Quadrupole Lenses Research Articles

Perturbed machine phase ellipse and particle tracking in ultrahigh-energy linear accelerators

An investigation is made to determine how inaccuracies in mounting the quadrupole lenses influence the dilution of the transverse emittance of the beam. The study is made for two specific designs of 500 GeV linear colliders, thermal and superconducting. The analytical prediction is compared with the results of numerical calculations on the averaging of the beam emittance dilution effects for various sets of random deviations of the lenses from the accelerator axis.

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.

The magnetic and diagnostics systems for the Advanced Photon Source self-amplified spontaneously emitting FEL

A self-amplified spontaneously emitting (SASE) free-electron laser (FEL) for the visible-to-ultraviolet spectral range is under construction at the Advanced Photon Source at Argonne National Laboratory. The amplifier part of the FEL consists of twelve identical 2.7-m-long sections. Each section includes a 2.4-m-long, 33-mm-period hybrid undulator, a quadrupole lens, and a set of electron beam and radiation diagnostics equipment. The undulators will operate at a fixed magnetic gap (approx. 9.3 mm) with K=3.1. The electron beam position will be monitored using capacitive beam position monitors, YAG scintillators with imaging optics, and secondary emission detectors. The spatial distribution of the photon beam will be monitored by position sensitive detectors equipped with narrow-band filters. A high-resolution spectrograph will be used to observe the spectral distribution of the FEL radiation.

Ion focusing properties of an isotrajectory quadrupole lens pair

Abstract The focusing properties of an isotrajectory quadrupole lens pair have been studied, and the results of thick lens calculations are presented in the form of graphs showing the nondimensional isotrajectory field strength parameters and instantaneous linear magnifications as functions of geometry and image distance.

Optimized short focusing systems for a nuclear microprobe

The paper describes short versions of optimized focusing systems based on a divided Russian quadruplet and a triplet of magnetic quadrupole lenses. The systems have a total length l < 3.5 m. The calculations include all dominant lens aberrations (chromatic, spherical, sextupole and octupole). The results are used to design new scanning nuclear microprobes in the Institute of Nuclear Physics in Cracow (Poland) and in the Institute of Applied Physics in Sumy (Ukraine). The expected resolutions of the microprobes are presented. The proposed systems are greatly promising for the next generation of compact and vertical microprobes.

Acceleration test of heavy-ion in RFQ linac for HIF basic experiments

A new heavy-ion acceleration system has been developed for basic research on heavy-ion inertial fusion and ion-pumped laser at Tokyo Institute of Technology. This system consists of the TIT-RFQ linac, a hexapole cusp-field type ion source, a solenoid lens, magnetic quadrupole lenses and an analyzing magnet. By using the new system, acceleration of N + beam by the TIT-RFQ was first possible. We could obtain N + beam with an energy of 3.066 MeV and a maximum intensity of 0.4 nA as the results of acceleration test. The outline of this system and the acceleration test are presented.

A space time-of-flight mass spectrometer for exobiologically-oriented applications

A new type of multi-turn time-of-flight mass spectrometer was designed and constructed as a laboratory model of the ‘COSAC’ project of the ‘ROSETTA’ mission cometary study. This miniature time-of-flight mass spectrometer (TOF/MS) comprises of four electric sectors and eight electric quadrupole lenses, and it was demonstrated that mass resolution can increase according to the number of cycles of the ions through the ion optical system.

A Microfocus X-ray Tube Used with Focusing Collimators

The design and performance are described of a low-power copper-target X-ray tube with an elongated focus foreshortened to a diameter between 10 and 20 µm. The tube is designed for use with a specularly reflecting ellipsoidal mirror placed between 10 and 20 mm from the source and focusing the X-rays onto the sample, which may be 600 mm distant. The design maximizes the solid angle of collection of the emitted X-rays and thus achieves a high intensity at the sample. The electron beam, of circular cross section, from the gun is focused by an axial magnetic lens and then drawn out by a quadrupole lens to form an elongated spot on the target which is viewed at a small take-off angle. The limits imposed on the maximum intensity at the specimen by aberrations in the lens and by the permissible power dissipation in the target are discussed. The observed intensity is in reasonable agreement with the calculated intensity; it is comparable with that achieved with nonfocusing X-ray optics used with conventional X-ray tubes operated at a power more than 100 times as great.

