Good Field Region Research Articles

High-homogeneity double-focusing stigmatic analyzer magnet for electromagnetic isotope separator

An electromagnetic Isotope Separator (EMIS) is used for separating isotopes by magnetic dispersion method. A dipole-bending magnet performs the fundamental function of separation and is an essential building block of EMIS. Unlike mass spectrometers and ion implantation systems, the EMIS prefers ribbon beams for effective mass separation and collection. The bending magnet described in this paper has an inbuilt hexapole and a tunable quadrupole doublet. This magnet separates the charged particles based on the mass-to-charge ratio, performs chromatic correction, and focuses the beam in both axes. All sector magnets focus the beam in the radial direction, the introduction of edge angle results in the vertical focusing of the beam at the expense of radial focusing. The exit pole of the magnet is rotatable for adjusting the focal point. The entry pole is curved for ensuring stigmatism correction in the beam and works like a hexapole. High magnetic field homogeneity is a key requirement for this magnet. This enhances the mass resolution. As per beam simulations, magnetic field non-homogeneity shall not exceed 200 ppm in good field region (GFR) of 200 mm (radial) and 60 mm(vertical). The paper discusses the design, production, installation, testing, and commissioning of a double-focusing Stigmator dipole magnet. A method for achieving low non-homogeneity by using non-magnetic cavities and compensation coils is described and implemented. Very high homogeneity magnets can be designed using this technique. The paper also describes an efficient method for the Magnetic qualification of bending magnets. Based on the design, a double-focusing stigmatic dipole magnet is produced, characterized, and installed.

KoBRA Wien filter for low-energy RI beam production and recoil separation

The Wien filter is one of the key components in ion optics to improve the mass separation performance. The KoBRA Wien filter will be installed at the low-energy beamline KoBRA of RAON in Korea. The specifications of the KoBRA Wien filter were determined based on the ion beams expected in the KoBRA beamline, especially, beam energies less than about 5 MeV/nucleon suitable for nuclear astrophysics experiments. The Wien filter is designed to have the maximum field intensities of 0.2 T for the magnetic field and 2.0 kV/mm for the electric field in the ±75(H)×±50(V)×2500(L)mm3 good-field region. Performance of the Wien filter was estimated by the ion optics calculations of the KoBRA beamline for 40Ar beams at 18.5 MeV/nucleon and 14O beams at 2.5 MeV/nucleon. The mass resolving powers are 42.65 and 517, respectively. Currently, the KoBRA Wien filter is being manufactured, and will perform a factory acceptance test.

Design of dipole magnets for Siam Photon Source II

Two types of dipole magnets are designed for the storage ring of Siam Photon Source II, the second synchrotron light source in Thailand. Magnetic field at the magnet center is 0.87 T, which bends a 3.0 GeV electron beam with the bending radius of 11.532 m and consequently the synchrotron radiation is generated. The first type of dipole magnet is a standard dipole with the magnet gap of 36 mm. The other type is designed for Infrared (IR) beamline with the larger magnet gap of 59 mm to accommodate a wide opening angle of IR radiation. The magnets are designed such that the operating current is the same while the turn number of magnet coils and the magnet gap are allowed to be different. Therefore, a single power supply can be used to excite all dipole magnets in the storage ring which will be connected in series. Magnet modelling and magnetic field calculation are performed in Opera-3D. The magnet poles are shimmed near the edges to improve magnetic field homogeneity to be within the requirement of 2×10−4 within the good field region. Mechanical analysis of magnet structure is performed in SOLIDWORKS and ANSYS where the maximum deformation of 18 - 23 µm is found at the magnet pole and the first-mode natural frequency is higher than 200 Hz.

