Sextupole Field Research Articles

Upgrade of the sextupole field for beam instability mitigation in rapid cycling synchrotron of China Spallation Neutron Source

Upgrade of the sextupole field for beam instability mitigation in rapid cycling synchrotron of China Spallation Neutron Source

Design Optimization of Combined Function Accelerator Magnet Using Truncated Singular Value Decomposition

The Japan Proton Accelerator Research Complex (J-PARC) is a world-class accelerator facility for particle and nuclear physics experiments such as the rare kaon decays experiment (KOTO), the T2K long-baseline neutrino experiment, and future projects such as COMET. A new stretcher ring (SR) comprising a combined function superconducting magnet is proposed to run all of the facilities at the same time, which can improve beam efficiency and increase operating time. In order to achieve the field quality requirements on the magnet aperture, it is critical to identify an optimum pole shape. Dipole, quadrupole, and sextupole fields are required for the combined function magnet. To find the best design parameters for this analysis, we employed singular value decomposition. The singular value decomposition (SVD) technique resulted in a solution to the desired parameters and a quick process to obtain a 2D pole profile.

Eddy current and structural analysis of the beam pipe for the BRing dipole magnet

Fast-ramping magnets will be used in the Booster Ring (BRing) of the High-Intensity Heavy Ion Accelerator Facility (HIAF), which is proposed by the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS). The dipole magnet will provide the field quality from the injection field of 0.0496 T up to the maximum value of 1.5786 T, with the maximum ramping rate of 12 T/s. The ramping magnetic field induces eddy currents that give rise to eddy loss and large force on the beam pipe, field delay and sextupole field appear to affect the field quality provided by the BRing dipole. An in-detail understanding of these effects is an essential aspect of the design. Based on the finite-element analysis, a simplified model by use uniform background magnetic field was used to the transient simulations, eddy current and the forces on the pipe at different times on the beam pipe were performed. This paper presents the results obtained for the eddy loss and magnetic field delay for different wall thicknesses. Then, mechanical design details are presented, and also stress distribution, the deformation in the beam pipe. The analysis results revealed that the eddy current and thus the field delay and eddy current-induced Lorentz force scales linearly with the derivative of the magnetic field and the thickness of the pipe. The power losses that cause heating of the pipe is linear with the square of the derivative of the magnetic field and the thickness of the pipe.

Multiobjective optimization of the dynamic aperture using surrogate models based on artificial neural networks

Modern synchrotron light source storage rings, such as the Swiss Light Source upgrade (SLS 2.0), use multi-bend achromats in their arc segments to achieve unprecedented brilliance. This performance comes at the cost of increased focusing requirements, which in turn require stronger sextupole and higher-order multipole fields for compensation and lead to a considerable decrease in the dynamic aperture and/or energy acceptance. In this paper, to increase these two quantities, a multi-objective genetic algorithm (MOGA) is combined with a modified version of the well-known tracking code tracy. As a first approach, a massively parallel implementation of a MOGA is used. Compared to a manually obtained solution this approach yields very good results. However, it requires a long computation time. As a second approach, a surrogate model based on artificial neural networks is used in the optimization. This improves the computation time, but the results quality deteriorates. As a third approach, the surrogate model is re-trained during the optimization. This ensures a solution quality comparable to the one obtained with the first approach while also providing an order of magnitude speedup. Finally, good candidate solutions for SLS 2.0 are shown and further analyzed.

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.

Nonlinear optics from off-energy closed orbits

This paper describes a novel scheme for correcting the second order (chromatic sextupole) magnet lattice and its deployment on a fourth generation multibend achromat electron storage ring. The method is analogous to the well-established linear optics from closed orbits scheme, but uses an off-energy orbit response matrix to characterize the second order optics of a lattice. The matrix is constructed from the difference between two orbit response matrices measured at off-nominal energy, and is approximately linear with chromatic sextupole field strengths. This is utilized in a least squares minimization to find a model which minimizes the difference between the measured and model off-energy orbit response matrix. From this model corrections to the chromatic sextupoles of the machine can be calculated. In effect, for the MAX IV 3 GeV ring, the proposed scheme, NOECO (nonlinear optics from off-energy closed orbits), brings initial sextupole strength variations between achromats in the order of $\ifmmode\pm\else\textpm\fi{}8%$ down to the order of $\ifmmode\pm\else\textpm\fi{}1%$. The chromatic machine functions were symmetrized, the measured chromaticities approached the nominal values, and the lifetime of the beam at delivery conditions, with the same level of emittance coupling, increased to 19 h from 11 h at previously used sextupole settings.

