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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Is tokenization needed for masked particle modeling?

In this work, we significantly enhance masked particle modeling (MPM), a self-supervised learning scheme for constructing highly expressive representations of unordered sets relevant to developing foundation models for high-energy physics. In MPM, a model is trained to recover the missing elements of a set, a learning objective that requires no labels and can be applied directly to experimental data. We achieve significant performance improvements over previous work on MPM by addressing inefficiencies in the implementation and incorporating a more powerful decoder. We compare several pre-training tasks and introduce new reconstruction methods that utilize conditional generative models without data tokenization or discretization. We show that these new methods outperform the tokenized learning objective from the original MPM on a new test bed for foundation models for jets, which includes using a wide variety of downstream tasks relevant to jet physics, such as classification, secondary vertex finding, and track identification.

conditional generative models↗
DOE OSTI2015

Background investigation in EDELWEISS-III

Protection from and rejection of backgrounds is a key issue for the EDELWEISS-III direct dark matter detection experiment which aims at exploring the 10{sup −9} pb cross-section region for spin-independent WIMP-nucleon interaction. The detector is located in the low radioactivity environment of the Modane Underground Laboratory and consists of 36 advanced FID germanium detectors operating at 18 mK in a dilution refrigerator in order to identify eventual rare nuclear recoils induced by elastic scattering of WIMPs from our Galactic halo. I will discuss the background and the methods of rejecting it with the FID detectors. Detector performances and the first analysis of data acquired in a long-term campaign will be presented as well. The FID detector technology is not limited to EDELWEISS-III but can further be employed in the next generation of cryogenic detector experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

TH-C-19A-12: Two-Dimensional High Spatial-Resolution Dosimeter Using Europium Doped Potassium Chloride

Purpose: Recent research has shown that KCl:Eu2+ has great potential for use in megavoltage radiation therapy dosimetry because this material exhibits excellent storage performance and is reusable due to strong radiation hardness. This work reports our attempts to fabricate 2D KCl:Eu2+ storage phosphor films (SPFs) using both a physical vapor deposition (PVD) method and a tape casting method. Methods: A thin layer of KCl:Eu2+ was deposited on a substrate of borosilicate glass (e.g., laboratory slides) with a PVD system. For tape casting, a homogenous suspension containing storage phosphor particles, liquid vehicle and polymer binder was formed and subsequently cast by doctor-blade onto a polyethylene terephthalate substrate to form a 150 μm thick SPF. Results: X ray diffraction analysis showed that a 10 μm thick PVD sample was composed of highly crystalline KCl. No additional phases were observed, suggesting that the europium activator had completed been incorporated into the KCl matrix. Photostimulated luminescence and photoluminescence spectra suggested that F (Cl−) centers were the electron storage centers post x ray irradiation and that Eu2+ cations acted as luminescence centers in the photostimulation process. The 150 μm thick casted KCl:Eu2+ SPF showed sub-millimeter spatial resolution. Monte Carlo simulations further demonstrated that the admixture of 20% KCl:Eu2+ and 80% low Z polymer binder exhibited almost no energy dependence in a 6 MV beam. KCl:Eu2+ pellet samples showed a large dynamic range from 0.01 cGy to 60 Gy dose-to-water, and saturated at approximately 500 Gy as a Result of its intrinsic high radiation hardness. Conclusions: This discovery research provides strong evidence that KCl:Eu2+ based SPF with associated readout apparatus could Result in a novel electronic film system that has all the desirable features associated with classic radiographic film and, importantly, water equivalence and the capability of permanent identification of each detector. This work was supported in part by NIH Grant No. R01CA148853. The authors would like to thank Paul Leblans (AGFA Healthcare, Belgium) for many helpful discussions on this topic.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2011

Neutron Time Projection Chamber for Nuclear Security and Verification Applications

