Effect Of Magnetic Field Strength Research Articles

Parallel transport of long mean-free-path plasmas along open magnetic field lines: Plasma profile variation

Parallel transport of long mean-free-path plasma along an open magnetic field line is characterized by strong temperature anisotropy, which is driven by two effects. The first is magnetic moment conservation in a non-uniform magnetic field, which can transfer energy between parallel and perpendicular degrees of freedom. The second is decompressional cooling of the parallel temperature due to parallel flow acceleration by conventional presheath electric field which is associated with the sheath condition near the wall surface where the open magnetic field line intercepts the discharge chamber. To the leading order in gyroradius to system gradient length scale expansion, the parallel transport can be understood via the Chew-Goldbeger-Low (CGL) model which retains two components of the parallel heat flux, i.e., qn associated with the parallel thermal energy and qs related to perpendicular thermal energy. It is shown that in addition to the effect of magnetic field strength (B) modulation, the two components (qn and qs) of the parallel heat flux play decisive roles in the parallel variation of the plasma profile, which includes the plasma density (n), parallel flow (u), parallel and perpendicular temperatures (T∥ and T⊥), and the ambipolar potential (ϕ). Both their profile (qn/B and qs/B2) and the upstream values of the ratio of the conductive and convective thermal flux (qn/nuT∥ and qs/nuT⊥) provide the controlling physics, in addition to B modulation. The physics described by the CGL model are contrasted with those of the double-adiabatic laws and further elucidated by comparison with the first-principles kinetic simulation for a specific but representative flux expander case.

Low-Frequency Instabilities in the Interaction of Ion Beam With Magnetized Plasma

The low-frequency instabilities in the interaction between an ion beam and a magnetoactive plasma are investigated taking into account the effects of the dissipation and thermal motion of the charged particles. Furthermore, the effects of magnetic field strength, ion beam velocity, and propagation angle on the resonance frequency and the growth rate of the instabilities are studied. It is shown that, according to the strength of the magnetic field and the ion beam velocity, the increase of the thermal velocity of the charged particles can increase or decrease the resonance frequency in the ion acoustic frequency range.

Echo-Time and Field Strength Dependence of BOLD Reactivity in Veins and Parenchyma Using Flow-Normalized Hypercapnic Manipulation

While the BOLD (Blood Oxygenation Level Dependent) contrast mechanism has demonstrated excellent sensitivity to neuronal activation, its specificity with regards to differentiating vascular and parenchymal responses has been an area of ongoing concern. By inducing a global increase in Cerebral Blood Flow (CBF), we examined the effect of magnetic field strength and echo-time (TE) on the gradient-echo BOLD response in areas of cortical gray matter and in resolvable veins. In order to define a quantitative index of BOLD reactivity, we measured the percent BOLD response per unit fractional change in global gray matter CBF induced by inhaling carbon dioxide (CO2). By normalizing the BOLD response to the underlying CBF change and determining the BOLD response as a function of TE, we calculated the change in R2 * (ΔR2 *) per unit fractional flow change; the Flow Relaxation Coefficient, (FRC) for 3T and 1.5T in parenchymal and large vein compartments. The FRC in parenchymal voxels was 1.76±0.54 fold higher at 3T than at 1.5T and was 2.96±0.66 and 3.12±0.76 fold higher for veins than parenchyma at 1.5T and 3T respectively, showing a quantitative measure of the increase in specificity to parenchymal sources at 3T compared to 1.5T. Additionally, the results allow optimization of the TE to prioritize either maximum parenchymal BOLD response or maximum parenchymal specificity. Parenchymal signals peaked at TE values of 62.0±11.5 ms and 41.5±7.5 ms for 1.5T and 3T, respectively, while the response in the major veins peaked at shorter TE values; 41.0±6.9 ms and 21.5±1.0 ms for 1.5T and 3T. These experiments showed that at 3T, the BOLD CNR in parenchymal voxels exceeded that of 1.5T by a factor of 1.9±0.4 at the optimal TE for each field.

Non-linear response of a magneto-elastic translating beam with prismatic joint for higher resonance conditions

The non-linear response of a magneto-elastic translating beam having prismatic joint for higher resonance conditions is studied. A periodically varying transverse magnetic field is applied to the system. Two frequencies of prismatic motion and oscillating transverse magnetic field are implemented to the system. The method of multiple scales as one of the perturbation techniques is used to derive two first order ordinary differential equations that govern the time variation of the amplitude and phase of the response. Then a stability analysis is conducted for subharmonic resonance and simultaneous resonance conditions. A parametric study is performed to investigate the effect of magnetic field strength, amplitude of prismatic motion, damping and payload mass on the frequency response curves for both the resonance conditions. The catastrophic failure of the system may occur due to the presence of saddle-node and pitchfork bifurcations. The results obtained by method of multiple scales are compared with those obtained by numerically integrating the reduced equations and are found to be in good agreement. The developed results can be applied to control the vibration of a beam with prismatic joint subjected to magnetic field for third order subharmonic resonance and simultaneous resonance conditions.

