Coaxial Channels Research Articles

Operational characteristics and plasma measurements in cylindrical Hall thrusters

The cylindrical Hall thruster (CHT) is an attractive approach to achieve a long lifetime thruster operation especially in low power space applications. Because of the larger volume-to-surface ratio than conventional coaxial Hall thrusters, the cylindrical Hall thrusters are characterized by a reduced heating of the thruster parts and potential lower erosion. Existing CHTs can feature a short coaxial channel in order to sustain a high ionization in the thruster discharge. A 5.6 cm diameter cylindrical Hall thruster was developed and operated with and without a short coaxial region of the thruster channel, in the power range of 70–300 W. It is shown that the CHT without coaxial region can operate stable and achieve higher thrust efficiency, 22%–32% more than that with a coaxial region. Plasma probe measurements inside the thruster channel and ion energy measurements in the plasma plume suggest that the ionization/acceleration region in the CHT is located near the anode region where a radial magnetic field is stronger.

Multi-spot modes of unsteady gasless combustion of a thick-walled cylinder under adiabatic conditions

Propagation of multi-spot spinning waves in a cylindrical specimen with a coaxial inner channel is studied by numerical methods under the assumption of the absence of heat removal from the outer surface of the specimen and from the channel surface. Variations of the spinning wave characteristics (longitudinal and tangential velocities, “pitch,” and maximum temperature and period) are demonstrated by an example of two-spot spinning waves for specimens of different sizes with a fixed channel radius, for specimens of a particular size with different channel radii, and for specimens with a constant wall thickness and varied inner and outer radii.

High-current oversized annular electron beam formation for high-power microwave research

The authors report the study of a high-current accelerator, capable of producing thin (2mm) annular, mildly relativistic (450keV) electron beams (up to 1.5kA) of diameter of 70mm. Propagation of an electron beam through a 2m long, coaxial beam channel, with inner and outer conductor radii of 30 and 40mm, respectively, was demonstrated with the electron beam current at the beam-channel output measured using a Rogowski coil. The results obtained are compared with those predicted via numerical simulation. The electron beam obtained was used for proof-of-concept work demonstrating the operation of a high-power maser operating at millimeter wavelengths, using two-dimensional distributed feedback.

Propagation of a one-spot spinning wave in a thick-walled cylinder under adiabatic conditions

Propagation of a one-spot spinning wave in a cylindrical specimen with a coaxial internal channel is studied by numerical methods under the assumption of the absence of heat removal from the outer surface of the specimen and from the channel surface. Variations of the spinning wave characteristics [maximum temperature, longitudinal and circumferential (tangential) velocities, “pitch,” and time of rotation of the hot spot around the specimen centerline] are tracked for a specimen of a particular size with a varied channel radius, for specimens of different sizes with a fixed channel radius, and for specimens with a constant wall thickness.

High Speed Transmission for a Coaxial Cable based In-Home Network

The in-home network is a crucial system for ubiquitous multimedia environments, in order to provide economical and effective high data rate transmission, we propose a transmission scheme based on the multi-carrier technique. We employ a coaxial cable channel as the transmission medium deployed for cable television (CATV). Through experiments, we show that it is possible to transmit a signal centered at 1.2 GHz with 528 MHz bandwidth without giving severe interference to the CATV system. With this observation, we propose an orthogonal frequency division multiplexing (OFDM)-based transmission scheme motivated by successful implementation of multiband OFDM (MB-OFDM) as the short range wireless transmission medium. The proposed OFDM-based system with several elementary techniques specialized in the coaxial cable for home network (CoHoNet) can achieve robust transmission over several experimental channel realizations with low power consumption.

A CMOS Finite Impulse Response Filter With a Crossover Traveling Wave Topology for Equalization up to 30 Gb/s

This paper describes a fully differential 3-tap finite impulse response filter in 90-nm CMOS. A traditional traveling wave filter topology is modified to alleviate its inherent delay-bandwidth-gain tradeoffs. Each tap gain is comprised of two transconductors whose outputs superimpose with the same group delay, similar to a distributed amplifier. This doubles the bandwidth of the filter for a given tap spacing and gain. Digital control is provided for the tap gains, an integrated pre-amplifier, and tuning varactors. Coupled differential spirals are used in the delay lines to help the design fit into an area 600 /spl mu/m/spl times/500 /spl mu/m. A 1-V supply voltage and 25-mW power consumption are enabled by the use of parallel differential pairs for sign control of the transconductances instead of Gilbert cell amplifiers. The input return loss is better than 16 dB and the output return loss is better than 9 dB up to 30 GHz. Equalization of NRZ data over a coaxial cable channel was demonstrated up to 30 Gb/s, making it faster than any previously reported CMOS equalizer.