Detection of fast neutrons produced by fission is a powerful method for discovering, verifying the presence, or monitoring significant quantities of special nuclear material (SNM) at up to moderate distances. Fast neutrons are relatively rare in the natural background and can be very penetrating, even in situations when the energetic gamma-rays are well shielded. Fast neutrons point in the direction of their source and can thus be considered for use in imaging, a feature desirable for rapid, high-signal-to-noise detection of concealed SNM and for nuclear verification. We describe the development and performance of a prototype neutron time projection chamber (nTPC) and its use for directional neutron detection and high-resolution neutron imaging. The nTPC is based on {approx}0.025 m{sup 3} of a hydrogen-methane mixture and utilizes a readout system with low channel count and is optimized for low event rates. We experimentally demonstrate robust operation, reliable particle identification, event-by-event directional reconstruction over the entire 4{pi} solid angle, and insensitivity to gamma-rays. High-efficiency and high-resolution modes of operation based on single and double neutron scatters, respectively, have also been demonstrated.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Constraints on the pMSSM from LAT observations of dwarf spheroidal galaxies

We examine the ability for the Large Area Telescope (LAT) to constrain Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest Supersymmetric Particles (LSPs) for a set of ∼ 71k experimentally valid supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find that none of these models can be excluded at 95% confidence by the current analysis; nevertheless, many lie within the predicted reach of future LAT analyses. With two years of data, we find that the LAT is currently most sensitive to light LSPs (m{sub LSP} < 50GeV) annihilating into τ-pairs and heavier LSPs annihilating into b b-bar . Additionally, we find that future LAT analyses will be able to probe some LSPs that form a sub-dominant component of dark matter. We directly compare the LAT results to direct detection experiments and show the complementarity of these search methods.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2014

In-Situ and Remote-Sensing Data Fusion Using Machine Learning Techniques to Infer Urban and Fire Related Pollution Plumes

Airmass type characterization is key in understanding the relative contribution of various emission sources to atmospheric composition and air quality and can be useful in bottom-up model validation and emission inventories. However, classification of pollution plumes from space is often not trivial. Sub-orbital campaigns, such as SEAC4RS (Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys) give us a unique opportunity to study atmospheric composition in detail, by using a vast suite of in-situ instruments for the detection of trace gases and aerosols. These measurements allow identification of spatial and temporal atmospheric composition changes due to various pollution plumes resulting from urban, biogenic and smoke emissions. Nevertheless, to transfer the knowledge gathered from such campaigns into a global spatial and temporal context, there is a need to develop workflow that can be applicable to measurements from space. In this work we rely on sub-orbital in-situ and total column remote sensing measurements of various pollution plumes taken aboard the NASA DC-8 during 2013 SEAC4RS campaign, linking them through a neural-network (NN) algorithm to allow inference of pollution plume types by input of columnar aerosol and trace-gas measurements. In particular, we use the 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) airborne measurements of wavelength dependent aerosol optical depth (AOD), particle size proxies, O3, NO2 and water vapor to classify different pollution plumes. Our method relies on assigning a-priori ground-truth labeling to the various plumes, which include urban pollution, different fire types (i.e. forest and agriculture) and fire stage (i.e. fresh and aged) using cluster analysis of aerosol and trace-gases in-situ and auxiliary (e.g. trajectory) data and the training of a NN scheme to fit the best prediction parameters using 4STAR measurements as input. We explore our misclassification rates as related to our ground-truth labels, and with multi-layered pollution plume cases. The next step in our analysis is to optimize parameter selection for a scheme that can be applied to space-borne aerosol and trace-gas observation platforms such as OMI, and future geostationary satellites such as TEMPO and GEO-CAPE.

Neural-network↗
DOE OSTI2011

The performance of the MICE muon beam line

The Muon Ionization Cooling Experiment is one lattice cell of a cooling channel suitable for conditioning the muon beam at the front end of a Neutrino Factory or Muon Collider. The beam line designed to transport muons into MICE has been installed, and data was collected in 2010. In this paper the method of reconstructing longitudinal momentum and transverse trace space using two timing detectors is discussed, and a preliminary simulation of the performance of a measured beam in the cooling channel is presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Detection of extended galactic sources with an underwater neutrino telescope

In this study we investigate the discovery capability of a Very Large Volume Neutrino Telescope to Galactic extended sources. We focus on the brightest HESS gamma rays sources which are considered also as very high energy neutrino emitters. We use the unbinned method taking into account both the spatial and the energy distribution of high energy neutrinos and we investigate parts of the Galactic plane where nearby potential neutrino emitters form neutrino source clusters. Neutrino source clusters as well as isolated neutrino sources are combined to estimate the observation period for 5 sigma discovery of neutrino signals from these objects.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Application of electron backscatter diffraction techniques to quantify effects of aging on sub-grain and spatial heterogeneity in NMC cathodes

