Numerical simulation of wave propagation and plasma response excited in field-reversed configuration plasma

A hybrid simulation (a model that treats ions as particles and electrons as fluid) is performed to analyse the propagation of waves excited in the field-reversed configuration plasma and the resulting plasma response. The current of the wave excitation antenna changes in a sine wave, and its frequency is set so that it has an ion cyclotron resonance point inside the separatrix. When the antenna current is maximum, a magnetic field with a magnitude of 40% of the external magnetic field is created on the separatrix. A toroidal magnetic field is excited in the plasma by applying waves. The observed propagation velocity of the toroidal magnetic field is comparable with the shear Alfvén wave outside the separatrix, and is on the same order within the separatrix. This result has a tendency similar to the propagation velocity outside the separatrix reported in the wave experiment in the past FIX machine. The simulation results also show that when the excited magnetic field propagates in the axial direction, the separatrix are compressed or expanded, and the high-density region of the ions formed thereby moves in the axial direction. In addition, the excited magnetic energy is rapidly decreased near the position where the velocities of the shear Alfvén wave and the ion sound wave are equal (local beta value is 0.88). It is found that the decay of the excited magnetic energy occurred at a point outside the ion cyclotron resonance point. This suggests that the compression and expansion of the plasma is caused while maintaining the quasi-equilibrium state according to the change in the external magnetic pressure.

Spin filtering and magnetically-controlled quantum switch in multiple triangular rings consisting of quantum dots

Electron transport characteristics through a system consisting of a series of triangular quantum dot rings are studied utilizing the non-equilibrium Green’s function. In the presence of a magnetic field, an additional anti-resonance point occurs in the conductance spectrum. As the number of triangular quantum dot rings increases, two anti-resonance points evolve into two well-defined insulating bands. The insulating band disappears as the magnetic flux takes an appropriate value, and therefore, an effective magnetically-controlled quantum switch can be achieved. If a Zeeman magnetic field is introduced, a spin-polarized window (SPW) can be formed, suggesting a physical scheme of a spin filtering. As the intradot Coulomb interactions are taken into consideration, more SPWs can be obtained. This work sheds lights onto the design of future quantum devices.

Features of the chemical potential of a quasi-two-dimensional electron gas at low-temperatures

An analysis is made of the low-temperature behavior of the chemical potential [Formula: see text] of a quasi-two-dimensional electron gas near the resonance point (at the bottom of the miniband) and far from it. Low-temperature analytical formulas for [Formula: see text] are obtained under the conditions of the existence of an arbitrary number of minibands. It is shown that with the increasing temperature near the resonance point, the chemical potential decreases linearly and exponentially slowly in the middle of the resonance points. Analytical formulas are compared to the numerical solutions.

Study on frequency selective/absorption/reflection multilayer composite flexible electromagnetic wave absorbing fabric

In order to realize wide-band, high-efficiency and flexible electromagnetic wave absorption, an effective method is the combination of different electromagnetic functional materials. How to use and make the multilayer materials with individual absorption, reflection and selective transmission characteristics is very important. In this work, multilayer composite flexible absorbing fabrics made of a frequency selective surface (FSS), carbonyl iron coated fabrics (CIFs) and copper-nickel plated conductive woven fabrics (CWFs) were prepared. The layered composite materials have a thin thickness, good flexibility and adjustable absorption band, which provide a reference for the development of lightweight and efficient electromagnetic wave absorbing materials. The influence of the resonance point, wave absorbent content and conductive layer on the absorbing properties were studied. CIF-3 with a surface density of 2046.9 g/m2 has the best absorption performance with a minimum reflectivity of –20.52 dB at 12.56 GHz. A one-layer FSS can broaden the absorption bandwidth; the broadening degree varies with the resonance point of the FSS, which also makes the absorption band adjustable. The bandwidth of f12/CIF-3 with reflectivity of less than –10 dB can reach 5.68 GHz. Besides, CWF is beneficial to increase the absorption intensity, and the best reflectivity of CIF-3/CWF can reach –27.73 dB. Furthermore, three-layer composites can improve the absorption strength and bandwidth of CIF at low frequency. Compared with CIF-3, the reflectivity of f14/CIF-3/CWF decreases 8.06 dB at 11.28 GHz, and the bandwidth is 4.72 GHz, which widens by 0.32 GHz.