Miter Bend Research Articles

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.

Study of a Miter Bend Polarizer for Central ECRH on GAMMA-10

The new polarizers with grooved mirrors were installed in ECRH system on the GAMMA 10 to get the optimal polarized wave. Numeric calculation and low power performance test of this pair of polarizers was agreed well. And it is found that the setting error of polarizer angle within +/- 5° gives negligible reduction of the X-mode ratio less than 1%. On the experiment in the GAMMA 10, it is shown that the fraction of X-mode has key role to heat plasma efficiently.

MITER BEND MIRROR DESIGN FOR CORRUGATED WAVEGUIDES

Miter bend mirror has been designed for microwave transmission between two corrugated waveguides of the same size by iterative phase correction method. Geometrical Optics (GO) approximation has been used in our design at a frequency of 110 GHz. The equivalence principle is also adopted to forward-propagate and backward-propagate the beam onto the miter-bend mirror. The designed miter bend mirror shows a coupling coefficient up to 99.619%, much better than that of a flat mirror. The convergence rate shows that the design is very efficient with only a few iterations required.

Low-Power Testing of Losses in Millimeter-Wave Transmission Lines for High-Power Applications

We report the measurement of small losses in transmission line (TL) components intended for high-power millimeter-wave applications. Measurements were made using two different low-power techniques: a coherent technique using a vector network analyzer (VNA) and an incoherent technique using a radiometer. The measured loss in a 140 GHz 12.7 mm diameter TL system, consisting of 1.7 m of circular corrugated waveguide and three miter bends, is dominated by the miter bend loss. The measured loss was 0.3±0.1 dB per miter bend using a VNA; and 0.22±0.1 dB per miter bend using a radiometer. Good agreement between the two measurement techniques implies that both are useful for measuring small losses. To verify the methodology, the VNA technique was employed to measure the extremely small transmission loss in a 170 GHz ITER prototype TL system consisting of three lengths of 1 m, 63.5 mm diameter, circular corrugated waveguide and two miter bends. The measured loss of 0.05±0.02 dB per miter bend may be compared with the theoretical loss of 0.027 dB per miter bend. These results suggest that low-power testing of TL losses, utilizing a small, simple TL system and a VNA, is a reliable method for evaluating performance of low-loss millimeter-wave TL components intended for use in high-power applications.

A clonal selection algorithm with varying order finite elements for the optimization of microwave devices

AbstractA real‐coded clonal selection algorithm (RCSA), which is a global search method based on the artificial immune systems paradigm, is applied for optimizing microwave devices. We couple RCSA with varying high‐order finite elements (FEs) to control the balance between the global and local search efforts in the algorithm. In this scheme, low‐order FEs are used in the global search, whereas varying high‐order FEs are used in the local search. The proposed technique is investigated in the designs of an E‐plane miter bend and a rectangular waveguide impedance transformer. The results illustrate the accuracy and computational savings of this method. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1392–1397, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23387

Effects of miter bend on pressure drop and flow structure in micro-fluidic channels

The characteristics of a pressure-driven water flow including flow micro-structures and pressure drops are investigated in serpentine micro-channels with miter bends. The micro-channels have rectangular cross-sections with hydraulic diameters of 0.209 mm, 0.412 mm and 0.622 mm, respectively. To segregate the bends and entrance effects individually from the total pressure drop, for each size three types of micro-channels: straight short, straight long and long serpentine, were fabricated to get the reliable pressure data without entrance effect. A micron-resolution particle image velocimetry system (micro-PIV) was develop and used to obtain the detailed velocity vector field. The experimental results show that the vortices around the outer and inner walls of the bend do not form when Re < 100. Those vortices appear and continue to develop with increasing Re number when Re is larger than a value around 100, and the shape and size of the vortices almost remain constant when the Re is larger than a value around 1000. The experimentally observed additional pressure drop due to the bend is commensurate with the strength of the calculated vortices. The bend loss coefficient K b was observed to be related only with the Re number when Re < 100, but with the Re number and channel size when Re > 100. It almost keeps constant and changes in the range of ±10% when the Re is larger than a threshold value somewhere in 1000–1500.

