Distribution Of Magnetic Field Gradient Research Articles

Optimization of proton imaging system including fringe field of magnetic lens

The proton imaging system is composed of four quadrupole magnetic lenses and a collimator. The quadrupole magnetic lenses can realize point-to-point imaging, and the collimator can improve image quality by controlling proton flux and realize material diagnosis. The magnetic field gradient of an ideal quadrupole lens becomes zero at the edge. Inside the lens, the magnetic field gradient is constant along the axis, while the magnetic field boundary of the actual lens extends outward. In the proton imaging system, the fringing field will affect the proton transport state and the performance of the imaging system as well. In this paper, a method to optimize the system is presented when the fringe field is considered. A proton imaging system of 1.6 GeV is established with the Geant 4 program, in which the magnetic field gradient distribution of the actual lens is approximated by the Bell function. In an ideal imaging system, the external drift length is 1.2 m, the internal drift length is 0.5 m, the length of the magnet is 0.8 m, and the magnetic field gradient is 8.09 T/m. The parameters of the practical imaging system can be obtained by using the optimization method: when the integral difference in magnetic field gradient distribution between the actual lens and the ideal lens is equal to zero, the outer drift length of the imaging system is 1.203 m and the inner drift length is 0.506 m; when the integral difference in the magnetic field gradient distribution between the actual lens and the ideal lens is equal to 1%, the outer drift length is 1.208 m and the inner drift length is 0.516 m. In the numerical simulation, a 1mm-thick copper plate and a concentric ball are chosen as the objects, and the influence of the fringing field on the collimator aperture and that on the proton flux error are studied. The results show that the optimized imaging system can reduce the flux error of protons passing through the object, and the difference in the aperture of collimator is on the order of 10<sup>–2</sup> when the integral difference is on the order of 10<sup>–2</sup> in magnitude.

Design of a 10 GHz minimum-B quadrupole permanent magnet electron cyclotron resonance ion source

This paper presents a simulation study of a permanent magnet electron cyclotron resonance ion source (ECRIS) with a minimum-B quadrupole magnetic field topology. The magnetic field is made to conform to conventional ECRIS with Bmin/BECR of 0.67 and a last closed magnetic isosurface of 1.86BECR at 10 GHz. The distribution of magnetic field gradients parallel to the field, affecting the electron heating efficiency, cover a range from 0 to 13 T/m, being similar to conventional ECRIS. Therefore it is expected that the novel ion source produces warm electrons and high charge state ions in significant number. Single electron tracking simulations are used to estimate plasma flux distribution on the plasma chamber walls and to provide an estimate of the ion density profile at the extraction slit then used in ion optical simulations demonstrating high transmission through the low energy beam transport. The designed ion source is intended to study if the quadrupole field topology could produce high charge state beams in comparable intensities to conventional ECRIS and efficiently transport them through a low energy beamline, thus paving the way for a superconducting ARC-ECRIS using the same field topology. Furthermore, the prospects of the presented ion source design as an injector of a single-ended accelerator for ion beam analysis are discussed.

A method of measuring micro-displacement based on spin magnetic resonance effect of diamond color center

As one of the excellent piezoelectric materials, piezoelectric ceramic has been widely used to develop a highly precise displacement measurement system, which is the key part of the scanning probe system of the high-precision measuring instrument.Based on the high-precision scanning probe system, the micro/nano structures can be easily and accurately detected by the instrument system.However, due to the limitations caused by the character of hysteresis and nonlinearity, it is difficult to further improve the precision of highly precise displacement measurement system.In this work, we present a novel method to develop the highly precise displacement measurement system based on the quantum spin effect.The nitrogen vacancy (NV) color center of single crystal diamond as a sensitive element senses the change of the micro-displacement.Based on the electron spin magnetic resonance effect of diamond nitrogen vacancy color center, the variation of the magnetic field generated from the magnetic steel can be detected with high precision by the electron spin.The relative relation between the displacement and the magnetic gradient field can be used to establish the correlation model between the displacement and the electron spin resonance peak.In the experiment, a corresponding micro-displacement measurement system is established based on the cylindrical permanent magnet, according to the correlation model between the electron spin resonance effect and micro-displacement.The linear region of magnetic field gradient is designed to detect the micro-displacement.Firstly, the intensity distribution of magnetic field gradient is measured by the gauss meter.As the measurement results show, the gradient value is -7.77 Gauss/mm along the core axis of cylindrical permanent magnet, and the intensity of magnetic field gradient distribution region is linear in the millimeter range.Meanwhile, the electron spin magnetic resonance peak of diamond nitrogen vacancy color center is achieved by the optically detected magnetic resonance technology.The electron spin magnetic resonance peak is approximately 2.79 MHz/Gauss in the magnetic field achieved by the fluorescence spectrum of diamond nitrogen vacancy color center, attributed to the relation model between Zeeman splitting effect and magnetic field. In the experiment, the electron spin magnetic resonance signal of diamond nitrogen vacancy color center is lockedin by the demodulation method to achieve the change of micro-displacement.As the results show, the sensitivity is about 16.67 V/mm at the corresponding demodulation frequency of 3000.56 MHz.By the calculation, the resolution of micro-displacement measurement system is about 60 nm based on our method.It proves out a high precision and well reliability method to detect the micro-displacement.By the further theoretical calculation, based on the electron spin effect, the detection resolution of our method can be enhanced up to sub-nanometer scale by reducing the distance between the NV color center and the magnet.It presents a new research direction and field for the micro-displacement detection system.