Identification and evaluation of structural heterogeneity in spent cathode materials is crucial to developing appropriate remediation strategies for novel recycling processes. Native heterogeneities may be exacerbated during the cell's operational lifetime, as sub-particle-scale variations induce anisotropic expansion and contraction upon cycling. Structural transformations resulting from repeated cycling and calendar aging predominantly occur at the secondary particle surface and at the grain boundaries (GBs) between primary particles. However, the diffusion and stress build up around and across GBs are poorly understood. In this study, electron backscatter diffraction (EBSD) is employed to track sub-grain lattice structure across a statistically relevant number of Li(Ni0.33Mn0.33Co0.33)O2 (NMC-111) particles. Specifically, differences in lattice misorientation – measured as the deviation from the grain's average orientation – are tracked as a function of position within the electrode (near current collector, middle, and near separator) and as a function of electrochemical cycling. Further, a novel method of structural analysis is developed, offering insight into sub-grain diffusion behavior by comparing lattice misorientation near the grain boundary versus in the grain bulk. The present results suggest that electrode-scale spatial heterogeneity in lattice structure is induced by initial manufacturing conditions, and that radial gradients in lattice misorientation evolve at the primary particle scale with repeated electrochemical cycling.

25 ENERGY STORAGE↗
DOE OSTI2018

Preparation and characterization of microwave absorbing composite materials with GSs or FeCo/GS composites

Highlights: • It is found that adding GSs or FeCo/GSs composite into the sample SiC/NR can greatly increase RL and the absorbing peak shifts to low-frequency with increasing the adding amount. • The optimum adding amount of GSs is 2%. The sample GS-200-2% possesses the lowest RL value of −31.27 dB at 7.6 GHz. • The optimum adding amount of FeCo/GSs composite is 3%. The sample AGS-450-3% possesses the lowest RL value of −20.67 dB at 7.8 GHz. - Abstract: This study mainly explored the synthesis method of graphene sheets (GSs) and FeCo/graphene sheet (FeCo/GS) composites and evaluated the microwave absorbing characteristics of composite materials containing GSs or FeCo/GS composites. First, graphite oxide (GO) was synthesized by the modified Hummers method. The synthesized GO was further used to synthesize GSs and FeCo/GS composites. Afterward, GSs or FeCo/GS composites were mixed with silicon carbide (SiC) and natural rubber (NR) to prepare microwave absorbing materials with thicknesses of 2 mm. Finally, identification and characterization of these samples were performed by XRD, FE-SEM, TEM, TGA, ESCA, RS, AFM and VNA. GSs were synthesized successfully at a low annealing temperature of 200 °C, and their thicknesses were between 0.848 nm and 2.115 nm, which corresponds to 2–6 stacked layers of graphene. FeCo/GS composites were also synthesized successfully at three different annealing temperatures. The nanoparticles of metals and metal oxides were well-dispersed on the surfaces of and the spaces between GSs. It was found that adding GSs or FeCo/GS composites into the SiC/NR sample can greatly increase reflection loss (RL) and that the absorbing peak shifts to lower frequencies as the concentration of added particles increases. The optimum concentration of added GSs was 2 wt.%. The GS-200-2% sample possessed the lowest RL value of −31.27 dB at 7.6 GHz. The optimum concentration of added FeCo/GS composites was 3 wt.%. The AGS-450-3% sample possessed the lowest RL value of −20.67 dB at 7.8 GHz.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Differential Probability Functions for Investigating Long-term Changes in Local and Regional Air Pollution Sources

