Beam Optics Calculations Research Articles

Design of the beam transport optics of TRIUMF’s new 300 keV H− ion source terminal

An ion beam transport system has been designed to transport a highly intense and bright beam extracted from the H− ion source. This new system will be installed at the new injection terminal for the TRIUMF’s 500 MeV H− cyclotron. The low energy part of the transport section (25 keV) in the injection terminal has been designed with magnetic optical elements in order to maintain space charge neutralization. The injection terminal includes a permanent magnet lens, magnetic steerers, a pulser, a beam dump, and a 300 kV acceleration column with electron and positive ion suppressor rings. Beam optics calculations have been performed, including space charge effects up to 1 mA. The simulation results of the beam optics design are presented in this paper.

Beam line design and beam transport calculation for the μSR facility at RAON

The Rare Isotope Science Project was launched in 2011 in Korea toward constructing the Rare isotope Accelerator complex for ON line experiments (RAON). RAON will house several experimental systems, including the Muon Spin Rotation/Relaxation/Resonance (μSR) facility in High Energy Experimental Building B. This facility will use 600-MeV protons with a maximum current of 660 pμA and beam power of 400 kW. The key μSR features will facilitate projects related to condensed-matter and nuclear physics. Typical experiments require a few million surface muons fully spin-polarized opposite to their momentum for application to small samples. Here, we describe the design of a muon transport beam line for delivering the requisite muon numbers and the electromagnetic-component specifications in the μSR facility. We determine the beam-line configuration via beam-optics calculations and the transmission efficiency via single-particle tracking simulations. The electromagnet properties, including fringe field effects, are applied for each component in the calculations. The designed surface-muon beamline is 17.3 m long, consisting of 2 solenoids, 2 dipoles affording 70° deflection, 9 quadrupoles, and a Wien filter to eliminate contaminant positrons. The average incident-muon flux and spin rotation angle are estimated as 5.2 × 106 μ+/s and 45°, respectively.

Beam optics of a superconducting proton-therapy gantry with a large momentum acceptance

In proton therapy, the last part of the beam transport system is installed on a rotatable gantry, so that the beam can be aimed at the tumor from different angles. Since such a gantry system consists of many dipole and quadrupole magnets, it is typically a 100–200 tons device of more than 10 m in diameter. The use of superconducting (SC) magnets for proton therapy allows gantries to be significantly lighter and potentially smaller, which is attractive for this medical application. In addition to that, SC combined function magnets enable beam optics with a very large momentum acceptance. The latter can be advantageous for patient treatment, since the irradiation time can then be significantly reduced by avoiding magnet current changes. To design such an achromatic system, we performed precise high-order calculations. To reach the required accuracy and to check consistency of the obtained results, we have used different simulation tools in our iterative design approach. Here, we will describe our beam optics calculations in the code COSY Infinity and particle tracking using OPAL (open source software from PSI) in 3D field maps obtained from detailed magnet calculations performed in Opera. Our method has shown to be advantageous in a complicated beam optics study and it reduces the risk of systematic errors in a design.

Large energy acceptance gantry for proton therapy utilizing superconducting technology

When using superconducting (SC) magnets in a gantry for proton therapy, the gantry will benefit from some reduction in size and a large reduction in weight. In this contribution we show an important additional advantage of SC magnets in proton therapy treatments. We present the design of a gantry with a SC bending section and achromatic beam optics with a very large beam momentum acceptance of 15% (corresponding to about 30% in the energy domain). Due to the related very large energy acceptance, approximately 70% of the treatments can be performed without changing the magnetic field for synchronization with energy modulation. In our design this is combined with a 2D lateral scanning system and a fast degrader mounted in the gantry, so that this gantry will be able to perform pencil beam scanning with very rapid energy variations at the patient, allowing a significant reduction of the irradiation time.We describe the iterative process we have applied to design the magnets and the beam transport, for which we have used different codes. COSY Infinity and OPAL have been used to design the beam transport optics and to track the particles in the magnetic fields, which are produced by the magnets designed in Opera. With beam optics calculations we have derived an optimal achromatic beam transport with the large momentum acceptance of the proton pencil beam and we show the agreement with particle tracking calculations in the 3D magnetic field map.A new cyclotron based facility with this gantry will have a significantly smaller footprint, since one can refrain from the standard degrader and energy selection system behind the cyclotron. In the treatments, this gantry will enable a very fast proton beam delivery sequence, which may be of advantage for treatments in moving tissue.

Development of a variable-energy, high-intensity, pulsed-mode ion source for low-energy nuclear astrophysics studies.

