Dual-coil System Research Articles

New pulsed-magnets for 100 T, long-pulse and diffraction measurements

Development of non-destructive pulsed magnet aiming at 100 T-generation beyond 80 T-field is our mission. For that purpose, we have been developing a new coil system, socalled "dual coil system" and succeeded in generation of 85 T. This magnet will open the nondestructive 100 T-field in the near future. New type of magnet with longer pulse duration also has been developed. This magnet has a gap between the inner coil and the outer one where liquid nitrogen can flow. Therefore, the magnet can be cooled down by liquid nitrogen rapidly. The repetition time has been reduced to 15 minutes for 60 T-field with the duration of about 30 msec. By means of this rapid-cooling technique, a magnet for X-ray diffraction measurement has been made. This magnet consists of split coils with a split gap of 5 mm and a duration time of about 30 msec. This magnet allows us to carry out X-ray diffraction measurement under pulsed high field. The maximum field of the magnet is found to be 38 T, which is limited by utilized energy of the capacitor bank.

Inductively-overcoupled coil design for high resolution magnetic resonance imaging

BackgroundMaintaining the quality of magnetic resonance images acquired with the current implantable coil technology is challenging in longitudinal studies. To overcome this challenge, the principle of 'inductive overcoupling' is introduced as a method to tune and match a dual coil system. This system consists of an imaging coil built with fixed electrical elements and a matching coil equipped with tuning and matching capabilities. Overcoupling here refers to the condition beyond which the peak of the current in the imaging coil splits.MethodsThe combined coils are coupled inductively to operate like a transformer. Each coil circuit is electrically represented by equivalent lumped-elements. A theoretical analysis is given to identify the frequency response characteristics of the currents in each coil. The predictions from this analysis are translated into experiments and applied to locally image rat spinal cord at 9.4 T using an implantable coil as the imaging coil and an external volume coil as the matching coil.ResultsThe theoretical analysis indicated that strong coupling between the coils divides the resonance peaks on the response curves of the currents. Once these newly generated peaks were tuned and matched to the desired frequency and impedance of operation, in vivo images were acquired from the rat spinal cord at high quality and high resolution.ConclusionAfter proper implementation, inductive overcoupling provides a unique opportunity for tuning and matching the coil system, and allows reliable and repeatable acquisitions of magnetic resonance data. This feature is likely to be useful in experimental studies, such as those aimed at longitudinally imaging the rat following spinal cord injury.

Adapted eddy current excitation using a dual gradiometric coil system

Adapted eddy current excitation using a dual gradiometric coil system

The “Practical Mathematics” of Recording Three-Dimensional Eye Position Using Scleral Coils

The “gold standard” for recording the three-dimensional rotation of the eye involves placing two coils of wire, embedded in a soft plastic ring, on the sclera of the eye, then placing the subject inside a set of orthogonal oscillating magnetic fields, and using the currents induced in the eye coils to deduce the position of the coil, and hence of the eye, in space. Eye movements are actually eye rotations, which can be described mathematically by a special class of matrices, rotation matrices, or, alternatively, by a rotation vector related to the axis of the rotation. This article deals with the mathematical tools needed to implement the signal processing from such a multifield, dual-coil system and compute the precise rotational movement of the eye. One reason for making such careful measurements is to study an interesting constraint on eye movements, called Listing's law, which expresses ocular torsion, or rotation of the eye about its line of sight, in terms of the direction of gaze. Techniques for experimentally quantitating these constraints are also presented. Following a treatment of the “ideal” case, with coils and eye in perfect alignment, the additional techniques for dealing with various departures from ideality that are almost always encountered experimentally are examined. A final section deals with developing a validation protocol for eye movement analysis techniques using mechanical and computer simulations of eye movements.

140. 前立腺検査におけるDual Coilの有用性について

140. 前立腺検査におけるDual Coilの有用性について

140.前立腺検査におけるデュアルコイルの有用性について(第24回秋季学術大会 一般研究発表予稿集)

140.前立腺検査におけるデュアルコイルの有用性について(第24回秋季学術大会 一般研究発表予稿集)

Dual multi-turn solenoids for the accurate magnetization measurements

A description is given of a pulsed magnet for a dual-coil system for measuring ferri- and ferromagnetic materials. In this design an extra coil is wound on a main solenoid coil, which produces a low field with long pulse width prior to the high field generated by the main coil. Since the rise rate of the magnetic field is small in the low-field region, the height of a spike voltage is reduced while the duration is elongated during the magnetization process. Consequently, the evaluation of saturation magnetization becomes accurate even for fields up to 55 T. The inner solenoid coil (Cu-Be) and the outer solenoid coil (Cu-Cr) are energized by capacitor banks of 75 kJ (10 kV) and 55 kJ (3 kV), respectively. The pulse magnet withstands more than 20 shots of a 50-T field. >

High field magnetization of R<inf>2</inf>Fe<inf>14</inf>B compounds measured up to 55 T

Magnetic field induced spin reorientation was studied in R 2 Fe 14 B (R = Nd, Tm and Er) single crystals up to 55 T under pulsed high magnetic fields and also up to to 23 T by means of a hybrid magnet. A dual coil system for the pulse magnet was developed for measuring the magnetization process with an initial steep increase accurately by an induction method. A brand-new mechanical system was developed for the magnetization measurement in the hybrid magnet using an extraction method. The magnetization processes of multiple samples were measured simultaneously in one generation of the magnetic field. The incipient stage of the transition from ferri-to ferromagnetism was clearly observed in the magnetization curve along the [100] and [110] directions in Er 2 Fe 14 B and Tm 2 Fe 14 B crystals. The transition fields were roughly estimated to be 70 T and 55 T along the [100] direction for Er and Tm compounds, respectively. The forced spin reorientation transition was measured in Nd 2 Fe 14 B crystal along the [100] direction at various temperatures. A steep increase of magnetization appeared at 200 K with decreasing temperature. The magnetization processes were also measured along several directions within the c-plane. When the field direction approached [110], the distinct transition diminished.

A Preshaping Transition Coil for a Small Minimum-B Magnetic Mirror

An additional coil between the plasma source and the mirror cell prefans incoming plasma to map it directly into the well-known twisted bow-tie shape and thus avoids reshaping drifts generated in conventional min-B mirror machines. This reduces vacuum chamber size requirements and eliminates any drift reshaping delay. Wound in series with the standard quadrupole loffe bar set, this dual-coil system features end connections which contribute no field on axis.