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Feb 2012

Volume 83, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 021101 (2012); http://dx.doi.org/10.1063/1.3681448 (28 pages)

Judah Levine

(Left image) The many faces of time and frequency metrology. © Salvador Dalí, Fundació Gala-Salvador Dalí / Artists Rights Society (ARS), New York, 2011.

Rev. Sci. Instrum. 83, 021102 (2012);http://dx.doi.org/10.1063/1.3682002 (7 pages)

Thomas E. Parker

(Right image) The SI second is realized by cesium fountain primary frequency standards such as NIST-F1 shown here. NISTF1 is operated by the National Institute of Standards and Technology in Boulder, Colorado, USA. However, other systems also play a significant role in the accuracy of the SI second as delivered to users
(©2005 Geoffrey Wheeler Photography).

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back to top Negative Ion Sources

Optimizing the front end test stand high performance H− ion source at RAL

D. Faircloth, S. Lawrie, C. Gabor, A. Letchford, M. Whitehead, T. Wood, and M. Perkins

Rev. Sci. Instrum. 83, 02A701 (2012); http://dx.doi.org/10.1063/1.3655526 (3 pages) | Cited 1 time

Online Publication Date: 1 February 2012

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The aim of the front end test stand project is to demonstrate that chopped low energy H− beams of high quality can be produced. The beam line currently consists of the ion source, a 3 solenoid low energy beam transport and a suite of diagnostics. A brief status report of the radio frequency quadrupole is given. This paper details the work to optimize the ion source performance. A new high power pulsed discharge power supply with greater reliability has been developed to allow long term, stable operation at 50 Hz with a 60 A, 2.2 ms discharge pulse and up to 100 A at 1.2 ms. The existing extraction power supply has been modified to operate up to 22 kV. Results from optical spectroscopy measurements and their application to source optimization are summarized. Source emittances and beam currents of 60 mA are reported.
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29.25.Ni Ion sources: positive and negative
29.27.Ac Beam injection and extraction
29.27.Fh Beam characteristics

Matrix of small-radius radio-frequency discharges as a volume-production based source of negative hydrogen ions

St. Lishev, Ts. Paunska, A. Shivarova, and Kh. Tarnev

Rev. Sci. Instrum. 83, 02A702 (2012); http://dx.doi.org/10.1063/1.3662019 (5 pages) | Cited 2 times

Online Publication Date: 6 February 2012

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Based on experience from a work—both theoretical and experimental one—on negative hydrogen ion beam sources studied regarding fusion applications, a novel design of a rf source with volume production of the ions is proposed. The suggestion is for a source constructed as a matrix of small-radius tandem discharges (with magnetic filters largely extended over the discharge length), inductively driven (by a single coil, for the whole matrix) and with a single aperture extraction from each of them.
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52.80.Pi High-frequency and RF discharges
52.50.Dg Plasma sources

Status of the plasma generator of the superconducting proton linac

M. Kronberger, D. Faircloth, J. Lettry, M. Paoluzzi, H. Pereira, J. Sanchez Arias, C. Schmitzer, and R. Scrivens

Rev. Sci. Instrum. 83, 02A703 (2012); http://dx.doi.org/10.1063/1.3662478 (3 pages) | Cited 1 time

Online Publication Date: 7 February 2012

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In the framework of the superconducting proton linac (SPL) study at CERN, a new non-cesiated H− plasma generator driven by an external 2 MHz RF antenna has been developed and successfully operated at repetition rates of 50 Hz, pulse lengths of up to 3 ms, and average RF powers of up to 3 kW. The coupling efficiency of RF power into the plasma was determined by the cooling water temperatures and the analysis of the RF forward and reflected power and the antenna current and amounts to 50%–60%. The plasma resistance increases between 10 kW and 40 kW RF power from about 0.45 Ω to 0.65 Ω. Measurements of RF power dissipated in the ferrites and the magnets on a test bench show a 5-fold decrease of the power losses for the magnets when they are contained in a Cu box, thus validating the strategy of shielding the magnets with a high electrical conductivity material. An air cooling system was installed in the SPL plasma generator to control the temperatures of the ferrites despite hysteresis losses of several Watts.
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29.20.Ej Linear accelerators