Particle optics for a plasma-based beam focusing and transport system

The ion optical properties of plasma-based final focusing and transport for a heavy ion ICF reactor are discussed. The advantages of plasma-based final focusing are mainly the structure of the field, the beam charge- and current neutralization and the reduction of beam rigidity due to stripping of electrons in the plasma. Two possible focusing modes are considered: the first one, more traditional, is the so-called coherent mode; it is based on the symmetric strong focusing which can be obtained with a cylindrical, or eventually shape optimized, “short” lens. The optical properties are in this case favorable compared to quadrupole lenses. The lens is, in particular, highly insensitive to chromatic aberrations. The disadvantage of this focusing scheme, in an ICF scenario, is the relatively short focal length, which requires a design with the lens integrated in the reactor chamber. A very interesting alternative is the use of a transport plasma channel, which can provide the required standoff distance from the pellet. In this case one can exploit the incoherent focusing of an adiabatic lens. The adiabatic lens has an extremely large acceptance both of beam emittance and momentum spread. Two examples of final focusing and transport systems adapted to different accelerator and target designs are presented in detail.

Ring design of the Prague synchrotron for cancer therapy

The paper presents main elements of a dedicated proton synchrotron for hadron therapy. The beam parameters for active scanning of tumours are discussed. The output energy of the beam should be variable in the range 60–220 MeV. The average current of the proton beam is equal to 10 nA. The repetition rate of the accelerator is chosen of 1 Hz to get a spill time for slow extraction of about 500 ms. The timing cycle of the accelerator including the quasi-adiabatic capture process and acceleration is described. The RF gymnastics is utilized to prepare the unbunched beam for slow extraction. The magnetic elements of the ring, compact RF and VCO systems are presented in the paper. The maximum magnet field of the dipole magnet should be 1.2 T and the maximum magnetic field on the pole of the quadrupole lenses should be less than 1 T. The resonator should work on the first harmonic with a frequency from 1.298 MHz till 4.804 MHz. The length of the resonator should be less than 1 m. The maximum voltage on the accelerator gap should be about 2 kV.

Growth and transport of structure-controlled hydrogenated Si clusters for deposition on solid surfaces

Hx+ (n=1, 7, 13) cations were always observed. Of these, the clusters with x=13 were the most stable, having a structure that corresponded to a ring structure with bulk-like sp3 bonding. The grown clusters were extracted as an ion beam from the ion trap through the inside of the quadrupole in the ion trap. The cluster ions extracted were mass-selected and were deflected by a quadrupole lens out of the path of the effusive flow from the cluster growth chamber. The cluster ion beam was slowed to a deposition energy of 1∼100 eV/atom and focused on the sample surface. It was confirmed that the characteristics of the cluster ion beam were controlled by the growth parameters in the ion trap.

An external milli-beam for archaeometric applications on the AGLAE IBA facility of the Louvre museum

External beam lines have been built on numerous IBA facilities for the analysis of works of art to avoid sampling and vacuum potentially detrimental to the integrity of such precious objects. On the other hand, growing interest lies on microprobe systems which provide a high lateral resolution but which usually work under vacuum. Until recently, the AGLAE facility was equipped with separate external beam and microprobe lines. The need of a better spatial resolution in the external beam mode has led us to combine them into a single system which exhibits numerous advantages and allows the analysis of small heterogeneities like inclusions in gemstones or tiny components of composite samples. The triplet of quadrupole lenses bought from Oxford is used to focus the beam. By using a 0.75 μm thick Al foil as the exit window, blowing a helium flow around the beam spot and reducing the window-sample distance below 3 mm, a beam size of about 30 μm can be reached. The experimental setup includes two Si(Li), a HPGe and a Si surface barrier detectors for the simultaneous implementation of PIXE, NRA and RBS. The full description of this device is given as well as a few applications to highlight its capability.

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.

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.

Main parameters of a coaxial electrostatic lens

Coaxial electrostatic lenses are used in combination with a magnetic field in plasma-optical and manometric devices [A. I. Morozov and S. V. Lebedev, in Reviews of Plasma Physics, Vol. 8, M. A. Leontovich (ed.), Consultants Bureau, New York (1980); V. P. Afanas’ev, A. A. Vydrik, L. P. Ovsyannikova, and E. V. Shpak, Sov. Phys. Tech. Phys. 25, 1049 (1980)]. Their employment in systems for transporting beams of high-energy charged particles is also known [P. Krejcik, B. V. King, and I. C. Kelly, Optik (Stuttgart) 55, 385 (1980)], since, along with quadrupole lenses, they have a large optical strength. Expressions for the trajectories of charged low-energy particles were obtained by L. P. Ovsyannikova and S. V. Pasovets [Sov. Phys. Tech. Phys. 32, 1422 (1987)] in the approximation of a rectangular field model with consideration of the variation of the energy at the entrance and exit from the field. The possibility, in principle, of focusing a parallel beam in a ring is demonstrated.