The primary challenge in directly measuring nuclear reaction rates near stellar energies is their small cross sections. The signal-to-background ratio in these complex experiments can be significantly improved by employing high-current (mA-range) beams and novel detection techniques. Therefore, the electron cyclotron resonance ion source at the Laboratory for Experimental Nuclear Astrophysics underwent a complete upgrade of its acceleration column and microwave system to obtain high-intensity, pulsed proton beams. The new column uses a compression design with O-ring seals for vacuum integrity. Its voltage gradient between electrode sections is produced by the parallel resistance of channels of chilled, deionized water. It also incorporates alternating, transverse magnetic fields for electron suppression and an axially adjustable beam extraction system. Following this upgrade, the operational bremsstrahlung radiation levels and high-voltage stability of the source were vastly improved, over 3.5 mA of target beam current was achieved, and an order-of-magnitude increase in normalized brightness was measured. Beam optics calculations, structural design, and further performance results for this source are presented.

Low energy ion beam dynamics of NANOGAN ECR ion source

A new low energy ion beam facility (LEIBF) has been developed for providing the mass analyzed highly charged intense ion beams of energy ranging from a few tens of keV to a few MeV for atomic, molecular and materials sciences research. The new facility consists of an all permanent magnet 10GHz electron cyclotron resonance (ECR) ion source (NANOGAN) installed on a high voltage platform (400kV) which provides large currents of multiply charged ion beams. Higher emittance at low energy of intense ion beam puts a tremendous challenge to the beam optical design of this facility. The beam line consists of mainly the electrostatic quadrupoles, an accelerating section, analyzing cum switching magnet and suitable beam diagnostics including vacuum components. The accelerated ion beam is analyzed for a particular mass to charge (m/q) ratio as well as guided to three different lines along 75°, 90° and 105° using a large acceptance analyzing cum switching magnet. The details of transverse beam optics to all the beam lines with TRANSPORT and GICOSY beam optics codes are being described. Field computation code, OPERA 3D has been utilized to design the magnets and electrostatic quadrupoles. A theoretical estimation of emittance for optimized geometry of ion source is given so as to form the basis of beam optics calculations. The method of quadrupole scan of the beam is used to characterize the emittance of the final beam on the target. The measured beam emittance increases with m/q ratios of various ion beams similar to the trend observed theoretically.

Deflection compensation for multiaperture negative ion beam extraction: analytical and numerical investigations

Deflection of negative ion beamlets due to the magnets embedded in the first extraction electrode for the purpose of dumping the co-extracted electrons is a serious issue for multiaperture ion accelerators of neutral beam injectors. Several kinds of magnet arrays which offer the possibility of cancelling ion deflection, employing crossed rows of magnets or even more compact parallel row arrangements, are discussed. A general equation for beamlet deflection is presented here, and the interference of the magnetic deflection and the electrostatic lens steering is carefully calculated; this equation may also include beamlet–beamlet interactions and image charge effects. Analytical expressions are given for the field and the line integrals for the magnet arrays, and these are simplified for beam optics calculations, but still retain an excellent agreement with numerical values. Optimization formulas for the filling fraction xy of the magnets are given, for cancellation of deflection both after the first electrode or after the second accelerating electrode. The latter case is of direct interest for the design of small accelerators (e.g., NIO1), for which compact solutions are proposed, while the former case may approximate well the design of a large accelerator such as MITICA, with a predicted xy = 0.1015 against a numerical optimized value of 0.0975 ± 0.005 in normal conditions. The detailed comparison between simulation results and theory shows that thin lens models are suitable approximations for calculating beam steering. Stability of optimal xy prediction with respect to the first accelerating gap length is shown, and the variation of xy with the voltage is discussed.

Achievement of 500 keV negative ion beam acceleration on JT-60U negative-ion-based neutral beam injector

Hydrogen negative ion beams of 507 keV, 1 A and 486 keV, 2.8 A have been successfully produced in the JT-60U negative ion source with a three-stage accelerator by overcoming a poor voltage holding of the accelerator with large-size grids of ∼2 m2. This is the first result of H− beam acceleration up to 500 keV at a high current of over 1 A. In order to improve the voltage holding capability, the breakdown voltages of the large-size grids and small-size electrodes with uniform and locally strong electric fields were examined by changing the gap length. It was found that the voltage holding of the large-size grids was below half of that of the small-size electrodes with a uniform electric field which was used in the design of the accelerator. This degradation was found to be caused by the local electric field concentrations in addition to the size. Based on the results of the voltage holding tests and beam optics calculations, the gap lengths of the large-size grids were tuned to have a capability to sustain 600 kV. As a result, the gap tuning realized stable voltage holding during beam accelerations without significant degradations of the beam optics and stripping loss. These results indicated that stable 500 keV beam accelerations required for JT-60SA are feasible and this gap tuning is also applicable for the design of ITER accelerator.

