Magnetic Cavity Research Articles

Baseband simulation model of the vector rf voltage control system for the J-PARC RCS

Vector rf voltage feedback control for the wideband magnetic alloy cavity of the J-PARC RCS is considered to be employed to compensate the heavy beam loading caused by high intensity proton beams. A prototype system of multiharmonic rf vector voltage control has been developed and is under testing. To characterize the system performance, full rf simulations could be performed by software like Simulink, while the software is proprietary and expensive. Also, it requires much computing power and time. We performed the simplified baseband simulations of the system in z-domain by using free software, the Python control library. It seems to be beneficial for searching the parameters that the baseband simulation can be performed quickly. In this presentation, we present the setup and results of the simulations. The simulations well reproduce the open and closed loop responses of the prototype system.

Wafer-Level Electrically Detected Magnetic Resonance: Magnetic Resonance in a Probing Station.

We report on a novel semiconductor reliability technique that incorporates an electrically detected magnetic resonance (EDMR) spectrometer within a conventional semiconductor wafer probing station. EDMR is an ultrasensitive electron paramagnetic resonance technique with the capability to provide detailed physical and chemical information about reliability limiting defects in semiconductor devices. EDMR measurements have generally required a complex apparatus, not typically found in solid-state electronics laboratories. The union of a semiconductor probing station with EDMR allows powerful analytical measurements to be performed within individual devices at the wafer level. Our novel approach replaces the standard magnetic resonance microwave cavity or resonator with a small non- resonant near field microwave probe. Using this new approach we have demonstrated bipolar amplification effect and spin dependent charge pumping in various SiC based MOSFET structures. Although our studies have been limited to SiC based devices, the approach will be widely applicable to other types of MOSFETs, bipolar junction transistors, and various memory devices. The replacement of the resonance cavity with the very small non- resonant microwave probe greatly simplifies the EDMR detection scheme and allows for the incorporation of this powerful tool with a wafer probing station. We believe this scheme offers great promise for widespread utilization of EDMR in semiconductor reliability laboratories.

Research on the method of measuring solution concentration based on the magneto-optical effect in permanent magnetic fields

In the magnetic fields built by neodymium–iron–boron (NdFeB) permanent magnets, the corresponding relationship among the concentration of sodium chloride solution, glucose solution and their magnetic rotation angles was researched in the temperature range 20–24°C. A helium–neon (He–Ne) laser with a wavelength of 632.8 nm was used in the experiment as light source. A new device is designed for assembling and adjusting the NdFeB permanent magnets. The permanent magnets have no thermal effect compared to an energized solenoid. The corresponding relationship between the concentration and rotation angle is calibrated by standard concentration gradient solutions. Then the concentration can be detected by using this relationship. The rotation angle of the solution is proportional to the concentration and increased with an increase of the magnetic induction intensity. In the magnetic cavity with Φ12 mm dimension, the rotation angles of sodium chloride solutions in the range 0–30 g/100 ml vary from 2.66° to 3.73° and their relative errors range from −1.39% to 1.34%. The rotation angles of glucose solutions in the range 0–50 g/100 ml vary from 2.66° to 26. 44° and their relative errors range from −0.55% to 1.00%. The uncertainty of this system is 0. 05°.

Dynamic unmagnetized plasma in the diamagnetic cavity around comet 67P/Churyumov–Gerasimenko

The Rosetta orbiter witnessed several hundred diamagnetic cavity crossings (unmagnetized regions) around comet 67P/Churyumov–Gerasimenko during its two year survey of the comet. The characteristics of the plasma environment inside these diamagnetic regions are studied using in situ measurements by the Rosetta Plasma Consortium instruments. Although the unmagnetized plasma density has been observed to exhibit little dynamics compared to the very dynamical magnetized cometary plasma, we detected several localized dynamic plasma structures inside those diamagnetic regions. These plasma structures are not related to the direct ionization of local cometary neutrals. The structures are found to be steepened, asymmetric plasma enhancements with typical rising-to-descending slope ratio of ∼2.8 (±1.9), skewness ∼0.43 (±0.36), mean duration of ∼2.7 (±0.9) min and relative density variation ΔN/N of ∼0.5 (±0.2), observed close to the electron exobase. Similar steepened plasma density enhancements were detected at the magnetized boundaries of the diamagnetic cavity as well as outside the diamagnetic region. The plausible scalelength and propagation direction of the structures are estimated from simple plasma dynamics considerations. It is suggested that they are large-scale unmagnetized plasma enhancements, transmitted from the very dynamical outer magnetized region to the inner magnetic field-free cavity region.

