Quadrupole Field Research Articles

Permanent Magnet Quadrupole for the Final Focus

The paper presents the general theory of permanent multipole magnets and describes the design of a Halbach-2 type quadrupole magnet as a final focus lens for colliders and similar projects. Optimal positions of permanent magnet segments and conditions for quadrupole field generation are investigated. Characteristics of the quadrupole such as aperture, gradient, gradient integral, length and number of segments are given. The results of measurements and calculations as well as the possibilities for gradient adjustment are discussed.

ECW assisted plasma startup with low toroidal electric field and full metal wall in EAST superconducting tokamak

Abstract Recent experimental results from the EAST superconducting tokamak with a full metal wall (without Li-coating) provide strong support for the ITER startup scheme with electron cyclotron wave (ECW) assistance. Detailed investigations were performed on the impact of different magnetic field geometries, including quadrupolar field configuration (QFC), wide null field configuration (NFC), and trapped particle configuration (TPC). All three configurations enabled the breakdown of neutral gas with ECW pre-ionization. However, in most discharges with QFC, the absence of closed flux surfaces after the breakdown was associated with unsuccessful plasma startups. Conversely, both NFC and TPC achieved successful plasma startups under normal conditions, with TPC demonstrating higher robustness against high impurity levels compared to NFC. Experiments found that the minimum ECW power required for a successful TPC startup is approximately 0.48 MW. Plasma startup failed if the prefill gas pressure exceeded optimal levels for a given ECW power (≥0.48 MW), with the critical gas pressure linearly dependent on the ECW power. Additionally, higher ECW power was required with increased impurity levels. With ECW assistance, the toroidal electric field at R=1.85 m in EAST routine operations (<0.15 V/m) is significantly lower than ITER's maximum value (0.3 V/m), suggesting the possibility of reducing flux consumption and lowering demands on coils and power supplies for ITER.

How Does a Low Surface Brightness Galaxy Form Spiral Arms?

The formation and evolution of spiral arms in low surface brightness galaxies (LSBs) are not well understood. We study the dynamics of spiral arms in two prototypical LSBs, FGC 568-VI and FGC 568-01, using both analytical models and N-body + hydrodynamical simulations. We first consider the disk as a two-component system of gravitationally coupled stars and gas in the force field of a spherical dark matter halo, subjected to local, nonaxisymmetric perturbations. However, no local spirals are formed. We next assume the disk to be a one-component system of stars in the net gravitational potential of a galaxy with a spherical dark matter halo perturbed by a global m = 2 instability. In this case, the growth time for spiral formation was low, equal to 0.78 and 0.96 Gyr, respectively, corresponding to a few dynamical times of the galaxies. Finally, we simulate the LSBs using the N-body + hydrodynamical simulation code RAMSES. Our results show that a quadrupolar field associated with an oblate halo with an axial ratio of 0.7 is necessary to drive a long-lived global spiral in the LSB disks. Further, feedback corresponding to a supernova mass fraction of ∼0.05 is essential to comply with the observed stellar surface density. The simulated spirals survive for about 10 dynamical times and the average pattern speed lies between 10 and 15 km s−1 kpc−1. The spiral arms thus formed are therefore a transient global pattern driven by the tidal field of the oblate dark matter halo.

A numerical approach to levitated superconductors and its application to a superconducting cylinder in a quadrupole field

Abstract Magnetically levitated superconductors in the Meissner state can be utilized as micro-mechanical oscillators with large mass, high quality factors and long coherence times. In previous works analytical solutions for the magnetic field distribution around a superconducting sphere in a quadrupole field have been found and used to derive the trap parameters, while non-spherical geometries have only been investigated in a few idealized cases. However, superconductors of almost arbitrary shape can be used as levitators in a magnetic trap and, as the trap’s properties depend strongly on the superconductor’s shape, allow for a wider parameter regime to be accessed. Finite element models are suitable to obtain the field distribution around arbitrarily shaped superconductors in arbitrary fields, but have not yet been used widely in the context of levitated superconductors. Here we present a simple numerical model for this purpose and use it to calculate the field distribution around cylindrical superconductors in a quadrupole field and to evaluate the trap parameters. We find that the cylindrical shape, compared to spherical levitators, allows for substantially higher trap frequencies and coupling strengths. This in turn reduces the demands on vibration isolation and significantly eases the requirements for feedback cooling to the ground state. The numerical model is provided in a file repository and can easily be adapted to various geometries and trap fields.

