Table of contents

The ninth International Symposium on Electron Beam Ion Sources and Traps and Their Applications — EBIS/T 2004 was held at the Tokyo Metropolitan University (TMU), 15–17 April 2004. There were about 40 participants and about 30 papers presented. The meeting has shown the remarkable progress in science and technology with the EBIS/T machines. In this meeting, besides the normal presentations related to the EBIS/T works, a special session was organized on the last day which was dedicated to Professors N Kobayashi and K Okuno, who have contributed to the EBIS/T development and to the physics of highly charged ions (HCI), to mark their retirement from the TMU in March 2004. In the evening of the first day, there was a laboratory tour where the participants enjoyed seeing the Tokyo EBIT facility and also a beer party in a small hall next to the laboratory. The banquet was held in a traditional Japanese restaurant in a village under Mt Takao with the Japanese meals and performances, after seeing the HCI-research activities in the TMU. The next EBIS/T symposium will be held in Heidelberg in the summer of 2007 as a satellite meeting of XXV ICPEAC. We are looking forward to the next exciting meeting there. Finally, we thank all of TMU staffs and students for their help during the meeting.

We have developed an electron beam ion source (EBIS) assembling three rings made of high-T_C superconductor as a solenoid, which enables us to construct a `table-top' EBIS operated at the liquid N<sub>2</sub> temperature with a strong magnetic field. Optimizing a pulse field magnetization procedure, the assembly yielded a magnetic field as high as 0.8 T under a persistent mode, which stably lasted more than two days. An electron beam of 12 keV–50 mA was successfully compressed and guided by the magnetic field along the axis of the drift tube and `soft-landed' on an electron collector with a collection efficiency of more than 99%. As a result, highly charged ions such as Ar¹⁷⁺ and Xe⁴²⁺ have been produced and extracted.

Here we summarise the present status of the experimental programme of the Oxford electron beam ion trap. Most notably this research has recently culminated in the successful measurement of the 2s_1/2–2p_3/2 transition in hydrogenlike nitrogen by a laser resonance method. We also introduce preliminary results from some computational investigations of both electron beam transport and the trapped ion ensemble. In particular, we show that the contribution of the magnetic field to ion confinement has a potentially measurable effect on the ion phase space distribution.

A partially neutralised electron beam can be considered as a well defined target of ions. Trapped in the electrostatic 3D-trap of the electron beam in an EBIS, they will—for low loss rates—acquire an energy distribution according to Boltzmann's law. The resulting spatial distribution then is well defined, once the ion temperature and the amount of ions are known. Both are related to each other by a monotone dependence, hence determination of either the ion temperature or the number of ions will give the second quantity.

Such a Coulomb target provides friction to the radial movement of newly injected ions, hence can be used to facilitate the trapping of low charged injected ions (external ion source, charge breeder) or of cooling of highly charged ions (created by deceleration). Due to the well known properties of such a target, it also may be used for collision studies between trapped ions and either a beam of atoms or of additionally injected ions.

Successful operation of the BNL EBIS with electron current up to 10 A provides optimism that EBIS operation with even higher electron current should be possible. We are now considering key aspects of the design for an EBIS operating with electron current 20 A. Several technical problems need to be resolved, including generation of a 20 A electron beam and dissipation of this electron beam power on the electron collector. Since we already have a tested concept of electron beam generation with the gun immersed in a magnetic field and subsequent purely magnetic compression of the electron beam, it makes sense to develop the new electron gun with immersed cathode but with higher perveance. To distribute the electron beam power on the surface of the electron collector more evenly, the emission current density from the cathode can be made bell-shaped with minimum close to zero on the periphery of the electron beam. With the already high requirements to the emission current density, and since such shaping of the electron beam makes these requirements even higher, perhaps the only available cathode material that can satisfy these requirements is IrCe. The problems of power dissipation on the electron collector (EC) include heat removal with cooling water and fatigue of the EC material. The first step in the EC design was electron beam transmission simulation with the goal to reduce `spikes' of power density on EC surface as much as possible. With the geometry of EC thus defined, the conditions of heat exchange for several modes of EBIS operation have been analyzed and cooling parameters, which provide adequate heat removal were found. The last step was stress analysis of several EC materials with ANSYS to find the material suitable for this application. Details of the 20 A electron gun and collector are presented.

To generate a dense high current electron beam for EBIS working at quasipermanent regime, high temperature cathodes are used. Though LaB₆ cathode is widely employed, an alloy of refractory metals with lanthanoides seems to have better operating characteristics. The IrCe cathode can produce twice-higher electron current than that of LaB₆-monocrystal at the same temperature, and has two-order lower an evaporation rate at the same time. So, the life-time of IrCe cathode is up to 40000 hours while generating current density of 15-17 A/cm². In the article one can find more detailed description of the IrCe.

