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10th International Symposium on the
Production and Neutralization of Negative Ions and Beams

September 14-17, 2004.


D1S1R1 means Day 1, Session 1, Report 1; other definitions are in the same way; in total, there are 3 Days and 5 Sessions, accordingly to the PROGRAM.

It is possible to load papers from PROCEEDINGS


Development of the Long Pulse Negative Ion Source for ITER


DRFC/CEA Cadarache, France

The International Thermonuclear Experimental Reactor (ITER) requires a 33 MW neutral beam (Dø) heating system that can operate for long pulses, up to 3600 s. The development of the ITER reference design of negative ion source for long pulse operation is being carried out at the DRFC, Cadarache on the KAMABOKO III negative ion source in collaboration with JAERI, Japan. ITER relevant D- current densities of >200 A/m2 have been extracted and accelerated from this source for 5 s pulses and pulses of 1000 s have been demonstrated. Unfortunately during long pulse operation the current density on the beam target at the "design" arc power and pressure was found to be to be low in comparison to that anticipated, >=200 A/m2. Two phenomena contributing to the reduced performance are currently under investigation at Cadarache:
a) The role of the plasma grid temperature. Increasing the temperature of the grid increases the negative ion yield by <=40%, substantially below that expected (100%).
b) The transmission of the accelerated power to the calorimeter, which is found to be only about 50%.
This paper will present results of experiments presently being carried out that are aimed at identifying the causes of these two phenomena.

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Status of Negative-Ion-Based Neutral Beam Injectors in LHD


National Institute for Fusion Science, Japan

Recent progress in LHD N-NBI system is described. The system was designed to provide 15 MW of port-through power by three beamlines (BL-1 to BL-3) with 180 keV hydrogen for 10 sec. However, the performance has not satisfied all its specifications at the same time yet. This is because several difficulties were found in large ion sources although the specifications were determined based on the R&D results of small ion sources. Among them, spatial non-uniformity of beam and unstable operation of high current arc discharge due to high voltage breakdowns were two big problems to be solved. Two approaches have been carried out in BL-1. One is the optimization of magnetic cusp structure by modifying the shape of plasma source, which increased the negative ion current.
The other is the adoption of slot aperture for the grounded grid, which reduces the conditioning time of the accelerator dramatically. By these two improvements, the specifications were satisfied in BL-1 and high power beam injection of 13.1MW has been achieved during the last experimental campaign. The remaining problem is a pulse length which is still limited due to high heat load on the grounded grid.

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Experimental results with the new ITER-like1 MV SINGAP accelerator


DRFC/CEA Cadarache, France

An "ITER-like" accelerator, which is a scaled down version of the ITER SINGAP (SINgle GAP, SINGle Aperture) accelerator, has been build and installed on the Cadarache 1 MV test bed. The objective is to demonstrate reliable D- beam acceleration as close as possible to 1 MeV with a current density j- ~ 200 A/m2 with the parameters and beam optics required for ITER. The pre-accelerator stage can be modified to have different arrangements of apertures, which have been chosen to test the predictions of the modelling.
Encouraging results have been obtained previously with a proof-of-principle SINGAP accelerator, which had the disadvantage of a largely un-cooled ion source and a pre-accelerator significantly different from that designed for ITER. With that prototype good agreement between simulations and experimental results has been demonstrated. The highest obtained beam energy was 911 keV with j- =50 A/m2 for 2 s. At 498 keV a current density of 120 A/m2 was reached.
This paper will describe the layout of the test bed with the new "ITER-like" accelerator system, and initial results from high voltage holding tests, beam extraction and acceleration will be presented. A comparison between the simulations and the measurements will also be given.

