Production Of Multicharged Ions Research Articles

Enhanced Production of Multicharged Ions by Mixing Low Z Gas and Emittance Measurement on Electron Cyclotron Resonance Ion Source

We have studied to enhance efficiency of producing multicharged ions in an electron cyclotron resonance ion source (ECRIS). The gas mixing method is known as an empirical method for highly efficient production of multicharged ions. This method is to mix low Z gas into the multicharged ions plasma. There are various explanations for the gas mixing effect. One of them is the ion cooling effect. It is necessary to obtain parameters related to the ion temperature in order to experimentally confirm the effect. We measured emittances for ion beams by using a wire probe and a multi-slit. He was mixed as a low Z gas into the operating Ar gas. Charged state distributions of ion beams was measured to confirm the gas mixing effect. We have also measured emittances for the multicharged Ar ion beams and compared root mean square emittances (ε rms) of those for pure Ar and Ar mixed by He. We confirmed that ε rms for Ar mixed by He was lower than that for pure Ar.

Initial Experimental Results of Producing Multicharged Ions Efficiently by Lower Hybrid Resonance Heating with Exciting Helicon Waves on Electron Cyclotron Resonance Ion Source

Based on experimental results, we considered the accessibility conditions for wave propagation in the magnetized plasma in an electron cyclotron resonance (ECR) ion source (ECRIS), and proposed introducing electromagnetic waves with frequencies lower than those of ECR. We generate the lower hybrid resonance (LHR) in the ECRIS by the electric field of the extra-ordinary mode (X-mode) on the helicon wave which additionally heat the electrons, and then it was conducted to improve the efficiency of multicharged ion generation successfully in over density condition. The electron energy distribution function obtained by the probe measurement shows an increase in the high-energy region in the corresponding LHR region. In this paper, for the first time we describe the initial experimental results on enhanced production of multicharged ions by the LHR of the low-frequency RF electromagnetic waves into the ECRIS.

Low Z gas mixing effects of Ar and Xe multicharged ions in electron cyclotron resonance ion source

An electron cyclotron resonance (ECR) ion source (ECRIS) has wide applications such as cancer therapy and material synthesis. We have constructed a single ECRIS capable of producing various ions with low to high mass/charge ratio, and have been conducting various experiments. We focus on the efficient production of multicharged ions and aim to increase the yield of multicharged ions by new effects of electromagnetic waves in ECRIS. We investigated the possibility of selective heating to low Z ions under low Z gas mixing. Therefore, as a preliminary step of these experiments, the low Z gas mixing effect with rare gases are investigated. The optimum mixing ratio of the main gas Ar and the low Z gas He was investigated by varying the mixing ratio. The Ar multicharged ion beam current, impurity fraction and plasma parameters were measured. As a result, it was confirmed that the Ar multicharged ion yield was sufficient reproducibly increased by mixing He gas into Ar plasma. In addition, this from the measured plasma parameters is not an effect of the plasma parameters, but maybe a cooling effect.

The preliminary test of multi-charged ions generation with a 2.45 GHz microwave-driven ion source.

A 2.45 GHz microwave-driven ion source for the generation of multicharged ions has been designed and built at Peking University recently. The magnetic field configuration of this ion source is a minimum-B type with a combination of a hexapole field and an axial mirror field. Argon was selected as the first tested beam generated by this ion source. A 63 µA Ar4+ ion beam at 35 kV extraction voltage was obtained in the pulsed mode (50 Hz/500 µs). Without the hexapole magnetic field, the highest charge state was only Ar2+, and no Ar4+ ion beam was detected. The comparison between the two sets of experimental results with different magnetic configurations has proven the rationality of the production of multicharged ions with this ion source. Both experimental results and discussion will be presented in this paper.

Upper hybrid resonance heating experiments by X-mode microwaves on electron cyclotron resonance ion source.