Effects of Lorentz force and induced electrical field on the thermal performance of a magnetic nanofluid-filled cubic cavity

In the present study, the effects of Lorentz force and magnetic field-based inductive electrical field on the thermal performance of a cubic cavity filled with a magnetic nanofluid are investigated. Both the three-dimensional governing equations of fluid flow and heat transfer and the governing equations of continuity of electric current density are solved. To validate the developed code and model, the results obtained from the numerical solutions are compared with the results of the relations that govern the magnetic fluid heat transfer and close agreement is found. The effects of other parameters such as the magnetic field imposing direction and power, nanoparticle volume fraction, and Rayleigh number on the Lorentz force are investigated as well. The results show that the imposing direction of the Lorentz force is vertical to the applied magnetic field and is opposite to the nanofluid velocity. The aforementioned force is considerably influenced by the volume fraction of nanoparticles, magnetic field power and nanofluid velocity. The obtained results show that the Lorentz force has no significant effect on the base fluid thermal performance.

Terahertz emission from the intrinsic Josephson junctions of high-symmetry thermally-managed Bi2Sr2CaCu2O8+δ microstrip antennas

We show for high-symmetry disk, square, or equilateral triangular thin microstrip antennas of any composition respectively obeying C∞v, C4v, and C3v point group symmetries, that the transverse magnetic electromagnetic cavity mode wave functions are restricted in form to those that are one-dimensional representations of those point groups. Plots of the common nodal points of the ten lowest-energy non-radiating two-dimensional representations of each of these three symmetries are presented. For comparison with symmetry-broken disk intrinsic Josephson junction microstrip antennas constructed from the highly anisotropic layered superconductor Bi2Sr2CaCu2O8+δ (BSCCO), we present plots of the ten lowest frequency orthonormal wave functions and of their emission power angular distributions. These results are compared with previous results for square and equilateral triangular thin microstrip antennas.

Nonlinear oscillations of TM-mode gyrotrons

This study investigates the interaction between the relativistic electrons and the waves in cavities with fixed field profiles. Both the transverse electric (TE) and the transverse magnetic (TM) cavity modes are examined, including three first-axial modes, TE011, TM011, and TM111, and two zero-axial modes, TM010 and TM110. The first-axial modes have the same resonant frequency, so a direct comparison can be made. By sweeping the electron pitch factor (α) and the electron transit angle (Θ), the optimal converting efficiency of TM modes occurs at α = 1.5 and Θ = 1.5π, unlike the TE mode of α = 2.0 and Θ = 1.0π. The converting efficiencies of both the first-axial TM modes are much lower than that of TE011 mode. The starting currents of TM011 and TM111 modes are four times higher than that of TE011 mode, indicating that these two TM modes are very difficult to oscillate. This evidences that under the traditional operating conditions, the TM-mode gyrotrons are insignificant. However, the two unique, zero-axial TM modes have relatively high converting efficiency. The highest converting efficiency of TM110 is 27.4%, the same value as that of TE011 mode. The starting currents of TM110 mode and TE011 mode are at the same level. The results suggest that some TM-mode gyrotron oscillators are feasible and deserve further theoretical and experimental studies.

The impact of preoperative magnetic resonance imaging and lumpectomy cavity shavings on re-excision rate in pure ductal carcinoma in situ-A single institution's experience.

