the respective afterglow peak. Our observations show that the physics of the afterglow peak is not yet fully understood. It remains questionable whether the afterglow peaks can be solely explained by a destruction of electrostatic confinement in the afterglow. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams
07.77.Ka Charged-particle beam sources and detectors
52.80.Hc Glow; corona

Enhanced production of multi-charged ions using pulse-modulated microwave in a 2.45 GHz electron cyclotron resonance source

Yushi Kato, Shigeki Kobayashi, and Shigeyuki Ishii

Rev. Sci. Instrum. 71, 657 (2000); http://dx.doi.org/10.1063/1.1150340 (3 pages) | Cited 5 times

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Fundamental phenomena of an electron cyclotron resonance (ECR) multi-charged ion source (2.45 GHz) have been experimentally studied. The ECR plasma is confined in the mirror field superimposed by the octupole magnetic field. An ECR zone and potential well are formed near the bottom of the mirror trap. Multi-charged ions pass through the extractor at the mirror end, and the charge state distributions of extracted ions are investigated. Pulse-modulated microwave produces the ECR plasma with afterglow, relaxes the potential well, and then enhances the extracted multi-charged ion currents. Time-averaged Ar4+−9+ currents increase, even when the microwave power is nearly equal to or lower than the continuous microwave. The rectangular pulse width and the duty ratio are typically about 0.05 ms and 50%, respectively. The origin of enhanced production by pulse-modulated microwave is discussed by taking account of plasma parameters. Measurement of plasma parameters by a Langmuir probe and dependence of current increment on the ionic charge suggest the relaxation of the potential well. © 2000 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.50.Gj Plasma heating by particle beams
52.80.Pi High-frequency and RF discharges
29.25.Ni Ion sources: positive and negative

Influence of plasma-wall interaction on high charge state production in electron cyclotron resonance ion sources

D. Meyer, H. Schmitz, Th. Daube, C. Mannel, and K. Wiesemann

Rev. Sci. Instrum. 71, 660 (2000); http://dx.doi.org/10.1063/1.1150341 (3 pages) | Cited 2 times

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In contrast to the widely accepted model of ion cooling, which is supposed to fully explain the gas mixing effect, we recently presented an alternative model of self-enhanced sputtering of wall material. In order to prove our model further, we numerically simulated different plasma parameters in the vicinity of plasma limiting edges of the discharge chamber (walls) via particle in cell and Monte Carlo methods. Both experimental investigations and simulations give clear evidence that the optimization of an electron cyclotron resonance ion source with respect to the high charge state production is sensitively influenced by the contamination of the plasma with heavy atoms sputtered off the walls. Any optimization of the charge state distribution in physical terms means nothing else than balancing the ratio of hot and cold electrons. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams
52.40.Hf Plasma-material interactions; boundary layer effects
52.65.Rr Particle-in-cell method
52.65.Pp Monte Carlo methods
07.77.Ka Charged-particle beam sources and detectors

Ionization equilibria and efficiency for electron cyclotron resonance ion sources

M. Cavenago

Rev. Sci. Instrum. 71, 663 (2000); http://dx.doi.org/10.1063/1.1150253 (3 pages) | Cited 2 times

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Kinetic equilibria implications on the ionization efficiency ηi of electron cyclotron resonance (ECR) ion sources when used as a charge breeder are discussed. The ion density distribution n(i) where i is the ion charge state is here expressed by a properly factorized formula, which allows analytic consideration. Agreement with some numerical simulation is excellent. In the case of low ion recombination rates, a detailed solution is given, and some relevant approximation of ionization rate Si and ionization energies are proposed. A useful approximation log(Si) = a−(cs−k3)i is found, with a and cs mainly related to ionization energies and macroscopic plasma parameters, such as the hot electron density nh and temperature Th, while k3 is related to the ambipolar electrostatic potential. Formulas for the charge state at which efficiency is maximum and for the maximum value are written in detail. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams
52.65.-y Plasma simulation
07.77.Ka Charged-particle beam sources and detectors

