Ion-optical Characteristics Research Articles

A computer model of comprehensive modeling of the laser time-of-flight analyzer.

This article offers a new approach to computer modeling of time-of-flight analyzers of mass spectrometers. The main feature of the model is comprehensive tracking of the processes from the laser plasma generation until the final stage, on which the isotopic or elemental composition is determined for the analyzed solid sample. Apart from usual models based on SIMION-8 3D or similar software, this article proposes fundamentally new modeling stages. These stages are (1) generation and spread of laser plasma, (2) formation of the ion packages, (3) ion detection, and (4) formation and processing of the analytical signals. In order to provide consistent modeling of all the stages, special software units were developed. Program control of the analyzer ion optics (electrodes voltages) allows scan of mass spectra by ion energy. Additional complex of the programs provides simulation of mass spectra digitization, summation of digitized mass spectra for a wide range of variable parameters, and consideration of the discriminatory effects. According to the data, the software calculates ion-optical characteristics of the analyzer and the analytical parameters of measurement results.

Radioactive nuclear beams of COMBAS facility

The basic ion-optical characteristics of the luminosity and the high-resolution of kinematic separator COMBAS realized for the first time on the strong focusing principle are presented. The developed facility allows to separate the high-intensity secondary radioactive beams in a wide range of mass numbers A and atomic numbers Z which are produced in heavy ion reactions in the energy range of 20 ≤ E ≤ 100 MeV/A (Fermi energy domain). Two distinct detector systems such as realized Si strip detector telescope and the promising development of the three dimension time-projection chamber are discussed. Program of the investigations of nuclear reaction mechanisms at intermediate energies of 20–100 MeV/A, measurement of the radii of unstable nuclei, study of the cluster structure of light nuclei near the nuclear drip-line and search of 26,28O resonances in exchange reactions is proposed. The upgrading of experimental facility by the integration of COMBAS separator with the Ion Catcher is discussed.

The COMBAS fragment separator

The basic ion-optical characteristics of the COMBAS fragment separator are analyzed. The momentum distributions of radioactive 6He, 8He, and 9Li nuclei obtained in the reaction 11B (33 A MeV, where A is the mass number of a particle) + 9Be (332.6 mg/cm2) have been investigated in forward-angle measurements on the COMBAS fragment separator. The momentum and angular (horizontal) acceptances of the COMBAS separator have been measured using the 6He, 8He, and 9Li beams. It has been ascertained that the images of the 6He, 8He, and 9Li nuclear beams in final achromatic focus of the separator Fa approximately twofold exceed the size of the beam on a producing target (input focus F0), at which the primary beam has a diameter of 6 mm. The intensities of 6He, 8He, and 9Li beams obtained at a 5-μA intensity of the primary 11B beam are 6.9 × 105, 2 × 104, and 4.7 × 105 particles/s, respectively. These values are sufficient for use in spectroscopic measurements. It is proposed that time-of-flight analysis of nuclear reaction products at the exit from the COMBAS separator will be used not only to measure the energy of transported particles over the whole operating range of the momentum acceptance, but also to identify them by mass A and charge Z without loss of these particles. The problem of reducing the count rates of detectors and further improvement of their energy resolution for detected particles can be solved by placing a high-resolution magnetic spectrometer past the second target accepting the secondary radioactive nuclear beams.

Nonlinear processes of probe formation of a beam with inhomogeneous phase density at nuclear microprobe

The work describes nonlinear processes of probe formation on the target with allowance for an inhomogeneous density of ion distribution in phase space in the object collimator plane taken from experimental data. The chromatic aberrations, intrinsic aberrations of the 3rd order and parasitic aberrations caused by sextupole and octupole components of the magnetic quadrupole lens field have been taken into account in the object-target phase coordinate transformation. The criterion of obtaining the optimal resolution was defined as the minimum spot size (FWHM) for a fixed ratio IFWHM/I0 of beam current in this spot to the total beam current. The conditions for which the initial density of ion distribution in phase space is matched with the ion-optical characteristics of the probe-forming system were considered. The influence of axial brightness and parasitic sextupole and octupole field components on the beam current distribution at the target has been determined.

One-stage probe-forming systems with quadrupole lenses excited by individual power supplies

The work deals with the ion-optical characteristics of the probe-forming systems based on a quadruplet of magnetic quadrupole lenses with four power supplies. The excitation of the lenses of a final doublet of such system is determined from the stigmatic focusing conditions, and the excitations of the first two lenses (downstream the beam) are free parameters which form a parametric set of the probe-forming systems. For this parametric set, the system acceptance reduced to the envelope dimensions in the target plane is determined as a figure of merit for the optimization task. The solution of this task gives optimal excitations of the first two lenses allowing an increase in demagnifications and acceptance of the probe-forming systems with individual power supplies in comparison with a separated Russian quadruplet.