Concept of scanning magnet with distributed winding coils for particle beam therapy

To reduce the size of a rotating gantry for a particle therapy system, it is desirable to reduce the size of the scanning system by substituting separated scanning magnets with a combined-function scanning magnet. A two-dimensionally designed scanning magnet with distributed winding coils (DW-SCM) is proposed. The DW-SCM can generate a rotating dipole magnetic field using a single power supply. The two-dimensional static magnetic field distributions of the DW-SCM were calculated using poisson superfish code and compared with those of an octupole scanning magnet (CW-SCM) and cos-theta-type scanning magnet ($\mathrm{Cos}\ensuremath{\theta}$-SCM) with the same bore diameter of 98 mm. The calculated two-dimensional magnetic field showed that the DW-SCM had the highest magnetic field strength of the three types of scanning magnets, and compared with the CW-SCM, the DW-SCM was 129% higher and the $\mathrm{cos}\text{ }\ensuremath{\theta}$-SCM was 72% higher. The good field region (radius) of field homogeneity within $\ifmmode\pm\else\textpm\fi{}0.5%$ of the DW-SCM had a symmetrical shape centered on a current phase of 30\ifmmode^\circ\else\textdegree\fi{}, and the minimum value was 24 mm. Also compared with the CW-SCM, the minimum good field region was 11% higher for the DW-SCM and 65% higher for the $\mathrm{cos}\text{ }\ensuremath{\theta}$-SCM. The results indicate that the proposed scanning magnet could generate a high-strength rotating dipole magnetic field, and it might be possible to reduce the size of a scanning system by substituting separated scanning magnets with the DW-SCM.

Superconducting Magnet Development for the HIAF Accelerator Complex

The High Intensity Heavy-ion Accelerator Facility (HIAF) is a new project under construction in China, which will provide beams of stable and unstable heavy ions with high energies, high intensities, and high quality. This paper discusses the superconducting magnet system for this accelerator complex. It will consist of a Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn magnet with the peak field of 12 Tesla for the ECR ion source operated at 45 GHz, 52 solenoids typically 676 mm long with an operating field of 7.5 Tesla for the superconducting Linac called iLinac, 11 superferric dipoles with 320 mm wide good field region, 13 coil-dominated multiplets with an aperture of 320 mm, gradient 13 T/m for the fragment separator HFRS. This paper reports the design and prototype development status of the main components.

Compact and strong window core steering magnets with homogeneous dipole field

A typical axially compact, square window core steering magnet has a very small 2D good field region (GFR) of 18% of the iron core aperture. It is weak with 85% of its dipole in the fringes. Increasing the current fed area (coil) to increase the dipole strength lowers the good field zone. Some novel and simple coil shapes can expand their 2D/3D GFR to 94/40% of the iron aperture. They are axially compact, i.e., stronger with 60–65% of the dipole in fringes. The reduction in error sextupole field is more profound. A novel 2D coil shape with vanished 2D sextupole proves the concept. For axially short cores, a gap between the coil and the iron aperture can increase the 3D sextupole, missing in 2D simulations. A new asymmetric one-axis steering magnet core and coil shape with high dipole field and homogeneity is also given. The new, practical coil shapes significantly improve the dipole field homogeneity and strength of these magnets.

Conceptual Design of DUNE Near Detector Superconducting Magnet System

The Deep Underground Neutrino Experiment (DUNE) formed a near detector design group (NDDG) which was tasked with delivering a CDR by the end of 2019. The DUNE Near Detectors will be housed in an underground hall on the Fermilab site. The two main detector systems are a liquid argon detector and a high-pressure gas time projection chamber (HPgTPC). The HPgTPC requires a magnet that generates a 0.5 T solenoidal magnetic field in a large volume of 6 m diameter, and 5 m length. In this paper, we present a superconducting magnet system design. We investigated: an open air core magnet with three coils, and a five-coil s system having two active fringe field shielding coils. Coils positions were optimized to obtain the specified field homogeneity in the magnet good field region, while minimizing the Lorentz forces and the superconductor volume. We discuss the magnetic, mechanical, and thermal conceptual designs.