Conditional probability functions are commonly used for source identification purposes in air pollution studies. CBPF (conditional bivariate probability function) categorizes the probability of high concentrations being observed at a location by wind direction/speed and investigate the directionality of local sources. PSCF (potential source contribution function), a trajectory-ensemble method, identifies the source regions most likely to be associated with high measured concentrations. However, these techniques do not allow the direct identification of areas where changes in emissions have occurred. This study presents an extension of conditional probability methods in which the differences between conditional probability values for temporally different sets of data can be used to explore changes in emissions from source locations. The differential CBPF and differential PSCF were tested using a long-term series of air quality data (12 years; 2005/2016) collected in Rochester, NY. The probability functions were computed for each of 4 periods that represent known changes in emissions. Correlation analyses were also performed on the results to find pollutants undergoing similar changes in local and regional sources. The differential probability functions permitted the identification of major changes in local and regional emission location. In Rochester, changes in local air pollution were related to the shutdown of a large coal power plant (SO 2 ) and to the abatement measures applied to road and off-road traffic (primary pollutants). The concurrent effects of these changes in local emissions were also linked to reduced concentrations of nucleation mode particles. Changes in regional source areas were related to the decreases in secondary inorganic aerosol and organic carbon. As a result, the differential probabilities for sulfate, nitrate, and organic aerosol were consistent with differences in the available National Emission Inventory annual emission values. Changes in the source areas of black carbon and PM2.5 mass concentrations were highly correlated.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Jet charge and machine learning

Modern machine learning techniques, such as convolutional, recurrent and recursive neural networks, have shown promise for jet substructure at the Large Hadron Collider. For example, they have demonstrated effectiveness at boosted top or W boson identification or for quark/gluon discrimination. We explore these methods for the purpose of classifying jets according to their electric charge. We find that both neural networks that incorporate distance within the jet as an input and boosted decision trees including radial distance information can provide significant improvement in jet charge extraction over current methods. Specifically, convolutional, recurrent, and recursive networks can provide the largest improvement over traditional methods, in part by effectively utilizing distance within the jet or clustering history. Furthermore, the advantages of using a fixed-size input representation (as with the CNN) or a small input representation (as with the RNN) suggest that both convolutional and recurrent networks will be essential to the future of modern machine learning at colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Surface Impedance of Superconducting Radio Frequency (SRF) Materials

Superconducting radio frequency (SRF) technology is widely adopted in particle accelerators. There remain many open questions, however, in developing a systematic understanding of the fundamental behavior of SRF materials, including niobium treated in different ways and various other bulk/thin film materials that are fabricated with different methods under assorted conditions. A facility that can measure the SRF properties of small samples in a range of 2-40 K temperature is needed in order to fully answer these questions. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. It consists of a sapphire-loaded cylindrical Nb TE011 cavity at 7.4 GHz with a 50 mm diameter flat sample placed on a non-contacting end plate and uses a calorimetric technique to measure the radio frequency (RF) induced heat on the sample. Driving the resonance to a known field on this surface enables one to derive the surface resistance of a relatively small localized area. TEo11 mode identification has been done at room temperature and 4 K, and has been compared with Microwave Studio® and SuperFish simulation results. RF loss mechanisms in the SIC system are under investigation. A VCO phase lock loop system has been used in both CW and pulsed mode. Two calorimeters, with stainless steel and Cu as the thermal path material for high precision and high power versions, respectively, have been designed and commissioned for the SIC system to provide low temperature control and measurement. A power compensation method has been developed to measure the RF induced power on the sample. Simulation and experimental results show that with these two calorimeters, the whole thermal range of interest for SRF materials has been covered. The power measurement error in the interested power range is within 1.2% and 2.7% for the high precision and high power versions, respectively. Temperature distributions on the sample surface for both versions have been simulated and the accuracy of sample temperature measurements have been analysed. Both versions have the ability to accept bulk superconductors and thin film superconducting samples with a variety of substrate materials such as AI, Al20 3 , Cu, MgO, Nb and Si. Tests with polycrystalline and large grain bulk Nb samples have been done at <15 mT magnetic field. Based on BCS surface impedance, least-squares fittings have been done using SuperFit2.0, a code developed by G. Ciovati and the author. Microstructure analyses and SRF measurements of large scale epitaxial MgB2 films have been reported. MgB2 films on 5 em dia. sapphire disks were fabricated by a Hybrid Physical Chemical Vapor Deposition (HPCVD) technique. The electron-beam backscattering diffraction (EBSD) results suggest that the film is a single crystal complying with a MgB2(0001 )//AI203(0001) epitaxial relationship. The SRF properties of different film thicknesses (200 nm and 350 nm) were evaluated using SIC system under different temperatures and applied fields at 7.4 GHz. A surface resistance of 9±2 1-10 has been observed at 2.2 K. Based on BCS theory with moving Cooper pairs, the electron states distribution at OK and the probability of electron occupation with finite temperature have been derived and applied to anomalous skin effect theory to obtain the surface impedance of a superconductor with moving Cooper pairs. We present the numerical results for Nb.

