Transverse Impedance Research Articles

A differential low frequency eddy current test method for detecting moisture content of high voltage cable water-blocking tape

ABSTRACT The excessive moisture content in the water-blocking tape has been one of the main causes of high voltage cable erosion failures in recent years. However, the 2–4 mm thick aluminium sheath wrapped around the water-blocking tape makes it challenging to detect the moisture content. This study introduces a method for detecting the moisture content of high voltage cable water-blocking tapes based on low-frequency eddy currents. Initially, longitudinal and transverse impedance measurement experiments of the water-blocking tape were conducted to establish the relationship between impedance and moisture content. Since the impedance of the water-blocking tape is significantly higher compared to the aluminium sheath, the eddy current signal was obtained using a differential detection method. An excitation frequency of 10 Hz was chosen to achieve a deeper skin depth. Additionally, an eddy current finite element analysis model was developed, showing that moisture content has an almost linear relationship with the amplitude and phase of the eddy current signal. Finally, an experiment was conducted on an equivalent high voltage cable structure, and the experimental results aligned well with the simulation results.

Collimator challenges at SuperKEKB and their countermeasures using nonlinear collimator

In SuperKEKB, movable collimators reduce the beam background noise in the Belle II particle detector and protect crucial machine components, such as final focusing superconducting quadrupole magnets (QCS), from abnormal beam losses. The challenges related to the collimator, which were not properly considered at the time of SuperKEKB design, have surfaced through experience with its operation. In this paper, we report the collimator operation strategy in SuperKEKB. In addition, a significant challenge of beam collimation due to the future increase in the beam background is highlighted. We also discuss another issue caused by unexpected and sudden beam losses in the machine that damage collimators, leading to weaker beam collimation performance and an increase in transverse impedance. Furthermore, we introduce a novel collimation approach called the nonlinear collimator (NLC) to address these challenges. We detail the concept of NLC and evaluate their effectiveness by assessing the collimator impedance, beam background reduction, and impact on the dynamic aperture. The possibility of using NLCs as absorber collimators to counteract events that damage the collimator is also shown to be helpful. Published by the American Physical Society 2024

Beam coupling impedance of the main extraction kickers in the CERN PS

In view of the High Luminosity (HL) upgrade of the LHC, the beam intensity must be doubled in the injector chain. To perform reliable beam dynamics simulations, the beam coupling impedance in the injectors, such as the Proton Synchrotron (PS), must be followed closely by including all contributing elements into the impedance model. The existing kicker magnets of the PS had been optimized for large kick strength and short rise/fall times, but not necessarily to minimise beam coupling impedance. Hence, unwanted beam induced voltage can build up in their electrical circuits, with an impact on the beam. The beam coupling impedances of the two main kicker magnets used for the fast extraction from PS, the KFA71 and KFA79, are extensively characterized in this study. In particular, electromagnetic simulation results for the longitudinal and transverse coupling impedance are shown. The critical impedance contributions are identified, and their effect on beam stability with a possible mitigation solution is discussed. Moreover, the impact of the cable terminations on the electromagnetic field pattern and possible mitigation techniques are presented, providing a complete impedance evaluation of the entire kicker installation.

Beam coupling impedance measurement based on Goubau line method

The Goubau line method has been recently proposed and used for the longitudinal beam coupling impedance measurement of vacuum components. To extend the application of this method, the measurement of transverse impedance using the Goubau line method is proposed in this work. The feasibility of measuring the transverse impedance using the Goubau line method has been tested using a pillbox cavity. Additionally, the frequency shift induced by the dielectric-coated wire in the Goubau line measurements has been investigated analytically. The contribution of the dielectric coating to the frequency shift has been studied. Finally, the Goubau line setup has been optimized and used to evaluate the longitudinal and transverse beam coupling impedance of key vacuum components in the High Energy Photon Source.

Coherent Betatron Oscillations in a Storage Ring at Injection

A single-turn (and single-bunch) injection often operates with an injection portion of high intensity, comparable with that of the circulating bunch. Collective effects due to transverse impedance provide interaction between groups of particles. This interaction may set serious limitations on the injection efficiency.We analyze the conditions of coherency of the betatron oscillations following the injection, while the beam is subject to decoherence resulting from the machine lattice nonlinearities. The theoretical results are supported by numerical tracking. The conclusions are compared with experimental data on dipole oscillations histories following the VEPP-2000 injection.