Computation of axisymmetric MHD flows in a channel with an external longitudinal magnetic field

A numerical study of two-dimensional plasma flows in coaxial channels of plasma accelerators is presented. Two new results are obtained. First, for the computation of MHD problems belonging to the class under consideration, Zalesak’s method is used. It is based on an explicit finite difference scheme with flux correction. This method is free of space splitting, and, therefore, is well suited for parallel computations on multiprocessors. Second, the statement of the problem is extended so that the acceleration of the plasma by the azimuth magnetic self-field goes on in the presence of an external longitudinal field. The results of test computations demonstrate the efficiency of the method and made it possible to investigate the influence of the longitudinal field on the properties of the plasma flows.

Search for the emission of π0 mesons from the neutron-induced fission of 235U nuclei

A nuclear-reactor experiment on the search for the emission of neutral pions from the neutron-induced fission of 235U nuclei has been carried out. To this end, an experimental setup for searching for the emission of π0 mesons with high sensitivity to this process has been designed and produced. This setup consisted of two Cherenkov total-absorption spectrometers for the detection and measurements of the energy of two gamma-ray photons from π 0-meson decay. The spectrometers were placed at the exits of two coaxial horizontal experimental channels. To protect the detectors from low-energy β and γ rays and neutron fluxes, 3.5-m-long water filters were situated in the channels. To reject the cosmic background, large-area scintillation counters operating in the anticoincidence mode were placed over each spectrometer. The energy and time resolution of the spectrometers, as well as the efficiency of detecting charged particles by scintillation counters, were tested on the secondary electron beam of the Tomsk electron synchrotron Sirius. Runs of measurements of the effect on the operating reactor (duration of 805 h) were alternated with runs of measurements of background on the stopped reactor (duration of 403 h). Statistical processing of the experimental results yields an upper limit of ≤5.3×10 −12 with a 90% confidence level for the probability of the emission of neutral pions from the neutron-induced fission of 235U nuclei. This result and results of other works carried out with sources of spontaneously fissioning 252Cf nuclei show that the probabilities of the emission of π0 mesons from spontaneous fission and fission induced by fission-spectrum neutrons are equal to each other.

Experimental Limit on the Probability of Neutral Pion Emission in Neutron-Induced Fission of235U Nuclei

Results of an experiment on the search for the emission of π0 mesons in neutron-induced fission of 235U nuclei based on the detection in coincidence of two γ-quanta from the π0-meson decay performed with the nuclear reactor developed at the Scientific-Research Nuclear Physics Institute at Tomsk Polytechnic University are described. The experimental setup comprised two Cerenkov spectrometers of total absorption for the detection and measurement of γ-quantum energy placed in two coaxial horizontal channels of the nuclear reactor. Water filters placed in the channels were used to protect the detectors from β-, γ-, and neutron fluxes. To reject the cosmic radiation, scintillation counters of large area, operating in anticoincidence mode, were placed above each spectrometer. The experimentally measured limitation on the probability of neutral pion emission in neutron-induced fission of nuclei was established ≤4.1·10–11 with a 90% confidence level. The energy spectrum of γ-quanta from the active reactor zone was measured in the range 32–65 MeV. The parameters of the spectrum deviated from the results of theoretical calculations and from the experiment performed with the nuclear pulse reactor developed at the Joint Institute for Nuclear Research (Dubna).

Simulation of the co-combustion of loaded activated charcoal in the combustion chamber of a waste incineration plant

Activated charcoal filters are widely used as the final stage of flue gas purification behind waste incineration plants. The used activated charcoal, loaded with sulphuric and nitric oxides, metals, mercury, dioxines, furanes and other pollutants, shall be burned in the combustion chamber of the plant. In order to achieve a stable ignition and a complete burnout of the charcoal, a newly developed oxygen-nitrogen solid fuel burner is used. The pulverized charcoal is fed by pneumatic transport with technical pure nitrogen as feed gas into the burner. Technical pure oxygen is added as oxidizing gas through coaxial channels and swirler blades. To predict both the efficiency of the burner and the influence on the flow field, emission and fouling behaviour of the combustor, simulations were carried out using the three-dimensional CFD code FLOREAN. Despite the small thermal capacity of the burner compared to the thermal capacity of the burned waste significant changes occur in the flow and temperature distribution inside the combustion chamber. Besides a slight rise of NOx emissions, the high local temperature peaks obtained can cause additional fouling and slagging of the furnace walls.

