@article{YatomRaitses2020,
title = { Characterization of plasma and gas-phase chemistry during boron-nitride nanomaterial synthesis by laser-ablation of boron-rich targets},
author = {S. Yatom and Y. Raitses},
url = {https://pubs.rsc.org/en/Content/ArticleLanding/2020/CP/D0CP02890H#!divAbstract},
doi = {10.1039/D0CP02890H},
year = {2020},
date = {2020-08-21},
journal = {Physical Chemistry Chemical Physics},
abstract = {In this work, solid targets made from boron and boron nitride (BN) materials are ablated by a nanosecond pulsed laser at sub-atmospheric pressures of nitrogen and helium gases. The excited species in the ablation plume from the target are probed by spatiotemporally resolved optical emission spectroscopy (OES). The evaluation of the chemical composition of the plasma plume revealed that for both boron-rich targets, emission from BN molecules is always observed in nitrogen-rich environments. In addition, BN molecules are also present when ablating a boron nitride target in a helium gas environment, an indication that BN molecules in the plume may originate from the solid target. Furthermore, the ablation of the BN target features emission of B2N molecules, regardless of the pressure and surrounding gas. These results suggest that the ablation of the BN target is more favorable for the generation of complex molecules containing boron and nitrogen species and possibly hint that BN is also more favorable feedstock for high-yield BN nanomaterial synthesis. Plasma parameters such as the electron temperature (peak value of 1.3 eV) and density (peak value of 2 × 10^18 cm^−3) were also investigated in this work in order to discuss the chemical dynamics in the plume.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Yatom2020,
title = {Characterization of plasma and gas-phase chemistry during boron-nitride nanomaterial synthesis by laser-ablation of boron-rich targets},
author = {S. Yatom and Y. Raitses},
url = {https://pcrf.princeton.edu/authorreprints-1/},
doi = {10.1039/D0CP02890H},
year = {2020},
date = {2020-08-21},
journal = {Physical Chemistry Chemical Physics},
number = {22},
pages = {20837 - 20850},
abstract = {
In this work, solid targets made from boron and boron nitride (BN) materials are ablated by a nano- second pulsed laser at sub-atmospheric pressures of nitrogen and helium gases. The excited species in the ablation plume from the target are probed by spatiotemporally resolved optical emission spectroscopy (OES). The evaluation of the chemical composition of the plasma plume revealed that for both boron-rich targets, emission from BN molecules is always observed in nitrogen-rich environments. In addition, BN molecules are also present when ablating a boron nitride target in a helium gas environment, an indication that BN molecules in the plume may originate from the solid target. Furthermore, the ablation of the BN target features emission of B2N molecules, regardless of the pressure and surrounding gas. These results suggest that the ablation of the BN target is more favorable for the generation of complex molecules containing boron and nitrogen species and possibly hint that BN is also more favorable feedstock for high-yield BN nanomaterial synthesis. Plasma parameters such as the electron temperature (peak value of 1.3 eV) and density (peak value of 2 􏰺 1018 cm􏰻3) were also investigated in this work in order to discuss the chemical dynamics in the plume.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Tacu2020,
title = {Convenient analytical formula for cluster mean diameter and diameter dispersion after nucleation burst},
author = {M. Tacu and A. Khrabry and I. D. Kaganovich},
url = {https://journals.aps.org/pre/pdf/10.1103/PhysRevE.102.022116},
doi = {10.1103/PhysRevE.102.022116},
year = {2020},
date = {2020-08-12},
journal = {Physical Review E},
volume = {102},
number = {2},
abstract = {We propose an alternative method of estimating the mean diameter and dispersion of clusters of particles, formed in a cooling gas, right after the nucleation stage. Using a moment model developed by Friedlander [S. K. Friedlander, Ann. N. Y. Acad. Sci. 404, 354 (1983)], we derive an analytic relationship for both cluster mean diameter and diameter dispersion as a function of two of the characteristic times of the system: the cooling time and the primary constituents collision time. These formulas can be used to predict diameter and dispersion variation with process parameters, such as the initial primary constituents' concentration or cooling rate. It is also possible to use them as an input to the coagulation stage, without the need to compute complex cluster generation during the nucleation burst. We compared our results with a nodal code (NGDE) and got excellent agreement.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Chen2020,