Study of 26Al measurement on the Shanghai Mini-cyclotron based AMS

We present a modification to the 14C-dedicated SMCAMS (Shanghai mini-cyclotron based AMS) system to allow the measurement of 26Al for biomedical applications with the existing devices. This is accomplished by determining the turn number, harmonic number and RF frequency theoretically and then making the appropriate orbit programming and beam optics calculation and experimental adjustments. The tests were conducted using pencil graphite (for the carbon pilot beam), Al2O3 powder and metal aluminum to accelerate ions with mass number of 24, 25, 26 and 27. The frequency response curves for those ions are shown. Finally, the Al2O3 standard sample with a known isotope ratio of 1.0 × 10−10 is measured. The 26Al− ions are detected and its frequency response curve shows the peak of 26Al− though very weak is well separated from the most neighboring interfering molecular ions 25MgH−.

The Fudan nuclear microprobe set-up and performance

A new scanning nuclear microprobe has been constructed at the Institute of Modern Physics in Fudan University, to replace the old microbeam system which had been running for more than ten years. The key parts were purchased from Oxford Microbeams Ltd., including triplet quadrupole lens (model OM-150), collimator slits, scanning system, target chamber, and data acquisition system. Ion beams are provided from a NEC 9SDH-2 Tandem accelerator. Three CCD cameras and multiple monitors were installed to assist beam adjust. The design of beam line and beam monitors is described. Beam optics calculations were carried out based on the specific Fudan microprobe system geometry, and the results regarding beam line performance and limitations of the spacial resolution are presented and discussed here. A comparison with experimental results is given as well. About 1.5 μm beam spot size could be achieved with a 3 MeV proton beam at a current of around 10 pA. Recently, the new microprobe is applied to obtain information of fly ash particle, algae cell and otoliths.

A new dual injection system for AMS facility

In order to measure long-lived radioisotopes such as 10Be with high sensitivity using an HVEE model 4130 AMS system, as well as to guarantee 14C measurements of high precision, a new dual injection system for the AMS system is proposed. The proposal is to add a Wien filter located between the ion source system and the recombinator of the HVEE model 4130. When a pulsing voltage is optionally applied to the Wien filter, a sequential injection mode is turned on. The isotopes would alternately pass on different trajectories through the recombinator. When the pulsing voltage and magnetic field are turned off, the Wien filter acts as a field-free drift space and the standard simultaneous injection mode is on. Beam optics calculation show that the new dual injection system will increase the number of radio-nuclides which can be analyzed, keep the high precision capability for radiocarbon dating and achieve high sensitivity for 10Be and 26Al measurements, together with simplifying the layout as compared to existing dual-injector and dual high-energy beam line systems.

A computer code for beam optics calculation — third order approximation*

Abstract To calculate the beam transport in the ion optical systems accurately, a beam dynamics computer program of third order approximation is developed. Many conventional optical elements are incorporated in the program. Particle distributions of uniform type or Gaussian type in the (x, y, z) 3d ellipses can be selected by the users. The optimization procedures are provided to make the calculations reasonable and fast. The calculated results can be graphically displayed on the computer monitor. Supported by National Natural Science Foundation of China (Grant No. 1057009)

Alkali suppression within laser ion-source cavities and time structure of the laser ionized ion-bunches

The chemical selectivity of the target and ion-source production system is an asset for radioactive ion-beam (RIB) facilities equipped with mass separators. Ionization via laser induced multiple resonant steps has such selectivity. However, the selectivity of the ISOLDE resonant ionization laser ion-source (RILIS), where ionization takes place within high temperature refractory metal cavities, suffers from unwanted surface ionization of low ionization potential alkalis. In order to reduce this type of isobaric contaminant, surface ionization within the target vessel was used. On-line measurements of the efficiency of this method is reported, suppression factors of alkalis up to an order of magnitude were measured as a function of their ionization potential. The time distribution of the ion-bunches produced with the RILIS was measured for a variety of elements and high temperature cavity materials. While all ions are produced within a few nanoseconds, the ion-bunch sometimes spreads over more than 100 μs. This demonstrates that ions are confined within high temperature metallic cavities. It is the internal electrical field of these cavities that causes the ions to drifts to the extraction region and defines the dwell time of the ions in the cavity. Beam optics calculations were carried out to simulate the pulse shape of a RILIS ion-bunch and are compared to the actual measurements.

