Small Gap Experiments in Magnetically Insulated Transmission Lines

We have performed experiments using magnetically insulated transmission. lines (MITL's) with anode-cathode gaps ranging from 0.15 to 0.40 cm. We have studied cathode plasma formation using laser schlieren photography, time resolved visible photography, and visible spectroscopy. Cathode plasma formation occurs within 10 ns of the application of the voltage pulse. Densities of 1015 cm-3-1017 cm-3 are inferred from the schlieren measurements. Negative ion formation in MITL's has also been observed which may result in losses in high-current-density small-gap power feeds.     

Numerical Computation of Self-sustaining Magnetically Confined Electron Clouds

In this paper the axisymmetrical self-sustaining magnetically confined electron clouds are studied by means of the numerical computational method on the basis of the fluid theory.The electron density distribution,electric potential distribution,drift angular frequency and electron temperature can be calculated with a simplified method in which the near-equilibrium state approximation is necessary.The results are,in principle,in agreement with the experiments.     

Active Plasma Boundary Sheath with Electron Emission

The influence of electron emission on the properties of the space charge sheath between plasma and wall is investigated theoretically using models of the stationary sheath. Especially, the following effects have been considered: Essential parameters of the sheath (e.g. potential drop, power flux density), of the wall surface (temperature, field strength, emission yield, Joule heat generation) and of the adjacent plasma layer (emission-caused change of the electron temperature) have been calculated under self-consistent conditions. From the obtained results several ways are discusséd indicating the development towards sheath instability and ending in the generation of plasma-induced arc spots.     

On The Motion of Ions in The Self-sustaining Magnetically Confined Electron Cloud

The motion of ions generated from the electron-atom ionization collisions in the self-sustaining magnetically confined electron cloud is studied.It is shown that the motion is chaotic.The method to determine the electric potential idstribution in the electron cloud by measurements of the ion current is discussed.     

Effect of Cathode and Anode Voltage on an Ion Sheath Thickness in a Magnetically Confined Diffusion Plasma

This article reports about the ion sheath thickness variation occurring in front of a negatively biased plate immersed in the target plasma region of a double plasma device. The target plasma is produced due to the local ionization of neutral gas by the high energetic electrons coming from the source region (main discharge region). It is observed that for an increase in cathode voltage (filament bias voltage) in the source region, the ion flux into the plate increases. As a result, the sheath at the plate contracts. Again, for an increase in source anode voltage (magnetic cage bias), the ion flux to the plate decreases. As a result, the sheath expands at the plate. The ion sheath formed at the separation grid of the device is found to expand for an increase in cathode voltage and it contracts for an increase in the anode voltage of the main discharge region. One important observation is that the applied anode bias can control the Bohm speed of the ions towards the separation grid. Furthermore, it is observed that the ion current collected by the separation grid is independent of changes in plasma density in the diffusion region but is highly dependent on the source plasma parameters. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of an S-Band Tapered Magnetically Insulated Transmission Line Oscillator

We present an improved structure of the tapered magnetically insulated transmission fine oscillator （MILO）. Simulation results show that this structure can obtain more microwave power with higher efficiency. Studies indicate that the distance between the load support legs and the last vane can affect the operation characteristics of this device. In the experiments, we obtain microwave with peak power of 2 GW, frequency of 2.63 GHz, and mode TMol. The beam to microwave power efficiency is 11%.     

Quantum-Secured Data Transmission in Urban Fiber-Optics Communication Lines

Quantum key distribution (QKD) provides theoretic information security in communication based on the laws of quantum physics. In this work, we report an implementation of quantum-secured data transmission in the infrastructure of Sberbank of Russia in standard communication lines in Moscow. The experiment is realized on the basis of already deployed urban fiber-optics communication channels with significant losses. We realize the decoy-state BB84 QKD protocol using the one-way scheme with polarization encoding for generating keys. Quantum-generated keys are then used for continuous key renewal in the hardware devices for establishing a quantum-secured VPN Tunnel between two offices of Sberbank. The hybrid approach used offers possibilities for long-term protection of the transmitted data; it is promising for integrating in the already existing information security infrastructure.     

Fluid Model of a Sheath Formed in Front of an Electron Emitting Electrode Immersed in a Plasma with Two Electron Temperatures

The formation of a sheath in front of a negatively biased electrode (collector) that emits electrons is studied by a one‐dimensional fluid model. Electron and ion emission coefficients are introduced in the model. It is assumed that the electrode is immersed in a plasma that contains energetic electrons. The electron velocity distribution function is assumed to be a sum of two Maxwellian distributions with two different temperatures, while the ions and the emitted electrons are assumed to be monoenergetic. The condition for zero electric field at the collector is derived. Using this equation the dependence of electron and ion critical emission coefficients on various parameters ‐ like the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons ‐ is calculated for a floating collector. A modification of the Bohm criterion due to the presence of hot and emitted electrons is also given. The transition between space charge limited and temperature limited electron emission for a current‐carrying collector is also analyzed. The critical potential, where this transition occurs, is calculated as a function of several parameters like the Richardson emission current, the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of Novel Focusing Mirrors in Gyrotron Transmission Lines

A novel focusing mirror based on the shifting of the beam phase according to the Gaussian beam optics enabled us to realize a focusing elements with different focal lengths in different directions and to convert the gyrotron output into a Gaussian-like beam. In this paper, we compare the quality of beams produced by the new system (which includes novel mirrors) and a conventional system consisting of a quasi-optical antenna, an ellipsoidal mirror and two parabolic cylinder mirrors.     