title = {Validated two-dimensional modeling of short carbon arcs: Anode and cathode spots},
author = {J. Chen and A. Khrabry and I. D. Kaganovich and A. Khodak and V. Vekselman and H. -P. Li},
url = {http://aip.scitation.org/doi/pdf/10.1063/5.0011044},
doi = {10.1063/5.0011044},
year = {2020},
date = {2020-08-04},
journal = {Physics of Plasmas},
volume = {27},
number = {8},
abstract = {In order to study the properties of short carbon arcs, a self-consistent model was implemented into a CFD code ANSYS-CFX. The model treats the transport of heat and electric current in the plasma and electrodes in a coupled manner and accounts for gas convection in the chamber. Multiple surface processes at the electrodes are modeled, including the formation of space-charge limited sheaths, ablation and deposition of carbon, and emission and absorption of radiation and electrons. The simulations show that the arc is constricted near the cathode and anode front surfaces, leading to the formation of electrode spots. The cathode spot is a well-known phenomenon, and mechanisms of its formation were reported elsewhere. However, the anode spot formation mechanism discovered in this work was not previously reported. We conclude that the spot formation is not related to plasma instability, as commonly believed in the case of constricted discharge columns, but rather occurs due to the highly nonlinear nature of heat balance in the anode. We additionally demonstrate this property with a reduced anode heat transfer model. We also show that the spot size increases with the arc current. This anode spot behavior was also confirmed in our experiments. Due to the anode spot formation, a large gradient of carbon gas density occurs near the anode, which drives a portion of the ablated carbon back to the anode at its periphery. This can consequently reduce the total ablation rate. Simulation results also show that the arc can reach the local chemical equilibrium state in the column region, while the local thermal equilibrium state is not typically achieved for experimental conditions. It shows that it is important to account for different electron and gas temperatures in the modeling of short carbon arcs.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Kaganovich2020,
title = {Perspectives on Physics of ExB Discharges Relevant to Plasma Propulsion and Similar Technologies},
author = {Igor D. Kaganovich and Andrei Smolyakov and Yevgeny Raitses and Eduardo Ahedo and Ioannis G. Mikellides and Benjamin Jorns and Francesco Taccogna and Renaud Gueroult and Sedina Tsikata and Anne Bourdon and Jean-Pierre Boeuf and Michael Keidar and Andrew Tasman Powis and Merio Merino and Mark Cappelli and Kentaro hara and Johan A. Carlsson and Nathaniel J. Fisch and Pascal Chabert and Irina Schweigert and Trevor Lafleur and Konstantin Matyash and Alexander V. Khrabrov and Rod W. Boswell and Amnon Fruchtman},
url = {https://arxiv.org/ftp/arxiv/papers/2007/2007.09194.pdf},
year = {2020},
date = {2020-07-17},
journal = {Physics of Plasmas},
abstract = {This paper provides perspectives on recent progress in the understanding of the physics of devices where the external magnetic field is applied perpendicularly to the discharge current. This configuration generates a strong electric field, which acts to accelerates ions. The many applications of this set up include generation of thrust for spacecraft propulsion and the separation of species in plasma mass separation devices. These ExB plasmas are subject to plasma-wall interaction effects as well as various micro and macro instabilities, and in many devices, we observe the emergence of anomalous transport. This perspective presents the current understanding of the physics of these phenomena, state-of-the-art computational results, identifies critical questions, and suggests directions for future research
},
keywords = {},
pubstate = {forthcoming},
tppubtype = {article}
}

@article{Efthimion2020,
title = {Critical Need for a National Initiative in Low Temperature Plasma Research},
author = {Philip Efthimion and Igor Kaganovich and Yevgeny Raitses and M. Keidar and Hyo-Chang Lee and Mikhail Shneider and R. Car},
url = {https://arxiv.org/ftp/arxiv/papers/2007/2007.09199.pdf},
year = {2020},
date = {2020-07-17},
journal = {Community Planning Process for fusion energy},
abstract = {Note from the webmaster: This is "Goals of Initiative", not an abstract.

