Terahertz electromagnetic signal enhancement in split ring resonators featuring waveguide modes.

To resolve the high attenuation issue in terahertz (THz) wave propagation in air, we propose a split ring resonator (SRR) structure, consisting of a subwavelength slit and a circular cavity in the wavelength size, which can support coupling resonant modes and achieve a remarkable omnidirectional electromagnetic signals gain (∼40 dB) at 0.4 THz. Based on the Bruijn method, we also develop and numerically confirm a new analytic approach which successfully predicts the dependence of field enhancement on key geometric parameters of the SRR. Compared to the typical LC resonance, the enhanced field at the coupling resonance exhibits a high-quality waveguide mode in the circular cavity, paving a way for direct detection and transmission of the enhanced THz signals in future communication systems.

Self-consistent kinetic model of nested electron- and ion-scale magnetic cavities in space plasmas.

NASA's Magnetospheric Multi-Scale (MMS) mission is designed to explore the proton- and electron-gyroscale kinetics of plasma turbulence where the bulk of particle acceleration and heating takes place. Understanding the nature of cross-scale structures ubiquitous as magnetic cavities is important to assess the energy partition, cascade and conversion in the plasma universe. Here, we present theoretical insight into magnetic cavities by deriving a self-consistent, kinetic theory of these coherent structures. By taking advantage of the multipoint measurements from the MMS constellation, we demonstrate that our kinetic model can utilize magnetic cavity observations by one MMS spacecraft to predict measurements from a second/third spacecraft. The methodology of "observe and predict" validates the theory we have derived, and confirms that nested magnetic cavities are self-organized plasma structures supported by trapped proton and electron populations in analogous to the classical theta-pinches in laboratory plasmas.

2D profile of poloidal magnetic field diagnosed by a laser-driven ion-beam trace probe (LITP).

Based on large energy spread of laser-driven ion beam (LIB), a new method, the Laser-driven Ion-beam Trace Probe (LITP), was suggested recently to diagnose the poloidal magnetic field (Bp) and radial electric field (Er) in toroidal devices. Based on another property of LIB, a wide angular distribution, here we suggested that LITP could be extended to get 2D Bp profile or 1D profile of both poloidal and radial magnetic fields at the same time. In this paper, we show the basic principle, some preliminary simulation results, and experimental preparation to test the basic principle of LITP.

Plasma rotation in the Peking University Plasma Test device.

Some preliminary results of plasma rotations in a linear plasma experiment device, Peking University Plasma Test (PPT) device, are reported in this paper. PPT has a cylindrical vacuum chamber with 500 mm diameter and 1000 mm length, and a pair of Helmholtz coils which can generate cylindrical or cusp magnetic geometry with magnitude from 0 to 2000 G. Plasma was generated by a helicon source and the typical density is about 1013 cm-3 for the argon plasma. Some Langmuir probes, magnetic probes, and one high-speed camera are set up to diagnose the rotational plasmas. The preliminary results show that magnetic fluctuations exist during some plasma rotation processes with both cylindrical and cusp magnetic geometries, which might be related to some electromagnetic processes and need further studies.