Internal Magnetic Field Measurements in the TCSU RMF Current Drive Experiment

A field-reversed configuration (FRC) is formed by applying a rotating magnetic field (RMF) much larger than the axial magnetic field to a cylindrical glass vacuum chamber filled with 10Pa argon gas without a preionization. The FRC with the plasma density 2.2×1019m−3, the temperature 8.0eV, the separatrix length 0.45m, and the separatrix radius 0.035m is sustained for the notably long period of 40ms. It is observed that the antenna current which produces the RMF is reduced by about half after the FRC is formed. The interaction between the plasma and the antenna circuit increases the antenna resistance and changes the inductance of the antenna so that the circuit becomes nonresonant. The RMF is sufficiently large to fully penetrate to the center during the period and drive the current with a rigid rotor profile. The RMF is shown to play a major role in sustaining the plasma pressure.

Field reversed configurations (FRCs) have been formed and sustained for up to 50 normal flux decay times by rotating magnetic fields (RMFs) in the translation, confinement, and sustainment experiment. For these longer pulse times a new phenomenon has been observed: switching to a higher performance mode delineated by shallower RMF penetration, higher ratios of generated poloidal to RMF drive field, and lower overall plasma resistivity. This mode switching is always accompanied by, and perhaps triggered by, the spontaneous development of a toroidal field with a magnitude up to 20% of the peak poloidal field. The global data cannot be explained by previous RMF theory based on uniform electron rotational velocities or by numerical calculations based on uniform plasma resistivity, but agrees in many respects with new calculations made using strongly varying resistivity profiles. In order to more realistically model RMF driven FRCs with such non-uniform resistivity profiles, a double rigid rotor model has been developed with separate inner and outer electron rotational velocities and resistivities. The results of this modelling suggest that the RMF drive results in very high resistivity in a narrow edge layer, and that the higher performance mode is characterized by a sharp reduction in resistivity over the bulk of the FRC.

Steady state solutions, suitable for field-reversed configurations (FRCs) sustained by rotating magnetic fields (RMFs) are obtained by properly including three-dimensional effects, in the limit of large FRC elongation, and the radial component of Ohm’s law. The steady electrostatic potential, necessary to satisfy Ohm’s law, is considered to be a surface function. The problem is analyzed at the midplane of the configuration and it is reduced to the solution of two coupled nonlinear differential equations for the real and imaginary parts of the phasor associated to the longitudinal component of the vector potential. Additional constraints are obtained by requesting that the steady radial current density and poloidal magnetic flux vanish at the plasma boundary which is set at the time-averaged separatrix. The results are presented in terms of the degree of synchronism of the electrons with the RMF and compared with those obtained when radial current effects are neglected. Three important differences are observed when compared with the case without radial current density. First, at low penetration of the RMF into the plasma there is a significant increase in the driven azimuthal current. Second, the RMF amplitude necessary to access the high synchronism regime, starting from low synchronism, is larger and the difference appears to increase as the separatrix to classical skin depth ratio increases. Third, the minimum RMF amplitude necessary to sustain almost full synchronism is reduced.

Three-dimensional simulations of field reversed configuration (FRC) formation and sustainment with rotating magnetic field (RMF) current drive have been performed with the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. The Hall term is a zeroth order effect with strong coupling between Fourier components, and recent enhancements to the NIMROD preconditioner allow much larger time steps than was previously possible. Boundary conditions to capture the effects of a finite length RMF antenna have been added, and simulations of FRC formation from a uniform background plasma have been performed with parameters relevant to the translation, confinement, and sustainment-upgrade experiment at the University of Washington [H. Y. Guo, A. L. Hoffman, and R. D. Milroy, Phys. Plasmas 14, 112502 (2007)]. The effects of both even-parity and odd-parity antennas have been investigated, and there is no evidence of a disruptive instability for either antenna type. It has been found that RMF effects extend considerably beyond the ends of the antenna, and that a large n=0 Bθ can develop in the open-field line region, producing a back torque opposing the RMF.