A one-dimensional axial electron cyclotron resonance source model

D. H. Edgell, J. S. Kim, S. K. Wong, R. C. Pardo, and R. Vondrasek

Rev. Sci. Instrum. 71, 666 (2000); http://dx.doi.org/10.1063/1.1150254 (3 pages) | Cited 3 times

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A conventional zero-dimensional (uniform plasma parameters with no spatial variations) fluid model will provide a good match with an experimental electron cyclotron resonance ion source (ECRIS) charge-state distribution (CSD) if provided with a judicious set of user inputs. However, this arbitrarily chosen set of inputs is not necessarily unique. To be truly predictive, an ECRIS model should rely on experimental parameters as inputs. A multi-species model for an ECRIS plasma using experimental parameters as inputs is under development. The model eliminates electron temperature as a user input by employing a 2 V(v,θ) Fokker–Planck code with an ECR heating term to calculate the non-Maxwellian anisotropic electron distribution function. Further arbitrary user inputs are eliminated in favor of controlled parameters by bounce averaging the Fokker–Planck coefficients for a one-dimensional (1D)/2 V axial model. The neutral gas modeling has been extended to 1D using axially coupled particle balance equations. The improved model is able to reproduce experimental Faraday cup (CSDA) from the Argonne National Laboratory’s ECR-II. Further elimination of arbitrary inputs is expected when the ion model is extended to 1D. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
52.65.Ff Fokker-Planck and Vlasov equation

Formation of multi-charged ions and plasma stability at quasigasdynamic plasma confinement in a mirror magnetic trap

S. V. Golubev, S. V. Razin, V. E. Semenov, A. N. Smirnov, A. V. Vodopyanov, and V. G. Zorin

Rev. Sci. Instrum. 71, 669 (2000); http://dx.doi.org/10.1063/1.1150255 (3 pages) | Cited 11 times

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It is known that an increase in plasma density in sources of multicharged ions leads to a substantial increase of ion current and slightly improves the ion distribution over charge states. The validity of this statement was verified in experiments with plasma densities not exceeding several units of 1012 cm−3. In the present work it is demonstrated experimentally that, for the electron densities exceeding 1013 cm−3, the regime of plasma confinement in a trap changes significantly and the quasigasdynamic regime of plasma confinement is realized. Comparison of numerical simulations and experimental data showed the essential influence of the anisotropy of electron velocity distribution in a plasma on the ion charge state distribution. This allows looking for the optimal conditions for the creation of highly charged ions in plasma. In this article we also address problems of plasma stability in an axisymmetric mirror trap under powerful microwave pumping. First experiments on ion extraction from a dense plasma pumped by millimeter wave radiation are described. © 2000 American Institute of Physics.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.50.Gj Plasma heating by particle beams
07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative

On the use of magnetic buckets for ion beam profile tailoring

R. A. MacGill, A. Vizir, and I. G. Brown

Rev. Sci. Instrum. 71, 672 (2000); http://dx.doi.org/10.1063/1.1150256 (3 pages) | Cited 1 time

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Magnetic multipole plasma confinement geometries employing permanent magnet “buckets” are used extensively for a range of laboratory plasma applications. Among the several consequences for plasma confinement is the important result that the plasma can acquire a more-or-less flat density profile, which when embodied in an ion source, can also lead to a flat profile for the extracted ion beam. For many applications a uniform ion beam current density profile is quite advantageous, for example, for carrying out large-area ion implantation. There are, however, inherent limitations on the extent to which this approach to beam “homogenization” can be utilized, and even for a perfectly flat profile in the immediate postextraction region, the beam will evolve toward Gaussian as it propagates downstream. Here we describe the rare-earth permanent magnet bucket that we have incorporated into our broad-beam vacuum arc ion source, and its effect on the beam profile at the extractor and downstream. The experimental results are compared with a simple model for the beam profile evolution with axial distance. We find that the beam loses memory of its initially flat profile and relaxes to a more-or-less Gaussian shape in a relatively short axial distance ∼ w/4θ, where w is the initial width of the flat beam profile and θ is the beamlet divergence half angle. © 2000 American Institute of Physics.
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29.27.Ac Beam injection and extraction
28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors

