Numerical simulation program of multicomponent ion beam transport from ECR ion source

In order to research multi-component ion beam transport process and improve transport efficiency, a special simulating program for ECR beam is becoming more and more necessary. We have developed a program written by Visual Basic to be dedicated to numerical simulation of the highly charged ion beam and to optimization of beam dynamics in transport line. In the program the exchange of electrons between highly charged ions and low charged ions or neutral atoms (residual gas in transport line) is taken into account, adopting classical molecular over-barrier model and Monte Carlo method, so the code can easily give the change of charge state distribution along the transmission line. The main advantage of the code is the ability to simultaneously simulate a large quantity of ions with different masses and charge states, and particularly, to simulate the loss of highly charged ions and the increase of low charged ions due to electron exchange in the whole transport process. Some simulations have been done to study the transmission line of LECR3 which is an ECR ion source for highly charged ion beam at IMP. Compared with experimental results, the simulations are considered to be successful.     

Electron beam ion traps and their applications

A brief introduction to the historical background and current status of electron beam ion traps (EBITs) is presented. The structure and principles of an EBIT for producing highly charged ions are described. Finally, EBITs as a potential tool in hot-plasma diagnostics and in studying frontier problems of highly charged ion physics are discussed.     

双频加热的LECR3离子源设计及初步的调试

研制成功了一台新的ECR（Electron Cyclotron Resonance）离子源LECR3（Lanzhou ECR No.3）。该离子源能为原子核物理与表面物理研究提供高电荷态离子束流，LECR3的设计主要基于IMP（Institute of Modern Physics）的14.5GHz ECR离子源（Lanzhou ECR No.2），但采用了双频加热、波导直接馈入微波功率及铝制等离子体弧腔等新技术和新方法。另外，LECR3的弧腔容积比LECR2的大，增加可注入的微波功率，可有效地增加引出的高电荷态离子束流的强度。虽然增大了弧腔的内么，但仍然保持径向六极磁铁在弧腔内壁上产生最大磁场强度与LECR2的同样大小。     

Scintillation light produced by low-energy beams of highly-charged ions

Measurements have been performed of scintillation light intensities emitted from various inorganic scintillators irradiated with low-energy beams of highly-charged ions from an electron beam ion source (EBIS) and an electron cyclotron resonance ion source (ECRIS). Beams of xenon ions Xe^q+ with various charge states between q = 2 and q = 18 have been used at energies between 5 and 17.5 keV per charge generated by the ECRIS. The intensity of the beam was typically varied between 1 and 100 nA. Beams of highly charged residual gas ions have been produced by the EBIS at 4.5 keV per charge and with low intensities down to 100 pA. The scintillator materials used are flat screens of P46 YAG and P43 phosphor. In all cases, scintillation light emitted from the screen surface was detected by a CCD camera. The scintillation light intensity has been found to depend linearly on the kinetic ion energy per time deposited into the scintillator, while up to q = 18 no significant contribution from the ions’ potential energy was found. We discuss the results on the background of a possible use as beam diagnostics, e.g. for the new HITRAP facility at GSI, Germany.     

AODO: Secondary ion emission and surface modification

In order to study the sputtering of secondary ions from well characterized surfaces, we constructed a new UHV system named AODO. It consists of a detector chamber, a target preparation and analysis chamber, and a target transfer rod. We present the lay-out of this new instrument. The detector allows measuring the time-of-flight of emitted secondary ions and their position on a 2D imaging detector (XY-TOF imaging technique). The analysis chamber can be used to study surface modification by means of LEED (low energy electron diffraction). We show preliminary results of the evolution of the LEED patterns as a function of the projectile fluence during irradiation of HOPG (highly oriented pyrolytic graphite) with slow Xe¹⁴⁺ ions at ARIBE (the low energy, highly charged ion beam line of the French heavy ion accelerator GANIL).     

Impact and energy deposition of slow, highly charged ions on a solid surface

A plasma region in nanometer scale may be created by a highly charged ion impact on solid surface. The charge imbalance leads to enormous electric fields and may further induce Coulomb explosion due to electrostatic repulsion in the region. Thus, the highly charged ion is thus expected to be a powerful tool to induce surface modification in the nanometer scale. The Coulomb explosion model is applied in order to interpret the interaction mechanism and to understand the impact and energy deposition of highly charged ions on a solid surface, and to obtain the energy deposited by the ion. The energy deposition ratio is dependent on the material and charge. A high temperature and high pressure environment will be formed by the deposited energy, causing the atoms to swell up and a hillock nano-defect to be formed on surface. The height of hillock is estimated from the Coulomb explosion.     