Ion-optical characteristics of a laser mass spectrometer with a coordinate-sensitive microelectronic detector

The ion-optical systems of a mass spectrometer with a laser ion source and coordinate-sensitive microelectronic detector are analyzed using the matrizant method. The dispersion properties of the mass spectrometer, as well as ion beam radial and axial focusings in its optimized ion-optical system, are determined, and first-and second-order angular and velocity aberrations of the image are corrected. The basic parameters and characteristics of a refined (according to calculation results) version of the laser mass spectrometer with a coordinate-sensitive microelectronic detector are presented.

The CR storage ring in an isochronous mode operation with nonlinear optics characteristics

In the Facility for Antiproton and Ion Research (FAIR), which is presently designed at GSI (Darmstadt, Germany) a variety of new short-lived nuclides will be generated with the Super-FRS by using projectile fragmentation or uranium fission. The storage rings for the CR-RESR complex have been designed for efficient cooling and accumulation of antiprotons and cooling and deceleration of rare isotopes beams. A new Collector Ring (CR) is planned to be constructed, where one of the functions is devoted also to mass measurements of very short-lived nuclei when it is tuned to an isochronous mode. The structure of the ring lattice and its ion-optical properties in the isochronous mode are described. Nonlinear ion-optical characteristics and their influence on an achievable mass resolving power in an isochronous mode operation of the CR are discussed.

Characterisation of the University of Surrey Ion Beam Centre in-air scanning microbeam

The University of Surrey Ion Beam Centre has recently commissioned a new in-air scanning microbeam. The new external beam uses a magnetic quadrupole doublet to focus a beam-spot of μm dimensions on the vacuum exit window so that there are no beam defining apertures close to the analysis region. A pre-lens magnetic dipole allows beam scanning for measuring two dimensional elemental distributions. The scanned area is limited by the diameter of the exit window to 3mm diameter at present. The sample is positioned using a front viewing video microscope and an alignment laser, and detectors for X-rays (high energy and low energy), backscattered particles and gamma rays are installed.This paper will detail the ion optical characteristics of the in-air scanning microbeam, and the methods used in the characterisation. A comparison between calculated optical properties of the in-air scanning microbeam, using the ray-tracing software TRAX, and the measured properties of the beam will be presented.

The low-field permanent magnet electrostatic plasma lens

We describe the status of ongoing research and development of the electrostatic plasma lens as used for the manipulation of high current broad beams of heavy ions of moderate energy. In some collaborative work at Lawrence Berkeley National Laboratory the lens was used to good effect for carrying out high dose ion implantation processing. In the process of this work a very narrow range of low magnetic field was found for which the ion-optical characteristics of the lens improved markedly. Subsequent theoretical analysis and computer modeling has led to an understanding of this phenomenon. These serendipitous results open up some attractive possibilities for the development of a new compact and low cost plasma lens based on permanent magnets rather than on current-driven field coils surrounding the lens volume. The development of this kind of lens, including both very low noise and minimal spherical aberration effects, may lead to a tool suitable for use in the injection beam lines of high current heavy ion linear accelerators. Here we briefly review the lens fundamentals, some characteristics of focusing heavy ion beams at low magnetic fields, and summarize recent theoretical and experimental developments, with emphasis on the relevance and suitability of the lens for accelerator injection application.

Comprehensive investigation of the angular transmission in magnetic spectrometers