An investigation into the mechanism of pseudospark producing metal ion beams

C. G. Cai, W. J. Zhao, S. Yan, X. Y. Le, B. X. Han, J. M. Xue, Y. G. Wang, and X. L. Jiang

Rev. Sci. Instrum. 71, 675 (2000); http://dx.doi.org/10.1063/1.1150257 (3 pages)

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A multiplate pseudospark chamber, whose electrodes were fabricated with different metal materials, was designed and tested as a metal ion source. The ion beam implantation combined with Rutherford backscattering (RBS) measurement was used to understand whether these ion beams come from the anode plasma or the cathode plasma. The RBS measurements have demonstrated the following results: (1) pseudospark produced metal ion beams mainly consist of ions from the cathode materials; (2) the ion beam current increases rapidly with the pseudospark discharge voltage first and then saturates; and (3) the energy of the extracted metal ions is much less than the voltage between the anode and the cathode, therefore the high discharge voltage does not correspond to the high ion energy. A possible mechanism of pseudospark producing metal ion beams is discussed. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
07.77.Ka Charged-particle beam sources and detectors
41.75.Ak Positive-ion beams

Approximation of the plasma inhomogeneity by broad-beam measurements and simulation

M. Tartz, E. Hartmann, R. Deltschew, and H. Neumann

Rev. Sci. Instrum. 71, 678 (2000); http://dx.doi.org/10.1063/1.1150258 (3 pages) | Cited 1 time

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In broad-beam ion sources an inhomogeneous plasma distribution has a strong effect on both the maximum extractable ion current and the broad-beam profile. An approximate plasma distribution function is determined by fitting calculated accelerator-grid currents to corresponding experimental data, thus efficiently replacing complicated and expensive plasma probe measurements. © 2000 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
29.27.Ac Beam injection and extraction
52.65.-y Plasma simulation
29.25.Ni Ion sources: positive and negative
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Ds Electric and magnetic measurements
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Selection of the powdery metal hydride best for producing H− by thermal desorption

H. Kawano, A. Tanaka, S. Sugimoto, T. Iseki, Y. Zhu, M. Wada, and M. Sasao

Rev. Sci. Instrum. 71, 853 (2000); http://dx.doi.org/10.1063/1.1150311 (3 pages) | Cited 3 times

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To find the metal hydride best for producing H− by thermal desorption, the desorption rates of H−, H2 and electron (e−) directly emitted from a powdery sample (∼1 mg) of NaH, LiH, MgH2, CaH2, SrH2, TiH2, ZrH2, KBH4, LiAlH4, or NaAlH4 heated up to ∼1000 K were determined simultaneously with a special system. Theoretical analysis of the experimental data thus achieved yields the following results. (1) Both H− and e− are emitted from those active spots (mainly consisting of alkali or alkali earth metal) created by thermal decomposition (e.g., LiH→Li+H2/2). (2) The active spots are readily destroyed and reconstructed by admission of H2 and by stopping the admission, respectively. (3) The work function (ϕ) of activated NaH is very low (∼2 eV), but NaH is rapidly depleted owing to its thermal instability. (4) Among the ten hydrides, CaH2 is concluded to be the best as a source material for thermal desorption of H− because activated CaH2 (ϕ≃5 eV) is most stable and strongest in H− ( ∼ 10−12 A or 10−10 A/cm2 after mass analysis) around 900 K. © 2000 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Selection of the substrate metal best for thermal positive ionization

H. Kawano, H. Mine, M. Moriyama, M. Tanigawa, and Y. Zhu

Rev. Sci. Instrum. 71, 856 (2000); http://dx.doi.org/10.1063/1.1150312 (3 pages) | Cited 2 times