Synergistic effects of Gd2O3 and SiO2 in enhancing the acoustic, mechanical, and shielding qualities of borate glasses

This study comprehensively analyzes the gamma radiation shielding, mechanical, and acoustic properties of novel glass composites formulated from B2O3, SiO2, and Gd2O3. Utilizing the MCNPX simulation code and Phy-X: PSD software, key parameters such as Linear Attenuation Coefficient, Half Value Layer (HVL), Mean Free Path (MFP), and Effective Atomic Number (Zeff) were meticulously evaluated for three distinct glass compositions, denoted as GL-1, GL-2, and GL-3. The investigation revealed that incorporating Gd2O3 and SiO2 notably enhances the radiation shielding efficiency of these glasses, which is evident from the decreasing trends in HVL and MFP values across the series. Employing the Makishima and Mackenzie (MM) model, this study further delved into the mechanical and acoustic characteristics of the glass samples. An increase in Gd2O3 and SiO2 content, substituting B2O3, was observed to augment the bond dissociation energy and adjust the packing density, consequently improving the elastic moduli. These mechanical enhancements were quantified through measurements of Young's modulus, bulk modulus, shear modulus, and longitudinal modulus. Acoustic properties were also calculated, including Longitudinal and Transverse velocities, mean velocity, and acoustic impedance. These parameters demonstrated a consistent improvement correlating with the increasing rigidity and mechanical strength of the glass samples, particularly for the GL-3 composition. The study concludes that the GL-3 glass sample exhibits superior performance regarding gamma photon attenuation, mechanical robustness, and acoustic properties. This underscores its potential as an effective material for radiation shielding in various industrial applications, benefiting from its enhanced mechanical and acoustic features.

Mitigation strategies for the instabilities induced by the fundamental mode of the HL-LHC Crab Cavities

The transverse impedance is one of the potentially limiting effects for the performance of the High-Luminosity Large Hadron Collider (HL-LHC). In the current LHC, the impedance is dominated by the resistive-wall contribution of the collimators at typical bunch-spectrum frequencies, and is of broad-band nature. Nevertheless, the fundamental mode of the crab cavities, that are a vital part of the HL-LHC baseline, adds a strong and narrow-band contribution. The resulting coupled-bunch instability, which contains a strong head-tail component, requires dedicated mitigation measures, since the efficiency of the transverse damper is limited against such instabilities, and Landau damping from octupoles would not be sufficient. The efficiency and implications of various mitigation strategies, based on RF feedbacks and optics changes, are discussed, along with first measurements using crab cavity prototypes at the Super Proton Synchrotron (SPS).

Impact of beam-coupling impedance on the Schottky spectrum of bunched beam

The Schottky monitors of the Large Hadron Collider (LHC) can be used for non-invasive beam diagnostics to estimate various bunch characteristics, such as tune, chromaticity, bunch profile or synchrotron frequency distribution. However, collective effects, in particular beam-coupling impedance, can significantly affect Schottky spectra when large bunch charges are involved. In such conditions, the available interpretation methods are difficult to apply directly to the measured spectra, thus preventing the extraction of beam and machine parameters, which is possible for lower bunch charges. To study the impact of impedance on such spectra, we introduce a method for building Schottky spectra from macro-particle simulations performed with the PyHEADTAIL code, applied to LHC beam conditions. In this case, the use of a standard Fast Fourier Transform (FFT) algorithm to recover the spectral content of the beam becomes computationally intractable memory-wise, because of the relatively short bunch length compared to the large revolution period. To circumvent this difficulty, a semi-analytical method was developed to efficiently compute the Fourier transform. The simulated Schottky spectrum is then compared against theoretical formulas and measurements of Schottky signals previously obtained with lead ion beams in the LHC where impedance effects are expected to be limited. Furthermore, this study provides preliminary interpretations of the impact of beam-coupling impedance on proton Schottky spectra by incorporating longitudinal and transverse resonator-like impedance models into the simulations. A theoretical framework is also introduced for the case of the longitudinal impedance, allowing the extension of the existing theoretical formalism.

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.