Kinetic study of plasma behavior and its effect on plasma facing surface in the castellated tile gap

The gaps between divertor tiles are ideal hideouts of impurities. To investigate the impurity deposition in the gaps, one needs to understand the plasma behavior well. This work employs a 2d3v PIC-MCC model to study the plasma characteristics inside and outside the tile gap. Under such plasma conditions from the simulation, the energy fluxes to the tile surfaces are obtained and the erosion rates of carbon-based tile plates are further evaluated. In addition, effects of magnetic field strength on the energy flux are also discussed.

Effects of magnetic field strength on the low frequency oscillation in Hall thrusters

In order to study the effect of magnetic field strength on low frequency oscillation in Hall thrusters, experiments were carried out with different operating parameters. Experimental results show that the effect of magnetic field strength on the low frequency oscillation changes with operating parameters. In the decline zone of magnetoampere characteristic curve, low frequency oscillation increases with the increase of magnetic field strength at low mass flow rate, while decreases with the increase of magnetic field strength at high mass flow rate. With further experiments and numerical simulations, it is found that the change of electron current at low mass flow rate and the change of ion current at high mass flow rate account for the variations of low frequency oscillation. Finally, the physical analysis is performed.

Putaminal magnetic resonance imaging features at various magnetic field strengths in multiple system atrophy

We delineated the effects of magnetic field strength on signal intensities to facilitate the specific findings of multiple system atrophy (MSA). Fifteen patients with probable MSA were imaged by 0.35T fast spin-echo (FSE), 1.5T FSE, and 3.0T FSE using a consistent protocol, testing all field strengths on the same day. Sixty patients with probable Parkinson's disease (PD) also underwent imaging. Moderate or marked hyperintensity at the dorsolateral outer putaminal margin, hyperintensity of the putaminal body, hypointensity relative to the globus pallidus at the dorsolateral putaminal margin, and infratentorial signal changes were evaluated as specific findings for MSA. As the field strength increased, the occurrence of hyperintensity both at the dorsolateral outer putaminal margin and of the putaminal body decreased, while the occurrence of hypointensity at the dorsolateral putaminal margin increased in MSA. The occurrence of uniform mild hyperintensity of the outer putaminal margin was evident in 7% at 0.35T, 40% at 1.5T, and 47% at 3.0T in MSA and in 5% at 0.35T, 60% at 1.5T, and 75% at 3.0T in PD. However, no PD patients showed hyperintensity at the dorsolateral outer putaminal margin and that of the putaminal body. Putaminal magnetic resonance imaging (MRI) findings in MSA were altered considerably by magnetic field strength. The severity and distribution of signal changes are important for assessing putaminal MRI findings in MSA.

Numerical study of steady magneto-convection around an adiabatic body inside a square enclosure in low Prandtl numbers

In this paper, the effects of Prandtl number on the steady magneto-convection around a centrally located adiabatic body inside a square enclosure are numerically investigated. Two-dimensional nonlinear governing equations are discretized using the control volume method and hybrid scheme. The equations are solved using SIMPLER algorithm. The results are displayed in the form of streamlines and isotherms when the Rayleigh number varies between 103 and 106, the Hartmann number changes between 0 and 100 and the Prandtl number ranges between 0.005 and 0.1. The ratio of the buoyancy force to the Lorentz force (Ra/Ha2) is introduced as an index to compare the contribution of natural convection and magnetic field strength on heat transfer. The results obtained from numerical modeling show that the Prandtl number has not considerable effect on heat transfer at low Rayleigh numbers. The effect of magnetic field strength on convection is increased by increasing Prandtl number. The effect of Prandtl number on the average Nusselt number in the presence of a magnetic field is less than the case without a magnetic field.

Nuclear magnetic resonance relaxation and diffusion in the presence of internal gradients: The effect of magnetic field strength

It is known that internal magnetic field gradients in porous materials, caused by susceptibility differences at the solid-fluid interfaces, alter the observed effective Nuclear Magnetic Resonance transverse relaxation times T2,eff. The internal gradients scale with the strength of the static background magnetic field B0. Here, we acquire data at various magnitudes of B0 to observe the influence of internal gradients on T2-T2 exchange measurements; the theory discussed and observations made are applicable to any T2-T2 analysis of heterogeneous materials. At high magnetic field strengths, it is possible to observe diffusive exchange between regions of local internal gradient extrema within individual pores. Therefore, the observed exchange pathways are not associated with pore-to-pore exchange. Understanding the significance of internal gradients in transverse relaxation measurements is critical to interpreting these results. We present the example of water in porous sandstone rock and offer a guideline to determine whether an observed T2,eff relaxation time distribution reflects the pore size distribution for a given susceptibility contrast (magnetic field strength) and spin echo separation. More generally, we confirm that for porous materials T1 provides a better indication of the pore size distribution than T2,eff at high magnetic field strengths (B0>1 T), and demonstrate the data analysis necessary to validate pore size interpretations of T2,eff measurements.

