Focusing Magnetic Field Research Articles

Comparison of aggregation effect of axial and polar Magnetotactic bacteria for tumor therapy

Magnetotactic bacteria (MTB), possessing chains of iron oxide nanoparticles, are potential tools for controlled therapy due to their responsiveness to weak magnetic fields. This study aims to evaluate the targeting and aggregation capabilities of axial AMB-1 and polar MO-1 MTB for therapeutic applications. A three-dimensional focusing magnetic field (fMF)-producing device was designed and established with a gradient magnetic field of 0.08 mT/mm at the central region for the guidance of MTB in vitro and in vivo. Under a unidirectional magnetic field, polar Magneto-ovoid MO-1 formed a single line in the culture dish, whereas axial Magnetospirillum magneticum AMB-1 displayed a small portion aggregated on the centerline. With simultaneous X and Y magnetic field application, MO-1 cells aggregated at a point, while AMB-1 bacteria gathered incompletely. Further, magnetic resonance imaging of breast cancer-bearing nude mice injected subcutaneously with MTB peritumorally and navigated by a fMF revealed more substantial aggregation of MO-1 cells within the tumor than AMB-1 bacteria. Prussian blue staining corroborated the penetration of MO-1 cells into the tumor tissue. These findings suggest that polar MO-1 bacteria exhibit superior targeting and aggregation properties compared to axial AMB-1, indicating their potential suitability for targeted therapeutic applications.

Modelling, optimization and application on C-shaped focusing magnetic field excitation device of electromagnetic torque sensor

To enhance accuracy and sensitivity of electromagnetic torque sensor, a highly focusing magnetic field is essential. This paper proposes a C-shaped excitation device designed to focus the magnetic field. The device is enclosed by dual layers of ferromagnetic metal shields. The C-shaped structure directs most of the magnetic field lines through its magnetic core, enhancing the focusing performance. Theoretical analysis of the device’s focusing magnetic field distribution was conducted under three conditions: unshielded, with a single-layer shield, and with a dual-layer shield, using magnetic path analysis techniques. Using COMSOL 6.1 to examine various configurations, we identified the optimal structure for the device. Subsequently, a physical prototype was fabricated, and the magnetic field distribution was measured. Furthermore, an analysis was conducted on the phase differences of the induced voltage generated under its influence. The nonlinearity of the measured phase differences was4.37%.

Gas sheet beam induced fluorescence based beam profile measurement for high intensity proton accelerators

The paper describes the design simulations, developmental details and characterization results of a dual gas sheet generator system for non-invasive beam profile measurement of high-intensity proton beams. The system is being developed for the Low Energy High Intensity Proton Accelerator facility at Bhabha Atomic Research Centre, India. To our knowledge, this is the first time an intense low energy proton beam was used to directly view the beam induced fluorescence of a gas sheet. The system works by generating two thin nitrogen gas sheets which produces fluorescence when a charged particle beam passes through them, thereby providing a visual representation of the beam's intensity profile. The gas sheets are generated at 45° to the beam axis, which allows the fluorescence created by the interaction to be viewed directly through a viewport or camera capture. The beam profile measurements were carried out with a typically 20 keV, 10 mA pulsed proton beam from an ECR ion source under different operating parameters like gas sheet pressure, beam current, beam energy and focusing magnetic field. The Geant4 simulation has been performed to study the scintillation process and optical transport. It may become useful to study methods of reconstructing the beam profile from image obtained.

The Research on the High-Current-Density Shielded Sheet Electron Beam Matching Focusing Magnetic Field

Increasing beam current density is a very effective approach to boost the output power in millimeter wave and terahertz vacuum devices. However, the current density of sheet electron beam (SEB) is severely limited, due to instabilities in the SEB transport, especially in the case of high current density. To overcome this limitation, a new approach for stably transporting a high-current-density SEB, named shielded SEB matching focusing magnetic field (shielded SEB-MFM), is presented in this article. This new focusing magnetic field consists of a small transverse magnetic field and a conventional shielded uniform magnetic field (shielded UM). Compared with the conventional shielded UM, about double the maximum beam current density can be transported by the shielded SEB-MFM, in the same strength as the magnetic field. In addition, an implementable scheme of an electron optical system based on the shielded SEB-MFM is designed and calculated to verify the feasibility of the shielded SEB-MFM. The results indicate that the SEB with a 636-A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula> current density can be well focused by a 0.8-T shielded SEB-MFM in a 40-mm tunnel. To achieve the same expansion degree of thickness, the conventional shielded UM must be around 1.5 T.