Polarizer Development for Electron Cyclotron Resonance Heating Systems in a HL-2A Tokamak

The paper presents the development of sinusoidally grooved polarizers for electron cyclotron resonance heating (ECRH) systems in the HL-2A tokamak. The polarizer groove shape was designed according to a sinusoidal function with a groove period p = 0.48λ and depth d = 0.5λ. Here, λ is the wavelength, whose value is 4.41 mm. The low-power test results of the polarizer performance are in agreement with a numerical calculation based on the integral method developed in vector theories of diffraction gratings. High-power experiments reveal that 340 kW high-power EC waves can be transmitted through the corrugated waveguide line with the polarizer assembled in a miter bend at atmospheric pressure. With the polarizer, ECRH/electron cyclotron current drive (ECCD) experiments in the extraordinary mode have been successful in a HL-2A tokamak.

Stresses in the vicinity of an unreinforced mitre intersection: An experimental and finite element comparison

The experimental investigation reported provides elastic stresses in the vicinity of the unreinforced intersection of a single 90° mitred bend, subjected to an in-plane bending moment. The specimen was extensively strain gauged on the outer surface. A small number of rosettes were also laid on the inside surface close to the welded intersection. The procedures used for the successful installation of the inside surface gauges are discussed. In the experiment, consideration was also given to deflections and rotations. Satisfactory comparisons with adaptive- p thin-shell finite element results were obtained in general and differences are explained in terms of the known experimental variables and finite element approximations. The nature of the stresses at such intersections is discussed and various methods of obtaining fatigue ‘hot-spot’ stresses are considered.

Mode Converter Synthesis by the Particle Swarm Optimization

Particle Swarm Optimization (PSO) is an effective, simple and promising method intended for the fast search in multi-dimensional space [1]. Besides special testing problems a number of engineering tasks of electrodynamics were solved by the PSO successfully [2,3]. On the other hand, the scattering matrix technique is a fast and accurate method of mode converter analysis. We illustrate PSO by a number of converter designs intended for high-power microwaves control: a matching horn for maser section, a design of built-in converter for multi-charged ion source, a TE01 miter bend.

Macroscopic Analysis of Pressure Loss Coefficient in Pipes and Ducts (1st Report, Loss Coefficient on Entrances)

For the famous formulas of pipes and ducts, for example, Weisbach's formulas of the pressure loss coefficients in entrance flush with wall at arbitrary angle, abrupt contraction, miter bend, and so on, it is still not clear that some of these formulas could be derived from a simple flow model or not. In this paper, an analysis was conducted by using linear momentum theorem for these equations from the macroscopic point of view. It was found that these formulas could be derived as modified ones of the equations obtained by using the momentum theorem. In the first report, the pressure loss coefficients of gradual and abrupt contraction, entrance flush with wall at arbitrary angle, and the effect of rounded entrance (r/D) on the loss coefficient were examined.

Macroscopic Analysis of Pressure Loss Coefficient in Pipes and Ducts (2nd Report, Loss Coefficient of Miter Bends)

For the famous formulas of pipes and ducts, for example, Weisbach's formulas of the pressure loss coefficients in entrance flush with wall at arbitrary angle, abrupt contraction, miter bend, and so on, it is still not clear whether some of these formulas could be derived from a simple flow model or not. In this paper, analysis was conducted by using linear momentum theorem for these equations from to the macroscopic point of view. It was found that these formulas could be derived as modified equations of the equations obtained by using the momentum theorem. In the second report, the pressure loss coefficient of miter bends (elbows) and the effect of inner rounded corner (r/D) were examined.

Commissioning of the 28-GHz Electron Cyclotron Resonance Heating System on ADITYA Tokamak

An electron cyclotron resonance heating system is commissioned on Aditya tokamak to carry out pre-ionization, start-up, and heating experiments. A high-power microwave source (gyrotron), capable of delivering 200-kW cw power at 28 ± 0.1 GHz, is commissioned successfully using a water dummy load for pulsed operation. The output mode of the gyrotron is TE02. The output power of the gyrotron is measured using microwave probe couplers, a spectrum analyzer, and calorimetric techniques. A hardwired interlock operates a rail-gap-based crowbar system in less than 10 μs under fault condition and protects the gyrotron. The rail-gap crowbar operation has been qualified with the high-voltage power supply by performing a 10-J wire-burn test prior to energizing the gyrotron.A transmission line consisting of matching optic units, dc break, polarizer, miter bend, and corrugated waveguides terminates with a boron nitride window. The total attenuation in the line is measured to be less than 1.1 dB. Based on quasi-optical theory, a beam launcher is designed, fabricated, and tested for ultrahigh-vacuum compatibility prior to commissioning on tokamak.After successful operation of the gyrotron on the dummy load, the gyrotron output has been coupled to the ADITYA tokamak, and successful breakdown of neutral gas is observed without assistance from an ohmic transformer.