Flow structure around a microswimmer at fluid–fluid interface

Living organisms such as bacteria and algae often form biofilms at air–liquid and/or liquid–liquid interfaces. Therefore, it is important to understand the hydrodynamic interaction between the fluid–fluid interface and microorganisms. In the present study, a squirmer model is employed to study the flow field structures around a symmetrically trapped spherical microswimmer at an interface separating two fluids with viscosity contrast. In these simulations, Reynolds ( Re ) and Capillary ( Ca ) numbers are very small, and hence the contribution of inertia and interface deformations are neglected. The squirmer model is validated against the analytical solution obtained by considering a source dipole. It is observed that the flow structure and vorticity distribution around the microswimmers are strongly influenced by the squirmer parameter (β) and viscosity contrast (λ). Furthermore, the interplay between force-dipole and source-dipole along with viscosity contrast leads to a range of flow structures such as symmetric four-lobe and asymmetric quadrupolar flow fields. This flow structure asymmetry around the swimmer is quantified with different steady state orientations (φ). The effect of flow profile on the passive tracer particle transport is explored in terms of trajectories. Specifically, larger values of φ result in more profound curly trajectories.

A simple numerical simulation model can elucidate the key factors for designing a miniaturized ion trap mass spectrometer

BackgroundMiniature ion trap mass spectrometer enables mass-to-charge ratio analysis of ions via quadrupole field in a low vacuum environment. It plays an important role in on-site detection due to its portability and specificity. In order to gain a deeper understanding of the analysis mechanism of miniature ion trap mass spectrometers, a quadrupole MS ion trajectory numerical simulation model (QITNS) is established in this paper for ions trajectory calculation under the action of quadrupole field, exciting field and neutral gas molecule collision. Compared with the existing methods, the model in this paper is simpler and more direct, which effectively explored the effects of dipole excitation and quadrupole excitation on ion manipulation under high background pressure. ResultsThe simulation results demonstrate that high RF amplitude, low auxiliary AC amplitude and quadrupole excitation can effectively improve the isolation resolution. Besides, it clarified the difference between the analysis mechanism of ion trap mass spectrometers under high background pressure (above 13.332 Pa) and absolute vacuum conditions. The relevant results are consistent with the conclusions of previous experiments and other theories, proving the applicability and accuracy of the proposed calculation model and solution method. SignificanceThis research bears the guiding significance for further understanding the mechanism of quadrupole mass spectrometry as well as designing and developing miniature mass spectrometers.

The design and application of magnetic landmark used for magnetic fiducialization of HEPS insertion devices*

Abstract Achieving high performance in synchrotron radiation light sources demands increased precision in fiducialization and alignment of insertion devices (IDs). Conventional sensor systems utilizing Hall probes for high-precision magnetic field measurements face limitations in determining the absolute position of the magnetic center of IDs. In this paper, the Magnetic Landmark (MLK), a novel solution based on a magnetized block structure, is designed to address this challenge. The MLK serves as an intermediary, establishing contact between the magnetic center of IDs and their externally accessible fiducials, thus enabling high-precision alignment. Through analysis of magnetic field distribution, self-calibration precision, and practical application of the MLK, the following conclusions are drawn: when the Hall probe is positioned within 0.5 mm of the magnetic field zero point inside the MLK, the measurement accuracy of the zero point for normal and skew quadrupole magnetic fields reaches 7 and 2 μm, respectively. Additionally, the self-measurement accuracy of the MLK is 10 and 4 μm in the transverse and vertical directions, respectively. These accuracies meet our usage requirements. The MLK demonstrates efficacy in aligning the magnetic center of High Energy Photon Source (HEPS) In-air undulators, achieving alignment accuracies of 16 μm in the transverse direction and 11 μm in the vertical direction, surpassing the 30 μm accuracy stipulated in the physical design. Furthermore, the device proves applicable for measuring the magnetic center of other types of HEPS insertion devices, including Cryogenic undulators.

Simulating charged particles in electromagnetic fields

Relativistic charged particles in electromagnetic fields follow paths that increase in complexity with an increasingly complex field. When traveling in these fields, the particles are acted upon by an electromagnetic force comprised of an electric component and a magnetic component. While solving for these paths in simple electromagnetic fields can be done analytically, the task becomes significantly more difficult when the fields get more complex. Thus, in these situations, numerical methods are required to find solutions. One of the most well-known such methods is the Boris method, which is explored in this paper. Before this method is applied to any complex situations, its accuracy must be ensured by testing on simple cases which are solvable by hand. These cases include a 1D electric field in the direction of the initial velocity of the particle, and a 1D magnetic field perpendicular to the particle's velocity. With the accuracy proven, the method was applied to the cases of a force-free field, a dipolar field, and a quadrupolar field. In the latter two cases the method produced very interesting results that could provide significant insight that would be very difficult to achieve analytically. In the case of the force-free field, however, the method shows some limitations, as a precise cancellation of the force produced by the electric and magnetic fields is required to produce a straight line and the Boris method has some difficulty achieving this, especially when using a large time step.