Analytical energy eigenvalues of a Dirac particle in focusing field of a quadrupole magnet

In this study, the motion of a charged spin-1/2 fermion is found out. It is assumed, in the system, that the free fermion is subjected to a linearly space-dependent magnetic field that can be supposed to be a focusing magnetic field of a quadrupole magnet in beam dynamics in the accelerator physics. In such an examination, two-component Dirac equation is solved via perturbation approximation of the asymptotic iteration method (AIM), which has been widely used for the last decades. The results show that the fermion is bounded to the magnetic field for a certain condition of the strength of the field. For such a system, the analytical form of the energy eigenvalues are obtained. Moreover, to see whether this analytical expression works properly, the numerical eigenvalues are compared with the ones obtained by direct use of the AIM. We have an inspiration that the studies on beam dynamics and magnet design in particle accelerator physics may gain from this work.

Preliminary Study of a G-Band Extended Interaction Oscillator Operating in the TM31-3π Mode Driven by Pseudospark-Sourced Multiple Electron Beams

This paper presents the first design that combines pseudospark-sourced (PS) electron beams with a multiple-beam extended interaction oscillator (EIO). The PS electron beam is an excellent choice for driving EIOs because it has high current density and does not require a focusing magnetic field. The EIO with coaxial structure adopts the method of multiple electron beams, which plays a crucial role in improving the average output power. At the same frequency, the EIO operating in the high-order TM31-3π mode has a larger cavity size than the EIO operating in the traditional TM01-2π mode. The high-order TM31-3π mode solves the problem of the EIO’s manufacture at high frequency. In order to verify the above points, a G-band PS multiple-beam EIO operating in TM31-3π mode has been designed. The beam–wave interaction particle-in-cell simulation results show that the EIO’s peak output power is 39.2 kW at 217 GHz, and that its efficiency is around 6.1%. The EIO with six pencil beams operates at a voltage of 43 kV. The total current of the six electron beams is 15 A (equally distributed among the six beams), and the corresponding current density is about 5000 A/cm2. Considering the ohmic loss and the effect of skin depth, the conductivity used in these simulations is 2 × 107 S/m. The design is an excellent way to improve the output power of EIO operating at high frequency.

Recent Developments in MaMFIS Technology for the Production of Highly Charged Ions

We present results for the production of highly charged ions in a rippled electron beam propagating in a multi-section drift tube with different electrostatic potentials in an axial magnetic focusing field. The inner-shell ionization of target atoms by electron impact occurs in local ion traps formed at the electron-beam crossovers. The utmost electron current density achieved is assessed at ~10 kA/cm2. The successive ionization of cathode materials and working substances such as xenon and bismuth was investigated as a function of the confinement time. The characteristic X-ray radiation from ions including Ir62+, Ce48+, Xe46+, and Bi60+ was detected. It is shown that it is possible to extract highly charged ions from local ion traps for a certain geometry of the drift tube structure and a certain distribution of the electric potentials.

Investigation of the Increment of Transverse Instability of a Kiloampere Electron Beam in a Linear Induction Accelerator for Its Use in a Terahertz FEL

The Institute of Nuclear Physics SB RAS in cooperation with the Russian Federal Nuclear Center VNIITF performs a series of researches aimed at acquiring a relative electron beam with energy up to 20 MeV, current up to 2 kA, and duration up to 200 ns at normalized emittance ca. 1000 π∙mm∙rad in a linear induction accelerator (LIA). In order to generate electron beams with such parameters we require thorough investigation of all main sources of perturbation of electron beam trajectory caused by different instabilities that occur during the transport and acceleration of a high currency beam in the accelerating structure of LIA. For the experimental series on measuring the dynamics of transverse oscillation of a beam, we applied a set of fast current transformers which are used for registration of beam current and mode fields caused by this beam in the structure. These measurements were performed for the electron beam with the energy of 8.5 MeV and current of 1 kA going through the structure at different modes of focusing magnetic fields size in LIA. As a result, we registered oscillation of the electromagnetic field of normal modes in the accelerating modules of LIA, as well as we determined the dependence of the oscillation amplitude of these modes’ EM field on the number of accelerating module. This dependence was compared with the result of modeling of development dynamics of transverse instability in LIA that was performed using the created program system. This allowed us to determine the size of the increment of transverse instability of a relativistic electron beam under the given experimental conditions. Based on the acquired results, we made the analysis of possibility to use the beam generated in ILA as a driver for the FEL generator of coherent impulses of THz radiation within the frequency range of 0.3–1.2 THz with a sub-gigawatt level of power.