Simulation and measurement of electromagnetic undulator prototype for production of THz radiation

This research focused on magnetic field simulation and measurement of an electromagnetic undulator prototype for generation of terahertz (THz) radiation from electron beam with energy of about 10 MeV at the PBP-CMU Electron Linac Laboratory of the Plasma and Beam Physics Research Facility. This undulator prototype has 6.5 periods with a period length of 64 mm. Its magnetic field was measured by using a Hall probe with a measuring system, which its position movement can be precisely controlled with automatic computer interface. The magnetic field of end-poles was compensated by adjusting the end-pole currents. It was found that at the main-pole current of 0.76 A, the optimal end-pole currents at the entrance and exit o f the undulator were 0.27 A and 0.19 A, respectively. At these currents the undulator has the transverse good field region of 19 mm. For magnetic field simulation, the computer program RADIA was used to model the undulator prototype for the ideal design. This was done for comparing the magnetic fields from the simulation and the measurement. The magnetic field of the two cases were not the same because the constructed prototype has different gaps for different lo ngitudinal positions. However, they could give the radiation in the THz regime, which were 97.6 μm for the simulation and 96.7 ± 0.1 μm for the measurement.

Single sided dipole-quadrupole magnet for the Extremely Brilliant Source storage ring at the European Synchrotron Radiation Facility

Combined function magnets with dipole and quadrupole components were designed and built for the Extremely Brilliant Source. These magnets are low power consumption single sided off-axis quadrupoles. The field of the magnets was optimized for particles with a curved trajectory and within an elliptical good field region. A specific moving stretched wire magnetic measurement method was developed for measuring the magnetic length of the magnets, the radius of curvature of the poles and the field multipoles. The effect of the curvature of the magnets on the field multipoles was investigated.

Design and prototyping of simplified multipole magnets

This paper presents the design and prototyping of novel structure magnets–simplified multipole magnets, one octupole and one dodecapole. The field measurements of the prototypes show very good agreement with the numerical field calculations. The octupole prototype can produce either an anti-symmetric or a symmetric field distribution. Magnets with this novel structure can supply much higher saturation fields, e.g. doubled pole-gap strength of 0.6 T for the dodecapole prototype. The intrinsic field errors for the integrated field distribution are within ±1% for a rectangular shape of good field region, which are acceptable for some applications such as beam spot uniformization. Some key technical issues of building the magnets are also discussed. The success of the prototyping will pave the way for applications of the magnet family.

Design and field measurement of a dipole magnet for a newly developed superconducting proton cyclotron beamline

The design, field quality optimization, multipole field analysis, and field measurement of a dipole for a newly developed superconducting proton cyclotron (SC200) beamline are presented in this paper. The maximum magnetic field of the dipole is 1.35 T; the bending radius is 1.6 m with a proton beam energy in the range of 70–200 MeV. The magnetic field was calculated with 2D and 3D simulations, and measured with a Hall mapping system. The pole shim and end chamfer were optimized to improve the field quality. Based on the simulated results, the multipole field components in the good-field region were studied to evaluate the field quality. The results showed that the field quality is better than ± 5 × 10−4 at 1.35 T with shimming and chamfering. For the transverse field homogeneity, the third-order (B3) and fifth-order (B5) components should be controlled with symmetrical shims. The second-order (B2) component was the main disturbance for the integral field homogeneity; it could be improved with an end chamfer. The magnet manufacturing and field measurement were performed in this project. The measurement results demonstrated that the magnetic design and field quality optimization of the 45° dipole magnet can achieve the desired high field quality and satisfy the physical requirements.

Accurate calculation of field quality in conventional straight dipole magnets

In the standard design method of straight dipole magnets, the good field region is symmetric to the magnet mechanical center both in 2D and in 3D, so the obtained field quality is not the actual one because the field integration lines are not consistent with the curved beam paths. In this paper, an improved method for straight dipole magnets aiming at obtaining accurate field quality is proposed. The field quality is calculated by taking into account the relationship of the good field region to the magnet straight geometry. General description of the improved method is introduced, and two application examples of straight dipole magnets are presented to investigate the detailed field quality difference between the improved and traditional methods. The result of the improved method is also compared with the field quality calculated along particle trajectory in OPERA-3D. It is shown that the difference in field quality between the improved and traditional methods cannot be neglected, and the field quality in the improved method is very close to the one calculated along real beam paths. The field quality in the improved method is accurate enough for practical application in a straight dipole magnet.