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Report title to be determined


Yamaguchi University, Japan

Report abstract is not available

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Correction of Beam Distortion in Negative Hydrogen Ion Source with Multi-Slot Grounded Grid


National Institute for Fusion Science, Japan

The beam accelerator with multi-slot grounded grid (MSGG) has been developed to increase the injection power of LHD-NBI. Using the accelerator, the maximum power of 5.7 MW was achieved at the beam energy of 186 keV in the beam injection to LHD plasma last year. Although the beam power increased compared with conventional accelerator with multi-aperture grounded grid, the accelerator with the MSGG includes a disadvantage having the bi-focal condition in parallel and perpendicular direction to the long side of the slots. When the beam width in one of those directions is made narrower, the width in another direction becomes wider. This disadvantage induces not only the loss of beam port-through power but also internal damages in neutral beam line. In order to reduce the disadvantage, an experiment has been done using a small-scaled negative ion source with racetrack-shaped apertures for the steering grid installed at beam upstream of the MSGG. By applying the racetrack apertures to the accelerator, it is observed that the beam widths in the parallel and perpendicular directions to the slot long side have almost the same focal condition to obtain minimal beam widths.

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Plasma Injection from Several Cesiated-Hollow Cathodes into the 1/3rd Scale Large H- Ion Source

Y.Oka, Yu.Belchenko, V.Davydenko, K.Ikeda, O.Kaneko, K.Nagaoka, M.Osakabe, Y.Takeiri, K.Tsumori, E.Asano, T.Kawamoto, T.Kondou, and M.Satou

National Institute for Fusion Science, Japan

The operation of 1/3rd scale source (plasma chamber volume 35W x 62H x ~20L cm3) with up to four hollow cathodes were tested on the test stand facility of the National Institute for Fusion Study. Two different designs of hollow cathodes, developed at BINP, were tested, including the novel one, having an isolated cathode body and a cascade discharge structure. The independent hydrogen, cesium and power supply systems for every cathode were used. Power supplies and discharge parameters were controlled by the data acquisition system. The reliable discharge ignition and operation with current up to 70 A per hollow cathode unit and pulse duration up to 5 s was tested.

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Progress in the modeling of negative ion sources


University of Bari, Italy

We present recent work performed by our group on the modeling of negative ion sources including multicusp magnetic plasmas, parallel plate reactors, RF inductive plasmas and microwave plasmas. In all the presented cases sophysticated kinetics for electronically and vibrationally excited states is solved coupled to the Boltzmann equation for the electron energy distribution function. Non local effectts are considered by using PIC-MCC (particle in cell with Monte Carlo collisions) collisions.
The new results include the enormous effort made by our group in these years for describing elementary processes involving electron-molecule interaction, atom-molecule and atom-surface recombination. Particular emphasis will be given to the importance of Rydberg states in enhancing the production of negative ions under non equilibrium conditions.

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Progress in Elementary Processes for Negative Ion Source Modeling


University of Bari, Italy

A great effort was made in the last decades in order to characterize H2 plasmas in different ion sources for fusion. A state-to-state kinetic approach is required for the realistic modeling of negative ion sources, due to non equilibrium conditions established in the plasma.
Electron collision induced processes affect strongly the distribution on the internal degrees of freedom of heavy species. The central role played by the dissociative attachment from vibrationally excited molecules, already cleared in literature, cannot explain observed rates of negative ion formation, opening questions about the relevance of alternative mechanisms, involving high lying Rydberg states. Vibronic transitions to low lying Rydberg states, contributing significantly to vibrational excitation through radiative cascade on the ground H2 state, have been studied in the framework of semiclassical impact parameter method.
The investigation of dissociative channels was extended to the calculation of state-to-state cross section for spin forbidden transitions in H2 which result in dissociation through b 3[SIGMA]u+ state. Also transitions between triplet states were considered, due to the metastable character of a 3[SIGMA]g+ and c 3[PI]u states. Quasibound character of vibrational levels can be taken into account when considering the dissociation through excited electronic states.
Also heavy collision processes play a significant role, VT energy transfers were considered for the vibrational manifold of H2 molecule.

