bluuebunny/crossref_metadata_2025 huggingface dataset:
The Xanthophyll Cycle in Green Algae (Chlorophyta): Its Role in the Photosynthetic Apparatus
Authors: Masojídek J. , Kopecká J. , Koblížek M. , Torzillo G.
Published: May 2004

Abstract: Light‐dependent conversion of violaxanthin to zeaxanthin, the so‐called xanthophyll cycle, was shown to serve as a major, short‐term light acclimation mechanism in higher plants. The role of xanthophylls in thermal dissipation of surplus excitation energy was deduced from the linear relationship between zeaxanthin formation and the magnitude of non‐photochemical quenching. Unlike in higher plants, the role of the xanthophyll cycle in green algae (Chlorophyta) is ambiguous, since its contribution to energy dissipation can significantly vary among species. Here, we have studied the role of the xanthophyll cycle in the adaptation of several species of green algae (Chlorella, Scenedesmus, Haematococcus, Chlorococcum, Spongiochloris) to high irradiance. The xanthophyll cycle has been found functional in all tested organisms; however its contribution to non‐photochemical quenching is not as significant as in higher plants. This conclusion is supported by three facts: (i) in green algae the content of zeaxanthin normalized per chlorophyll was significantly lower than that reported from higher plants, (ii) antheraxanthin + zeaxanthin content displayed different diel kinetics from NPQ and (iii) in green algae there was no such linear relationship between NPQ and Ax + Zx, as found in higher plants. We assume that microalgae rely on other dissipation mechanism(s), which operate along with xanthophyll cycle‐dependent quenching.
Experiments with biased cylinder in electron cyclotron resonance ion source (plenary)
Authors: Drentje A. G. , Kitagawa A. , Muramatsu M. , Ogawa H. , Sakamoto Y.
Published: May 2004

The shape of the magnetic field of an electron cyclotron resonance ion source (ECRIS) gives rise to different particle fluxes (losses) from the plasma to the end plates (mainly diffusion of electrons), and to the side walls (mainly ions). The electron fluxes to the injection end plate can be reduced by negatively biasing this plate (or so-called biased disk); this appeared to be successful to improve the output of highly charged ions (HCIs). In the present experiment it was demonstrated that by positively biasing the side walls, the HCI production can be improved as well. Electrons leaking from the ECRIS plasma to the side wall find their way easiest at the “pole” areas (of the hexapole magnet) because these are the areas where fieldlines pass the plasma chamber. A special construction was made to study the effect of biasing two different regions: (1) the areas between the six poles, and (2) the parts corresponding to the poles. Measurements show that method (2) gives better performance of the source. The relative improvement for the highest observed charge states is the best, and in absolute sense the application of the method is giving, e.g., a four times higher intensity for Ar11+ beams.
Production of multicharged ions in a 2.45 GHz electron cyclotron resonance source directly excited in a circular TE01 mode cavity resonator
Authors: Kato Yushi , Furuki Hideyuki , Asaji Toyohisa , Ishii Shigeyuki
Published: May 2004

In order to study the upgrading feasibility of the low frequency electron cyclotron resonance (ECR) plasma by using 2.45 GHz microwaves for multicharged ion sources, we have conducted various experiments in the TAIKO device (Toyama Pref. University). In this article the experimental study concentrates on the production of multicharged ions with respect to a microwave mode, especially, a circular TE01 mode, which is expected to enhance the efficiency of electron cyclotron resonance. The electric field of the circular TE01 mode has only a circumferential component in the same direction as electron cyclotron motion, perpendicular to the magnetic mirror field. We can assign the peak position of the electric field of the standing waves to the ECR zone in the cavity resonator, i.e., the vacuum chamber. We investigated the features of the plasma source in the cavity resonator of the circular TE01 mode microwave directly excited. We described the results of the simulation experimentally, and the design of the new source in detail, preliminary results of the new source, and then relevant discussions.
Numerical simulation multicomponent ion beam transport from ECR ion source
Authors: Ma L. , Song M. T. , Zhang Z. M. , Cao Y. , Chen X. Y.
Published: May 2004

We are developing a multicharged ion beam transport program. The program is dedicated to numerical simulation of the behavior of highly charged ion beam and optimization of beam optics in transport lines and is realized on a PC with Windows user interface of Microsoft Visual Basic. Among all the ions with different charge states in the beam, the exchange of electrons between highly charged ions and low charged ions or neutral atoms of residual gas are taken into account using classical molecular over-barrier model and Monte Carlo method. Therefore, the code is able to describe the changing charge state distribution along the transmission line. The initial charged state distribution of ions may be input from experimental data or calculated from some classical density distribution such as uniform, Gaussian, water bag, or parabolic. The main advantage of the code is the ability to simultaneously simulate a number of ions with different masses and charge states, particularly the decrease of the highly charge ions and the increase of low charged ions due to electron capture. Some simulation results for a transmission line of a highly charged ECR ion source are presented.
First operation of ECR ion source at Kochi University of Technology
Authors: Momota Sadao , Nojiri Yoichi , Saihara Miwako , Sakamoto Asako , Hamagawa Hisayoshi , Hamaguchi Kensuke
Published: May 2004