Xiao, Binping↗
DOE OSTI2019

Proteomics for Microbial Forensics

Mass spectrometry-based proteomics is a powerful tool for the detection and characterization of microbes of forensic and national security concern. Both targeted and untargeted proteomics methods have been developed for the taxonomic classification of unknown microbial samples. Targeted proteomics assays are can be designed for specific microbes of security concern. Untargeted, library-based matrix-assisted laser desorption-ionization time of flight (MALDI-TOF) mass spectrometry is now extensively used in the medical field for microbial identification. Several research groups have developed data analysis pipelines for organism identification/taxonomic classification from untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) data, an application which has some overlap with the field of metaproteomics. This chapter reviews these organism identification techniques. However, organism identification/classification is also commonly done by whole genome sequencing. Using examples from published literature, this chapter also highlights several examples of how proteomics approaches can provide information that cannot be acquired from DNA sequencing alone, such as distinguishing laboratory-adapted bacteria from closely-related wild isolates, and characterizing the growth medium of bacteria and the host cells of virus particles.

proteomics, microbial forensics, mass spectrometry↗
DOE OSTI2025

Level structure of light neutron-rich La isotopes beyond the 𝑁 = 82 shell closure

Here, the high spin excited states of Lanthanum isotopes 140–143 La, above the 𝑁 = 82 closed shell, were populated in fission reactions. The prompt 𝛾-ray transitions were measured using two complementary methods: (a) in coincidence with the isotopically identified fragments produced in the fission of the 238 U + 9 Be system using the Variable Mode Spectrometer (VAMOS++) and the Advanced Gamma Tracking Array (AGATA) spectrometer, and (b) high statistics threefold 𝛾−𝛾−𝛾 and fourfold 𝛾−𝛾−𝛾−𝛾 coincidence data from the spontaneous fission of 252 Cf using the Gammasphere. This work reports the first identification of a pair of parity doublet structures in 143 La and the new high spin level structure in 140–142 La from prompt 𝛾-ray spectroscopy. The level structures are interpreted in terms of the systematics of neighboring odd-𝑍 nuclei above the 𝑍 = 50 shell closure and large-scale shell model calculations. The present results indicate the presence of stable octupole deformation in 143 La. The excitation energy pattern and their comparison with neighboring isotones, moving away from the 𝑁 = 82 closed shell, point towards a transition from single-particle structures to an alternating parity rotational band structure in the La isotopic chain.