Two years after the relocation of the Heidelberg EBIT, several experiments are already in operation. Spectroscopic measurements in the optical region have delivered the most precise reported wavelengths for highly charged ions, in the case of the forbidden transitions of Ar XIV and Ar XV. The lifetimes of the metastable levels involved in those transitions has been determined with an error of less than 0.2%. A new, fully automatized x-ray crystal spectrometer allows systematic measurements with very high precision and reproducibility. Absolute measurements of the Lyman series of H-like ions are currently underway. Dielectronic recombination studies have yielded information on rare processes, as two-electron-one photon transitions in Ar¹⁶⁺, or the interference effects between dielectronic and radiative recombination in Hg⁷⁷⁺. The apparatus can now operate at electron beam currents of more than 500 mA, and energies up to 100 keV. A further beam energy increase is planned in the near future. Ions can be extracted from the trap and transported to external experiments. Up to 4 × 10⁷ Ar¹⁶⁺ ions per second can be delivered to a 1 cm diameter target at 10 m distance. Charge-exchange experiments with U⁶⁴⁺ colliding with a cold He atomic beam have been carried out, as well as experiments aiming at the optimization of the charge state distribution of the extracted via dielectronic recombination. Two new EBITs, currently in advanced state of construction in Heidelberg, will be used for experiments at the VUV free electron laser at TESLA (Hamburg) and for the charge breeding of short-lived radioactive isotopes at the TRIUMF ISAC facility.

The design of EBIS for nanoprocess using HCI is presented. The EBIS uses commercial super-conducting magnet cooled by a closed-cycle refrigerator. We have made trajectory simulation of electron beam in 100 mA range to determine the configuration of electrodes and magnet coils appropriate to obtain high current density beam at the drift tube region.

We report present status of a beam line for transportation of highly charged ions (HCIs) extracted from the Tokyo EBIT. We have produced continuous beams of 2.5 × 10⁵ cps for Xe⁴⁴⁺ through a 1 mm aperture. With slightly high energy operation (electron beam energy: 78 keV) of the Tokyo EBIT, we have also obtained 10³ ions/pulse for Ta⁷⁰⁺ HCIs extracted by a pulse mode (trapping time: 3 sec). We are going to apply such HCI beams to nano-processes on solid surfaces by utilizing some useful characteristics of the HCI-interactions. Future perspective of HCI-based nano-science and -technology is presented.

A new electron beam ion trap (EBIT) is under constructiin in Shanghai. In this paper we describe the design and the features of this apparatus. Finally the current status of Shanghai EBIT is shown.

The laboratory condition where charged particle fusion reactions have been done is not exactly the same as that of stellar condition. To probe details of reaction and to test the prediction of standard solar model we need more precise data for charged particle fusion experiments in the laboratories. We propose several experimental approaches to reduce the ambiguity of the estimation of screening potential value which is crucial for obtaining the astrophysical S-factor. Experiment with bare target and bare beam interaction will be done by using proposed Electron Beam Ion Trap apparatus (NARITA).

The dynamics of mixed ensembles of highly charged argon/xenon and krypton/xenon ions in an electron-beam ion trap (EBIT) was studied by recording the characteristic x-ray emission of the trapped ions. Sawtooth-like signatures manifest in the x-ray spectra for a variety of trap parameters. The effect can be understood as arising from the feedback between low-Z and high-Z ions.

Cancer therapy synchrotrons profit from single turn injection in terms of size, costs and easy operation. The MEdically Dedicated EBIS (MEDEBIS), built in Frankfurt, will deliver short (~1.5 µs) and intense (~1.3 mA) pulses of highly charged light ions (C, N, O) to meet the requirements for therapy facilities. The MEDEBIS operates with an electron beam of 400 mA at 5 keV and a ratio of beam to drift tube of 1/20. Drift tube potentials up to 1.6 kV are switched in some 100 ns to deliver a 1.5 µs ion pulse at an axial field gradient of 6.5 kV/m. On extraction, all potentials applied to the drift tubes are set to a given primary potential to define the extraction gradient. During extraction the drift tubes are not held at constant voltage to avoid spreading out of the pulse due to the restoration of the full space charge depression at locations where ions have already been extracted. To locally distribute the action of the applied potentials the drift tubes are fully interpenetrating each other with tapered fingers. Combining these features result in a potential wall, which follows the extracted ion pulse and produces a compressed short ion pulse for single turn injection. In the future similar constructions could be considered for the RHIS EBIS device or proposed for LHC to provide the advantage with respect to lowest emittance and highest luminosity to the accelerators at BNL and CERN.