To study nano-scale manufacturing using highly charged ion beams, a facility to produce and irradiate heavy ion beams has been installed at Kochi University of Technology (KUT). The facility includes an ECR ion source (ECRIS), a beam transport and analysis system, and an irradiation system. The first beam was extracted from ECRIS in January 2003. To evaluate the performance of ECRIS, the measurements of the current and mass spectrum of ion beams as a function of the voltage for the beam extraction and of the rf power have been carried out. It is concluded from the present results that the combined use of the ECRIS and acceleration system with the transport and analysis system build at KUT works normally.
A version of the Trasco Intense Proton Source optimized for accelerator driven system purposes
Authors: Ciavola G. , Celona L. , Gammino S. , Presti M. , Andò L. , Passarello S. , Zhang XZh. , Consoli F. , Chines F. , Percolla C. , Calzona V. , Winkler M.
Published: May 2004

A full set of measurements of the magnetic field has been carried out to define a different design of the TRASCO Intense Proton Source (TRIPS) magnetic system, based on permanent magnets, in order to increase the reliability of the source. The two coils of the source generate a maximum field of 150 mT and the optimum field was determined around 95 mT. The OPERA-3D package was used to simulate the magnetic field and a new magnetic system was designed as a combination of three rings of NdFeB magnets and soft iron. The high voltage insulation has been completely modified, in order to avoid any electronics at 80 kV voltage. The description of the magnetic measurements and the comparison with the simulations are presented, along with the mechanical design of the new version permanent magnet TRIPS (PM-TRIPS) and the new design of the extraction system. Finally the modification of the low energy beam transfer line (LEBT), which now includes a 30° bending magnet, will be outlined, with special regard to the accelerator availability improvement which can be obtained with the installation of two PM-TRIPS sources or more on the LEBT.
A high intensity microwave ion source for high current RFQ
Authors: Cui B. , Wang R. , Ma Y. , Li L. , Jiang C. , Jiang W.
Published: May 2004

A high intensity microwave ion source for high current RFQ has been developed at China Institute of Atomic Energy (CIAE), China, for the China Demonstration Prototype of Accelerator Driven Sub-critical System (CDPADS) project. The aim of the source is to produce up to 50 mA cw proton beams at 75 keV at the RFQ match point. A more uniform magnetic field of the source is produced by electrical solenoids with the aid of permanent magnets. A hydrogen beam of more than 60 mA at 75 keV can be routinely extracted from a single 6.5-mm-diam aperture. To measure reliability/availability of the source, a continuous 120 h run has been performed. This article will report the main features and the current status of the source.
Recent results with the mVINIS ion source
Authors: Dobrosavljević A. , Šiljegović M. , Draganić I. , Čizmić B.
Published: May 2004

The mVINIS ion source is a part of the TESLA Accelerator Installation, in Belgrade. It is an ECR ion source used as a stand-alone machine delivering multiply charged ion beams to a low energy experimental channel for modification of materials (the L3A channel). In the future, it will be also used as a heavy ion injector for the VINCY Cyclotron. In this article we present the recently introduced hardware and software changes resulting in an improved operation of the mVINIS: the emittance measurement system, the inlet system for precious gases, the improved control system of the microwave generator, a new power supply for the injection stage coil, and the improved program for recording and analysis of the ion beam spectra.
Status of the Trasco Intense Proton Source and emittance measurements
Authors: Celona L. , Ciavola G. , Gammino S. , Chines F. , Presti M. , Andò L. , Guo X. H. , Gobin R. , Ferdinand R.
Published: May 2004

The Trasco Intense Proton Source (TRIPS) was installed at INFN-LNS in May 2000 and has been fully operational since the Fall of 2000; now the source fulfills all the requirements of the TRASCO (Trasmutazione Scorie) project. The proton beam intensity easily exceeds 40 mA at the operating voltage of 80 kV. A set of emittance measurements was carried out for different source conditions and confirmed the simulations performed with the AXCEL code: in all the cases the rms normalized emittance is well lower than the value required for the injection into the RFQ (0.2 π mm mrad); the results will be shown and discussed. Finally a beam reliability of 99.8% has been found during a long run test lasting over 142 h.
Heavy-ion beams required for the RIA accelerator
Authors: Pardo R. C. , Jiang C. L. , Nolen J. N. , Rehm K. E. , Savard G.
Published: May 2004

The proposed Rare Isotope Accelerator Facility (RIA) will provide beams of heavy ions with up to 400 kW power in order to produce radioactive beams of nuclei far from stability for research on fundamental questions in nuclear physics and astrophysics. The exact mix of heavy-ion driver beams that will be needed by RIA will depend on the actual experimental programs undertaken, but will surely encompass a wide range of isotopes. We will explore a possible facility operations model and identify the driver beams required. One aspect of that model will be to optimally “illuminate” the r-process path nuclei. Present published ECR ion source performance for the identified mix of beams and assumed charge states will be compared to the requirements of the RIA facility needed to achieve the beam power goals of the facility.
Extraction of space-charge-dominated ion beams from an ECR ion source: Theory and simulation
Authors: Alton G. D. , Bilheux H.
Published: May 2004