To initiate a national program in Low Temperature Plasma (LTP) to take advantage of the
research opportunities of 3 rapidly growing areas (nanomaterial plasma synthesis, plasma
medicine, microelectronics). The main theme is to achieve a fundamental understanding of
Low Temperature Plasmas as they are applied to these different applications. This
understanding will allow U.S. industry to meet the challenges of international competition. },
keywords = {},
pubstate = {forthcoming},
tppubtype = {article}
}

@article{Shneider2020,
title = {Dipole scattering of a short radiation pulse on hydrogen-like atoms},
author = {M. N. Shneider and V. V. Semak},
url = {https://pcrf.princeton.edu/osac-3-7-1819/},
doi = {10.1364/OSAC.399109},
year = {2020},
date = {2020-07-15},
journal = {OSA Continuum},
volume = {3},
number = {7},
abstract = {Our theoretical model of forced dipole oscillation demonstrates that when the
amplitude of the forcing field is changing fast, the oscillations of the bound electron in the atom
or molecule initially proceed at two frequencies: the frequency of the natural electron oscillations
and the frequency of the forcing field. Particularly, applied to the science of scattering, this
model of transient forced atomic and molecular oscillations suggests that accurate interpretation
of the laser scattering experiments using short laser pulses must include both the conventionally
known scattering at the laser frequency (Rayleigh) and the predicted by our theoretical spectral
emission that corresponds to the natural frequency of the electronic oscillations. This article
presents the results of numerical simulations using our model performed for the hydrogen atom.
The characteristics of the components of scattered radiation, their polarization, and Doppler
thermal broadening are discussed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Lan2020b,
title = {Neutralization of ion beam by electron injection: Accumulation of cold electrons},
author = {C. Lan and I. D. Kaganovich},
url = {http://aip.scitation.org/doi/pdf/10.1063/1.5128521},
doi = {10.1063/1.5128521},
year = {2020},
date = {2020-04-23},
journal = {Physics of Plasmas},
volume = {27},
number = {4},
abstract = {Ion beam charge neutralization by electron injection is a complex kinetic process. Recent experiments show that the resulting self-potential of the ion beam after neutralization by plasma is much lower than the temperature of plasma electrons [Stepanov et al., Phys. Plasmas 23, 043113 (2016)], indicating that kinetic effects are important and may affect the neutralization of the ion beam. We performed a numerical study of the charge neutralization process of an ion beam making use of a two-dimensional electrostatic particle-in-cell code. The results show that the process of charge neutralization by electron injection is composed of two stages. During the first stage, the self-potential of the beam is higher than the temperature of injected electrons (Te/e) and all injected electrons are captured by the ion beam. During the second stage, hot electrons escape from the ion beam and the beam self-potential (φ) decreases because cold electrons slowly accumulate resulting in the beam self-potential φ to become much lower than Te/e in agreement with previous experimental observations at Princeton Advanced Teststand. We also determined that the resulting φ scales as φ∼Te⎯⎯⎯⎯√, in agreement with previous experimental observations from Gabovich's group. In addition, the results show that the transverse position of the electron source has a great impact on ion beam neutralization. A slight shift of the electron source as relevant to the ion thrusters leads to a large increase in the beam self-potential because of an increase in potential energy of injected electrons.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Lan2020,
title = {Neutralization of ion beam by electron injection: Excitation and propagation of electrostatic solitary waves},
author = {C. Lan and I. D. Kaganovich},
url = {https://aip.scitation.org/doi/pdf/10.1063/1.5128523},
doi = {10.1063/1.5128523},
year = {2020},
date = {2020-04-10},
journal = {Physics of Plasmas},
volume = {27},
number = {4},