Influence of a Longitudinal Magnetic Field on the Hall Effect in the Plasma Accelerator Channel

An analytic model of steady-state two-dimensional flows in coaxial plasma-accelerator channels in the presence of a longitudinal magnetic field is proposed. The solution of the problem is found in the smooth channel approximation for the MHD equations of an ideal two-component plasma. An example of the developing axisymmetric flows is given and the features of the plasma-dynamic processes are investigated. It is found that the Hall effect and the anode flow zone can be reduced using a longitudinal field and plasma rotation.

The motion of a neutral spherical particle between coaxial cylindrical surfaces

The tangential and normal components of a dipole force acting upon a neutral spherical particle moving parallel to the axis of symmetry of a coaxial cylindrical channel with different permittivities of the internal and external walls are calculated in a nonrelativistic approximation of the fluctuational electromagnetic theory. Upon a limiting transition, the obtained formulas coincide with the previous results for a particle moving inside a cylindrical channel or parallel to the generatrix of a convex cylindrical surface. The problem is considered in the general case of different temperatures of the particle and the surface.

Portable spectrometer based on segmented HPGe detector with background suppression

The results of development of a portable spectrometer based on a segmented HPGe detector with background suppression for radioactive waste monitoring are presented. The detector has a planar and a coaxial segments, 68 mm in diameter and, respectively, 20 and 50 mm in length. The energy resolution of the planar segment was 1.3 keV on the energy of 122 keV and of the coaxial segment-2.5 keV on the energy of 1.33 MeV. The relative efficiency of the whole crystal was 60% at the energy of 1.33 MeV. The background suppression system has independent channels for amplifying and shaping the spectrometric pulses at the planar, coaxial and common outputs of the segmented detector. The planar and coaxial channels have a nonswitchable shaping time constant of 2 /spl mu/s and the common channel-a switchable shaping time constant of 2 /spl mu/s or 4 /spl mu/s. The background suppression system is PC-controlled by the special software. Testing of the spectrometer with isotopes Cs-137 and Cs-137 + Co-57 has shown that the relative improvement in peak-Compton ratio for registration with and without suppression is 1.4 for the energy of 662 keV and exceeds 1.5 for the energy of 136 keV.

On electrostatic acceleration of plasmas with the Hall effect using electrode shaping

Resistive magnetohydrodynamics (MHD) is used to model the electromagnetic acceleration of plasmas in coaxial channels. When the Hall effect is considered, the inclusion of resistivity is necessary to obtain physically meaningful solutions. In resistive MHD with the Hall effect, if and only if the electric current and the plasma flow are orthogonal (J⋅U=0), then there is a conserved quantity, in the form of U2/2+w+eΦ/M, along the flow, where U is the flow velocity, Φ is the electric potential, w is the enthalpy, and M is the ion mass. New solutions suggest that in coaxial geometry the Hall effect along the axial plasma flow can be balanced by proper shaping of conducting electrodes, with acceleration then caused by an electrostatic potential drop along the streamlines of the flow. The Hall effect separation of ion and electron flow then just cancels the electrostatic charge separation. Assuming particle ionization increases with energy density in the system, the resulting particle flow rates (Jp) scales with accelerator bias (Vbias) as Jp∝Vbias2, exceeding the Child–Langmuir limit. The magnitude of the Hall effect (as determined by the Morozov Hall parameter, Ⅺ, which is defined as the ratio of electric current to particle current) is related to the energy needed for the creation of each ion–electron pair.

Laminar Heat Transfer in Diffuser Flow in a Coaxial Conical Channel in the Case of Boundary Conditions of the First Kind

Consideration is given to the problem of convective heat transfer in slow diffuser flows in coaxial annular conical channels of constant width. A solution for thermal boundary conditions of the first kind is obtained by the method of separation of variables. The dependence of the temperature on the coordinates is represented in the form of a sum of two infinite series in confluent hypergeometric functions of the transverse coordinate that are multiplied by an exponential dependence on the longitudinal coordinate. The solution is of interest due to its being a superposition of two solutions, each having its own eigenfunctions and eigenvalues. Relations for evaluation of the initial thermal portion in the considered flows are also given.

