Charge breeding results and future prospects with electron cyclotron resonance ion source and electron beam ion source (invited)

The Californium Rare Ion Breeder Upgrade (CARIBU) of the Argonne National Laboratory ATLAS facility will provide low-energy and reaccelerated neutron-rich radioactive beams for the nuclear physics program. A 70 mCi (252)Cf source produces fission fragments which are thermalized and collected by a helium gas catcher into a low-energy particle beam with a charge of 1+ or 2+. An electron cyclotron resonance (ECR) ion source functions as a charge breeder in order to raise the ion charge sufficiently for acceleration in the ATLAS linac. The final CARIBU configuration will utilize a 1 Ci (252)Cf source to produce radioactive beams with intensities up to 10(6) ions∕s for use in the ATLAS facility. The ECR charge breeder has been tested with stable beam injection and has achieved charge breeding efficiencies of 3.6% for (23)Na(8+), 15.6% for (84)Kr(17+), and 13.7% for (85)Rb(19+) with typical breeding times of 10 ms∕charge state. For the first radioactive beams, a charge breeding efficiency of 11.7% has been achieved for (143)Cs(27+) and 14.7% for (143)Ba(27+). The project has been commissioned with a radioactive beam of (143)Ba(27+) accelerated to 6.1 MeV∕u. In order to take advantage of its lower residual contamination, an EBIS charge breeder will replace the ECR charge breeder in the next two years. The advantages and disadvantages of the two techniques are compared taking into account the requirements of the next generation radioactive beam facilities.     

Thermal and electrostatic simulations of the diagnostic calorimeter for the source for production of ion of deuterium extracted from RF plasma beam

To study and optimise negative ion production for the ITER neutral beam injectors, a test facility is under construction in Padova with the aim of testing beam characteristics and to verify the source proper operation. The instrumented calorimeter STRIKE (short-time retractable instrumented kalorimeter experiment) is being developed to characterise the SPIDER (Source for Production of Ion of Deuterium Extracted from RF plasma) beam during short operations. The paper presents an investigation of the response of STRIKE measurement systems. It results that biasing is necessary to cope with the influence of secondary electrons on current measurements; moreover, despite the discretisation of the recorded thermal patterns introduced by the pixels of thermal cameras, a sufficient spatial resolution is expected.     

Prospects for advanced electron cyclotron resonance and electron beam ion source charge breeding methods for EURISOL

As the most ambitious concept of isotope separation on line (ISOL) facility, EURISOL aims at producing unprecedented intensities of post-accelerated radioactive isotopes. Charge breeding, which transforms the charge state of radioactive beams from 1+ to an n+ charge state prior to post-acceleration, is a key technology which has to overcome the following challenges: high charge states for high energies, efficiency, rapidity and purity. On the roadmap to EURISOL, a dedicated R&D is being undertaken to push forward the frontiers of the present state-of-the-art techniques which use either electron cyclotron resonance or electron beam ion sources. We describe here the guidelines of this R&D.     

New methods for high current fast ion beam production by laser-driven acceleration

An overview of the last experimental campaigns on laser-driven ion acceleration performed at the PALS facility in Prague is given. Both the 2 TW, sub-nanosecond iodine laser system and the 20 TW, femtosecond Ti:sapphire laser, recently installed at PALS, are used along our experiments performed in the intensity range 10(16)-10(19) W∕cm(2). The main goal of our studies was to generate high energy, high current ion streams at relatively low laser intensities. The discussed experimental investigations show promising results in terms of maximum ion energy and current density, which make the laser-accelerated ion beams a candidate for new-generation ion sources to be employed in medicine, nuclear physics, matter physics, and industry.     

Demonstration of charge breeding in a compact room temperature electron beam ion trap

For the first time, a small room-temperature electron beam ion trap (EBIT), operated with permanent magnets, was successfully used for charge breeding experiments. The relatively low magnetic field of this EBIT does not contribute to the capture of the ions; single-charged ions are only caught by the space charge potential of the electron beam. An over-barrier injection method was used to fill the EBIT's electrostatic trap with externally produced, single-charged potassium ions. Charge states as high as K(19+) were reached after about a 3 s breeding time. The capture and breeding efficiencies up to 0.016(4)% for K(17+) have been measured.     

