K. H. Tsui

Time-dependent magnetohydrodynamic self-similar extragalactic jets

Extragalactic jets are visualized as dynamic eruptive events modeled by time-dependent magnetohydrodynamic (MHD) equations. The jet structure comes from the temporally self-similar solutions in two-dimensional axisymmetric spherical geometry. The two-dimensional magnetic field is solved in the finite plasma pressure regime, or finite-β regime, and it is described by an equation where plasma pressure plays the role of an eigenvalue. This allows a structure of magnetic lobes in space, among which the polar axis lobe is strongly peaked in intensity and collimated in angular spread compared to the others. For this reason, the polar lobe overwhelms the other lobes, and a jet structure naturally arises in the polar direction. Furthermore, within each magnetic lobe in space, there are small secondary regions with closed two-dimensional field lines embedded along this primary lobe. In these embedded magnetic toroids, plasma pressure and mass density are accordingly much higher. These are termed secondary plasmoids. The magnetic field lines in these secondary plasmoids circle in alternating sequence such that adjacent plasmoids have opposite field lines. In particular, along the polar primary lobe, such periodic plasmoid structure happens to be compatible with radio observations in which islands of high radio intensities are mapped.

Coronal loop heating by wave-particle interactions

According to observations, the MHD perturbations in coronal loops carry enough energy density to fuel the loops. The damping mechanisms for tapping this energy source are examined, and wave-particle interactions are proposed as a hopeful candidate. Results of analyses of the magnetosonic surface wave and the kinetic Alfven wave show that the wave-particle resonant interactions can dissipate energy fast enough to sustain the coronal temperatures. 11 refs.

Magnetosonic and kinetic Alfvén current drive analysis

Quasilinear equations are used together with the energy conservation equation to assess the merits of magnetosonic and kinetic Alfven current drive. It is found that the Alfven mode has a higher gain in terms of efficiency and current than the magnetosonic mode.

High gain strong pump free‐electron lasers with fast 2π/kw spatial oscillations

In the high gain strong pump regime, the radiation field amplitude and phase can vary substantially over a wiggler period. Also, due to the periodic transverse motion, the longitudinal electron energy suffers large variations over the same distance. Because of these considerations, the spatial average that leads to the classical one‐dimensional free‐electron laser equations is not applicable here. Thus the rederived equations suitable for the high gain strong pump regime contain 2π/kw periodic terms. Comparisons with the Electron Laser Facility (ELF) experiments of the Lawrence Livermore National Laboratory [Phys. Rev. Lett. 54, 889 (1985); 57, 2172 (1986); Phys. Rev. A 35, 2184 (1987)] on the operational characteristics including the relative phase of the radiation field are made.

OBSERVATION OF MUON EXCESS AT GROUND LEVEL IN RELATION TO GAMMA-RAY BURSTS DETECTED FROM SPACE

In this paper we examine the possibility of the ground observation of the gigaelectronvolt counterparts associated with the Monitor of All-sky X-ray Image transient event (trigger 58072727) and the Swift GRB140512A event. In both cases, there was a muon excess with a statistical significance above 4σ. The coordinates of the events were located in the field of view (FOV) of the Tupi muon telescopes at the time of the occurrence. Since 2013 August, the Tupi experiment has been operating a new extended array of five muon telescopes, located at ground level at (, 3 m above sea level). This location coincides with the South Atlantic Anomaly central region. We consider a hypothesis that the muon excess could be due to photonuclear reactions in the Earths atmosphere induced by gamma rays with energies above 10 GeV. We describe a data analysis for candidate events identified by internally triggered (by the Tupi experiment) as well as untriggered (dependent on external observations) modes of search. In light of the Fermi LAT () gamma-ray bursts (GRBs) catalog, we examine the possibility of the ground observation of similar transient events within the FOV of the extended Tupi array and perform a systematic analysis of the Tupi data. Using a Monte Carlo simulation, we discuss the experimental conditions that allow the detection of signals from GRBs at ground level.

Superradiant free-electron lasers in the high-gain strong pump regime

Time‐dependent high‐gain free‐electron laser equations are generalized to the strong pump regime where fast, 2π/kw, spatial oscillations can no longer be eliminated by spatial averages, and evolution of the radiation phase needs to be taken into account. The equations are solved numerically along the characteristics of the beam and the laser field for superradiant solutions in the strong pump regime using the parameters of the Electron Laser Facility (ELF) of the Lawrence Livermore National Laboratory, [Phys. Rev. Lett. 54, 889 (1985); Nucl. Instrum. Methods A 250, 144 (1986); 285, 217 (1989); Phys. Rev. A 35, 2184 (1987)]. With beam pulses short compared to the wiggler length and long compared to the cooperation length, numerical solutions show that the initial laser fields get amplified to the steady‐state level intensity in only a few bucket distances in the slippage region along the beam characteristics. The underlying mechanism for this superradiant gain gradient is due to the amplification of the in...

Coronal Loop Heating by the Fast Surface Wave

Although coronal plasmas are considered to be collisional, it is well known that particle collisions do not provide effective energy dissipation. It is shown that the wave-particle resonant interactions can dissipate energy fast enough to sustain the coronal temperature.