Flow characteristics of water in straight and serpentine micro-channels with miter bends

Flow characteristics of pressure-driven de-ionized water were investigated experimentally in straight and serpentine micro-channels with miter bends. The micro-channels had rectangular cross-sections with hydraulic diameters of 0.209 mm, 0.395 mm and 0.549 mm. To evaluate bend loss coefficient in the serpentine micro-channel and micro-scale size effect on it, the additional pressure drop due to the miter bend must be obtained. This additional pressure drop can be achieved by subtracting the frictional pressure drop in the straight micro-channel from the total pressure drop in the serpentine micro-channel. Since currently there still has a debate on the relationship between the friction factor and Re number in the straight micro-channel, the frictional pressure drop had to be obtained experimentally here. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. The experimental results show that after considering the measurement uncertainties the experimental Poiseuille number can be well predicted by the conventional laminar incompressible flow theory when Re number is less than some value around 1500, the discrepancy observed by the former researchers can be attributed to not accounting for the additional pressure drop in the entrance region. The onset of transition to turbulence might be at 1500–1700. For serpentine micro-channels, the additional pressure drop can be divided into two regions. One is Re < 100. It is very small since no circulation exists. The other one is Re larger than some value in 100–200. At this time the circulation appears and develops at the inner and outer wall of the bend. The additional pressure drop increases sharply with Re number. The bend loss coefficient was observed to decrease and tend to be a constant with decreasing Re number. It is found to be larger than the predicted value for macro-channel turbulent flow and related with the channel size when flow separation appears, namely Re > 100–200.

Design and development of EC H&CD antenna mirrors for ITER

The steering mirrors of the ITER EC H&CD antenna (250 mm × 350 mm × 30 mm) are designed to reflect 20 MW millimeter (mm)-wave beams and to control their injection angle into plasma. The mirror would be exposed to high-energy neutrons and heat flux from plasma and also heated by incident wave beams. The result of thermo-mechanical analysis indicates that the mirror design with copper alloys (dispersion strengthened copper or copper chrome zirconium) plate with stainless steel (SS316) cooling tubes inside is considered to be acceptable. Since the mirror is rotated to change the injection angle of mm-wave beams, a flexible tube to supply cooling water into the steering mirror is necessary. A mock-up of the mirror for a 90° miter bend was fabricated and the mm-wave transmission with power/pulse length of 420 kW/4.7 s was carried out. Temperature increase agrees with the expected value. Ohmic loss is estimated to be 0.21% of the incident power, which agrees with the calculation based on the electrical resistivity of DSCu at 1.8 × 10 −8 Ω m. The result also indicates 1 MW, CW transmission capability of the miter bend.

Test and Commissioning of 82.6 GHz ECRH system on SST-1

Electron Cyclotron Resonance Heating (ECRH) system will play an important role in plasma formation, heating and current drive in the Superconducting Steady state Tokamak (SST-1). Commissioning activity of the machine has been initiated. Many of the sub-systems have been prepared for the first plasma discharge. A radial and a top port have been allotted for low field side (LFS) and high field side (HFS) launch of O and X- modes in the plasma.The system is based on a gyrotron source operating at a frequency of 82.6±0.1GHz (GLGD-82.6/0.2) and capable of delivering 0.2 MW / 1000s with 17% duty cycle. The transmission line consisting of ∼15 meters length 63.5mm corrugated wave guide, DC break, wave guide switch, mitre bend, polariser, bellows that terminates with a vacuum barrier CVD window. A beam launching system used to steer the microwave beam in the plasma volume is connected between the end of the transmission line and the tokamak radial and top ports. A VME based real time data acquisition and control (DAC) system is used for monitoring, acquisition and control. Hard-wired interlock operates a rail-gap based crowbar system in less than 10µs under any fault condition. Burn patterns are recorded at various stages in the transmission line. The gyrotron is tested for ∼200 kW / 1000s operation on a water dummy load. Transmission line is tested at various power levels for long pulse operation. The paper highlights the experimental results of successful commissioning of the system.

