Axial Extraction Research Articles

External Coupled Millimeter Wave Magnetron With Simple Diffraction Output

We proposed an external coupling structure of the millimeter wave magnetron that has the potential to utilize the diffraction output for axial power extraction. For such a structure, a 24-vane anode resonator operated in the $\pi $ mode was tightly coupled to an external coupling structure operated in the $2\pi $ mode through slots in the back walls of alternate cavities of the anode resonator. Moreover, we designed and simulated a Ka-band external coupled magnetron (ECM) in order to demonstrate the effectiveness of the new configuration. The simulation results showed the achievement of maximum microwave power of 108 kW at 35.0 GHz, with 29.6% efficiency.

Development of a quantitative preclinical screening model for implant osseointegration in rat tail vertebra

ObjectivesFunctional tooth replacement and bone regeneration are parts of the daily practice in modern dentistry, but well-reproducible and relatively inexpensive experimental models are still missing. We aimed to develop a new small animal model to monitor osseointegration utilizing the combination of multiple evaluation protocols.Material and methodsAfter cutting the tail between the C4 and C5 vertebrae in Wistar rats, costume made, parallel walled, non-threaded implants were placed into the center of the tail parallel with its longitudinal axis using a surgical guide. Osseointegration of the titanium implants was followed between 4 and 16 weeks after surgery applying axial extraction force, and resonance frequency analysis as functional tests, and histomorphometry and micro-CT as structural evaluations.ResultsIn functional tests, we observed that both methods are suitable for the detection of the time-dependent increase in osseointegration, but the sensitivity of the pull-out technique (an approximately five times increase with rather low standard error) was much higher than that of the resonance frequency analysis. In structural evaluations, changes in the detected bone implant contact values measured by histomorphometry (yielding 1.5 times increase, with low variations of data) were more reliable than micro-CT based evaluations to screen the developments of contact between bone and implant.ConclusionOur results provide evidence that the caudal vertebrae osseointegration model is useful for the preclinical evaluation of implant integration into the bone.Clinical relevanceThe combination of the biomechanical and structural tests offers a well-reproducible small animal system that can be suitable for studying the integration of various implant materials and surface treatments.

Compact, high power and high efficiency relativistic magnetron with L-band all cavity axial extraction

To reduce the size and the weight of the relativistic magnetron (RM), a highly compact RM using an all cavity extraction and transparent cathode is investigated. Compared with the traditional RM design [Sayapin et al., IEEE Trans. Plasma Sci. 45(2), 6792062 (2017) and Sayapin and Shlapakovski, J. Appl. Phys. 109(6), 063301 (2011)] this configuration occupies only 0.55λ (radius) * 1.55λ (length). Both simulation and experimental results demonstrate that a microwave power of 508 MW is generated at 1.57 GHz when the input beam voltage is 369 kV and the corresponding efficiency is ∼33%. This provided work paths a way to finally achieve high power, high efficiency, and compact microwave sources.

Theoretical treatment of cold penning ion source with axial extraction

Theoretical treatment of cold penning ion source with axial extraction

Theoretical investigations on radiation generation of TEM, linearly or circularly polarized TEn1 coaxial waveguide mode in relativistic magnetron

The physical mechanism of the radiation generation of all possible output modes of the relativistic magnetron (RM) with all cavity-magnetron axial extraction technique is theoretically analysed, and the necessary conditions for generating these modes are obtained respectively. Assuming that n0 is the number of the electron spokes, N ≥ 4 as the total number of the cavities is an even number, and k is a nonnegative integer, some conclusions can be drawn as follows. If n0 = kN is true, no mode can be excited in the coaxial waveguide; if n0 = (2k + 1)N/4 is true, the linearly polarized modes can be excited in the coaxial waveguide; if n0 = (4k + 2)N/4 is true, the TEM mode and the linearly polarized modes can be excited in the coaxial waveguide; if n0 takes other value, the left and right circularly polarized modes can be excited in the coaxial waveguide and the directions of rotation of the circularly polarized modes can be reversed with the reversion of the direction of rotation of the electron spokes; in addition, some other regular characteristics of the corresponding mode excitation are presented in detail in this paper. Such unique attractive properties that have been verified by the cold and hot simulations in this paper make it possible for this type of RM to meet application requirements of various high power microwave (HPM) modes.

