Magnetic Quadrupole Lenses Research Articles

High demagnification probe-forming systems with spherical aberration correction for a nuclear microprobe

Probe-forming systems with high demagnification (up to 900) based on a separated orthomorphic quadruplet of magnetic quadrupole lenses are considered. Spherical aberrations are corrected using an octupole lens system. Three, two, and one lens correctors are used. The calculation of the octupoles parameters was carried out using the Matrizant method. The focusing properties of the systems are determined by optimizing the process of probe formation based on the value of the maximum reduced collimated acceptance in the range of beam spot sizes on the target from 10 to 100 nm. The possibility of implementing the considered systems in experimental setups for various applications is demonstrated by the results of the numerical analysis performed.

HIGH RESOLUTION PROBE-FORMING SYSTEM WITH SPHERICAL ABERRATION CORRECTION FOR NUCLEAR MICROPROBE

A probe-forming system based on a separate orthomorphic quadruplet of magnetic quadrupole lenses with a short working distance is considered, allowing the system demagnification to be significantly increased. Three magnetic octupole lenses are used to correct spherical aberrations. The parameters of the octupole corrector are calculated using the matricant method. The focusing properties of the system are determined by means of a probe formation optimization process based on the value of the maximum reduced collimated acceptance. The calculations performed showed the feasibility of such a probe forming system for microanalysis and proton beam writing technique.

The parameters of radio frequency quadrupole linear accelerator for DARIA project

The new proton linear accelerator (linac) with output energy 13 MeV and 100 mA current is under development at NRC “Kurchatov Institute” - ITEP for DARIA project. The linac consists of Radio-Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) with operating frequency 162.5 MHz. The RFQ is based on 4-vanes structure with shifted coupling windows. DTL has a modular structure and consists of separated individually phased cavities with focusing magnetic quadrupoles located between the cavities. The DTL is based on interdigital H-mode (IHDTL) 5-gaps cavities. The 6D beam matching between RFQ and DTL is provided by magnetic quadrupole lenses and RF-bunchers. The paper presents results of the radio-frequency (RF) design, thermal analyses and RF tuning of RFQ linac accelerating structure.

Upgrade of the external beamline at the microanalytical center of the Jožef Stefan Institute

The existing external beamline at the Microanalytical Centre of the Jožef Stefan Institute (JSI) in Ljubljana has been upgraded in order to extend the capabilities towards in-air PIXE imaging across relatively large sample surface area (∼1 cm2) with lateral resolution of sub 100 µm. For that purpose, a doublet of magnetic quadrupole lenses was installed on the beamline together with the newly designed exit nozzle with a 200 nm Si3N4 exit window resulting finally in ∼ 50 × 50 μm2 lateral resolution. Additionally, an in-vacuum beam chopper was installed before the exit nozzle to measure the proton dose deposited on the sample. The beam characterization results are presented together with the first application from the field of biology, namely quantitative concentration maps of a longitudinal section of a whole thick wheat grain.

Magnetically focused 70MeV proton minibeams for preclinical experiments combining a tandem accelerator and a 3GHz linear post-accelerator.

Radiotherapy plays an important role for the treatment of tumor diseases in two-thirds of all cases, but it is limited by side effects in the surrounding healthy tissue. Proton minibeam radiotherapy (pMBRT) is a promising option to widen the therapeutic window for tumor control at reduced side effects. An accelerator concept based on an existing tandem Van de Graaff accelerator and a linac enables the focusing of 70MeV protons to form minibeams with a size of only 0.1mm for a preclinical small animal irradiation facility, while avoiding the cost of an RFQ injector. The tandem accelerator provides a 16MeV proton beam with a beam brightness of as averaged from 5µs long pulses with a flat top current of 17µA at 200Hz repetition rate. Subsequently, the protons are accelerated to 70MeV by a 3GHz linear post-accelerator consisting of two Side Coupled Drift Tube Linac (SCDTL) structures and four Coupled Cavity Linac (CCL) structures [design: AVO-ADAM S.A (Geneva, Switzerland)]. A 3GHz buncher and four magnetic quadrupole lenses are placed between the tandem and the post-accelerator to maximize the transmission through the linac. A quadrupole triplet situated downstream of the linac structure focuses the protons into an area of (0.1×0.1)mm2 . The beam dynamics of the facility is optimized using the particle optics code TRACE three-dimensional (3D). Proton transmission through the facility is elaborated using the particle tracking code TRAVEL. A study about buncher amplitude and phase shift between buncher and linac is showing that 49% of all protons available from the tandem can be transported through the post-accelerator. A mean beam current up to 19nA is expected within an area of (0.1×0.1)mm2 at the beam focus. An extension of existing tandem accelerators by commercially available 3GHz structures is able to deliver a proton minibeam that serves all requirements to obtain proton minibeams to perform preclinical minibeam irradiations as it would be the case for a complete commercial 3GHz injector-RFQ-linac combination. Due to the modularity of the linac structure, the irradiation facility can be extended to clinically relevant proton energies up to or above 200MeV.