Ion beam capture and charge breeding in electron cyclotron resonance ion source plasmas

Beam capture of injected ions and charge breeding in electron cyclotron resonance (ECR) charge breeder ion source plasmas has been investigated utilizing an ECR plasma modeling code, the generalized ECR ion source model, and a Monte Carlo beam capture code. Beam capturing dynamics, charge breeding in the plasma, and the extracted charged ion states are described. Optimization of ion beam energy is performed for (1) high beam capture efficiency and (2) high charge state ion beam extractions. A sample case study for ANL-ECR has been performed. Ions entering ECR ion source plasma are slowed down mostly by the background ions. Assuming Maxwellian plasma ions, maximum beam energy loss occurs when the beam velocity is around the background thermal velocity in magnitude. It is also found that beam capture location affects charge state distribution. For instance, with a majority of beam ions captured near the middle of the device higher currents for higher charge states are obtained. The beam ions captured near the entry have a higher probability of backstreaming after they are captured. For this reason, the optimum beam energy of the injected Ar(+) beam ions for charge breeding is generally higher than the optimum input beam energy for maximum beam energy loss.     

Laser ion sources for radioactive beams (invited)

Resonant ionisation laser ion sources are nowadays extensively used, when available, at many leading on-line facilities. Moreover, new laser ion sources are now under development in most of the recent on-line facility projects under construction worldwide. This success is mainly due to the reliability, the ionization efficiency and the high purity that this type of source can achieve for the production of radioactive species and for a large range of chemical elements. Laser ion sources for radioactive beams gather many different systems such as dye laser or all-solid state titanium:sapphire laser systems, high or low repetition rates, hot cavities or gas cells, additional selectivity by using chemical techniques, or the LIST technique (laser ion source trap). In this paper, the physics of laser ion sources will be described with the current limitations and challenges for the future. An overview of the laser ion source facilities will be given, with an emphasis on the ongoing developments and perspectives on LIS.     

Rhenium ion beam for implantation into semiconductors

At the ion source test bench in Institute for Theoretical and Experimental Physics the program of ion source development for semiconductor industry is in progress. In framework of the program the Metal Vapor Vacuum Arc ion source for germanium and rhenium ion beam generation was developed and investigated. It was shown that at special conditions of ion beam implantation it is possible to fabricate not only homogenous layers of rhenium silicides solid solutions but also clusters of this compound with properties of quantum dots. At the present moment the compound is very interesting for semiconductor industry, especially for nanoelectronics and nanophotonics, but there is no very developed technology for production of nanostructures (for example quantum sized structures) with required parameters. The results of materials synthesis and exploration are presented.     

Laser ion source with solenoid for Brookhaven National Laboratory-electron beam ion source

The electron beam ion source (EBIS) preinjector at Brookhaven National Laboratory (BNL) is a new heavy ion-preinjector for relativistic heavy ion collider (RHIC) and NASA Space Radiation Laboratory (NSRL). Laser ion source (LIS) is a primary ion source provider for the BNL-EBIS. LIS with solenoid at the plasma drift section can realize the low peak current (～100 μA) with high charge (～10 nC) which is the BNL-EBIS requirement. The gap between two solenoids does not cause serious plasma current decay, which helps us to make up the BNL-EBIS beamline.     

Subcutoff microwave driven plasma ion sources for multielemental focused ion beam systems

A compact microwave driven plasma ion source for focused ion beam applications has been developed. Several gas species have been experimented including argon, krypton, and hydrogen. The plasma, confined by a minimum B multicusp magnetic field, has good radial and axial uniformity. The octupole multicusp configuration shows a superior performance in terms of plasma density (~1.3 x 10(11) cm(-3)) and electron temperature (7-15 eV) at a power density of 5-10 Wcm(2). Ion current densities ranging from a few hundreds to over 1000 mA/cm(2) have been obtained with different plasma electrode apertures. The ion source will be combined with electrostatic Einzel lenses and should be capable of producing multielemental focused ion beams for nanostructuring and implantations. The initial simulation results for the focused beams have been presented.     

Bipolar pulse generator for intense pulsed ion beam accelerator

A new type of pulsed ion beam accelerator named "bipolar pulse accelerator" (BPA) has been proposed in order to improve the purity of intense pulsed ion beams. To confirm the principle of the BPA, we developed a bipolar pulse generator for the bipolar pulse experiment, which consists of a Marx generator and a pulse forming line (PFL) with a rail gap switch on its end. In this article, we report the first experimental result of the bipolar pulse and evaluate the electrical characteristics of the bipolar pulse generator. When the bipolar pulse generator was operated at 70% of the full charge condition of the PFL, the bipolar pulse with the first (-138 kV, 72 ns) and the second pulse (+130 kV, 70 ns) was successfully obtained. The evaluation of the electrical characteristics indicates that the developed generator can produce the bipolar pulse with fast rise time and sharp reversing time.     