Simulation of an Octupole Scanning Magnet for Spot Scanning in Proton Therapy

Current proton therapy scanning systems always use two independent dipole magnets for spot scanning in proton therapy. However, the space occupied by these two dipole magnets located after the final gantry bending magnets is very large and increases the overall size of the gantry. In order to construct a compact nozzle and decrease the size of the gantry, we decide to design an octupole scanning magnet to replace these two separate dipole magnets. The octupole scanning magnet, which is completely different from traditional octupole magnet, can generate rotating dipole magnetic field with the change of the loaded sinusoidal current phases. In this paper, we have finished the static optimization of an octupole scanning magnet model, including the length and shape of the poles, the diameter of the gap, and the shims on the pole edges, both in Opera two-dimensional (2-D) and 3-D. The corresponding relationship between the size of the gap and the good field region was also studied. The effect of eddy currents on magnetic field stability was also simulated in Opera 3-D. All the simulation results are presented in this paper.

Longitudinally Variable Field Dipole Design Using Permanent Magnets For CLIC Damping Rings

The latest CLIC damping ring lattice is based on magnets with longitudinally variable dipole fields in order to achieve ultralow beam emittance while keeping the ring circumference small. These magnets need to provide a focusing gradient of 11 T/m as well. The good field region radius is 5 mm. The field harmonics shall be in the order of 1E-4 of the main one. Since only a small variation of the field is requested, permanent magnets are the most cost-effective solution. Beam dynamics calculations have provided idealized field profiles, and magnetic calculations have been performed to check their feasibility. FEM electromagnetic computations are complicated because the cross-section of the magnet is not constant. Therefore, iron poles cannot be modeled by extrusion, and only 3-D computations are meaningful. Finally, this paper shows that small variations of field strength are possible by using movable parts.

Development of a Field Mapper for the Determination of the Multipole Components of the Curved HESR Dipole Magnets

The high-energy storage ring (HESR) will comprise various normal-conducting magnets, in particular 44 dipole magnets each with a length of 4.2 m and a curvature providing the optimum good-field region for antiprotons with a maximum momentum of 15 GeV/c. All the dipole magnets have already been manufactured and delivered. For their quality control a field mapping device has been designed and built, which can be moved automatically along the curved central particle trajectory in order to measure the magnetic fields on a reference radius. From these data, we are able to extract the local multipole components at the required field strengths. Here, we focus on the design of this field mapper and present an example of a field measurement, which will be applied to a subset of the HESR dipole magnets.

Hybrid high gradient permanent magnet quadrupole

This paper presents an innovative compact permanent magnet quadrupole with a strong gradient for potential use in future light source lattices. Its magnetic structure includes simple mechanical parts, rectangular permanent magnet blocks and soft iron poles. It has a wide aperture in the horizontal plane to accommodate an x-ray beam port, a common constraint in storage ring-based light sources. This specificity introduces field quality deterioration because of the resulting truncation of the poles; a suitable field quality can be restored with an optimized pole shape. A $82\text{ }\text{ }\mathrm{T}/\mathrm{m}$ prototype with a bore radius of 12 mm and a 10 mm vertical gap between poles has been constructed and magnetically characterized. Gradient inhomogeneities better than ${10}^{\ensuremath{-}3}$ in the good field region were obtained after the installation of special shims.

