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Item Open Access Prospects for using a new phosphorus-containing extractant in uranium technology(The 6th International Conference on Nanomaterials and Advanced Energy Storage Systems. Institute of Batteries LLP, Nazarbayev University, and PI “National Laboratory Astana”., 2018-08-08) Nalibayeva, Arailym; Bishimbayeva, Gaukhar; Saidullayeva, Sabina; Kopbaeva, Mariya; Verkhoturova, Svetlana; Arbuzova, Svetlana; Gusarova, Nina; Kydyrbayeva, UldanaPhosphorus-containing compounds are widely used in industrial hydrometallurgical processes as extragents and complexes of color, noble, rare-earth metals and transuranium elements [1]...Item Open Access Radiation-induced synergistic effects of athermal and thermal mechanisms on erosion and surface evolution of advanced electrode and condenser optics materials(Proceedings of SPIE, 2004-02) Allain, J. P.; Hassanein, A.; Burtseva, T.; Yacout, A.; Insepov, Z.; Taj, S.; Rice, B. J.In extreme ultraviolet lithography (EUVL) environments transient plasma dynamics dictate conditions for particle/surface interactions. A critical challenge facing EUVL development is optic component lifetime both in gasdischarge produced plasmas (GDPP) and laser-produced plasmas (LPP) devices. Optic components are exposed to impingent species, impurities (H,C,O,N) and debris leading to their degradation and consequently limiting 13.5 nm light reflection intensity. Experiments in the PRIME (Particles and Radiation Interaction with Matter Experiments) facility at the Argonne National Laboratory study the synergy between radiation-induced athermal and thermal mechanisms that influence the behavior of EUVL materials (electrodes and condenser optics) under irradiation conditions including: incident particle energy (50 eV – 5 keV), angle-of-incidence (near-normal to oblique), incident flux (1011-1017 ions/cm2/s), surface coatings (impurity: C,O or capping layers: Ru, W), and surface temperature (100 – 1000 °C). Results of electrode and optical component interaction with singly-charged inert gases (Xe) are presented. Critical issues under study include: radiation enhanced diffusion, radiation induced segregation, preferential sputtering, collisional mixing, surface segregation, surface amorphization, thermal diffusion and thermal spike evolution. Experiments in PRIME will be complemented with atomistic modeling to study how these mechanisms modify surfaces and how these mechanisms can work synergistically to introduce solutions to enhance component lifetime of electrode and condenser optic materials.Item Open Access Modeling arcs(American Institute of Physics, 2011-12) Insepov, Z.; Norem, J.; Vetizer, S.; Mahalingam, S.Although vacuum arcs were first identified over 110 years ago, they are not yet well understood. We have since developed a model of breakdown and gradient limits that tries to explain, in a self-consistent way: arc triggering, plasma initiation, plasma evolution, surface damage and gradient limits. We use simple PIC codes for modeling plasmas, molecular dynamics for modeling surface breakdown, and surface damage, and mesoscale surface thermodynamics and finite element electrostatic codes for to evaluate surface properties. Since any given experiment seems to have more variables than data points, we have tried to consider a wide variety of arcing (rf structures, e beam welding, laser ablation, etc.) to help constrain the problem, and concentrate on common mechanisms. While the mechanisms can be comparatively simple, modeling can be challenging.Item Open Access Comparison of back-scattering properties of electron emission materials(Proceedings of 2011 Particle Accelerator Conference, New York, 2011) Insepov, Z.; Ivanov, V.; Jokela, S.; Wetstein, M.We use “microscopic” Monte Carlo (MC) simulations, empirical theories, and comparison with experiments to identify the influence of back-scattered electrons and the saturation effect on the emissive properties of materials and to study the gain and transit times for various microchannel plates (MCPs). We have applied this method to Al2O3 and MgO emissive materials of various thickness and surface quality. The experimental secondary emission yield (SEY) data were obtained at normal electron impacts and were used as the reference data for adjusting our MC simulations. The SEY data were calculated at oblique angles of the primary electrons in the interval of 0-80°. The energy dependence of backscattered electron coefficients (BSCs) for various primary electron incidence angles was calculated by MC for both materials, and the results were compared with experimental “average” values obtained in the literature. Both