Higher-order mode analysis for SOLEIL-type superconducting cavity

A 499.8 MHz SOLEIL-type superconducting cavity was simulated and designed for the first time in this paper. The higher-order mode (HOM) properties of the cavity were investigated. Two kinds of coaxial HOM couplers were designed. Using 4 L-type and 4 T-type HOM couplers, the longitudinal impedance was suppressed to 3 kΩ, and the transverse impedance below 30 kΩ/m. The HOM damping requirements of Hefei Advanced Light Facility (HALF) were satisfied. This paper conducts an in-depth study on the radio frequency (RF) design, multipacting optimization, and thermal analysis of these coaxial couplers. Simulation results indicated that under operating acceleration voltage, the optimized couplers does not exhibit multiplicating or thermal breakdown phenomena. The cavity has the potential to reach a higher acceleration gradient.

A low-frequency normal conducting cavity with higher-order mode damping for fourth-generation synchrotron radiation sources.

The utilization of a low-frequency (<200MHz) RF system in storage facilitates the attainment of ultra-low emittances in synchrotron light sources through on-axis injection. This paper focuses on the development of a low-frequency normal conducting (NC) cavity with higher-order mode (HOM) damping for fourth-generation synchrotron light sources. We propose a novel approach to achieve efficient HOM damping in a NC cavity by optimizing the lowest frequency HOM and implementing a beam-line absorber. Notably, unlike conventional NC cavities, the presence of a large beam tube for the beam-line absorber does not compromise the accelerating performance in a coaxial resonant cavity, enabling effective HOM damping while maintaining a high shunt impedance. Through simulations, the prototype design of a 166.6MHz HOM-damped cavity demonstrates a fundamental mode impedance of ∼8 MΩ, with longitudinal and transverse HOM impedances below 2.0 and 50 kΩ/m, respectively.

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).

1256 Fabricating Artificial Kidney Stones of Different Physical Properties for Ex Vivo Experimentation

Abstract Introduction There have been several new technologies introduced recently for lithotripsy. The optimal settings of these devices are unknown for different kidney stone densities. This study aims to develop artificial kidney stones for ex vivo studies. Method BegoStone was prepared with a powder to water ratio (by weight) ranging from 15:3 to 15:6. The phantoms' acoustic properties were characterised by using an ultrasound transmission technique, from which the corresponding mechanical properties can calculated based on elastic wave theory. Results The measured parameters for BegoStone phantoms of different water contents were assessed with regard to longitudinal wave speed &amp; density. If transverse wave speeds were measured then longitudinal acoustic impedance, transverse acoustic impedance, Young's modulus, bulk modulus, and shear modulus can be derived. Longitudinal (CL (m/s)) and density (ρ (Kg/m3)) of BegoStone phantoms with different powder to water ratios corresponded to the known properties reported in natural kidney stones (Calcium Oxalate Monohydrate, Brushite, Uric acid and Struvite). A BegoStone water ratio of 15:3 had similar properties to Calcium Oxalate Monohydrate, 15:4 to be similar to Brushite, 15:5 was similar to Uric acid, and 15:6 was similar to Struvite. Conclusions This BegoStone preparation method can be used to fabricate artificial stones with physical properties matched with those of natural kidney stones of various chemical compositions.

Combined phenomenon of transverse impedance and beam-beam interaction with large Piwinski angle

Combined phenomenon of transverse impedance and beam-beam interaction with large Piwinski angle

Millimeter-Wave Ferromagnetic Resonance of a Saturated Magnetic Transmission Line

Saturated ferrites exhibit microwave and millimeter wave absorption because they consist of nano- magnetic harmonic oscillators. The absorption frequency and line width are dictated by the strength and range of interactions between the magnetic dipoles. The forced orientation of magnetic dipoles along the magnetic bias results in Zeeman splitting in the energy levels. The incoming electromagnetic wave can excite dipoles to transition between these energy levels. In order to investigate the effects of input frequency and Gilbert damping constant on the electromagnetic properties, a magnetic transmission line model is presented for a saturated ferrite. The enhanced power loss during ferromagnetic resonance is contributed to the strong spike of longitudinal magnetic admittance and transverse magnetic impedance.

