Coupling Impedance Research Articles

Influence of quality factor on operating mode of TM<sub>02</sub> mode relativistic backwave oscillator

<sec>The mode competition in an overmoded relativistic backward wave oscillator is studied through theoretical analysis and three-dimensional particle-in-cell simulation in this work. Based on the quality factor and coupling impedance, the mode selection for a TM<sub>02</sub> mode backward wave oscillator is achieved, and its output power and magnetic field strength are optimized in the simulation.</sec><sec>The quality factor is related to the group velocity and end reflection of each mode. The dispersion curves of some non-axisymmetric modes are very close, and the group velocities are basically equal. Therefore, the end reflection needs considering to distinguish between the quality factors of different modes. In frequency domain simulation, analyzing the quality factor of each mode by using the <i>S</i><sub>11</sub> parameter curve can avoid calculating the end reflection.</sec><sec>The three-dimensional simulation results show that the coupling impedance and quality factor jointly affect the operating mode. When the coupling impedance advantage of the working mode is not obvious, changing the resonant frequency of the high-frequency structure can affect the beam-wave interaction process, thereby changing the excitation mode. When the advantage is obvious, the beam-wave interaction of the excitation mode will not be destroyed by the resonant mode, and other modes of microwave output mainly come from the conversion of the same frequency modes. Due to the constant dispersion curve, the effect of resonance on the mode is essentially the effect of the quality factor on the mode dominated by the end reflection.</sec><sec>The insensitive parameters and the electron beam radius obtained from the simulation are used as the optimal parameters, and the automatic optimization algorithm is used in combination with the two-dimensional simulation to perform multi-objective optimization design in the above device. The final output power of the backward wave oscillator reaches 534 MW, with an efficiency of 23.64%, an increase of 221.7% compared with the efficiency of the original device. The device operating mode remains stable, with a power ratio of TM<sub>02</sub> mode reaching 94.95%.</sec>

Beam Coupling Impedance Contribution of Flange Aperture Gaps: a Numerical Study for Elettra 2.0

The accurate analysis of any possible source of beam instability is mandatory for the design of a new particle accelerator, especially for high-current and ultra-low emittance synchrotrons. In the specific case of instabilities driven by the coupling between the charged particle beam and the electromagnetic field excited by the beam itself, the corresponding effect is estimated through the beam coupling impedance. The modeling of this effect is essential to perform a rigorous evaluation of the coupling impedance budget able to account for all devices present in the entire machine. To deal with this problem, this paper focuses on the estimation of the contribution of the joints lying between the different vacuum chamber sections, by performing a comparative numerical analysis that takes into account different aperture gaps between the flanges. The results point out the criticality of many small-impedance contributions that, added together, must be lower than a predefined impedance threshold.

Operational experience of a low beam coupling impedance injection kicker magnet for the CERN SPS ring

The CERN SPS injection kicker magnets (MKP) were developed in the 1970’s, before beam power deposition was considered an issue. There are two types of these magnets in the SPS: MKP-S (small aperture) and MKP-L (large aperture) versions. The MKP-L magnets are very lossy from a beam impedance perspective: this would be an issue during SPS operation with the higher intensity beams needed in the future for HL-LHC. Hence, a beam screen has been developed, which is inserted in the aperture of each MKP-L module. The screen consists of silver fingers applied to alumina U-shaped chambers: the fingers have been optimized to achieve both adequately low beam induced power deposition and good high voltage (HV) behaviour. A surface coating, with a low secondary electron yield, is applied to the inner surface of the alumina chambers to reduce dynamic vacuum. The low-impedance MKP-L has been extensively HV tested in the lab before installation in the SPS. This paper briefly presents the design and focuses on the operational experience in the SPS, including heating and vacuum.

