Low-charge Ions Research Articles

Beam extraction from a compact Ku-band electron cyclotron resonance ion source with double resonance modes

Beam extraction tests were carried out using a new compact Ku-band electron cyclotron resonance (ECR) ion source. In the case of a single rf frequency operation, a B2 zone can contribute for increase of single and low charged state ion beams when the gas flow rate is relatively higher than that for the basic ECR mode. The scheme seems, however, not so effective for the production of multicharged state ion beams. A double frequency heating (12 and 14 GHz) is, on the other hand, effective for increase of extracted ion current when the rf power is injected into the chamber from both the axial and the radial ports, as succeeded at the LBL experiment.

Demonstration of XUV amplification to the ground state in low-charged nitrogen ions

We report the first demonstration of the gain to the ground state in low-charged nitrogen ions by optical-field ionization. A small signal gain coefficient of 9.6 cm −1 and a gain–length product that it is in the range 3.8–3.9 for the NIII 3 s( 2 S)−2 p( 2 P) transition XUV laser at a wavelength of 45.2 nm were obtained by an only 25-mJ linearly-polarized 100-fs laser pulse.

Issues in risk assessment from solar particle events

Uncertainties in risk assessment from solar particle events (SPE) include the role of high linear energy transfer (LET) secondary ions, the assessment of dose-rate effects as they relate to acute injury, the risk of cancer mortality and the modification of health effects due to the stress of spaceflight. We discuss several issues where new knowledge is required for improving estimates of radiation risk from SPE’s. Secondary particles such as neutrons and low energy and charge ions (LZE) may dominate radiation risk behind a storm shelter and their biological effects are poorly understood, especially at low dose-rate. Dose-rate modulation of radiation response is also related to genetic pre-disposition an important determinant of radiation sensitivity. Molecular pathways that control cell death and tissue response have been elucidated in recent years and should provide new understanding of dose-rate effects for risk assessment. We consider some of these factors and discuss calculations using radiation transport codes, track structure models of energy deposition, and a molecular kinetics approach to model radiation response.

Charge-changing processes involving fast low-charged ions

The beam lifetimes and the charge-changing cross sections for fast many-electron systems, Mg 1+, Ar 2+, Pb 29+, U 4+, U 10+ and U 28+, were calculated in the energy range of 1–500 MeV/u and compared with experimental data recently obtained at SIS GSI. An agreement of the calculations with experimental data within a factor of 3 was obtained. It was found that the heavy components of the residual gas (N 2 and Ar) play a key role in the projectile charge-changing processes in the energy range considered.

Electron-impact single ionization of low-charged titanium ions

The electron-impact single ionization of low-charged Ti ions was studied both experimentally and theoretically. Absolute cross sections for ions in charge states q = 1 to 6 except 3 were measured using a crossed-beams technique as well as calculated with the configuration-average distorted-wave method, including both direct ionization and excitation-autoionization contributions. For charge states q = 4, 5 and 6, the measurements are in good agreement with the calculations considering that large components of the incident ion beam were in metastable configurations. The cross sections for single ionization of and were determined in part with a high-resolution energy-scan method. Besides contributions of excitation-autoionization mechanisms, a remarkable number of structures arising from resonant-excitation double-autoionization (REDA) processes could be observed.

Modelling of pressure-driven membrane separation of electrolytes.: `High temperature' approximation

A model of pressure-driven membrane process of electrolyte separation is presented. The electric field potential assumed as being known, exact solution for permeate composition is readily obtained. All species are assumed to have the same convection velocity. Local electroneutrality condition is not used. The electric potential has been taken into account under high temperature approximation, thus reducing the problem to algebraic equation in exp(Ψ), where Ψ is dimensionless flow potential, and making it possible to calculate concentrations of ions in permeate. Negative retention is shown to be possible for one-component electrolyte solution. For electrolyte mixtures, concentration of ion with high charge is shown to “govern” the membrane selectivity in respect to low-charge ions. Results obtained are in qualitative accordance with the earlier experimental data on membrane separation of reaction mixtures in homogeneous catalysis.