An ITER-relevant evacuated waveguide transmission system for the JET-EP ECRH project

An over-moded evacuated waveguide line was chosen for use in the transmission system for the proposed JET-enhanced performance project (JET-EP) electron cyclotron resonance heating (ECRH) system. A comparison between the quasi-optical, atmospheric waveguide and evacuated waveguide systems was performed for the project with a strong emphasis placed on the technical and financial aspects. The evacuated waveguide line was chosen as the optimal system in light of the above criteria. The system includes six lines of 63.5 mm waveguide for transmitting 6.0 MW(10 s) at 113.3 GHz from the gyrotrons to the launching antenna. The designed lines are on average 72 m in length and consist of nine mitre bends, for an estimated transmission efficiency of ∼90%. Each line is designed to include an evacuated switch leading to a calorimetric load, two dc breaks, two gate valves, one pumpout tee, a power monitor mitre bend and a double-disc CVD window near the torus. The location of waveguide support is positioned to minimize the power converted to higher-order modes from waveguide sagging and misalignment. The two gate valves and CVD window are designed to be used as tritium barriers at the torus and between the J1T and J1D buildings. The last leg of the waveguide leading to the torus has to be designed to accommodate the torus movement during disruptions and thermal cycles. All lines are also designed to be compatible with the ITER ECRH system operating at 170 GHz.

Optimization of microwave devices using 3-D finite elements and the design sensitivity of the frequency response

Direct optimization of microwave devices is more efficient if sensitivities of the cost function are available. An earlier method for finding sensitivities of the scattering matrix efficiently over a range of frequencies, from a finite-element analysis, is applied here to the optimization problem. The method is tested on rectangular waveguide components with 1-4 design parameters: a right-angle miter bend, an E-plane U-bend, and a waveguide impedance transformer.

STUDY OF THE IMPULSE WAVE DISCHARGED FROM THE EXIT OF A RIGHT-ANGLE PIPE BEND

The impulse wave, which is usually generated by a shock wave discharge from the exit of a pipe, almost always leads to undesirable noise and vibration problems. The present study addresses experimental and computational work of the impulse wave discharged from the exit of two kinds of right-angle pipe bends, which are attached to the open end of a simple shock tube. The weak normal shock wave with its magnitude of Mach number from 1·02 to 1·20 is employed to obtain the impulse wave propagating outside the exit of the pipe bends. A Schlieren optical system is employed to visualize the impulse wave discharged from the exit of the pipe bends at an instant. The experimental data of the magnitude of the impulse wave and its propagation directivity are analyzed to characterize the impulse waves discharged from the exit of the pipe bends and compared with those discharged from a straight pipe. Computational analysis using the unsteady, inviscid, compressible equations is complemented to represent the major features of the impulse wave obtained from the shock tube experiments. Computational results well predict the experimented dynamic behaviors of the impulse wave. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulse wave and its directivity toward to the pipe axis, compared with the straight pipe. It is believed that the right-angle miter bend pipe can play one role of a passive control against the impulse wave.

Parametric survey of upper and lower bound limit in-plane bending moments for single mitred pipe bends of various geometries

The problem of limit analysis for a cylinder–cylinder intersection forming a single mitred pipe bend subject to in-plane bending has been investigated. Lower bound analysis with new equations of force and moment equilibrium together with a higher number of parameters resulted in more stability as compared to a previous analysis of the same problem [PhD Thesis, The University of Manchester, 1991]. Concurrently, abaqus finite element plastic collapse moments were obtained as upper bounds to the problem. Two sets of results were compared, showing good agreement with each other. It could be finally concluded that the true limit moments are bounded in between.

Accuracy control in the optimization of microwave devices by finite-element methods

Automatically optimizing the design of a microwave device can be prohibitively time-consuming when a numerical electromagnetic-field analysis is necessary at each iteration. However, the time taken for the field analysis depends on the accuracy required, and in the early stage of the optimization relatively inaccurate solutions are adequate. This idea is exploited in a scheme that combines a quasi-Newton constrained optimizer with a two-dimensional p-adaptive finite-element method for finding scattering parameters. The scheme has been tested on three H-plane rectangular waveguide devices: a T-junction, a miter bend with a dielectric column, and a two-cavity iris-coupled filter. Time savings of more than an order of magnitude were obtained, compared to the standard approach of requiring equally high accuracy throughout the optimization.