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Effects of a Weak Transverse Magnetic Field and a Spatial Potential on Negative Ion Transport in Negative Ion Sources

T.Sakurabayashi, A.Hatayama and M.Bacal

Keio University, Japan

The effects of the weak transverse magnetic field on the plasma transport in a negative ion source are studied by means of a two-dimensional electrostatic particle simulation. Electron can be easily magnetized by the magnetic field (a few tens of Gauss) and lost along the field line, while positive ions (H+) cannot be magnetized because of the larger Larmor radius. This difference of the dynamics between electrons and H+ ions perturbs the plasma neutrality and affects the structure of the spatial potential near the wall. In order to examine these effects, a particle-in-cell (PIC) model is used which simulates the motion of the charged particles in their self-consistent electric field. Under this situation, the modification of the plasma neutrality and the resultant electric potential due to the magnetic field are very important for the increase of H- extraction. In this study, we focus our attention mainly on the two important effects; (i) the electron diffusion across the magnetic field and (ii) the variation of magnetic field strength along the field line. Although these effects weaken the difference of the dynamics between electrons and H+ ions, the presence of the magnetic field still has a large contribution to the enhancement of the H- extraction.

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2D PIC-MCC code for electron-hydrogen gas interaction study in H- ion sources


LPGP, France

In order to make a reliable H- ion source, a hybrid PIC 2D MCC 3D [1] fluid code has been developed. The aim of the code is to study the effect of electron injection into a cylindrical gas chamber. This new version takes into account the 2D space charge distribution. Thus, it is possible to calculate the H- ion distribution everywhere in the plasma chamber. Many results have been brought as well as the best injected energy and the electron penetration length efficiency. Moreover, the calculations explain why it is more problematic to get an efficient volume production at high pressure (100 mTorr) than at low pressure (6 mTorr). The temporal H- production evolution is finally discussed.
[1] K. Benmeziane, R. Ferdinand, R. Gobin, G. Gousset, 'Study and preliminary results for a new type of ECR H- ion source', Review of scientific instruments Vol 75 N5 (May 2004)

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Relevance of volume and surface-plasma formation of negative ion in gas discharge ion sources


Brookhaven Technology Group, Inc. NY USA

Relative ratio of volume and surface-plasma formation of negative ion in gas discharge ion sources will be discussed. Features of volume production of negative ions in plasma (VP) will be considered. Peculiarities of surface-plasma formation of negative ions (SPF) in gas discharges with cesium and without cesium will be reviewed. Comparison of volume and surface plasma formation in real discharges demonstrates that in good "Volume sources' without cesium the surface plasma production is a dominant mechanism of negative ion formation, as in all discharges with cesium. In these cases, the term 'volume ion source' is misleading since most of the H- results from surface, rather than volume ionization processes. Volume production of negative ions takes place only in poorly designed ion sources. For design of good negative ion source it is necessary to suppress volume production as much as possible. Really, good volume sources are sources with a strongly suppressed volume production of negative ions.

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Separation of H- Ions and Co-Extracted Electrons at Full Energy

J.Dietrich and R.Becker

IAP, Universitat Frankfurt/M, Germany

For the study of the extraction of volume produced H- ions and their separation from co-extracted electrons, a 3D Poisson solver has been developed with integrated ray tracing routines [1], which can also take into account 3D magnetostatic fields. With this program we have simulated the separation of H- ions from electrons at full acceleration energy. The electrons are bent out of the H- beam by the transverse magnetic field of a Helmholtz coil by an angle of 90. This bent is especially useful to provide large divergence angles for the electron beam, facilitating the recuperation of energy and the collection of electrons. A second but reversed set of Helmholtz coils with same excitation is used to minimize the effect of the magnetic field on the final H- beam.
[1] Jan Dietrich, Diplomarbeit IAP, Universitat Frankfurt, 2003

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ECR-driven multicusp volume H- ion source

M.Bacal, A.A.Ivanov Jr, C.Rouille, S.Bechu and J.Pelletier

Laboratoire LPTP, Ecole Polytechnique, France

We studied the negative ion current extracted from the plasma created by seven elementary dipolar ECR minisources, operating at 2.45 GHz placed in the magnetic multiple structure Camembert III. We varied the pressure from 1 to 4 mTorr, with a maximum power of 1 kW. We also studied the plasma created by this system and measured the varions plasma parameters, including the density and temperature of the negative hydrogen ions. We found that the electron temperature is optimal for negative hydrogen ion production. We found that the wall state degradation affects the extracted negative ion current. Tantalum evaporation can enhance this current.
The support of EEC (Contract No. HPRI-CT-2001-50021) is gratefully acknowledged.