Temporal and spatial study of differently charged ions emitted by ns-laser-produced tungsten plasmas using time-of-flight mass spectroscopy

Tungsten (W) is an important material in tokamak walls and divertors.The W ion charge state distribution and the dynamic behavior of ions play important roles in the investigation of plasma-wall interactions using laser-ablation-based diagnostics such as laser-induced breakdown spectroscopy and laser-induced ablation spectroscopy.In this work,we investigate the temporal and spatial evolutions of differently charged ions in a nanosecond-laser-produced W plasma in vacuum using time-of-flight mass spectroscopy.Ions with different charge states from 1 to 7 (W+ to W7+) are all observed.The temporal evolutions of the differently charged ions show that ions with higher charge states have higher velocities,indicating that space separation occurs between the differently charged ion groups.Spatially-resolved mass spectroscopy measurements further demonstrate the separation phenomenon.The temporal profile can be accurately fitted by a shifted Maxwell-Boltzmann distribution,and the velocities of the differently charged ions are also obtained from the fittings.It is found that the ion velocities increase continuously from the measured position of 0.75 cm to 2.25 cm away from the target surface,which indicates that the acceleration process lasts through the period of plasma expansion.The acceleration and space separation of the differently charged ions confirm that there is a dynamic plasma sheath in the laser-produced plasma,which provides essential information for the theoretical laser-ablation model with plasma formation and expansion.     

Use of the Hot-Electron Mirror Machine Interem as a High-Z Ion Source

Production of the high-Z charge states in helium, nitrogen, and argon has been measured in the INTEREM device at the Oak Ridge National Laboratory. The INTEREM device contains a hot electron (~500 keV) plasma trapped in a minimum B geometry. The device is of interest because its parameters, electron density and energy, and ion lifetime are consistent with those required for the production of highly charged ions. Ion charge and ion energy spectra were measured independently using an einzel lens type energy analyzer combined with a quadrupole mass filter. For helium, most of the ions were doubly charged under proper operating conditions. For nitrogen, we found the ion yield to be peaked at Q = 4, and under these conditions the yield at Q = 6 was down by a factor of about 20. Energy distribution curves for different charge states show interesting features, from which important information may be inferred about the plasma in INTEREM. Although discrepancies exist in the ion yields we conclude that an INTEREM-like device employing a minimum B geometry and electron cyclotron resonance heating may be expected to be a good high-Z ion source.     

Studies of the interaction of slow very highly charged ions with solid surfaces using the LLNL EBIT facility

A summary of the present status of the LLNL EBIT based research program on highly charged ion-solid surface interaction is presented. New results for coincidence measurements of K−K^β X-ray emission for Fe²⁶⁺ incident on Al, using two Ge detectors are presented. It is shown that excellent resolution of the satellite and hypersatellite lines are achieved, in excess of what is possible with single Ge detector measurements. Recent results from ongoing investigations on electron emission, sputtered ion and energy loss phenomena are presented. Results from charge-state analysis of grazing incidence specular scattering of highly charged ions off atomically flat surfaces of gold, carbon and mica indicate that the incident ion essentially reaches ground state of its electronic distribution within the ion-surface interaction time of 100 fs. Atomic force microscopy is used to investigate the formation of a new type of ion induced surface defect, peculiar to highly charged ion-surface interactions. A linear correlation, between the defect volume and the incident ion charge, supports a mechanism of defect formation due to potential energy induced electron emission and subsequent collective displacement due to local charge imbalance.     

Nanostructuring of BaF2 (1 1 1) surfaces by single slow highly charged ions

The creation of surface nanostructures in BaF₂ (1 1 1) surfaces was studied after irradiation with slow highly charged Xe ions from the Dresden-EBIT (electron beam ion trap). After irradiation, the crystals were investigated by scanning force microscopy (SFM). Using specific ion parameters, the topographic images show nanohillocks emerging from the surface. Additionally, we used the technique of selective chemical etching to reveal the lattice damage created by ion energy deposition below and above threshold needed for surface hillocks formation. The role of both potential and kinetic energy as well as a comparison with results for swift heavy ion irradiations of BaF₂ single crystals are presented.     

Relativistic, QED and nuclear effects in highly charged ions revealed by resonant electron-ion recombination in storage rings

Dielectronic recombination (DR) of few-electron ions has evolved into a sensitive spectroscopic tool for highly charged ions. This is due to technological advances in electron-beam preparation and ion beam cooling techniques at heavy-ion storage rings. Recent experiments prove unambiguously that DR collision spectroscopy has become sensitive to 2nd order QED and to nuclear effects. This review discusses the most recent developments in high-resolution spectroscopy of low-energy DR resonances, experimental studies of KLL DR of very heavy hydrogen like ions, isotope shift measurements of DR resonances, and the experimental determination of hyperfine induced decay rates in divalent ions utilizing DR.     