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To select the substrate metal best for producing thermal positive ions from incident sample molecules, a beam of diatomic molecule (MX) such as LiCl, NaBr, or TlCl was directed with a constant flux ( ∼ 1012–1014 molecules cm−2 s−1) onto a polycrystalline thin wire (∼0.01–0.02 cm in diameter) of refractory metal (Nb, Mo, Ta, W, Re, Ir, or Pt) heated in vacuum ( ∼ 10−7–10−5 Torr), and the total emission current ( ∼ 10−10–10−8 A) of the positive ion (M+) was measured as a function of wire temperature (∼900–2300 K). The experimental data newly achieved were analyzed by our theoretical model to determine the ionization efficiency (β+) and also the work function (ϕ+) effective for the ionization. Among the seven metals, Re is concluded to be best for the ionization because Re is highest in ϕ+( ∼ 7.5 eV), thereby making it possible to produce M+ efficiently (β+ = 1) and stably (within ±1%) from those 30 elements (M) whose ionization energy is less than ∼6.5 eV. © 2000 American Institute of Physics.
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79.40.+z Thermionic emission
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.30.+y Surface double layers, Schottky barriers, and work functions

Influence of electron injection on electron cyclotron resonance plasma properties and reflected mode electrons (abstract)

V. P. Ovsyannikov, F. Ullmann, and G. Zschornack

Rev. Sci. Instrum. 71, 859 (2000); http://dx.doi.org/10.1063/1.1150145 (1 page)

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The injection of an additional strong focused electron beam from a special designed electron gun into a magnetic electron cyclotron resonance (ECR) confinement field is studied. The electron gun uses a cathode with a long lifetime and resistiveness providing high emission current densities with electron currents up to 50 mA and voltages up to 4 keV. A sequence of aluminum foils is used to investigate the trajectories of the electrons in the magnetic field without plasma. The high density electron beam passes through the foils, welds them, and prints its image into the foils. Details of this technique are described in Ref. 1. Using this technique we see that before the electrons enter the sextupole region the beam moves along the magnetic straight lines preserving its structure. Only a central beam passes through the sextupole region, thereby changing its form due to the interaction with radial components of the magnetic field. A new operation method at our 14.5 GHz ECR ion source is based on so-called reflection mode electrons (RMEs) analogous to a known electron beam ion source operation regime.2 The basic idea is that electrons, which traveling from the cathode in a strong axial field, meet an anticathode potential, are reflected from it, move back to the cathode, and will be reflected again and so on. It can be supposed that the electrons will make reflections up to the moment when the anode aperture of the gun is fulfilled and the electrons will be collected on the anode electrode. Investigations are performed extracting nitrogen ions using the RME beam. As a result we got a clear increase in the beam current of the extracted ions (e.g., at 10 mA electron injection an increase of the current of N5+ ions up to 400%) and a shift of the measured ion charge state distribution to higher mean ionization stages. Measured x-ray spectra from a neon loaded plasma show for the case of RME operation increasing energy shifts to the high energy side of the spectra, i.e., the mean ionization degree of the ions in the plasma increases. They also increase the intensity of the neon K x rays (more than 100% increase for RME injection of Ee=4 keV and Ie = 10mA) indicating that for the same operation parameters the mean density of energetic electrons rises at RME injection, i.e., there are more electrons with energies high enough to ionize K-shell electrons in neon. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.40.Mj Particle beam interactions in plasmas
29.27.Ac Beam injection and extraction

Production of intense 48Ca ion beam at the U-400 cyclotron

V. B. Kutner, S. L. Bogomolov, A. A. Efremov, A. N. Lebedev, V. Ya. Lebedev, V. N. Loginov, A. B. Yakushev, and N. Yu. Yazvitsky

Rev. Sci. Instrum. 71, 860 (2000); http://dx.doi.org/10.1063/1.1150313 (3 pages) | Cited 4 times