Initial study of the optical spectrum of the ISIS H− ion source plasma

S. R. Lawrie, D. C. Faircloth, and K. Philippe

Rev. Sci. Instrum. 83, 02A704 (2012); http://dx.doi.org/10.1063/1.3662959 (3 pages)

Online Publication Date: 7 February 2012

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The front end test stand is being constructed at the Rutherford Appleton Laboratory, with the aim of producing a 60 mA, 2 ms, 50 Hz, perfectly chopped H− ion beam. To meet the beam requirements, a more detailed understanding of the ion source plasma is required. To this end, an initial study is made of the optical spectrum of the plasma using a digital spectrometer. The atomic and molecular emission lines of hydrogen and caesium are clearly distinguished and a quantitative comparison is made when the ion source is run in different conditions. The electron temperature is 0.6 eV and measured line widths vary by up to 75%.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
52.50.Dg Plasma sources

Simulation of H− ion source extraction systems for the Spallation Neutron Source with Ion Beam Simulator

T. Kalvas, R. F. Welton, O. Tarvainen, B. X. Han, and M. P. Stockli

Rev. Sci. Instrum. 83, 02A705 (2012); http://dx.doi.org/10.1063/1.3663244 (3 pages) | Cited 2 times

Online Publication Date: 7 February 2012

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A three-dimensional ion optical code IBSimu, which is being developed at the University of Jyväskylä, features positive and negative ion plasma extraction models and self-consistent space charge calculation. The code has been utilized for modeling the existing extraction system of the H− ion source of the Spallation Neutron Source. Simulation results are in good agreement with experimental data. A high-current extraction system with downstream electron dumping at intermediate energy has been designed. According to the simulations it provides lower emittance compared to the baseline system at H− currents exceeding 40 mA. A magnetic low energy beam transport section consisting of two solenoids has been designed to transport the beam from the alternative electrostatic extraction systems to the radio frequency quadrupole.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
52.50.Dg Plasma sources

Optimization of negative ion current in a compact microwave driven upper hybrid resonance multicusp plasma source

D. Sahu, S. Bhattacharjee, M. J. Singh, M. Bandyopadhyay, and A. Chakraborty

Rev. Sci. Instrum. 83, 02A706 (2012); http://dx.doi.org/10.1063/1.3670346 (3 pages) | Cited 2 times

Online Publication Date: 13 February 2012

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Performance of a microwave driven upper hybrid resonance multicusp plasma source as a volume negative ion source is reported. Microwaves are directly launched into the plasma chamber predominantly in the TE11 mode. The source is operated at different discharge conditions to obtain the optimized negative H− ion current which is ∼33 μA (0.26 mA/cm2). Particle balance equations are solved to estimate the negative ion density, which is compared with the experimental results. Future prospects of the source are discussed.
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52.50.Dg Plasma sources
52.25.Fi Transport properties
52.80.Pi High-frequency and RF discharges
29.25.Ni Ion sources: positive and negative

Development of a versatile multiaperture negative ion source

M. Cavenago, T. Kulevoy, S. Petrenko, G. Serianni, V. Antoni, M. Bigi, F. Fellin, M. Recchia, and P. Veltri

Rev. Sci. Instrum. 83, 02A707 (2012); http://dx.doi.org/10.1063/1.3670350 (3 pages) | Cited 1 time

Online Publication Date: 13 February 2012

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A 60 kV ion source (9 beamlets of 15 mA each of H−) and plasma generators are being developed at Consorzio RFX and INFN-LNL, for their versatility in experimental campaigns and for training. Unlike most experimental sources, the design aimed at continuous operation. Magnetic configuration can achieve a minimum |B| trap, smoothly merged with the extraction filter. Modular design allows for quick substitution and upgrading of parts such as the extraction and postacceleration grids or the electrodes in contact with plasma. Experiments with a radio frequency plasma generator and Faraday cage inside the plasma are also described.
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29.25.Ni Ion sources: positive and negative
52.50.-b Plasma production and heating

