Spark source for multiply-charged ions

Most well-known spark sources for multiply-charged ions make use of weak inductively-coupled sparks which are obtained by means of a Tesla coil [1], [2]. These sources have not been used in charged-particle accelerators because of the small ion current, low charge multiplicity of the ions which are obtained, and general unstable operation.Starting in 1953 the authors have been carrying out an investigation of hot vacuum sparks obtained by the discharge of high-voltage condensers in an effort to obtain intense beams of multiply-charged ions with high charge multiplicities. In 1954 a source was constructed and found suitable for use in pulsed accelerators of multiply-charged ions.In conclusion the authors wish to express their gratitude to A. T. Kapin for help in this work.     

Production of Multiply-Charged Ions of Ne, Ar, Kr and Xe by the Electron-Bonbarded Hot Cathode IoN Source of IPCR

Production of multiply-charged ions of Ne, Ar, Kr and Xe has been studied by use of an electron-bombarded hot cathode type ion source of the IPCR 160cm cyclotron, which is similar to Morozov's source. These multiply-charged ions were accelerated by a 3rd harmonics acceleration mode in the cyclotron and detected with a beam probe fixed at the radius of 55cm. Observed multiply-charged ions are Ne2+, Ne3+, Ne4+, Ne5+, Ar3+, Ar4+ Ar5+, Ar6+, Ar7+, Ar8+, Kr6+, Kr7+, Kr8+, Kr9+, Xe9+, Xe10+ and Xe11+. Relative abundance of each charge state of four elements were measured. In case of Kr and Xe , the intensity of observed multiply-charged ions decreased to 1/3 or 1/4 when the charge number is increased by one. Intensities of Ar4+, Ar6+, Ar8+, Kr6+ and Kr8+ were measured as a function of the operation conditions of the ion source, such as arc voltage, arc power and gas flow rate. It was found that a smaller gas flow and a higher arc power brought about a higher yield in all the measured ions. Obtained current intensities of ion source output are 40?A Ar8+, 600?A Kr6+, 40?A Kr9+, 150?A Xe9+ and 10?A Xe11+ respectively.     

Generation and Storage of Multiply-Charged Ions within a RF Quadrupole Trap

A three-dimensional rf quadrupole field trap has been designed for generation of multiply-charged ions by successive electron impacts, and for studies of physical processes occurring during charge transfers. Optimum operating conditions have been derived from theoretical considerations, and preliminary experimental results are given. At the end, some limitations and prospects of the quadrupole trap as a tool for physical investigations are briefly discussed.     

Accel-Decel Method of Producing High-Q Low Velocity Ions

The double EN tandem Van de Graaff accelerators at the University of Pittsburgh's Nuclear Physics Laboratory have been used in part since 1978, operating in the 3-stage mode, as a source of highly stripped but low velocity ions for experiments of interest to atomic physics. Much of the work has involved investigating the technical details of this new accel-decel technique and gaining practical experience in operating the accelerators in the acceldecel mode. Decelerations to a final energy a factor of ? 50 less than the stripping energy have been achieved for fully stripped oxygen ions, and some charge exchange measurements on He published, demonstrating the potential of the accel-decel technique for supplying atomic physics with data from a previously unattainable energy and charge state regime. Practical problems encountered and the technical developments leading to these first prototype experiments will be reviewed. Subsequent developmental work, the present status of the project, and future technical plans at Pittsburgh are summarized. Finally, the future possibilities of the accel-decel technique generally are discussed.     

Charge transfer processes in astrophysical plasmas

Charge transfer processes involving multiply-charged ions modify the ionization structure of astrophysical plasmas and exert a major influence on plasmas created by the absorption of high frequency radiation. As a recombination mechanism, charge transfer suppresses the higher ionization stages. In hot plasmas, charge transfer ionization may enhance the abundances of highly charged systems. Charge transfer excitation also occurs and the resulting emission lines provide a unique diagnostic probe of the neutral content of the plasma, the ionization distribution and the nature of the ionization source.Examples of the role of charge transfer as a recombination, ionization and excitation mechanism in astrophysical plasmas are presented.     

The Intense Neutron Generator and Future Factory Type Ion Accelerators

A neutron factory is likely to sell its product in the form of isotopes. Today neutron factories are nuclear reactors. Ion accelerators may also produce isotopes by direct interaction and, at high enough energies, mesons and hyperons. The challenge of the electrical production of neutrons goes far beyond the isotope market. It challenges the two popular concepts for long term large scale energy, the fast breeder reactor and controlled thermonuclear fusion. For this use about 4% of nuclear generated power would be applied in a feedback loop generating extra neutrons. Competition rests on operating and processing costs. The Intense Neutron Generator proposal now cancelled would have been full scaloe for such a use, but much further advance in accelerator engineering is required and anticipated. Perhaps most promising is the application of the ion drag principle in which rings of fast electrons are accelerated along their axis dragging ions with them by electrostatic attraction. Due to the much larger mass of the ions they can acquire much higher energy than the electrons and the process could be efficient. Such accelerators have not yet been made but experimental and theoretical studies are promising.     

