arXiv subjects

Sergey V. Baryshev

Publications and source records attributed to Sergey V. Baryshev.

At least 19 recordsLinked to original sources

arXiv2025

3D Printing as a Rapid Prototyping Approach for Novel RF Cavity Designs

3D-printing of radiofrequency (RF) cavity resonators could provide a cost-effective solution that enables rapid prototyping and design flexibility compared to traditional fabrication of full-metal cavities. In this work, the feasibility of fabrication of a useful multi-mode GHz cavity is explored. Two kinds of plastics, two slicing approaches and two metal coating techniques were used to build a series of clamped cavities with thin inner copper surface on otherwise 3D printed plastic surface. The cavities were then bench-tested to identify spatial field distributions, operating frequencies and quality factors (Q-factor). Pros and cons of the used fabrication approaches were identified and understood, and the performance of longitudinally sliced painted cavity design demonstrated considerable practicality of 3D-printing approach in designing rf systems.

physics.acc-ph↗

arXiv2025

Desynchronization in multilayer p-i-n drift step recovery diode

The impact semiconductor drift step recovery diodes (DSRDs) can have on high-power microwave applications make them a device of interest for future solid-state electronics. However, there is little known about their functionality and degradation under over-voltaging or high average power dissipation conditions that could therefore hinder their continual design and optimization toward better performance. The experiments on a Si seven layer DSRD conducted in the present paper allowed to broaden the understanding of its opening switching performance under over-voltaging conditions. A striking desynchronization was discovered and linked to junction and electro-neutral region damage through experiments and PSpice modelling.

physics.plasm-ph↗

arXiv2025

Heating of Cs2Te Photocathode via Field Emission and RF Pulsed Heating: Implication Toward Breakdown

The occurrence of radio-frequency (rf) breakdown limits operational electromagnetic gradients in accelerator structures. Experimental evidence often suggests that breakdown events are associated with temperature and dark current spikes on the surface of rf devices. In the past decade, there has been increased interest in unveiling the mechanism behind breakdown initiation in metal copper and copper alloys. However, effort regarding breakdown phenomenon in photocathode relevant semiconductors have been more limited. In this work, we explore field-emission-assisted heating via Nottingham and Joule processes, as a possible candidate for breakdown initiation. For this, field emission from intrinsic Cs2Te ultra-thin film coated on a copper substrate was modeled within the Stratton/Baskin/Lvov/Fursey (SBLF) formalism, describing the processes and effects in the bulk and on the surface of a photocathode exposed to high radio-frequency electromagnetic fields. It is shown that field emission characteristic deviates significantly from the classical Fowler-Nordheim (FN) theory, whereby predicting that dark current is orders of magnitude lower than one expected by FN law. Conventional pulsed heating was also found to impose negligible heating to the photo-cathode. Both conclusions suggest that Cs2Te photocathode coated on a metal substrate would be insensitive to catastrophic thermal-material runaway breakdown, unlike what is observed for metal surfaces. Finally, a few unconventional breakdown candidate scenarios are identified and discussed including thermo-elastic deformation and avalanche breakdown.

physics.acc-ph↗

arXiv2024

Dual-mode rf cavity: design, tuning and performance

We present the design and characterization of a dual-mode radiofrequency (rf) cavity, a novel electromagnetic structure with potential benefits such as compactness, efficiency, cost reduction and multifunctionality. The cavity was designed to balance the dual-mode structure considering several factors, such as mode frequencies, quality factor (Q-factor), and minimizing cross talk between couplers. We preformed various tests to verify that this cavity preformed as expected compared to simulated results. As exampled here, a combination of the the fundamental mode TM 010 and the TM 011 mode, tuned to a harmonic of the fundamental, was realized to linearize the off-crest electric field, thereby enabling concurrent bunching and acceleration of charged particle (e.g. electrons) beam in high power systems. The reduction in the number of cavities required to bunch and accelerate promises cost and space savings over conventional approaches. This research lays the foundation for further exploration of multi-mode cavity applications and optimization for specific use cases, with potential implications for a wide range of fields including quantum information platforms.