Influence of electron cooling on the polarization lifetime of a horizontally polarized storage ring beam

A previous publication has shown that the in-plane polarization (IPP) component of a polarized 0.97-GeV/c deuteron beam in the COSY storage ring may acquire a polarization half-life in excess of 1000 s through a combination of beam bunching, electron cooling (prior to any spin manipulation), sextupole field adjustment, and a limitation of the beam intensity. This paper documents further tests pointing to additional gains in the IPP lifetime if cooling is active throughout the beam store.

Excitation and Magnetic Field Performances of a Prototype REBCO Sextupole Coil at 4.2 K

A prototype REBa2Cu3Oy (REBCO) sextupole coil was designed and fabricated for the chromaticity correction of an asymmetric–energy collider, named SuperKEKB. The REBCO sextupole coil consists of the six two-layer-rectangular coils, which are wound with a 4-mm-wide coated conductor and impregnated with the epoxy resin. The inner bore radius and coil length are 75 mm and 200 mm, respectively. The designed sextupole field gradient is 200 T/m2 at an operating current of 250 A. We conducted a series of the experiments on the REBCO sextupole coil after the fabrication. In this paper, we present the experimental results of the excitation test and magnetic field measurement at 4.2 K.

Design and optimization of beam optics for a superconducting gantry applied to proton therapy

PurposeProton therapy (PT) is a precise and effective radiotherapy method for tumors. To reduce the weight and footprint of normal conducting gantries applied to PT, a lightweight superconducting (SC) gantry with large momentum acceptance is studied at Huazhong University of Science and Technology. MethodsTo limit the frequency of field changing in SC magnets, a local-achromaticity beamline is designed with large momentum acceptance. Based on the analysis of high order aberrations, the lattice of the gantry beamline is composed of two symmetric bending sections to limit high-order aberrations, and sextupole fields are superimposed to further eliminate dispersion up to second order. ResultsWe presented a second order beam optics design of a SC gantry. The optics fitting is completed with COSY Infinity and the result of particle tracking shows a momentum acceptance of ±8%. Alternating gradient canted-cosine-theta (CCT) magnets are applied to implement combined functions of beam bending and focusing. Some methods are proposed to minimize the field distortion in curved CCT magnets. ConclusionsThe beam optics with high order considerations of a lightweight SC gantry with large momentum acceptance is presented.

Plasma diagnostic tools for ECR ion sources-What can we learn from these experiments for the next generation sources.

The order-of-magnitude performance leaps of ECR ion sources over the past decades result from improvements to the magnetic plasma confinement, increases in the microwave heating frequency, and techniques to stabilize the plasma at high densities. Parallel to the technical development of the ion sources themselves, significant effort has been directed into the development of their plasma diagnostic tools. We review the recent results of Electron Cyclotron Resonance Ion Source (ECRIS) plasma diagnostics highlighting a number of selected examples of plasma density, electron energy distribution, and ion confinement time measurements, obtained mostly with the second-generation sources operating at frequencies from 10 to 18 GHz. The development of minimum-B ECR ion sources based on the superposition of solenoid and sextupole fields has long relied on semiempirical scaling laws for the strength of the magnetic field with increasing plasma heating frequency. This approach is becoming increasingly difficult with the looming limits of superconducting technologies being able to satisfy the magnetic field requirements at frequencies approaching 60 GHz. Thus, we discuss alternative ECRIS concepts and proposed modifications to existing sources that are supported by the current understanding derived from the plasma diagnostics experiments.

J-PARC RCS: high-order field components inherent in the injection bump magnets and their effects on the circulating beam during multi-turn injection

We investigated the cause of the residual beam loss during multi-turn injection of the J-PARC 3-GeV rapid cycling synchrotron (RCS). In the RCS, four sets of injection bump magnets (pulsed dipole magnets) are employed for multi-turn injection. Numerical simulations considering the actual magnetic field profiles of the injection bump magnets well reproduced the empirical beam loss, and pointed that a 3rd-order random betatron resonance driven by a sextupole field component inherent in the injection bump magnets is the major source of the beam loss. In this paper, we describe the detailed mechanism of emittance growth and beam loss caused by such a high-order field component of the injection bump magnets including their correction scenario.

Characterizing and studying the nonlinear beam dynamics performance of Iranian Light Source Facility storage ring

In this paper, we will investigate the nonlinear beam dynamics issues (performance and optimization) of Iranian Light Source Facility storage ring. The strong sextupole fields together with the imperfections in a low emittance machine will result in the large detuning effects and driving the different order of the resonance lines. We have used most recently achievement for the nonlinear optimization of the storage ring. We have optimized the nonlinearity of the lattice by analyzing the resonance driving terms, direct dynamic aperture tracking and frequency map analysis calculations. We have evaluated the performance of the lattice against different imperfections such as magnet misalignments, multipole harmonics, fringe field of the quadrupoles and insertion devices. Furthermore, the effect of the lattice imperfections on the off-momentum particles dynamics has been studied through momentum acceptance and lifetime calculations.

