Determining the Current-Compensation Factor for a High-Current Relativistic Electron Beam in the Presence of an External Liner

The current-compensation factor f _m of a high-current relativistic electron beam (REB) with an energy E _e = 1.1 MeV, a current I _b = 24 kA, and a pulse duration t _p = 60 ns was investigated. The beam traveled in a metallic drift pipe filled with air at a pressure of 1 to 760 Torr. The dependence of the current compensation of the REB on the resistance of an external liner and the gas pressure was determined by two methods: using Rogowski loops placed around the transport channel or resistive back-current shunts inserted in the breaks of the drift pipe. It was ascertained that f _m of the high-current REB slightly varied with the gas pressure and was virtually independent of the resistance of the external liner. It was shown that the current compensation could be correctly determined by measuring the total current with the Rogowski loops placed inside the drift pipe and not with resistive shunts.     

Theoretical analysis of novel weak current sensor using FeCuNbSiB single nanocrystalline toroidal core and double-winding

An Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline toroidal core made by isothermal furnace annealing shows good thermal stability of magnetic properties and excellent soft magnetic properties due to the full release of the internal stresses of the core during the annealing process. Based on the feature of the magnetic core, a novel non-contact type weak current sensor adopting single nanocrystalline core and double-winding excited by multivibrator bridge is proposed. The measuring principles for static current are given in theory by an established mathematical model of the sensor. The theory is in good agreement with the experimental results and it indicated clearly the key factors affecting performance parameters for the sensor. The multivibrator bridge output signal was analyzed by Fourier transform. Furthermore, according to the theoretical results, the method to design the signal conditioning circuit was introduced. __________ Translated from Chinese Journal of Scientific Instrument, 2005, 26(12) (in Chinese)     

A source of a high-power relativistic electron beam with high brightness

A ribbon diode of a U-2 accelerator (800 kV, ∼30 kA) intended for generating a high-intensity electron beam for heating plasma in a GOL-3 multimirror magnetic trap (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences) is described. The parameters of the beam characterized by a high brightness (∼7 kA/(cm² sr)) in a magnetic field of ∼5 T resulting from a numerical simulation of the beam formation process are presented. The results of simulation of the beam transport and transformation of the profile of its cross section during movement of electrons in a curvilinear guiding magnetic field are presented. The calculated cross section is compared to the beam imprint on a target.     

A capacitor cell of a capacitive energy storage with a switch based on reverse switch-on dynistors

A capacitor cell of a capacitive energy storage designed for operating with an arc load is described. The cell that stores an energy of 64 kJ is based on a high-voltage (18 kV) capacitor and allows formation of current pulses with an amplitude of up to 60 kA. The discharge circuit of the cell contains a semiconductor switch in the form of an assembly of reverse switch-on dynistors (RSDs) connected in series, a crowbar diode switch, and a replaceable toroidal inductor. An assembly of protecting diodes connected in series to the RSD switch excludes the possibility of a flow of reverse-current pulses through dynistors. All elements of the cell are mounted on the capacitor and occupy a volume of 120 dm³.     

A high-current subnanosecond electron accelerator with a gas-filled former

A subnanosecond electron accelerator prototype based on the ARSA small-size accelerator with a gas-filled former (nitrogen ~4 MPa) has been developed and studied. The operation principle of the former involves charging of a short storage line and its discharge to a stepped line with an accelerating tube that generates electrons. The recorded electron-beam current pulse length was t_0.5 = 0.3 ns, the current amplitude was at least 1.5 kA, and the maximum electron energy was ~850 keV.     

Diamagnetic flux measurement in Aditya tokamak

Measurements of diamagnetic flux in Aditya tokamak for different discharge conditions are reported for the first time. The measured diamagnetic flux in a typical discharge is less than 0.6 mWb and therefore it has required careful compensation for various kinds of pick-ups. The hardware and software compensations employed in this measurement are described. We introduce compensation of a pick-up due to plasma current of less than 20 kA in short duration discharges, in which plasma pressure gradient is supposed to be negligible. The flux measurement during radio frequency heating is also presented in order to validate compensation.     