Forty years of surface plasma source development

Vadim Dudnikov

Rev. Sci. Instrum. 83, 02A708 (2012); http://dx.doi.org/10.1063/1.3670600 (5 pages) | Cited 1 time

Online Publication Date: 13 February 2012

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The cesiation effect, a significant enhancement of negative ion emission from a gas discharge with decrease of co-extracted electron current below negative ion current, was observed for the first time on July 1, 1971 by placing into the discharge a compound with 1 mg of cesium. Subsequent developments of surface plasma sources (SPS) for highly efficient negative ion production caused by the interaction of plasma particles with electrodes on which the adsorbed cesium reduced the surface work function are described. In the last 40 years, the intensity of negative ion beams has increased by cesiation up to 104 times from 3 mA to tens of amperes. Here, the main attention is concentrated on earlier SPS developments because recent results are well known and widely available.
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52.80.-s Electric discharges
41.75.Cn Negative-ion beams

Correlation between the plasma parameters and the extracted current density in the volume-production based sources of negative hydrogen ions

St. Lishev, A. Shivarova, and Kh. Tarnev

Rev. Sci. Instrum. 83, 02A709 (2012); http://dx.doi.org/10.1063/1.3670604 (4 pages)

Online Publication Date: 13 February 2012

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Unified description of a volume-production based source of negative hydrogen ions, including its three regions—the driver, the plasma expansion through the magnetic filter, and the extraction of the ions at the position of the first electrode of the extraction system—is presented within a two-dimensional fluid plasma model. The results display the crucial role of the potential of the first electrode of the extraction system and show that the optimized conditions for the source operation should ensure proper balance between the local and non-local processes in the discharge. The role of the material of the plasma electrode is also discussed.
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29.25.Ni Ion sources: positive and negative
41.75.Cn Negative-ion beams
52.50.-b Plasma production and heating
52.80.-s Electric discharges

MeV negative ion source from ultra-intense laser-matter interaction

S. Ter-Avetisyan, B. Ramakrishna, D. Doria, R. Prasad, M. Borghesi, A. A. Andreev, S. Steinke, M. Schnürer, P. V. Nickles, and V. Tikhonchuk

Rev. Sci. Instrum. 83, 02A710 (2012); http://dx.doi.org/10.1063/1.3670741 (3 pages) | Cited 2 times

Online Publication Date: 14 February 2012

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Experimental demonstration of negative ion acceleration to MeV energies from sub-micron size droplets of water spray irradiated by ultra-intense laser pulses is presented. Thanks to the specific target configuration and laser parameters, more than 109 negative ions per steradian solid angle in 5% energy bandwidth are accelerated in a stable and reliable manner. To our knowledge, by virtue of the ultra-short duration of the emission, this is by far the brightest negative ion source reported. The data also indicate the existence of beams of neutrals with at least similar numbers and energies.
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29.25.Ni Ion sources: positive and negative
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Beam purification by photodetachment (invited)

Y. Liu, P. Andersson, J. R. Beene, O. Forstner, A. Galindo-Uribarri, T. Gottwald, D. Hanstorp, C. C. Havener, A. O. Lindahl, and K. Wendt

Rev. Sci. Instrum. 83, 02A711 (2012); http://dx.doi.org/10.1063/1.3671747 (5 pages)

Online Publication Date: 14 February 2012

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Ion beam purity is of crucial importance to many basic and applied studies in nuclear science. Selective photodetachment has been proposed to suppress unwanted species in negative ion beams while preserving the intensity of the species of interest. A highly efficient technique based on photodetachment in a gas-filled radio frequency quadrupole ion cooler has been demonstrated. In off-line experiments with stable ions, up to 104 times suppression of the isobar contaminants in a number of interesting radioactive negative ion beams has been demonstrated. For selected species, this technique promises new experimental possibilities in studies on exotic nuclei, accelerator mass spectrometry, and fundamental properties of negative atomic and molecular ions.
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29.25.Ni Ion sources: positive and negative
41.75.Cn Negative-ion beams
29.25.Rm Sources of radioactive nuclei
07.77.Ka Charged-particle beam sources and detectors