Study of eddy current effect in BRing at HIAF

In the Booster Ring (BRing) of High Intensity heavy ion Accelerator Facility (HIAF), the magnetic field with a ramping speed of 12 T/s will generate non-negligible eddy current in the magnet and the metal vacuum chamber. The eddy current effect will deteriorate the quality of beam. The attenuation and hysteresis effect of magnetic field, eddy loss and eddy-current Lorentz force are analyzed by the code OPERA 3D. Moreover, the effect of eddy-current-induced multi-pole field on the optical parameters is studied by the code MAD. In order to reduce the attenuation and hysteresis effect, the 0.3 mm thick ultra-thin vacuum chamber is selected and the varying curve of magnetic field is corrected. The results show that the maximum temperature of magnet and vacuum chamber caused by eddy loss is below 60.7 °C. The influence of eddy-current Lorentz force on the vacuum chamber is negligible. The chromaticity shift caused by eddy-current-induced sextupole field is large, and the strength of sextupole-correction magnets is modified to fulfill the requirement of chromaticity correction.

Superconducting ECR ion source: From 24-28 GHz SECRAL to 45 GHz fourth generation ECR.

The development of superconducting ECR source with higher magnetic fields and higher microwave frequency is the most straight forward path to achieve higher beam intensity and higher charge state performance. SECRAL, a superconducting third generation ECR ion source, is designed for 24-28 GHz microwave frequency operation with an innovative magnet configuration of sextupole coils located outside the three solenoids. SECRAL at 24 GHz has already produced a number of record beam intensities, such as 40Ar12+ 1.4 emA, 129Xe26+ 1.1 emA, 129Xe30+ 0.36 emA, and 209Bi31+ 0.68 emA. SECRAL-II, an upgraded version of SECRAL, was built successfully in less than 3 years and has recently been commissioned at full power of a 28 GHz gyrotron and three-frequency heating (28 + 45 + 18 GHz). New record beam intensities for highly charged ion production have been achieved, such as 620 eμA 40Ar16+, 15 eμA 40Ar18+, 146 eμA 86Kr28+, 0.5 eμA 86Kr33+, 53 eμA 129Xe38+, and 17 eμA 129Xe42+. Recent beam test results at SECRAL and SECRAL II have demonstrated that the production of more intense highly charged heavy ion beams needs higher microwave power and higher frequency, as the scaling law predicted. A 45 GHz superconducting ECR ion source FECR (a first fourth generation ECR ion source) is being built at IMP. FECR will be the world's first Nb3Sn superconducting-magnet-based ECR ion source with 6.5 T axial mirror field, 3.5 T sextupole field on the plasma chamber inner wall, and 20 kW at a 45 GHz microwave coupling system. This paper will focus on SECRAL performance studies at 24-28 GHz and technical design of 45 GHz FECR, which demonstrates a technical path for highly charged ion beam production from 24 to 28 GHz SECRAL to 45 GHz FECR.

Simulation, measurement, and mitigation of beam instability caused by the kicker impedance in the 3-GeV rapid cycling synchrotron at the Japan Proton Accelerator Research Complex

The transverse impedance of eight extraction pulsed kicker magnets is a strong beam instability source in the 3-GeV rapid cycling synchrotron (RCS) at the Japan Proton Accelerator Research Complex. Significant beam instability occurs even at half of the designed 1 MW beam power when the chromaticity ($\ensuremath{\xi}$) is fully corrected for the entire acceleration cycle by using ac sextupole (SX) fields. However, if $\ensuremath{\xi}$ is fully corrected only at the injection energy by using dc SX fields, the beam is stable. In order to study realistic beam instability scenarios, including the effect of space charge and to determine practical measures to accomplish 1 MW beam power, we enhance the orbit particle tracking code to incorporate all realistic time-dependent machine parameters, including the time dependence of the impedance itself. The beam stability properties beyond 0.5 MW beam power are found to be very sensitive to a number of parameters in both simulations and measurements. In order to stabilize a beam at 1 MW beam power, two practical measures based on detailed and systematic simulation studies are determined, namely, (i) proper manipulation of the betatron tunes during acceleration and (ii) reduction of the dc SX field to reduce the $\ensuremath{\xi}$ correction even at injection. The simulation results are well reproduced by measurements, and, as a consequence, an acceleration to 1 MW beam power is successfully demonstrated. In this paper, details of the orbit simulation and the corresponding experimental results up to 1 MW of beam power are presented. To further increase the RCS beam power, beam stability issues and possible measures beyond 1 MW beam power are also considered.