SEY and BSC data were used as input files to our “macroscopic” trajectory simulation, which models MCP amplifiers as whole devices and is capable of gain and transit time calculations. The deposition and characterization experiments were conducted for the Large Area Picosecond Photodetector project at Argonne National Laboratory.Item Open Access Beam-Induced Electron Loading Effects in High Pressure Cavities for a Muon Collider(Proceedings of IPAC’10, Kyoto, Japan, 2010) Chung, M.; Tollestrup, A.; Jansson, A.; Yonehara, K.; Insepov, Z.Ionization cooling is a critical building block for the realization of a muon collider. To suppress breakdown in the presence of the external magnetic field, an idea of using an RF cavity filled with high pressure hydrogen gas is being considered for the cooling channel design. One possible problem expected in the high pressure RF cavity is, however, the dissipation of significant RF power through the beam-induced electrons accumulated inside the cavity. To characterize this detrimental loading effect, we develop a simplified model that relates the electron density evolution and the observed pickup voltage signal in the cavity, with consideration of several key molecular processes such as the formation of the polyatomic molecules, recombination and attachment. This model is expected to be compared with the actual beam test of the cavity in the MuCool Test Area (MTA) of Fermilab.Item Open Access Advanced Surface Polishing For Accelerator Technology Using Ion Beams(American Institute of Physics, 2009-03) Insepov, Z.; Norem, J.; Hassanein, A.; Wu, A. T.Surface erosion problems are common in the development of TeV accelerators, fusion and fission reactors, semiconductor, optical and magnetic storage devices, and Extreme Ultra-Violet (EUV) lithography devices. We have reviewed various erosion mechanisms of ion interactions with the surfaces studied by experiment and computer simulation. Nanoscale surface roughness in rf-linacs and contamination cause field emission of electrons, field evaporation of ions and fragments, plasma formation, and lead to high-gradient rf vacuum breakdown of electrodes which is a limiting factor in the development of high-gradient rf technology for future TeV accelerators. A few mechanisms of nanoscale surface fracture under a high-gradient electric field were developed and will be discussed. A Gas Cluster Ion Beam (GCIB) technology was successfully applied to surface treatment of Cu, Stainless steel, Ti and Nb samples and to Nb rf-cavities by using accelerated cluster ion beams of Ar, O2, N2, and NF3, and combinations of them, with accelerating voltages up to 35 kV. DC field emission (dark current) measurements and electron microscopy were used to investigate metal surfaces treated by GCIB. The experimental results showed that GCIB technique can significantly reduce the number of field emitters and also change the structure of the Nb oxide layer on the surface. The RF tests on the GCIB treated Nb rf-cavities showed improvement of the quality factor Q at 4.5 K. The superconducting gap was also enhanced by using the oxygen GCIB irradiation exposure. GCIB may become a standard technique to modify and control the oxygen content on the surface and a promising surface treatment technique for Nb SRF cavities in particle accelerators. Computer simulation of bombardment of Nb surfaces with Ar and O2 clusters by molecular dynamics and phenomenological surface dynamics equations confirms experimental results.Item Open Access Computer simulation of bubble formation(Joint International Topical Meeting on Mathematics & Computation and Supercomputing in Nuclear Applications, 2007-04) Insepov, Z.; Bazhirov, T.; Norman, G.; Stegailov, V.Properties of liquid metals (Li, Pb, Na) containing nanoscale cavities were studied by atomistic Molecular Dynamics (MD). Two atomistic models of cavity simulation were developed that cover a wide area in the phase diagram with negative pressure. In the first model, the thermodynamics of cavity formation, stability and the dynamics of cavity evolution in bulk liquid metals have been studied. Radial densities, pressures, surface tensions, and work functions of nano-scale cavities of various radii were calculated for liquid Li, Na, and Pb at various temperatures and densities, and at small negative pressures near the liquid-gas spinodal, and the work functions for cavity formation in liquid Li were calculated and compared with the available experimental data. The cavitation rate can further be obtained by using the classical nucleation theory (CNT). The second model is based on the stability study and on the kinetics of cavitation of the stretched