Electron cyclotron resonance sources: Historical review and future prospects (invited)

Low charge state electron cyclotron resonance ion source (ECRIS) work since 1965 and high charge state ECRIS since 1974. These ECR sources are categorized into three main sections: (1) Low charged ion (ECRIS) inside simple magnetic mirror or Bucket configurations. (2) High charged ion ECRIS inside min-B mirror configurations. (3) Short pulsed ECRIS with highly charged ions where the ion confinement is disturbed for a short while, which allows the extraction of intense ion pulses. Future prospects are based on rational scaling of the magnetic confinement including high B modes, by increasing the radio frequency (rf) frequency and ECR magnetic field. In this case, charge exchange has to be minimized and plasma instabilities have to be avoided. However, clever empirical tricks lead also to outstanding not always predicted improvements. Let us cite: optimized rf plasma coupling, electron guns, gas mixing, wall coating, biased electrodes, and more recently multiple ECR frequency heating. ECRIS have not yet achieved their optimal possibilities. Let us wait for the next generation of superconducting ECRIS and the possible use of subcentimeter waves.

Electron cyclotron resonance sources: Historical review and future prospects (invited)

Low charge state electron cyclotron resonance ion source (ECRIS) work since 1965 and high charge state ECRIS since 1974. These ECR sources are categorized into three main sections: (1) Low charged ion (ECRIS) inside simple magnetic mirror or Bucket configurations. (2) High charged ion ECRIS inside min-B mirror configurations. (3) Short pulsed ECRIS with highly charged ions where the ion confinement is disturbed for a short while, which allows the extraction of intense ion pulses. Future prospects are based on rational scaling of the magnetic confinement including high B modes, by increasing the radio frequency (rf) frequency and ECR magnetic field. In this case, charge exchange has to be minimized and plasma instabilities have to be avoided. However, clever empirical tricks lead also to outstanding not always predicted improvements. Let us cite: optimized rf plasma coupling, electron guns, gas mixing, wall coating, biased electrodes, and more recently multiple ECR frequency heating. ECRIS have not yet achieved their optimal possibilities. Let us wait for the next generation of superconducting ECRIS and the possible use of subcentimeter waves.

Manufacture of a compact Ku-band electron cyclotron resonance ion source with two resonance zones and variable frequency

A compact ECR ion source working at a Ku band has been manufactured for the production of both low and multiple charged ions. This source can be formed for both the ordinal ECR zone and second Bernstein resonance zone with a half Becr field. The B minimum field configuration is realized by the use of permanent magnets and its axial mirror field can be adjusted within ±0.03 T by a small auxiliary solenoid. Microwave power can be injected from both axial and radial ports. Effective power of 200–250 W can be supplied to the source with a continuously variable frequency in the range of 12.0–14.5 GHz and with a variable pulse mode. The outer dimension of the source is φ180×230 and its total weight is just 30 kg. The design, manufacture and results of the preliminary test are reported.

Beam lifetimes of low-charged ions in storage rings

The beam lifetimes and the charge-changing cross-sections for fast low-charged ions are calculated for the energy range of 1–100 MeV/u and compared with experimental data for Mg1+ and U10+ ions recently measured at SIS GSI, Darmstadt. A moderate agreement of calculations with experiment was obtained. The results show that the heavy components of the residual gas (N2 and Ar) play a key role for projectile charge-changing processes in the energy range considered.

Recombination of Sc3+ ions with free electrons

Recombination of Ar-like Sc3+ ions has been studied experimentally at the TSR for center of mass energies ranging from approximately 12–18 eV. In this energy range rather broad resonances from short lived Sc2+(3s23p53d2 2F) intermediate states are expected. For these resonances recent theoretical work predicts strongly asymmetric lineshapes due to quantum mechanical interferences between radiative and dielectronic recombination channels. The study of this heavy, low-charged ion suffered from a high background due to electron capture and the outcome of our experiment does not yet allow for a conclusive test of the theoretical predictions.

Analysis of macromolecules using nanoelectrospray ionization mass spectrometry and low-energy collision activation.

The mass spectrometric analysis of several proteins using nanoelectrospray (nanoES) with elastic collisions showed an improvement in the sensitivity over nanoES without collisional activation. We believe this effect is due to a better declusterization/ionization process. Optimization of the collision parameters can be easily performed during the long experiment time allowed using the nanoES source. Moreover, an apparent shift in the charge-state distribution is observed, with lower charged ions becoming relatively more abundant with increasing either target gas pressure or kinetic energy of the precursor ions. Higher charge-state ions might be expected to have higher collision frequencies and correspondingly lose more kinetic energy than lower charge-state ions.

The charge state of recoils under surface bombardment by multiple charge ions

A model of charge state formation of particles sputtered of a metal surface bombarded by low energy multiple charged ions was proposed. It is based on the idea of sensitivity of electron exchange processes to the local surface electron density. The model describes the dependence of the degree of sputtered particle ionization on the charge and the initial energy of the bombarding ions. It has been found that a larger primary charge of bombarding ions causes a higher degree of ionization of sputtered particles. The results are in a good agreement with measurements.