FANM: A software for focus and aberrations of nuclear microprobe

Focus and Aberrations of Nuclear Microprobe (FANM) is a new beam optics package to achieve fast and accurate design of a nuclear microprobe. FANM achieves a balance between speed of focusing and accuracy of high order aberrations. A combined method proposed in FANM is to achieve focusing conditions using a matrix method and to calculate aberration coefficients using a numerical ray tracing method. FANM has two optional optimization algorithms (derivative-free method and particle swarm optimization), offering a powerful choice for multi-variable optimization. Numeric variables in FANM are stored as 64-bit (8-byte) double-precision floating-point values to reduce calculation errors. Results obtained with FANM are compared with six existing computational tools (PRAM, TRANSPORT-PSI, TRANSPORT-PBO, WinTRAX, GEANT4-nanobeam and Zgoubi). The reasons for discrepancies between the different packages are discussed. Calculated currents of magnetic quadrupole lenses obtained with FANM are compared with experimental values of a nuclear microprobe in the National University of Singapore.

PRECISION DOUBLET OF MAGNETIC QUADRUPOLE LENSES FOR ION BEAM FORMATION

The precision doublet of magnetic quadrupole lenses is presented. The doublet yoke and poles made from a single piece of soft magnetic iron. Doublet manufacturing technology provides of alignment of the geometric axes in the lenses with an accuracy of a few microns. The doublet geometry was chosen to obtain the maximum magnetic induction at the poles for a given radius of the lens aperture as a result of numerical simulation. An experimental study of the doublet properties was carried out using a setup for field reconstruction technique for magnetic quadrupole lenses. The relative position of the physical axes of the lenses (the geometrical location of points with zero magnetic induction) and the magnitudes of the parasitic multipole field components were determined.

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.

Beam optics of upgraded high energy heavy ion microbeam in Lanzhou

In order to expand applications of the Lanzhou microbeam the resent improvements were introduced in its slits, lens system and target chamber. In this study a beam optics of the new system was calculated for the 12C+6 ion beam of 966 MeV. To compensate a negative influence of a sector magnet dispersion on the beam dynamics an excitation of the magnetic quadrupole between two bending dipoles was determined. By varying parameters of the final triplet of magnetic quadrupole lenses a set of the microbeam systems with a stigmatic focusing were obtained. The best two of them were selected applying an optimization for a beam collimation by object and divergence slits. Simulation of the beam dynamics after the collimation allowed to determine the slit sizes that provide the highest current in the 1 µm probe on the target for these microbeam systems.Additionally, to improve the beam parameters at the microbeam entrance and then match the system parameters with this beam, the approach of an automatic probe-forming system is proposed. It is aimed at providing the highest possible resolution of the microbeam for the different beam varieties from a cyclotron.

The radiobiology beam line facility at the Centre for Ion Beam Applications, National University of Singapore

A new beam line facility dedicated to investigations into the radiobiology of biological single cells has been constructed at the Centre for Ion Beam Applications, National University of Singapore. This facility, which has a horizontal layout, has some novel features including post lens magnetic ion deflection and scanning and provision for a diamond exit window and confocal fluorescence microscope for high performance online investigations.The radiobiology facility uses a system of Oxford Microbeam compact magnetic quadrupole lenses enabling high demagnifications (up to 123 × 51) at the cell plane, and a relatively short lens to cell distances (22.5 cm). Beam optics and SRIM calculations have indicated a theoretical design performance of up to 450 nm for the proton spot size at the cell surface.To measure the spatial resolution of the proton beam at the cell position, we positioned a gold calibration grid inside the external cell chamber at a position normally occupied by cells. Preliminary results were obtained by scanning a 2 MeV focused beam over a grid and using a surface barrier detector to construct a STIM image of the grid we have measured an in-air spot size of sub-500 nm at the cell position.In this paper, the design of the new radiobiology beam line, preliminary results of resolution tests, as well as presenting first investigations into the damage caused by focused proton beam irradiation of human liver cancer cells by detecting DNA damage markers gamma-H2AX and 53BP1.