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Peculiarities of Compact Surface-Plasma Sources Operation (Practical Aspects)


Brookhaven Technology Group, Inc., Setauket, NY USA

Operation Experience of Compact Surface-Plasma Sources (CSPS) under operation in different laboratories around the World, will be considered. Features of CSPS are small volume, small gaps between electrodes, high plasma density and high emission current density. These features have complicated the long time operation of CSPS with high beam parameters, because a sputtering rate, flakes formation, deposition of insulators surface and probability of short circuit of electrodes should be high. But in many versions of CSPS was reached a very long operation time. Features of CSPS important for long time operation will be considered.

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Volume production of high negative hydrogen ion density in low-voltage cesium-hydrogen discharge.

F.Baksht, V.Ivanov, S.Shkolnik, M.Bacal

Ioffe Physics-Technical Institute, St. Petersburg, Russia, LPTP, Ecole Polytechnique, Palaiseau, France

In the state-of-the-art hydrogen negative ion sources the vibrationally excited hydrogen molecules, which are the precursors of the negative ions, are produced by collisions of electrons with energy of a few tens of eV with molecules. To avoid the destruction of the negative ions by the energetic electrons, the ion source is formed by two chambers separated by a magnetic filter. In this paper the possibility of generating a record H- density of about 10E13 cm-3 in a low-voltage (LV) cesium-hydrogen discharge with a hot cathode will be reported. In this kind of discharge high density of vibrationally excited H2 molecules is obtained in a single chamber. The strategy of obtaining this result is as follows: a high electron concentration is created by the ionization of the cesium additive, not of hydrogen. The discharge voltage is limited to less than 8.8 V - the threshold of H2 direct dissociation by electron impact. This leads to a small density of atomic hydrogen and privents the formation of atomic and molecular hydrogen ions, with the result that the V-t (vibration - translation) exchange between hydrogen molecules and H atoms is reduced. This improves significantly the vibrational pumping of hydrogen molecules. The negative ion density is determined by measuring the absorption of laser radiation in the discharge plasma. It is shown that a density of 10E12 - 10E13 cm-3 is obtained if the plasma electron temperature is in the range 0.5-1 eV. Theoretical modeling shows that with a very high electron emission from the cathode (10 A/cm2), the maximum negative ion density of 10E13 cm-3 is located next to the anode, which allows the negative ion extraction through a small opening in the anode.
One of the authors (M.B.) acknowledges the support of the European Community (Contract HPRI-CT-2001-50021)

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Finding the Optimum Frequency and the H- Distribution in the HERA RF-Volume Ion Source


DESY, Hamburg, Germany

The HERA RF-Volume Source is the only source available that delivers routinely an Hminus current of 40 mA without Cs.
The dependency of the quality of the Hminus beam on the frequency was investigated. A frequency range of 1.65 - 9 Mhz was scanned and the emittance was measured for several Hminus currents up to 40 mA.
The production mechanism for Hminus ions in this type of source is still under discussion. Laser photodetachment measurements have been started at DESY in order to measure the Hminus distribution in the source. The measurements have also been done under extraction conditions at high voltage.
The results of the measurements with and without extraction are a basis for the development of a theory for the transition between plasma and vacuum (sheath), a cornerstone for beam transport programs.
Knowledge of the Hminus distribution and where they are produced makes further source improvements possible.
The support of EEC (Contract HPRI-CT-2001-50021) is gratefully acknowledged.

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- source with volumetric - plasma formation of ions

Yu.Kursanov, P.Litvinov, V.Baturin

Institute of Applied Physics, Sumy, Ukraine

In the presented work results of experimental researches of two versions of - ions source with axial-symmetric and slot-hole geometry of ions extraction are submitted. Formation of ions occurs in them in a volume of hydrogen plasma (without additives of caesium) due to two-step dissociative attachment of thermalized electrons by vibrationally excited molecules. These sources were executed in such a manner that processes of vibrating excitation and dissociative attachment of electrons are divided in space. It allows optimizing these elementary processes separately. In these sources ions are extracted from paraxial plasma along a divergent magnetic field. Due to this fact the suppression of electrons occurs.