physics.app-ph↗

arXiv2024

Thermal Emittance Isolation by Cathode Retraction

In this work, a combination of cathode retraction and two-slit emittance measurement technique is proposed as an advanced means to individually modify emittance growth components, specifically, rf injector fringe fields, to isolate and directly measure the thermal emittance, the fundamental beam emittance metric for an electron beam. A case study of the LCLS-II-HE Low Emittance Injector (LEI), a state-of-the-art superconducting radiofrequency (SRF) gun, designed for LCLS-II HE upgrade is used to showcase the power of the two-slit technique. Particularly, it is demonstrated that generating a high resolution phase-space distribution map, dominated by the intrinsic emittance of the electron bunch, is possible. This result goes beyond the normal single-parameter distribution characterizations (e.g. RMS emittance and Twiss parameters) provided by the solenoid scan. One key feature making this technique work (and in the end practically useful) is the ability to retract the cathode, because it provides the ability to compensate for radiofrequency (rf) de-focusing. It is demonstrated how the cathode retraction can serve as an additional optimisation tool for tailoring the routine performance of the photoinjector. We posit that a variable position cathode may be a useful method for optimizing photoinjector performance across multiple parameters regimes.

physics.acc-ph↗

arXiv2024

Importance of Gas Heating in Capacitively Coupled Radiofrequency Plasma-assisted Synthesis of Carbon Nanomaterials

In pursuit of diamond nanoparticles, a capacitively-coupled radio frequency (CCRF) flow-through plasma reactor was operated with methane argon gas mixtures. Signatures of the final product obtained microscopically and spectroscopically indicated that the product was an amorphous form of graphite. This result was consistent irrespective of combinations of the macroscopic reactor settings. To explain the observed synthesis output, measurements of C2 and gas properties were carried out by laser-induced fluorescence and optical emission spectroscopy. Strikingly, the results indicated a strong gas temperature gradient of 100 K per mm from the center of the reactor to the wall. Based on additional plasma imaging, a model of hot constricted region (filamentation region) was then formulated. It illustrated that, while the hot constricted region was present, the bulk of the gas was not hot enough to facilitate diamond sp3 formation: characterized by much lower reaction rates, when compared to sp2, sp3 formation kinetics are expected to become exponentially slow. This result was further confirmed by experiments under identical conditions but with a H2/CH4 mixture, where no output material was detected: if graphitic sp2 formation was expected as the main output material from the methane feedstock, atomic hydrogen would then be expected to etch it away in situ, such that the net production of that sp2-hybridized solid material is nearly a zero.

physics.plasm-ph↗

arXiv2023

Evidence of Gas Phase Nucleation of Nano Diamond in Microwave Plasma Assisted Chemical Vapor Deposition

The mechanism of ballas like nano crystalline diamond formation (NCD) still remains elusive, and this work attempts to analyze its formation in the framework of activation energy ($E_\text{a}$) of NCD films grown from H$_\text{2}$/CH$_\text{4}$ plasma in a 2.45 GHz chemical vapor deposition system. The $E_\text{a}$ is calculated using the Arrhenius equation corresponding to the thickness growth rate while using substrate temperature ($\sim1000-1300$ K) in all the calculations. While the calculated values match with the $E_\text{a}$ for nano diamond formation throughout the literature, these values of $\sim$10 kcal/mol are lower compared to $\sim$15 -- 25 kcal/mol for standard single crystal diamond (SCD) formation, concluding thus far, that the energetics and processes involved are different. In this work, To further investigate this, the substrate preparation and sample collection method are modified while keeping the growth parameters constant. Unseeded Si substrates are physically separated from the plasma discharge by a molybdenum plate with a pinhole drilled in it. Small quantities of a sample substance are collected on the substrates. The sample is characterized by electron microscopy and Raman spectroscopy confirming it to be nano diamond, thus, suggesting that nano diamond self nucleates in the plasma and flows to the substrate which acts as a mere collection plate. It is hypothesized then, if nano diamond nucleates in gas phase, gas temperature has to be used in the Arrhenius analysis. The $E_\text{a}$ values for all the nano diamond films are re-calculated using the simulated gas temperature ($\sim1500-2000$ K) obtained from a simple H$_\text{2}$/CH$_\text{4}$ plasma model, giving values within the range characteristic to SCD formation. A unified growth mechanism for NCD and SCD is proposed concluding that the limiting reactions for NCD and SCD formation are the same.