Charge Exchange between Hydrogen Atoms and Fully Stripped Heavy Ions

Charge exchange between multicharged ions and background atomic and molecular gases represents one of the limitations to the attainment of high charge states in heavy ion sources, particularly containment sources. This work is an attempt to study systematically a particularly simple but in many respects representative class of such reactions, namely, charge transfer between atomic hydrogen and fully stripped heavy ions. Approximate cross sections for these processes in the low keV range of collision energies were obtained using a multistate Landau-Zener method. The energy and Z dependences of the cross sections are discussed.     

Mixed Ne/Ni beams for radiation damage studies on the harwell variable-energy cyclotron

Ion irradiation facilities which use metal ions beams concurrently with beams of He or He+H have been developed extensively in recent years for the simulation of radiation effects which occur in metals during neutron irradiation in fission or fusion reactors. Helium ions are considered necessary to simulate the effect of helium on cavity nucleation and the metal atom is used to create an adequate atomic displacement rate. Many of these dual-beam facilities require the provision of two accelerators, one to produce a gas atom and the other a metal atom beam, and commonly employ low-energy metal ions (eg. 4 MeV ⁵⁸Ni⁺) which have a limited range (0.75 μm) in metals of practical interest. Damage can be created at greater depths by use of high energy ions (eg 45 MeV ⁵⁸Ni) in a cyclotron, but charge-to-mass constraints make it difficult to produce a mixed beam of concurrent He and metal ions. It is noted that the heavier inert gas atom neon has similarities in atomistic behaviour in metals to those of helium and could possibly be used as an analogue for helium. In this report we consider this aspect and show than by suitable matching of $\text{e}\text{m}$ ratio a mixed beam of 15 MeV ²⁰Ne²⁺ and 45 MeV ⁶⁰Ni⁶⁺ can be obtained from the Harwell VEC with gas/metal atom ratios and beam currents that are suitable for use in radiation damage simulation experiments in metals. It is proposed that exploratory studies should be carried out with mixed Ne/Ni beams into nickel to investigate the possibility of using neon as an analogue for helium in radiation damage simulation studies.     

The Unilac Ion Source and Injection System

The design of the UNILAC injector was particularly governed by aspects of maintenance and reliable performance. Thus an open air 254 kV high gradient single gap acceleration was chosen for Uranium 11+ particles, corresponding to an injection energy of 11.7 keV/amu and a charge-to-mass ratio of 0.046. This allows fast ion source changes because only a short time for tube conditioning is required and takes into account the lifetime of present sources for multiply-charged heavy ions. Two independent Faraday-rooms, symmetrically arranged to the axis of the main accelerator, are housing each a 300 kV oil-insulated Cockcroft-Walton generator, a duoplasmatron and a Penning source with the associated equipment. Hereby a fast switch over to the stand-by source in case of an ion source failure is provided. Magnetic quadrupole lenses focus and match the beam through a magnetic deflection system, a 50 Hz chopper and a double drift buncher into the linac.     

A new tool to compare neutron and ion irradiation in materials

The slowing down of neutrons produced in nuclear plants or in spallation sources generates many defects in a material, driving this material far from its equilibrium state. This concentration of defects leads to important structural modifications of solids. To model the impact of radiation in solids, particle accelerators are useful tools. The nature and the energy of ions in accelerators must be chosen to produce similar effects to those occurring in nuclear plants. A new program, DART, based on the binary collision approximation, has been developed to optimize the choice of incident particles. In this program, the anisotropy of the neutron atom interaction is treated with a new formalism. Such a formalism allows us to compute accurate displacement cross sections and recoil spectra for all kinds of particles (ions, neutrons, or electrons). The comparison of these displacement cross sections as well as recoil spectra due to ions, electrons and neutrons permits to define the nature and the energy of ions able to simulate damages in reactors.     