The new Sumy nuclear microprobe with single-stage quintuplet lens system

The new Sumy nuclear microprobe for high resolution applications has the same beam line with the present microprobe and uses the same object and aperture collimators. The new probe-forming system is based on five magnetic quadrupole lenses of integrated design with four independent power supplies. It consists of quadrupole doublet of the present microprobe and quadrupole triplet which is allocated after the target chamber of the present microprobe. The electrostatic scanning system of a dog-leg type is located before the triplet. The new target chamber of rectangular design has an optical microscope, secondary electron detector, charged particle detector, target stage and possibility to equip additional devices. Such configuration allows one to install two microprobes for different applications at one beam line, that significantly reduces the cost of the new facility. The present paper describes the status of the new Sumy microprobe, its beam optics and design.

A high excitation magnetic quadrupole lens quadruplet incorporating a single octupole lens for a low spherical aberration probe forming lens system

Abstract This paper describes the design of a new probe forming lens system consisting of a high excitation magnetic quadrupole lens quadruplet that incorporates a single magnetic octupole lens. This system achieves both a high demagnification and a low spherical aberration compared to conventional high excitation systems and is intended for deployment for the Harbin 300 MeV proton microprobe for applications in space science and ion beam therapy. This relative simplicity of the ion optical design to include a single octupole lens minimizes the risks associated with the constructional and operational precision usually needed for the probe forming lens system and this system could also be deployed in microprobe systems that operate with less magnetically rigid ions. The design of the new system is validated with reference to two independent ion optical computer codes.

Long-distance characterization of high-quality laser-wakefield-accelerated electron beams

Beam quality degradation during the transition from a laser wakefield accelerator to the vacuum is one of the reasons that cause the beam transport distortion, which hinders the way to compact free-electron-lasers. Here, we performed transition simulation to initialize the beam parameters for beam optics transport. This initialization was crucial in matching the experimental results and the designed evolution of the beamline. We experimentally characterized properties of high-quality laser-wakefield-accelerated electron beams, such as transverse beam profile, divergence, and directionality after long-distance transport. By installing magnetic quadrupole lenses with tailored strength gradients, we successfully collimated the electron beams with tunable energies from 200 to 600 MeV.

Proton Radiography for the Diagnostics of a Dense Plasma

The possibility of using high-energy proton radiography for dense plasma diagnostics is discussed. The designed telescopic ion optical system for a proton radiography installation with a 1 GeV beam is presented. The schematic diagram of the proton microscope is given. It is shown that the estimate of spatial resolution for the installation obtained with consideration of chromatic aberrations of magnetic quadrupole lenses is limited from below.

A study of GeV proton microprobe lens system designs with normal magnetic quadrupole

Abstract High energy proton irradiation has many applications to the study of radiation effects in semiconductor devices, biological tissues, proton tomography and space science. Many applications could be extended and enhanced by use of a high energy proton microprobe. However the design of a GeV proton microprobe must address significant challenges including beam collimation that minimizes ion scattering and the probe forming lens system for ions of high rigidity. Here we address the probe forming lens system design subject to several practical constraints including the use of non-superconducting normal magnetic quadrupole lenses, the ability to focus 1–5 GeV protons into 5 µm diameter microprobes and compatibility with the beam parameters of GeV proton accelerators. We show that 2, 3 and 4 lens systems of lenses with effective lengths up to 0.63 m can be employed for this purpose with a demagnification up to 58 and investigate the probe size limitations from beam brightness, lens aberrations and machining precision.

The design of the 300 MeV proton microprobe system in Harbin

In Harbin, a 300MeV proton microprobe system is under development for many applications in space science studies including upset studies in microelectronic devices, radiation hardness of materials for satellites and radiation effects in human tissues. The microprobe system, as a component of Space Environment Simulation Research Infrastructure (SESRI), will employ a purpose-built synchrotron to provide the proton beam. Our design goal for the 300MeV proton microprobe is for energy spread 0.1%, emittance 10π mm mrad, intensity 109 per pulse and a probe size of 10μm. A magnetic quadrupole lens system will be used to focus the microprobe with a demagnification of 50. This paper presents a systematic investigation of the ion beam optics to optimize the design. The feasibility of the design for the Harbin system is evaluated by comparison with existing microprobe systems designed for high energy ions.