cond-mat.mtrl-sci↗

arXiv2023

Emittance Mapping in rf Guns

This paper discusses the trends and trade-offs between transverse sigma x and longitudinal sigma z bunch dimensions, rf injector gradient, bunch charge, and intrinsic electron mean transverse energy (MTE), where all can be chosen to be independent, and the resulting effects on emittance and transverse brightness. Using a practical example of a quarter wave normal conducting photoinjector, it is computationally found that regardless of MTE and bunch charge, there is a universal relation between the gradient E and the aspect ratio of the bunch (sigma x /sigma z ) leading to the highest brightness. This computational result is understood using an analytical formalism consisting of K J Kim's emittance formulation and a two-dimensional space charge model. The results, obtained computationally and interpreted in a robust physical framework, could therefore provide the basis for an express mapping approach for emittance forecasting when used with practical injector system design requirements and limitations.

physics.acc-ph↗

arXiv2023

Thermal and electric field driven breakdown precursor formation on metal surfaces

The phenomenon of electric breakdown poses serious challenge to the design of devices that operate under high gradient environments. Experimental evidence often points towards breakdown events that are accompanied by elevated temperatures and dark current spikes, presumably due to high-asperity nano-structure formation that enhances the local electric field and triggers a runaway process. However, the exact mechanistic origin of such nano-structures under typical macroscopic operational conditions of electric gradient and magnetic-field-mediated heating remains poorly understood. In this work, a model is presented that describes the evolution of a typical copper surface under the combined action of the electric fields and elevated temperatures. Using a mesoscale curvature-driven growth model, we show how the copper surface can undergo a type of dynamical instability that naturally leads to the formation of sharp asperities in realistic experimental conditions. Exploring the combined effect of fields and temperature rise, we identify critical regimes that allow for the formation of breakdown precursors. These regimes strongly resonate with previous experimental findings on breakdown of copper electrodes, hence suggesting surface diffusion to be a crucial breakdown precursor mechanism.

physics.app-ph↗

arXiv2023

Scalable Production and Supply Chain of Diamond using Microwave Plasma: a Mini-review

Discovered and reported exactly 40 years ago, microwave plasma assisted chemical vapor deposition (MPACVD) pointed out an economic technology that could potentially produce lab-grown diamond stones at scale. After this breakthrough discovery, demonstrating that diamond can be growth at low pressure and temperature, the progress quickly curbed and synthetic single crystal diamond (SCD) size and quality could not be improved toward attaining requirements critical in solid-state electronics. This led to the early promise of MPACVD to not come true and slowed the level of investments, thereby further stalling the progress in diamond syntheses. With the invention of a few novel homo- and hetero-epitaxy growth techniques, the diamond research and technology has recently reinvigorated. This mini review attempts to capture the momentum of recent progress in diamond MPACVD that could finally bring scalable manufacturing of high quality large size wafers for future electronics and optics.

physics.app-ph↗

arXiv2023

Computationally Assessing Diamond as an Ultrafast Pulse Shaper for High Power Ultrawide Band Radar

Diamond holds promise to reshape ultrafast and high power electronics. One such solid-state device is the diode avalanche shaper (DAS), which functions as an ultrafast closing switch where closing is caused by the formation of the streamer traversing the diode much faster than 10$^7$ cm/s. One of the most prominent applications of DAS is in ultrawide band (UWB) radio/radar. Here we simulate a diamond-based DAS and compare the results to a silicon-based DAS. All DAS were simulated in mixed mode as ideal devices using the drift-diffusion model. The simulations show that diamond DAS promises to outperform Si DAS when sharpening kilovolt nanosecond input pulse. The breakdown field and streamer velocity ($\sim$10 times larger in diamond as compared to those in Si) are likely to be the major reasons enabling kV sub-50 ps switching using diamond DAS.

