Electrostatic Quadrupole Lenses Research Articles

Focusing properties of a very thin electrostatic quadrupole lens

The rainbow effect in transmission of a proton beam of energy of 10 keV through a very thin electrostatic quadrupole lens is considered theoretically. The incident ion velocity vectors are taken to be parallel to the lens axis. The distance between the positively or negatively charged lens electrodes is 10 mm and the electrode voltage modulus is 1 kV. The approach is based on the momentum approximation. The rainbow effect is studied via a detailed analysis of the ion differential transmission cross-section, which is determined by the Jacobian of the ion transmission angle components. This variable contains a term describing the ion deflection from the individual electrodes and a term describing the coupling of the electrodes that is seen by the ion. It has been found that the latter term is the source of the rainbow effect, which is, thus, a complex effect in ion beam dynamics. The final conclusion of the calculations is that the lens acts on the ion beam in a way to reshape it qualitatively into a beam containing four narrow sub-beams directed between the lens electrodes.

Development of a magnetic quadrupole lens for low energy heavy ion beam transport

A magnetic quadrupole lens system coupled to a 30° bending deflection magnet was designed and constructed to realize a beam focusing of Xe+ ions with the energy less than 200 eV. Compared to a triplet electrostatic quadrupole lens system, the quadrupole doublet magnetic lens system showed a larger beam transmission, indicating the mitigation of the space charge in the beam transport region free of the electrostatic field. The misalignment of the magnetic field axis was observed probably due to a slow change in magnetization of magnetic materials to construct the magnetic circuit of the quadrupole lens. A countermeasure to realign the beam axis by coupling the permanent magnets to trim coil electromagnets is proposed.

Comparison between the imaging properties of two different types of electrostatic quadrupole doublet lenses

The comparisons between the optical properties of two types of electrostatic quadrupole lenses with the same dimensions and operation conditions are made. The optimum voltages of the electrodes which give the stigmatic image for both focusing planes with are calculated. The calculations are carried out for point-to-point focusing mode. The effects of changing the electrode shape on the optical properties of the lenses are investigated, where the magnification, electron-beam trajectories, and aberration figures are studied, and the comparisons are made. The effects of variation the object and image positions with respect to lens are studied and the comparison between the results for the two lens systems is done. The results show that the electrode shape of the lens play important role in the imaging properties of the electrostatic quadrupole doublet lens systems, especially in the aberrations figures at the image plane. The b-type electrostatic quadrupole doublet lens system gives the best imaging properties in comparison with a-type.

A new fast-cycling system for AMS at ANU

In order to perform higher precision measurements, an upgrade of the ANU accelerator is underway. Fast switching times on the low-energy side, with maximum settling times of 30ms, are achieved by holding the injector magnet field constant while changing the energy of the different isotopes by changing the pre-acceleration voltage after the ion source. Because ions of the different isotopes then have different energies before injection, it is necessary to adjust the strength and steering of the electrostatic quadrupole lens that focusses the beam before entry into the accelerator. First tests of the low-energy system will be reported. At the high energy end, a larger vacuum box in the analyzing magnet has been designed, manufactured and installed to allow the transport of differences in mass as large as 10% at constant terminal voltage. For the cases where more than one isotope must be transported to the detector an additional refinement is necessary. If the accelerator voltage is to be kept constant, then the trajectories of the different isotopes around both the analyzing and switching magnets must be modified. This will be achieved using bounced electrostatic steerers before and after the magnets. Simulations have been performed with the ion optic code COSY Infinity to determine the optimal positions and sizes of these steerers.

A compact high-resolution elastic recoil detection system for lithium depth profiling

A compact high-resolution elastic recoil detection analysis (ERDA) system was developed for precise Li analysis. 200–400keV He+ ions were used as primary ions and the energy spectra of recoiled Li ions were measured using a magnetic spectrometer. Due to its dispersion the background originating from the scattered primary ions is reduced. The recoiled ions of the substrate other than Li, which may also contribute to the background, were rejected by a thin mylar foil placed in front of a focal plane detector. An electrostatic quadrupole lens was installed at the entrance of the magnetic spectrometer to improve the depth resolution by correcting the effect of the kinematic broadening. The performance of the developed high-resolution ERDA was examined by measuring several samples. A thin Li layer (1.5×1015cm−2) deposited on a graphite surface was clearly observed and the detection limit was estimated to be less than 0.01ML under typical measurement conditions. The depth resolution was estimated to be 0.5nm at the surface and was better than 3nm in the surface region within 5nm from the surface.

Ion Beam Acceleration With Radio Frequency Powered Rainbow Lens

The electrostatic quadrupole lens, quadrupole accelerator and square rainbow lens as well as radio frequency quadrupole accelerator all have similar structure with four rod-like electrodes. Unlike the last one, which is powered by the alternating voltage, the first three are electrostatic devices. Each two adjacent electrodes of a common electrostatic lens have equal magnitude and opposite signs of their electric potentials, whereas, electric potentials of rainbow lens's electrodes are all equal in magnitude as well as in sign. If powered by the appropriate radio frequency instead of a DC voltage, the rainbow lens transforms into an ion beam accelerator which could cost-effectively broaden the available energy range of low energy ion beam facilities.