A Study on the Optimization of an HTS Quadrupole Magnet System for a Heavy Ion Accelerator Through Evolution Strategy

This paper attempted to use a high-temperature superconductor (HTS) quadrupole magnet in a heavy ion accelerator. In such application, HTS quadrupole magnets are superior to conventional superconducting magnets because their heat loads can be removed more efficiently. Generally, the magnetic field quality of quadrupole magnets is assessed through harmonic analysis. In quadrupole magnets, the second (four-pole) component is the main magnetic field, and the field inhomogeneity is composed of the sixth (12-pole) component, the tenth (20-pole) component, and so on because of its symmetry. Therefore, the harmonic contents in a good field region can be defined to express the field quality of a quadrupole magnet by using higher order components (order > 2) with respect to the second component. In conventional analysis, multipole components can be obtained by a Fourier series of the radial field component. This paper analyzed the difference between radial and azimuthal multipole components. The HTS quadrupole magnet is wound with a rectangular tape and requires specific structures for refrigeration, which increases the harmonics. In this paper, the effects on the harmonic contents in relation to the HTS coil position and the shape of the iron pole were analyzed based on the HTS quadrupole magnet of the RAON system for the Rare Isotope Science Project in Korea. Several parameters were selected in designing the HTS quadrupole magnet system by using the evolution strategy method. Finally, all harmonic contents were optimized, and an HTS quadrupole magnet design was suggested.

Field Measurements of Magnets for Modern SR Sources and FEL

Magnets for modern accelerators and storage rings may have a rather complex field distribution and strict quality requirements. The Budker Institute of Nuclear Physics (Novosibirsk, Russia) is a well-known producer of magnets for various accelerator projects worldwide. This paper describes our magnet measurement facility with examples of NSLS-II booster magnets, small-aperture X-FEL quadrupoles, and PETRA-III dipoles. NSLS-II booster dipoles have quadrupole and sextupole components with a rather high field quality of $1\cdot 10^{-3}$ in the good field region of ±2 cm, providing booster operation at energy from 170 MeV to 3.15 GeV with a 2-Hz repetition rate. We designed a special bench with a ceramic rotation coil to measure X-FEL quadrupoles. The equipment provided measurements of the magnetic axis with accuracy better than 5 $\mu\text{m}$ . We used the system of three temperature-stabilized Hall sensor arrays distributed vertically to obtain a three-dimensional field map from a single measurement of PETRA-III dipole magnets.

Magnetic field characteristics from HTS quadruple magnet of in-flight separator for a heavy ion accelerator

Quadruple magnet is an essential component for the accelerator, and the field uniformity in the good field region reflects the quality of quadruple magnet. In this paper, the total magnetic field B was separated into the coil-induced magnetic field <TEX>$B_s$</TEX> and the iron-induced magnetic field <TEX>$B_c$</TEX> to explain why the total magnetic field B has some inhomogeneity. Using Fourier analysis, harmonic components of <TEX>$B_s$</TEX>, <TEX>$B_c$</TEX> and B have been analyzed at good field region, respectively. The harmonics of multipole magnet and Fourier analysis are helpful to show the uniformity of magnetic field. Several geometries of yoke and coils were defined to analyze the effect on field uniformity of an HTS quadruple magnet. By the analysis, it was found that the sixth harmonics which is the main factor of field inhomogeneity can be reduced to zero. It means that the sixth harmonics of the magnetic field B can be removed by adjusting the geometry of the magnet pole and the position of coils. We expect that this result can effectively improve the uniformity of an HTS quadruple magnet.

Experimental validation for the compensation method of nonlinearities in periodic magnets

Nonlinearities from any periodic magnet in accelerators may strongly degrade the dynamics of the beams. This may be especially critical for magnets where the beam excursions are comparable to the good field region, as for example in wigglers, since the beam trajectory can be of the order of the pole width. A general method based on alternately shifting the magnetic axis of each pole to compensate this effect was proposed and applied to the $\mathrm{DA}\mathrm{\ensuremath{\Phi}}\mathrm{NE}$ wigglers, where an important integrated octupole was measured. This approach has been optimized by multipolar analyses and the effect on the beam dynamics verified by tracking studies. In this paper we report about the experimental validation of the magnetic model and the verification of the method by beam based measurements. The latter were performed after all the wigglers in the $\mathrm{DA}\mathrm{\ensuremath{\Phi}}\mathrm{NE}$ main rings had been modified according to the optimal configuration. These measurements were in agreement with the expectations and allowed experimentally proving the method.