Goniometry for Interface Studies in Transmission Electron Microscopy

A method using a double-tilt goniometer stage for determining the orientation of crystalline specimens in transmission electron microscopy (TEM) is described. The procedure involves visual identification of two zone axes, and using the corresponding goniometer settings to plot these poles stereographically. Crystal orientations and misorientations can be established rapidly, and the method is intended for use as a practical complement to more precise but time-consuming techniques. The commutative operation of double-tilt stages and their goniometric capability are also discussed. Using Rodrigues-Frank space, it is shown that the set of attainable operations for such stages is represented by points on an hyperboloidal surface.     

Structure of a Plasma-Focus Current Sheath from Magnetic and Optical Measurements

Simultaneous measurements of the magnetic-field distribution and the light intensity emitted by the current sheath (CS) generated in a Plasma Focus (PF) device are presented. For operating deuterium pressures in the range 0.55-2.5 mbar, we derive the plasma density and the mean hydrodynamic velocity in a frame of reference fixed to the sheath, where both quantities are in agreement with the ones predicted by the strong ionizing shock theory. The electric field in the quoted frame is also deduced, and the obtained values are consistent with those reported by other authors.     

Quasioptical Transmission Lines for ECRH at TJ-II Stellarator

Two mirror lines have been used to transmit the microwave power from the powerful microwave generators to the TJ-II plasmas. Both lines have been tested at nominal power level and they are in operation now. This paper deals with the final design of the transmission lines and their testing. Before starting operation at high power level, measurements of the wave beam parameters at low power level were performed. Two horn antennas were designed to simulate the gyrotron output. The results are presented in this paper. A computer code based on Huygens diffraction theory was developed to simulate the propagation of the beam along the mirror lines. A comparison of the theoretical and the experimental results is also shown here.     

Low-Power Testing of Losses in Millimeter-Wave Transmission Lines for High-Power Applications

We report the measurement of small losses in transmission line (TL) components intended for high-power millimeter-wave applications. Measurements were made using two different low-power techniques: a coherent technique using a vector network analyzer (VNA) and an incoherent technique using a radiometer. The measured loss in a 140 GHz 12.7 mm diameter TL system, consisting of 1.7 m of circular corrugated waveguide and three miter bends, is dominated by the miter bend loss. The measured loss was 0.3 ± 0.1 dB per miter bend using a VNA; and 0.22 ± 0.1 dB per miter bend using a radiometer. Good agreement between the two measurement techniques implies that both are useful for measuring small losses. To verify the methodology, the VNA technique was employed to measure the extremely small transmission loss in a 170 GHz ITER prototype TL system consisting of three lengths of 1 m, 63.5 mm diameter, circular corrugated waveguide and two miter bends. The measured loss of 0.05 ± 0.02 dB per miter bend may be compared with the theoretical loss of 0.027 dB per miter bend. These results suggest that low-power testing of TL losses, utilizing a small, simple TL system and a VNA, is a reliable method for evaluating performance of low-loss millimeter-wave TL components intended for use in high-power applications.     

Closed-form Analysis of Lossy Cosine-Squared Tapered Nonuniform Transmission Lines

The rigorous analytical solutions and the ABCD matrix of the lossy Cosine-Squared tapered nonuniform transmission lines (CSTNTL) are presented in this paper. According to different boundary conditions, the unique solution is obtained mathematically. Through the numerical calculations based on analytical solutions, the distributed voltages and currents in different terminated cases are shown to explain the transmission characteristics of CSTNTL. Especially in the lossy case the distributed power values are simulated to show the attenuation phenomenon.     

Electrochemic and Photophysics Properties of Pyridine-Based Electron Transmission Material

A pyridine-based polybenzobisoxazole (PBOPy) was synthesized via solution condensation polymerization. The polymer was characterized by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis, ultraviolet-visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, electrochemical cyclic voltammetry, and time-resolved PL decay dynamics. Results showed that the introduction of pyridine groups made the oxidation potential (1.82 eV) relatively larger than that of poly(p-phenylenebenzobisoxazole) (PBO) (1.65 eV), while the reduction potential (?1.18 eV) was smaller than that of PBO (?1.28 eV). It can be concluded, by comparing UV-Vis absorption spectroscopy and PL spectroscopy of PBOPy in film and in methanesulfonic acid (MSA), that PBOPy has a stronger protonation effect in the latter. The optical properties of PBOPy exhibited a PL emission band at 473 nm in thin films and a strong orange fluorescence (498 nm) after being protonated with MSA. The protonation effect resulted in a large Stokes shift, about 71 nm.     

An Optimum Sectional Waveguide Taper for Quasioptical Transmission Lines

The paper considers an optimum sectional waveguide taper (OSWT) which at a shortest length of the transition region provides nearly adiabatic propagation of the fundamental mode between circular, widely different in diameter quasioptical transmission lines of class hollow dielectric waveguide (HDW). Derived as a consequence of coaxial circular-horn sections, the OSWT offers all the advantages of a simple geometry and lends itself to simple fabrication techniques. The relationships among the critical geometrical parameters and the loss calculation formulae are presented. The comparison studies show that even at a few sections, the OSWT is almost as good in performance as the parabolic taper, but the OSWT is much better from a mechanical viewpoint. And compared to the ordinary linear taper, the OSWT allows essential cut in length and loss with the broadbandness kept. The HDW-based four-sectional OSWT has been fabricated and tested in a quite broad wave range 2,5-8 mm. The testing results lend a good support to the analytical formulae lying at the basis of the design software.