Surface plasma source with saddle antenna radio frequency plasma generator

V. Dudnikov, R. P. Johnson, S. Murray, T. Pennisi, C. Piller, M. Santana, M. Stockli, and R. Welton

Rev. Sci. Instrum. 83, 02A712 (2012); http://dx.doi.org/10.1063/1.3672111 (3 pages)

Online Publication Date: 15 February 2012

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A prototype RF H− surface plasma source (SPS) with saddle (SA) RF antenna is developed which will provide better power efficiency for high pulsed and average current, higher brightness with longer lifetime and higher reliability. Several versions of new plasma generators with small AlN discharge chambers and different antennas and magnetic field configurations were tested in the plasma source test stand. A prototype SA SPS was installed in the Spallation Neutron Source (SNS) ion source test stand with a larger, normal-sized SNS AlN chamber that achieved unanalyzed peak currents of up to 67 mA with an apparent efficiency up to 1.6 mA/kW. Control experiments with H− beam produced by SNS SPS with internal and external antennas were conducted. A new version of the RF triggering plasma gun has been designed. A saddle antenna SPS with water cooling is fabricated for high duty factor testing.
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52.50.Dg Plasma sources
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides

Surface plasma source with anode layer plasma accelerator

Vadim Dudnikov

Rev. Sci. Instrum. 83, 02A713 (2012); http://dx.doi.org/10.1063/1.3672115 (3 pages)

Online Publication Date: 15 February 2012

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Proposed plasma generation system can be used for high current negative ion beam production and for directed deposition by flux of sputtered neutrals and negative ions. The main mechanism of negative ion formation in surface plasma sources is the secondary emission from low work function surface bombarded by a flux of positive ion or neutrals. The emission of negative ions is enhanced significantly by introducing a small amount of cesium or other substance with low ionization potential. In the proposed source are used positive ions generated by Hall drift plasma accelerator (anode layer plasma accelerator or plasma accelerator with insulated channel, with cylindrical or race track configuration of emission slit). The target-emitter is bombarded by the ion beam accelerated in crossed ExB fields. Negative ions are extracted from the target surface with geometrical focusing and are accelerated by negative voltage applied between emitter and plasma, contacting with the plasma accelerator. Hall drift ion source has a special design with a space for passing of the emitted negative ions and sputtered particles through the positive ion source.
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52.50.Dg Plasma sources
52.38.Kd Laser-plasma acceleration of electrons and ions

Absolute beam brightness detector

Vadim Dudnikov

Rev. Sci. Instrum. 83, 02A714 (2012); http://dx.doi.org/10.1063/1.3672118 (3 pages)

Online Publication Date: 15 February 2012

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In generally accepted emittance measurement, main attention is concentrated on emittance areas ɛx, ɛy occupied by desired part of ion beam in transverse phase space and shape of these areas. The absolute beam phase density (brightness) as usually is not measured directly and the average beam brightness B is calculated from a beam intensity I and the transverse emittances. In the ion source and low energy beam transport (LEBT) optimization, it is important to preserve the beam brightness because some aberration of ion optic and beam instabilities can decrease the brightness of the central part of ion beam significantly. For these brightness measurements, it is convenient to use an absolute beam brightness detector with the brightness determination from one short considered in this article.
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41.85.-p Beam optics
29.25.Ni Ion sources: positive and negative

Plasma characterization of the superconducting proton linear accelerator plasma generator using a 2 MHz compensated Langmuir probe

C. Schmitzer, M. Kronberger, J. Lettry, J. Sanchez-Arias, and H. Störi

Rev. Sci. Instrum. 83, 02A715 (2012); http://dx.doi.org/10.1063/1.3672109 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2012

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The CERN study for a superconducting proton Linac (SPL) investigates the design of a pulsed 5 GeV Linac operating at 50 Hz. As a first step towards a future SPL H− volume ion source, a plasma generator capable of operating at Linac4 or nominal SPL settings has been developed and operated at a dedicated test stand. The hydrogen plasma is heated by an inductively coupled RF discharge e− and ions are confined by a magnetic multipole cusp field similar to the currently commissioned Linac4 H− ion source. Time-resolved measurements of the plasma potential, temperature, and electron energy distribution function obtained by means of a RF compensated Langmuir probe along the axis of the plasma generator are presented. The influence of the main tuning parameters, such as RF power and frequency and the timing scheme is discussed with the aim to correlate them to optimum H− ion beam parameters measured on an ion source test stand. The effects of hydrogen injection settings which allow operation at 50 Hz repetition rate are discussed.
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52.38.Kd Laser-plasma acceleration of electrons and ions