A frequency tunable relativistic magnetron with a wide operation regime

A frequency tunable relativistic magnetron (RM) with a wide operation regime is proposed. With the all cavity-magnetron axial extraction technique, the RM can output TEM mode with the operating frequency of 4.3 GHz, which is demonstrated as the dominating output mode by theoretical analysis, cold simulations and hot simulations respectively, corresponding to the output power of 466 MW and the power conversion efficiency of 56.4 %. It also can achieve a wide frequency tuning with the bandwidth of 0.96 GHz and the relative bandwidth of 20.8 %, corresponding to the output power of above 400 MW and the power conversion efficiency of above 40 %. Further simulation results show that the RM has strong performance robustness to the perturbations of the electrical parameters and almost all structural parameters except the cathode radius, anode radius and cavity radius, however two methods proposed in this paper can be taken to further improve the RM performance. The performance robustness enables the RM to operate with a wide parameter regime while keeping a good performance. In addition, a GW-level RM with the power conversion efficiency of 55.9 % also can be obtained.

Investigation of the operating characteristics of a 12 stepped-cavity relativistic magnetron with axial extraction driven by an “F” transparent cathode using particle-in-cell simulations

We explore the performance of a 12 stepped-cavity relativistic magnetron with axial extraction (12 stepped-cavity RMDO) driven by an “F” transparent cathode (the “F” transparent cathode is a coaxial transparent cathode with two azimuthal periods of increased thickness and which looks like the letter “F,” so we call it “F” transparent cathode) through particle-in-cell (PIC) simulations. It is shown that using the “F” transparent cathode, an electronic efficiency of 70% with gigawatt output power is obtained while reducing the axial leakage current by about 50% compared to using the usual transparent cathode. Further PIC simulations demonstrate that frequency bifurcation occurs and mode switching can be achieved using several hundred kilowatts input RF power in the 12 stepped-cavity RMDO driven by an “F” transparent cathode. For example, it was found that using an applied driver power of 180 kW for 10 ns, the operating TE31 mode can be switched to the TE41 mode. It is also found that the secondary electron and backscattered electron emission and axial leakage current were two disturbing factors for the 12 stepped-cavity RMDO when it works at a stable operation mode but when the 12 stepped-cavity RMDO works near the critical magnetic field at the boundary between two modes, these two factors would lead to the operation modes changing.

A novel relativistic magnetron with circularly polarized TE11 coaxial waveguide mode

A novel relativistic magnetron (RM) with a circularly polarized TE11 coaxial waveguide mode and its corresponding mode excitation are investigated in this paper. By operating in the 4π/5 mode in the ten-cavity RM and compactly designing the RM structure with the all cavity-magnetron axial extraction technique, the RM can directly output a circularly polarized TE11 coaxial waveguide mode in a reversible direction of rotation without any mode converters. In addition, the analysis of mode excitation can be generalized to a 2N-cavity RM, where 2N > 4 is the number of cavities. Results of the 3D particle-in-cell (PIC) simulation show that a high power microwave (HPM) with an operating frequency of 4.15 GHz and an output power of 700 MW is obtained from the RM, corresponding to the power conversion efficiency of 50.0%.

Primary Stability of Uncemented Total Hip Stems with Different Ceramic and Titanium Surface Coatings

The necessity of coatings for endoprosthetic implants is discussed controversially. Thereby hydroxyapatite coatings are objects of the debate [1, 2]. Therefore, we investigated four different coatings (calcium-phosphate (CaP), titanium-calcium-phosphate (TiCaP), titanium-plasma-spray (TPS) and bilayer-composite calcium-phosphate (CaP-bc)) in comparison with rough uncoated test specimens to evaluate the impact of the osteoconductive coatings on the initial implant stability which is the key factor for its secondary stability. Dimensions of the test specimens were defined according to a conventional total hip stem and their geometry was simplified to a conical one for comparison of the surface-related parameters. The specimens were force-controlled pressed in artificial bone counterparts made of foam material while the displacement was monitored by the test machine to determine the subsidence behavior. Consecutively a displacement-controlled axial extraction of the test specimens was performed and the pull-out force was recorded. Roughness and geometry of the test specimens before testing were measured and correlated to type of coating and initial stability. The uncoated specimens showed highest extraction forces (3.9 kN) with moderate surface roughness compared to the coated specimens. In contrary to our assumption no correlation between surface roughness and the measured subsidence as well as pull-out force was found and a reduced subsidence or increased pull-out force for the different titanium and calcium-phosphate coatings could not be derived from the experimental tests.