Precise centering method for triplet of magnetic quadrupole lenses using single rigid frame

Separated probe-forming systems can be applied to enhance the resolution of a scanning nuclear microprobe with a comparatively large working distance to accommodate the detectors at backward angles. In such systems, magnetic quadrupole lenses are placed at the considerable distance and hence require their precise alignment with the beam axes. Violation of this requirement results in a considerable increasing of a spot size on the target for a constant beam current. Positioning of magnetic quadrupole lenses in a doublet can be implemented in a single-unit design, where a yoke and poles of two lenses are made from one piece of soft iron by precise electrical discharge machining. In a case of triplet, lens manufacturing as a single-unit has technological difficulties. A lens triplet configuration presented in this work comprises placement of three single magnetic quadrupole lenses in a single rigid frame. An approach to lens alignment by the magnetic field reconstruction method was developed and successfully realized.

Single-stage quintuplet for upgrading triplet based lens system: Simulation for Atomki microprobe

Among different configurations of lens systems for nuclear microprobes, the most common one is a triplet of magnetic quadrupole lenses. Nowadays, microanalysis and material modification will undoubtedly benefit from an improvement in spatial resolution. This work presents the results of simulations for improvement of the Oxford Triplet lens system at the Atomki microprobe with consideration of its system parameters and measured beam brightness distribution. For this purpose, an additional single-unit doublet of lenses with two power supplies was introduced. Using earlier developed methods, such a quintuplet system was optimized in order to determine the parameters which provided the highest resolution for different current operational modes with the same microprobe geometry. The tolerances for lens positioning accuracy were also calculated. The obtained quintuplet parameters indicate a resolution improvement for the Atomki microprobe compared to the Oxford Triplet system and these results validate further experimental testing of the proposed quintuplet.

Analytical possibilities of highly focused ion beams in biomedical field

At the Centre for Ion Beam Applications (CIBA), a 3.5MV HVEE Singletron™ accelerator serves to provide MeV ion beams (mostly protons or He+) to six state-of-the-art beam lines, four of which are equipped with Oxford triplet magnetic quadrupole lens systems. This facility is used for a wide range of research projects, many of which are in the field of biomedicine. Here we presented a discussion of currently ongoing biomedical work carried out using two beamlines:(a)The Nuclear Microscopy (NM) beamline is mainly used for trace elemental quantitative mapping using a combination of Particle Induced X-ray Emission (PIXE), to measure the trace elemental concentration of inorganic elements, Rutherford Backscattering Spectrometry (RBS), to characterise the organic matrix, and Scanning Transmission Ion Microscopy (STIM) to provide information on the lateral areal density variations of the specimen. Typically, a 2.1MeV proton beam, focused to 1–2μm spot size with a current of 100pA is used.(b)The high resolution single cell imaging beamline is equipped with direct STIM to image the interior structure of single cells with proton and alpha particles of sub-50nm beam spot sizes. Simultaneously, forward scattering transmission ion microscopy (FSTIM) is utilized to generate images with improved contrast of nanoparticles with higher atomic numbers, such as gold nanoparticles, and fluorescent nanoparticles can be imaged using Proton Induced Fluorescence (PIF). Lastly, in this facility, RBS has been included as an option if required to determine the depth distribution of nanoparticles in cells, albeit with reduced spatial resolution.

Magnetic quadrupoles lens for hot spot proton imaging in inertial confinement fusion

Imaging of DD-produced protons from an implosion hot spot region by miniature permanent magnetic quadrupole (PMQ) lens is proposed. Corresponding object-image relation is deduced and an adjust method for this imaging system is discussed. Ideal point-to-point imaging demands a monoenergetic proton source; nevertheless, we proved that the blur of image induced by proton energy spread is a second order effect therefore controllable. A proton imaging system based on miniature PMQ lens is designed for 2.8MeV DD-protons and the adjust method in case of proton energy shift is proposed. The spatial resolution of this system is better than 10μm when proton yield is above 109 and the spectra width is within 10%.