abstract = {The charge neutralization of an ion beam by electron injection is investigated using a two-dimensional electrostatic particle-in-cell code. The simulation results show that electrostatic solitary waves (ESWs) can be robustly generated in the neutralization process and last for a long time (for more than 30 μs) and therefore, ESWs can strongly affect the neutralization process. The ESWs propagate along the axis of the ion beam and reflect from the beam boundaries. The simulations clearly show that two ESWs can pass through each other with only small changes in amplitude. Partial exchange of trapped electrons in collisions of two ESWs is observed in the simulations and can explain interaction during collisions of two ESWs. Coalescence of two ESWs is also observed.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Galea2020,
title = {Coherent microwave scattering from xenon resonance-enhanced multiphoton ionization-initiated plasma in air},
author = {Christopher A. Galea and Mikhail N Shneider and Mark Gragston and Zhili Zhang},
url = {https://pcrf.princeton.edu/j-appl-phys-127-053301-2020/},
doi = {10.1063/1.5135316},
year = {2020},
date = {2020-02-04},
journal = {Journal of Applied Physics},
volume = {127},
number = {5},
abstract = {Here we present the experimental and computational study of resonance-enhanced multiphoton ionization (REMPI) of xenon and subsequent avalanche ionization of air. Xenon was excited from the ground state to the excited 6p state (89162cm−1) by two photons at 224.3 nm. The third photon at 224.3 nm subsequently produced ionization of xenon in air. The seed electrons from the ionization served as the medium to further absorb the laser pulse for the rotational and vibrational excitation and avalanche ionization of O2 and N2. Plasma chemistry of O2 and N2 in air was included in the model. The results are useful for understanding REMPI-initiated plasma in air and possibly new diagnostics tools based on REMPI-initiated plasma emissions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Sanchez2019,
title = {Relativistic Particle Beams as a Resource to Solve Outstanding Problems in Space Physics},
author = {Ennio R. Sanchez and Andrew T. Powis and Igor D. Kaganovich and Robert Marshall and Peter Porazik and Jay Johnson and Michael Greklek-Mckeon and Kailas S. Amin and David Shaw and Michael Nicolls},
url = {https://www.frontiersin.org/articles/10.3389/fspas.2019.00071/pdf},
doi = {10.3389/fspas.2019.00071},
year = {2019},
date = {2019-11-27},
journal = {Frontiers in Astronomy and Space Sciences},
volume = {6},
abstract = {The Sun's connection with the Earth's magnetic field and atmosphere is carried out through the exchange of electromagnetic and mass flux and is regulated by a complex interconnection of processes. During space weather events, solar flares or fast streams of solar atmosphere strongly disturb the Earth's environment. Often the electric currents that connect the different parts of the Sun-Earth system become unstable and explosively release the stored electromagnetic energy in one of the more dramatic expressions of space weather ─ the auroral storm and substorm. Some aspects of the magnetosphere-ionosphere connection that generates auroral arcs during space weather events are well-known. However, several fundamental problems remain unsolved because of the lack of unambiguous identification of the magnetic field connection between the magnetosphere and the ionosphere. The correct mapping between different regions of the magnetosphere and their foot-points in the ionosphere, coupled with appropriate distributed measurements of plasma and fields in focused regions of the magnetosphere, is necessary to establish unambiguously that a given magnetospheric process is the generator of an observed arc. The three most important problems for which the correct magnetic field mapping would provide closure to are the substorm growth phase arcs, the expansion phase onset arcs and the system of arcs that emerge from the magnetosphere-ionosphere connection during the development of the early substorm expansion phase phenomenon known as substorm current wedge (SCW). Energetic electron beams, used as magnetic field tracers, can enable the closure needed. However, the application of beams as tracers require demonstration that the beams can be injected into the loss cone, that the spacecraft potentials induced by the beam emission are manageable, and that sufficient electron flux reaches the atmosphere to be detectable by optical or radio means after the beam has propagated thousands of kilometers under competing effects of beam spread and constriction as well as effects of beam-induced instabilities. In this communication we provide a review of the latest results of synergistic research carried out under the NSF INSPIRE program to address these challenges and discuss the next steps toward the realization of active experiments in space using relativistic electron beams.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}