Miter Bend Research Articles

Galerkin boundary method for static analysis of single thin mitered bend

The problem of a single unreinforced thin-walled mitered bend under static loading (inner pressure or bending in-plane moment) is examined. Despite its age and long history, few practically efficient developments have been made for this problem. The essence of current solution consists in consideration of the stress-strain state of a straight thin cylindrical shell and projecting its inner forces onto the miter plane. All parameters of the shell are expanded into Fourier series with respect to circumferential coordinate. Analytical expressions for eigenfunctions of the shell are found using the decoupling procedure. Then, boundary conditions are satisfied by the Galerkin boundary method. Comparison with known theoretical and FEA results shows great efficiency of proposed approach.

ITER ECH Transmission Line System Design and Status

The electron cyclotron (EC) heating & current drive (H&CD) system on ITER provides plasma heating by generating, transmitting, and launching high-intensity, high-frequency (170 GHz) electromagnetic wave energy steerable across the plasma cross-section. The transmission line (TL) subsystem connects the Matching Optics Unit (MOU) on each of the 24 gyrotrons to the 32 feed points in the four upper launchers and the 24 feed points in the equatorial launcher. Each TL must be able to operate at up to 1.2 MW of input power for up to 1 hour pulse lengths. The TL system contains 50 mm water-cooled corrugated waveguide, 90o miter bends, 140o miter bends, polarizer miter bend pairs, switches, expansion units, pumpouts, DC breaks, MOU-TL adapters, Radio Frequency (RF) loads, and isolation shutter valves. A detailed finite element analysis has been used to verify the thermo-mechanical performance of each component. The microwave performance has been analyzed using a 2-D electromagnetic code combined with a Monte Carlo code. This approach allows the impact of manufacturing and installation tolerances to be assessed and optimized to provide a high probability of achieving the system performance requirements. Prototypes of the waveguide and TL components have been fabricated and tested at high-power. Production contracts are now being issued for fabrication and delivery of the waveguide and components to ITER.

Multi-hole coupling power monitor with tapered sub-waveguide for dual-frequency high-power gyrotron

In magnetically confined fusion plasmas, a gyrotron is an essential auxiliary heating device for generating and sustaining plasma through electron cyclotron resonance heating owing to its ability to generate high-power microwaves. Microwaves emitted from a gyrotron are often transmitted through waveguides, and the transmitted power is monitored by a power monitor with a multi-hole directional coupler at the miter bend of the transmission line. Recently, a high-power dual-frequency gyrotron has been installed and operated in the Large Helical Device. A power monitor with good sensitivity to multiple frequencies is required to monitor the power transmission of the different frequencies at the same transmission line. In order to realize the power monitor, which can couple with the multiple-frequency microwaves, we focused on a sub-waveguide shape in the power monitor and investigated the influence of the tapered sub-waveguide by conducting electromagnetic simulations using a simple model. We also performed the high-power test using a power monitor with a tapered sub-waveguide. The experimental result was different from the simulation, but enough receiving power was obtained at both 116 and 154 GHz.

Synthesis of Broadband Oversized Miter Bend for High-Power Millimeter Wave System

An optimum approach for designing a TE01 mode broadband oversized miter bend is proposed by synthesizing a mixture beam with the characteristics of conical Gaussian beam. With the analysis of the characteristics realized by the simple mixture modes based on the gap theory, the optimized mixture mode under different waveguide dimensions for high transmission efficiency miter bend is deduced. According to the analysis results and the broadband mode synthesis technology, a Ka -band oversized waveguide miter bend propagating circular TE01 mode is designed, fabricated, and measured. According to the transmission measurement results, the miter bend can achieve the transmission efficiency up to 95% in the frequency range of 32–38 GHz, which verifies the broadband and high-efficient characteristic of the component. The near-field test results further demonstrate the high output vector purity of the TE01 mode over 95.5% and the scalar purity over 98% is acquired in the working frequency band.

Fluid-dynamic and thermo-mechanical analyses of the ITER electron cyclotron Miter bend mirror for the off-centered beam scenario

Fluid-dynamic and thermo-mechanical analyses of the ITER electron cyclotron Miter bend mirror for the off-centered beam scenario

Numerical Synthesis of the Dual Frequency 28/35 GHz Power Monitor in the 160° Circular Miter Bend

A numerical method of the synthesis of the array pattern for the linear holes coupler embedded on the miter bend is proposed in this article. This method allows pattern control with the arbitrary incident angle when the waveguide operates at dual frequency. Combined with the analysis method, an algorithm has been developed for synthesizing the antenna pattern. As an example, a power monitor has been designed for a 28/35 GHz waveguide with an incident angle of 55°. An arrangement of the holes array has been obtained to get the desired array pattern at a given angle, and the directivity of the power monitor is larger than 40 dB at 28/35 GHz.

