Miter Bend Research Articles

Polarization and Mode Control of EAST 140 GHz ECRH&CD System

The 140 GHz electron cyclotron heating and current drive (ECRH&CD) project was launched in 2011 on EAST tokamak facility, which is designed to launch 4 MW of total power for the duration up to 1,000 s into the plasma. The heating and current drive efficiencies depend on the wave coupling mode in plasma and the coupling performance relies on polarization characteristics of injected beam, so polarization control is necessary for efficient plasma heating and current drive. Two polarizer miter bends will be used to control the wave polarization for each transmission line on EAST ECRH&CD system, any required wave polarization can be produced by adjusting the mirror rotation angle of each polarizer miter bend. This work mainly shows the calculated polarizer mirror settings as a function of the injection angles for pure second extraordinary harmonic mode coupling.

Progress of the ECRH Upper Launcher design for ITER

The design of the ITER ECRH system provides 20MW millimeter wave power for central plasma heating and MHD stabilization. The system consists of an array of 24 gyrotrons with power supplies coupled to a set of transmission lines guiding the beams to the four upper and the equatorial launcher. The front steering upper launcher design described herein has passed successfully the preliminary design review, and it is presently in the final design stage. The launcher consists of a millimeter wave system and steering mechanism with neutron shielding integrated into an upper port plug with the plasma facing blanket shield module (in-vessel) and a set of ex-vessel waveguides connecting the launcher to the transmission lines.Part of the transmission lines are the ultra-low loss CVD torus diamond windows and a shutter valve, a miter bend section and the feedthroughs integrated in the plug closure plate. These components are connected by corrugated waveguides and form together the first confinement system (FCS). In-vessel, the millimeter-wave system includes a quasi-optical beam propagation system including four mirror sets and a front steering mirror. The millimeter wave system is integrated into a specifically optimized upper port plug providing structural stability to withstand plasma disruption forces and the high heat load from the plasma side with a dedicated blanket shield module. A recent update in the ITER interface definition has resulted in the recession of the upper port plug first wall panels, which is now integrated into the design. Apart from the millimeter wave system the upper port plug houses also a set of shield blocks which provide neutron shielding. An overview of the actual ITER ECRH Upper Launcher is given together with some highlights of the design.

Interactive visualization system to analyze corrugated millimeter-waveguide component of ECH in nuclear fusion with FDTD simulation

We have simulated distribution of electromagnetic waves through the system composed of miter bends by Finite-Difference Time-Domain (FDTD) simulation. We develop the interactive visualization system using a new interactive GUI system which is composed of the virtual reality system and android tablet to analyze the FDTD simulation. The effect of the waveguide system with grooves have been investigated to quantitatively by visualization system. Comparing waveguide system with grooves and without grooves, grooves have been confirmed to suppress the surface current at the metal surface. The surface current at complex shape such as the miter bend have been investigated.

Simple Correctors for Elimination of High-Order Modes in Corrugated Waveguide Transmission Lines.

When using overmoded corrugated waveguide transmission lines for high power applications, it is necessary to control the mode content of the system. Ideally, overmoded corrugated transmission lines operate in the fundamental HE11 mode and provide low losses for long distances. Unwanted higher order modes (HOMs), particularly LP11 and HE12, are often excited in the experimental systems due to practical misalignments in the transmission line system. This paper discusses how the unwanted modes propagate along with the fundamental mode in the transmission line system by formulating an equation that relates the center of power offset and angle of propagation of a beam (for the HE11 and LP11 modes) or the waist size and phase front radius of curvature of a beam (for the HE11 and HE12 modes). By introducing two miter bend correctors into the transmission system-miter bends that have slightly angled or ellipsoidal mirrors-the HOMs can be precisely manipulated in the system. This technique can be used to eliminate small quantities of unwanted modes, thereby creating a nearly pure fundamental mode beam with minimal losses. Examples of these applications are calculated and show the theoretical conversion of up to 10% HOM content into the fundamental HE11 mode with minimal losses.

高功率TE01过模斜接弯头设计

高功率TE01过模斜接弯头设计

Finite-Difference Time-Domain Simulation on Transmission of Millimeter Waves through Miter Bends

We have simulated the distribution of electromagnetic (EM) waves through a system composed of miter bends by finite-difference time-domain (FDTD) simulation. To study the effect of mode conversion by miter bends, three shapes of miter bends have been simulated. For the miter bend that has processed grooves inside, the profile of the output EM waves is changed slightly from that of the input wave (HE11 mode). As a result, this case exhibits the best shape of the miter bend in our simulation. In the miter bend without processed grooves inside, the output EM waves change more than in the case of the miter bend with grooves, because mode conversion occurs at the surface in miter bends without grooves. In the simple bend, which changes the direction of EM waves gradually, the profile of the output EM waves is deformed and the input profile is not conserved. Comparing the above three cases, we found that the grooves lead to more efficient to conservation of the profile of EM waves.