Network numerical analysis of hydromagnetic squeeze film flow dynamics between two parallel rotating disks with induced magnetic field effects

We study numerically the hydromagnetic squeeze film between two rotating disks using the numerical network simulation method. The external magnetic field, H, generates an induced magnetic field, B, with radial (B_r), tangential (B_θ) and axial (B_z) components between the two disks, which rotate with different angular velocities, Ω₁ and Ω₂, and at time t are separated by a distance D(1−αt)^1/2. The applied magnetic field at the lower disk is assumed to be zero. The conservation equations for mass, momentum and induced magnetic field are reduced to a set of ordinary differential equations using a series of transformations, in terms of four dependent variables, f (axial velocity), g (azimuthal velocity), m (axial magnetic field component) and n (azimuthal magnetic field component) and a single independent variable, η (dimensionless disk separation), with appropriate boundary conditions. The transformed ordinary differential equations have collective order of 10 and are shown to be controlled by rotational Reynolds number (R₁), squeeze Reynolds number (R₂=Re_m/Bt), dimensionless parameter based on the magnetic force in the axial direction (R₃), dimensionless parameter based on magnetic force strength in the azimuthal (tangential) direction (R₄), magnetic Reynolds number (Re_m), disk rotational velocity ratio (S) and Batchelor number (Bt). In the present study we examine the flow regime at various Batchelor numbers (for the case of unity value of the squeeze Reynolds number, Re_m=Bt). Excellent comparison of NSM solutions is achieved with earlier analytical and shooting solutions. The present study finds applications in hydromagnetic lubrication of braking devices, slider bearings, rotating machinery, etc. Applications also arise in hydraulic shock absorbers employing electrically conducting liquids such as sodium where electro-magnetical braking of streams can be achieved in liquid metal cooled nuclear reactors for arresting control rods. Finally in the context of astronautical vehicles, the present study has applications in electromagnetic braking for potential spacecraft in planetary orbits.     

Solute-enriched surface layers and X-ray microanalysis of thin foils of a commercial aluminium alloy

Thin foils of the commercial Al alloy 7075 were subjected to X-ray microanalysis in a Jeol 100 CX TEMSCAN using a modified double-tilting stage. The ratio of the Cu K_x and Al K_x peaks, I_cu/I_Al, was found to decrease rapidly with increasing foil thickness, t, in regions thinner than about 200 nm. This was attributed to the formation of surface layers enriched in Cu during electropolishing, consistent with the findings of other investigators. An equation predicting the variation of I_B/I_A with t in an A-rich alloy in which B (or additional solute elements) is dilute is derived for a sample with surface layers enriched in B. The derivation predicts that I_B/I_A should vary linearly with t^?1, and that the intercept of such a plot should be positive. It is suggested that consistency with this prediction serves as a criterion for true surface enrichment. Our data on Cu obey these predictions, and further analysis indicates that the layers on both surfaces are enriched by a factor of about 5.6. The ratio of the intensities of the Zn K_x and Al K_x X-ray peaks was found to be nearly independent of foil thickness to t?400 nm. This result, combined with additional analysis, indicates that the apparent enrichment observed by other investigators is most likely due to the influence of instrumental factors.     

Toroidal versus ball nose and flat bottom end mills

This paper compares the surface roughness along and across the feed directions produced by toroidal, ball nose, and flat bottom end mills. The study is conducted numerically and by cutting tests of aluminium. The results show that the toroidal cutter inherits the merits of the other two cutters; it produces small scallops across the feed direction, and low roughness along the feed direction.Nomenclature h scallop height - R _s radius of curvature of surface - inclination angle - 2a _c cross-feed - 2 subtended angle between the point of contact on the tool profile and the surface - R _a surface roughness - e offset distance of insert from tool axes for toroidal cutter - r _c cutter radius - r _i radius of insert for toroidal cutter - f _t feed per tooth - h _u undercut height - y, , intermediate variables     