High-frequency Resonance Analysis and Impedance Reshaping Control of MMC-HVDC System Based on Frequency Coupling Impedance Model

High-frequency Resonance Analysis and Impedance Reshaping Control of MMC-HVDC System Based on Frequency Coupling Impedance Model

Studies of FCC-ee Single Bunch Instabilities with an Updated Impedance Model

The design of the FCC-ee collider is ongoing with the goal of optimizing beam parameters and developing various accelerator systems. As a result, the modelling of coupling impedance is continuously evolving to take into account the design of the collider vacuum chamber and hardware components. Concurrently, estimates of collective effects and instabilities are being continually updated and refined. This paper presents the current FCC-ee impedance model and reports the findings of the single-bunch instability studies. Additionally, some potential mitigation techniques for these instabilities are discussed.

Capacitive BPM electromagnetic design optimisation

Capacitive beam position monitors (BPM) are widely used as diagnostics tools in particle accelerators. Typically due to a large number of BPM in an accelerator, their contribution to the beam coupling impedance cannot be neglected. In addition to the broadband part at low frequencies, the impedance exhibits resonant peaks at higher frequencies due to electromagnetic fields trapped around the BPM button and in the feedthrough assembly. Coupling of these peaks with beam spectrum lines can result in the BPM overheating. In this paper, we discuss the BPM design optimization aimed at the beam coupling impedance minimization while keeping the BPM signal transfer impedance.

Study of beam-beam interaction in FCC-ee including updated transverse and longitudinal Impedances

Beam-beam interaction in FCC-ee can be seriously affected by the vacuum chamber coupling impedance resulting in a safe tune areas reduction, tune shifts and spread, bunch length and energy spread variation. The interplay of the two effects has a drastic impact on the stability of colliding bunches and respectively on the achievable luminosity. In this paper, beam-beam collisions in FCC-ee with 4 interaction points are studied including the updated transverse and longitudinal impedances.

Overview of material choices for HL-LHC collimators

In view of the High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN, different materials were investigated for the upgrade of the LHC collimation system. A key objective was to determine how the jaws of the new collimators could be manufactured to meet the demanding requirements of HL-LHC, such as thermo-mechanical robustness and stability, beam coupling impedance, Ultra-High Vacuum (UHV), etc. During the Long-Shutdown 2 (LS2), five primary and ten secondary low-impedance collimators were already produced using novel materials. For LS3, in addition to more secondary collimators, the production and installation of other types of devices, including tertiaries and physics-debris collimators, is planned. This paper details the final mate-rial choices and rationale for each collimator family.

Upgrade the impedance model in RCS of CSNS

The Rapid Cycling Synchrotron (RCS) in the China Spallation Neutron Source (CSNS) is a high-intensity proton accelerator that is susceptible to collective instabilities and performance limitations due to its impedance. With impedance study of key components and new component installations, the impedance model should be updated. This article presents a comprehensive estimate of the coupling impedance and outlines the impedance model of the RCS.

Characterization of the longitudinal beam coupling impedance and mitigation strategy for the fast extraction kicker KFA79 in the CERN PS

In the framework of the High Luminosity Upgrade of the LHC (HL-LHC) the beam intensity from the injectors must be doubled while keeping longitudinal beam parameters unchanged. As such, high-quality beams with high intensities are required also from the Proton Synchrotron (PS). The beam coupling impedance plays a crucial role and mitigation measures must be taken to remain within a stringent impedance budget. Kicker magnets are important contributors to the overall broadband impedance of the PS. Moreover, the detailed study of kicker impedances revealed additional resonant modes which may be critical for the beam stability. The longitudinal beam coupling impedance for the fast extraction kicker KFA79 is presented in this study, and a solution to reduce the impedance of the critical resonant modes is introduced. Electromagnetic (EM) simulations have been performed to determine the impedance behaviour. Finally, the insertion of transition pieces between magnet modules is presented as a measure for mitigating the low frequency resonant impedance contributions.