Extraction of high quality space-charge-dominated ion beams from plasma ion sources constitutes an optimization problem centered about finding an optimal concave plasma emission boundary that minimizes half-angular divergence for a given charge state, independent of the presence or lack thereof of a magnetic field in the extraction region. The curvature of the emission boundary acts to converge/diverge the low velocity beam during extraction. Beams of highest quality are extracted whenever the half-angular divergence, ω, is minimized. Under minimum half-angular divergence conditions, the plasma emission boundary has an optimum curvature and the perveance, P, current density, j+ext, and extraction gap, d, have optimum values for a given charge state, q. Optimum values for each of the independent variables (P, j+ext and d) are found to be in close agreement with those derived from elementary analytical theory for extraction with a simple two-electrode extraction system, independent of the presence of a magnetic field. The magnetic field only increases the emittances of beams through additional aberrational effects caused by increased angular divergences through coupling of the longitudinal to the transverse velocity components of particles as they pass though the mirror region of the electron cyclotron resonance (ECR) ion source. This article reviews the underlying theory of elementary extraction optics and presents results derived from simulation studies of extraction of space-charge dominated heavy-ion beams of varying mass, charge state, and intensity from an ECR ion source with emphasis on magnetic field induced effects.
Operation of rf ovens in ECR ion sources
Authors: Cavenago M. , Kulevoy T. , Petrenko S.
Published: May 2004

A 34-mm-diam rf oven system previously developed on bench [Cavenago, Kulevoy, and Petrenko, Rev. Sci. Instrum. 73, 552 (2002)] was inserted and tested into the electron cyclotron resonance (ECR) ion source Alice, producing beams from natural copper and silver samples; charge range was typically i=10–14 for copper and i=10–19 for silver, which compares well to previous source yield for xenon (charges 11–20). The ion source operation depends on the oven distance Loe from ECR plasma; different crucible materials (tantalum or steel), and oven position Loe=70–105 mm were successfully tried. Moreover another prototype using a robust tungsten rf coil was designed and tested on bench; numerical simulation and experimental results are described.
ECRIS charge breeding: High resolution spectra and emittance
Authors: Lamy T. , Bouly J.-L. , Curdy J.-C. , Sole P. , Sortais P. , Thuillier T. , Vieux-Rochaz J.-L. , Voulot D.
Published: May 2004

The charge breeding process, consisting of a low charge state ion beam (1+) plasma capture followed by a multi-ionization process, has been developed for more than ten years in LPSC Grenoble (previously ISN) using ECRIS. The challenge has been to optimize the 1+ capture and then the reextraction of the multicharged ions produced, keeping a “reasonable ECRIS working.” There are now three ECRIS PHOENIX Booster in the world (LPSC-Grenoble, CLRC-Daresbury, and TRIUMF-Vancouver). The LPSC-ECRIS has recently been set up in a completely renewed test bench equipped with a high resolution n+ mass spectrometer and a high resolution emittance meter. The CLRC-ECRIS is dedicated to online experiments with radioactive ions at REX-ISOLDE and the TRIUMF-ECRIS will soon be ready to undergo a validation process. We will present the preliminary results obtained with the new setup of the LPSC PHOENIX Booster with a special attention to the 1+ emittance and the characterization of the unwanted beams (usually called “impurities” by the RIB production specialists) present in a spectrum of a non-UHV ECRIS.
Recent developments in production of radioactive ion beams with the selective laser ion source at the on-line isotope separator ISOLDE
Authors: Catherall R. , Fedosseev V. N. , Köster U. , Lettry J. , Suberlucq G. ,   the ISOLDE Collaboration, Marsh B. A. , Tengborn E.
Published: May 2004

The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser stepwise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS compliments the mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric contamination. Using a system of dye lasers pumped by copper vapor lasers, ion beams of 22 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5%–30%. As part of the ongoing RILIS development, recent off-line resonance ionization spectroscopy studies have determined the optimal three-step ionization schemes for yttrium, scandium, and antimony.
Latest results obtained at GANIL with new target-source systems dedicated to radioactive ion production
Authors: Jardin P. , Saint-Laurent M. G. , Farabolini W. , Gaubert G. , Cornell J. C. , Dubois M. , Gibouin S. , Lecesne N. , Leroy R. , Pacquet J. Y. , Pellemoine F. , Stodel C. , Tuske O. , Verney D. , Villari A. C. C. , Barue C. , Canet C. , Dupuis M. , Durantel F. , Flambard J.-L. , Huet-Equilbec C. , Leherissier P. , Lemagnen F. , Angélique J. C. , Maunoury L.
Published: May 2004

Two new target-source systems have been realized and used to produce radioactive elements with primary beams of Kr78 (68.5 A MeV) and Ar36 (95 A MeV). The production yields of Kr73,72, Ar35,33,32, P30,29, S31,30, Cl34,33,32 and of some other condensable elements such as Br73,72 and Se73,71 are presented. The results of the improvements between the two versions of the production system are discussed.
Optimization of the mVINIS ion source extraction system
Authors: Šiljegović M. , Dobrosavljević A. , Beličev P.
Published: May 2004