Developments of a Pulse Kicker System for the Three-Dimensional Spiral Beam Injection of the J-PARC Muon g-2/EDM Experiment

The development of a vertical kicker system is an important part of a three-dimensional spiral-injection scheme. The beam injected at a pitch angle of a few tens of degrees was controlled by applying a pulsed magnetic field using a vertical kicker system inside the storage magnet. The stored muon beam then followed a vertical betatron motion around the midplane of the storage magnet owing to the weak focusing magnetic field. Accurate control of the pulsed kick is crucial for minimizing the amplitude of the vertical betatron oscillation. The specifications of the pulsed magnetic field and detailed design of the kicker system at the test beam bench are discussed herein.

Double-mode and double-beam staggered double-vane traveling-wave tube with high-power and broadband at terahertz band

In this paper, a 220 GHz broadband and high-power staggered double-vane traveling-wave tube has been designed and verified. Firstly, a planar double-beam staggered double-vane slow-wave structure is proposed. By using the double-mode operation scheme, the transmission performance and bandwidth have been almost increased with twice as the single mode. Second, to satisfy the high output power requirement and improve the stability of the traveling-wave tube, a double pencil-beam electron optical system has been designed, the 20–21 kV driven voltage and the 2 × 80 mA current are set as the design target. By using the mask portion and the control electrode in the double beam gun, the two pencil beams can be focused with a compression ratio of 7 along their respective centers with narrow distances of about 0.18 mm with good stability. The uniform magnetic focusing system has also been optimized. The stable transmission distance of planar double electron beams could reach 45 mm with the focusing magnetic field of 0.6 T, which was long enough to cover the whole high-frequency system (HFS). Then, to verify the availability of the electron optical system and the performance of the slow-wave structure, particle-in-cell (PIC) simulation has also been carried out with the whole HFS. Results demonstrate that the beam-wave interaction system can get a nearly 310 W peak output power at 220 GHz with a 20.6 kV optimized beam voltage and beam current of 2 × 80 mA, the gain is of 38 dB with the 3-dB bandwidth over 35 dB about 70 GHz. Finally, the high precision microstructures fabrication has been carried out to verify the performance of the HFS, the results show that the bandwidth and the transmission properties are in good agreement with simulation result. Thus, the proposed scheme in this paper is expected to develop the high-power and ultra-wideband terahertz band radiation source with potential applications in the future.

Simulation of High-Power Klystrons with Heterogeneous Focusing Magnetic Field

The work shows a significant effect of the focusing magnetic field on the output characteristics of the klystron. When the calculations are done using nonlinear one-dimensional models, optimization of the parameters makes it possible to obtain versions of devices with the efficiency of 0.8 – 0.9 and higher. However, when testing these options using nonlinear two-dimensional models that take into account the radial motion of electrons, there is a significant discrepancy in the output characteristics obtained from the one-dimensional and two-dimensional models. This is due to the fact that during the motion of the electron beam, the radii of the leading centers of the large particles change the coefficients of interaction of the particle fields with the electromagnetic fields of the resonators change, which leads to a change in the output characteristics of the klystrons: efficiency, output power, and gain. On the other hand, it seemed that setting a large focusing magnetic field to exclude the radial motion of particles could eliminate this drawback, however, another problem arises here - the magnetic system for focusing becomes unacceptably large and it is technically difficult to obtain magnetic induction values of more than 2 T (the weight of the magnetic system can be several hundred kilograms). Therefore, one should choose the magnetic field induction for focusing the electron beam no more than 1T. In this paper, a twodimensional nonlinear mathematical model (2.5D) is proposed that takes into account the azimuthal component in the equations of motion. In the model, the induction of the focusing magnetic field is set in the form of tables. This makes it possible to set the inhomogeneity of the magnetic field at any place in the interaction space of the klystron. The calculation of a powerful relativistic klystron with an accelerating voltage of 1000 kV and the beam current of 250 A was carried out. The use of an inhomogeneous magnetic field makes it possible to reduce the deposition of electrons in the region of the gaps. Therefore, a decrease in the electron deposition leads to an increase in the durability of klystrons.