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Flash chamber of a quasi-continuous volume source of negative ions

P.Litvinov, V.Baturin

Institute of Applied Physics, Sumy, Ukraine

In the work the design is described and results of experimental researches of plasma generator with the cold cathode for a source of negative ions are submitted. The generator consists of three consistently connected chambers with dosed gas leaking between them.
The electrode system of the first chamber (of high pressure) and the second one (of low pressure), represents two-chambered inverse gas magnetron. The second chamber through an annular slot connects with the third (emission) chamber in which plasma of the tubular form is generated. In the third chamber plasma is divided into two areas (peripheral and paraxial) where necessary conditions for effective formation of negative ions are created.
The submitted generator will allow optimizing a design of negative ions source.

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Report title to be determined


Technical University of Crete, Greece

Report abstract is not available

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Physical Insights and Test Stand Results for the LANSCE H-Surface Converter Source

J.Sherman, G.Rouleau and E.Chacon-Golcher

Los Alamos National Laboratory, Los Alamos, NM USA

The Los Alamos Neutron Science Center (LANSCE) H- surface converter source has been under development for several years to reach 25-40 mA current with 7 ([pi]cm-mrad) lab emittance (95% beam fraction). The duty factor is 12% (120 Hz, 1ms pulse length). Experimental test stand measurements will be summarized. Currents up to 25mA H- have been observed from a modified production source with 20% emittance growth. This emittance growth may be acceptable to 800 MeV linac perations. A summary of physical principles of emittance growth mechanisms and converter physics will be given.

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H- source developments at CERN

C.Hill, D.Kuechler, R.Scrivens, T.Steiner

AB Department/CERN, Switzerland

Future CERN programmes for LHC and ISOLDE require increasing the beam intensity and brightness from the PS Booster. This could be achieved by injection from a higher energy, H- linac. A new injector will require a high performance, high reliability, negative hydrogen ion source. This paper will present the requirements for such a source together with the first results for a prototype microwave driven source (being developed within the framework of a EEU research initiative, HP-NIS)

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Study of direct current negative ion source for the medicine accelerator

Yu.Belchenko, I.Ivanov, I.Piunov

Budker Institute of Nuclear Physics, Novosibirsk, Russia

Report abstract is not available

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Source of negative hydrogen ions with hot cathode

G.Kuznetsov, M.Batazova

Budker Institute of Nuclear Physics, Novosibirsk, Russia

In the report an H- ion source with following parameters is described. Ion energy is up to 30 keV, current is up to 5 mA, pulse duration varies from 1 to tens microseconds. H- ions appear in magnetron discharge near a hot cathode surface made of LaB6 or IrCe, which is 6 mm in diameter. H- ions are extracted through 0.8x6 mm slot. Input of gas is by means of electromagnetic valve. Ion current depends on discharge current that in turn is defined by cathode temperature, discharge voltage, and hydrogen pressure. Two permanent magnets fixed on magnetic core generate magnetic field for magnetron discharge. There is a magnetic correction of extracted H- ions.
The H- ion source has been used as an injector for tandem accelerator with following proton beam parameters: energy is 1.4 MeV, current is 3mA, and pulse duration is 2 microseconds. Simulation of the ion beam trajectories in source, transportation channel, and tandem accelerator, showed good correlation with experiments on the working installation.

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Poarized Negative Light Ions at the Cooler Synchrotron COSY/Juelich


Institute for Nuclear Physics - COSY/ Juelich, Germany

The polarized ion source at the cooler synchrotron facility COSY of the research centre Juelich, Germany, delivers negative polarized protons or deuterons for about 30 % of over 7250 hours per year of beam time for medium energy experiments. Inside the synchrotron circulating mA beams with a polarization up to 90% have been delivered.
The polarized ion source, originally built by the universities of Bonn, Erlangen and Cologne, is based on the colliding beams principle, using an intense pulsed neutralized cesium beam for charge exchange with a pulsed highly polarized hydrogen beam. The source is operated at 0.5 Hz repetition rate with 20 ms pulse length which is the maximum useful length for the injection into the synchrotron. Routinely intensities of 20 A are delivered for the injector cyclotron of COSY. Reliable long term operation for experiments at COSY for up to 9 weeks has been achieved. The status of the source and details of recent investigations will be reported.