The ion-optical properties of the single gap extraction system of the mVINIS ion source are investigated. The pepper-pot method was used to measure the effective emittances of the ion beams extracted from the plasma. The emittances have been analyzed as functions of the extraction electrode position for various charge states of the ion species.
A profile-/emittance monitor at the Frankfurt 14 GHz ECRIS
Authors: Stiebing K. E. , Kaiser M. S. , Meyer J. D. , Schmidt L. , Schmidt-Böcking H. , Strekalovskij O. , Alexandrov V. , Kayukov A. , Koryevkina M. , Shirkov G.
Published: May 2004

A beam profile-/emittance monitor has been developed and tested at the Frankfurt 14 GHz electron cyclotron resonance ion source. It consists of a standard moving slit system in combination with a new type of profile monitor that can easily be integrated into the diagnose boxes of the existing beam line. Utilizing the standard Faraday cup measurements of the beam diagnosis, the system is permanently integrated into the beam line. This is in contrast to the device used so far, which always demanded for a major reconfiguration of the existing beam line, merely for the case of emittance measurements. This device(s) will be introduced at certain diagnose boxes of the beam transport system to meet the increased need of an improved characterization of the beam quality during normal operation as well as for optimizing source parameters. It is also an important input for transport calculations of new beam lines. Such calculations are necessary to control the matching of the beam emittance to the acceptance of the variable-energy radio frequency quadrupole postaccelerator.
The design of a high charge state all permanent ECR ion source
Authors: Sun L. T. , Zhao H. W. , Zhang Z. M. , Hitz D.
Published: May 2004

In recent years, many research activities on atomic physics have been carried out in the Institute of Modern Physics and with the broadening of the research fields, besides the present electron cyclotron resonance ion source (ECRIS) in Lanzhou, some extra high performance ECR ion sources are demanded. Now, an ECRIS put on a high voltage (HV) platform, which can be applied to a HV up to 300 kV is under construction. For the sake of high electric power consumption and some critical engineering requirements, an all permanent magnet instead of a solenoid coil ECRIS is adopted. The axial magnetic mirror peaks are 1.45 and 1.17 T at the injection and extraction side, respectively. The inner diameter of the plasma chamber is designed to be 67 mm while keeping the radial magnetic field at the inner wall of the plasma chamber up to 1.2 T. Some interesting aspects on designing the hexapole as well as optimization design of the source will be presented.
A new technique for diagnosing multicharged ion beams produced by ECR ion source
Authors: Zhang Z. M. , Zhao H. W. , Cao Y. , Ma L. , Ma B. H. , Li J. Y. , Wang H. , Feng Y. C. , Du J. F.
Published: May 2004

In order to study the transmission properties of multicharged ion beams between the electron cyclotron resonance (ECR) ion source and the analyzing magnet, a new diagnostic system composed of three Wien filters with three single wires has been built and installed on the IMP ECR source test bench. The single wire is used to measure the beam profile and the beam density distribution, and the Wien filter is used to measure the charge state distribution of ion beam. The single wire and the Wien filter were tested successfully. With this diagnostic system, the beam profile, charge state distributions and beam losses along the transmission line from IMP LECR3 to the analyzing magnet are experimentally studied in different conditions of the ion source.
Emittance studies of the 2.45 GHz permanent magnet ECR ion source
Authors: Zelenak A. , Bogomolov S. L. , Yazvitsky N. Yu.
Published: May 2004

During the past several years different types of permanent magnet 2.45 GHz (electron cyclotron resonance) ion sources were developed for production of singly charged ions. Ion sources of this type are used in the first stage of DRIBs project, and are planned to be used in the MASHA mass separator. The emittance of the beam provided by the source is one of the important parameters for these applications. An emittance scanner composed from a set of parallel slits and rotary wire beam profile monitor was used for the studying of the beam emittance characteristics. The emittance of helium and argon ion beams was measured with different shapes of the plasma electrode for several ion source parameters: microwave power, source potential, plasma aperture-puller aperture gap distance, gas pressure. The results of measurements are compared with previous simulations of ion optics.
Recent ion source developments for production of radioactive beams (invited)
Authors: Panteleev V. N.
Published: May 2004

Presently, worldwide radioactive ion beam facilities based on the separator online are the main instruments for nuclear structure study and for solving many important questions about astrophysics. Investigations of short-lived neutron-rich and neutron-deficient nuclei, that are far from stability give a unique possibility for testing many aspects of modern nuclear structure theory. Therefore, the development of highly efficient, selective, and fast ion source-target systems (ISTS) for modern and next generation ISOL facilities is the crucial point for future progress of nuclear science and experimental astrophysics. The last decade demonstrates a burst of new developments in the field of ion source-target systems for ISOL installation use. The main task of this review is to show the latest results obtained with different types of ion sources, specially designed for short-lived isotope production, and to designate some directions of the ISTS development that can be noticed presently and very likely will be used in the near future.
Nd–YAG laser ion source for direct injection scheme
Authors: Kashiwagi H. , Hattori T. , Hayashizaki N. , Yamamoto K. , Takahashi Y. , Hata T. , Okamura M. , Jameson R. A. , Katayama T. , Mescheryakov N.
Published: May 2004