Autonomous Navigation of In-Pipe Inspection Robot Using Contact Sensor Modules

Pipes, which are the main means of transporting resources, deteriorate over time, thereby leading to defects or accidents. Therefore, periodic inspection of pipes is required, and a pipe robot that moves and inspects the inside of a pipe is one of the solutions. Herein, we propose an inspection robot system capable of autonomous driving inside buried pipes. This robot is called a Multifunctional Robotic Caterpillar for in-pipe INSPECTion (MRCINSPECT) and has been developed for pipes with a 0.5-m diameter. The robot utilizes a caterpillar mechanism and a wall-press mechanism to ensure that it can drive on slopes and generate a high traction force. In addition, we developed a miter bend recognition method using contact sensor modules. Therefore, MRCINSPECT can autonomously navigate in accordance with the estimated pipe information, and simultaneously, an operator can check the robot’s location and pipe information in real time. We verified the performance of the robot system through indoor experiments and its field applicability through outdoor tests.

Performance Analysis of 1x4 RMPA Array using Step Cut and DGS Techniques with Different Feed Techniques for LTE, Wi-Fi, WLAN and Military Communications

This paper presents four different models of 1x4 antenna arrays excited by quarter wave transformer and mitered bend feeding techniques. These four antennae were designed and developed to examine the various radiation performance characteristics. The Ansys HFSS tool was used to simulate the four antenna models over the frequency range (1-5GHz). The simulation results were compared to identify the optimized design model. Both types of 1X4 arrays with mitered bend feed network showed better results than quarter wave transformer and were resonating at 2.4, 3.6, 4.5 and 4.7 GHz frequencies with a maximum gain of 13.118dB. The proposed antennae are suitable for Wi-Fi, Long Term Evolution (LTE), Wireless Local Area Network (WLAN) and military communication applications. The optimized four 1x4 array models were fabricated and tested using Vector Network Analyzer E507C. The measured results had good matching with the numerical values of the simulation results.

Fracture response of mitred X70 pipeline with crack defect in butt weld: Experimental and numerical investigation

Crack defects in mitred bends seriously affect the structural safety of steel pipelines. Therefore, particular attention should be paid to fracture failure of mitred bends due to stress concentration and formation of defects. In this paper, the fracture response of mitred butt girth weld pipeline with crack defect was investigated by conducting full-scale experiments on failure pressure of mitred bend with crack in girth weld. The experimental results estimated the failure pressure of cracked mitred pipes with different mitre angles of 0° and 5° to 11.85 MPa and 11.38 MPa, respectively. At constant mitre angle, circumferential burst failure appeared for defect-free mitred bend, while longitudinal leakage failure occurred on cracked mitred pipe. A refined finite element model of mitre pipe with crack defect was then established based on the experimental results. Also, parametric numerical simulation analyses were carried out to study the effects of defect location, soil spring stiffness, as well as geometric parameters of pipes and crack like mitre angle, mitre length, pipe diameter, wall thickness, crack length, and crack depth on crack driving force of mitred bend. The data revealed unsafe service of mitred pipe for defects located on the internal angle and outer wall of mitred pipe. The crack driving force increased with the increment in mitre angle, wall thickness, crack length, and crack depth. A negative correlation was observed between crack driving force and other factors, such as mitre length and soil spring stiffness. Based on the 6800 numerical results derived from parametric numerical model realized by python and ABAQUS, a hybrid prediction model employing support vector regression (SVR) and particle swarm optimization (PSO) was established to predict the pipe’s crack driving force at the weld. A relative error of 13.3% was obtained between the numerical and established driven model results. In sum, the proposed method looks useful for integrity assessment of mitred X70 pipes. It can also be referenced for fitness for service assessment of energy pipes. Finally, some suggestions about maximum allowable mitre angle for mitred bends with various mitre lengths are given.

Design and experimental research of a 28 GHz TE01 mode 160° miter bend for electron cyclotron resonance ion source.