Transverse impedance studies of 2D azimuthally symmetric devices of finite length

The accurate calculation of the beam coupling impedance for particle accelerators is necessary to carefully assess the machine stability against impedance-driven collective effects. A first order evaluation of the beam coupling impedance is often done by means of analytical formulas and/or 2D numerical codes. The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be a less accurate approximation for segmented devices. In this work, we present the application of the mode matching method to the calculation of the transverse dipolar impedance of a cylindrical cavity loaded with a toroidal insert. By choosing different insert electromagnetic properties (permittivity, permeability, and conductivity) and dimensions, the model can represent a beam pipe, a thin insert, a lossy cavity, or a collimator for which the effect of the finite length is investigated. The method is successfully benchmarked against available analytical formulas, field-matching codes, and 3D commercial solvers. The proposed model allows for performing wide parametric scans and reaching accurate results, therefore becoming an essential tool for the impedance evaluation of accelerator devices.

The resistive wall impedance and the effects of the non-evaporable getter thickness in an ultra-low emittance ring

In modern particle accelerators with ultra-low emittance, the vacuum chambers are designed based on Non-Evaporable Getter (NEG)-coated vacuum chambers. The thickness of the NEG coating plays a critical role in the dynamic beam effects. So, in this paper, the longitudinal and transverse impedance of a copper chamber coated with a NEG are investigated, and the effects of the NEG thickness over a wide range of frequencies have been studied. A good selection of NEG layer thickness could minimize the coating effects on the longitudinal and transverse beam impedance. The numerical results in this work show that the beam dynamic effects could be minimal with selecting a NEG coating thickness of about 1 μm.

Potential impedance reduction by REBCO-coated conductors as beam screen coating for the Future Circular Hadron Collider

The Future Circular Collider study creates a conceptual design for a post-LHC particle accelerator using 16 T superconducting dipoles to achieve collision energies of up to 100 TeV in a 90 km circumference ring. A copper-coated beam screen, similar to that used in the LHC, is planned. However, the undertaken research indicates that copper at the high working temperature of 50 K has a strong influence on the accelerator's performance, particularly at injection energy. In this work, we relate the experimentally determined properties of REBCO-coated conductors with their potential performance in the FCC-hh beam screen. Specifically, we use a round pipe approximation to demonstrate that a beam screen coated with a combination of REBCO and copper can have a much lower resistive wall impedance than one using only copper. The reduction is substantial (several orders of magnitude), and is observed in both the longitudinal and transverse wall impedance. Such a reduction has important effects on beam stability, operating costs, potential reduction in beam screen size, and lowering the stringent specifications of the 16 T magnets required for the Future Circular Hadron Collider.

Hand Gestures Classification Using Electrical Impedance Tomography Images

Human–computer communication using hand gestures has always been difficult. More than half a century ago, people used differentways of interactionwith computers from the early mediums such as perforated game cards. Nowadays, if a richer lexicon of gestures is given, people can communicate more effectively with computers. Machine learning is now used to recognize and classify hand gestures in amore preciseway. In order to increase the communication between computers and humans, we proposed a technique, which uses a wearable low-cost device to generate the electrical impedance tomography (EIT) images to recover the inner impedance structure of a user’s wrist. This is done by measuring the transverse impedance between all the 16 pairs of electrodesofwrist band that lie on the skin of the user hand. The proposedtechnique is enough to integrate the technology into the prototypewrist band tomonitor and classify gestures in real time. We have conducted a study of 16 gestures with a focus on gross hand and pinch finger gestures. The results evaluation shows that the gross hand gestures achieved 90% accuracy inwrist position, while pinch gestures achieved 93% accuracy.

Impedance modelling and collective effects in the Future Circular e+e− Collider with 4 IPs

The FCC-ee impedance model is being constantly updated closely following the vacuum chamber design and parameters evolution. In particular, at present, a thicker NEG coating of 150 nm (instead of previous 100 nm) has been suggested by the vacuum experts, and a more realistic impedance model of the bellows has been investigated. Moreover, also the transverse impedance has been updated by considering the same sources as for the longitudinal case. Therefore, the FCC-ee impedance database is getting more complete and the impedance model is being refined. In this paper we describe the presently available machine coupling impedance in both longitudinal and transverse planes, and study the impedance-driven single bunch instabilities (with and without beam-beam interaction) for the new FCC-ee parameter set with 4 interaction points (IPs). The results are compared with the previously obtained ones and a further possible mitigation of the beam-beam head-tail instability (X-Z instability) is proposed.