We have considered the accessibility condition of electromagnetic and electrostatic waves propagating in an electron cyclotron resonance (ECR) ion source (ECRIS) plasma and then investigated experimentally their correspondence relationships with production of multicharged ions. It has been clarified that there exists an efficient configuration of ECR zones for producing multicharged ion beams and has been suggested that a new resonance, i.e., upper hybrid resonance (UHR), must have occurred. We have been trying to perform advanced experiments with 4-6 GHz X-mode microwaves to the 2.45 GHz ECRIS plasma, and we have succeeded in enhancing the production of multicharged ions by launching X-mode microwaves of these bands. Furthermore, at the same time, we have observed sharp increases in electron energy distribution functions in the ECRIS plasma by means of probe methods. It has been concluded that the UHRs must have occurred when applying multiplex microwaves with their frequencies away from those frequencies for ECR in the ECRIS. In this paper, we will describe in brief the theoretical background and the results of these new experiments.

Improving multipole magnets and background vacuum conditions on electron cyclotron resonance ion sources

Electron cyclotron resonance ion sources (ECRISs) are used in various fields such as accelerator physics, engineering, cancer therapy, and ion engines in the satellite. We are aiming to improve the production of multicharged ions efficiently at the point of view from the length of multipole magnets and vacuum conditions in the ECRIS. The diameter of the connection pipe between the main chamber and diffusion pump was made larger to improve vacuum conductance. Moreover, the length of multipole magnets with the direction along the geometrical axis in the ECRIS was extended. The effects of these improvements are investigated experimentally to measure the pressure in the vacuum chamber, beam intensity, charge state distributions of extracted ion beams, and plasma parameters. The purity of extracted ion beams and magnetic confinement have been enhanced. These results are expected to have positive effects on the production of various species and synthesized ion beams, e.g., production of iron endohedral fullerene in the future experiments in the ECRIS.

Experimental results of superimposing 9.9 GHz extraordinary mode microwaves on 2.45 GHz ECRIS plasma.

Efficient production of multicharged ions has been investigated on the tandem-type ECRIS in Osaka University. According to the consideration of the accessibility conditions of microwaves to resonance and cutoff regions, it was suggested that the upper hybrid resonance (UHR) heating contributed to enhancement of ion beam intensity. In order to enhance multicharged ion beams efficiently, injecting higher frequency microwave with extraordinary (X-mode) toward UHR region has been tried. In this study, 2.45 GHz frequency microwaves are used for conventional ECR discharge, and 9.9 GHz frequency microwaves with X-mode are superimposed for UHR heating. The effects of additive microwave injection are investigated experimentally in terms of plasma parameters and electron energy distribution function (EEDF) measured by Langmuir probe and ion beam current. As the results show, it is confirmed that the electrons in the high energy region are affected by 9.9 GHz X-mode microwave injection from the detailed analysis of EEDF.

Mono-energetic ions emission by nanosecond laser solid target irradiation

An experimental campaign aiming to investigate the acceleration mechanisms through laser–matter interaction in nanosecond domain has been carried out at the LENS (Laser Energy for Nuclear Science) laboratory of INFN-LNS, Catania. Pure Al targets were irradiated by 6ns laser pulses at different pumping energies, up to 2J. Advanced diagnostics tools were used to characterize the plasma plume and ion production. We show the preliminary results of this experimental campaign, and especially the ones showing the production of multicharged ions having very narrow energy spreads.

Accessibility condition of wave propagation and multicharged ion production in electron cyclotron resonance ion source plasma.

A new tandem type source of electron cyclotron resonance (ECR) plasmas has been constructing for producing synthesized ion beams in Osaka University. Magnetic mirror field configuration with octupole magnets can be controlled to various shape of ECR zones, namely, in the 2nd stage plasma to be available by a pair mirror and a supplemental coil. Noteworthy correlations between these magnetic configurations and production of multicharged ions are investigated in detail, as well as their optimum conditions. We have been considering accessibility condition of electromagnetic and electrostatic waves propagating in ECR ion source plasma, and then investigated their correspondence relationships with production of multicharged ions. It has been clarified that there exits efficient configuration of ECR zones for producing multicharged ion beams experimentally, and then has been suggested from detail accessibility conditions on the ECR plasma that new resonance, i.e., upper hybrid resonance, must have occurred.