In this paper the theoretical estimations and numerical simulations of tubular beams are presented. Steady-state of a tubular beam is described analytically in a thin-beam approximation and stability properties of tubular beams are studied in a framework of the magnetic hydrodynamics. The idea of the off-axis ion extraction is illustrated with 3-D numerical simulations.

Radioactive ion beams (RIBs) are an important tool for experiments at the foremost frontier of nuclear physics. The quasi-continuous radioactive beams from target ion sources of RIB-facilities have to be accelerated to energies at and beyond the Coulomb barrier. An efficient acceleration requires a suitable A/q of the ions determined by the accelerator design, which can be reached via the stripping method or by using a charge state breeder like the REX-ISOLDE system. In order to get comparable efficiencies for a charge state breeder with the stripping scheme, the breeding efficiency in one charge state has to be optimized by narrowing the charge state distribution. In addition good beam quality and thus small emittances are required to achieve best transmission in the following accelerator, which is mandatory for high intensity RIBs. For EBIS/T devices the maximum intensity of the radioactive ion beam is a critical issue, and high current EBIS/T devices will be necessary to deal with intensities of second generation RIB facilities.

The `charge state breeder' BRIC (BReeding Ion Charge) is based on an EBIS source and it is designed to accept Radioactive Ion Beam (RIB) with charge state +1, in a slow injection mode, to increase their charge state up to +n. BRIC has been developed at the INFN section of Bari (Italy) during these last 3 years with very limited funds. Now, it has been assembled at the LNL (Italy) where are in progress the first tests as stand alone source and where, in the future, with some implementation, it will be tested as charge breeder at ISOL/TS facility of that laboratory. BRIC could be considered as a solution for the charge state breeder of the SPES project under study also at the LNL. The new feature of BRIC, with respect to the classical EBIS, is given by the insertion, in the ion drift chamber, of a radio frequency (RF) - quadrupole aiming to filter the unwanted masses and then making a more efficient containment of the wanted ions. In this paper, the first ion charge state measurements and analysis and the effect of the RF field applied on the ion chamber will be reported and discussed. The first RF test measurements seem confirm, as foreseen by simulation results carried out previously, that a selective containment can be obtained. However, most accurate measurements needed to study with more details the effect. For this reason, few implementations of the system are in order to improve the accuracy of the measurements. The proposed modifications of the BRIC device, then, will be also presented and shortly discussed.

A project to cool highly charged ions (HCIs) with positron and electron cooling techniques is under way. Trapped 10¹⁰ electrons and 10⁷ positrons in a multi-ring trap are used as energy absorbers for HCIs. The detail of the cooling procedure is reviewed.

Highly charged ions have a great potential for further insight in atomic physics or nuclear physics. We are planning an x-ray-induced fluorescence spectroscopy experiment on highly charged ion trapped in EBIT. In the present paper we report an estimation of the feasibility of the experiment with EBIT and the present status of the demonstration experiment with synchrotron radiation and highly charged ion beam produced by a laser ion source.

The experimental atomic physics group of Tokyo Metropolitan University now intensively promotes three projects: (1) research of huge molecular ions by a liquid-nitrogen-cooled electrostatic ion storage ring, (2) research of highly-charged ion interaction with a crystal using high-energy heavy-ion storage ring, and (3) research of the very low-energy ion–atom interaction through ion swarms in helium gas cooled down to 4 K. In this report, these projects are briefly introduced in a comprehensive manner.

The well known `SLAC Electron Trajectory Program' (EGUN) has been ported to PCs and has been developed into a family of programs for the design and the optimization of particle optics devices including electron and ion guns, beam transport sections and collectors. We will discuss the application of these tools for the design and the optimization of the essential parts of EBIS/T devices. The discussion will include conditions in which restrictions in the reliability of simulations may occur due to the mathematical modeling and how to overcome them.