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Production of the intense accelerated 48Ca ion beam is the key problem in the experiments on synthesizing of new heavy nuclei. For this purpose an axial injection system with the electron cyclotron resonance (ECR)-4M ion source was created for the U400 cyclotron. The task was to achieve an accelerated beam with an intensity of 0.5 pμA of 48Ca5+ at the 48Ca consumption of ∼0.5 mg/h. To solve this problem, a new method for the solid material feed into the ECR source was developed. The combination of a micro oven with a hot tantalum sheet inside the discharge chamber allowed the production of intense beams of ions of metals with relatively low melting point. The present article describes the method, technique, and experimental results on the production of 48Ca ion beam at the U-400 cyclotron from the ECR-4M ion source. The analysis of the working substance balance in the ion source including the ion beam extraction and material regeneration is performed. The analysis based on the experimental data has shown that the efficiency of Ca atom transformation into ion beam is close to that obtained for the gases such as Ar, and the intensity of 48Ca5+ constitutes about 20% of the extracted ion beam. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
29.27.Ac Beam injection and extraction
29.20.dg Cyclotrons

Effect of a biased probe on the afterglow operation of an ECR4 ion source

C. E. Hill, D. Küchler, F. Wenander, and B. H. Wolf

Rev. Sci. Instrum. 71, 863 (2000); http://dx.doi.org/10.1063/1.1150314 (3 pages) | Cited 1 time

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Various experiments have been performed on a 14.5 GHz ECR4 in order to improve the ion yield. The source runs in pulsed afterglow mode, and provides currents ∼120 eμA of Pb27+ to the CERN Heavy Ion Facility on an operational basis. In the search for higher beam intensities, the effects of a pulsed biased disk on axis at the injection side were investigated with different pulse timing and voltage settings. No proof for absolute higher intensities was seen for any of these modifications. However, the yield from a poorly tuned/low-performing source could be improved and the extracted pulse was less noisy with bias voltage applied. The fast response on the bias implies that increases/decreases are not due to ionization processes. A good tune for high yield of high charge states during the afterglow coincides with a high plasma potential. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams
29.27.Ac Beam injection and extraction
52.80.Hc Glow; corona
29.20.-c Accelerators

Comparison of electron cyclotron resonance plasma characteristics discharged by 7.0, 8.0, and 9.4 GHz

Y. Kawai, T. Saburi, S-H. Kim, Y. Fujii, and T. Suzuki

Rev. Sci. Instrum. 71, 866 (2000); http://dx.doi.org/10.1063/1.1150315 (3 pages) | Cited 3 times

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Argon electron cyclotron resonance plasma characteristics discharged by 7.0, 8.0, and 9.4 GHz microwaves are measured at 0.013 and 0.080 Pa in a cylindrical chamber. The plasma densities and electron temperatures were found to be almost independent of the microwave frequency at 0.013 Pa, whereas clear differences were seen at 0.080 Pa. At 0.080 Pa, the plasma densities were observed to increase with the increase in the discharge frequency. Electron temperatures at 0.080 Pa also appeared to become higher with the increase in discharge frequency. © 2000 American Institute of Physics.
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52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges

Production of highly charged ions in electron cyclotron resonance ion sources using an electrode in two modes

S. Biri, L. Kenéz, A. Valek, T. Nakagawa, M. Kidera, and Y. Yano

Rev. Sci. Instrum. 71, 869 (2000); http://dx.doi.org/10.1063/1.1150316 (3 pages) | Cited 1 time

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One of the most known ways to obtain higher beam intensities in electron cyclotron resonance (ECR) ion sources is to install an electrode (usually disk) into the plasma chamber. We found that a majority of the groups observed the beam intensity improvement by supplying a suitable biased voltage to the electrode and an electron current was injected into the plasma. A few groups observed the enhancement, however, when the electrode operated at floating potential—without being an electron donor. In spite of the great success of the “biased disk” method, the mechanism is still not completely clear. In this contribution, as a step toward of understanding, we examined the above mentioned two modes. The experiments were performed at the 18 GHz RIKEN and at the 14.5 GHz ATOMKI ECR ion sources. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors

Increasing the space-charge limit and other effects of cesium seeding in hydrogen negative ion sources