Abundant evidence has substantiated the positive effects of pulsed electromagnetic fields (PEMF) and static magnetic fields (SMF) on inhibiting osteopenia and promoting fracture healing. However, the osteogenic potential of rotating magnetic fields (RMF), another common electromagnetic application modality, remains poorly characterized thus far, although numerous commercial RMF treatment devices have been available on the market. Herein the impacts of RMF on osteoporotic bone microarchitecture, bone strength and bone metabolism were systematically investigated in hindlimb-unloaded (HU) rats. Thirty two 3-month-old male Sprague-Dawley rats were randomly assigned to the Control (n = 10), HU (n = 10) and HU with RMF exposure (HU+RMF, n = 12) groups. Rats in the HU+RMF group were subjected to daily 2-hour exposure to moderate-intensity RMF (ranging from 0.60 T to 0.38 T) at 7 Hz for 4 weeks. HU caused significant decreases in body mass and soleus muscle mass of rats, which were not obviously altered by RMF. Three-point bending test showed that the mechanical properties of femurs in HU rats, including maximum load, stiffness, energy absorption and elastic modulus were not markedly affected by RMF. µCT analysis demonstrated that 4-week RMF did not significantly prevent HU-induced deterioration of femoral trabecular and cortical bone microarchitecture. Serum biochemical analysis showed that RMF did not significantly change HU-induced decrease in serum bone formation markers and increase in bone resorption markers. Bone histomorphometric analysis further confirmed that RMF showed no impacts on bone remodeling in HU rats, as evidenced by unchanged mineral apposition rate, bone formation rate, osteoblast numbers and osteoclast numbers in cancellous bone. Together, our findings reveal that RMF do not significantly affect bone microstructure, bone mechanical strength and bone remodeling in HU-induced disuse osteoporotic rats. Our study indicates potentially obvious waveform-dependent effects of electromagnetic fields-stimulated osteogenesis, suggesting that RMF, at least in the present form, might not be an optimal modality for inhibiting disuse osteopenia/osteoporosis.

Eagle Harbor Technologies, Inc. (EHT) and the University of Michigan (UM) made the first direct performance measurement of a continuously operating Rotating Magnetic Field (RMF) – Field-Reversed Configuration (FRC) Thruster using a standard inverted-pendulum thrust stand in space-like conditions. EHT developed the power system, and UM constructed the RMF-FRC thruster and conducted measurements in their Large Vacuum Test Facility.

We study how the rotation of a classical magnetic field influences vacuum birefringence. In spite of the fact that solutions of the wave equation depend in a nontrivial way on the relative magnitude of the strength of vacuum birefringence and the angular rotation frequency of the magnetic field, the induced ellipticity of the light ray does not depend on the magnetic field angular rotation frequency. Hence, in contrast to recent claims, the result of the PVLAS experiment cannot be explained by conventional nonlinear quantum electrodynamic000.

Five years ago, the feasibility research program of fusion ignition for magnetized plasma initiated by our Institute and CAEP in China, which aimed to 1) building the ”MC-1-like” device to generate the ultrahigh magnetic fields; 2) building the so- call ”Ying Guang 1” facility to create the high temperature and high density target of field reversed configuration (FRC); 3) developing a simulation tool to describe the process of formation and transportation of FRCs. After five years now, the ultrahigh magnetic fields over 1400 Tesla has been achieved at CAEP of China, which is believed to be important to suppress the heat conduction from charged particles and deposit the energy of alpha particle to promote the ignition process while the ”YG 1 facility ” has been built and it is believed that the centimeter's length and diameters of the formed FRC is formed, which has the average density is 1.3×10 ^ 16 cm^-3, and the average temperature is 137 eV. The two dimensional magneto hydrodynamic code, which is so called MPF-2D tools, has been developed to simulate and investigate the process of the formatting process of FRC. As the primary progress, the simulating results of this 2-D MHD code agree well with the experiment approximately. On the other hand, we are investigating the feasibility of achieving ignition of magnetized plasma by Magneto- Hydrodynamic simulation. The ignition condition for plasma target with the embedded magnetic field has been investigated. Due to the progress mentioned above, the new scheme of ignition by compressing the magnetized plasmoids with the solid liner merged by the colliding process of two FRCs has been proposed as next five years plan. This scheme should promote the ignition process economically and quickly. At the first step, one of high temperature plasmiods with the close configuration of magnetic field line has be confirmed to be formed after head-to-head collision of two high speed FRCs and the feasibility of ignition by the compressing process of solid liner should be investigated by our two dimensional simulating results. We believe this national five-year plan can help us to get the goal of fusion ignition for magnetized plasma in the near future.

A liquid membrane containing ferromagnetic powder (LM-FP) was proposed for controlling the molecular permeation rate through a liquid membrane in a rotating magnetic field (R-MF) in a previous paper. This paper presents details concerning the property of LM-FP under exposure to R-MF or an alternating magnetic field (A-MF). Magnetite and phenylglyoxylic acid (PGA) were used as a ferromagnetic powder and a substance for permeation, respectively. Various factors, such as the magnetite concentration in LM-FP, the intensity of the magnetic field and the number of rotations of R-MF, both of which affect the PGA permeation rate, were investigated in order to understand the behavior of magnetite powder in LM-FP. Magnetized particles of magnetite powder in LM-FP were found to rotate in R-MF, but not to move in A-MF. R-MF exerted an acceleration of the PGA permeation rate through LM-FP more than did A-MF. It is suggested that magnetized particles of magnetite powder behave as micro-magnetic stirrers in LM-FP to accelerate molecular transport. Data concerning the PGA permeation rate were simulated by assuming a concentration change of PGA in LM-FP after turning R-MF on or off. We obtained simulation curves which were in accord with the experimental results.