Installation of a 134-sample MC-SNICS ion source at NOSAMS and first results

In April 1999, the National Ocean Sciences AMS (NOSAMS) facility received the shipment of a 134-sample MC-SNICS ion source from the National Electrostatics Corporation (NEC). It replaced one of the two 59-sample spherical ionizer sources (US-AMS Model 3090A, HVEE Model 846). In this paper, we will describe the adaptation of the NEC ion source to the US-AMS/HVEE recombinator injector at NOSAMS. This is the first time that the two leading sputter ion source designs are directly comparable on the same system. We will present ion beam optics calculations for both in comparison with measured results. Once fully operational, the new ion source will assume all of the sputter sample measurements at NOSAMS, while the remaining 59-sample source will be replaced by the newly developed microwave gas ion source. One of the most desirable features of the MC-SNICS design is the smaller cathode geometry. At comparable extracted currents, the surface diameter of the pressed samples is reduced from 1.5 to 1 mm. A new, automatic sample pressing procedure is being developed for this design. This will improve the capability for preparing and analyzing smaller sputter samples (carbon weight <100 μg). Our US-AMS cathodes showed considerable reduction in the extracted currents when the sample diameter was reduced to 1 mm, even with samples of normal size (>200 μg C).

A beam rocking system for the Oxford nuclear microprobe: A new approach to channeling analysis

This paper describes the design and implementation of a beam rocking system for the Oxford nuclear microprobe. This system varies the angle of incidence of a focused MeV ion beam on a sample using two set of dipole scan coils of equal and opposite fields, allowing the sample to remain fixed while the beam is rocked in angle about a small area. This method of producing angle-resolved channeling images and scans does not require any modifications to existing data-acquisition software nor the use of a high-precision motorized goniometer. Beam optics calculation results are presented for a beam rocking system using three different standard microprobe focusing systems. The maximum angular range of this system is 3.15°. Channeling images and measurements of angular rotation in a strained Si 0.90Ge 0.10 Si crystal are presented using this technique.

Sub-micron microbeam apparatus for high resolution materials analyses

The JAERI light-ion microbeam apparatus was constructed for high resolution materials analyses using PIXE, RBS or NRA with sufficient beam current. A minimum beam spot size of 0.3 μm with a beam current of 11 pA was obtained with a doublet quadrupole lens system. Simulation of the beam size and the brightness by using the second order beam optics calculation code shows that a beam size of 0.25 μm with a beam current 100 pA will be theoretically possible in our apparatus connected to an electrostatic accelerator having a voltage stability of 10 −5 and with a energy analyzing system having an energy resolution of 10 −5.

Electron beam optics calculations for rotationally symmetric systems possessing third order aberrations

Based on theory of electron beam optics[1], the beam optical calculations for an immersion lens and a unipotential lens have been performed. The computational results show that the beam optical calculations are consistent to the ray tracing and that the beam emittance is conserved, even if the third order aberrations exist.

Deconvolution of scanning electron microscopy images

AbstractThis paper describes a method of removing blurs in scanning electron microscopy (SEM) images caused by the existence of a finite beam size. Although the resolution of electron microscopy images has been dramatically improved by the use of high‐brightness electron guns and low‐aberration electron lenses, it is still limited by lens aberration and electron diffraction. Both are inevitable in practical electron optics. Therefore, a further reduction in resolution by improving SEM hardware seems difficult. In order to overcome this difficulty, computer deconvolution has been proposed for SEM images. In the present work, the SEM image is deconvoluted using the electron beam profile estimated from beam optics calculation. The results show that the resolution of the deconvoluted image is improved to one half of the resolution of the original SEM image.

A new microbeam formation system

A new concept of a compact microbeam formation system is proposed and being constructed by slightly modifying an existing 400 keV ion accelerator at ULVAC. In this system, an object slit is placed on the high voltage terminal and the acceleration tube incorporated with a quadrupole doublet forms the reduced image on the sample position. The beam acceleration between the object and image results in the image size reduction which is profitably used in this design. The effects of the lens action at the entrance of the acceleration tube are discussed based on the beam optics calculation by using the standard matrix formalism.

A NEW INJECTION LINE FOR THE TWO ECR SOURCES AT SARA

A new injection line for two ECR sources is under construction at SARA. The beam delivered by MINIMAFIOS or FERROMAFIOS has to be transported down to the inflector at the center of the injector cyclotron over a distance of 18 meters. The line includes a 11 m long electrostatic channel. Beam optics calculations and first results of emittance measurements of FERROMAFIOS are presented.