J. H. Whealton, M. Bacal, J. Bruneteau, and R. J. Raridon

Rev. Sci. Instrum. 71, 872 (2000); http://dx.doi.org/10.1063/1.1150317 (3 pages) | Cited 2 times

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The role of cesium seeding in increasing the negative ion current in volume sources is described. By a reduction in the local plasma potential the current of extracted electrons is vastly reduced. As a result, cesium increases the fraction of the transverse space-charge limit available to the ions by as much as a factor of 3. In addition, cesium can increase the total space-charge limit by injection of Cs+ into the presheath—a newly recognized phenomenon consistent with experimental measurements and determined from application of a Double–Vlasov model for negative ion extraction. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Dg Plasma sources

Beam instability excited by the magnetic filter

Hiroshi Naitou, Kazuo Ohi, and Osamu Fukumasa

Rev. Sci. Instrum. 71, 875 (2000); http://dx.doi.org/10.1063/1.1150318 (2 pages) | Cited 6 times

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By the one-dimensional electrostatic particle simulation, the ion beam instability is observed in the plasma divided by the magnetic filter (MF). The strength of the MF is selected to influence only electron dynamics; ions move freely across the MF. There are grounded walls at the left and right ends of the system. Particles hitting the walls are absorbed there. The high temperature and high density plasma (main plasma) faces the low temperature and low density plasma (subplasma) across the MF located at the center of the system. The averaged space potential of the main plasma is higher than that of the subplasma. Due to the potential gap at the MF, ions in the main plasma are accelerated into the subplasma. Depending on the extent of the asymmetry of the system, steady or the periodic (dynamic) state manifests. For the periodic state, high density clumps get into the subplasma and excite the strong ion beam instability. The new clump comes into the subplasma when the old clump reaches the wall. © 2000 American Institute of Physics.
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52.40.Mj Particle beam interactions in plasmas
52.65.Rr Particle-in-cell method

Relation between vapor Cs and adsorbed Cs in H− ion source

M. Ogasawara, T. Morishita, and A. Hatayama

Rev. Sci. Instrum. 71, 877 (2000); http://dx.doi.org/10.1063/1.1150319 (3 pages) | Cited 1 time

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The relation between gaseous Cs density and the coverage of Cs on the plasma grid surface is determined in the existence of the effect of Cs deposit on the cold surface. An equation for the deposit of Cs on the cold surface in the ion source is obtained by considering the saturation of the deposit. The Cs coverage is expressed as a function of gaseous Cs density in the volume of the ion source by considering the relation τθ≪τa, where τθ is the time scale of the Cs adsorption to the plasma grid surface and τa is that of the Cs adsorption to the cold surface. The coverage varies with the slow time scale through the variation of the gaseous density related to the deposit of Cs on the cold surface. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams

Numerical simulation of cesium cooling effects in H− ion source

T. Morishita, M. Ogasawara, and A. Hatayama

Rev. Sci. Instrum. 71, 880 (2000); http://dx.doi.org/10.1063/1.1150320 (3 pages) | Cited 2 times

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Cesium volume reactions are included in a two-point model numerical code for a high power hydrogen negative ion source. The energy balance equation for the electron temperature and rate equations of Cs and Cs+ are included in our code to investigate the electron cooling and volume effects by cesium seeding. Cesium density in the ion source is taken as a variable for the calculation. Cesium is ionized over 95% in the driver region of the ion source. The electron temperature begins to decrease at cesium density 1011 cm−3 and the electron density increases because of the ionization of cesium. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Gj Plasma heating by particle beams
52.65.-y Plasma simulation

Monte Carlo simulation of negative ion production in the negative hydrogen ion source

M. Uematsu, T. Morishita, A. Hatayama, T. Sakurabayashi, and M. Ogasawara

Rev. Sci. Instrum. 71, 883 (2000); http://dx.doi.org/10.1063/1.1150321 (4 pages) | Cited 15 times