A TE01 mode generator for testing high power transmission devices

To verify the performance of high power waveguide transmission devices such as the miter bend, the waveguide taper, and the quasi-optical mode converter by the low power measurement, a TE01 mode generator, converts the rectangular waveguide TE10 mode into the cylindrical waveguide TE01 mode, for Ka-band is designed, fabricated, and measured. The proposed generator consists of a TE10 to TE20 rectangular waveguide mode converter and a rectangular TE20 to circular TE01 mode converter. The converting process in each section is analyzed and the working principles are discussed. Two prototypes are built and tested. The back-to-back transmission measured results agree well with the numerical calculations. The measured optimum transmissions are 97% with a 1-dB bandwidth from 29.2 GHz to 31.6 GHz. The angle-independent transmissions demonstrate high mode purity and the presence of TE01 mode confirmed by the far-field measurement. The proposed mode generator features high conversion efficiency, high mode purity, and moderate broad bandwidth.

Shakedown analysis of 90-degree mitred pipe bends

Abstract The behaviours of smooth 90-degree pipe bends under cyclic loading have received substantial attention in recent years where shakedown and ratchetting domains have been determined. However, such data are considerably lacking for mitred pipe bends. In the current research, the lower bound shakedown limit loads of 90-degree mitred pipe bends are determined via a simplified direct non-cyclic numerical technique recently developed by Abdalla et al. (2007) The analysed mitred pipe bends are subjected to the combined effect of steady internal pressures and cyclic in-plane or out-of-plane bending moments. Both in-plane closing and opening bending moment cases are considered. The shakedown boundaries of three mitred pipe bend geometries with one, two, and three welded joints are determined and compared with the shakedown boundary of a smooth 90-degree pipe bend. All analysed bends have diameter to thickness ratio of 25 and bend radius of 1.5 times the pipe mean diameter. The results indicate that the shakedown boundaries of mitred bends have reduced domains compared with the smooth pipe bend of similar geometrical parameters. Shakedown domains of mitred bends increase in size as the number of welded joints increase until it approaches the shakedown boundary of the smooth pipe bend simulating a mitred bend with infinite number of welded joints. The percentage of the area under shakedown domain for the mitred pipe bends to that of the smooth pipe bend ranges from 20% for the single mitred pipe bend to 75% for the 3-weld mitred bend. Results also revealed that reducing the number of mitred welded joints, dominates reversed plasticity response at the expense of ratchetting response. Out-of-plane bending generally showed larger shakedown domain than the in-plane bending shakedown domain. Additionally, the shakedown domains for in-plane closing and opening moments are quite similar.

Optimization of a corrugated millimeter-wave waveguide and a miter bend by FDTD simulation

We estimate the transmission efficiency of the electromagnetic wave through the system composed of waveguide and miter bend by Finite-Difference Time-Domain (FDTD) simulation. As the fisrt approach of this estimation, we choose the case that the input wave is TE11 mode. In this case, the efficiency is estimated as 99.65 % for the system without grooves and 76.48 % for the system with grooves (which is called as "corrugate"). Comparing the distributions of the input electric field with that of the output electric field, the effect of the grooves is found as follows: Because the TE11 mode has an anisotropy, its shape is changed by the miter bend. This property appears in the corrugated system more strongly than the non-corrugated system.

Numerical Estimation of Ohmic Loss of High Power Wideband Diplexer for ECCD System

A diplexer for high power millimeter wave has been developed as a fast switching device in ECCD system for improving a stabilizing efficiency of neoclassical tearing modes. The switching operation of diplexer was confirmed with the FDTD code developed in our laboratory and low power tests using a mock-up diplexer. The cooling design of half mirror will be a key issue of this development, so that the Ohmic loss of a miter bend and a half mirror of the ring resonator was estimated by the numerical simulations.

Numerical simulation of ratcheting and fatigue behaviour of mitred pipe bends under in-plane bending and internal pressure

This paper investigates the ratcheting and fatigue behaviour of 90° single unreinforced mitred pipe bends subjected to a cyclic in-plane closing moment with a non-zero mean value and constant internal pressure. An experiment was conducted to induce ratcheting and low cycle failure of the mitred pipe bend. Material and structural response is considered both locally and globally using strain gauges at the locations of highest strain and also by measuring the displacement of the mitre end. These results along with the number of cycles to failure are compared with those produced from nonlinear finite element analysis. The predicted crosshead displacement from the multi linear model showed a good agreement with the test results. However, the finite element model failed to accurately replicate the strain level or trend from the tests, indicating the weakness of the material model used in simulating the cyclic hardening effect. It was also found that the FE models proposed were not able to model the final failure mode of the mitre due to the exclusion of crack simulation in the analysis, i.e. interaction between ratcheting and low cycle fatigue cracking was not considered in the idealised numerical model.