Extraction of negative hydrogen ions from a compact 14 GHz microwave ion source

M. Wada, T. Kasuya, T. Kenmotsu, S. Maeno, T. Nishida, M. Nishiura, K. Shinto, and H. Yamaoka

Rev. Sci. Instrum. 83, 02A716 (2012); http://dx.doi.org/10.1063/1.3672473 (3 pages)

Online Publication Date: 16 February 2012

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A pair of permanent magnets has formed enough intensity to realize electron cyclotron resonance condition for a 14 GHz microwave in a 2 cm diameter 9 cm long alumina discharge chamber. A three-electrode extraction system assembled in a magnetic shielding has formed a stable beam of negative hydrogen ions (H−) in a direction perpendicular to the magnetic field. The measured H− current density was about 1 mA/cm2 with only 50 W of discharge power, but the beam intensity had shown saturation against further increase in microwave power. The beam current decreased monotonically against increasing pressure.
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29.25.Lg Ion sources: polarized
29.40.Cs Gas-filled counters: ionization chambers, proportional, and avalanche counters
75.50.Ww Permanent magnets

Analysis of H atoms in a negative ion source plasma with the non-equilibrium electron energy distribution function

S. Koga, T. Shibata, R. Terasaki, N. Kameyama, A. Hatayama, M. Bacal, and K. Tsumori

Rev. Sci. Instrum. 83, 02A717 (2012); http://dx.doi.org/10.1063/1.3673009 (4 pages)

Online Publication Date: 16 February 2012

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In negative ion sources for the neutral beam injection, it is important to calculate H atom flux onto the plasma grid (PG) surface for the evaluation of H− production on the PG surface. We have developed a neutral (H2 molecules and H atoms) transport code. In the present study, the neutral transport code is applied to the analysis of the H2 and H transport in a NIFS-R&D ion source in order to calculate the flux onto the PG surface. Taking into account non-equilibrium feature of the electron energy distribution function (EEDF), i.e., the fast electron component, we have done the neutral transport simulation. The results suggest that the precise evaluation of the EEDF, especially in the energy range 15 eV < E < 30 eV is important for the dissociation rate of H2 molecules by the electron impact collision and the resultant H atom flux on the PG.
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29.25.Ni Ion sources: positive and negative
52.50.Dg Plasma sources

Research and development of H− ion source and low energy beam transport for a kaon-neutrino factory

Q. Ji, J. Staples, A. Sy, T. Schenkel, and D. Li

Rev. Sci. Instrum. 83, 02A718 (2012); http://dx.doi.org/10.1063/1.3673011 (3 pages)

Online Publication Date: 17 February 2012

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A baseline H− ion source and low energy beam transport (LEBT) system have been identified for Project X. The filament-discharge H− ion source has been fabricated by D-Pace, Inc. and is now in operation at LBNL. The source is capable of delivering over 10 mA of H− beam in cw operation with normalized 4 rms emittances less than 0.7 π mm mrad. A two-solenoid magnetic lens LEBT system has been design. The design has been validated with simulations of beam transport for 5 mA 30 keV H− beams using various simulation codes.
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29.25.Lg Ion sources: polarized
13.85.Dz Elastic scattering

Effect of non-uniform electron energy distribution function on plasma production in large arc driven negative ion source

T. Shibata, S. Koga, R. Terasaki, T. Inoue, M. Dairaku, M. Kashiwagi, M. Taniguchi, H. Tobari, K. Tsuchida, N. Umeda, K. Watanabe, and A. Hatayama

Rev. Sci. Instrum. 83, 02A719 (2012); http://dx.doi.org/10.1063/1.3673485 (3 pages)