Tribological Performance of Fe<Subscript>67</Subscript>B<Subscript>33</Subscript> Alloy Prepared by a Self-Propagating High-Temperature Synthesis Technique

A bulk Fe₆₇B₃₃ alloy was prepared by a self-propagating high-temperature synthesis technique that is convenient, low in cost, and capable of being scaled up for tailoring the bulk materials. The Fe₆₇B₃₃ alloy is composed of dendrites with the t-Fe₂B phase and eutectic matrix with the α-Fe and t-Fe₂B phases. The content of the dendrite t-Fe₂B is above 80 vol.%. The compressive fractured strength and Vickers microhardness are 3400 MPa and 12.4 GPa, respectively. The tribological performance of the Fe₆₇B₃₃ alloy is investigated under dry sliding and water lubricant against Si₃N₄ ceramic ball. The wear rates of the Fe₆₇B₃₃ alloy are of the magnitude of 10⁻⁵ to 10⁻⁴ mm³/m under water lubricant. It is lower than that of the Fe₆₇B₃₃ alloy under dry sliding (10⁻⁴ mm³/m). But both the friction coefficients are almost identical. Oxide layers form in both environments via different tribochemical mechanisms, which led to significant differences in wear behavior.     

On the causes of the formation of a maximum in the dependences of the coercive force of simple carbon steels on the tempering temperature

The dependences of the coercive force H _c of quenched specimens made of simple carbon steels on the tempering temperature T _t were measured at room and liquid-nitrogen temperatures. These studies showed that the formation of the character of H _c(T _t) dependences for the mentioned steels within the region of medium and high tempering temperatures is caused by the content of cementite and its magnetic hysteresis properties.     

Dependence of the Detectability of Flaws on the Distribution of the Magnetizing Field in the Vicinity of a Flaw

It is shown that the flaw detectability of the magnetic-powder inspection method depends on the ratio of the normal H _n and tangential H _t components of the field in the flaw's vicinity and that H _n/H _t < 3 is a condition that ensures the detectability of surface flaws.     

400-kV trigatrons for high-power low-inductance pulse generators

A series of four-channel trigatrons operating at a voltage of up to 400 kV and a current of 280 kA per channel have been developed and tested. The control electrode is coaxially arranged in a hole of the main (positive) high-voltage electrode. This design ensures a small spread (jitter) of the operation delay time (Δt _d < 1 ns) for the discharge gap filled with elegas (SF₆). The electric strength of lateral surfaces of the device body is increased without using dielectric fluids. The service life of switches is increased by using tubular metal (steel) screens in the working volume. For the parallel operation of trigatrons, the Δt _d value is also below 1 ns, but it sharply increases if the gap between the main electrodes exceeds 11–12 mm.     

Influence of glass substrate thickness in laser scribing of glass

The thickness of the glass substrate used in liquid crystal displays continues to be decreased from its original thickness of 1.1 mm for the purpose reducing size and weight. The aim of this study was to clarify the influence of the glass substrate thickness during laser scribing with crack propagation caused by laser heating followed by quick quenching. The laser scribe conditions for soda-lime glass substrates with thickness equal to or less than 1.1 mm were obtained in laser irradiation experiments. Two-dimensional thermal elasticity analysis was conducted with a finite element method based on the scribable conditions obtained in the experiment. The laser scribable conditions can then be estimated by the upper limit of the maximum surface temperature, T_max, and the lower limit of the maximum tensile stress, σ_tmax, in the cooling area, regardless of the glass substrate thickness. There is a substrate thickness with which the maximum tensile stress σ_tmax becomes the largest under each scribe condition. The substrate thickness with which σ_tmax becomes the largest is obtained at a faster scribe velocity for thinner glass substrate and at slower scribe velocity for thicker glass substrate. Owing to these relations, the crack depth also has almost the same tendency as σ_tmax.     