In this paper, a 28 GHz TE01 mode 160° miter bend employing two plane mirrors is proposed based on the quasi-optical technique and the coupled wave theory to realize high-efficiency transmission for the electron cyclotron resonance ion source. First, the TE01 mode was converted to TE0n hybrid modes with Gaussian beam characteristics by means of the designed mode converter. Second, the phase shift section was implemented to eliminate the phase difference of the hybrid modes. Then, upon reflection of two plane mirrors, the propagation direction of a wave beam is deviated by 160°. Finally, the hybrid modes were converted to the TE01 mode using the same structures of the phase shift section and the mode converter. The simulation results reveal that the TE01 mode transmission efficiency reaches 95.22% at the central frequency of 28 GHz. Additionally, the designed 160° miter bend has been fabricated, installed, and measured. The experimental results show that the power transmission efficiency reaches 98.54% including diffraction losses and ohmic losses.

High power experiment and heat load evaluation of transmission line for the ECH/CD system in JT-60SA

Temperature rise of the waveguide transmission line for high-power long-pulse ECH/CD system has been evaluated experimentally using the dummy load transmission line in JT-60SA. It has been demonstrated that the waveguide components with the inner diameter of 60.3 mm are applicable for 1 MW/100 s transmission at 110/138 GHz required in JT-60SA. A newly developed pre-load installed in front of the dummy load reduced the temperature rise of the waveguide due to the reflection from the dummy load. With this pre-load, the temperature rise distribution in the 37 m-long test transmission line was measured to simulate the real transmission line condition for tokamak experiment. As a result of the high-power experiments, it has been clarified that the temperature of the waveguides close to miter-bends could be increased by approximately 120 K for 1 MW/100 s operation at 110 GHz, in the worst case, and it is marginal for the stable operation with the waveguides made of aluminum alloy. The heat loads on the waveguides have been evaluated as 23 kW/m2 for the worst case between miter bends, 12–23 kW/m2 within 4 m from miter bend and 4–12 kW/m2 for waveguide far from miter bends. The evaluated heat loads will be taken into account for the final design of the TL components and cooling for the JT-60SA ECH/CD system.

Design and development of 42GHz transmission line for ECRH application

This work represents the design and development of overmoded circular waveguide- based mode converters. It transforms unpolarized mode into linearly polarized mode used in plasma applications. This transmission line system (TLS) consists of TE03 to HE11 mode converters, corrugated waveguides, and other components. These are used to carry 200 kW power generated from gyrotron at a frequency of 42±0.2 GHz to the applicator or dummy load (in offload condition).A conservative design goal of insertion loss (1.5 dB) for the TLS is used as a design driver. It consists of different overmoded circular waveguide mode converters, miter bends (MBs), and corrugated waveguide. For efficient transmission of power between components, proper phase matching and accurate calculations of geometrical dimensions (perturbation amplitude, bending angle, and many more) are prerequisites. Analytical study, design technique, manufacturing process and simulation studies of TLS are discussed and summarized. After carrying out simulation studies of the various TLS components, the estimated insertion loss of the TLS is approximately 1.3 dB.The TLS along with seals is compatible to high vacuum (10−6 torr) and pressurization of 1 bar absolute pressure. Similar joints have been used at the joints of the various components in the TLS. The worst case leak rate of any of the TLS joint seal is 10−6 mbar liter per second.

Development of a new analytic method for miter bend polarizer on ECW transmission line

For successful tokamak operation with adequate mode selection of the electron cyclotron wave, launching wave polarization should be accurately controlled. In this study, a new method is proposed to efficiently identify the response of polarizers using a geometric approach in the Stokes space, focusing on the fact that polarization can be represented as a vector in Stokes space and the response of a polarizer can be described as a rotation. The proposed methods are intended (i) to determine the response parameters of a polarizer or (ii) to determine the response parameters of two polarizers simultaneously. A simple measurement system was prepared to observe the polarizers’ output polarization in the 110/138 GHz transmission line. The determined response parameters of two polarizers can reproduce measured polarizations with sufficient accuracy above 99%. The direction of an output polarization circularity, the only feature of a polarization that could not be directly known from the prepared measurement, could also be determined with sufficient accuracy.