Online Publication Date: 17 February 2012

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Spatially non-uniform electron energy distribution function (EEDF) in an arc driven negative ion source (JAEA 10A negative ion source: 10 A NIS) is calculated numerically by a three-dimensional Monte Carlo kinetic model for electrons to understand spatial distribution of plasma production (such as atomic and ionic hydrogen (H0/H+) production) in source chamber. The local EEDFs were directly calculated from electron orbits including electromagnetic effects and elastic/inelastic collision forces. From the EEDF, spatial distributions of H0/H+ production rate were obtained. The results suggest that spatial non-uniformity of H0/H+ productions is enhanced by high energy component of EEDF.
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52.50.Dg Plasma sources
52.55.Fa Tokamaks, spherical tokamaks
52.65.Pp Monte Carlo methods
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties

Radio frequency discharge with control of plasma potential distribution

Vadim Dudnikov and A. Dudnikov

Rev. Sci. Instrum. 83, 02A720 (2012); http://dx.doi.org/10.1063/1.3673489 (3 pages)

Online Publication Date: 17 February 2012

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A RF discharge plasma generator with additional electrodes for independent control of plasma potential distribution is proposed. With positive biasing of this ring electrode relative end flanges and longitudinal magnetic field a confinement of fast electrons in the discharge will be improved for reliable triggering of pulsed RF discharge at low gas density and rate of ion generation will be enhanced. In the proposed discharge combination, the electron energy is enhanced by RF field and the fast electron confinement is improved by enhanced positive plasma potential which improves the efficiency of plasma generation significantly. This combination creates a synergetic effect with a significantly improving the plasma generation performance at low gas density. The discharge parameters can be optimized for enhance plasma generation with acceptable electrode sputtering.
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52.80.Pi High-frequency and RF discharges
52.20.Fs Electron collisions
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

Analysis of the H− ion emissive surface in the extraction region of negative ion sources

N. Kameyama, T. Fukuyama, S. Wada, S. Kuppel, K. Tsumori, H. Nakano, A. Hatayama, K. Miyamoto, A. Fukano, and M. Bacal

Rev. Sci. Instrum. 83, 02A721 (2012); http://dx.doi.org/10.1063/1.3673495 (4 pages)

Online Publication Date: 17 February 2012

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To understand the plasma characteristics in the extraction region of negative H− sources is very important for the optimization of H− extraction from the sources. The profile of plasma density and electrostatic potential in the extraction region with and without extraction grid voltage are analyzed with a 2D particle in cell modeling of the NIFS-RD H− sources. The simulation results make clear the physical process forming a double ion plasma layer (which consists only of positive H+ and negative H− ions) recently observed in the Cs-seeded experiments of the NIFS-R&D source in the vicinity of the extraction hole and the plasma grid. The results also give a useful insight into the formation mechanism of the plasma meniscus and the H− extraction process for such double ion plasma.
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52.50.Dg Plasma sources
52.65.Rr Particle-in-cell method
52.25.-b Plasma properties
52.40.Kh Plasma sheaths

Effects of adsorption and roughness upon the collision processes at the convertor surface of a plasma sputter negative ion source

T. Kenmotsu and M. Wada

Rev. Sci. Instrum. 83, 02A722 (2012); http://dx.doi.org/10.1063/1.3673624 (3 pages)

Online Publication Date: 21 February 2012

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Atomic collision processes associated with surface production of negative hydrogen ions (H−) by particle reflection at molybdenum surface immersed in hydrogen plasma have been investigated. To calculate sputtering yields of Cs, as well as energy spectra and angular distributions of reflected hydrogen atoms from molybdenum surface by H+ ion and Cs+ ion bombardments, a Monte Carlo simulation code ACAT (Atomic Collision in Amorphous Target) was run with the corresponding surface conditions. A fractal surface model has been developed and adopted to ACAT for evaluating the effect due to roughness of target material. The results obtained with ACAT have indicated that the retention of hydrogen atoms leads to the reduction in sputtering yields of Cs, and the surface roughness does largely affect the sputtering yields of Cs.
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29.25.Ni Ion sources: positive and negative
52.50.Dg Plasma sources
52.65.Pp Monte Carlo methods
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.43.Mn Adsorption kinetics