Ion optics for multi-turn time-of-flight mass spectrometers with variable mass resolution

The ion optics of multi-turn time-of-flight (TOF) mass spectrometry was investigated. Two feasible systems using toroidal sector plus quadrupole lenses and cylindrical sectors plus quadrupole doublets were found. The combination of a linear TOF with a figure-of-eight type multi-turn system is proposed. © 1997 John Wiley & Sons, Ltd.

Development and characterization of an electrospray ionization ion trap/linear time-of-flight mass spectrometer

On-line analysis of compounds from solution has been greatly facilitated by the advent of electrospray ionization mass spectrometry (ESI-MS). Although quadrupole mass analyzers are most commonly used with ESI at present, time-of-flight (TOF) mass spectrometers offer several potential advantages including high data acquisition rates, which are desirable for fast separation techniques. One method of coupling ESI and TOF uses an ion trap for temporary storage and accumulation of the electrosprayed ions prior to TOF mass analysis. Previous studies have not fully addressed the effects of several key variables on the analytical capabilities of this type of instrument. In this study, the characterization of an ion trap/linear TOF instrument for ESI is described. The behavior of various analytes is divided into two separate groups; each one is found to have its own optimal set of operating conditions. The reasons for the observed differences between groups are explored. Issues relevant to mass resolution, sensitivity, mass range, mass-to-charge ratio discrimination, and mass measurement accuracy are addressed. Finally, it is suggested that the analytical capability of this type of instrument could be significantly improved by changing the ion optics from the existing focusing lenses to a rf-only quadrupole lens.

Experiments with field-emitter arrays for free electron micro-laser applications

Propagation characteristics of beams extracted from double-gated field-emitter arrays (FEAs) were investigated. The beams were accelerated to several keV in a 15-mm long gun region and the whole beam traversed a distance of 1 m. Separate images of emitting tips were formed, when operating the focus lens of FEAs, on a fluorescent screen located at the downstream end. The images became clearer when the beam focusing was assisted by either an electrostatic or magnetic lens arranged in the transport system. A quadrupole lens was employed to determine the emittance diagram of the beam. It was verified that beamlets emitted from the tips were distributed on a straight line in the transverse trace plane. Normalized emittance of the beam thus obtained was a few times 10 −7 π m rad, independently of the beam current within a measured range of 10 nA–50 μA.

Field reconstruction technique for testing magnetic quadrupole lenses

A number of analytical instruments make use of strong magnetic quadruple lenses. Performance properties of such instruments are determined by the presence of lens aberrations that arise from the structure of the lens magnetic field. This paper describes a technique for reconstruction and analysis of the 3-D field of the magnetic quadrupole lens. Measurements of the radial B r or longitudinal B z component of the field are used as boundary conditions for the Laplace equation for magnetic scalar potential. Application of the charged density method for the solution of the boundary-value problem allows the field and its multipole components to be determined to a high accuracy. The field reconstruction technique can be used for determination of both intrinsic and parasitic multipole components of the field in a magnetic quadrupole lens. This technique is suitable either for a single magnetic multipole lens or for a magnetic multipole lens system.

Analysis of the fringe field region of magnetic quadrupole lenses: field measurements and ion optical calculations

An investigation into the minimisation of the duodecapole fringe field components of magnetic quadrupole lenses has been conducted at Melbourne. As part of this program, a detailed field mapping of the fringe field region of the Melbourne magnetic quadrupole lenses has been conducted (G.R. Moloney, D.N. Jamieson and G.J.F. Legge, Nucl. Instr. and Meth. B 54 (1991) 24). The field mapping technique measures the radial magnetic field component, B r over the three cylindrical coordinates, r, α and z. We have also conducted a program of modifying the pole tip termination of the lenses to reduce the duodecapole field components. Complete magnetic field measurements for the modified lens pole tips have been presented previously (G.R. Moloney, D.N. Jamieson and G.J.F. Legge, Nucl. Instr. and Meth. B 77 (1993) 35–38). This paper presents an Ion Optical analysis of the effects of the fringe field components on the beam optics of the Melbourne Microprobe systems. The optical effects are calculated with a new computer code developed at Melbourne. Standard numerical ray tracing is performed utilising Runge-Kutta techniques.