Magnetic spectrometers are largely used in experimental nuclear physics. These devices allow one to perform precise measurements of the reaction kinematics or to separate and fully identify the reaction residues for nuclear-dynamics and structure studies. They can also be used as separators to produce radioactive nuclear beams. However, all these applications are affected by the limited transmission of the reaction residues through the spectrometer. The final transmission depends on the ion-optical characteristics and the mechanical constraints of the spectrometer but also on the kinematic properties of the considered nuclei. The ion optics are characterised by the bending and focusing powers of the magnetic elements which constitute the spectrometer. The reaction mechanism determines the kinematics of the particles. The transmission losses in any magnetic spectrometer can be attributed to its limited acceptance in longitudinal momentum and angle. The limitation in longitudinal momentum can be overcome by combining different magnetic settings [Nucl. Phys. A 658 (1999) 47; Nucl. Phys. A 683 (2001) 513]. In the case of a zero-degree spectrometer, the angular acceptance can only be estimated with calculations. Standard ion-optical transport codes [Transport, SLAC-R-95-462; Nucl. Instr. and Meth. B 126 (1997) 284] are commonly used to determine the transmission of charged particles through magnetic spectrometers. Although these codes describe precisely the trajectories of the ions according to their kinematics within the spectrometer, they are rather time consuming. Therefore, experiments in which a large amount of different nuclides with specific kinematic properties are investigated [Nucl. Phys. A 658 (1999) 47; Nucl. Phys. A 683 (2001) 513; Phys. Rev. Lett. 84 (2000) 5736] cannot afford for such calculations. In this work we present a new method to estimate the angular transmission in zero-degree magnetic spectrometers [Nucl. Instr. and Meth. A 478 (2003) 493]. This method is based on a parameterisation of the angular aperture of the spectrometer for any possible value of the magnetic rigidity of the transmitted particles. The parameterisation of the angular aperture together with a description of the kinematics of the reaction mechanism allows one to determine the angular transmission analytically, avoiding tedious Monte-Carlo calculations. The analytical solutions are implemented for residual nuclei produced in fission, projectile-fragmentation and fusion-evaporation reactions.

Computer program “TRIO-DRAW” for displaying ion trajectory and flight time

Abstract Computer program “TRIO-DRAW” was constructed to calculate and display ion trajectories and simulate overall ion optical characteristics such as image shape and mass resolution. Flight-time information can be obtained as well.

Computer Code 'TRIO-TOF' for the Third-Order Calculation of Ion Flight Times.

A new computer code ‘TRIO-TOF’ has been constructed. The code can calculate ion flight times in time-of-flight (TOF) mass spectrometers to a third-order approximation. Ion-optical characteristics and focusing properties of time-of-flight mass spectrometers, which consist of toroidal electrostatic condensers and electrostatic quadrupole lenses, can be estimated by this code. The influences of the fringing field on ion flight times have been taken into consideration. The precise calculation of ion flight times in the fringing-fields has been also described.

Optimization of an rf ion source for production of a high-energy ion microbeam

A unit has been designed and implemented expressly for the measurement of brightness, energy spread and mass composition of the ion beam extracted from an ion source. This unit has been used for investigation of the main ion optical characteristics of standard and modified rf ion sources. A magnet system (“mirror” type) consisting of permanent magnet and ferrite materials has been used in the modified rf ion source. The capabilities and advantages of this source are shown in this paper.

Application of luminous ion beams in direct ion optical characteristics measurements

A novel direct technique for measuring the ion optical characteristics of systems used for the focusing, selection, transportation, energy analysis and mass-separation of ion beams is proposed. This method is based on detecting the light (350–600 nm) emitted because of decay ( τ≈10 −5s) of the metastable excited ions produced by electron-atom collisions. We found that the beam trajectories formed by such ions are visible in free space as well as in electric or magnetic fields under UHV conditions. Some widely employed ion optical elements have been investigated by using the proposed method. For example, our measurements of the focal length, the location of the principal plane, and the aberrations of well-known symmetrical electrostatic lenses are in agreement with computer calculations. This technique may be useful for ion optical characteristics studies and practical designs of ion beam equipment.

Study of the ion-optical properties of the mass spectrometer Lidia

The ion-optical characteristics of the ultrasensitive mass spectrometer LIDIA designed to search for superheavy elements ( A > 250) with a sensitivity of up to 10 −14 at./at. using a laser plasma ion source and a multistage separation system have been calculated. The main ones (acceptance, momentum dispersion, resolution and line shape) have been measured by means of 249Cf and 226Ra α-particle beams. A good agreement of the obtained results with the calculated ones is shown. The mass spectrometer is made operational with a laser plasma ion source. This will enable one to carry out the mass-spectrometric analyses of natural samples with fairly high utilization of the specimen material (10 −6–10 −3) and wish a resolution sufficient to resolve the mass lines of the superheavy elements searched.

The influence of inclination of field boundaries of an electrostatic energy analyser on its ion-optical characteristics

The influence of inclination of field boundaries of an electrostatic energy analyser on its ion-optical characteristics

The electromagnetic isotope separator of the laboratory of nuclear reactions, JINR

The report gives the calculation and the description of the mass separator of the LNR-JINR. The mass separator is made on the basis of a commercially available electromagnet with magnetic shims at the entrance and at the exit of the analyzer. The mass separator is designated to analyze nuclear reaction products with mass number up to M = 260. The report presents the ionoptical characteristics of the mass separator and the experimental results in a 205Tl and 203Tl isotope separation.