中国粒子加速器的发展现状和趋势

我国的粒子加速器近20年来发展迅速,在加速器不同的类型、规模和应用方向上全面向世界先进水平靠近。本文以几个主要加速器研究或应用方向如先进光源、强流质子-重离子加速器、粒子对撞机、民生应用型加速器为主线,介绍其中几台典型装置的建设和发展,以及它们在国际上的地位和在相应学科研究中所发挥的作用。同时,也介绍我国在加速器物理和技术方面的快速进步,这些进步不仅对已经建造和正在建造的大型加速器装置是个极为重要的支持,也是加速器学科的自身发展,并为未来更先进的加速器装置的发展提供了可能性。本文对我国未来若干年的加速器事业发展作了展望,期望我国的加速器在10年后将全面处于国际先进水平,同时也对我国在激光等离子体尾场加速领域近些年来的飞速发展作一个简单评述。     

应用于离子注入的RFQ加速器

射频四极场(Radio frequency quodrupole,RFQ)加速器是一种非常适于用作MeV级能量离子注入的加速器.它具有束流强、体积小、使用方便、离子源处在地电位,还可同时加速正、负两种离子等优点.本文介绍了RFQ加速器在国际上的发展状况及其基本原理、北京大学研制的1 MeV RFQ加速器的具体结构、性能以及一种新型RFQ-SFRFQ组合加速器的特点.     

The Use of Lasers to Simulate Radiation-Induced Transients in Semiconductor Devices and Circuits

High levels of ionization can be created in semiconductor devices by irradiating the devices with short pulses of light. If the light frequency is properly selected, sufficient and relatively uniform energy deposition is obtained which results in ionization rates orders of magnitude above those presently attainable from other sources. It is shown that a pulsed-infrared laser can be used as a relatively simple, inexpensive, and effective means of simulating the effects caused by intense gamma ray sources on semiconductors. Experimental results are presented which show that the transients induced in various types of silicon transistors when exposed to a neodymium laser are essentially identical to those obtained when the transistors are exposed to pulses of 25 MeV electrons from a linear accelerator and 600 kvp flash X-ray machine. Good agreement exists between the peak photocurrents obtained using these three sources over a dose range of 10-1 to 104 rads. Calculations based upon published as well as experimental absorption data for silicon show that energy deposition is very nearly uniform for the wavelength of light obtained from neodymium lasers (1. 06 microns - 1. 17 ev photons). By defocusing the laser light beam, dose rates in excess of 10R12 rads/ sec (silicon) in 40 x 1-99 seconds over an area of 50 cm2 have been obtained from a Q-switched 10 megawatt neodymium laser. This greatly exceeds the maximum dose rate of 1011< rads/ sec silicon) over approximately 1 c2m attainable from linear accelerators.     

Development of precise energy spectrum measurement technique for high-power pulsed X-ray sources for industrial use

It is difficult to obtain an accurate energy spectrum by measurement for X-rays which are produced by linear accelerators because so many photons are emitted within a very short period and the photons have energies in a wide range. In order to solve the problem, we developed a new technique utilizing the Bayesian estimation method combined with attenuation curve measurement using a step-shaped attenuation material. We experimentally confirmed the validity of the presented technique for an X-ray computed tomography (CT) system. By using the accurate energy information of emitted X-rays obtained by the developed technique, the quality of non-destructive inspection images can be expected to be improved for industrial X-ray radiography, X-ray CT and so on, using high-power X-ray sources.     

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.     

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.     

Impact of Accelerators on Technology

Accelerators and accelerator technology has rapidly expanded into Medicine and Industry. The 2500 accelerators in the USA, which represent about 2/3 the worldwide census of accelerators are primarily devoted to practical applications, although the major impact on technology has been produced by a relatively few excellent facilities. Approximately 80% of the current accelerators in the USA are found to be in medical and industrial use representing a capital investment by industry of $200,000,000. Of greater importance is their impact on the treatment of cancer, and the improvement or creation of better products for industrial and consumer use. The development of new accelerators and techniques are required in order to insure continuing benefits to the public.     

ACCELERATOR-BASED ATOMIC PHYSICS AT THE LAWRENCE BERKELEY LABORATOTY:COLLISIONS OF FAST,HIGHLY-CHARGED IONS WITH ATOMS

Research on accelerator-based atomic physics at the Lawrence Berkeley Laboratory super-HILAC and Bevalac accelerators is described. This research covers several important topics in collisions of fast, highly charged ions with atoms: charge transfer, ionization, and excitation. Multiple - electron processes are emphasized. Electron correlation is important in some of these processes, e.g., resonance transfer and excitation (RTE) multiple-electron capture in close collisions. A variety of experiments and results for energies from 1 to 420 MeV/u are presented.     

Enhanced beam deflection in bent crystals using multiple volume reflection

This paper presents simulations of the trajectories of high-energy ions through several bent crystal layers. At certain layer alignments volume reflection occurs from each layer and the resultant multiple volume reflection angle is correspondingly increased, along with the range of entrance angles over which ions undergo volume reflection. Another feature is that the range of entrance angles for which bent crystal channeling occurs is also increased in passing through several bent layers. The use of several bent crystal layers to produce multiple volume reflection provides an alternative approach to the design of a space shield or radiation protection at accelerators based on bent crystals.