Fröhlich resonance splitting in hybrid GaN nanowire-Ag nanoparticle structures

Plasmonic nanoparticles (NPs) have attracted significant attention due to their unique optical properties and broad optoelectronic and photonic applications. We investigate modifications of emission in hybrid structures formed by 60 nm silver NPs and GaN planar nanowires (NWs). Bare GaN NWs exhibit photoluminescence (PL) spectra dominated by broad bands peaking at ∼3.44 eV and ∼3.33 eV, attributed to basal plane stacking faults. In hybrids, two new narrow PL lines appear at 3.36 and 3.31 eV, resulting in PL enhancement at these energies. While the 3.36 eV line in hybrid structures can be explained using the Fröhlich resonance approximation based on the electric dipole concept, the appearance of two features at 3.36 and 3.31 eV indicates the splitting of resonance lines. This phenomenon is explained in framework of theoretical model based on the interaction of the dipole with its charge image, taking into account the quadrupole moment of the silver sphere and the quadrupole field of the charge image. A good agreement is obtained between the calculated Fröhlich resonance frequencies and the experimental PL lines in hybrid structures.

Elastic to plastic transition in amorphous solids.

The response of amorphous solids to mechanical loads is accompanied by plasticity that is generically associated with "non-affine" quadrupolar events seen in the resulting displacement field. To develop a continuum theory, one needs to assess when these quadrupolar events have a finite density, allowing the development of a field theory. Is there a transition, as a function of the material parameters and the nature of the loads, from isolated plastic events whose density is zero to a regime governed by a finite density? And if so, what is the nature of this transition? The aim of the paper is to explore this issue. The motivation for the present study stems from recent research in which it was shown that gradients of the quadrupolar fields act as dipole charges that can screen elasticity. Analytically soluble examples of mechanical loading that lead to screening and emergent length scales (that are absent in classical elasticity) have been analyzed and tested. However, "gradients of quadrupolar fields" make sense only when the density of quadrupoles is finite, and hence, the issue is central to this article. The article introduces a notion of polarizability under the strain of Eshelby quadrupoles and concludes that the onset of a density of such quadrupoles with random orientations can only appear when the polarizability is finite.

Dynamic screening by plasticity in amorphous solids.

In recent work it was shown that elasticity theory can break down in amorphous solids subjected to nonuniform static loads. The elastic fields are screened by geometric dipoles; these stem from gradients of the quadrupole field associated with plastic responses. Here we study the dynamical responses induced by oscillatory loads. The required modification to classical elasticity is described. Exact solutions for the displacement field in circular geometry are presented, demonstrating that dipole screening results in essential departures from the expected predictions of classical elasticity theory. Numerical simulations are conducted to validate the theoretical predictions and to delineate their range of validity.

New Avenues for Organic Solar Cells Using Intrinsically Charge-Generating Materials.

The molecular electron acceptor material Y6 has been a key part of the most recent surge in organic solar cell sunlight-to-electricity power conversion efficiency, which is now approaching 20%. Numerous studies have sought to understand the fundamental photophysical reasons for the exceptional performance of Y6 and its growing family of structural derivatives. Though significant uncertainty about several details remains, many have concluded that initially photogenerated excited states rapidly convert into electron-hole charge pairs in the neat material. These charge pairs are characterized by location of the electron and hole on different Y6 molecules, in contrast to the Frenkel excitons that dominate the behavior of most organic semiconductor materials. Here, we summarize the current state of knowledge regarding Y6 photophysics and the key observations that have led to it. We then link this understanding to other advances, such as the role of quadrupolar fields in donor-acceptor blends, and the importance of molecular interactions and organization in providing the structural basis for Y6's properties. Finally, we turn our attention to ways of making use of the new photophysics of Y6, and suggest molecular doping, crystal structure tuning, and electric field engineering as promising avenues for future exploration.

Hall physics during magnetic reconnection with collision effect

The Hall effect, decoupling between the ion and electron motions, is the core mechanism triggering fast reconnection. In plasmas with collision effects such as laboratory facilities, collision can suppress the Hall effect and influence the triggering of fast reconnection. Here, by conducting a series of kinetic simulations with varying collision parameters, we show that collisions can suppress the electron outflow, impairing the quadrupole Hall magnetic field. Besides, collision weakens the inflow of magnetic flux by reducing the charge separation and increasing the thermal pressure at the reconnection site, leading to a reduction of the Hall electric field. As the collisionality becomes larger, the Hall electric field diminishes more easily than the Hall magnetic field. We propose that the quadrupolar Hall magnetic field can be a significant indicator in reflecting Hall reconnection.