Improved Design of a Multistage Axial Vircator With Reflectors for Enhanced Performances

The basic design of an axial virtual cathode oscillator (vircator) with axial extraction operating in TM01 mode is modified by introducing thin conducting disks, also called reflectors, into the cylindrical waveguide. The operation principal of this novel type of device relies on the formation of a series of virtual cathodes, located at the center of adjacent quasi-cavities. The behavior of this new type of multistage vircator is numerically investigated using CST Particle Studio 3-D particle-in-cell code. Progressively decreasing the radii of the reflectors installed upstream in the tube allows the mitigation of spurious modes. Tapering the radii of the reflectors turns out to be crucial in focusing the electron beam on axis in the downstream region and maximizing the TM01 power conversion efficiency. This novel architecture enables a five-reflector vircator operating with an injected electron beam of 508-kV mean voltage and 19-kA mean current to deliver up to 2-GW mean power sustained only by the TM01 mode in the S-band with a power conversion efficiency close to 21%.

Particle-in-cell based parameter study of 12-cavity, 12-cathode rising-sun relativistic magnetrons for improved performance

Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage currents in a 12-Cavity, 12-Cathode rising-sun magnetron with diffraction output (MDO). The central goal is to conduct a parameter study of a rising-sun magnetron that comprehensively incorporates performance enhancing features such as transparent cathodes, axial extraction, the use of endcaps, and cathode extensions. Our optimum results demonstrate peak output power of about 2.1 GW, with efficiencies of ∼70% and low leakage currents at a magnetic field of 0.45 Tesla, a 400 kV bias with a single endcap, for a range of cathode extensions between 3 and 6 centimeters.

Particle Size Distribution and yield control in continuous Plug Flow Crystallizers with recycle

Plug Flow Crystallizers (PFCs) are one of the most widely employed forms of continuous crystallizers. PFCs are usually selected for processes with fast kinetics and short residence times. One key limitation of PFCs is that normally they do not operate at equilibrium conditions as a consequence of the short residence times. Thus, the resultant yield from PFCs is generally less than that of the equivalent batch process.Recycling the mother liquor back through the PFC is one approach, which can potentially be used in order to mitigate against this drawback, allowing for an amelioration in the continuous process yield.In the present work, the effects of introducing a recycle stream and adjusting critical recycling parameters, namely recycling ratio and axial extraction position, on an idealized PFC are examined. Particular attention is focused on the resultant volume average size of particles d4,3, and the process yield η. The influence of feed velocity along with the recycle parameters on the maximum and minimum yield and size of crystals achievable is also investigated.The proposed continuous PFC, as conceptualized and modeled with recycle, facilitates practical application in an industrial setting, allowing for augmented continuous process yields, whilst furthermore facilitating PSD control.

Numerical Investigation of the Relativistic Magnetron Using a Novel Semitransparent Cathode

A semitransparent cathode is proposed for an efficient operation of the relativistic magnetron (RM) with axial extraction. The semitransparent cathode is a kind of shaped cathode. It is achieved using a cylindrical cathode with longitudinal strips removed. The cross section of each removed strip is fan-shaped and all the emit strips are connected in the central area of the cathode. Results of the 3-D particle-in-cell simulations show that the using a semitransparent cathode yields similar performance benefits compared with that using the transparent cathode proposed by the University of New Mexico. Simulation results also show that output characteristics of the RM using the semitransparent cathode are insensitive to the depth and width of each cathode slot. Thus, the semitransparent cathode might be more robust for practical applications.

Operation Characteristics of A6 Relativistic Magnetron Using Single-Stepped Cavities With Axial Extraction

We report the performance of an A6 relativistic magnetron with single-stepped cavities output. Particle-in-cell simulation shows the electronic efficiency of an A6 relativistic magnetron with an anode block made of six single-stepped cavities can be up to 78% with an output power of one gigawatt for an applied voltage of 400 kV. When the A6 relativistic magnetron with axial extraction using six single-stepped cavities is applied with a voltage of \(V \sim 400~{\rm kV}\pm 50\) kV the electronic efficiency can be as high as 60%, while the output power can be as high as 1 GW. And, when a 10-ns voltage pulse of 400 kV is applied on this magnetrons with diffraction output using single-stepped cavities, the output power pulse can be as high 1.2 GW. The results in this paper will provide a reference for choosing a cavity that is easily manufactured, so that a physical experiment is more feasible.