Magnetic Separation of Phosphorus Enriched Phase from Multiphase Dephosphorization Slag

The authors have found that phosphorus exhibits remarkable segregation in exhausted actual hot-metal pretreatment slag (dephosphorization slag), and it exists as a 3CaO·P2O5–2CaO·SiO2 solid solution with the FeO–CaO–SiO2 matrix. Since their magnetic properties are significantly different, it is possible to separate them with the aid of a superconducting strong magnetic field. To investigate the effects of magnetic field strength, the particle size of the slag, etc., an experiment on magnetic separation has been carried out using simulated dephosphorization slag (18.1FetO–45.9CaO–20.3SiO2–6.6P2O5–2.5MnO–5.5MgO in mass%) and a superconducting magnet with 0.5–2.5 T. In a stronger magnetic field, the quality of the recovered slag becomes better due to less contamination of the FetO matrix phase, while its quantity worsens and the amount of recovered slag declines. However, the quantity of the recovered slag can be improved by repeating the procedure. In the present experiment, about 65% of the phosphorus enriched phase can be recovered with less than 10% of FetO matrix phase contamination at conditions of 0.5 T, a particle size of less than 35 μm, and a water/slag ratio of 32 with a single procedure. The P2O5 content in the recovered slag is close to that in the phosphorus-enriched phase in the initial slag, and the FeO content decreases markedly with magnetic separation.

The effect of magnetic field on acceptor impurity in a diluted magnetic quantum well system

We investigate the effects of magnetic field strength over the ground state binding energy of a hydrogenic acceptor impurity confined in a Cd 1 − x i n Mn x i n Te / Cd 1 − x o u t Mn x o u t Te quantum well. We apply the variational method using 1s-hydrogenic wavefunction, in the framework of the single band effective mass approximation. The effect of valence band degeneracy is considered through the energy dependent effective mass. The magnetic field dependence of the barrier height is discussed. The band gap tuning in an external magnetic field for different compositions of Mn ions is achieved using an empirical formula. Spin polaronic shifts are estimated using mean field theory for different magnetic field strengths and the well sizes. We present a theoretical study of diluted magnetic semiconductors treating the local p–d exchange interaction J between the itinerant carriers and the Mn electrons within a realistic band structure. These results are compared with the other existing available literature.

Magnetic field and electromagnetic wave properties of carbon monoxide with high-pressure disproportionation single-walled carbon nanotubes

A double-fluid theory is used to find the electromagnetic wave absorption of carbon monoxide with iron-catalyzed high-pressure disproportionation (HiPco)-grown single-walled carbon nanotubes (SWNTs). The electromagnetic wave absorption of carbon monoxide with HiPco SWNTs is obtained and is studied numerically. The absorption is then deduced and their functional dependence on the number density, collision frequency, cyclotron frequency, and angle of propagation is studied. The double-fluid theory predicts that there is an electromagnetic frequency dependency on the energy absorption properties of the system under investigation. The calculation results show that effects of magnetic field strength and the angle of microwave propagation on the absorption coefficient as well as the frequency band of resonant absorption are very significant.

Fiber-Based Magneto-Optic Sagnac Optical Modulator

In this paper, a fiber-based, magneto-optic (MO) optical modulator based on Sagnac interferometry is proposed. The system uses a Faraday rotator to produce optical modulation with low magnetic fields. The Sagnac geometry allows for increased modulation at lower fields than traditional MO modulators. A formulation of the system is provided using Jones calculus. Experimental results at 1550 nm using single mode fiber are reported, including a discussion of dynamic range and effect of magnetic field strength. Theoretical and practical advantages and limitations are discussed. Methods for improving modulation speed, dynamic range, and performance are presented.

Effect of magnetic field strength on deposition rate and energy flux in a dc magnetron sputtering system

Variations in the magnetic field strongly affect the plasma parameters in a magnetron sputtering system. This in turn affects the throughput as well as the energy flux to the substrate. The variation in the magnetic field in this study, for a dc magnetron process, is achieved by shifting the magnet assembly slightly away from the target. Measurements of the plasma parameters show that while the electron density at the substrate increases with decrease in magnetic field, the electron temperature decreases. The cooling of the electron temperature is consistent with results reported elsewhere. The deposition rate per input magnetron power is found to increase slightly with the decrease in magnetic field for the process conditions considered in this study. Results suggest that the energy flux to the substrate tends to show a general decrease with the shift in the magnet assembly.

