Multicharged Ion Source Research Articles

Investigations in the Joint Institute for Nuclear Research on the improvement of highly charged ion production in ion sources

The main statements of the new Joint Institute for Nuclear Research (JINR) research and development (R&D) project ‘‘Investigations on the Physics of Multicharged Ion Sources for JINR and CERN Hadron Accelerators’’ are presented in this report. The project will be performed with the purpose of improving the source efficiency for the JINR and CERN accelerator complexes. The project will include the theoretical and experimental investigations as well as x-ray spectroscopy of highly charged ion plasma in the sources.

Collisions of highly charged ions with electrons, atoms and surfaces

At the Oak Ridge Multicharged Ion Source Facility, an experimental atomic collisions physics program is centered around a recently upgraded Electron Cyclotron Resonance (ECR) multicharged ion source. The 10 GHz CAPRICE source has been in operation since October 22, 1992, and has provided more intense, higher charge ion beams than our previous ECR ion source. Intense metallic beams have recently become available with the installation of a metallic oven on the source. In addition to measurements of electron-impact excitation, carried out in collaboration with the Joint Institute for Laboratory Astrophysics (JILA), experiments are presently on-line to study electron-impact ionization, low-energy ion-atom collisions, and ion-surface interactions. A brief summary of our various activities with an emphasis on the new capabilities is presented.

Recent progress in making highly charged ion beams

In this paper a review of the basic creation processes of multicharged ions will be made through the description of the principles of ECRIS (electron cyclotron resonance ion source) and EBIS (electron beam ion source). A comparison between the beam characteristics of these sources will be made in order to show the main fields of application of these different devices for atomic physics interests. We shall especially describe the efforts made to control the different ways of producing a wide range of gaseous and metallic elements (by direct evaporation in ECRIS or by monocharged ion injection with EBIS). We shall especially show the latest developments in the production of very highly charged ions with ECRIS like the MSU super conducting source or ECR4 Ganil source (Ar 16+ and Ar 17+ in CW mode) or EBIS machines like the CRYSIS EBIS from Stockholm (fully stripped Ar or Xe 43+ in pulsed regime). We shall also show how one could simplify the multicharged ion source technology by using ultra compact ECRIS entirely built with permanent magnets (NANOGAN from GANIL/Caen or BECRIS from HMI/Berlin).

Single-stage 5 GHz ECR-multicharged ion source with high magnetic mirror ratio and biased disk

A low-cost, single-stage 5 GHz electron cyclotron resonance (ECR) multicharged ion source (MCIS) has been constructed for various atomic collision experiments. It features an axial magnetic field with a mirror ratio of up to five, and a magnetic hexapole field produced by a simple Nd–Fe–B permanent-magnet assembly. A disk probe axially mounted near the ECR resonance zone opposite to the ion extraction, and negatively biased with respect to the ECR plasma potential, permits reduction of the appropriate neutral feeding gas pressure by an order of magnitude, resulting in greatly improved ion charge state distributions, as normally offered by two-stage ECR–MCIS only. We present performance data for multicharged ion production from Ar and N2, including measured ion current emittances.

The ECR ion source DECRIS

The design of the electron cyclotron resonance (ECR) multicharged ion source DECRIS (Dubna ECR ion source, 14 GHz) was started at the Flerov Laboratory of Nuclear Reactions at the beginning of 1990 and in January 1992 the first plasma was ignited. A classical magnetic configuration based on the MINIMAFIOS with some ‘‘features’’ served as the basis for the source design. The DECRIS was installed on the ECR test bench. The first study of the source was carried out in continuous mode of operation at strict control of hexapole temperature. The ion source has been tested with He, N, O, and Ar ions. The results of these initial measurements are presented.

Role of a biased electrode in the first stage of electron cyclotron resonance multicharge ion source

The fundamental physics of the beneficial effect of a biased electrode, positioned in the first stage, on the output ion currents have been investigated on the basis of the measurements of plasma parameters. Conventional Langmuir probes were used for diagnostics in both stages. It was found that the plasma space potential in the first stage changes with the variation of disk potential and consequently a potential difference occurs between the first stage and the second one. Without the first stage plasma, the beneficial effect was also obtained when negative potential was directly applied to the first stage chamber wall. Probe measurements showed that the electron density and temperature in the second stage increased with the application of negative potential. It was suggested that the beneficial effect is mainly caused by the improvement of the electron confinement in the second stage.

Design of an advanced minimum B for electron cyclotron resonance multicharged ion sources

An advanced configuration of minimum-B field is designed for the electron cyclotron resonance (ECR) multicharged ion sources. The aim is to dramatically increase the efficiency of ion beam extraction by correcting the deformed magnetic flux tube containing hot plasma. The correction is performed by reversing the polarity of successive multipoles in the longitudinal direction. This method enables us to adopt the quadrupole that causes the greatest deformation. In addition, the most intense electron acceleration can be achieved with the quadrupole, since the radial field gradient is the largest of all multipoles.

Influence of ionization cross sections on the gas mixing effect for the production of Ar9+ ions in a CAPRICE ECR source

The gas mixing effect in the electron cyclotron resonance (ECR) multicharged ion sources is analyzed while taking into account the ionization cross sections of different support gases such as H2, He, Ne, N2, and O2. The Ar9+ ion currents delivered by a CAPRICE ECR ion source are measured as a function of the support gas pressure. The efficiency of ionization of these different gases by electron impact may partially explain the improvement of the extracted Ar9+ ion current.