A Programmable Device for Experiments Employing a Superheated Probe in the Pulsed Operation Mode

A device was developed for experiments on the controlled heating of a thin wire probe immersed in the substance being analyzed, with penetration into the region of short-lived (superheated) states of the substance. The thermostabilization of the probe, pulse-heated to the selected temperature T _pl(t > t _pl), is described. Using the iteration method, the software fits the coefficients of the heating function to reproduce the required temperature regime with an error of <0.5% over 10–20 cycles. The length of the stabilization pulse in the experiments was 1–10 ms at probe temperatures as high as 1000 K. The sensitivity of the compensation technique of relative measurements to relative changes in the thermophysical properties of a superheated substance was 10^–3 at a characteristic time of 10 s.     

Magnetoimpedance Properties of Amorphous CoFeSiB Wires in a Wide Frequency Range: Focus on Sensor Applications

The magnetic properties and specific features of giant magnetoimpedance in rapidquenched amorphous wires of composition (Co_0.94 Fe_0.06 )_72.5Si_12.5 B₁₅ are investigated. The working interval and sensitivity to changes in an external quasistatic magnetic field have been calculated for the alternating current frequencies from 1 MHz to 1 GHz. Parameters that are optimum for using such wires as sensitive elements in magnetic field sensors have been calculated, and the probe sensitivity to the external magnetic field has been determined. A sensor prototype was designed that, when tested, confirmed the possibility of using the giant magnetoimpedance in sensors based on amorphous CoFeSiB wires for flaw detection.     

Experimental investigation and optimization of EDM process parameters for machining of aluminum boron carbide (Al–B4C) composite

This study investigates the effect of electric discharge machining (EDM) process parameters [current, pulse-on time (T_on), pulse-off time (T_off) and electrode material] on material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) during machining of aluminum boron carbide (Al–B₄C) composite. This article also summarizes a brief literature review related to aluminum metal matrix composites (Al-MMCs) based on different process and response parameters, work and tool material along with their sizes, dielectric fluid and different optimization techniques used. The MMC used in the present work is stir casted using 5% (wt) B₄C particles of 50 micron size in Al 6061 metal matrix. Taguchi technique is used for the design of experiments (L₉-orthogonal array), while the experimental results are analyzed using analysis of variance (ANOVA). Response table for average value of MRR, EWR and SR shows that current is the most significant factor for MRR and SR, while electrode material is most important for EWR. ANOVA also confirms similar results. It is also observed that the optimum level of process parameters for maximum MRR is A₃B₁C₃D₃, for minimum EWR is A₁B₂C₃D₁, and for SR is A₁B₃C₃D₃.     

The Coaxial Shunt for Measurement of Current Pulses of Artificial Lightning with the Amplitude up to ±220 kA

The improved construction of the coaxial shunt SC-300M intended for measurement of decaying sine and aperiodic pulses of artificial lightning current with amplitudes up to ±220 kA is described. The results of tests of the instrument shunt in the high-current discharging circuit of power high-voltage generator of lightning current (g.l.c.) under pulsed A-component with the first amplitude -198 kA corresponding to time ≈35 µs and an action integral of the simulated pulse of current of lightning discharge equal to ≈2.38 × 10⁶ J/Ω are presented. The quantity of electricity under single action on the shunt by a current pulse of artificial lightning with logarithmic decrement of oscillations ≈2.06 that passed through the current-carrying elements of its construction was ≈-9.9 C. It was shown that, simultaneously with registration of pulsed A-component of lightning current, the shunt, owing to using of a matching voltage divider at the end of its cable communication line, allows also to measure normalized amplitude-time parameters of aperiodic shortened long-term C*-component of artificial lightning current (-568 A; ≈5 ms;τ_C* ≈18 ms; -16 C) that was being formed in the discharging circuit of the generator.     

Effect of Magnetic Parameters and Dimensions of Uniformly Magnetized Bodies on Inductive Coercive Force

From the Fröhlich approximation of changes in the magnetization of a ferromagnetic material on the descending branch of the hysteresis loop, an analytical expression for the inductive coercive force H _B of a homogeneously magnetized body has been derived. Effects of magnetic parameters of the material and demagnetizing factor on H _B have been studied.