Characterizing the effects of magnetic field strength on specificity in functional MRI: Application in pre-surgical mapping

Characterizing the effects of magnetic field strength on specificity in functional MRI: Application in pre-surgical mapping

MHD STABILITY OF INTERSTELLAR MEDIUM PHASE TRANSITION LAYERS. I. MAGNETIC FIELD ORTHOGONAL TO FRONT

We consider the scenario of a magnetic field orthogonal to a front separating two media of different temperatures and densities, such as cold and warm interstellar gas, in a 2-D plane-parallel geometry. A linear stability analysis is performed to assess the behavior of both evaporation and condensation fronts when subject to incompressible, corrugational perturbations with wavelengths larger than the thickness of the front. We discuss the behavior of fronts in both super-Alfvenic and sub-Alfvenic flows. Since the propagation speed of fronts is slow in the ISM, it is the sub-Alfvenic regime that is relevant, and magnetic fields are a significant influence on front dynamics. In this case we find that evaporation fronts, which are unstable in the hydrodynamic regime, are stabilized. Condensation fronts are unstable, but for parameters typical of the neutral ISM the growth rates are so slow that steady state fronts are effectively stable. However, the instability may become important if condensation proceeds at a sufficiently fast rate. This paper is the first in a series exploring the linear and nonlinear effects of magnetic field strength and orientation on the corrugational instability, with the ultimate goal of addressing outstanding questions about small-scale ISM structure.

EFFECTS OF MAGNETIC FIELD STRENGTH AND ORIENTATION ON MOLECULAR CLOUD FORMATION

We present a set of numerical simulations addressing the effects of magnetic field strength and orientation on the flow-driven formation of molecular clouds. Fields perpendicular to the flows sweeping up the cloud can efficiently prevent the formation of massive clouds but permit the build-up of cold, diffuse filaments. Fields aligned with the flows lead to substantial clouds, whose degree of fragmentation and turbulence strongly depends on the background field strength. Adding a random field component leads to a "selection effect" for molecular cloud formation: high column densities are only reached at locations where the field component perpendicular to the flows is vanishing. Searching for signatures of colliding flows should focus on the diffuse, warm gas, since the cold gas phase making up the cloud will have lost the information about the original flow direction because the magnetic fields redistribute the kinetic energy of the inflows.

Effect of magnetic field strength and admixture gas on current interrupting capability of a CO2 rotary‐arc load‐break switch

AbstractFirst, current interrupting experiments were performed for a rotary‐arc type of load‐break switch filled with pure CO2 at a total pressure of 0.1 MPa. Increase in the coil turns for generating magnetic field from 1 to 1.8, 2.5, and 3.6 (arbitrary unit) raised the current interrupting capability from 2.6 kA to 3.2, 3.5, and 4.1 kA. Second, experiments were performed for CO2 gas mixture under the condition of 3.6 coil turns. Gases of He, O2, N2, and air were admixted to CO2. Adding either He or O2 to CO2 at a concentration of 30% allows the switch to have higher interrupting capability than using pure CO2. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 21–27, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20742

マルチフェーズ脱リンスラグからのリン濃縮相の磁気分離

The authors have found that phosphorus exhibits remarkable segregation in the exhausted actual hot metal pretreatment slag (dephosphorization slag) and it exists as 3CaO·P2O5–2CaO·SiO2 solid solution together with FeO–CaO–SiO2 matrix. Since their magnetic properties are significantly different, it is possible to separate them with the aid of superconducting strong magnetic field. In order to investigate effects of magnetic field strength, particle size of slag and so on, the experiment of the magnetic separation has been carried out by using simulated dephosphorization slag (18.1FetO–45.9CaO–20.3SiO2–6.6 P2O5–2.5MnO–5.5MgO in mass%) and super conducting magnet with 0.5 to 2.5 T. At stronger magnetic field, the quality of the recovered slag becomes better due to smaller contamination of FetO matrix phase while its quantity becomes worse and the amount of recovered slag is smaller. However, the quantity of the recovered slag can be improved by repeating the magnetic separation procedure. In the present experiment, about 65% of phosphorus enriched slag can be recovered with less than 10% of FetO matrix phase contamination at the condition of 0.5 T, particle size of smaller than 35 mm and water/slag ratio of 32 with single procedure. P2O5 content in the recovered slag is very close to that in the phosphorus enriched phase in the initial slag and FetO content is markedly decreased with magnetic separation.

Diffusion-fMRI update: response to very short stimulation and the effect of magnetic field strength

Diffusion-fMRI update: response to very short stimulation and the effect of magnetic field strength