The impact of preoperative magnetic resonance imaging (pMRI) and cavity shave margins (CSM) on re-excision rate (RR) in DCIS is unclear. We investigated whether either modality was associated with RR in DCIS. This is a single-institution retrospective study of 295 women undergoing breast conservation surgery for pure DCIS (2010-2013). CSM were the systematic resection of 4-6 margins during lumpectomy whereas selective shave margins (SSM) were the selective resection of 1-3 margins. Patient demographics and clinical characteristics were abstracted. RR was analyzed according to the use of pMRI, SSM, or CSM with respect to three high-volume breast surgeons at our institution. RR was not associated with the use of pMRI (P = 0.87). Any shave margins (P = 0.05), DCIS size (P < 0.001), and DCIS grade (P = 0.14) associated with a lower RR. Of our high-volume surgeons, RR was lower for Surgeon A (P = 0.02). Multivariate analyses showed larger DCIS (OR 1.35, P = 0.005) and practices specific to surgeons B (OR 3.23, P = 0.04) and C (OR 3.57, P = 0.04) increased re-excision odds. SSM/CSM and pMRI use varied among surgeons. Our results suggested the routine use of CSM, not pMRI, could lower re-excision rate, which highlighted a quality improvement opportunity at our institution.

Control of unsteady laser-produced plasma-flow with a multiple-coil magnetic nozzle

We report an experimental demonstration of controlling plasma flow direction with a magnetic nozzle consisting of multiple coils. Four coils are controlled separately to form an asymmetric magnetic field to change the direction of laser-produced plasma flow. The ablation plasma deforms the topology of the external magnetic field, forming a magnetic cavity inside and compressing the field outside. The compressed magnetic field pushes the plasma via the Lorentz force on a diamagnetic current: j × B in a certain direction, depending on the magnetic field configuration. Plasma and magnetic field structure formations depending on the initial magnetic field were simultaneously measured with a self-emission gated optical imager and B-dot probe, respectively, and the probe measurement clearly shows the difference of plasma expansion direction between symmetric and asymmetric initial magnetic fields. The combination of two-dimensional radiation hydrodynamic and three-dimensional hybrid simulations shows the control of the deflection angle with different number of coils, forming a plasma structure similar to that observed in the experiment.

Re-Acceleration of Energetic Particles in Large-Scale Heliospheric Magnetic Cavities

AbstractCase studies show that some energetic particle flux enhancements up to MeV/nuc. observed at 1 AU cannot be treated as a consequence of particle acceleration at shocks or during flares. Atypical energetic particle events (AEPEs) are often detected during crossings of magnetic cavities formed by strong current sheets of various origins in the solar wind. Such cavities confine small-scale magnetic islands (SMIs) produced by magnetic reconnection. SMIs, in turn, trap and re-accelerate energetic particles according to predictions based on the theory of Zank et al. describing stochastic particle energization in the supersonic solar wind via numerous dynamically interacting SMIs. AEPEs possess energies that overlap SEP events and can be an important component in understanding space weather.

Terahertz Emission From Thermally Managed Square Intrinsic Josephson Junction Microstrip Antennas

We show for thin square microstrip antennas that the transverse magnetic electromagnetic cavity modes are greatly restricted in number due to the point group symmetry of a square. For the ten lowest frequency emissions, we present plots of the orthonormal wave functions and of the angular distributions of the emission power obtained from the uniform Josephson current source and from the excitation of an electromagnetic cavity mode excited in the intrinsic Josephson junctions between the layers of a highly anisotropic layered superconductor.

An efficient study of circular microstrip antenna on suspended and composite substrates

In this paper, an efficient full-wave analysis of a circular microstrip patch printed on suspended and composite substrates is performed using a dyadic Green’s function formulation. Galerkin’s technique is used in the resolution of the integral equation of the electric field. The TM set of modes issued, from the magnetic wall cavity model, are used to expand the unknown currents on the circular patch. The radiation patterns are expressed regarding the transforms of the currents. The convergence of the method is proven by calculating the resonant frequencies, half-power bandwidths, and quality factors for several configurations. The computed results are found to be in excellent agreement with those observed in the literature. The numerical results obtained show that the bandwidth increases with the increase in the thickness of the suspended or composite substrates, especially for low permittivity of the second layer. Also, it is demonstrated that the resonant frequencies of the circular microstrip patch on suspended and composite substrates can be adjusted to obtain the maximum operating frequency of the antenna. Finally, the effect of the presence of the second layer under the circular patch on the radiation patterns is also investigated.