Prototype mitre bends of the ex-vessel waveguide system for the ITER upper launcher: Thermal hydraulic simulations and experiments with off-center mm-wave beams

On ITER, long pulse gyrotrons are required as a power source for electron cyclotron heating (ECH) and current drive (CD). The microwaves are guided from the gyrotrons, which are placed far from the Tokamak, into the plasma by transmission lines (TLs) and a launching antenna (launcher). Each of the four ECH Upper launchers features eight waveguide (WG) TLs, with at least 95% of the power from the gyrotrons coupled into in the main HE11 mode of the TLs. In the ex-vessel portion of the system between the port-plug closure plate and the isolation valve and diamond window, there are miter bends (MBs) that change the direction of the TL by reflecting the millimeter waves (mm-waves) using mirrors; the mirrors must handle 1.31 MW, 170 GHz, 3600 s pulses. Various MBs perform these reflections at an angle of 90 degrees, or nearly 100 degrees. As a result of the ohmic dissipation, an intensive peaked heat flux appears near the center of the MB mirror and thus, a dedicated cooling system is present to ensure the temperature control of the mirror and housing e.g. [1]. The power that is not found in the HE11 mode can cause the beam to be not perfectly centered, resulting in an off-centered heat flux on the mirror surface; as is the case for the experiments described here. This study presents new finite element modeling of such beams, created in CFX of ANSYS Workbench [2], compared to the experimental findings for pulses of 170 GHz, 0.5 MW and 240 s. Monitor points are placed in the same positions as TCs that have been fitted in the mirror close to the heated surface and direct comparison of the temperature values is performed. Through transient simulation the time constants are calculated and compared with those of the experiments.

Performance demonstration of vacuum microwave components critical for the operation of the ITER low-field side reflectometer.

Final design studies in preparation for manufacturing have been performed for functional components of the vacuum portion of the ITER Low-Field Side Reflectometer (LFSR). These components consist of an antenna array, electron cyclotron heating (ECH) protection mirrors, phase calibration mirrors, and vacuum windows. Evaluation of these components was conducted at the LFSR test facility and DIII-D. The antenna array consists of six corrugated-waveguide antennas for simultaneous profile, fluctuation, and Doppler measurements. A diffraction grating, incorporated into the plasma-facing miter bend, provides protection of sensitive components from stray ECH at 170GHz. For in situ phase calibration of the LFSR profile reflectometer, an embossed mirror is incorporated into the adjacent miter bend. Measurements of the radiated beam profile indicate that these components have a small, acceptable effect on mode conversion and beam quality. Baseline transmission characteristics of the dual-disk vacuum window are obtained and are used to guide ongoing developments. Preliminary simulations indicate that a surface-relief structure on the window surfaces can greatly improve transmission. The workability of real-time phase measurements was demonstrated on the DIII-D profile reflectometer. The new automated real-time analysis agrees well with the standard post-processing routine.

Fluid-dynamic and thermo-mechanical analyses of the Monoblock Mitre Bend for the ITER electron cyclotron Upper launcher

The ITER Electron Cyclotron Heating (ECH) system will be used to counteract magneto-hydrodynamic plasma instabilities by aiming up to 20 MW of mm-wave power at 170 GHz. The primary vacuum boundary at the Electron Cyclotron Upper Launcher (EC UL) extends into the port cell region through eight beamlines, defining the so-called First Confinement System (FCS). Each beamline, designed for the transmission of 1.31 MW, is delimited by the closure plate at the port plug back-end and by a diamond window in the port cell. The FCS essentially consists of a Z-shaped set of straight corrugated waveguides (WG) connected by Mitre Bends (MB) with a nominal inner diameter of 50 mm. Due to the space restrictions, the eight MBs at the last FCS section are grouped into two monoblocks. Each Monoblock Mitre Bend (MBMB) consists of a body with corrugated feedthroughs defining a specific angle for each beamline and four mirrors attached by bolted connection to reflect the mm-wave power. The thermal expansion arising from the ohmic losses, the cooling pressure, the bolt pre-tension and the imposed displacements coming from the connection with the transmission lines are the primary design loads for the MBMBs. The fluid-dynamic analyses performed for both upper and lower MBMBs show that highest temperature takes place in the MB mirrors, reaching a maximum value of 203 °C at the beam center. The thermo-mechanical analyses demonstrate that the peak stress also occurs at this location with a maximum value of 324 MPa. These stresses are categorized and compared with the allowable limits defined in the ASME code, what probes that the current design of both upper and lower MBMBs are able to withstand the loads taking place during the mm-wave normal operation.