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Two Monte Carlo simulation codes: (a) neutral transport code and (b) negative ion (H−) transport code, have been developed to understand transport phenomena in negative ion sources. In the neutral transport code, Boltzmann equations for hydrogen molecules (H2) and atoms (H) are solved. Three dimensional (3D) spatial distributions of H2, H, and H− production are obtained for a tandem negative ion source. The volume production of H− is limited to the area around the gas inlet in the first chamber and near the plasma grid in the second chamber. On the other hand, distribution of H− surface production is shown to be almost uniform over all the plasma grid surface. In the negative ion code, H− trajectories are calculated by numerically solving the 3D equation of motion for H− ions. The effects of the magnetic filter on the extraction probability of surface produced H− ions are mainly studied. The dependence of the extraction probability on the field strength is small. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.65.Pp Monte Carlo methods
52.50.Gj Plasma heating by particle beams
52.25.Fi Transport properties
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Some consequences to ion source behavior of high plasma drift velocity

I. G. Brown, O. R. Monteiro, M. M. M. Bilek, M. Keidar, E. M. Oks, and A. Vizir

Rev. Sci. Instrum. 71, 1086 (2000); http://dx.doi.org/10.1063/1.1150392 (4 pages) | Cited 3 times

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We consider the case of energetic ion beam formation when the ion streaming velocity within the source plasma is substantial, i.e., when the ions have a drift speed (in the positive downstream direction) that is on the order of or greater than the ion acoustic speed in the plasma. Some interesting consequences can follow, including the capability of a negatively biased substrate located in the plasma stream to maintain high bias voltage, and of an ion source with no extractor or “conventionally poor” extractor providing a kind of plasma immersion ion implantation mode of operation. Here we summarize the kind of plasma geometry in which this situation can occur, and describe some experimental observations we’ve made of these effects, with reference to a simple theoretical basis for the mechanism. © 2000 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
29.27.Ac Beam injection and extraction

Bipolar extraction neutralization: Time resolved characterization

D. Korzec, R. Dahlhaus, and J. Engemann

Rev. Sci. Instrum. 71, 1090 (2000); http://dx.doi.org/10.1063/1.1150393 (4 pages) | Cited 2 times

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By switching the polarization of the screen and accelerator grid of a two grid extraction system, an ion or electron beam can be extracted from the same gas discharge. Such ion source operation mode, called bipolar extraction neutralization (BEN), allows a filamentless current neutralization of electrically insulated substrates. In this study BEN was used for a broad (12 cm), high current (0.36 A) ion beam from an electron cyclotron resonance ion source. The neutralization process is controlled by the duty cycle and frequency of the electron extraction pulses. An electrostatic monitor was positioned in the vicinity of the sputter target and used for monitoring the beam plasma potential and control of the neutralization parameters. The beam potential and extraction grid currents are presented time resolved for neutralization frequency from 20 to 80 kHz and duty cycle from 10% to 80%. This kind of monitoring allows not only control of the ion/electron extraction but also determination of the ion time of flight between the extraction grid and the substrate. © 2000 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
41.85.Ar Particle beam extraction, beam injection
52.80.Pi High-frequency and RF discharges
41.85.Qg Particle beam analyzers, beam monitors, and Faraday cups

Numerical simulation and optimization of multicomponent ion beam from RIKEN electron cyclotron resonance ion sources

V. Alexandrov, T. Nakagawa, V. Shevtsov, and G. Shirkov

Rev. Sci. Instrum. 71, 1094 (2000); http://dx.doi.org/10.1063/1.1150394 (3 pages) | Cited 1 time

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A new version of a program library for numerical simulation of ion beam transportation is presented. The library is aimed at high current and low energy multicomponent beams from ion sources and based on the macroparticle method. It has been used to simulate and optimize the transport line between the 18 GHz ECR ion source and RFQ linac at RIKEN. It is shown that it is possible to improve the ion transportation efficiency to a factor of 2 or 3 using the solenoid instead of the present einzel lens as a first element of the line. © 2000 American Institute of Physics.
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29.27.Eg Beam handling; beam transport
29.27.Bd Beam dynamics; collective effects and instabilities
29.25.Ni Ion sources: positive and negative
29.27.Ac Beam injection and extraction
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