Study on vibration phenomena of guide vane inside bend by fluid structure interaction analysis

Vibration phenomena of a guide vane seem to be generated by a fluid exciting force working on the guide vane in unsteady flow field. Thus, in order to understand the vibration mechanism of the guide vane, it is important to reveal unsteady field inside a bend having the guide vane. In this paper, vibration phenomena of the guide vane inside the bend were considered by using numerical simulation. In order to decide analysis conditions of Large Eddy Simulation (LES), the results of LES were compared to the ones of Particle Image Velocimetry (PIV) for the downscaling model. Moreover, Fluid-Structure Interaction (FSI) analysis was conducted for the mitre bend having the guide vane modelled in actual scale. As a result, stress fluctuation at the centre of the trailing edge of the guide vane was largest. This result indicates that vibration phenomena are possible to occur on the trailing edge of the guide vane.

Numerical and experimental investigation of a 5-port mitre-bend directional coupler for mode analysis in corrugated waveguides

A directional coupler array with 5 ports integrated into a mitre bend for corrugated waveguide transmission lines at 140 GHz has been manufactured. The design is reviewed, and calculations on the performance for in-situ power measurement and mode discrimination are shown. Emphasis is given on detection of errors in alignment of the transmission system. Experimental tests are performed to benchmark the calculations. The results confirm the predictions and show that such a coupler is a viable tool for power measurement and basic mode analysis in high-power transmission systems.

Progress on corrugated waveguide components suitable for ITER ECH&CD transmission lines

The 2 MW cw requirement for ITER EC transmission lines has led GA to design a number of new and modified components, namely power monitors and polarizers to meet this requirement. In addition, the ITER transmission lines may require sliding joints or bellows to accommodate the thermal expansion of the lines and/or vessel motion. The ex-vessel sections of the EC launchers require double seal waveguides, miter bends and possibly double seal sliding joints to assure tritium retention in this region. GA has developed designs for many of these components and some of them have already been tested at high power at the JAEA RF Test Stand. Thermal analyses of the standard GA power monitor miter bend show that our standard design is suitable for 1 MW cw operation when the H-field is in the plane of the miter bend. For 2 MW cw operation a modified design, which also requires H-plane orientation, has been developed and a prototype has been fabricated and is ready for testing. For long pulse/cw operation, a 2 MW calorimetric miter bend with thermally isolated mirror has been designed and a prototype has been fabricated. Since the mirror is thermally isolated, calorimetry on the mirror cooling water can provide a measure of absorbed power. Such a miter bend, when made in a double seal version, could be useful for monitoring total power at the end of an EC transmission line just before the in-vessel section of an EC launcher. A mode analyzer using an all metal water-cooled beam splitter is being developed for use in measuring in real time the HE11 and higher order mode content or total power in EC transmission lines. Such a high power diagnostic can be very useful in optimizing the alignment of the MOU output into a transmission line and in monitoring the HE11 mode purity at various locations in a transmission line. Prior to making a 63.5 mm 170 GHz version suitable for use on ITER, several prototype 31.75 mm 110 GHz versions have been fabricated and tested at DIII-D. A 170 GHz version is now being fabricated. This paper addresses the performance characteristics, design features and test results for the new and modified components being developed to assure low loss transmission and acceptable component stresses for 2 MW cw operation.

In-situ characterization of spurious modes in HE11transmission lines with a 5-port coupler

Real-time in-situ measurement of spurious modes in HE11 trans- mission lines is becoming an important topic for the design of next-generation ECRH installations (e.g. ITER), because the acceptable tolerances for the align- ment of the waveguides and coupling optics are small for oversized waveguides. Also, the effects of spurious modes (ohmic heating, wrong beam parameters at the launcher) become increasingly critical. We present a method for in-situ char- acterization of 4 dominant spurious modes by using a 5-port coupler, which is integrated into a miter bend. The coupler signals can be directly transformed into the mode spectrum by a matrix multiplication. A general formalism for obtaining the coefficients of the transformation matrix is presented along with a method for optimizing the coupler positions in order to obtain the maximum dynamic range for the diagnostics.

Microchannel miter bend effects on pressure equalization and vortex formation

Simulations have been carried out for water flow in a square microchannel with a miter bend. The simulation considered a pressure-driven flow in a channel-hydraulic diameter of 5 μm for series of Reynolds number (Re) range from 0.056 to 560, in order to investigate water flow at bends. The result shows formation of two vortices after the miter bend, which are more discernible above Re 5.6. The critical inlet velocity for the generation of vortex in this particular geometry occurs at 1 m/s. A simple energy mechanism is postulated to explain the vortex formation as well as core skew direction. The high pressure region at the outer wall before and after the bend is a major factor for vortex formation since the liquid needs to reduce the additional energy effected by the high pressure region. Navier–Stokes equation is utilized with a no slip boundary condition for a total microchannel centerline length of 795 μm which is sufficient to produce a laminar flow pattern at the outlet.

