Influence Of Magnetic Field Inhomogeneity Research Articles

Influence of magnetic field inhomogeneity of the plane wiggler on the spectral distribution of spontaneous radiation and on the gain

The spectral distribution of spontaneous emission and the gain for electrons moving in a plane wiggler (an undulator) with inhomogeneous magnetic field are calculated. It is shown that electrons perform composite motion, consisted of a slow (strophotron) and fast (undulator) components. The equations of coupled motion of electrons is obtained by averaging the equations of undulator motion. It is shown that the allowance for the magnetic field inhomogeneity leads to an appearance of additional peaks both in the spectral distribution of spontaneous radiation and in the gain.

Applying alpha-channeling to mirror machines

The α-channeling effect entails the use of radio-frequency waves to expel and cool high-energetic α particles born in a fusion reactor; the device reactivity can then be increased even further by redirecting the extracted energy to fuel ions. Originally proposed for tokamaks, this technique has also been shown to benefit open-ended fusion devices. Here, the fundamental theory and practical aspects of α channeling in mirror machines are reviewed, including the influence of magnetic field inhomogeneity and the effect of a finite wave region on the α-channeling mechanism. For practical implementation of the α-channeling effect in mirror geometry, suitable contained weakly damped modes are identified. In addition, the parameter space of candidate waves for implementing the α-channeling effect can be significantly extended through the introduction of a suitable minority ion species that has the catalytic effect of moderating the transfer of power from the α-channeling wave to the fuel ions.

Effect of field inhomogeneity on the magnetisation measurements in the peak effect region of CeRu 2 superconductor

Detailed magnetisation measurements are presented for a cubic Laves phase superconducting single crystal CeRu 2. These measurements have been performed in the peak effect regime using Quantum Design SQUID Magnetic Property Measurement System (MPMS). To understand the influence of magnetic field inhomogeneity of this set up, on the measured magnetisation, all the data is recorded for different scan lengths. We clearly demonstrate that some of the anomalous magnetisation results reported in literature are artefacts of field inhomogeneity. We also present a model based on Critical State Model to simulate the effect of field inhomogeneity on the measured magnetisation.

Simulation of the influence of magnetic field inhomogeneity and distortion correction in MR imaging

We describe a technique for simulation and correction of the effects of an arbitrary distribution of undesired components of the static and gradient magnetic fields. This technique is applicable to direct Fourier NMR imaging. The mathematical basis and details of this technique are fully described. Computer simulation demonstrates the effectiveness of this method.

Effect of magnetic field inhomogeneity on exact mass determination in ICR spectrometry

At present, in ICR spectrometry increasing interest exists in the development of ICR spectrometers utilizing superconducting solenoid magnets with magnetic field strength up to about 80 kG, which extend the measurable mass range into the region of higher masses. But, due to such high magnetic field strengths, inhomogeneities, which grow in proportion to field strength increasingly affect the accuracy of measurements. Therefore, magnets with the highest possible homogeneous fields are the aim of technical developments. The extent to which it is necessary to improve the homogeneity of solenoid magnets used in ICR spectrometers by the aid of expensive technology in order to achieve a still measurable effect with respect to exact mass determination is investigated in this work. For this purpose, the change of cyclotron frequency due to magnetic field inhomogeneity will be calculated and the resulting difference between measured and actual masses determined. As the mathematical form of this problem is complicated in the frame of classical mechanics, it is advantageous to use a different method. Regarding the quantum mechanical Schrödinger equation of this problem, we calculate the contributions due to inhomogeneity perturbation theoretically with the aid of a wavepacket formalism. The relation between shift of cyclotron frequency and experimental parameters is given and the order of magnitude of the perturbation is estimated for limiting conditions. It is shown that, even in the most unfavorable case, the influence of magnetic field inhomogeneity is negligibly small.

Kinetic instability of flute oscillations

The author considers the effect of resonance particles drifting under the influence of magnetic field inhomogeneity with a velocity close to the phase velocity of flute oscillations on those oscillations. He investigates the instability of these oscillations at densities below the critical density of the hydrodynamic flute instability Ra/d2 ≪ 1 (R – radius of curvature of the magnetic field lines, a – transverse dimension of the plasma, d – Debye radius).It is shown that, when resonance particles are present, the branch of oscillations with frequency (ω0 – ionic plasma frequency, ωc – ionic cyclotron frequency, k – transverse wave number) is always unstable. For an ion transverse velocity distribution function having the form of a δ-function with an admixture of hot ions, it is shown that the branch of oscillations with a frequency only slightly dependent on density and close to (v0 – mean ion velocity) is also unstable. Both instabilities also occur in the hydrodynamically stable case; i.e. when the magnetic field lines are convex with respect to the plasma.