liquid metals. A MD method was used to simulate cavitation in a metastable Pb and Li melts and determine the stability limits. States at temperatures below critical (T < 0.5Tc) and large negative pressures were considered. The kinetic boundary of liquid phase stability was shown to be different from the spinodal. The kinetics and dynamics of cavitation were studied. The pressure dependences of cavitation frequencies were obtained for several temperatures. The results of MD calculations were compared with estimates based on classical nucleation theory.Item Open Access Breakdown in RF cavities(Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee, 2005) Norem, J.; Hassanein, A.; Insepov, Z.; Konkashbaev, I.We present a simple model of breakdown in rf cavities. For most events this involves tensile stress and tensile strength, however other effects can also contribute. We discuss the effects of different materials, fatigue, high pressure gas, primary and secondary emission sites, local field enhancements, dark currents, secondary emission, work functions, magnetic fields, macro and microscopic fracture mechanisms high current densities, surface and subsurface defects, and astronomical power densities. While primarily devoted to normal conductors, this work also has consequences for superconducting rf surfaces.Item Open Access Simulations of Fast X-Ray Detectors Based on Multichannel Plates(Proceedings of IPAC2012, New Orleans, Louisiana, 2012) Adams, B.; Insepov, Z.; Ivanov, V.; Norem, J.High-performance detectors with high spatial and time resolutions are required in applications such as imaging of fast processes, time-resolved coherent scattering, and time-resolved X-ray spectroscopy. Recently a new type of X-ray detector was proposed, based on microchannel plates (MCP) coated with resistive and emissive layers inside the pores by using atomic-layer deposition with better functional optimizations. Two microscopic Monte Carlo codes were used to calculate the characteristics of secondary electrons emitted from a photocathode irradiated by X-rays with energies of 1–15 keV and by electrons with energies in the interval of 0– -2 keV. WO3 was selected as the photocathode and the electron emissive material. The emissive characteristics obtained by the microscopic Monte Carlo codes were used as input data for a third, macroscopic MCP simulation Monte Carlo code, for calculating the gain and transit time spread of a MCP-based X-ray detector. Our simulation results showed that the X-ray detector should improve the spatial and time resolution and push the development of high-quantum-yield photocathodes based on MCPs.Item Open Access Ion Solid Interaction And Surface Modification At RF Breakdown In High‐Gradient Linacs(American Institute of Physics, 2011-06) Insepov, Z.; Norem, J.; Veitzer, S.Ion solid interactions have been shown to be an important new mechanism of unipolar arc formation in high-gradient rf linear accelerators through surface self-sputtering by plasma ions, in addition to an intense surface field evaporation. We believe a non-Debye plasma is formed in close vicinity to the surface and strongly affects surface atomic migration via intense bombardment by ions, strong electric field, and high surface temperature. Scanning electron microscope studies of copper surface of an rf cavity were conducted that show craters, arc pits, and both irregular and regular ripple structures with a characteristic length of 2 microns on the surface. Strong field enhancements are characteristic of the edges, corners, and crack systems at surfaces subjected to rf breakdown.Item Open Access Simulation of ion implantation into nuclear materials and comparison with experiment(American Institute of Physics, 2011-06) Insepov, Z.; Yun, D.; Ye, B.; Rest, J.; Starikov, S.; Yacout, A. M.Radiation defects generated in Mo formed by sub-MeV Xe ion implantations were studied by atomistic molecular dynamics based on interatomic potential matched to density functional calculations. The results of the simulations were qualitatively compared with defect distributions in CeO2 and CeLaO2 crystals used as surrogate materials for UO2 obtained from experiments by implantation of these ions at a dose of 1×1017 ions/cm2 at several temperatures. A combination of in situ Transmission Electron Microscopy (TEM) and ex situ TEM experiments was used to study the evolution of defect clusters during implantation of Xe and Kr ions at energies of 150-700 keV, depending on the experimental conditions. The simulation and irradiation were performed on thin-film, single-crystal materials. The formation of defects, dislocation loops, and precipitates was studied by simulation