A New Method: Study on Individual Magnetic Nanoparticles by Frequency-Modulated Magnetic Force Microscopy

Individual magnetic Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanoparticles were imaged using the developed frequency-modulated magnetic force microscopy (FM-MFM) technique. High-resolution imaging of ac magnetic field from individual magnetic nanoparticles was demonstrated by FM-MFM with a high-coercivity FePt tip. It was found that the amplitude and phase images of ac magnetic field were obtained separately using the technique with a lock-in amplifier. The distribution of magnetic field gradient of the individual nanoparticles is clearly presented. It was observed that magnetic nanoparticles can be more precisely detected by FM-MFM. The results are significant for study of the real magnetic field distribution of individual magnetic nanoparticles (~20 nm), which provide some valuable information for the analysis of nanoscale magnetic features.

Detection of wire element breakage in power transmission line using HTS-SQUID

We have proposed the application of nondestructive evaluation (NDE) using HTS-SQUID gradiometer to detect wire breakage in compressive conductor joints in overhead transmission line. In this study, we prepare an aluminum conductor steel reinforced (ACSR) transmission line with a broken wire. The ends of the ACSR cable were compressed with Al sleeves. An AC current was injected toward into the cable axis by applying AC voltage across the both ends of the sleeves. Then the two-dimensional distribution of magnetic field gradient above the cable was measured by a HTS-SQUID gradiometer. In the case of the compressed ACSR with a wire breakage, the field gradient changed periodically along the spiral of the broken wire. In contrast, such changes did not appear above the ACSR cable without defects. These results suggested the possibility to detect the wire breakage in the compressive conductor joints by this method. We also conducted electromagnetic field simulation to verify the experimental results.

Study of inspection of wire breakage in aluminum transmission line using SQUID

Taking advantage of the unsurpassed high-magnetic sensitivity of high-temperature superconductor (HTS) superconducting quantum interference device (SQUID), HTS-SQUID-non-destructive evaluation (NDE) technique was applied to detection of single wire breakage in hard-drawn aluminum transmission line (HAL), which was twisted from 19 aluminum wires. While applying AC current of 2.6 mA at 200 Hz to the HAL, distribution of magnetic field gradient above the HAL was two-dimensionally scanned by a HTS-SQUID gradiometer. A periodic pattern was detected along the locus of the broken wire in the distribution from the HAL with wire breakage, while such pattern was not observed in that from normal HAL without wire breakage. These results indicate the possibility of detection of single wire breakage by the magnetic inspection technique.

NMR Study of the Water Dynamics in Aqueous Colloidal Magnetic Fluids at Different pH's and Grains Concentrations

In a previous NMR study [González, C.E.; et al. J. Chem. Phys. 1998, 109, 4670] we observed that the 1H and 2H spectra of both surfacted and ionic ferrofluids are broad and asymmetric. In ionic ferrofluids, this effect could be due to (i) electric interactions between the electrically charged magnetic grains and the electric dipole moments of water molecules and/or (ii) the interaction between water molecules and the distribution of magnetic field gradients in the intergrain volume. In this work we study a series of ionic ferrofluids prepared at different magnetic grains concentrations and with different surface charge densities. Our experiments clearly show that the sign and the density of the electric charge of the magnetic grains have no influence on the NMR spectra. On the other hand, spectral widths increase with the magnetic grains concentration, all the samples being far from the motional narrowing regime.

A pulsed-gradient multiple-spin-echo NMR technique for measuring diffusion in the presence of background magnetic field gradients

A pulsed-gradient multiple rf pulse spin-echo NMR technique for measuring diffusion in the presence of nonuniform background magnetic field gradients is discussed. The amplitude of one echo in the Carr-Purcell-Meiboom-Gill (CPMG) echo train is measured as the spacing, Δ, is varied between two fixed-amplitude field-gradient pulses inserted into the echo train. It is shown by calculation and experiment that the dependence of this echo amplitude upon Δ and upon the diffusion coefficient is independent of background gradients or their distribution in the sample. This technique is applicable to diffusion measurements of atomic species in systems in which there exists a random variation of the magnetization, causing a distribution of magnetic field gradients which makes diffusion measurements by other pulsed-gradient spin-echo techniques impractical. The technique is illustrated by measurement of diffusion coefficients (∼ 10 −5 cm 2/sec) for hydrogen in powdered NbH 0.55 in which random gradients ∼20 G/cm exist.