Two-cavity ECR source of multicharged ions

The plasma density in ECR sources is limited by the cutoff plasma frequency, which prevents producing multicharged ions if one uses for plasma heating such low frequency microwaves as 2.45 GHz. In order to overcome this limitation a device consisting of two cavities located symmetrically in mirror regions was investigated. The ECR heating took place in the cavities and the plasma was accumulated in the zero microwave field space between the cavities. The cavities were fed with microwave power of 2.2 kW at 2.45 GHz. At an argon pressure of 0.04 mTorr, the plasma density of 2.4×1012 cm−3 in the central region of the trap was about 30 times higher than the cutoff value. A significant improvement in performance was found in comparison with the HELIOS-12. The expression for the lifetime of ions trapped into an electrostatic pit was defined. The charge state distributions both for the plasma and the extracted ion beam was calculated.

Laser-plasma ion sources (invited)(abstract)

Basic principles of the operation of laser-plasma multicharged ion sources are given. Specific features of the interaction of high-intensity laser beams with solids are discussed, together with formation and main characteristics of multicharged ion beams, such as charge state distribution, angular distribution, emittance and time structure, and the influence of magnetic fields. Laser ion sources constructed for linear accelerators, synchrotrons, and cyclotrons are presented and experimental data are compared with theoretical considerations.

Investigation of an injector with an arc multicharged ion source

An injector with a PIG ion source has been designed for the axial injection system of the U-200 cyclotron. An accel-decel electrode system and Wien filter are used for extraction of the ion beam. Some results of computer simulations of the ion trajectories in such an ion optical system and the experimental results of the ion beam formation and transport are presented.

Influence of ionization cross sections on the gas mixing effect for the production of Ar9+ ions in an ECR CAPRICE source

An interpretation of the gas mixing effect in ECR multi-charged ion sources is presented, taking into account the ionization cross sections of different support gases as H2, He, Ne, N and O2. Using an ECR CAPRICE ion source, Ar9+ ion currents were measured as a function of the mixing gas pressure. The efficiency of ionization of different gases by electron impact is discussed in order to increase the production of multi-charged ions.

Study of laser MSEC plasma

Abstract An experiraental installation for investigation of plasma formed by long laser pulse (tp = 40 μec) is described. Charge spectra and energy distributions for Al, Cu and Ta ions are presented. Maximum ion charge for aluminium is (+ 8), for copper (+ 8), for tantalum (+11). Conclusion on the possibility to build an effective source of multi-charged ions on the basis of CO2-laser with long laser pulse duration is made.

Exploration axiale du plasma RCE d'une source d'ions multichargés CAPRICE

Axial exploration of the plasma in a multicharged ECR CAPRICE ion source was performed with a Langmuir probe and a thermocouple. The hot electron density profile is hollow at the center and the density peaks are found near the electron cyclotron resonance zones. When the plasma density increases, the microwave heating occurs between the ECR zone and the upper-hybrid resonance. The axial electron density profiles appear to be modulated in space and the gaps between two current peaks equal 1 2 of the injected wavelength. The CAPRICE ion source performances are achieved when the resonance zones coincide with the peaks of modulation of the electric field distribution in the plasma chamber. This process enables us to rationally optimize all the CAPRICE sources. These results could be explained by the presence of standing waves in the plasma cavity and the dominance of the electromagnetic TEM mode when the plasma density increases.

The design of a high current, low emittance multiply charged ion source

A novel design of multicharged ion source is currently under construction at Culham Laboratory. The physical processes upon which it is based — stepwise ionisation and magnetic cusp confinement together with energy and particle balance — are described. These principles have been combined in a model from which it is possible to characterise the new source. A zero dimensional computer code has been developed to solve the model equations numerically. Results from the code are presented for the source under construction. From the results the optimum operating conditions in terms of pressure, input power and cusp field strength may be determined.

Improvement of an ECR multicharged ion source

Experimental results are shown for the yield of high charge state ions depending on the field configuration and the type of microwave launcher. The presence of an octupole improves the yield by a factor of 8. A tandem mirror configuration improves the yield by a factor of 7. A multifilar helical antenna on the magnetic axis improves the yield by a factor of 2. Extension of the mirror distance, with the mirror ratio kept unchanged, has little effect on the yield.

A universal multi-charge ion source

Abstract The development of a multi-charge ion source is described. This source consists of a duoplasmatron and eight electron guns. The radial potential distribution in the ion chamber is defined.

Results of a new ‘‘OCTOPUS’’ ECR ion source at 6.4 GHz

The first OCTOPUS electron cyclstron resonance (ECR) multicharged heavy ion source was built in 1985 at the Centre de Recherches du Cyclotron of the University of Louvain (Belgium). This first source used an ECR frequency of 14.3 GHz in the injector stage and 8.5 GHz in the main confinement stage. A new OCTOPUS source has now been built for a new cyclotron to be installed at the Japan Atomic Energy Research Institute (JAERI). The design of this new OCTOPUS source is identical to the first OCTOPUS source, but uses an ECR frequency of 6.4 GHz in the main confinement stage. The experimental results are described, and a comparison is made between the two sources. However, the available data does not allow any clear conclusion to be drawn on frequency scaling.

Fundamental study of ECR multicharged ion sources

Multicharged argon ions were observed up to Ar 11+ in an ECR discharge with a microwave of 2.45 GHz in an octupole-mirror field. The yield of the ions was increased by increasing the mirror ratio of the magnetic field and by choosing a suitable intensity of the octupole field.

Nd-Fe-B magnets for hexapolar field configuration

A hexapolar configuration with NdFeB permanent magnets is described which is able to produce a radial confinement of a hot plasma at a frequency close to 25 GHz. Such magnets have high intrinsic coercivity (18 kOe) to resist the demagnetization which could be induced by the longitudinal field needed for such a high plasma frequency. The magnets with their high induction remanence help construct more powerful electron cyclotron resonance multicharged ion sources.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>