Based on a capacitively coupled electrical discharge scheme, it is demonstrated that an array of plasma torches can be lit up simultaneously to form a dense plasma layer in the open air by a single ac power source. The number of torches is only limited by the power handling capability of the source. The measured v–i characteristic of the discharge indicates that the torch is operating in the diffuse arc mode. Experiments have been performed to explore the effect of the plasma torches on the propagation of microwaves in an X-band rectangular waveguide by passing the plasma of the torches through holes in the top and bottom walls of the waveguide. The results show that the plasma torches can effectively attenuate microwaves. The wave–plasma interaction process is also analyzed numerically. The plasma parameters deduced from the theoretical model, by matching the numerical results with those of experiments, are shown to agree well with the experimental measurements.
Abstract. It is shown that a spatially distributed mode current of whistler waves, oscillating at the modulation frequency of the ground-transmitted powerful HF wave, can be induced in the Eregion of the lfigh-latitude ionosphere through the coupling between HF wave-modulated electrojet current and induced density irregularities. As shown in Kuo et. al. [1999], these density irregularities generated by the I-IF wave via a thermal instability vary periodically along the geomagnetic field. This current produces wlfisfler waves directly rather than through an antelma radiation process. Tiffs mechanism generates whistler waves in the VLF range (3-30 KHz) wi.'th reduced harmonic components. The frequencies of produced whistler waves depend on the polarization, frequency, power, and modulation scheme of the I-IF wave. It is predicted that whistler waves at frequencies around 25 KHz can be most favorably excited, awaiting the corroboration of future ionospheric heating experiments.
Abstract. A new mechamism is investigated to generate spatially periodic temperature and density irregularities along the geomagnetic field in the ionospheric E-region, using ground transmitted powerful I-IF (high frequency) waves. A thermal instability is first excited and then stablized by the nonlinear damping from the inelastic electron collisions with N2 and 02. Electron temperature enhanced by powerful HF waves reduces the recombination rates of electrons and NO + and 02 + ions, and subsequently increases the plasma density. The tl•ermal diffusion of electrons evolves the perturbation into spatially periodic density irregularities along the geomagnetic field. The spatial period between 400 m and 1.6 km of the irregularities varies with the I-IF wave power and frequency. The optimal conditions for excith•g these irregularities are achievable at sites for ionospheric heating experiments. The investigated mechanism works effectively only in the presence of ionization sources, such as UV radiations during the daytime and precipitated energetic particles at night.
Abstract. Z-mode wave converted from O-mode heater wave is considered as the pump wave in Tromso I-IF heating experiments for the parametric excitation of lower hybrid decay mode together with electron Bernstein sidebands in the region above the O-mode reflection layer. This is the process, suggested by Mishin et al. [ 1997], which generates superthermal electrons by the excited lower hybrid waves. These superthermal electrons produce plasma waves in the region above the O-mode reflection layer, with frequencies much greater than the heater wave frequency, as observed by Isham et al. [1990, 1996]. Our detailed analyses of this process are carried out for two experimental cases wherein the pump wave frequencies are near the third and fifth harmonic electron cyclotron frequencies, respectively. The results show that the minimum threshold field of the instability in either case is less than 0.2 V m -•. However, because the wavelength of the instability is also short, the collisionless dampings restrict the instability occurrence to narrow wavelength and frequency ranges. For 1 V m -• pump field intensity, the instability can be excited in less than I ms. Since the excited lower hybrid waves are strongly Landau damped, superthermal electrons are efficiently generated by them.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.