Time-varying, azimuthal electron current is obtained from measured two-dimensional profiles of excited magnetic fields, using the Rotating Magnetic Field (RMF) plasma acceleration method in an open magnetic field configuration. The RMF is applied orthogonally to cylindrical plasma, leading to the azimuthal current drive via the Hall effect. Here, dc azimuthal current, whose magnitude is equivalent to that of ac azimuthal current with twice the RMF frequency, is verified for the first time. In addition, an expected current reversal is found, with the RMF rotation direction changing by 180°.

Collisional merging experiments of a field-reversed configuration (FRC) plasma at the super-Alfvénic velocity have been conducted in the FAT (FRC Amplification via Translation)-CM (Collisional Merging) device. In the experiments, two FRCs are collided and merged in a confinement section with a quasi-static confinement magnetic field. Therefore, it is necessary to measure the high-frequency pulsed magnetic field superposed on a quasi-stationary signal. The magnetic field is generally measured by a magnetic coil probe in the pulse discharge experiments; however, in such measurements, errors arise in the low-frequency band in the conducted FRC experiments. Therefore, a Hall sensor has been applied for low-frequency magnetic field measurements in the FAT-CM experiments. Calibration of the Hall sensor involves confirming that the sensor has a sufficient response speed and linear characteristics for the magnetic field with a rising time of approximately 240 µs and that its output voltage does not saturate up to a magnetic field of 0.7 T. Combination of the Hall sensor and the magnetic coil probe ensures a comprehensive measurement of the magnetic field in the range of FAT-CM experiments. In this study, accurate magnetic measurements were performed in a collisional merging experiment in the FAT-CM device by using a combined magnetic diagnostic system.

Magnetic nanoparticles stimulation to enhance liquid-liquid two-phase mass transfer under static and rotating magnetic fields

We describe a field reversed configuration (FRC) experiment featuring in-vessel θ-pinch coils and open-field-line plasmas confined in a tandem mirror. Two FRCs, formed near the west and the east mirror throats of a central cell, are ejected toward the mid-plane for colliding and merging. Each FRC consists of four groups of pulsed power supplies and four groups of coils, having diameters 35, 35, 40, and 45 cm. The rise time of the main reversal field is 7.15 μs, and the maximum voltage is 40 kV with total currents of 416 kA, corresponding to a magnetic field of 1690 G. The total capacitive stored energy is 115.2 kJ. A fast pulse gas injection system was designed and tested to inject neutral gas into the FRC formation region with controlled directions. The successful installation of the θ-pinch coils inside the vacuum vessel offers greater freedom for diagnostics and control instruments as well as preserving magnetic tandem mirror configuration. The magnetic field reversal is confirmed by internal magnetic field measurements. The plasma temperature, density, and lifetime are, respectively, ∼100 eV, ∼3.0 × 1018 m-3, and ∼300 μs for the current operating conditions.

Experimental investigation of the effect of mechanical vibration and rotating magnetic field on the hydrothermal performance of water-Fe3O4 ferrofluid inside a rifled tube

For collisional merging field-reversed configurations (FRCs), it is desired to have both FRCs tuned to be approximately the same, as well as to optimize each FRC to have high temperature and high translation speed so as to retain most of the equilibrium flux after traveling a distance to the middle plane for merging. The present study reports the experimental study of a single-translated FRC in the KMAX-FRC device with various diagnostics, including a triple probe, a bolometer, several magnetic probe arrays, and a novel 2D internal magnetic probe array. According to the measurements conducted in the present study, a maximum toroidal magnetic field equal to ∼1/3 of the external magnetic field inside the FRC separatrix radius is observed, and the typical parameters of a single-translated FRC near the device’s mid-plane are n e ∼ (2–4)×1019 m−3, T e ∼ 8 eV, T i ∼ 5 eV, r s ∼ 0.2 m, l s ∼ 0.6 m and ϕ p(RR) ∼ 0.2 mWb. The 2D magnetic topology measurement revealed, for the first time, the time evolution of the overall internal magnetic fields of a single-translated FRC, and an optimized operation regime is given in the paper.