arXiv subjects

Igor Kaganovich

Publications and source records attributed to Igor Kaganovich.

29 records · Page 2Linked to original sources

arXiv2018

Electrostatic solitary waves in ion beam neutralization

The excitation and propagation of electrostatic solitary waves(ESWs) are observed in two-dimensional particle-in-cell simulations of ion beam neutralization by electron injection by a filament. Electrons from the filament are attracted by positive ions and bounce inside ion beam pulse. Bouncing back and forth electron streams then starts to mix, creating the two-stream instability. The instability saturates with the formation of ESWs. These ESWs reach several centimeters in longitudinal size and are stable for a long time. The excitation of large-amplitude ESWs reduces the degree of neutralization of the ion beam pulse. In addition, the dissipation of ESWs causes heating of neutralizing electrons and their escape from the ion beam, leading to further reduction of neutralization degree.

physics.plasm-ph↗

arXiv2018

Root-Growth of Boron Nitride Nanotubes: Experiments and \textit{Ab Initio} Simulations

We have synthesized boron nitride nanotubes (BNNTs) in an arc in presence of boron and nitrogen species only, without transition metals. We find that BNNTs are often attached to pure boron nanoparticles, suggesting that root-growth is a likely mechanism for their formation. To gain further insight into this process we have studied key mechanisms for root growth of BNNTs on the surface of a liquid boron droplet by ab initio molecular dynamics simulations. We find that nitrogen atoms reside predominantly on the droplet surface where they organize to form boron nitride islands below 2400 K. To minimize contact with the liquid particle underneath, the islands assume non-planar configurations that are likely precursors for the thermal nucleation of cap structures. Once formed, the caps are stable and can easily incorporate nitrogen and boron atoms at their base, resulting in further growth. Our simulations support the root-growth mechanism of BNNTs and provide comprehensive evidence of the active role played by liquid boron.

physics.chem-ph↗

arXiv2018

Spatial symmetry breaking in single-frequency CCP discharge with transverse magnetic field

An independent control of the flux and energy of ions impacting on an object immersed in a plasma is often desirable for many industrial processes such as microelectronics manufacturing. We demonstrate that a simultaneous control of these quantities is possible by a suitable choice of a static magnetic field applied parallel to the plane electrodes in a standard single frequency capacitively coupled plasma device. Our particle-in-cell simulations show a 60% reduction in the sheath width (that improves control of ion energy) and a four fold increase in the ion flux at the electrode as a consequence of the altered ion and electron dynamics due to the ambient magnetic field. A detailed analysis of the particle dynamics is presented and the optimized operating parameters of the device are discussed. The present technique offers a simple and attractive alternative to conventional dual frequency based devices that often suffer from undesirable limitations arising from frequency coupling and electromagnetic effects.

physics.plasm-ph↗

arXiv2018

Evolution of the electron cyclotron drift instability in two-dimensions

The Electron Cyclotron Drift Instability (ECDI) driven by the electron $E\times B$ drift in partially magnetized plasmas is investigated with highly resolved particle-in-cell simulations. The emphasis is on two-dimensional effects involving the parallel dynamics along the magnetic field in a finite length plasma with dielectric walls. It is found that the instability develops as a sequence of growing cyclotron harmonics demonstrating wave breaking and complex nonlinear interactions, being particularly pronounced in ion density fluctuations at short wavelengths. At the same time, nonlinear evolution of fluctuations of the ion and electron density, as well as the anomalous electron current, shows cascade toward long wavelengths. Tendency to generate long wavelength components is most clearly observed in the spectra of the electron density and the anomalous current fluctuations. An intense but slowly growing mode with a distinct eigen-mode structure along the magnetic field develops at a later nonlinear stage enhancing the tendency toward long wavelength condensation. The latter mode having a finite wavelength along the magnetic field is identified as the Modified Two-Stream Instability (MTSI). It is shown that the MTSI mode results in strong parallel heating of electrons.

physics.plasm-ph↗

arXiv2018

Synthesis of nanoparticles in carbon arc: measurements and modeling

This work studies the region of nanoparticle growth in atmospheric pressure carbon arc. Detection of the nanoparticles is realized via the planar laser induced incandescence (PLII) approach. Measurements revealed large clouds of nanoparticles in the arc periphery, bordering the region with high density of diatomic carbon molecules. Two-dimensional computational fluid dynamic simulations of the arc combined with thermodynamic modeling explain these results due to interplay of the condensation of carbon molecular species and the convection flow pattern. The results have shown that the nanoparticles are formed in the colder, outside regions of the arc and described the parameters necessary for coagulation.

physics.plasm-ph↗

arXiv2018

Particle-in-cell simulations of anomalous transport in a Penning discharge

Electrostatic particle-in-cell simulations of a Penning discharge are performed in order to investigate azimuthally asymmetric, spoke-like structures previously observed in experiments. Two-dimensional simulations show that for Penning-discharge conditions, a persistent nonlinear spoke-like structure forms readily and rotates in the direction of ExB and electron diamagnetic drifts. The azimuthal velocity is within about a factor of two of the ion acoustic speed. The spoke frequency follows the experimentally observed scaling with ion mass, which indicates the importance of ion inertia in spoke formation. The spoke provides enhanced (anomalous) radial electron transport, and the effective cross-field conductivity is several times larger than the classical (collisional) value. The level of anomalous current obtained in the simulations is in good agreement with the experimental data. The rotating spoke channels most of the radial current, observable by an edge probe as short pulses.

