Search results for "Magnetic"

Enhancement of the Multipactor Threshold Inside Nonrectangular Iris

2018

Multipactor breakdown is studied inside the capacitive iris of a rectangular waveguide with a skewed slot along its longitudinal cross section. Both the iris length and height are assumed to be small compared to the electromagnetic wavelength. Therefore, the quasi-static approximation is applied so as to describe the RF field distribution inside the iris gap, whereas a 2-D model is used to analyze the electron motion. The peculiarities of RF field structure are studied using the conformal mapping approach, which shows that the electric field lines can be approximated by circular arcs when the iris length is much larger than its height. The electron motion inside the iris gap is analyzed usi…

Permanent magnet system to guide superparamagnetic particles

2017

A new concept of permanent magnet systems for guiding superparamagnetic particles on arbitrary trajectories is proposed. The basic concept is to use one magnet system with a strong and homogeneous (dipolar) magnetic field to magnetize and orient the particles. A second constantly graded field (quadrupolar) is superimposed to the first to generate a force. In this configuration the motion of the particles is driven solely by the component of the gradient field which is parallel to the direction of the homogeneous field. Then the particles are guided with constant force in a single direction over the entire volume. The direction can be adjusted by varying the angle between quadrupole and dipo…

Synchronous precessional motion of multiple domain in a ferromagnetic nanowire by perpendicular field pulses

2014

Magnetic storage and logic devices based on magnetic domain wall motion rely on the precise and synchronous displacement of multiple domain walls. The conventional approach using magnetic fields does not allow for the synchronous motion of multiple domains. As an alternative method, synchronous current-induced domain wall motion was studied, but the required high-current densities prevent widespread use in devices. Here we demonstrate a radically different approach: we use out-of-plane magnetic field pulses to move in-plane domains, thus combining field-induced magnetization dynamics with the ability to move neighbouring domain walls in the same direction. Micromagnetic simulations suggest …

Piezo-electrical control of gyration dynamics of magnetic vortices

2019

In this work, we first statically image the electrically controlled magnetostatic configuration of magnetic vortex states and then we dynamically image the time-resolved vortex core gyration tuned by electric fields. We demonstrate the manipulation of the vortex core gyration orbit by engineering the magnetic anisotropies. We achieve this by electric fields in a synthetic heterostructure consisting of a piezoelement coupled with magnetostrictive microstructures, where the magnetic anisotropy can be controlled by strain. We directly show the strong impact of the tailored anisotropy on the static shape of the vortex state and the dynamic vortex core orbit. The results demonstrate the possibil…

Erratum: “Concentric transmon qubit featuring fast tunability and an anisotropic magnetic dipole moment” [Appl. Phys. Lett. 108, 032601 (2016)]

2018

Broadband microwave emission spectrum associated with kinetic instabilities in minimum-B ECR plasmas

2017

Plasmas of electron cyclotron resonance ion sources (ECRISs) are prone to kinetic instabilities due to the resonant heating mechanism resulting in anisotropic electron velocity distribution. Frequently observed periodic oscillations of extracted ion beam current in the case of high plasma heating power and/or strong magnetic field have been proven to be caused by cyclotrontype instabilities leading to a notable reduction and temporal variation of highly charged ion production. Thus, investigations of such instabilities and techniques for their suppression have become important topics in ECRIS research. The microwave emission caused by the instabilities contains information on the electron e…

Measurements of the energy distribution of electrons lost from the minimum B-field -- the effect of instabilities and two-frequency heating

2020

Further progress in the development of ECR ion sources (ECRIS) requires deeper understanding of the underlying physics. One of the topics that remains obscure, though being crucial for the performance of the ECRIS, is the electron energy distribution (EED). A well-developed technique of measuring the EED of electrons escaping axially from the magnetically confined plasma of an ECRIS was used for the study of EED in unstable mode of plasma confinement, i.e. in the presence of kinetic instabilities. The experimental data were recorded for pulsed and CW discharges with a room-temperature 14 GHz ECRIS at the JYFL accelerator laboratory. The measurements were focused on observing differences bet…

Analytical induced force solution in conducting cylindrical bodies and rings due to a rotating finite permanent magnet

2020

Abstract Using exact expression of the magnetic field we derive analytical expression for the induced current density and volume force in a solid conducting cylinder and ring due to a coaxial rotating finite permanent magnet with transverse magnetization. The integral torque is calculated from these expressions and validated with numerical and experimental results. Conditions for useful magnetic field approximations are found.

2019

We present a design for producing precisely adjustable and alternating single-axis magnetic fields based on nested Halbach dipole pairs consisting of permanent magnets only. Our design allows for three dimensional optical and mechanical access to a region with strong adjustable dipolar fields, is compatible with systems operating under vacuum, and does not effectively dissipate heat under normal operational conditions. We present a theoretical analysis of the properties and capabilities of our design and construct a proof-of-concept prototype. Using our prototype, we demonstrate fields of up to several kilogauss with field homogeneities of better than 5%, which are harmonically modulated at…

Analytic $JV$ -Characteristics of Ideal Intermediate Band Solar Cells and Solar Cells With Up and Downconverters

2017

The ideal diode equation is regularly used to describe the $\textit {JV}$ -characteristic of single junction solar cells. The connection between the diode equation and fundamental physics is the application of the Boltzmann approximation to describe the fluxes of photons emitted by the cell. In this paper, this approximation is used to derive analytic $\textit {JV}$ -characteristics for three photovoltaic high-efficiency concepts, intermediate band solar cells, and solar cells optically coupled to up and downconverters. These three concepts share the common feature that they allow excitation of electrons between at least three energy levels, which assures a better utilization of the solar s…