An ultra-compact in-situ 3He polarizer for high Q-range SANS: on-beam test and future upgrades

We present an ultra-compact 3He polarizer to be used as a polarization analyzer for separation of incoherent background for soft matter research. The 3He will be polarized in-situ within a very compact, 18 cm long, magnetic cavity that can be placed between the sample and the detector tank of small-angle scattering diffractometer KWS2 at MLZ [1]. This allows for the angular coverage of 38°, that corresponds to the maximal momentum transfer Qmaxλ=0.85 Å−1 for neutrons with wavelength λ=4.5Å. The Qmax can be extended to 1.28 Å−1 following the recent upgrade of KWS2 for neutron wavelength λ=3Å. The optical pumping will be done by the diode laser array bar frequency narrowed by the ultra-compact volume Bragg grating. The full system will be readily hand transportable and thus useful as an instrument add-on.

MHD phase change heat transfer in an inclined enclosure: Effect of a magnetic field and cavity inclination

ABSTRACTThe MHD phase change heat transfer of a phase change substance in the presence of a uniform magnetic field is theoretically studied in a cavity. A fixed grid method associated with the enthalpy–porosity method is utilized. The governing equations are transformed into a non-dimensional form and solved using the finite element method. The impacts of the crucial parameters such as the Hartmann number and the inclination angle on the phase change process are investigated. It is found that any increase in Hartmann number and the inclination angle of the cavity leads to a decrease in the rate of the melting process.

MHD natural convection in an inclined square porous cavity with a heat conducting solid block

This paper deals with natural convection in an inclined porous cavity with a heat conducting solid body placed at its center under the influence of the applied magnetic field of different orientations. The left and right vertical walls of the cavity are maintained at different temperatures Th and Tc, respectively, while the horizontal walls are adiabatic. The governing coupled partial differential equations were solved using a finite volume method on a uniformly staggered grid system. The effects of the inclination angles of the magnetic field and cavity and the Hartmann number on the flow and thermal fields are investigated in detail. Numerical results are presented in terms of isotherms, streamlines and average Nusselt numbers. In general, the results indicate that the inclusion of the magnetic field reduces the convective heat transfer rate in the cavity. It is also found that an increase in the angle of the applied magnetic field produces a non-linear variation in the average Nusselt numbers.

Cavity mode enhancement of terahertz emission from equilateral triangular microstrip antennas of the high-Tc superconductor Bi2Sr2CaCu2O8 + δ

We study the transverse magnetic (TM) electromagnetic cavity mode wave functions for an ideal equilateral triangular microstrip antenna (MSA) exhibiting C3v point group symmetry. When the C3v operations are imposed upon the antenna, the TM(m,n) modes with wave vectors are much less dense than commonly thought. The R3 operations restrict the integral n and m to satisfy , where and for the modes even and odd under reflections about the three mirror planes, respectively. We calculate the forms of representative wave functions and the angular dependence of the output power when these modes are excited by the uniform and non-uniform ac Josephson current sources in thin, ideally equilateral triangular MSAs employing the intrinsic Josephson junctions in the high transition temperature Tc superconductor Bi2Sr2CaCu2, and fit the emissions data from an earlier sample for which the C3v symmetry was apparently broken.