The feasibility of a “direct injection scheme” using Nd–yttritium–aluminum–garnet laser has been studied experimentally. The relationship between charge distribution and laser power density was measured. The obtained yield rate of C6+ was 46.8% at the peak current pulse with 1.6×1011 W/cm2 laser intensity. The current dependence of the distance from the target at this intensity was measured. The peak current of C6+ will be 60 mA with φ4.8 mm extraction aperture. It was found from the input beam condition simulation by the code PTEQ–HI that high current (from 12 to 28.6 mA) can be accelerated by the TIT–RFQ.
Electron gun and collector simulations for RHIC EBIS at BNL
Authors: Pikin A. , Alessi J. G. , Beebe E. N. , Kponou A. , Prelec K. , Ritter J. , Snydstrup L. , Kuznetsov G. , Tiunov M.
Published: May 2004

Based on the successful experience of the Brookhaven National Laboratory test electron beam ion sources (EBIS), the relativistic heavy ion collider (RHIC) EBIS design utilizes a 10 A electron beam to produce the required ion source output intensity of 3.4×109 of Au32+ ions per 10–40 μs pulse. In order to provide increased cathode lifetime and reliability at the required 10 A, and accommodate future upgrades of RHIC EBIS ion intensity, it is desirable to upgrade the electron gun. Simulations have been made for a new electron gun and electron collector capable of generating and dissipating an electron beam with current up to 20 A. The method of forming the electron beam using magnetic compression and inverse magnetron geometry of the electron gun are the same as has been tested successfully on the electron beam test stand. The new gun has higher perveance and partially shielded spherical cathode. A bell-shaped radial current density distribution with reduced current density on a periphery of the beam, combined with a modified shape of the electron collector magnet shim, yields a simulated power density on the surface of the electron collector below 400 W/cm2 for electron beam currents up to 20 A.
Enhancement of ionization efficiency of surface, electron bombardment and laser ion sources by axial magnetic field application
Authors: Panteleev V. N. , Barzakh A. E. , Fedorov D. V. , Ionan A. M. , Ivanov V. S. , Moroz F. V. , Orlov S. Yu. , Volkov Yu. M.
Published: May 2004

Effect of an axial magnetic field influence on the ionization efficiency of surface and laser ion sources has been observed. The axial magnetic field applying in the range 500–800 G gives an increase of the ion current of atoms of all elements those are ionized in a hot cavity of the surface or laser ion source. Moreover, if for ionization of atoms with low ionization potentials such as K, Rb, and Cs the magnetic field applying effect is negligible, for elements with ionization potentials higher than 6 eV, such as Gd, Tm, Yb, Lu, and others it reaches value about 20 in the ion source temperature region of 2100–2500 °C. The results of on-line experiments are presented confirming the influence of the axial magnetic field on the ionization efficiency rise of neutron-deficient isotopes of rare-earth elements produced in the combined ion source-target assembly (ionizing target) and Eu isotopes resonantly ionized in the laser ion source and in the high temperature ionizing target.
Design of an electron-beam ion trap to be situated at Queen’s University, Belfast
Authors: Watanabe H. , O’Rourke B. E. , Currell F. J.
Published: May 2004

An electron-beam ion trap (EBIT) has been designed for atomic physics experiments at the Queen’s University of Belfast. A pair of permanent magnets will be used to produce an axial magnetic field to compress an electron beam, whereas pairs of superconducting magnets have been used for traditional EBITs. The design of the new EBIT is detailed and possible experiments are explained to show the feasibility of the EBIT.
X-ray-induced fluorescence spectroscopy with highly charged ion beam produced by a laser ion source
Authors: Ozawa S. , Wakasugi M. , Okamura M. , Katayama T. , Koizumi T. , Serata M.
Published: May 2004

We designed and tested a beam line for transport of highly charged ions produced by a laser ion source. The ion beam is prepared for an x-ray spectroscopy experiment based on a laser-induced fluorescence spectroscopy. A C4+ beam which has a peak current of 160 μA and bunch width of 500 ns was obtained. It corresponds to 1.3×108 ions/pulse, and the quantity enables the x-ray spectroscopy experiment.
Formation of a high intensity low energy positron string
Authors: Donets E. D. , Donets E. E. , Syresin E. M. , Itahashi T. , Dubinov A. E.
Published: May 2004

The possibility of a high intensity low energy positron beam production is discussed. The proposed Positron String Trap (PST) is based on the principles and technology of the Electron String Ion Source (ESIS) developed in JINR during the last decade. A linear version of ESIS has been used successfully for the production of intense highly charged ion beams of various elements. Now the Tubular Electron String Ion Source (TESIS) concept is under study and this opens really new promising possibilities in physics and technology. In this report, we discuss the application of the tubular-type trap for the storage of positrons cooled to the cryogenic temperatures of 0.05 meV. It is intended that the positron flux at the energy of 1–5 eV, produced by the external source, is injected into the Tubular Positron Trap which has a similar construction as the TESIS. Then the low energy positrons are captured in the PST Penning trap and are cooled down because of their synchrotron radiation in the strong (5–10 T) applied magnetic field. It is expected that the proposed PST should permit storing and cooling to cryogenic temperature of up to 5×109 positrons. The accumulated cooled positrons can be used further for various physics applications, for example, antihydrogen production.
Reduction of the carbon contamination of an electron cyclotron resonance ion source
Authors: Tarvainen O. , Suominen P. , Koivisto H. , Pitkänen I.
Published: May 2004