Research of the Oscillation Start-Up Time in an Extended Interaction Oscillator Driven by a Pseudospark-Sourced Sheet Electron Beam

High current density and high brightness are critical factors for high-power and compact extended interaction oscillators (EIOs) which are operated in the terahertz (THz) waveband. The pseudospark-sourced (PS) sheet electron beam, which combines merits including high current density, a relatively big beam cross-section and no requirement for the external focusing magnetic field, is a good choice for application to high-frequency EIO. The pulse generated by the PS electron beam can last around tens of nanoseconds or even less, thus the EIO’s oscillation start-up time (OST) should be short enough. This paper researched how to reduce OST in an EIO driven by the PS sheet electron beam. The authors realized that the OST of EIO was very sensitive to the gap length under the equal period. The distribution of the electric field is optimized by adjusting the length of the gap. The strong electric field strength is conducive to the beam-wave interaction, and the OST is affected by the beam-wave interaction. When the gap length reaches a suitable value, the OST becomes the shortest. The simulation results showed the EIO’s shortest OST was 8 ns and the corresponding peak output power was 2 kW at 0.19 THz, while the current density was 500 A/cm2. When current density reached 10,000 A/cm2, the shortest OST could even be 1.9 ns.

Design of a Ka-Band Traveling Wave Tube Using Low Turn-On Field Emission Electron Source Made by Carbon Nanotubes

This article designed a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band traveling wave tube (TWT) with the single wall carbon nanotubes (SWCNTs) field emission cathode electron gun. The designed cold-cathode TWT was miniaturized and could instantly startup at room temperature because of the field emission cathode. First, SWCNT cathode was made by imprinting. The field emission measurement results showed that its turn-on field was as low as 0.57 MV/m, and the maximum emission current was about 10 mA. Then, a grid-controlled electron gun with planar field emission cathode was simulated based on the experiment results, which had low operation voltage of the electron gun and would prevent their grid mesh from burning. The optimized electron beam waist radius of the electron gun was 0.15 mm with the structure of the focusing magnetic field. According to experiment and simulation results, we preliminarily designed a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band helix TWT with an average output power of 8.6 W and a gain of 24.6 dB at 28 GHz. The designed miniaturized TWT with a low-operation-voltage field emission cathode electron gun is expected to be used in low-power applications including 5G communication.

Electron-Beam Corkscrew Motion in an Advanced Linear Induction Accelerator

Scorpius is a multipulse linear induction accelerator (LIA) under development for flash radiography. Because it has substantially more cells than present LIAs, higher magnetic focusing fields are needed to suppress beam breakup (BBU). Therefore, it is more susceptible to corkscrew motion of the beam, which also depends on beam energy spread and focusing magnet misalignments. For energy spread and alignment tolerances expected for Scorpius, a magnetic tune designed to suppress BBU is shown to produce corkscrew motion within the range that can be controlled through the use of steering dipoles on existing LIAs. A gap-voltage modulation scheme is shown to almost completely eliminate chromatic effects such as corkscrew.

Study of a hexagonal lattice defect photonic crystal waveguide slow wave structure for G-band traveling wave tube

A defect photonic crystal waveguide (DPCW) slow wave structure (SWS) for G-band traveling wave tube (TWT) is proposed. This DPCW SWS is arrayed in hexagonal lattice with the center defect cells. The TWT based on DPCW SWS operates at 16 kV beam voltage and 120 mA beam current with a 0.6 T focusing magnetic field. A saturated output power of 22.3W, corresponding to a gain of 36.5 dB, is achieved with an input power of 5 mW. The output power is over 10W in a 30 GHz bandwidth. Stable output signal can be achieved without attenuator or sever which shows that the proposed DPCW SWS can depress the oscillation and harmonic in nature. A DPCW SWS sample was fabricated by computer control (CNC) milling, and the measured results show great agreement with the simulation results.