Analysis of the Shattered Pellet Injection Fragment Plumes Generated by Machine Specific Shatter Tube Designs

Shattered pellet injector systems have been installed on DIII-D, JET, and KSTAR and used to experimentally determine the effectiveness of the shattered pellet injection (SPI) process in mitigating the deleterious effects of a tokamak plasma disruption. Pellets are fired, and before entering the plasma, strike a bent tube known as a shatter tube causing the pellet to shatter. The process of pellet fragmentation is a chaotic process that can be described in terms of fragment size distribution through a statistical model that incorporates the effects of the pellet material and impact characteristics. In addition to the fragment size distribution, the shatter plume has other characteristics of interest, such as a fragment velocity distribution and temporal mass evolution. The fragment velocity distribution is important because it is needed to accurately model the spread and location of the ablation and the deposition of impurities in the plasma over time. The temporal mass evolution is necessary to determine the time-resolved delivery of mass to the plasma. Due to installation constraints, the shatter tube currently installed on JET has a unique geometry with a modest S-bend followed by a 20-deg bend at the end of the tube. The DIII-D and KSTAR shatter tube design is a simple tube bent through an angle of 20 deg followed by a straight section. The resulting shatter sprays from the JET shatter tube and a 20-deg miter bend shatter tube were experimentally characterized for various pellet materials and speeds. Laboratory testing of these shatter tubes allows for the use of fast cameras to capture the fragment spray traveling through a large vacuum chamber. These high-speed videos of the shatter plumes allow the fragment size distribution, temporal mass evolution, and velocity distribution of the fragments within the plume to be determined. This paper presents a comparison of the unique geometry of the JET shatter tube to the miter bend geometries used for shattering and some insight into the variables that may be adjusted to produce the optimal shatter spray. The impact of entrained propellant gas on the resulting shatter spray was examined during testing.

High-Power Testing of Guided-Wave Components for the ITER ECH Upper Launcher at the FALCON Test Facility

Each of the four ITER electron cyclotron heating (ECH) upper launchers (ULs) features eight transmission lines (TLs) made of guided-wave components used to inject 170-GHz microwave power into the plasma at a level of up to 1.31 MW per line, at the TL diamond window unit (DWU). The guided-wave components include a DWU, an isolation valve (IV), waveguides (WGs), and miter bends (MBs). These form part of the first confinement system (FCS) of the ITER UL. They must withstand the nominal mechanical structural stresses, the electromagnetic forces, and the dynamic loads (VDE, MD, and Seismic), while being compatible with the most stringent ITER vacuum and safety classification. Here, we report new results on plans for high-power testing of guided-wave components that the Swiss Plasma Center (SPC) of the Swiss Federal Institute of Technology Lausanne (EPFL) has developed for the FCS. FALCON is home to testing equipment provided by Fusion for Energy (F4E) and ITER, including an ITER-grade 170-GHz GYCOM gyrotron and a matching optics unit (MOU), an evacuated TL including a power monitor MB (PMMB), a downtaper (DT) to the 50-mm ITER TL diameter, and a matched RF load (RFL). The facility is operated by the SPC.

Design Analysis of Microstrip Rectangular Patch Array Antenna 16×1 on X-band Radar

Radar has been widely used for various purposes such as monitoring atmospheric precipitation. For that purpose, it gives more accurate results than satellites do. Previous research has developed navigation radar that alters its functions into an atmospheric precipitation monitoring radar. To improve the development of the radar, an antenna system will be developed in this research. The purpose of developing this antenna is to obtain better data reception results. This antenna is a microstrip rectangular array antenna that works on X-band with a frequency of 9.41 GHz. Microstrip antenna is chosen since it has several advantages such as small dimensions and relatively low costs. The designed antenna gain ≥ 12 dB, bandwidth of 60 MHz, and horizontal polarization. Antenna fabrication produces a microstrip rectangular 16 x 1 array antenna using the mitered bend method at a frequency of 9.4 GHz with a reflection coefficient of -22.8 dB, VSWR of 1.2, gain of 13.21 dB, unidirectional radiation patterns and horizontal polarization.

Quasi-optical polarizer system for ECHCD experiments in the QUEST

A new transmission line from 28 GHz gyrotron to QUEST spherical tokamak (ST) has been developed for the highly efficient electron cyclotron heating and current drive (ECHCD) experiments. The ECHCD effect depends on the incident mode or polarization states of the injected beam. Although two corrugated-polarizer miter bends were developed and assembled to transmission line in the QUEST, arcing events were frequently detected at the polarizer miter bend when the high-power millimeter-wave were transmitted. A new quasi-optical (QO) concept for the polarizer system composed of two corrugated plate and a QO mirror was proposed to avoid the arcing at polarizer. The QO mirror was designed for coupling of input and output HE11 modes at the polarizer, its coupling property is discussed with Kirchhoff integral. Polarization-setting performance of the developed QO polarizer was examined in a low-power test system, and is discussed with grating-polarizer calculation.