Analysis and Weakening of Sequence Impedance Coupling in Grid-Forming Converters

Analysis and Weakening of Sequence Impedance Coupling in Grid-Forming Converters

(Invited) Nanoscale Devices for Accelerating AI Algorithms

The energy consumption of training and deploying state-of-the-art artificial intelligence (AI) models has experienced exponential growth, driven by increasing model parameters and the necessary training data. Recent models demand over 1 billion PetaFLOPs of total computation for training, potentially taking weeks to complete. With current GPU performance at approximately 1-3 TOPS/W, GPU training energy consumption alone can exceed 100,000 kWh, equivalent to the monthly energy expenditure of 100 US households. Over the next decade, these models are expected to scale up further, driving total computing energy to constitute a significant portion of global consumption. In this talk, we describe both synaptic and neuronal devices that can accelerate AI algorithms with potentially multiple orders of magnitude improvement in power efficiency.First, we describe an oscillatory retinal neuron (ORN) that directly converts incident DC light into voltage spikes. Coupled arrays of this device result in an imager that carries out in-sensor processing while capturing an image. Uniquely, the conversion from input light to output voltage spikes occurs without external power. When coupled in arrays, the neighboring neurons interact with each other to influence the spiking frequency spectrum. This allows the arrays to carry out frequency multiplexed computation on an input image. It is shown that this approach can achieve>20,000 TOPS/W, multiple orders of magnitude greater than the current approaches. Theory and simulation is used to elucidate how coupled ORNs carry out computation on an input image. When coupled, each output frequency band encodes a unique computation on the input image. By tuning the coupling impedances and the frequency bands, user defined computations can be carried out on the input. We experimentally show that this can be carried out with a 3x3 array that demonstrates simultaneous edge detection, intensity filtering, image segmentation and other functions. This hardware is then used to demonstrate improvement in MNIST handwritten digit classification accuracy over a traditional imager connected to a fully connected network.Next, we describe spiking synaptic devices that can be directly fabricated in the back-end of line of CMOS devices. These devices consist of an InP transistor channel with an engineered gate stack. Using a uniform gate insulator, we can demonstrate behaviors of biological synapses, such as potentiation, depression, spike number dependent plasticity, and spike timing dependent plasticity. By introducing a heterostructured gate insulator, it is shown that short-term to long-term memory transitions can be designed into the device. Finally, by using a transparent gate, an in-sensor synaptic phototransistor is demonstrated and the performance of these devices at a system level is demonstrated.

Optimization of hybrid microperforated panel and nonuniform space-coiling channels for broadband low-frequency acoustic absorption

Broadband noise cancellation at low frequencies (<1000 Hz) with thin absorbers has been a long-standing demand in acoustic engineering. Here, a design method is proposed for a subwavelength hybrid absorber, consisting of a microperforated panel (MPP) backed by nonuniform space-coiling channels. The low-frequency absorption performance is analyzed by impedance theory and complex frequency method. The sensitivity of the absorption band to the parameters of the MPP and the coiled channels is investigated, based on which a genetic algorithm is employed to costume quasi-perfect absorption at the desired frequency. Furthermore, a parallel integration of multiple inhomogeneous units is developed to broaden the absorption spectrum. An optimization strategy is proposed to effectively mitigate the performance degradation caused by the impedance coupling effect. The influence of the number of combined units and the objective function is analyzed for the optimization results. Numerical simulations, experiments, and theoretical predictions verify the effectiveness of the design method. Furthermore, the as-designed combination absorber achieves continuous absorption from 305 Hz to 1088 Hz. The proposed design approach may offer a promising solution for practical applications in broadband noise reduction.

Analysis of grounding system transient with consideration of soil ionization and mutual coupling effect