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Status of the negative hydrogen ion test stand at CEA Saclay

R.Gobin, K.Benmeziane, O.Delferriere, R.Ferdinand, A.Girard, F.Harrault

Commissariat a l'Energie Atomique, France

At Saclay, in 2003, the new 2.45 GHz ECR source, based on pure volume H- ion production, showed a dramatic increase of the H- extracted ion beam. In fact, since the rectangular plasma chamber is separated in two different parts by a stainless steel grid, the extracted H- current rose from few A to 1.5 mA. Of course the grid position and its potential (equal to the plasma electrode voltage) with respect to the plasma chamber were optimised. Ceramic plates allow increasing the electron density and lead to an improvement of the negative ion production. Plasma characterization is planned using Langmuir probes. It is also expected to work with a more powerful magnetron RF generator. The last results will be reported and discussed. A 10 GHz permanent magnet source has been designed at CEA Grenoble; the general philosophy of this project will be presented. This work is supported by the European Union under contract HPRI-CT-2001-50021.

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Acceleration of 100 A/m2 negative ion beam by vacuum insulated beam source


Japan Atomic Energy Research Institute, Japan

The accelerator for the ITER NB system is required to produce 1 MeV, 40 A D-ion beams for 16.5 MW neutral beam injection per module. In the ITER NB system, conventinal gas insulated beam source cannot be adopted because of the radiation-induced conductivity of the insulation gas. Thus a vacuum insulated beam source (VIBS), where the whole beam source is immersed in vacuum, had been developed in JAERI. Recently, voltage holding capability of the VIBS was drasticaly improved by installing the large stress ring, which reduces the electric field concentration at the negative side triple junction. Having improved the voltage holding capability of the VIBS, the H- ion beams were extracted with seeding cesium to enhance the negative ion currents.
Up to now, we had been secceeded in accelerating the H- beam of 102 A/m2 (140mA) at 800 keV and 80A/m2 (120mA) at 900 keV (pulse length 0.5sec). The beam acceleration was quite stable and accomplished for several hundreds shots in several experimental campaigns. Thus the development of vacuum insulated accelerator has solved technical issues of high voltage insulation of 1 MV level under the presence of H- ion beams.

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Space Charge Lens for Focusing of Negative Ion Beams

I.Soloshenko, V.Goretsky and A.Zavalov

Institute of Physics, Kiev, Ukraine

In the report brief review of the results of experimental and theoretical studies of the space charge lens for focusing negative ion beam is presented. An idea of such lens was formulated earlier by the first two authors. For the present time, two versions of the lens are studied experimentally and calculated numerically. In the first version focusing space charge is formed in the lens in result of gas ionization by the negative ion beam itself; in the second version - in result of gas ionization by both the beam ions and the electrons with energy of about 100 eV introduced from the special emitter placed in the lens volume. In both regimes focusing field values of about 100 V/cm are reached, which enable obtaining focal length of less or about 20 cm. However, in the first case working gas (argon, krypton, xenon) pressure comprises about 10E-3 Torr. At such pressure significant portion of negative ions is lost due to collisions with neutral particles. Introduction of additional ionizer enables essential lowering of the working gas pressure and avoiding losses of the ions.
Calculations performed by means of particle-in cell method are in a good agreement with the experiment.
The developed lens represents the simplest device - 3 electrodes with a voltage applied between them, which is one order of magnitude less than that at the ion source. Power consumed by the lens in the first regime is 2-3 orders of magnitude less than the beam power.

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Stripping target of 2.5 MeV 10 mA tandem accelerator


Budker Institute of Nuclear Physics, Novosibirsk, Russia

An electrostatic tandem-accelerator with 2.5 MeV 10 mA proton beam is under development at BINP. One of the accelerator important parts is a target that converts the half energy accelerated negative hydrogen ions into the proton beam. In the tandem-accelerator an argon stripping target with 1 cm tube diameter and 40 cm tube length will be used. To reduce argon flux from the target to accelerator gaps a gas recirculation by turbomolecular pump installed in target electrode is provided. Processes of plasma production and ultraviolet emission due to target ionization by fast ions and stripped electrons are considered in the report.