Most design goals of the BNL Test EBIS Project have been exceeded and we are confident that an EBIS meeting RHIC requirements can be built. Achieved parameters include 10 A electron beam current, ion charge state above Au³²⁺, and greater than 55 nC total extracted ion charge. The Test EBIS utilizes the full electron beam power but has only half the trap length and operates at a reduced duty factor compared with an EBIS for RHIC, which would produce at least 85 nC total ion charge in 10–40 microsecond pulses, containing ~3 × 10⁹ particles/pulse of Au³²⁺ ions. Normalized rms emittance values for 1–3 mA extracted ion beams have been in the range of 0.08–0.1 pi mm mrad. Present development of the source is focused on establishing operational reliability and facilitating future upgrades in ion intensity and species, since the major emphasis is now on integrating the EBIS into a pre-injector facility, including an RFQ and linac. Recent progress towards this goal includes the following: (1) An IrCe electron gun cathode and modified anode have been installed in an electron gun chamber separable from the source ionization region by a gate valve. A very low loss 10 A, electron beam has been propagated with the new configuration, with 100 kW peak power dissipation at the electron collector. (2) A new electron collector power supply configuration has been tested which can lower the cost compared to our present setup, while improving the stability of the electron beam launch. This is an important first step towards placing the EBIS on a nominal 50 kV platform, necessary for efficient highly charged ion transport to the RFQ. (3) A hollow cathode ion source obtained from CEA Saclay, has been tested and is being installed. This will allow us to provide a variety of ion species to the RHIC and NASA Space Radiation Laboratory facilities, and is valuable at the present project stage for beamline development and emittance studies of heavy and light ion beams of highly charged ions from the EBIS. (4) An electron collector for RHIC has been designed which would allow operation exceeding 10 A electron beams at 100% duty factor. The RHIC collector design could allow upgrades to 300 kW electron beam power. (5) Controls for pulse to pulse switching and diagnostics for charge state and charge fraction verification have been developed.

We report on computer studies to determine the acceptance of the Electron Beam Ion Source Test Stand (EBTS) at BNL. Knowledge of the acceptance is a useful guide in selecting a source of primary ions, and in designing a transfer line which best matches the primary ion beam to the acceptance of the EBTS. In this work, an ion beam with suitable parameters is tracked out of the EBIS, to a plane where knowledge of the acceptance is wanted. The emittance of the extracted beam in this plane gives a starting point for determining a more reliable value of acceptance. The result will be compared with a theoretical estimate.

A new Electron Beam Ion Trap has been designed for use at the Queen's University, Belfast. We describe our design, with particular reference to the machine's versatility and inclusion of new features which will make the machine particularly suited to the study of electron–ion interactions. An initial experimental program, making use of these features is described as is other information pertinent to potential collaborators.

This article reviews early EBIS/T-based HCI research in Japan designed to understand atomic processes of highly charged impurity ions in plasmas. In particular the work of the NICE (Naked Ion Collision Experiments) project is discussed. The NICE experiment showed for the first time that translational energy spectroscopy would give useful information about the intermediate multiple-excited states in the transfer ionization processes, and therefore it would be a powerful method for spectroscopy of so-called hollow atoms.

We review measurements based on translational energy spectroscopy which are being used to identify and assess the relative importance of the various collision mechanisms involved in one-electron capture by slow multiply charged ions in collisions with simple atoms and molecules.

The aim of the CORONA project was to study targets after collisions with highly charged ions (HCI) as a part of a research project `Atomic Physics of Multi-Charged Ions'. Experimental results were obtained in four areas: (1) differential cross section measurements of electron–ion collisions, (2) snap shots of highly charged molecular ions produced by electron capture reactions of HCI, (3) polarization spectroscopy of charge transfer reactions, and (4) sputtering and deformation of solid surfaces by slow HCI.

Electron string phenomenon arises as a result of phase transition of a state of multiply reflected electron beam to this new discovered state of one component electron plasma and can be easily observed in the reflex mode of EBIS operation. The transition goes via a strong instability, which causes considerable electron energy spread, which in its turn suppresses the instability. Electron string state is a stationary state of hot pure electron plasma, which is heated by injected electron beam and cooled because of electron loses. Electron string is quiet in broad regions of experimental parameters, so that it is used for confinement and ionization of positive ions by electron impact to highly charge states similar to electron beams in EBIS. Application of electron strings instead of electron beams for ion production allows to save about 99% of electric power of electron beam and simultaneously to improve reliability of an ion source considerably. The JINR EBIS `Krion-2' in the string mode of operation is used for production of N<sup>7+</sup>, Ar<sup>16+</sup> and Fe<sup>24+</sup> ion beams and their acceleration to relativistic energies on the facility of the JINR super conducting one turn injection synchrotron `Nuklotron'.

The tubular electron string possibly can exist and it is under study now theoretically and experiments are prepared now. Estimations show that a Tubular Electron String Ion Source (TESIS) could have up to three orders of magnitude higher ion output then a Linear one (LESIS). In frames of nuclear astrophysics electron strings can be used for research of fusion nuclear reactions at low energies in conditions when both beam and target nuclei do not carry orbital electrons. The project NARITA — Nuclear Astrophysics Researches in an Ion Trap Apparatus is proposed. Polarization effects also can be studied.

Combination techniques of the Mini-EBIS and OPIG have been used for cross section measurements of multiply charged ions and for study of collision dynamics in multiply charged ion-molecule collisions. The general features of single- and multiple-charge changing cross sections measured at low energies below 1 keV per charge and some topics of collision dynamics in multiply charged ion-molecule collisions studied by a new multi-coincident technique are presented.