Nucleosynthesis in magnetorotational supernovae: impact of the magnetic field configuration

ABSTRACT The production of heavy elements is one of the main by-products of the explosive end of massive stars. A long sought goal is finding differentiated patterns in the nucleosynthesis yields, which could permit identifying a number of properties of the explosive core. Among them, the traces of the magnetic field topology are particularly important for extreme supernova (SN) explosions, most likely hosted by magnetorotational effects. We investigate the nucleosynthesis of five state-of-the-art magnetohydrodynamic models with fast rotation that have been previously calculated in full 3D and that involve an accurate neutrino transport (M1). One of the models does not contain any magnetic field and synthesizes elements around the iron group, in agreement with other CC-SNe models in literature. All other models host a strong magnetic field of the same intensity, but with different topology. For the first time, we investigate the nucleosynthesis of MR-SNe models with a quadrupolar magnetic field and a 90° tilted dipole. We obtain a large variety of ejecta compositions reaching from iron nuclei to nuclei up to the third r-process peak. We assess the robustness of our results by considering the impact of different nuclear physics uncertainties such as different nuclear masses, β−-decays and β−-delayed neutron emission probabilities, neutrino reactions, fission, and a feedback of nuclear energy on the temperature. We find that the qualitative results do not change with different nuclear physics input. The properties of the explosion dynamics and the magnetic field configuration are the dominant factors determining the ejecta composition.

Simulation study of a planar quadrupole mass filter for MEMS mass spectrometer

Micro-electro-mechanical system (MEMS) based mass spectrometry, MEMS mass spectrometry, emerges a new technique branch of miniature mass spectrometry. One of the main challenges hindering the development of MEMS mass spectrometry is the poor compatibility between the complex electrode structure of traditional ion optics and MEMS processes. This paper proposed a planar quadrupole mass filter utilizing a highly simplified stacked-layer structure and film electrodes, which is easy to fabricate with high precision by MEMS surface micromachining. The ion trajectory simulation model of the MEMS mass spectrometry chip involving all necessary ion optics was elaborated for investigating the preliminary performance of the planar quadrupole mass filter. By optimizing the crucial parameters such as the frequency of radio frequency voltage, the ratio of direct current voltage and radio frequency voltage, pre-pole length, main-pole length, and injection kinetic energy, the preliminary simulation result of planar quadrupole mass filter achieved a 1–2 Da peak width (at 50% of peak height) and 20–80% ion transmission efficiency. Importantly, the planar quadrupole mass filter demonstrated a maximum working pressure of 0.1 Pa (using air as the buffer gas), 100 times higher than that of conventional quadrupole mass filters, while maintaining a 0.7–1.8 Da peak width and ∼5% ion transmission efficiency. Additionally, to modify the theoretical formulas for the non-ideal quadrupolar field of planar quadrupole mass filter, a novel approach based on stability diagrams obtained by simulation was also introduced. The pretty good linearity (R2=1) between ion masses in the range of 10 to 100 Da and the corresponding radio frequency voltages was verified through the simulated mass spectra. Notably, the proportional coefficient of ion mass and radio frequency voltage exhibited a minimal 4% deviation between the simulated value (4.7132 V0P/Da) and the calculated value (4.9036 V0P/Da) through the modified formula. In conclusion, the preliminary simulation results demonstrated that the planar quadrupole mass filter possessed moderate performance, high-pressure tolerance, and excellent theoretical consistency, which proved it a promising technology of MEMS mass spectrometry. It can find applications in the fields of gas detection, including the rapid response to hazardous gas emissions and in situ detection of dissolved gases in the deep sea.

Penning-trap eigenfrequency measurements with optical radiofrequency detectors

We use an electric-dipole laser-driven transition to precisely measure the cyclotron-frequency ratios of the pairs Ca+42−Ca+40, Ca+44−Ca+40, and Ca+48−Ca+40 in a 7-tesla Penning trap. A single laser-cooled (T≈1 mK) ion serves, together with photon-counting and photon-imaging units, as a radiofrequency detector covering a broadband frequency spectrum, in the present case from kHz to a few MHz. Such detectors (Ca+40,42,44,48) allow measuring extremely small forces increasing the sensitivity in Penning-trap mass spectrometry. The direct determination of the ions' amplitudes makes a cyclotron-frequency measurement process more robust against inhomogeneities of the magnetic field and/or deviations of the electric quadrupole field due to mechanical imperfections of the trap. Published by the American Physical Society 2024