Electromagnetic and Particle-in-Cell Simulation Studies of a High Power Strap and Vane CW Magnetron

This paper presents electromagnetic and particle-in-cell (PIC) simulation studies of ring strapped vane resonator of a 2.45 GHz 1-kW magnetron using Computer Simulation technology microwave studio and MAGIC-3-D. The aim was to gain design understanding through the analysis of constituent parts of the resonant system and to deduce results having significant engineering value. The electromagnetic analysis includes modeling the effect of the end-gap length, the straps, the coupling antenna, and the surface roughness of cavity wall on resonant frequency. It was found that a clearance of 4 mm and beyond between cavity resonator and end plate have negligible effect on resonance frequency. Straps influence the resonant frequency of the \(\pi \) mode maximum, and can be used to control and fine tune the resonant frequency of the desired \(\pi \) mode. A surface roughness of 1 \(\mu \) m or more affects the unloaded \(Q\) of the resonator cavity adversely. Coupling antenna height is found to play an important role to achieve desired \(Q_{l}\) and \(Q_{\rm ext}\) for the segment loaded axial extraction of power. The PIC simulation study predicted that the hot resonant frequency differ from cold resonant frequency by \(\sim 9\) MHz. The computed frequency, power, and efficiency were found to be 2.462 GHz, 1.3 kW, and 70%, respectively.

Direct numerical simulation of Open Von Kármán Swirling Flow

Direct numerical simulations are used to investigate the Open Von Kármán Swirling Flow, a new type of unsteady three-dimensional flow that is formed between two counter-rotating coaxial disks with an axial extraction enclosed by a cylinder chamber. Solution verification shows that monotonic convergence is achieved on three systematically refined grids for average pressure at the disk periphery with a small grid uncertainty at 3.5%. Effects of the rotational speeds and flow rates on the flow field are examined. When the disks are rotating at the lowest speed, ±100 RPM, only circular vortices are formed regardless of the flow rates. When the disks are rotating at ±300 RPM and ±500 RPM, negative spiral vortex network is formed. The radial counterflow concept for such spiral vortex network is verified by examining various horizontal cuts and radial velocity component, which show radial outflows in two bands near the two disks and radial inflow in one band between them. Overall, the flow is similar to the Stewartson type flow but with significant differences for all three velocity components due to the axial suction at the upper disk center and gap between the disk periphery and chamber wall.

The double well mass filter

Various mass filter concepts based on rotating plasmas have been suggested with the specific purpose of nuclear waste remediation. We report on a new rotating mass filter combining radial separation with axial extraction. The radial separation of the masses is the result of a “double-well” in effective radial potential in rotating plasma with a sheared rotation profile.

All Cavity-Magnetron Axial Extraction Technique

A compact axial π-mode extraction scheme, which is based on a patent by Greenwood, is demonstrated in conjunction with the UM/L-3 relativistic magnetron using the particle-in-cell code ICEPIC. Cases utilizing Greenwood's extraction technique were compared with power extraction using traditional radial waveguides. Average extracted power values in all simulated axial cases were found to be within +/-6.5% of the radial cases. Cases utilizing 85 ° and 90° sector waveguides were found to have efficiencies up to ten percentage points higher than the radial case. The best performing case was found to use a set of three axially oriented 90 ° sector waveguides, shorted on the upstream side, with the short located 15 cm from the center of the magnetron apertures.

On the Extraction of Milling Tools Out of Shrink Fit Chucks

Thermal shrink fit chucks are widely used in high performance machining where excellent concentricity and high torque transmission are required. It was reported that in those milling operations, severe damage of tools, workpieces, and also machine tools occurs due to an extraction of the milling tool out of the shrink fit chuck during the process. Although, theoretically the interference fit assembly should withstand certain process forces, milling tools are apparently pulled out under special process conditions. The resulting increase of the cutting depth often leads to tool overload and breakage. So far, the phenomenon of tool extraction could not be explained. This paper presents an experimental approach of the investigation of the phenomenon of axial tool extraction. Therefore, a unique type of test rig for main spindles and tool interfaces is used. Experimental investigations on dynamic force and torque combinations leading to tool extraction are described. Results show, that the holding force is not only affected by geometrical parameters of the shrink fit chuck, but also by the applied dynamic load.

Suppression of Leakage Current in a Relativistic Magnetron Using a Novel Design Cathode Endcap

In relativistic magnetrons, explosive electron emission cathodes are typically used to generate the electron flow in the crossed field between the coaxial electrodes. Electrons that axially leave the interaction space and the cathode edge reduce magnetron efficiency, which can lead to window breakdown when axial microwave extraction is used, e.g., a magnetron with diffraction output. Because of this, numerous publications have been devoted to different solutions of decreasing the leakage current and protecting the dielectric window from electron bombardment. In this paper, we present the results of our initial experiments to suppress leakage current in the well-known A6 magnetron using a thin dielectric coating on a cathode endcap that is extended downstream of the interaction space in a uniform magnetic field. We found that using a relatively thin dielectric coating on a polished graphite endcap with radius that extends beyond the cathode radius decreased the leakage current from over 1 kA down to about 10 A.