New ion source for KSTAR neutral beam injection system

The neutral beam injection system (NBI-1) of the KSTAR tokamak can accommodate three ion sources; however, it is currently equipped with only one prototype ion source. In the 2010 and 2011 KSTAR campaigns, this ion source supplied deuterium neutral beam power of 0.7-1.6 MW to the KSTAR plasma with a beam energy of 70-100 keV. A new ion source will be prepared for the 2012 KSTAR campaign with a much advanced performance compared with the previous one. The newly designed ion source has a very large transparency (～56%) without deteriorating the beam optics, which is designed to deliver a 2 MW injection power of deuterium beams at 100 keV. The plasma generator of the ion source is of a horizontally cusped bucket type, and the whole inner wall, except the cathode filaments and plasma grid side, functions as an anode. The accelerator assembly consists of four multi-circular aperture grids made of copper and four electrode flanges made of aluminum alloy. The electrodes are insulated using PEEK. The ion source will be completed and tested in 2011.     

Shunting arc plasma source for pure carbon ion beam

A plasma source is developed using a coaxial shunting arc plasma gun to extract a pure carbon ion beam. The pure carbon ion beam is a new type of deposition system for diamond and other carbon materials. Our plasma device generates pure carbon plasma from solid-state carbon material without using a hydrocarbon gas such as methane gas, and the plasma does not contain any hydrogen. The ion saturation current of the discharge measured by a double probe is about 0.2 mA∕mm(2) at the peak of the pulse.     

Application of ion beam sputtering for high-resolution electron microscopy

Ion beam sputtering for high-resolution electron microscopy has basically provided miscellaneous operational features such as atomic shadowing, uncoated observation, and etching of biological specimens coupled with tungsten sputter coating and thinning of solid materials. Based on the power-potential law of Lindhard for ionic impact phenomena on metal surfaces, the universal yield-energy relationship has been derived. Thereby the sputtering deposition rate with reference to the sputtering removal rate was obtained as a function of sputtering yield, and the most important angular distribution of sputtering yield could be measured by using the hemicylindrical specimen stage. Evidence is presented to show that ion beam sputtering has become one of the most powerful tools for high-resolution electron microscopy.     

Spatial dose uniformity monitor for electrically scanned ion beam

A technique is described for direct and precise monitoring of the spatial dose uniformity of an electrically scanned ion beam. The method employs a two-dimensional 10x10 array of Faraday cups, individually connected to a current integrator, to measure local dose distribution. It also employs a microprocessor for rapid data processing and topographic data display. The technique is applicable to high quality ion implantation processes as a uniformity monitor with an accuracy of 1%. In addition, a new concept for uniform ion beam scanning is proposed.     

光学镜面离子束加工的可达性

提出了离子束加工可达性问题的理论描述和定义,分析了驻留函数解的存在条件,进而分析了采用不同直径的离子束去除不同频率面形误差时额外去除量的大小,最后进行了仿真验证。分析结果表明,对于高斯型的束函数,驻留函数解总是存在的。但是面形误差频率越高,驻留函数解越大,去除面形误差时去除的额外材料越多。额外的材料去除量随着离子束径和空间误差波长之比(d/λ)的增加而指数增加。当d/λ=0.5时,额外材料去除量为15%,还是可以接受的;当d/λ=1时,额外材料去除量迅速上升到73%,该值即很难被接受。理论分析和仿真结果表明,为了优化加工过程,d/λ应该＜0.5。     

Precipitation induced by ion beam thinning

Ion beam thinning of aluminium–lithium alloys under conventional conditions required to produce electron microscope thin foils is shown to induce significant microstructural changes, equivalent to heating the specimen in excess of ～400 K.     

Low background cold cathode ion source for molecular beam detection

An extractor gauge type electron bombardment ion source using carbon fiber bundles as field electron emitters is described. The cold cathode permits operation of the ionizer within a liquid He cooled cryopump. The high pumping speed for all molecules (except helium) together with its low background pressure make this ion source a very promising detector for crossed molecular beam scattering experiments.