Ion, X-ray, UV and Neutron Microbeam Systems for Cell Irradiation.

The array of microbeam cell-irradiation systems, available to users at the Radiological Research Accelerator Facility (RARAF), Center for Radiological Research, Columbia University, is expanding. The HVE 5MV Singletron particle accelerator at the facility provides particles to two focused ion microbeam lines: the sub-micron microbeam II and the permanent magnetic microbeam (PMM). Both the electrostatic quadrupole lenses on the microbeam II system and the magnetic quadrupole lenses on the PMM system are arranged as compound lenses consisting of two quadrupole triplets with "Russian" symmetry. Also, the RARAF accelerator is a source for a proton-induced x-ray microbeam (undergoing testing) and is projected to supply protons to a neutron microbeam based on the (7)Li(p, n)(7)Be nuclear reaction (under development). Leveraging from the multiphoton microscope technology integrated within the microbeam II endstation, a UV microspot irradiator - based on multiphoton excitation - is available for facility users. Highlights from radiation-biology demonstrations on single living mammalian cells are included in this review of microbeam systems for cell irradiation at RARAF.

Development of Multi-Turn Time-of-Flight Mass Spectrometers and Their Applications

The mass resolution of a time-of-flight (ToF) mass spectrometer is directly proportional to its total flight path length. We have developed multi-turn ToF mass spectrometers, where ions are stored in a fixed orbit within electrostatic sectors and allowed to propagate the said orbit numerous times. With each successive orbit, the flight path is correspondingly increasing. The first multi-turn ToF mass spectrometer, the MULTUM Linear plus, was developed for cometary exploration. The spectrometer consists of four cylindrical electrostatic sectors and 28 electrostatic quadrupole lenses. The size of the analyzer is 40 cm square. Mass resolution is demonstrated to increase according to the number of ion cycles. A mass resolution of greater than 350,000 was achieved after 501.5 cycles. Another multi-turn ToF mass spectrometer, the MULTUM II, which consists of only four toroidal electrostatic sectors, was also developed in an effort to reduce the number of quadrupole lenses. We are developing various types of mass spectrometer based on the MULTUM II technology, a ToF/ToF mass spectrometer "MULTUM- TOF/TOF", a stigmatic imaging mass spectrometer "MULTUM-IMG" and miniature mass spectrometers of high mass resolving power, the "MULTUM-S" series.

Focusing of He+ beams using a compact electrostatic quadrupole lens system

Abstract A compact electrostatic quadrupole lens system has been developed, and experiments have been conducted to study transport and focusing of intense He + beams with β=v/c =0.0029 and generalized perveance (Theory and Design of Charged Particle Beams, Wiley, New York, 1994) K=0.0013. Such beams are transported without any loss of beam particles and focused at a distance of about 0.6 m from the source with emittance growth less than a factor of about 1.8. This compact ESQ system has merits to satisfy a critical demand for developing intense He 0 beams for alpha-particle diagnostics in fusion-relevant machines.

Aberrations caused by mechanical misalignments in electrostatic quadrupole lens systems

Abstract Image aberrations resulting from small misalignments in quadrupole lenses multiplets have been analysed. Analytical formulas for the coefficients of the beam displacement, astigmatism and coma associated with misalignments in a general quadrupole lens system have been derived. Numerical computations of systems of three and four quadrupole lenses have also been carried out. The aberration figures obtained for systems with and without a mechanical defect are compared. The aberration coefficients that have been obtained can be used for estimating tolerance limits for lens misalignments.

The optimal construction of an electrostatic quadruplet as focusing microprobe system

A general analytical and numerical technique for finding high-quality probe-forming systems is proposed and developed. This optimisation procedure includes mathematical and physical modeling based on the matrizant method and on the boundary element method, respectively.The Separated Russian Quadruplet with electrostatic quadrupole lenses consisting of four copper rods as the microprobe focusing system is numerically simulated. The influence of the rod diameter and the energy spread on the beam spot size is investigated for different emittances.

Minimisation of the aberrations of electrostatic lens systems composed of quadrupole and octupole lenses

Aberrations are investigated and compared for two types of multiplets based on electrostatic quadrupole and octupole lenses: “mid-acceleration” systems where an accelerating potential is applied to the middle lenses of a set of quadrupole lenses and systems where some of the quadrupole lenses are replaced by combined quadrupole–octupole lenses. It is shown that for systems consisting of three lenses the mid-acceleration type has the smaller aberrations. For systems consisting of four or five lenses the third order aperture aberration can be eliminated in the quadrupole–octupole type. The mid-acceleration type has the advantages of lower levels of chromatic and fifth order aperture aberrations and also relative simplicity of construction and voltage adjustment.

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.