Navin, A. [Centre National de la Recherche Scienti↗
DOE OSTI2016

Recent Advances in Analytical Electron Microscopy for Irradiated Materials

Analytical electron microscopy (AEM) in the scanning transmission electron microscope (STEM) has long been a staple of post-irradiation examination (PIE) and materials development campaigns. Recently, new advances in both STEM hardware and post-processing data-analysis software, along with ancillary advances such as in focused ion beam (FIB) sample preparation, has led to exciting advances in the quantity and quality of data that can be obtained. This talk will summarize recent experiments performed at Oak Ridge National Laboratory (ORNL), especially work on neutron-irradiated materials and fuels taking advantage of a newly-installed latest-generation AEM tool in the ORNL irradiated materials laboratories. ORNL installed a new FEI Talos F200X microscope, a 200 keV, high-brightness Schottky emission AEM system optimized for high-speed, high-efficiency X-ray mapping experiments. The F200X features the FEI 'SuperX' four-sector silicon drift detector (SDD) X-ray detector, which provides 0.9 sr solid angle of collection. By combining the high-brightness electron source, latest-generation electron optics, and fast computers and pulse processors, X-ray mapping speed is increased by a factor of 50-100 x compared to the previous-generation instruments. In addition to improvements in hardware, data mining via multivariate statistical analysis (MVSA) allows for maximum insight to the data obtained from the new hardware. MVSA data mining of the X-ray maps allows, for instance, unbiased computational identification of the phases present, and discovery of small phases or precipitates not expected by the human analyst. This talk will present examples of experiments performed using the most modern AEM tools and software. Silicon carbide is a major candidate for next-generation nuclear applications. Nano-infiltration by transient eutectic (NITE) SiC requires low sintering temperatures. X-ray mapping of the NITE structure find pockets of different oxides, such as Zr-Y-oxide, Y-Al-oxide, and yttria. MVSA data mining finds the regions where different oxides are present and indicates that Y additions preferentially wet grain boundaries, where Zr additions are preferentially concentrated at grain triple points. SiC coatings from AGR-I experiment TRISO particles were found to contain significant quantities of fission products (e.g., Pd) as well as actinides (U, Pu). MVSA data mining found complex precipitates and grain boundary films of the fission products and actinides deep (∼several microns) into the SiC layer. Advanced AEM methods, combined with MVSA data mining, makes possible both rapid and detailed PIE. Ferritic alloys, such as accident-tolerant FeCrAl grades, benefit greatly from advanced AEM examination. Neutron-irradiated FeCrAl precipitates the detrimental Cr-rich α' phase. Because the SuperX SDD system has four detectors, it is possible to obtain high X-ray count rates even on a highly tilted specimen, as might be needed to obtain STEM images of dislocation loops. Results on neutron-irradiated FeCrAl indicates that α' size and number density can be obtained by AEM, and MVSA results determine that minor elements (such as Si) has complex radiation-induced segregation behavior at grain boundaries. We have also developed and validated computer models of the AEM experiment, allowing different microstructures' X-ray map results to be simulated for different STEM instruments. This allows X-ray mapping to be more quantitative, such as by estimating what size nanoclusters in an oxide-dispersion strengthened steel would be visible or invisible in STEM. In summary, new advanced AEM technology provides a major leap forward in experiments possible in PIE of irradiated materials. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Improvement in the Mass Resolution of Single Particle Mass Spectrometry Using Delayed Ion Extraction

A specific delayed ion extraction (DIE) technique, which combines a standard rectangular extraction pulse with an exponential pulse, was introduced for a single particle mass spectrometry (SPMS) instrument, and it can focus ions in a wide mass range and results in a mass resolution improvement for the mass range of the studied ions. The experimental results indicate that the average mass resolution for positive ions is about 1000 when the mass-to-charge ratio (m/z) is greater than 70, and for negative ions, when the m/z is greater than 70, the average resolution can reach 2000. The highest mass resolutions achieved so far are 1260 for positive ions and 2400 for negative ions for SPMS, which are very beneficial for mass peak interpretation and chemical compound identification. The primary applications for atmospheric particle measurements show that the high mass resolution of SPMS with the DIE technique is very beneficial for the analysis of carbon and metallic element containing particles, and {sup 39}K{sup +} with C{sub 3}H{sub 3}{sup +} and {sup 41}K{sup +} and C{sub 3}H{sub 5}{sup +} in organic particles were successfully differentiated using SPMS. The results indicate that SPMS with DIE technique can significantly ease mass peak interpretation and improve the mass assignment ability during analysis. Furthermore, existing SPMS instruments can be improved by a facile retrofitting process to implement the DIE technique. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Two-frequency RF fields induced multipactor in coaxial transmission lines

This study presents a comprehensive investigation of two-surface multipactor discharge in coaxial transmission lines under two-frequency radio frequency (RF) excitation using one-dimensional Monte Carlo simulations validated against three-dimensional particle-in-cell simulations and experimental data. The results show that introducing a second carrier mode can suppress multipactor by reshaping and shrinking the susceptibility region, with the extent and location of suppression strongly dependent on the device's aspect ratio and the relative phase of the second carrier mode. Distinct suppression patterns are observed across different fd regimes, while in some cases, susceptibility expansion also occurs under two-frequency operation. A key outcome is the identification and delineation of pure and mixed multipactor modes in coaxial geometry, where analytical mode boundaries are not readily available. Unlike planar geometries, pure-mode regions in coaxial systems overlap with mixed-mode domains, complicating mode identification. Additionally, image charge forces are found to have negligible influence on susceptibility thresholds but strongly affect electron growth rates. These findings offer valuable insights into the use of waveform engineering for controlling multipactor in high-power RF systems.

43 PARTICLE ACCELERATORS↗