The MIVOC method can be used for the production of metal ion beams with an electron cyclotron resonance ion source. The drawback of the method is the inevitable carbon contamination of the plasma chamber, which lowers the performance of the ion source. After the production of metal ion beams, the carbon contamination has to be removed in order to return the maximum performance of the ion source. In this work the cleaning of the plasma chamber with the aid of nitrogen and oxygen plasmas has been studied. The achieved extraction rate of carbon was found to be two times higher with oxygen plasma. It was also found that the carbon contamination is concentrated on the area of the plasma chamber surface covered by the electron flux escaping from the plasma.
Design studies for a H− ion extraction system
Authors: Ushakov A. , Volk K. , Klein H. , Ratzinger U.
Published: May 2004

At the University of Frankfurt, a high current H− ion source was developed and tested. A H− beam current of 120 mA with an energy of 35 keV was extracted using an emission opening radius of 5 mm. This source was equipped with a diode extraction system. Thus, the extraction voltage determines the beam energy, depending on the plasma density. In order to adjust the extraction voltage independently from the beam energy, a 65 kV extractor is being designed. It consists of a compact four electrode (tetrode) system. The electron dumping will be performed after the tetrode system. For computing three dimensional magnetic field distributions the code AMPERES has been used. The influence of magnetic fields on the beam path has been taken into account. The article presents the layout of a compact 65 kV extractor for 120 mA H−.
Problems of intense negative ion beam transport (invited)
Authors: Soloshenko I. A.
Published: May 2004

The results of research of physical processes in intense negative ion beams without magnetic fields are presented. As a result of this research: (1) mechanisms of space charge compensation in negative ion beams are determined, (2) stability of compensated states with respect to excitation of plasma oscillations is analyzed, (3) mechanisms of nonlinear limitation of oscillation amplitudes are determined, and (4) values of steady and alternating fields in the beam are found and their influence on transport characteristics of the beams is estimated. It is demonstrated that ion-ion instability at low gas pressure may lead to catastrophic consequences: practically total decompensation of the beam and unacceptable angular scattering. A method of stabilization of this instability, and a technique of focusing negative ion beams by space charge fields are proposed.
Simulation of negative hydrogen ion production and transport
Authors: Bandyopadhyay M. , Wilhelm R.
Published: May 2004

Negative hydrogen ion production by volume process and its transport in a negative hydrogen ion source has been simulated by a combination of three three-dimensional Monte Carlo codes: (1) neutral transport, (2) negative hydrogen ion production, and (3) negative hydrogen ion transport. Neutral transport code has been used to calculate the spatially resolved density spectrum nv of the vibrationally excited H2 molecules. With the negative hydrogen ion production code, the production and distribution of H− ion density n− in the discharge volume has been calculated. And with the negative hydrogen ion transport code, the calculation of the survival probability of H− ions up to the extraction grid has been carried out. In all cases, the experimentally observed plasma parameters, as well as background gas density and temperature profiles, are inputs during trajectory calculation. It has been found that the negative ion density is almost uniform from the ion production zone (driver) to the grid. However, H− ions, which are produced within a few centimeters from the grid, are only able to reach the extraction hole. To compare the code calculation, a zero-dimensional particle balance rate equation is also solved.
NIGUN: A two-dimensional simulation program for the extraction of H− ions
Authors: Becker R.
Published: May 2004

A new theory for a multiparticle plasma sheath in the case of H− extraction recently provided the basis to modify the well-established two-dimensional (2D) computer program IGUN.© As in the case of IGUN, stability of convergence is obtained for the very nonlinear sheath region by directly inserting the analytical space charge according to the Poisson equation for each mesh point above the wall potential. For three-component plasmas (e, p, and H−) only the relation of proton birth potential to electron energy and H− energy to electron energy is needed to obtain all parameters. For four-component plasmas (e, p, H−, and Cs+) the density and energy ratios of protons and Cs+ ions are required as input for the calculations. Up to 10 different positive ion species may be declared, also requiring the input of the corresponding ratios for density and energy. The actual field strength in the extraction gap is used to determine the proper densities of all particles by the program. The numerical “proof” will be given that, as predicted by theory, an angle of 45° between the beam boundary and the wall electrode will provide rectilinear flow once the density matches the field in the extraction gap.
Negative ion source improvement by introduction of a shutter mask
Authors: Belchenko Yu. I. , Oka Y. , Kaneko O. , Takeiri Y. , Tsumori K. , Osakabe M. , Ikeda K. , Asano E. , Kawamoto T.
Published: May 2004