Connection between zero chromaticity and long in-plane polarization lifetime in a magnetic storage ring

In this paper, we demonstrate the connection between a magnetic storage ring with additional sextupole fields set so that the x and y chromaticities vanish and the maximizing of the lifetime of in-plane polarization (IPP) for a 0.97−GeV/c deuteron beam. The IPP magnitude was measured by continuously monitoring the down-up scattering asymmetry (sensitive to sideways polarization) in an in-beam, carbon-target polarimeter and unfolding the precession of the IPP due to the magnetic anomaly of the deuteron. The optimum operating conditions for a long IPP lifetime were made by scanning the field of the storage ring sextupole magnet families while observing the rate of IPP loss during storage of the beam. The beam was bunched and electron cooled. The IPP losses appear to arise from the change of the orbit circumference, and consequently the particle speed and spin tune, due to the transverse betatron oscillations of individual particles in the beam. The effects of these changes are canceled by an appropriate sextupole field setting.16 MoreReceived 23 October 2017DOI:https://doi.org/10.1103/PhysRevAccelBeams.21.024201Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeam diagnosticsBeam polarizationLow-energy multiple-particle dynamicsAccelerators & Beams

A concept for canceling the leakage field inside the stored beam chamber of a septum magnet

The Advanced Photon Source (APS) is planning to upgrade its storage ring from a double-bend achromat to a multi-bend achromat lattice as part of the APS Upgrade Project (APS-U). A swap-out injection scheme is planned for the APS-U in order to keep the beam current constant and to reduce the dynamic aperture requirements. The injection scheme, combined with the constraints in the booster to storage ring transfer region of the APS-U, results in requiring a septum magnet which deflects the injected 6 GeV electron beam by 89 mrad, while not appreciably disturbing the stored beam. The proposed magnet is straight; however, it is rotated in yaw, roll, and pitch from the stored beam chamber to meet the on-axis swap-out injection requirements for the APS-U lattice. The concept utilizes cancellation of the leakage field inside the 8 mm x 6 mm super-ellipsoidal stored beam chamber. As a result, the horizontal deflection angle of the 6 GeV stored beam is reduced to less than 1 μrad with only a 2-mm-thick septum separating the stored beam and the 1.06 T field seen by the injected beam. This design also helps to minimize the integrated skew quadrupole and normal sextupole fields inside the stored beam chamber.

Investigation of Gyroscopic Stabilization for Single-Stage Saddle Sextupole Field Electromagnetic Launcher

This paper presents a novel single-stage saddle multipole field electromagnetic launching mode for the realization of projectile linear acceleration with gyroscopic stabilization. The hollow cylindrical projectile with three symmetrical vertical slots can change the eddy current and magnetic field density distribution on the projectile surface. When twisted an angle relative to saddle multipole coils along the circumference, the projectile will be linear accelerated with spinning motion under the action of pulse current. In this paper, analytical calculations and simulation methods were used to analysis this mode, the simulation results indicated that the axial acceleration force and circumferential torque acting on the projectile were generated simultaneously, and an optimal initial twisted angle was existed to make the muzzle rotation speed reach peak. To verify the conceptual feasibility, a single-stage saddle sextupole field electromagnetic launcher was built and tested. The experiment demonstrate that the mode is indeed possible to realize the projectile linear acceleration moving with the gyroscopic stabilization, launching performance can be adjusted by changing the initial voltage or twisted angle, and the experimental results are accordant with the simulation results.

Experiment and Numerical Simulation on Quench Characteristics of ReBCO-Impregnated Coil

The SuperKEKB project underway at KEK will increase the KEKB luminosity by 40 times using nanobeam interaction-region focusing optics. The chromaticity correction of the collision beams is crucial to achieve the high luminosity. Sixteen special sextupole magnets, which can simultaneously produce normal and skew sextupole fields, are required in the 100-m-long straight sections around the interaction point for the chromaticity correction. As a candidate for the sextupoles, a cryocooled high-temperature superconducting (HTS) magnet was proposed and the development has started. In HTS magnets, quench protection is a major concern. Especially for accelerator magnets, reliable quench detection and protection systems are essential. In this study, we have performed heat-induced quench tests and numerical simulations on the ReBCO-impregnated double pancake coils at operating temperatures of 30, 40, and 50 K. Two test coils with different thickness of the copper stabilizer were prepared for the tests to compare the quench characteristics. The hot spot temperature was discussed with the operating conditions and quench detection criteria. The copper stabilizer thickness of the sextupole ReBCO coils was designed by using the validated numerical model.

How to Reach a Thousand-Second in-Plane Polarization Lifetime with 0.97-GeV/c Deuterons in a Storage Ring.

We observe a deuteron beam polarization lifetime near 1000s in the horizontal plane of a magnetic storage ring (COSY). This long spin coherence time is maintained through a combination of beam bunching, electron cooling, sextupole field corrections, and the suppression of collective effects through beam current limits. This record lifetime is required for a storage ring search for an intrinsic electric dipole moment on the deuteron at a statistical sensitivity level approaching 10^{-29} e cm.