and compared to experiment. Various sets of quantitative experimental results were obtained to characterize the dose and temperature effects of irradiation. These experimental results include size distributions of dislocation loops, voids, and gas bubble structures created by irradiation.Item Open Access The problem of RF gradient limits(American Institute of Physics, 2010-03) Norem, J.; Insepov, Z.; Huang, D.; Mahalingam, S.; Veitzer, S.We describe breakdown in rf accelerator cavities in terms of a number of mechanisms. We divide the breakdown process into three stages: 1) we model surface failure using molecular dynamics of fracture caused by electrostatic tensile stress, 2) the ionization and plasma growth is modeled using a particle in cell code, 3) we model surface damage by assuming unipolar arcing. Although unipolar arcs are strictly defined with equipotential boundaries, we find that the cold, dense plasma in contact with the surface produces very small Debye lengths and very high electric fields over a large area, and these high fields produce strong erosion mechanisms, primarily self sputtering, compatible with crater formation.We compare this model with arcs in tokamaks, plasma ablation, electron beam welding, micrometeorite impacts, and other examples.Item Open Access Study of Electron Swarm in High Pressure Hydrogen Gas Filled RF Cavities(Fermilab, 2010) Yonehara, K.; Chung, M.; Popovic, M.; Moretti, A.; Wang, H.; Alsharo'a, M.; Insepov, Z.A high pressure hydrogen gas filled RF cavity has been proposed for use in the muon collection system for a muon collider. It allows for high electric field gradients in RF cavities located in strong magnetic fields, a condition frequently encountered in a muon cooling channel. In addition, an intense muon beam will generate an electron swarm via the ionization process in the cavity. A large amount of RF power will be consumed into the swarm. We show the results from our studies of the HV RF breakdown in a cavity without a beam and present some results on the resulting electron swarm dynamics. This is preliminary to actual beam tests which will take place late in 2010.Item Open Access The Interactions of Surface Damage on RF Cavity Operation(Fermilab, 2006-06) Norem, J.; Bross, A.; Hassanein, A.; Qian, Z.; Yoon, K. E.; Moretti, A.; Li, D.Studies of low frequency RF systems for muon cooling has led to a variety of new techniques for looking at dark currents, a new model of breakdown, and, ultimately, a model of RF cavity operation based on surface damage. We find that cavity behavior is strongly influenced by the spectrum of enhancement factors on field emission sites.Three different spectra are involved: one defining the initial state of the cavity, the second determined by the breakdown events, and the third defining the equilibrium produced as a cavity operates at its maximum field. We have been able to measure these functions and use them to derive a wide variety of cavity parameters: conditioning behavior, material, pulse length, temperature, vacuum, magnetic field, pressure, gas dependence. In addition we can calculate the dependence of breakdown rate on surface field and pulse length. This work correlates with data from Atom Probe Tomography. We will describe this model and new experimental data.Item Open Access A General Model of Vacuum Arcs in Linacs(Proceedings of NAPAC2016, Chicago, IL, USA, 2017-01) Norem, J.; Insepov, Z.We are developing a general model of breakdown and gradient limits that applies to accelerators, along with other high field applications such as power grids and laser ablation. We have considered connections with failure modes of integrated circuits, sheath properties of dense, non-Debye plasmas and applications of capillary wave theory to rf breakdown in linacs. In contrast to much of the rf breakdown effort that considers one physical mechanism or one experimental geometry, we find an enormous volume of relevant material in the literature that helps to constrain our model and suggest experimental tests.Item Open Access Computational problems in modeling arcs(American Institute of Physics, 2016-10) Norem, J.; Insepov, Z.We explore the reasons why there seems to be no common model for vacuum arcs, in spite of the importance of the field and the level of effort expended over more than one hundred years.Item Open Access Multiscale simulation of ion beam impacts on a graphene surface(IOP Publishing, 2016-09) Dybyspayeva, K. B.; Zhuldassov, A.; Ainabayev, A.; Vyatkin, A. F.; Alekseev, K.; Insepov, Z.Multiscale study of single and multilayer graphene irradiation is presented in this paper. Ab-initio density-functional theory (DFT) was used to study point defects, and a large scale parallel molecular-dynamics (MD) simulations were used for studying formation of gas cluster ion impacts. Moreover, Raman spectra of pure and defect graphene samples were studied from DFT calculations. Threshold energies for creating craters on the surface of graphene were obtained from MD and compared with published papers. The results of simulations were also compared with experimental craters and surface shape.Item Open Access A design for large-area fast photo-detectors with transmission-line readout and waveform sampling(In Real Time Conference, 2009. RT'09. 