Merging formation and current amplification of field‐reversed configuration

The merging formation of the field‐reversed configuration (FRC) has been developed in the TS‐3 merging experiment, leading us to a new scenario of FRC slow formation, heating and current amplification. Two force‐free spheromaks with opposing toroidal fields were merged together in the axial direction to form a high‐β FRC with higher efficiency than the conventional field‐reversed theta‐pinch method. This unique relaxation from the force‐free (β ∼ 0.05 − 0.1) spheromaks to the high‐β (β ∼ 0.7 − 1) FRC is attributed to the conversion of toroidal magnetic energy into ion thermal energy through the reconnection outflow. A central ohmic heating (OH) coil worked successfully to amplify the FRC plasma current by a factor of 2. Toroidal mode analysis of magnetic structure indicated that the tilting stability of the oblate FRC was provided by an ion kinetic effect. This oblate FRC is also useful as an initial equilibrium to produce a high‐β_p spherical tokamak (ST) with diamagnetic toroidal magnetic field, suggesting the close relationship between FRCs and high‐β_p STs in the second stable region of the ballooning mode. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Properties of anisotropic Ba‐Zn‐Cu system W‐type hexagonal ferrite magnets

Experiments were carried out to investigate the magnetic and physical properties of Ba‐Zn‐Cu W‐type hexagonal ferrites sintered without atmosphere control. Compositions were chosen according to the formula BaZn_2–xCu_xFe₁₆O₂₇, where x was varied 0 ˜ 0.5 and 1.0. The effect of BaO addition after semisintering treatment on magnetic properties of Ba‐Zn‐Cu compounds was examined. It was found that BaO addition for Ba‐Zn‐Cu compounds was very useful in stabilizing the W‐type hexagon. The optimum condition of making magnets and some properties of typical specimens are as follows: composition—BaZn_1.7Cu_0.3Fe₁₆O₂₇ with 4 wt% Ba added; semisintering conditions—1275 °C for 1.0 h in air; sintering conditions—1175°C for 0.5 h in air; magnetic properties and lattice constant are J_m = 0.405 T, J_r = 0.370 T, H_cJ = 88.15 kA/m, (BH)_max = 19.12 kJ/m³, T_c = 356 °C, H_A = 994.7 kA/m, K_A = 2.01 × 10⁵ J/m³, c = 32.928 × 10^–10 m, a = 5.927 × 10^–10 m, c/a = 5.556. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 36–42, 2001     

Magnetic properties of Pr‐Fe‐Co‐V‐W‐Si‐B system exchange spring magnets

The melt‐spun ribbons of Pr‐Fe‐Co‐V‐W‐Si‐B system alloys were prepared by single roller rapid‐quenching method. The effects of composition, surface velocity, and heat treatment on the magnetic properties were investigated. The P₉sFe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy ribbons prepared at a surface velocity of 12.5 m/s were crystallized by heat treatment, and the optimum heat‐treatment condition was found to be at 575°C for 3 min, for which the magnetic properties were (BH)_max = 136.1 kJ/m³, J_r = 0.93 T, H_cJ = 652.2 kA/m, and H_cB = 528.3 kA/m. The temperature coefficients of J_r and H_cJ for the ribbons crystallized from melt‐spun ribbons of Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy were α(J_r)_ave = ?0.057%/°C and α(H_cJ) = ?0.450%/°C. The value of (B)_max for the compression molding Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 isotropic bonded magnet prepared by using the ribbons annealed at 575°C for 3 min is 80.0 kJ/m³, and the density is 6.24 Mg/m³. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 10–16, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20211 Copyright © 2006 Wiley Periodicals, Inc.     