physics.app-ph↗

arXiv2023

Useful Circuit Analogies to Model THz Field Effect Transistors

The electron fluid model in plasmonic field effect transistor (FET) operation is related to the behavior of a radio-frequency (RF) cavity. This new understanding led to finding the relationships between physical device parameters and equivalent circuit components in traditional parallel resistor, inductor, and capacitor (RLC) and transmission models for cavity structures. Verification of these models is performed using PSpice to simulate the frequency dependent voltage output and compare with analytical equations for the drain potential as a function of frequency.

physics.app-ph↗

arXiv2023

Bright Spatially Coherent Beam from Carbon Nanotube Fiber Field Emission Cathode

Large area carbon nanotube (CNT) cathodes made from yarns, films or fibers have long been promising as next generation electron sources for high power radio frequency (rf) and microwave vacuum electronic devices. However, experimental evidence have been pointing out spatial incoherence of the electron beam produced by such cathodes that, in turn, impeded the progress toward high brightness CNT electron sources and their practical applications. Indeed, typically large area CNT fibers, films or textiles emit stochastically across their physical surface at large emission angles and with large transverse spread, meaning large emittance and hence low brightness. In this work, using high resolution field emission microscopy, we demonstrate that conventional electroplating of hair-thick CNT fibers followed by a femtosecond laser cutting, producing emitter surface, solves the described incoherent emission issues extremely well. Strikingly, it was observed that the entire (within the error margin) cathode surface of a radius of approximately $75\,μ\text{m}$ emitted uniformly (with no hot spots) in the direction of the applied electric field. The normalized emittance on the fiber surface was estimated of 52 nm with brightness of $>$$10^{15}\frac{\text{A}}{\text{m}^2\text{rad}^2}$ (or $>$$10^7$ A m$^{-2}$sr$^{-1}$V$^{-1}$) estimated for pulsed mode operation.

physics.app-ph↗

arXiv2022

Spectral Emission Properties of a Nitrogen-doped Diamond(001) Photocathode: Hot Electron Transport and Transverse Momentum Filtering

The electron emission properties of a single-crystal nitrogen-doped diamond(001) photocathode inserted in a 10kV DC photoelectron gun are determined using a tunable (235-410nm) ultraviolet laser radiation source for photoemission from both the back nitrogen-doped substrate face and the front homo-epitaxially grown and undoped diamond crystal face. The measured spectral trends of the mean transverse energy (MTE) and quantum efficiency (QE) of the emitted electrons are both anomalous and non-monotonic, but are shown to be consistent with (i) the known physics of electron photoexcitation from the nitrogen substitution states into the conduction bands of diamond, (ii) the energy position and dispersion characteristics of the conduction bands of diamond in the (001) emission direction, (iii) the effective electron affinity of the crystal faces, (iv) the strong electron-(optical)phonon coupling in diamond, and (v) the associated hot electron transport dynamics under energy equipartition with the optical phonons. Notably, the observed hot electron emission is shown to be restricted parallel to the photocathode surface by the low transverse effective masses of the emitting band states - a transverse momentum filtering effect.

cond-mat.mtrl-sci↗

arXiv2022

Evaluating Effects of Geometry and Material Composition on Production of Transversely Shaped Beams from Diamond Field Emission Array Cathodes

Field emission cathodes (FECs) are attractive for the next generation of injectors due to their ability to provide high current density bright beams with low intrinsic emittance. One application of FECs worthy of special attention is to provide transversely shaped electron beams for emittance exchange that translates a transverse electron beam pattern into a longitudinal pattern. FECs can be fabricated in a desired pattern and produce transversely shaped beams without the need for complex masking or laser schemes. However, reliable and consistent production of transversely shaped beams is affected by material properties of the FEC. This paper reports the results of testing two diamond field emitter array (DFEA) FECs with the same lithography pattern and emitter geometry but different material and tip characteristics. Although both cathodes were able to sustain gradients of 44 MV/m and produce maximum output integral charge of 0.5 nC per radiofrequency (rf) pulse, their emission patterns were quite different. One cathode did not produce a patterned beam while the other one did. Differences in field emission characteristics and patterned beam production were explained by the differences in the tip geometry and the cathode material properties. The main practical takeaway was found to be that the tip sharpness was not a prerequisite for good patterned beam production. Instead, other material characteristics, such as the ballast resistance, determined cathode performance.