Wavelength dispersive measurements of characteristic K X-rays of an ECR krypton plasma

X-rays from different transitions of the K series were used to analyze components of the ion charge state distribution inside a microwave heated krypton plasma. It is shown that X-ray transitions involving outer-shell electrons show spectra with clearly resolvable satellite lines arising from low charged ions. In contrast to the evaluation of Kα spectra this allows to get information about the ion charge state distribution in the low ionization region.

Electron-impact single ionization of low-charged molybdenum ions.

The electron-impact single ionization of low-charged Mo ions is studied both experimentally and theoretically. The absolute cross sections for ${\mathrm{Mo}}^{\mathit{q}+}$ ions in charge states q=1--8 are measured using a crossed-beam technique. Distorted-wave calculations are made including both direct ionization and excitation-autoionization contributions. For ions in charge states q=6--8, the measured cross sections are in good agreement with calculations involving only the lowest-energy metastable configuration. For ions in charge states q=3--8, the good agreement between experiment and theory confirms the dominant role played by excitation-autoionization contributions to the total ionization cross section. \textcopyright{} 1996 The American Physical Society.

Design of low frequency RFQ accelerators for ion implantation

The development of the 4-Rod RFQ as an injector for low charged heavy ions has demonstrated that structures with spiral-shaped or straight stems can be made highly efficient, very stable, and compact. The design of the RFQ structures and results of optimizations with respect to impedance and field quality will be discussed.

State-selective electron capture in low velocity multiply charged ion, helium collisions.

Recoil ion momentum spectroscopy has been applied to study low energy, state-selective single electron capture by highly charged projectiles. The specific systems investigated are fully stripped 6.82 keV/u ${\mathrm{Ne}}^{10+}$ and 6.75 keV/u ${\mathrm{Ar}}^{18+}$ on He. Measurements of the ${\mathrm{He}}^{+}$ recoil ion longitudinal momenta are used to determine the final n-state dependence of the captured electron. Simultaneous measurement of the transverse momenta of the recoil ion yields information about the impact parameter dependence of the reaction and the reaction window for electron capture.

Design aspects of the Debrecen ECR ion source

In the ATOMKI a 14 GHz ECR ion source has been designed and is being built. The main design aspects and the results of some checking measurements are briefly summarized. The designing of an extraction-focusing optics is shown in detail. Based on a theoretical model (developed by the authors earlier), the axial distribution of the electrostatic potential in the extraction region must be a superposition of linear and cosinusoidal parts. The behavior of such an extraction optics has been checked experimentally on a low-charged hollow-cathode ion source. The development and usage of the TrapCAD code has also been continuing. The code is suitable to visualize the magnetic structure of any magnetic bottle in 3D and also to simulate the charged particle movement in it. The code—with some restrictions—is suitable for plasma modeling as well.

Soft-x-ray lasing to the ground states in low-charged oxygen ions.

Optimal schemes for the creation of a transient population inversion between the ground and excited states of an ion in a subpicosecond-pulse laser-produced plasma are discussed. First results on experimental investigations of possible amplification in the soft-x-ray spectral region on transitions to the gorund states in O ii, O iii, C iii, and N iii ions are reported. Ions are produced due to optical field ionization of ${\mathrm{O}}_{2}$, ${\mathrm{CO}}_{2}$, and ${\mathrm{N}}_{2}$ gases in an intense Ti:sapphire laser field. Amplificaiton on the 2p3s${(}^{3}$P)-2${\mathit{p}}^{2}$${(}^{3}$P) transition (\ensuremath{\lambda}=374.12 \AA{}) in O iii ions and on the 2${\mathit{p}}^{2}$3s${(}^{2}$P)-2${\mathit{p}}^{3}$${(}^{2}$D) transition (\ensuremath{\lambda}=616.56 \AA{}) in O ii ions has been observed.

Efficiency measurements for a low charge state ionic injection into an electron beam ion source

We report injection efficiency measurements when an external primary low charge ion beam is injected into Dioné EBIS. These measurements have been performed using nitrogen and argon ion beams. The total efficiencies reach 59 and 52% respectively. The partial efficiencies, related to the main ionic charge state, reaches 30% for N 7+ and 9.4% for Ar 14+. These results correspond to an injection before the confinement period (fast injection mode). The other method (injection during the confinement time) has been also performed using nitrogen ions. The results are less spectacular: only a 0.4% total efficiency has been measured.