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

First, 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     

Development of NbTi superconducting strands and cables for the field winding of a 200‐MW‐class high‐energy‐density superconducting generator

The NbTi superconducting strands and cables for the field winding of the 200‐MW‐class high‐energy‐density‐type superconducting generator are developed. They are composed of Cu/Cu‐10wt%Ni/Nb‐46.5wt%Ti superconducting strands and the 10‐kA (at 5 T)‐class 9‐strand compacted cables. The diameter of strands is 1.33 mm, and the 9‐strand compacted cables are 2.4 mm thick and 6.0 mm wide. In order to produce high‐current‐density NbTi strands, we made strands under controlled aging heat treatments, the total and final strains, and the strains between heat treatments, by using large‐scale extruder. Moreover, in order to produce high‐stability and low‐AC‐loss NbTi strands and cables, the matrix ratio of strands and the cross sections of strands are optimized. The current density of NbTi filaments for the four‐time‐aging manufactured 1.33‐mm‐diameter strands was J_C=3150 A/mm² at 5 T, 1150 A/mm² at 8 T. The critical current of the 9‐strand compacted cable is 10.7 kA at 5 T. The AC losses of the final compacted cables are less than 100 kW/m³ at 5 T, 5 T/s, that is, decreased to less than half of the target of the AC loss value (< at 5 T, 5 T/s). Compared with the strand (Cu ratio 1.77), the minimum quench energy (MQE) of the strand (Cu ratio>2) increased about 40% at the operation mode current of the superconducting generator. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(3): 24– 31, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20266     

Switched‐capacitor‐voltage‐multiplier boost DC–AC inverter with adaptive stages

A multistage switched‐capacitor‐voltage‐multiplier inverter (SCVMI) is proposed with a variable‐conversion‐ratio phase generator and a sinusoidal pulse‐width‐modulation controller for boost DC–AC conversion and high‐efficiency regulation. Its power unit contains: SCVM booster and H‐bridge. The SCVM booster includes two m_c‐stage switched‐capacitor cells and two n_c‐stage switched‐capacitor cells in the interleaving operation to realize DC–DC boost gain of m_c × n_c at most. Here, the variable‐conversion‐ratio phase generator is suggested and adopted to change the running stage number and topological path for a suitable gain level of m × n (m = 1, 2, ?,m_c, n = 1, 2, ?,n_c) to improve efficiency, especially for the lower AC output. The H‐bridge is employed for DC–AC conversion, where four switches are controlled by sinusoidal pulse‐width‐modulation not only for full‐wave output but also for output regulation as well as robustness to source/loading variation. Some theoretical analysis and design include: SCVMI model, steady‐state/dynamic analysis, conversion ratio, power efficiency, stability, capacitance selection, output filter, and control design. Finally, the closed‐loop SCVMI is simulated, and the hardware circuit is implemented and tested. All the results are illustrated to show the efficacy of this scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

A gain/efficiency‐enhanced bidirectional switched‐capacitor DC‐DC converter

A closed‐loop gain/efficiency‐enhanced bidirectional switched‐capacitor converter (BSCC) is proposed by combining an adaptive‐conversion‐ratio (ACR) phase generator and pulse‐width‐modulation (PWM) controller for bidirectional step‐up/down DC‐DC conversion and regulation. For realizing gain‐enhanced, the power part consists of one m_c‐stage cell and one n_c‐stage cell in cascade between low‐voltage (LV) and high‐voltage (HV) sides to boost HV voltage into m_c × n_c times voltage of LV source at most, or convert LV voltage into 1/(m_c × n_c) times voltage of HV source at most. For realizing efficiency‐enhanced, the ACR idea with adapting stage number m, n is built in the phase generator to obtain a suitable step‐up/down gain: m × n or 1/(m × n) (m = 1, 2, …, m_c, n = 1, 2, …, n_c). Further, the output regulation and robustness to source/loading variation can be enhanced by PWM on the LV/HV sides. Some theoretical analysis and control design are included as: modeling, steady‐state analysis, conversion ratio, efficiency, capacitance selection, and control design. Finally, the performance of this scheme is verified experimentally on a BSCC prototype, and all results are illustrated to show the efficacy of this scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

Z Copy‐Controlled Gain‐Current Differencing Buffered Amplifier and its applications

The Z Copy‐Controlled Gain‐Current Differencing Buffered Amplifier (ZC‐CG‐CDBA) is introduced in the paper. In addition to the well‐known CDBA, the input Current Differencing Unit (CDU) is modified and completed by special circuits. Analogously to the conventional CDBA, the z terminal is internally connected to the input of voltage buffer. The current gain from the difference input p, n to the output z can be controlled electronically or by an external device. In addition, an independent high‐impedance output zc is available, providing difference current I_p?I_n. In the paper, the extension of application range of the ZC‐CG‐CDBA compared with the conventional CDBA is referred to. The novel circuit element is assembled from commercial integrated circuits and its principle is verified experimentally on a universal second‐order filter. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparative studies on magnetic flux relaxations of varied spherical toroids produced by co‐helicity merging