Charge transfer and excitation in high-energy ion-atom collisions

Coincidence measurements of charge transfer and simultaneous projectile electron excitation provide insight into correlated two-electron processes in energetic ion-atom collisions. Projectile excitation and electron capture can occur simultaneously in a collision of a highly charged ion with a target atom; this process is called resonant transfer and excitation (RTE). The intermediate excited state which is thus formed can subsequently decay by photon emission or by Auger-electron emission. Results are shown for RTE in both the K-shell of Ca ions and the L-shell of Nb ions, for simultaneous projectile electron loss and excitation, and for the effect of RTE on electron capture.     

An Experimental Apparatus for Low Energy High Charge Heavy Ions to Study Collisions on Atomic Hydrogen

The design and performance of a recoil ion source system which includes a recoil ion source, atomic hydrogen thermal oven target and an electrostatic analysis system will be discussed. The recoil ion source produces low velocity highly charged ions via collisions between heavy fast pump beams from the EN tandem accelerator and target gases. Time-of-flight techniques provide initial recoil charge state separation. Collisions of the recoils with atomic hydrogen are being studied. The atomic hydrogen is provided by a thermal oven which features long life time operation and low input power requirements. Dissociation fractions of 80% are achieved for 300 watts of input power. A hemispherical electrostatic analyzer allows the final charge states of the recoil ions to be determined thereby allowing the measurement of charge exchange processes for an energy range of 100 eV/q to 5000 eV/q for the incident recoil ions.     

Non-kinetic damage on insulating materials by highly charged ion bombardment

We have measured the damage caused by the impact of low velocity, highly charged ions on insulating surfaces. Atomic force microscopy allows us to observe directly the surface topography with nanometer resolution. Using constant velocity (100 keV) Xe^q+ ions (25 ⩽ q ⩽ 50) impinging on mica, we observe damage caused by single ion impacts. Impact sites typically are circular hillocks. Within the range and accuracy of the data, the height and volume of the damaged regions are well approximated by a linear function of ion potential energy.     

Search for short-time phase effects in the electronic damage evolution - A case study with silicon

This work focusses on the production and decay properties of inner-shell vacancies and valence-band excitations induced by swift highly charged ions interacting with amorphous and crystalline Si. High resolution electron spectra have been taken for fast heavy ions at 1.78-5 MeV/u as well as for electrons of similar velocity incident on atomically clean Si targets of well defined phase. Various Auger-electron structures are analyzed concerning their width, their intensity and exact peak position. All measured peaks show a small shift towards lower energy when the charge of the projectile is increased. This finding is an indication for a nuclear-track potential inside the ion track. A detailed analysis of the Auger-electron spectra for amorphous Si and crystalline Si(1 1 1) 7 × 7 points to a small but significant phase effect in the short-time dynamics of ion tracks.     

Design of a single ion hit facility

The aim of this project is to develop a new system for single ion irradiation of cells for genetic and cell biology studies. This charged particle focused microbeam system will provide a fully computer controlled irradiation facility with submicron (subcellular) resolution and will open many new avenues into studies of radiobiological mechanisms. In the first stage of this project a system for single ion detection has been developed. A thin diamond window has been tested as vacuum/atmosphere window and as a possible source of secondary electrons and/or photons for single ion detection. A detection efficiency of 97% has been achieved.     

Duoplasmatron Ion Sources

A survey on questions related to the production of multiply charged ions with the Duoplasmatron ion source is given. In spite of differences of the multiply charged ion source and the mass separator type, design considerations show that high containment is a common feature to be attained in both subjects. Multiply charged metal ions are produced by material evaporation into the magnetically confined anodic plasma and auxiliary gas feed into the cathode discharge regions. Energy spreads of ion beams from the low and the high arc current source are compared. The Duoplasmatron ion source proves to be a hygieneous source of high containment that permits the production of medium charge states up to 9+ for xenon at modest energy spread and good brilliance of the extracted ion beam in a high current-low voltage discharge mode.     

A new generation of single-ended Van de Graaff accelerators for ion implantation and ion beam analysis

High voltage Engineering Europa B.V., The Netherlands developed a new generation of single-ended Van de Graaff accelerators for ion implantation and ion beam analysis. The new HVEE Van de Graaff accelerators are equipped with a unique (patented) ion source exchange system capable of handling four lands of ion sources, mass separation at high voltage level and an X-ray intensity suppression system. The accelerators are able to produce a large variety of continuously, homogeneous and highly collimated mass-analyzed ion beams of several hundred μA in the energy range from 50 keV up to l MeV (l MV model) or from 100 keV up to 2 MeV (2 MV model), using singly charged ions, whereby the maximum energy can be easily reached and maintained without conditioning and virtually no X-rays are produced. Combined with two dedicated end stations (one for ion beam analysis using RBS, channeling, NRA and PIXE, and one with an automatic wafer-handling system for both single-wafer implantation and batch processing), these systems are very suitable for research as well as industrial applications.