Studies of a multicusp source were recently done at the National Institute for Fusion Science by plasma grid masking. The maximal H− ion yield is ∼1.4 times greater for the shutter mask case than that for the standard source. Negative ion current evolution during the cesium feed to the masked plasma grid evidenced that about 60% of negative ions are produced on the shutter mask surface, while about 30% are formed on the plasma grid emission hole edges, exposed by cesium with the mask open.
Compact surface plasma sources for heavy negative ion production
Authors: Dudnikov Vadim , Farrell J. Paul
Published: May 2004

Features of a compact surface plasma source designed for heavy negative ion beam production are considered. Discharges in crossed E×B fields with hollow cathodes were used for efficient plasma generation. Production of heavy negative ion beams by plasma interaction with the surface of spherical focusing emitters made of different materials, such as copper and lanthanum hexaboride, with cesium catalysis are presented. The dynamics of emitter activation is discussed. dc ion beams with current up 0.9 mA have been extracted from the compact surface plasma sources with a 12-mm-diam LaB6 emitter and a emission aperture of 3 mm diam. Minimizing plasma and gas thickness between emitter and emission aperture is essential for minimizing negative ion destruction and maximizing high intensity beam production. A small mass analyzer and secondary ion mass spectroscopy were used to quantify boron ion yield. Presence of atomic and molecular boron negative ions is confirmed. The estimated emittance of the 0.5 mA heavy negative ion beam is ε=13 π mm mrad(MeV)1/2.
Thermal modeling of the ISIS H− ion source
Authors: Faircloth D. C. , Thomason J. W. G. , Lau W. , Yang S.
Published: May 2004

The development of H− ion sources with performances exceeding those achieved today is a key requirement for the next generation of high power proton accelerators. The ISIS Penning surface plasma source, which routinely produces 35 mA of H− ions during a 200 μs pulse at 50 Hz for uninterrupted periods of up to 50 days, is regarded as one of the leading operational sources in the world, and should provide an excellent starting point for a development program. One goal is to produce pulse widths of 1.2 ms at 50 Hz and 2.5 ms at 50/3 Hz, thereby increasing the duty factor from 1% to as much as 10%. Increasing pulse widths will necessitate an improved cooling system to offset increased heating. The most effective cooling strategy will be determined by thermal finite element analysis of the ISIS source. The modeling will then be extended to find an optimal means of offsetting increased heat loading, and will minimize the amount of engineering required to produce an effective solution. Modeling of the ISIS source has established the temperature profiles of the source components. At the specific locations where temperatures are measured in operation using thermocouples the model values match those seen in practice. Transient modeling has been used to provide temperature variations for the source during the 20 ms period of the 50 Hz cycle.
Development of an H− ion source based on the electron cyclotron resonance plasma generator at CEA/Saclay
Authors: Gobin R. , Delferrière O. , Ferdinand R. , Harrault F. , Benmeziane K. , Gousset G. , Sherman J. D.
Published: May 2004

Electron cyclotron resonance (ECR) plasma generators have demonstrated their efficiency, reproducibility, and long lifetime for the production of light positive ions like protons or deuterons. These sources generally work in cw mode. A 2.45 GHz ECR test stand based on a pure volume H− ion production is currently under development. This negative ion source is working in pulsed mode, 1 ms at 10 Hz. The first H− ions have been observed at the beginning of 2002 with a poor efficiency. Only a few μA were produced. To avoid negative ions destruction by a nonabsorbed microwave close to the extraction aperture, a stainless steel grid was installed in the rectangular plasma chamber. As a result, the chamber is now effectively separated into two zones: the ECR plasma generator and the H− production zone. By plotting the extracted current versus the production zone length, the H− ion intensity reached more than 100 μA with the grid located 25 mm from the aperture. A voltage difference on the order of 10 V can be applied between the two parts of the plasma chamber in order to modify the electron energy entering the production zone.
Effect of argon additive on H− density and temperature in volume negative ion source
Authors: Ivanov A. A. , Bacal M. , Rouillé C. , Nishiura M. , Sasao M.
Published: May 2004

Various plasma parameters were measured for several hydrogen–argon mixtures in the multicusp H− ion source Camembert III, equipped with tantalum filaments. The density and the temperature of electrons were measured with the Langmuir probe situated in the center of the source and associated with the photodetachment diagnostics. The two-laser photodetachment diagnostics was used to obtain the temperatures of the two negative ion populations. At low hydrogen pressure (0.8 mTorr) a small concentration of argon additive enhances the hydrogen negative ion density (by approximately 60%), it also increases the electron density. The negative ion population fractions having the high- and low-temperature values behave differently when varying the total pressure in pure hydrogen and in hydrogen with argon additive. Several possible explanations of the drastic change of the relative ratio of negative ion populations when the argon fraction is increased, are proposed. Another interesting phenomenon observed during the experiments is the decrease with time of the H− density in the presence of argon. After adding the argon during the time interval of ∼1 h the H− density goes down and finally establishes at a minimum value. The final H− density is lower than the H− density in pure hydrogen plasma before adding argon. This “poisoning” is discussed in terms of wall production of vibrationally excited H2 molecules.
H
−
ion production in electron cyclotron resonance driven multicusp volume source
Authors: Ivanov A. A. , Rouillé C. , Bacal M. , Arnal Y. , Béchu S. , Pelletier J.
Published: May 2004