The co‐helicity merging operations of compact toroid (CT) and spherical tokamak (ST) have been performed with external toroidal fields in the CT/ST merging device TS‐4. The low‐q (safety factor) CT merging as the compact RFP merging and the spheromak merging show the flux conversion from toroidal to poloidal in the course of the reconstruction of the Taylor force free state. The relaxation to the Taylor state proceeds through the following three states: (1) axisymmetric merging with increasing toroidal flux; (2) increase in the poloidal flux Ψ; and (3) relaxation to the Taylor state. The high‐q ST merging shows different relaxation process from those of the compact RFP and the spheromak mergings. Increases in Ψ were not clearly observed in the ST merging. The measured eigenvalues λ show that ST's, especially high‐q ST's, approach a unique intrinsic equilibrium state that has a λ proportional to Ψ with a longer lifetime than that of CT's. When external toroidal field is set in a certain range between the low‐q operation and the high‐q operation for ST's, an abnormal phenomenon was found in the ST formation, namely, a drastic decrease in the plasma lifetime. This phenomenon is characterized by very weak poloidal flux generations during the initial plasma production phase and the subsequent plasma separation phase when the plasma starts detaching from the flux core. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 7–15, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20069     

Formation of a negative impulse discharge induced by an XeCl excimer laser in a long rod‐to‐rod electrode gap in air

Negative discharge induction experiments were performed with a rod‐to‐rod electrode configuration having a gap length of 0.8 m using a high‐power XeCl excimer laser of maximum output energy of 2 J/pulse and an impulse generator of maximum voltage of 1.2 MV. Development of a leader in the laser‐ionized plasma channel was observed by using an image converter camera. When an XeCl excimer laser is applied at a carefully controlled instant, the guiding effect for an impulse discharge is optimized. Three main results were obtained. First, the discharge started near the focal point and then developed bidirectionally toward the high‐voltage electrode and the grounded electrode. Midgap leaders were frequently observed. Second, it was observed that the lifetime of the laser‐ionized plasma channel was about 1 μs. Third, the discharge processes were classified into six stages. The mechanism of the streamer and leader propagation is discussed. © 2000 Scripta Technica, Electr Eng Jpn, 134(2): 11–18, 2001     

Application of a force‐balanced coil to a tokamak device

High field is very favorable for magnetically confined fusion devices such as a tokamak, but electromagnetic force derived from the field becomes a fatal problem. In particular, the largest in‐plane centering force hinders toroidal field coils from operating at higher fields. Variable pitch multihelical coils, which we term force‐balanced coils (FBCs), by which this force is drastically reduced, are proposed for the coil system of tokamaks. FBCs can also provide poloidal flux swing for plasma breakdown and current induction during the ramp‐up phase of the coil current. In this paper, we indicate how to design FBCs for tokamaks. The fusion reactor‐size FBCs are designed and compared with that of the conventional toroidal field coil system. © 1999 Scripta Technica, Electr Eng Jpn, 130(3): 39–48, 2000     

Study on grounding in the vicinity of the work site on 1000-kV power transmission line. Part 2. Electromagnetic induction and its protection

In order to clarify the grounding conditions for protecting workers on a de-energized circuit from induction from a live circuit and to determine the required current capacity of the grounding conductor for a 1,000 kV double-circuit power transmission line, the phenomena caused by electromagnetic induction resulting from a live circuit are discussed. The electromagnetic induction current I_g flowing through the body of a worker and the electromagnetic induction current I_gO flowing through the grounding conductor can be analyzed by dividing the various power line conditions into three main factors, and using electromagnetic induction current calculations for a power line of infinite length. The zone where I_g does not exceed 1 mA is within 1 km of the grounding point on the de-energized circuit owing to the grounding resistance (0.1 Ω) of the substations at the ends of the line and the difference in the phase configurations on the line when the current I₁ of the live circuit is a constant 1 kA through the line. Similarly the value of I_gO is determined by the grounding resistance of the substations at the ends of the line and the difference in the phase configurations on the line. I_gO is approximately 10 A per 1 kA of I₁. The currents I_g and I_gO produced by electromagnetic induction are additive, allowing I_g and I_gO in the actual power line to be evaluated by summation.     