physics.acc-ph↗

arXiv2022

RF Accelerator Technology R&D: Report of AF7-rf Topical Group to Snowmass 2021

Accelerator radio frequency (RF) technology has been and remains critical for modern high energy physics (HEP) experiments based on particle accelerators. Tremendous progress in advancing this technology has been achieved over the past decade in several areas highlighted in this report. These achievements and new results expected from continued R&D efforts could pave the way for upgrades of existing facilities, improvements to accelerators already under construction (e.g., PIP-II), well-developed proposals (e.g., ILC, CLIC), and/or enable concepts under development, such as FCC-ee, CEPC, C3, HELEN, multi-MW Fermilab Proton Intensity Upgrade, future Muon Colloder, etc. Advances in RF technology have impact beyond HEP on accelerators built for nuclear physics, basic energy sciences, and other areas. Recent examples of such accelerators are European XFEL, LCLS-II and LCLS-II-HE, SHINE, SNS, ESS, FRIB, and EIC. To support and enable new accelerator-based applications and even make some of them feasible, we must continue addressing their challenges via a comprehensive RF R&D program that would advance the existing RF technologies and explore the nascent ones.

physics.acc-ph↗

arXiv2021

Confirmation of Transit-Time Limited Field Emission in Advanced Carbon Materials with Fast Pattern Recognition Algorithm

An accurate estimation of the experimental field-emission area remains a great challenge in vacuum electronics. The lack of convenient means, which can be used to measure this parameter, creates a critical knowledge gap, making it impossible to compare theory to experiment. In this work, a fast pattern recognition algorithm was developed to complement a field emission microscopy, together creating a methodology to obtain and analyze electron emission micrographs in order to quantitatively estimate the field emission area. The algorithm is easy to use and made available to the community as a freeware, and therefore is described in detail. Three examples of dc emission are given to demonstrate the applicability of this algorithm to determine spatial distribution of emitters, calculate emission area, and finally obtain experimental current density as a function of the electric field for two technologically important field emitter materials, namely an ultrananocrystalline diamond film and a carbon nanotube fiber. Unambiguous results, demonstrating the current density saturation and once again proving that conventional Fowler-Nordheim theory, its Murphy-Good extension, and the vacuum space-charge effect fail to describe such behaviour, are presented and discussed. We also show that the transit-time limited charge resupply captures the current density saturation behaviour observed in experiments and provides good quantitative agreement with experimental data for all cases studied in this work.

physics.app-ph↗

arXiv2021

Travelling Wakefield Tube: THz Source Powered by Nonrelativistic Electron Beam

High peak power, tunable, narrowband terahertz emitters are becoming sought after given their portability, efficiency, and ability to be deployed in the field for industrial, medical, and military applications. The use of accelerator systems producing THz frequencies via Cherenkov radiation, generated by passing an electron beam through a slow-wave wakefield structure, is a promising method to meet future THz requirements. To date, efforts have been dedicated to analysis and design of sources utilizing laser seeded bunched electron beam drivers with relativistic energies beyond 5 MeV. Presented here is a wakefield THz generation scheme based on passing a long quasi-dc nonrelativistic beam (200 keV) through a dielectric loaded travelling wave structure. Reduced energy allows for compactness and portability of the accelerator as the size and weight of the dielectric slow wave structure is vanishingly small compared to the accelerator unit. The presented scheme can serve as a tunable high peak power THz source operated between 0.4-1.6 THz and produces power gain by a factor of five with an average efficiency of 6.8\%.

physics.app-ph↗