APMP.QM-S19: Toxic elements in seafood

Main textSeafood is one of the major food resources for human consumption in the world. The CODEX Alimentarius Commission and many jurisdictions have set maximum levels of metallic contaminants in seafood. The use of reliable methods for measurement of metallic contaminants is important in safeguarding the quality of these products and public health.The Supplementary Comparison APMP.QM-S19: Toxic Elements in Seafood was coordinated by the Government Laboratory, Hong Kong, China (GLHK). Four measurands (arsenic, cadmium, mercury and lead) in seafood were chosen. The last CCQM or RMO key comparison / supplementary comparison in the area of metallic contaminants in seafood was organized by GLHK in 2011 (APMP.QM-S5). Hence, it was timely to organize another comparison that covers different measurands. This Supplementary Comparison (APMP.QM-S19) offers different analytical challenges (e.g. in analysis of mercury and a different range of measurands) as compared to the previous comparison. Moreover, it enabled National Metrology Institutes / Designated Institutes (NMIs/DIs) that did not participate in the previous comparisons to demonstrate their measurement competencies.Nineteen institutes participated in APMP.QM-S19. Most participating NMIs/DIs employed microwave-assisted acid digestion for sample dissolution. Inductively coupled plasma mass spectrometry (ICP-MS), including triple quadrupole and sector field, were the most commonly used instrumental techniques. Results of all participating NMIs/DIs were evaluated against the supplementary comparison reference value (SCRV). The SCRV and associated uncertainty were determined from results of NMIs/DIs that participated in the supplementary comparison using methods with demonstrated metrological traceability. Median was used as estimator of the SCRVs. For arsenic, the SCRV was 1.342 mg/kg calculated from 15 participating NMIs/DIs. For arsenic, cadmium, mercury and lead, the SCRVs were 1.342 mg/kg, 0.3630 mg/kg, 0.1230 mg/kg and 0.4101 mg/kg, respectively, calculated from 15, 14, 13 and 11 participating NMIs/DIs.Participating NMIs/DIs that have successfully participated in APMP.QM-S19 have demonstrated measurement capabilities in determining inorganic elements, in a mass fraction range from 0.02 mg/kg to 50 mg/kg in high organic content matrix, including seafood of animal origin and high protein food.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The Leakage Field of the New High-Field Septum Magnets for Fast Extraction in Main Ring of J-PARC

As part of the effort to increase the beam power of the Main Ring (MR) for fast extraction (FX) in J-PARC to 750 kW, five new septum magnets for FX (FX-septa) were installed in the MR in 2022. The most significant goal for the magnets was to achieve an extremely low leakage field in the circulating line. To realize the low leakage field, new pure iron duct-type magnetic shields were mounted in the circulating ducts of the two high-field FX-septa in 2022. In July 2022, we verified that the impact of the leakage field of all of the FX-septa on the 3-GeV circulating beam was below 10% of that of the previous FX-septa. We also measured the leakage field in the circulating ducts of the two high-field FX-septa with new shields in October 2022, and confirmed that the quadrupole field component was reduced to ≈1% of that of the previous high-field FX-septa.

Development of an X-band RF gun with four-feed coupler

With the high accelerating gradient, radiofrequency (rf) gun has a significant feature of suppressing the growth of transverse emittance caused by space charge. Field emission cathodes were first used in vac-uum electronic devices, which do not require the high electron beam intensity, but the compact geometry size of the cathode. A new X-band (11.424 GHz) rf electron gun has been proposed with the highlight of four-feed coupler, which can eliminate the quadrupole field component observed and analysed from the imagine experiment carried on, which have affected the resolu-tion of the imaging system to some content.

The High-Efficiency Calculation and Analysis of Different Quadrupole Fields Based on the Method of Fundamental Solution.

The calculation and analysis of electric fields are indispensable steps in the design of mass spectrometry. In this work, an approach for this calculation was established based on the method of fundamental solution (MFS). It was proved to be much faster and more accurate than the other popular methods, and its optimum parameters were found for the calculation of different quadrupole fields. After this, quadrupole fields with round rods and different shielding covers were computed to investigate the impact of shielding covers, and a strategy of nonequilibrium allocation in the MFS was proposed to further improve the calculational efficiency. Moreover, through field calculation and mass analysis, the performances of the quadrupole fields with rectangular rods and different electrode cross section lengths were demonstrated, and their optimum sizes were also found. The proposed method and results of analysis in this work provided a highly efficient calculational approach and useful instruction for the design of a quadrupole mass filter.