physics.plasm-ph↗

arXiv2017

Validation and benchmarking of two particle-in-cell codes for a glow discharge

The two particle-in-cell codes EDIPIC and LSP are benchmarked and validated for a parallel-plate glow discharge in helium, in which the axial electric field had been carefully measured, primarily to investigate and improve the fidelity of their collision models. The scattering anisotropy of electron-impact ionization, as well as the value of the secondary-electron emission yield, are not well known in this case. The experimental uncertainty for the emission yield corresponds to a factor of two variation in the cathode current. If the emission yield is tuned to make the cathode current computed by each code match the experiment, the computed electric fields are in excellent agreement with each other, and within about 10\% of the experimental value. The non-monotonic variation of the width of the cathode fall with the applied voltage seen in the experiment is reproduced by both codes. The electron temperature in the negative glow is within experimental error bars for both codes, but the density of slow trapped electrons is underestimated. A more detailed code comparison done for several synthetic cases of electron-beam injection into helium gas shows that the codes are in excellent agreement for ionization rate, as well as for elastic and excitation collisions with isotropic scattering pattern. The remaining significant discrepancies between the two codes are due to differences in their electron binary-collision models, and for anisotropic scattering due to elastic and excitation collisions.

physics.plasm-ph↗

arXiv2017

Nonlinear structures and anomalous transport in partially magnetized $\mathbf{E\times B}$ plasmas

Nonlinear dynamics of the electron-cyclotron instability driven by the electron $\mathbf{E\times B}$ current in crossed electric and magnetic field is studied. In nonlinear regime the instability proceeds by developing a large amplitude coherent wave driven by the energy input from the fundamental cyclotron resonance. Further evolution shows the formation of the long wavelength envelope akin to the modulational instability. Simultaneously, the ion density shows the development of high-k content responsible for wave focusing and sharp peaks on the periodic cnoidal wave structure. It is shown that the anomalous electron transport (along the direction of the applied electric field) is dominated by the long wavelength part of the turbulent spectrum.

physics.plasm-ph↗

arXiv2017

Migration of a Carbon Adatom on a Charged Single-Walled Carbon Nanotube

We find that negative charges on an armchair single-walled carbon nanotube (SWCNT) can significantly enhance the migration of a carbon adatom on the external surfaces of SWCNTs, along the direction of the tube axis. Nanotube charging results in stronger binding of adatoms to SWCNTs and consequent longer lifetimes of adatoms before desorption, which in turn increases their migration distance several orders of magnitude. These results support the hypothesis of diffusion enhanced SWCNT growth in the volume of arc plasma. This process could enhance effective carbon flux to the metal catalyst.

physics.atm-clus↗

arXiv2014

Intense Ion Beam Neutralization Using Underdense Background Plasma

Producing a dense background plasma for neutralization purposes is experimentally difficult and requires a large amount of energy. We show that even an underdense background plasma with a small relative density can achieve high neutralization of intense ion beam pulses. Using particle-in-cell simulations, we show that if the total plasma electron charge is not comparable to the beam charge, electron emitters are necessary for effective neutralization, but are not needed if the plasma volume is large. Several plasma densities are investigated, including the case of electron emitters without plasma, which does not effectively neutralize the beam. Over 95% neutralization is achieved for even very underdense background plasma. We compare with an analytic model of neutralization and find close agreement with the particle-in-cell simulations. Further, we show experimental data from the NDCX-II group that verifies the result that underdense plasma can neutralize intense heavy ion beams effectively.

physics.plasm-ph↗

arXiv2011

Collisionless filamentation, filament merger and heating of low-density relativistic electron beam propagating through a background plasma

A cold electron beam propagating through a background plasma is subject to filamentation process due to theWeibel instability. If the initial beam radius is large compared with the electron skin depth and the beam density is much smaller than the background plasma density, multiple filaments merge many times. Because of this non-adiabatic process, the beam perpendicular energy of initially cold beam grows until all filaments coalesce into one pinched beam with the beam radius much smaller than initial radius and smaller than the electron skin depth. It was shown through particle-in-cell simulations that a significant fraction of the beam is not pinched by the magnetic forces of the pinched beam and fills most of the plasma region. The resulting electron beam energy distribution in the perpendicular direction is close to a Maxwellian for the bulk electrons. However, there are significant departures from a Maxwellian for low and high perpendicular energy (deeply trapped and untrapped electrons). An analytical model is developed describing the density profile of the resulting pinched beam and large low-density halo around it. Based on this analytical model, a calculation of the energy transfer from the beam longitudinal kinetic energy to the transverse beam kinetic energy, the self-magnetic field, and the plasma electrons is performed. Results of analytical theory agree well with the particle-in-cell simulations results.

physics.plasm-ph↗