The grounding system of an electrical substation provides safety to both operator and equipment. The lightning current waveform has a major influence on the dynamic performance of ground electrodes. If lightning current is large enough, soil will be ionized, which will have a great effect on the transient performance of the grounding system. Many numerical models have been developed to evaluate the transient performance of grounding system, still it is a challenging task to analyze the impulse behavior of grounding system efficiently. In this paper, the transient behavior of grounding systems with consideration of nonlinear and dynamic effects of soil ionization is presented. Grounding systems such as vertical rod, horizontal conductor and grounding grid buried in the homogeneous soil are considered as case study. Proposed model is the combination of circuit theory approach and method of moment with consideration of frequency-dependent impedance and mutual coupling effect between the conductor segments. Self and mutual component of inductance and resistance are considered in the analysis. Initially, transient performance of grounding system is analyzed for single vertical rod, horizontal and square grounding electrodes, further it is extended for vertical rod (more than one), horizontal conductor and grounding grids with different configurations. The analysis of grounding system with the consideration of mutual coupling effect is compared with devoid of mutual coupling, and differences between them are evaluated. For validating the developed method, simulated results are compared with the results reported in the literature, and good agreements are found. Analysis shows that the grounding impulse impedance decreased with increasing the magnitude of injected current. Developed method will help to improve the modeling of simple as well as complex grounding system buried in homogeneous soil.

Design and Characterization of Ultrasonic Langevin Transducer 20 kHz Using a Stepped Horn Front-Mass

Ultrasonication is a method that is widely used in various fields. One of its applications is to accelerate the process of homogenization, emulsification, and extraction. In the ultrasonicator system, the transducer is an extremely important device. The resonant frequency, longitudinal vibration amplitude, and electromechanical coupling are the targets in designing an ultrasonic transducer. In this investigation, the main contribution was the development of a simple and effective method for mechanically tuning the resonant frequency of the transducer by adding mass to the front end of the mass or stepped horn. This study also aimed to obtain optimal results by examining the effects of geometric dimensions, bolt prestress, stress distribution, resonant frequency, amplitude, and electrical impedance. The ultrasonic transducer model was designed with a resonant frequency of 20 kHz and simulated using the finite element analysis. The steps involved included calculating the dimensions and geometric structure of the transducer, modeling using the finite-element method, and experimental validation. The simulation results and measurements showed that the series resonant frequency, electrical impedance, and effective electromechanical coupling of the Model-4 transducer 16∙13 mm radiator configuration were 20.15 kHz, 100 Ω, and 0.2229 from the simulation results, and 20.17 kHz, 24.91 Ω, and 0.2033 from the measurement results. A percentage difference, or relative error, of 0.1% was obtained between the simulation and the experimental results for this Model-4 with bolt prestressing at 15 kN.

Measurement and optimization of the beam coupling impedance of a novel 3D-printed titanium alloy cage inside the thin-wall vacuum chamber.

Dipole magnet vacuum chambers are among the most critical and costly components of rapid-cycling accelerator facilities. Alternative approaches to traditional ceramic chambers have been explored for the implementation of fast-ramping dipole-magnet vacuum chambers, including thin-wall metallic beam pipe chambers strengthened with transverse ribs and ceramic rings inside thin-walled chambers. Here, we report a novel 3D-printed titanium alloy cage inside the thin-wall vacuum chamber, which is designed for high-intensity heavy ion accelerator facility (HIAF) to reduce manufacturing difficulty and cost, shorten the production cycle, and improve the quality. Comprehensive studies were undertaken to characterize the impedance of the 3D-printed titanium alloy cage inside the thin-wall vacuum chamber. The beam-coupling impedance and eddy currents of the new thin-wall vacuum chamber were studied mostly numerically. Strategies for further reducing the beam-coupling impedance were explored. In addition, impedance bench measurements using the "half wavelength" resonant method were conducted to identify the longitudinal and transverse impedances of the 3D-printed titanium alloy cage inside the thin-wall vacuum chamber prototype experimentally. The simulated and measured results for the impedance were consistent. Furthermore, a campaign for resonance-check measurements on the 3D-printed titanium alloy ring loaded inside a thin-wall vacuum chamber prototype was launched. This novel thin-wall vacuum chamber structure is now entering the fabrication stage and will soon be ready for installation in the Booster Ring (BRing).