Formation of an anisotropic electron velocity distribution function and production of multicharged ions in the micropinch discharge plasma

Analysis of the results of polarimetric measurements of X-ray line radiation of multicharged ions in a Z-pinch discharge indicates that the formation of an anisotropic electron velocity distribution in the neck of the current channel and the generation of highly charged ions are separated in time. The generation of a fast electron beam in the longitudinal ohmic electric field in the stage of plasma compression in the neck results in the polarization of X-ray bremsstrahlung continuum. In the stage of expansion of the hot dense micropinch plasma, the radial electric field prevails, due to which X-ray line radiation of multicharged ions becomes linearly polarized.

Production of multicharged ions and behavior of microwave modes in an electron cyclotron resonance ion source directly excited in a circular cavity resonator

Electron cyclotron resonance ion sources (ECRIS) have been widely used for production of high-intensity multicharged ion beams. Making good use of microwave modes is proposed for enhancing the efficiency of ECR for production of multicharged ions (TAIKO II). We can assign the peak position of the electric field of the standing waves to the ECR zone in the directly excited cavity resonator, i.e., the vacuum chamber with the fixed and the mobile plates for selecting and tuning the modes. Periodicity of the extracted multicharged ion currents and plasma parameters is observed as the position of the mobile plate moves. We measure the intensity of the electric field in the ECR plasma by using the insulated semidipole probe and the standing waves are observed. The correlation between the production of multicharged ions and the microwave modes is clarified by measuring the electric field and plasma parameters in the circular cavity resonator.

ECR multi-charged ion source directly excited in a circular TE01 mode cavity resonator

A new concept is proposed for enhancing the efficiency of an electron cyclotron resonance (ECR) plasma for production of multi-charged ions (TAIKOII). The plasma chamber is a circular cavity resonator with two metal plates. A fixed plate is installed at the tip of the ion extractor. The distance between the fixed plate and the antenna installed at the side wall is equal to a quarter of the guided wavelength λg for the circular TE01 mode microwave. A mobile plate is inserted from the opposite side along the geometrical axis to tune the microwave. Excitation of single TE01 mode has been confirmed. The electric field has only a circumferential component and is axially symmetric in the same direction as electron cyclotron motion. The peak value of the electric field is located at the ECR zone. Multi-charged ions are extracted by a voltage of 10kV and the charge state distribution (CSD) of their ion currents are measured by using the sector magnet and the faraday cap. The extracted Ar4+ ion current changes periodically when the mobile plate moves in the plasma and the interval of the mobile and the fixed plates is several times λg/2 in the TE01 mode microwaves. We present and discuss production of multi-charged ions by applying the TE01 mode microwave in order to enhance efficiency of the ECR in the optimized magnetic field.

Cluster-enhanced generation of multicharged xenon ions in nanosecond laser ionization of xenon beam

Multicharged xenon ions with charge up to 20 have been observed in laser ionization of xenon beam by a 25ns Nd:YAG 1064nm laser with a laser intensity of 1011—1012 W·cm-2 Experimental results indicate that the multicharged ions appeared only when the laser interacted with the middle part of the pulsed beam, and its intensity increases with the increase of the backing pressure of Xe source gas. These indicate that the clusters in the beam is essential to the production of multicharged ions. We also discuss the possible mechanism of the generation of the multicharged ions.

Production of multi-charged ions in the RIKEN 18 GHz ECRIS

Beam intensities of multi-charged Ar, Kr and Xe ions have been measured under the various conditions. Beam intensities were strongly dependent on the plasma electrode and bias disc positions, and on the negative voltage of bias disc. By optimizing these parameters, 2 mA of Ar 8+ , 0.6 mA of Kr 13+ and 0.3 mA of Xe 18+,20+ were obtained.

Production of multi-charged ions in the RIKEN 18 GHz ECRIS

Beam intensities of multi-charged Ar, Kr and Xe ions have been measured under the various conditions. Beam intensities were strongly dependent on the plasma electrode and bias disc positions, and on the negative voltage of bias disc. By optimizing these parameters, 2 mA of Ar8+, 0.6 mA of Kr13+ and 0.3 mA of Xe18+,20+ were obtained.

Production of multicharged ions in a 2.45 GHz electron cyclotron resonance source directly excited in a circular TE01 mode cavity resonator

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.