Compact Broadband Directive Slot Antenna Loaded With Cavities and Single and Double Layers of Metasurfaces

In this paper, a compact wideband directive metasurface (MS)-based antenna is proposed. A pair of edge-fed slots, assisted by a fictitious short, is used to excite the MS layer which is made up of a periodic arrangement of rectangular loop-based unit cells along both the $x$ - and $y$ -directions. The proposed MS-based slot antenna is compact and provides good matching over the entire bandwidth with a broadside radiation pattern. A metallic cavity and an artificial magnetic conductor-based cavity are integrated on the MS-based antenna to reduce its backward radiation. Finally, a pair of edge-fed slot antennas combined with two layers of MSs having compact ground plane area of 1.04 $\lambda _{0}^{2}$ ( $\lambda _{0}$ is the operating wavelength in free space) is proposed for the improvement of gain, bandwidth, and forward radiation. The overall antenna has a low profile of 0.05 $\lambda _{0}$ . The proposed configuration shows a 21% measured bandwidth with an average gain of 9.6 dB over its bandwidth. Over its bandwidth, the antenna efficiency is >89%. The design is validated by a full-wave simulation study followed by the experimental verification.

Josephson effect in topological superconducting rings coupled to a microwave cavity

We theoretically study a one dimensional p-wave superconducting mesoscopic ring interrupted by a weak link and coupled inductively to a microwave cavity. We establish an input-output description for the cavity field in the presence of the ring, and identify the electronic contributions to the cavity response and their dependence on various parameters, such as the magnetic flux, chemical potential, and cavity frequency. We show that the cavity response is $4\pi$ periodic as a function of the magnetic flux in the topological region, stemming from the so called fractional Josephson current carried by the Majorana fermions, while it is $2\pi$ periodic in the non-topological phase, consistent with the normal Josephson effect. We find a strong dependence of the signal on the cavity frequency, as well as on the parity of the ground state. Our model takes into account fully the interplay between the low-energy Majorana modes and the gaped bulks states, which we show is crucial for visualizing the evolution of the Josephson effect during the transition from the topological to the trivial phase.

Boosting figures of merit of cavity plasmon resonance based refractive index sensing in dielectric-metal core-shell resonators.

We theoretically investigate the sensing performance of the dielectric-metal core-shell resonators (DMCSRs) that support multipolar sharp magnetic and electric-based cavity plasmon resonances. We show that at the cavity resonances the ability of the DMCSRs to strongly confine the optical fields inside the cavity is robust against the existence of nano-openings in the metal shell layer. As a result, both the perfect DMCSRs having a complete metal shell layer and the non-perfect DMCSRs with nano-openings in the metal shell layers exhibit high refractive index sensitivities of 700 ~1200 nm/RIU. Furthermore, we demonstrate that such high refractive index sensitivities could be well maintained in an array of interconnected non-perfect DMCSRs. The narrow linewidths of the cavity plasmon resonances coupled with their high index sensitivities make the array of non-perfect DMCSRs possess high figure of merit (FOM) values up to ~88, approaching the theoretically estimated upper limit (FOM ≈108) for gold standard prism coupled surface-plasmon sensors.

Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 05: Not all geometries are equivalent for magnetic field Fano cavity tests

The coupling of MRI and radiation treatment systems for the application of magnetic resonance guided radiation therapy necessitates a reliable magnetic field capable Monte Carlo (MC) code. In addition to the influence of the magnetic field on dose distributions, the question of proper calibration has arisen due to the several percent variation of ion chamber and solid state detector responses in magnetic fields when compared to the 0 T case (Reynolds et al., Med Phys, 2013). In the absence of a magnetic field, EGSnrc has been shown to pass the Fano cavity test (a rigorous benchmarking tool of MC codes) at the 0.1 % level (Kawrakow, Med.Phys, 2000), and similar results should be required of magnetic field capable MC algorithms. To properly test such developing MC codes, the Fano cavity theorem has been adapted to function in a magnetic field (Bouchard et al., PMB, 2015). In this work, the Fano cavity test is applied in a slab and ion‐chamber‐like geometries to test the transport options of an implemented magnetic field algorithm in EGSnrc. Results show that the deviation of the MC dose from the expected Fano cavity theory value is highly sensitive to the choice of geometry, and the ion chamber geometry appears to pass the test more easily than larger slab geometries. As magnetic field MC codes begin to be used for dose simulations and correction factor calculations, care must be taken to apply the most rigorous Fano test geometries to ensure reliability of such algorithms.