A new approach of using low magnetic field to focus SEB

The transport of sheet electron beam (SEB) is of critical importance for the success of a number of high-power millimeter wave and terahertz vacuum devices. In this paper, the condition to achieve the SEB's stable transport in uniform longitudinal magnetic field is studied. Based on this stability condition, a new approach, named sheet electron beam matching focusing magnetic (SEB-MFM) field, which consists of a longitudinal component and a tiny transverse component, is presented. The SEB-MFM field can be generated by adding extra transversely magnetized magnets to the conventional uniform magnetic (UM) system. For demonstrating the effect of the SEB-MFM field, the simulation work of the SEB-MFM field and conventional UM field is carried out for an electron optical system employing a SEB. The simulation results show that the SEB-MFM field effectively eliminates the instabilities, such as distortion and deformation, arising from the longitudinal magnetic field. In addition, comparing with conventional UM field, the SEB-MFM can achieve the stable and long-distance transport of a SEB with a pretty low magnetic field strength. Finally, a new magnetic system generating SEB-MFM field is designed, fabricated, and measured.

Beam Envelope Stability in an Advanced Linear Induction Accelerator

A new linear induction accelerator (LIA) is under development for multipulse flash radiography. Because it has substantially more cells than present LIAs, higher magnetic focusing fields are needed to suppress beam breakup (BBU). It is, therefore, more susceptible to the parametric beam envelope instability (PEI), which has an instability threshold that has usually been typified by the vacuum phase advance per cell exceeding some large fraction of $\pi $ . Here we derive a threshold criterion for PEI that depends not only on the magnetic field, but also on the beam space charge and emittance. A tune designed to suppress BBU in Scorpius is shown to be stable to the PEI according to this criterion, and also by the lack of emittance growth in particle-in-cell (PIC) code simulations.

Cyclotron trap

The cyclotron trap was developed at SIN/PSI to increase the stopping density of negatively charged particle beams for the formation of exotic atoms in low pressure gases. A weak focusing magnetic field, produced by superconducting solenoids, is used. Particles are injected radially through the fringe field to a moderator, which decelerates them into orbits bound by the field. Further deceleration by moderators and/or low-pressure gases leads the particles to the centre of the device, where they can be stopped or eventually extracted. Experiments became feasible with this technique, such as those dealing with pionic hydrogen/deuterium at SIN/PSI. Muonic hydrogen laser experiments also became possible with the extraction of muons from the cyclotron trap. The formation of antiprotonic hydrogen in low pressure targets led to successful experiments at LEAR/CERN.

Novel S-Band Metamaterial Extended Interaction Klystron

A miniaturized, high electronic efficiency, S-band metamaterial extended interaction klystron (MEIK) is proposed. The metamaterial-based extended interaction resonant cavities were designed, fabricated, and tested, the assembled and cold-tested results confirm the feasibility of miniaturization in MEIK. Furthermore, the particle-in-cell (PIC) simulation predicts that, typically, when the beam voltage and current are 30 kV and 3 A, respectively, the focusing magnetic field is 1000 G, a 3-cavity MEIK yields the output power of 56 kW at 2.453 GHz, with the saturated gain of 47 dB and the electronic efficiency of 62%, and, importantly, with the cavity diameter of its interaction structure being ~1/2 of a conventional extended interaction klystron. As a power amplifier, the emerging MEIK with its miniaturization and high electronic efficiency has potential applications such as in future accelerators and microwave heating systems.

Hybrid High-Power Multiple-Beam Generator With Double-Gap Coupling Resonator System

The results of numerical analysis of a new design of a hybrid powerful microwave generator based on a virtual cathode are presented. Its electrodynamic system is a double-gap resonator with seven transit channels where a multipath electron beam moves. The dimensions of the resonator were chosen in such a way as to provide a monotron effect in the in-phase mode. From an analysis of the Fourier spectra and phase portraits of the output signal oscillations, five characteristic generation regimes were revealed in the considered ranges of the induction of the focusing magnetic field and electron beam current. Oscillations close to single-frequency are observed in one of the regimes (regime A). In other regimes, chaotic oscillations are observed, which differ in spectral composition. From the particle-in-cell (PIC) simulation results, it follows that the generation in regime A occurs at a frequency of the in-phase mode and is characterized by high value efficiency. The maximum efficiency value of 13.6% was obtained with an electron beam current of 3 kA and a focusing magnetic field of 0.7 T.