Laser‐induced discharge in a rod–plane electrode in the presence of a negative dc electric field

Discharge induction experiments were performed between a plate and a rod on a plate electrode configuration with a gap length of 1 m using a high‐power CO₂ laser and a dc voltage generator. The electrodes are parallel planes. Each plate electrode consists of a central flat part having a diameter of 3 m with a circular edge on a cross section. The length of the rod is 10 cm. A chain of plasma beads of length 10 cm was created on the tip of the rod by the CO₂ laser and used for artificial triggering of negative high‐voltage sparkover. The behavior of streamer, leader, and return stroke was observed by an image converter camera. It was found that a positive upward traveling leader can be triggered from the tip of the rod on the lower plane to the upper plane by the chain of plasma beads created by the CO₂ laser. This apparatus is useful for study for realization of laser‐induced lightning. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 19–27, 2000     

Design and optimization of a 3‐coil resonance‐based wireless power transfer system for biomedical implants

This paper presents a resonance‐based wireless power transfer system using a single layer of inductor coil windings, in a pancake configuration, in order to obtain a compact system for implantable electronic applications. We theoretically analyzed the system and characterized it by measuring its inductance, self‐resonant frequency, and quality factor Q. In our resonance‐based wireless power transfer prototype, we proposed a 3‐coil system, using two 15‐mm radius implantable coils, with a resonance frequency of 6.76 MHz. This system can effectively transfer power for a distance of up to 50 mm. Moreover, our proposed 3‐coil system can achieve a high Q‐factor and has a comparable power transfer efficiency (PTE) to previously reported works about 3‐coil and 4‐coil systems. The experimental PTE can achieve 82.4% at a separation distance of 20 mm and more than 10% PTE at a distance of 40 mm. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface induction motor for two‐dimensional drive

In this paper, the authors propose an induction type surface or planar motor for smooth two‐dimensional drive including rotating operation. The secondary member is composed of the flat conducting plate without directional qualities and the back‐iron plate as secondary yoke. The primary member is composed of the torodial core and the armature winding which can supply the current in every coil embedded in a slot. For the rotating drive, all the coils are used and the same rotating magnetic field as an ordinary rotating motor is generated. For the linear drive, a partial rotating field is generated in the direction of movement in each region separated into two groups every half of toroidal core. For the armature winding, two types of methods are used which are a ring‐winding supplied current at each slot and a double‐layer‐winding supplied current to each coil. The two‐dimensional electromagnetic analysis in Cartesian coordinate system is shown for the analysis, in which an effect of circular shape is considered as an edge effect. The thrust and normal force characteristics at standstill were confirmed practically by using test machine. It was cleared that the surface motor had high transformation rate of about 79% for thrust in spite of the circular shape. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 107–115, 2000     

Considerations on the thrust‐to‐input ratio of a cylindrical moving‐coil‐type linear dc motor

Linear dc motors (LDMs) are widely used for servo‐actuators, compressors, and so on. High‐efficiency LDMs are strongly desired for compressors. To realize LDMs with high‐efficiency characteristics, decreasing the copper losses, namely, thrust‐to‐input ratio, F/P, must be increased. This paper describes an optimization method for the F/P of a moving‐coil‐type LDM. The following results are obtained:

• 1 Simplified expression for the F/P of the LDM is derived from the permeance analysis method. The effects of dimensions of the LDM on the F/P of the LDM are investigated through the simplified expression for the F/P. As a result, the optimum dimension of the LDM for maximizing the F/P exists.
• 2 When the static thrust is 100 N, the measured F/P of the initial LDM is 7.9 N/W, and the errors using the simplified expression for the F/P and the finite element method (FEM) are 33 and 8%, respectively. Derived simplified expression for the F/P is useful because the F/P can be calculated easily.
• 3 An improved LDM, which has 26% higher F/P than those of the initial LDM, is designed by using the permeance analysis method and the FEM. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 103–111, 2000

     

Mapping of circuit variables into two‐port network variables in basic amplifier structures: identifying new topologies

In this paper, we report on a unique observation which enables the unification of the analysis for different amplifier structures. In particular, we report that the change from one type of amplifier to the other can be understood via a mapping of source‐load circuit variables (V_s, R_s, I_i, I_o, I_L, V_o) into two‐port network variables (V₁, V₂, I₁, I₂). As such, unified expressions for (A_v,Z_i,A_i,Z_o) are derived. Further, a Matlab code is written to search for all valid mappings out of 3⁸ different possibilities. Copyright © 2013 John Wiley & Sons, Ltd.     