Numerical analysis of surface produced H− ions by using two-dimensional particle-in-cell method

K. Miyamoto, S. Okuda, A. Hatayama, and M. Hanada

Rev. Sci. Instrum. 83, 02A723 (2012); http://dx.doi.org/10.1063/1.3673627 (4 pages) | Cited 1 time

Online Publication Date: 21 February 2012

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The modeling and analysis of a negative ion source is proceeding by using a 2D particle-in-cell simulation. The effect of the H− ion production on the plasma grid (PG) surface is investigated. It is shown that with the increase of H− ions per time step, the H− ion current density is enhanced, while the electron current density decreases with increasing the H− production rate on the PG surface. These results agree well with the experimental results observed in typical negative ion sources. Moreover, it is found that plasma quasi-neutrality is held mainly by both H+ and H− ions in the bulk plasma around the PG.
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73.30.+y Surface double layers, Schottky barriers, and work functions

Features of semiplanotron surface plasma sources

Vadim Dudnikov

Rev. Sci. Instrum. 83, 02A724 (2012); http://dx.doi.org/10.1063/1.3678645 (3 pages)

Online Publication Date: 22 February 2012

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Features of the semiplanotron surface plasma sources (SPS) with cesiation used for high efficient negative ion beam production from first development to modern condition are considered. Design features of semiplanotrons SPS with cylindrical and spherical geometric focusing and the features of the negative ion production in the semiplanotrons are reviewed. Several versions of semiplanotrons with efficiency up to 0.1 A of H− per kW of discharge power are discussed. Modifications of the semiplanotrons for dc operation and for heavy negative ion production are reviewed.
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52.50.Dg Plasma sources
52.75.-d Plasma devices
52.80.-s Electric discharges
07.77.Ka Charged-particle beam sources and detectors
29.27.Bd Beam dynamics; collective effects and instabilities

H− radio frequency source development at the Spallation Neutron Source

R. F. Welton, V. G. Dudnikov, K. R. Gawne, B. X. Han, S. N. Murray, T. R. Pennisi, R. T. Roseberry, M. Santana, M. P. Stockli, and M. W. Turvey

Rev. Sci. Instrum. 83, 02A725 (2012); http://dx.doi.org/10.1063/1.3678651 (4 pages) | Cited 2 times

Online Publication Date: 23 February 2012

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The Spallation Neutron Source (SNS) now routinely operates nearly 1 MW of beam power on target with a highly persistent ∼38 mA peak current in the linac and an availability of ∼90%. H− beam pulses (∼1 ms, 60 Hz) are produced by a Cs-enhanced, multicusp ion source closely coupled with an electrostatic low energy beam transport (LEBT), which focuses the 65 kV beam into a radio frequency quadrupole accelerator. The source plasma is generated by RF excitation (2 MHz, ∼60 kW) of a copper antenna that has been encased with a thickness of ∼0.7 mm of porcelain enamel and immersed into the plasma chamber. The ion source and LEBT normally have a combined availability of ∼99%. Recent increases in duty-factor and RF power have made antenna failures a leading cause of downtime. This report first identifies the physical mechanism of antenna failure from a statistical inspection of ∼75 antennas which ran at the SNS, scanning electron microscopy studies of antenna surface, and cross sectional cuts and analysis of calorimetric heating measurements. Failure mitigation efforts are then described which include modifying the antenna geometry and our acceptance/installation criteria. Progress and status of the development of the SNS external antenna source, a long-term solution to the internal antenna problem, are then discussed. Currently, this source is capable of delivering comparable beam currents to the baseline source to the SNS and, an earlier version, has briefly demonstrated unanalyzed currents up to ∼100 mA (1 ms, 60 Hz) on the test stand. In particular, this paper discusses plasma ignition (dc and RF plasma guns), antenna reliability, magnet overheating, and insufficient beam persistence.
Show PACS
52.50.Dg Plasma sources
29.20.Ej Linear accelerators
29.25.Dz Neutron sources
29.25.Ni Ion sources: positive and negative
29.27.Bd Beam dynamics; collective effects and instabilities
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
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