Generation of Multicharged Xenon Ions in Nanosecond Laser Ionization of Xenon Beam

Multicharged xenon ions with charge upto 11 have been observed in laser ionization of xenon beam by a 25 ns Nd-YAG 532 nm laser at laser intensity about 10(11) W . cm(-2). Experiment results indicated that the multicharged ions appeared only when the laser interacted with the middle part of the pulsed beam, and its intensities increase with increase the backing pressure of Xe source gas, indicates that the clusters in the beam is essential to the production of multicharged ions. From the experimental results, we think that the cluster is ionized via multiphoton ionization and form a nanoplasma ball, which can absorb the laser resonantly to further ionize the single charge ion to high charge state.

High current density production of multicharged ions with ECR plasma heated by gyrotron transmitter

In order to study the possibilities to produce high currents of pulsed heavy ion beams dedicated to synchrotron injection, two new approaches of ECR devices are now underway. The basic principle consists in maintaining a functioning point of the source with the highest density as possible and a minimum confinement time for the production of a given charge state. It means that for a constant neτi product we try to maximize ne and minimize τi. For this purpose two experiments are in progress at ISN/Grenoblea and IAP/Nizhny Novgorod.b The first one consists of using a minimum |B| magnetic structure with a 1.8 mirror ratio characteristic value with a 28 GHz frequency injection. In this case we explore different functioning points up to 10 kW of UHF power. The second one consists of a simple mirror magnetic system (simple mirror ion source, SMIS) working at 37.5 GHz with a mirror ratio up to 3 (2.5 T) where we study discharges with a peak power up to 100 kW. We will show that, in spite of a very short rising time of the current, we can maintain the production of multicharged ions and that we can observe very high current densities. In the future, the challenge will be the design of an extraction geometry matching theses current levels.

ECRIS as ion source and charge breeder

We will recall the main characteristics of ECR ion sources and their very good property of ionization efficiency. We will start with a review of on line use of ECR ion sources for production of mono or multicharged radioactive ions, and then we will specially focus our attention on charge breeding process for multicharged ion production. Initially developed for the PIAFE project from ISN Grenoble, the ECR charge breeder shows that the beam injection of a primary beam inside an ECR ion source is a very general process for beam production. We will review the latest results obtained on the ISN Grenoble test bench for the production of CW or pulsed metallic ion beams with the so called ‘1 +/ n +’ method. New results are given for CW operation where the efficiency is particularly optimized for application to multicharged radioactive ion production (for example, 3.5% for Zn 1+→Zn 9+, 4.2% for Pb 3+→Pb 24+, 5% for Rb 1+→Rb 15+). Different ion sources have been used to study the variation of the efficiency as a function of the energy of the 1 + primary beam. Charge-state distributions are especially measured for Pb and Rb ions. A new mode of operation, the Electron Cyclotron Resonance Ion Trap (ECRIT) breeder/buncher, which permits the trapping and the bunching of the n + ion beam is demonstrated and experimentally verified. This new method shows that it is possible to modify the time structure of the injected beam, just by trapping the ions inside the plasma and reextracting them by using the ‘afterglow pulsed mode’. We will finish by the presentation of the first result obtained with the first especially dedicated ECR booster developed at the ISN and called PHOENIX.

Enhanced production of multi-charged ions using pulse-modulated microwave in a 2.45 GHz electron cyclotron resonance source

Fundamental phenomena of an electron cyclotron resonance (ECR) multi-charged ion source (2.45 GHz) have been experimentally studied. The ECR plasma is confined in the mirror field superimposed by the octupole magnetic field. An ECR zone and potential well are formed near the bottom of the mirror trap. Multi-charged ions pass through the extractor at the mirror end, and the charge state distributions of extracted ions are investigated. Pulse-modulated microwave produces the ECR plasma with afterglow, relaxes the potential well, and then enhances the extracted multi-charged ion currents. Time-averaged Ar4+−9+ currents increase, even when the microwave power is nearly equal to or lower than the continuous microwave. The rectangular pulse width and the duty ratio are typically about 0.05 ms and 50%, respectively. The origin of enhanced production by pulse-modulated microwave is discussed by taking account of plasma parameters. Measurement of plasma parameters by a Langmuir probe and dependence of current increment on the ionic charge suggest the relaxation of the potential well.