Miniaturized time-of-flight mass spectrometer for peptide and oligonucleotide analysis.

A matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer was developed which uses a novel reflectron composed of a grounded cylinder and an adjustable endcap electrode to provide high-order kinetic energy focusing for a miniaturized mass analyzer. The nearly quadratic potential form of the reflecting field focuses ions desorbed from a source of very small dimensions formed by placing the sample probe within the centered hole of the coaxial dual channel plate detector. At the same time, the depth of the reflectron can be adjusted to accommodate a short drift length between the source/detector and the reflectron. For larger drift lengths, in particular to allow the addition of an XY stage for the analysis of sample arrays, endcap reflectron focusing can be combined with time-delayed ion extraction to achieve good mass resolution. The instrument has been used for the analysis of peptides digested with trypsin or carboxypeptidase, and also small DNA oligomers.

Determination of microturbulence enhanced electron collisionality in magnetized coaxial accelerator channels by direct magnetic field measurement

A miniature magnetic probe array, consisting of 10 spatially separated coils, has been used to obtain profile information on the time varying magnetic field within the 2.54 cm wide flow channel of the coaxial plasma source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)]. The magnetic field data have been used, together with a resistive, Hall magnetohydrodynamic (MHD) model of applied field distortion by the flowing plasma, to obtain estimates of the microturbulent enhancement to electron collisionality within the CPS-1 flow channel. These measurements provide direct experimental evidence of anomalous electron collisionality, a previously predicted effect in these devices. The anomaly parameter, a=νan/νcl, determined both from the distortion of contours of constant magnetic flux, and from local Bθ and Bz measurements scales with the classical electron magnetization parameter (Ωcl=ωce/νecl), indicating that collisionality plays a strong role in determining the level of anomalous transport in the plasma. When this anomaly parameter scaling is cast in terms of the ratio νecl/ωlh, it is found that the resistivity enhancement scales with νecl/ωlh, and becomes significant at νecl/ωlh⩽1, suggesting that a lower hybrid drift instability may be the responsible mechanism for enhanced transport.

Direct magnetic field measurement of flow dynamics in magnetized coaxial accelerator channels

A miniature magnetic probe array, consisting of ten spatially separated coils, has been used to obtain profile information on the time-varying magnetic field within the 2.54 cm wide flow channel of the Coaxial Plasma Source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)] at the North Carolina State University. Two-dimensional (2-D) current profiles within the annular flow channel, which were constructed from the time-varying magnetic field data, reveal several complex features reflecting the influence of gun inductance, the Hall effect, and the applied magnetic field. When an external, electrode linking magnetic field is applied, the evolution of the 2-D current profile shows evidence of an ionizing shock front identified by a narrow current sheet propagating through the channel during the first few microseconds of the discharge. The thickness of this current sheet is on the same order as both the collisional mean-free path and the ion electromagnetic skin depth. In this applied field case, the plasma is prevented from advancing ahead of the current sheet by the applied magnetic field, which turns the ions and electrons without collisions. In the absence of an applied field, plasma is able to advance ahead of the current sheet, where it may initiate ionization downstream before the advance of the ionization front.

A radio-frequency bandpass mass filter for broad ion beams

A bandpass mass filter for broad ion beams based on mass selective radio-frequency acceleration of ions is described. The ions are extracted from a broad beam ion source by a conventional hole two-grid extraction system. The mass separation consists in multiaperture coaxial hole channels formed of seven grids. The dimensions of the channels are calculated. This arrangement is investigated by ion ray tracing and by experimental investigation. Results for mass resolution (M/ΔM), transmission, and beam current density are presented. For nitrogen, argon, and krypton a transmission of 5%, a beam current density of 4 μA/cm2, and a mass resolution of 4 are achieved.

Hall effect in the MHD model of plasma channel flow

The steady flow regime with quasi-radial electric current and nonequipotential boundaries is obtained in calculating axisymmetric plasma flow in a coaxial channel with an azimuthal self-magnetic field. The calculations were carried out using the MHD model with allowance for the Hall effect. The regime obtained describes the flow in the stream core of the channel of a modern quasi-steady heavy-current plasma accelerator outside thin near-electrode layers. Estimates of the Hall corrections relating to these layers are given.