A switch‐utilization‐improved switched‐inductor switched‐capacitor converter with adapting stage number

A novel closed‐loop switched‐inductor switched‐capacitor converter (SISCC) is proposed by using the pulse‐width‐modulation (PWM) compensation for the step‐up DC–DC conversion/regulation, and together by combining the adaptive‐stage‐number (ASN), control for the higher switch utilization and wider supply voltage range. The power part of SISCC is composed of two cascaded sub‐circuits, including (i) a serial‐parallel switched‐capacitor circuit with n_c pumping capacitors and (ii) a switched‐inductor booster with m_c resonant capacitors, so as to obtain the high step‐up gain of (n_c + 1) × m_c /(1 ? D) at most, where D is the duty cycle of PWM adopted to enhance output regulation as well as robustness to source/loading variation. Besides, the ASN control is presented with adapting the stage number n (n = 0, 1, 2, …, n_c) of pumping capacitors to obtain a flexible gain of (n + 1) × m_c /(1 ? D), and further in order to make the SISCC operating at a properly small duty cycle for improving switch utilization and/or supply voltage range. Some theoretical analysis and control design include formulation, steady‐state analysis, ASN‐based conversion ratio, efficiency, output ripple, stability, inductance and capacitance selection, and control design. Finally, the performance of this scheme is verified experimentally on an ASN‐based SISCC prototype, and all results are illustrated to show the efficacy of this scheme. Copyright © 2015 John Wiley & Sons, Ltd.     

Low‐noise blue light generation of intracavity frequency‐doubled LD‐pumped Cr:LiSAF laser by single‐mode method

We have demonstrated the production of low‐noise blue SHG (Second Harmonic Generation) light by single‐mode oscillation in an intracavity frequency‐doubled laser diode (LD)‐pumped Cr‐doped LiSrAlF₆ (Cr:LiSAF) solid‐state laser. The SHG crystal was LiB₃O₅ (LBO). A birefringent filter and an etalon plate were used for the single‐mode Cr:LiSAF laser oscillation wave. A maximum blue SHG output power of 32 mW was obtained by using a 1‐mm‐thick birefringent filter and an etalon plate 200 μm thick with 20% reflectivity. The oscillation wavelength varied by 0.24 pm/hPa in response to changes in atmospheric pressure. A long‐term stability of 300 hours was obtained with the cavity enclosed in a barostat. © 2001 Scripta Technica, Electr Eng Jpn, 138(1): 49–55, 2002     

High‐tuning‐range CMOS band‐pass IF filter based on a low‐Q cascaded biquad optimization technique

A design procedure for high‐order continuous‐time intermediate‐frequency band‐pass filters based on the cascade of low‐Q biquadratic cells is presented. The approach is well suited for integrated‐circuit fabrication, as it takes into account the maximum capacitance spread dictated by the available technology and maximum acceptable sensitivity to component variations. A trade‐off between noise and maximum linear range is also met. A novel, wide‐tuning‐range transconductor topology is also described. Based on these results, a 10‐pole band‐pass filter for a code division multiple‐access satellite receiver has been designed and tested. The filter provides tunable center frequency (f₀) from 10 to 70 MHz and exhibits a 28‐MHz bandwidth around f₀ = 70 MHz with more than 39‐dB attenuation at f₀/2 and 2f₀. Third‐order harmonic rejection is higher than 60 dB for a 1‐Vpp 70‐MHz input, and equivalent output noise is lower than 1 mV_rms. The circuit is fabricated in a 0.25‐µm complementary metal oxide semiconductor process, and the core consumes 12 mA from a 2.5‐V supply, offering the best current/pole ratio figure. The die area resulted to be 0.9 × 1.1 mm². Copyright © 2014 John Wiley & Sons, Ltd.