Linearly Polarized Modes of a Corrugated Metallic Waveguide

A linearly polarized (LPmn) mode basis set for oversized, corrugated, metallic waveguides is derived for the special case of quarter-wavelength-depth circumferential corrugations. The relationship between the LPmn modes and the conventional modes (HEmn, EHmn, TE0n, TM0n) of the corrugated guide is shown. The loss in a gap or equivalent miter bend in the waveguide is calculated for single-mode and multimode propagation on the line. In the latter case, it is shown that modes of the same symmetry interfere with one another, causing enhanced or reduced loss, depending on the relative phase of the modes. If two modes with azimuthal (m) indexes that differ by one propagate in the waveguide, the resultant centroid and the tilt angle of radiation at the guide end are shown to be related through a constant of the motion. These results describe the propagation of high-power linearly polarized radiation in overmoded corrugated waveguides.

A Polarizer with Sinusoidal Grooves in the Electron Cyclotron Resonance Heating System of the HL-2A Tokamak

Theoretical calculation and experimental results for a polarizer with sinusoidal grooves used in the electron cyclotron resonance heating (ECRU) system of the HL-2A tokamak are presented. The calculation is based on an integral method developed in the vector theory of diffraction gratings, and the polarization characteristics obtained with a low-power test are in good agreement with the numerical calculated results. With the polarizer assembled in a miter bend in the ECRU transmission line, pure ordinary mode (O-mode) and extraordinary mode (X-mode) polarized waves are also expected in the high-power experiment, depending on the polarizer rotation angle and the toroidal injection angle of the electron cyclotron (EC) wave beam. Second-harmonic X-mode experiments were successfully explored in HL-2A. Experimental result revealed that the electron temperature increased from 0.8 keV (Ohmic heating phase) to 1.5 keV (second X-mode heating phase).

Design and manufacturing of the ITER ECRH upper launcher mirrors

Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control magnetohydrodynamic (MHD) instabilities [1,2]. In order to achieve the stabilisation of the neoclassical tearing modes (NTM) and sawtooth oscillation, a deposition of a very localized and peaked current density profile over a broad poloidal steering range is required. In the present optical configuration eight 2 MW mm-wave beams enter each of the four upper launchers (UL) through waveguides into the vacuum vessel. Each beam line comprises consecutive corrugated waveguide sections with two mitre bends, orientating the poloidal and toroidal directions and three sections of quasi-optical transmission [3]. The beam waist locations and beam shaping properties in free space propagation are defined by two additional mirrors, the first being a static focusing mirror and the second a plane poloidally steerable mirror. Each mirror reflects a group of 4 mm-wave beams. The three types of UL mirrors (mitre bend, focusing and steering) absorb heat generated essentially by three sources: the ohmic loss of the RF beam reflected at the mirror surfaces and the nuclear and thermal radiation coming from the plasma. While the average heat load is within reasonable engineering limits, three elements condition the actual mirror design, the peak ohmic heat load (Gaussian or Bessel type heat deposition profiles), the electromagnetic forces generated in vertical disruption events (VDE), and the ITER cooling water requirements. This paper provides an overview of the different upper port-plug mirror designs and cooling schemes and an outlook on the prototype manufacturing activities and the future test program. The optimized mm-wave layout within the ECH port plugs is also presented.

Calorimetric Measurements of the Radio-Frequency Power and of the Transmission Line Losses on the DIII-D ECH System

The measurement of the power injected by the electron cyclotron heating (ECH) system in the DIII-D tokamak is a critical requirement for analysis of experiments, for tuning the gyrotrons for maximum power and efficiency, for tracking long-term operational trends, and for providing a warning of problems with the system. The ECH system at General Atomics consists of six 110-GHz, 1-MW-class gyrotrons. The radio-frequency (rf) power generated by each gyrotron is determined from calorimetry, using the relevant temperature and flow measurements from the cooling circuits of the cavity, matching optics unit, and dummy loads (DLs). The rf pulse length and time dependence are measured using an rf monitor at the first miter bend in the transmission line. The cavity power loading measured directly gives the generated rf power using a previously determined relationship between cavity loading and rf production. The direct measurement of the efficiencies of four of the transmission lines was performed using a high-power DL placed alternately in two positions of each DIII-D waveguide line, at accessible points close to the beginning and the end of each line. Total losses in the transmission lines range from 21.2 to 30.7%. Experimental results are compared to theoretical predictions of the performance of the components and waveguide lines.