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Sub Microsecond Electromagnetic Beam Notching at Low Energy Utilizing a Magnetron Ion Source with a Split Extractor


Fermilab, Batavia, IL USA

A technique for sub-microsecond beam notching has been developed near 20 KeV utilizing a Magnetron ion source with a slit extraction system and a split extractor. Each halve of the extractor is treated as part of a 50 ohm transmission line which can be pulsed at +-700 volt to deflected the ion beam. This system along with the associated electronics is electrically floated on top of a pulsed extraction voltage. Beam notches with 20 ns fall times and better than 95% beam reduction have been observed at the end of the Fermilab 400 MeV Linac. Beam recovery times of less than a microsecond have been observed independent of the selected notch width which has been varied between 100 ns and 2 s.

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Mathematical Formulation and Numerical Modelling of the Extraction of Volume Produced H- Ions


IAP, Universitat Frankfurt/M, Germany

In the past, ion extraction of volume produced H- ions has either been simulated with programs for the extraction of positive ions [1] or by programs, which wrongly claimed to have a "real" and "genuine" option for H- ions [2]. Although "reasonable" results have been obtained in both ways, the mathematical formulation of the physics at the plasma sheath is wrong, and the modelling of electrodes near the sheath [3] must fail. In this paper a self consistent formulation of the extraction problem for H- ions is presented, which takes into account any number of positive ions, like fast or thermal protons, thermal cesium and molecular ions like H2 and H3, which all are essential for the generation of H- ions in the plasma volume. Equally important is the porting of this formulation to a simulation program and the verification of experimental results. This has lead to the development of the program nIGUN.
[1] Leitner, M.A., D.C.Wutte, K.N.Leung, Nucl. Instrum. and Meth., A 427, 242 (1999)
[2] Boers, J.E.,
[3] Welton, R.F. et al., Rev. Sci. Instrum. 73, 1013 (2002)

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Report title to be determined



Report abstract is not available

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Neutralization of H- Ions on the Plasma Target

V.Baturin, P.Litvinov

Institute of Applied Physics, Sumy, Ukraine

This work describes a plasma neutralizator for ion beams and investigation results of conversion of H- ions into neutral atoms on the plasma target. The working medium of neutralizator is thermal plasma (potassium, cesium). The design of neutralizator allows to receive an integrated density of a plasma target ~ 10E15 1/cm2 a degree of ionization of plasma may be adjusted. Dimensions of the neutralizator - diameter of 240 mm., length - 350 mm. Power consumption - 10 kw.
In this work coefficients of conversion of - ions into neutral atoms and angular dispersions of neutral atoms on a plasma target depending on ions energy, thickness of a target and degree of plasma ionization were measured.
Comparisons of characteristics of Ho beams received by neutralization of - ions on various targets (gas, vapor, plasma, photon) were carried out.

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Energy spectrum of atoms stripped from negative ions in a multi-stage negative ion accelerator


Japan Atomic Energy Research Institute, Japan

Energy spectrum of H0 atoms with fractional energies, that are stripped from H- ions in a 5-stage negative ion accelerator developed for ITER, has been measured by analyzing penetration depth of H0 atoms in the single-crystal silicon wafer where 725keV, 9.3mA H- ion beams were implanted. The negative ion source was operated at 0.3 Pa that is the ITER design value. Energy distribution of H0 density with fractional energies was a superposition of continuous spectrum and particular lines of 145keV, 290keV, 415keV, 560keV. These energies were energies of the intermediate grids, where line density of the residual gas molecules is relatively high because the intermediate grids are as thick as 20 mm. The H0 density with fractional energies decreased steeply with energy because residual gas molecules and cross-sections for stripping losses of the negative ions are relative low at the downstream of the accelerator. The stripping loss was 20% of the beam current mainly in the energy region of 10 - 415keV, i.e., in the region from the extractor to the third acceleration grid.

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