Conducted EMI Simulation for a DC-DC Converter: a DC Brush Motor System Considering Showering Arc at Mechanical Contacts

This paper provides an overview of a circuit analysis model for a DC brush motor, taking into consideration showering arc events. A mechanical contacts model that reproduces showering arc behavior is developed by combining new variable resistors with the steady arc model. As a result, spike surge waveforms can now be simulated via circuit analysis. It is also become clear that spike surges with continuous showering arcs constitute the maximum condition of conducted EMI. The measured and simulated conducted EMI show good agreement within 9 dB up to 108 MHz, in accordance with the CISPR 25 standard. Moreover, it is now possible to quantitatively predict the amount of conducted EMI in a system comprising a step-down DC-DC converter and a DC brush motor, by considering a dominant magnetic coupling and parasitic impedances.

Design and thermal analysis of the BPM-bellows assembly front-end photon block for Hefei Advanced Light Facility

The BPM-bellows front-end photon block with ellipse cross-sections has been designed for Hefei Advanced Light Facility (HALF). Such structure has lower longitudinal coupling impedances than the photon block with commonly-used circle cross-sections. In addition, two types of cooling structures have been designed, which are shared water-cooling pipe (cooling structure 1, CS1) and independent water-cooling tank (cooling structure 1, CS2), respectively. The CS1 is simple and space-saving, while the CS2 has better heat dissipation capability. In order to calculate power density on complex light-receiving surfaces, the Monte Carlo simulation tool, Synrad, was applied. By building finite element models and importing power density data from Syrand, the temperature and thermal stress distributions of photon blocks with two different cooling structures were calculated. The thermal analysis indicates that the maximum temperature (37.73°C) is located at CS1, but the maximum stress (16.28 MPa) is on CS2 due to the difference in structure and heat dissipation capability. Moreover, the maximum temperature and thermal stress values are far below the material criteria of CuCrZr. Therefore, the simple and space-saving CS1 is more suitable for HALF, which can reduce manufacturing costs and better satisfy the compact layout in the storage ring.

A Wideband 220-GHz Traveling Wave Tube Based on Slotted Piecewise Sine Waveguide

A slotted piecewise sine waveguide (SPWSWG) is suggested as the slow wave structure (SWS) to develop the terahertz traveling wave tube (TWT). This letter is the first to report the SPWSWG SWS with the advantages of flat dispersion and large coupling impedance from our calculation. Based on this novel SWS, a wideband 220-GHz TWT has been designed, fabricated and tested. The cold test results show that the reflection parameters at the input and output port of the TWT are less than -15.2 dB in the frequency range of 209-235 GHz. Moreover, the hot test results demonstrate that the maximum saturated output power reaches 28.6 W at 215 GHz and the 3-dB bandwidth exceeds 15.5 GHz, which are basically consistent with the simulation results.

Study of temperature and frequency dependant dielectric, impedance, AC resistivity, modulus spectroscopy and electromechanical coupling properties of [BaNd0.1Ti0.8Nb0.1O3](1-x)[Na0.5Bi0.5TiO3]x relaxor ferroelectric ceramics

[BaNd0.1Ti0.8Nb0.1O3](1-x)[Na0.5Bi0.5TiO3]x ceramics with x = 0.25, 0.40, 0.60, 0.65 & 0.70 were prepared through solid-state sintering route. In the present study, temperature and frequency dependant dielectric, Impedance, AC resistivity, modulus spectroscopy and electromechanical coupling properties carried out. These materials showed modulus resonance and anti-resonance i.e. electromechanical coupling (M″ vs. frequency). From these modulus resonance and anti-resonance studies piezoelectric charge constant (d33) was obtained. The values of the piezoelectric charge constant (d33) are 3.34 nm V−1, 6.26 nm V−1, 11.58 nm V−1, 14.10 nm V−1 & 10.70 nm V−1 for x = 0.25, 0.40, 0.60, 0.65 & 0.70, respectively. In the present study, the modulus electromechanical was studied in jig with spring which applies constant stress on the ceramic sample. The higher value of electromechanical coupling conversion in the present study may be attributed to this constant applied stress, higher temperature and polarized oxygen vacancies at the crystal lattice at these elevated temperatures (773 K & 873 K).