16th IEEE-NPSS (pp. 49-61). IEEE., 2009) Adams, B.; Anderson, J. T.; Attenkofer, K.; Bogdan, M.; Byrum, K.; Drake, G.; Insepov, Z.We present a preliminary design and the results of simulation for a photo-detector module to be used in applications requiring the coverage of areas of many square meters with time resolutions less than 10 picoseconds and position resolutions of less than a millimeter for charged particles. The source of light is Cherenkov light in a radiator/window; the amplification is provided by panels of micro-pores functionalized to act as microchannel plates (MCPs). The good time and position resolution stems from the use of an array of parallel 50 Ω transmission lines (strips) as the collecting anodes. The anode strips feed multi-GS/sec sampling chips which digitize the pulse waveform at each end of the strip, allowing a measurement of the time from the average of the two ends, and a 2-dimensional position measurement from the difference of times on a strip, and, in the orthogonal direction, the strip number, or a centroid of the charges deposited on adjacent strips. The module design is constructed so that large areas can be `tiled' by an array of modules.Item Open Access High Surface Fields in Superconducting rf Cavities. In Proceedings of SRF(Proceedings of the 12th International Workshop on RF Superconductivity, Cornell University, 2005) Norem, J.; Insepov, Z.; Bauer, P.; Seidman, D.N.; Sebastian, J.; Yoon, K.Field emission in cavities requires electric fields that can be high enough to damage materials. We outline a model of breakdown and field emission from local asperities, and show how electric field effects, and field emission of electrons, field evaporation of ions, ultimately fracture, can limit accelerating fields. Although based on data from copper cavities and preliminary results from atom probe tomography experiments, the model seems to be generally valid for DC to 30 GHz, 10-11 to 105 Torr, different materials, temperatures, conditioning status, secondary emitters, strong magnetic fields, atom probe data, and the variety of surfaces encountered during copper cavity conditioning. We believe studies of normal materials can help to understand mechanisms operating in SCRF, such as fracture, field emission and evaporation effects, control of the surface, and surface metallurgy.Item Open Access Molecular dynamics study of implant and damage formation in low-energy boron cluster ion implantation(Ion Implantation Technology Proceedings, 1998 …, 1999, 1999) Aoki, T.; Matsuo, J.; Insepov, Z.; Yamada, I.Cluster ion implantation using decaborane (B,J-I,,) has been proposed as a useful technique for shallow junction formation. In order to examine the characteristics and advantages of cluster ion implantation, molecular dynamics simulations of small B cluster and monomer implantation were performed B,, B4 and B,, are irradiated on Si (001) substrates with acceleration energy of 230eV/atom so that B, and 6, are accelerated with 0.Y2keV and 2.3keV, respectively. Those three show the same implant profile and implant efficiency, which agrees with the experimental result of &,,HI, implantation. This result suggests that each B atom in a B cluster acts individually in similar way to a monomer ion. B clusters show the same properties in projection range and implant efficiency as the monomer whereas non-linearity is shown in damage formation. The number of displacements by one B atom once increases to the same maximum value for both a B cluster and a B monomer. However, the damage recovery process is different depending on the cluster sue. Damage induced by B,, recovers more slowly and 4 times as many displacements remain compared to B, 8ps after impact. These displacements by B,, clusters concentrate in the near surface region of the impact point, while the ones by B, reside around the implanted B atom as the end-of-range damage. This characteristic damage formation by B,, cluster is expected to avoid transientenhanced-diffusion of incident B atoms and achieve the formation of high-quality shallow p-type junction.