Design of a microengineered electrostatic quadrupole lens

The design of a miniature quadrupole lens based on metallized glass electrodes mounted in two anisotropically etched silicon mounts that are separated by precision spacers is described. The analysis of conventional quadrupole lenses is first reviewed. The fabrication process is then described, and the analysis techniques are applied to the new geometry. The potential distribution near the axis is first calculated using a finite difference method. Expansion into solutions of Laplace's equation in cylindrical coordinates is then used to determine the potential distortion introduced by the microengineered mount. Design rules are given for a mount and an electrode radius that achieve minimal distortion.

Dielectric response of particle beams to periodic focusing.

Dielectric response of particle beams to periodic focusing.

Emittance Diagram of Electron Beams Generated by a Field-emitter Array

The emittance diagram of electron beams generated with a field-emitter array (FEA) was obtained by a new method of diagnostics. The beams were accelerated to several keV, propagated over a distance of 1 m through a focusing lens, and projected on a fluorescent screen. A magnified image of the FEA was formed on the screen, and images of the emitting tips were observed separately. An electrostatic quadrupole lens, inserted halfway between the focusing lens and the fluorescent screen, was used to modify the electron trajectories. The width of the fluorescent pattern in the defocusing direction showed a minimum, when the strength of the quadrupole lens was increased. This provided a simple way of determining a parallelogram enclosing the electron distribution in trace space.

An electrostatic LEBT for a low-emittance injector: transport and focusing of a high-brightness H − beam from a magnetron ion source

In the context of developing an efficient low-energy beam transport (LEBT) system for a low-emittance injector the problem of transport and matching of a 30 mA, 35 kV H − beam from a magnetron-type ion source is studied; the analysis is done incorporating important experimental constraints. A 30 cm-long LEBT, consisting of six electrostatic quadrupole lenses and a short einzel lens, is designed. Its control parameters are optimized to achieve a solution which matches with the acceptance of a small-aperture radio-frequency quadrupole (RFQ) accelerator. The results of beam dynamics calculations are discussed, and the key issues for emittance growth and its control are acknowledged.

Anamorphotic quadrupole lens system for highly demagnified round spot

Paraxial and aberration properties have been studied theoretically for an electrostatic quadrupole lens system that demagnifies the line shaped emission area with a high aspect ratio of a LaB 6 source to a sub-micron round spot. For a quadrupole lens doublet, it was indicated that the target paraxial performances, M x = 1 100 and M y = 1 1000 , can be achieved with a large object distance by providing a round lens in front of the doublet. However, it was clear that a combined doublet with a round lens is not suitable for practical sub-micron spot optics because the spot growth due to the object distance error by the round lens is not negligible. On the other hand, for a quadrupole lens triplet with a low second lens excitation, the target performances can be obtained by operating the first lens with higher excitation; the aberration properties can be reduced by optimizing the geometrical parameters. Finally, it was recognized that the triplet is suitable for practical anamorphotic optics, in which a 10 μm × 100 μm line source is demagnified to a round spot of 0.1 μm in diameter.

An inductively coupled plasma-time-of-flight mass spectrometer for elemental analysis. Part II: Direct current quadrupole lens system for improved performance

An electrostatic quadrupole lens has been substituted for a cylindrical lens system used in the original inductively coupled plasma-time-of-flight mass spectrometer (ICP-TOFMS). With an improved vacuum system also installed, the cylindrical and quadrupole lenses are compared to each other and to the performance of the prototype ICP-TOFMS. The quadrupole lens requires no tradeoff between ion throughput and resolving power as was encountered with cylindrical lenses. The background noise in both ion-optical systems is within the same order of magnitude. Images of the ion beam formed by each ion-optical system have been obtained on a microchannel plate-phosphor screen. The quadrupole lens shows a higher ion-beam flux and produces a slitlike focus required in the orthogonal ICP-TOFMS instrument. Signal-to-noise ratios in the ICP-TOFMS can be improved by using a technique called pulsed-ion injection that is particularly convenient with the quadrupole lens. In this technique, one quadrupole electrode is pulsed to prevent ions from entering the extraction zone except when an ion packet is to be extracted for mass analysis. This technique significantly reduces the noise over continuous ion injection. In the orthogonal ICP-TOFMS with pulsed-ion injection, 0.5 frnol of analyte could be detected in 1.4 ms with a proper data acquisition system. Overall, the combination of a quadrupole lens and pulsed-ion injection may provide detection limits for the ICP-TOFMS that are competitive with those of quadrupole inductively coupled plasma-mass spectrometry instruments.

Analysis of the properties of an electrostatic triplet quadrupole lens used as an electron beam transport device

The electron optical properties of an electrostatic triplet quadrupole lens used as an electron beam transport device were reexamined, both analytically and by computer simulation, in order to derive limits on the choice of the design parameters of the lens. Furthermore, computer simulation of electron trajectories through a single quadrupole lens, and comparison with experimental results obtained by other authors, have led to a graphical relation between the fringing field end correction and the aspect ratio of the lens.