We have used the existing magnetic multicusp configuration of the large volume H− source Camembert III to confine the plasma created by seven elementary multidipolar electron cyclotron resonance (ECR) sources, operating at 2.45 GHz. We varied the pressure from 1 to 4 mTorr, while the total power of the microwave generator was varied between 500 W and 1 kW. We studied the plasma created by this system and measured the various plasma parameters, including the density and temperature of the negative hydrogen ions which are compared to the data obtained in a chamber with elementary ECR sources without multicusp magnetic confinement. The electron temperature is lower than that obtained with similar elementary sources in the absence of the magnetic multicusp field. We found that at pressures in the range from 2 to 4 mTorr and microwave power of up to 1 kW, the electron temperature is optimal for H− ion production (0.6–0.8 eV). This could indicate that the multicusp configuration effectively traps the fast electrons produced by the ECR discharge.
Contribution of local H− density to extracted H− beam current in a cesium seeded hydrogen plasma
Authors: Matsumoto Y. , Nishiura M. , Matsuoka K. , Sasao M. , Wada M. , Yamaoka H.
Published: May 2004

Temporal behavior of H− beam current after photodetachment was measured by means of the irradiation of laser light inside the plasma near a plasma electrode in a hydrogen negative ion source. As the distance between the laser path and the extraction hole was increased, the change in H− beam current due to photodetachment decreased indicating a smaller contribution to the extracted beam by H− ions transported from the region deeper inside of the ion source. Addition of Cs into the discharge increased the extracted H− current, while the change in H− current due to photodetachment showed stronger dependence upon the distance between the laser path and the plasma electrode.
Investigation of negative ion generation in a cusp plasma electromagnetic trap with a hollow-cathode Penning source of electrons
Authors: Petrushenya A. A. , Borisko V. N.
Published: May 2004

Results are reported from experimental studies of negative ion generation in a cusp plasma electromagnetic trap by using an electron beam injected into the trap. Owing to a wide energy distribution of the electron beam, a one-chamber scheme of negative ion generation could be realized in the trap. A negative hydrogen ion current of 300 μA with a density of 0.7 mA/cm2 was obtained for an injected electron beam current of 300 mA at conditions far from optimum.
Effects of the weak magnetic field and electron diffusion on the spatial potential and negative ion transport in the negative ion source
Authors: Sakurabayashi T. , Hatayama A. , Bacal M.
Published: May 2004

The effects of the weak magnetic field on the negative ion (H−) extraction in a negative ion source have been studied by means of a two-dimensional electrostatic particle simulation. A particle-in-cell model is used which simulates the motion of the charged particles in their self-consistent electric field. In addition, the effect of the electron diffusion across the weak magnetic field is taken into account by a simple random-walk model with a step length Δx per time step Δt; Δx=2D⊥Δt⋅ξx, where D⊥ and ξx are the perpendicular diffusion coefficient and normal random numbers. Under this simple diffusion model, the electron diffusion has no significant effects on the H− transport. Most electrons are magnetized by the weak magnetic field and lost along the field line. As a result, more H− ions arrive instead of electrons in the region close to the plasma grid in order to ensure the plasma neutrality.
Space charge lens for focusing negative ion beam: Theory and experiment
Authors: Soloshenko I. A. , Goretsky V. P. , Gorshkov V. N. , Zavalov A. M.
Published: May 2004

Detailed researches the of space charge lens for focusing negative ion beam are performed for the cases when positive space charge forming is done either by the beam itself, or by special flow of electrons. Numerical simulations of space charge fields and beam ion trajectories are accomplished, and results of the calculations are compared with experimental data. It is shown both theoretically and experimentally that in the proposed device electric field strength reaches a value of ∼100 V/cm, thus providing a focal length of <20 cm.
Charge-energy distribution of Ta ions from plasmas produced by 1ω and 3ω frequencies of a high-power iodine laser
Authors: Láska L. , Jungwirth K. , Králiková B. , Krása J. , Pfeifer M. , Rohlena K. , Skála J. , Ullschmied J. , Badziak J. , Parys P. , Wolowski J. , Woryna E. , Torrisi L. , Gammino S. , Boody F. P.
Published: May 2004

The high-power iodine laser system PALS (λ0=1.315 μm at the fundamental laser frequency, 1ω, and λ1/3=0.438 μm at the third harmonic frequency, 3ω), with a maximum laser intensity IL of up to about 3×1016 W/cm2, was used to generate highly charged Ta ions. Maximum ion charge states slightly above z=50+ were determined by using an electrostatic ion energy analyzer and the maximum energy of emitted ions, estimated from the ion collector signals, was even higher than Ei=22 MeV, as determined by track detectors. Charge-state distributions, as well as charge-energy distributions were evaluated for both 1ω and 3ω laser frequencies. The focus position with regard to the target surface (in addition to the focus spot size) determines not only the laser power density deposited and the amount of produced ions, but it also directly influences the mechanisms of ion generation. Highly charged ions with the charge states above 50+ can be generated either by using a sufficiently high laser intensity (about 1×1016 W/cm2) or, at lower laser intensities (IL>2×1014 W/cm2), in the case where the conditions for the relativistic self-focusing are met.