@article{Zhang2021,

title = {Electron generation and multiplication at the initial stage of nanosecond breakdown in water},

author = {Xuewei Zhange and Mikhail N. Schneider},

url = {https://pcrf.princeton.edu/j-appl-phys-129-103302-2021water-2/},

doi = {10.1063/5.0044415},

year  = {2021},

date = {2021-03-09},

journal = {J. Appl. Phys.},

volume = {129},

number = {103302},

abstract = {Electrical breakdown of liquid dielectrics under nanosecond pulsed high voltage has been investigated extensively in the last decade.

Prior studies have focused on either experimental characterization of the breakdown process and discharge plasma or formulation/verification

of the electrostrictive cavitation mechanism of the breakdown initiation. There remain knowledge gaps toward a clear physical picture of how

the first plasma is generated in a region saturated by nanoscale cavities created by electrostrictive forces in inhomogeneous fields at the nanosecond

timescale. Initial plasma results from the multiplication of primary electrons that gain energy collisionlessly in the cavities to cause collisional

ionization of water molecules on the cavity walls. This paper quantitatively discusses the possible sources of primary electrons that seed

the plasma discharge. Electron detachment from hydroxide is shown to be the most probable and sustainable electron source. Using numerical

modeling, this study demonstrates the plausibility of an electron multiplication mechanism involving two neighboring cavities. The drift of

hydrated electrons from one cavity to the next is the rate-limiting step and sets the minimum electric field requirement. This work will inform

subsequent experimental studies and have implications in various applications such as plasma sources in biomedical applications, cavitation

study, and insulation of pulsed power equipment.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gershman2021,

title = {A low power flexible dielectric barrier discharge disinfects surfaces and improves the action of hydrogen peroxide},

author = {S. Gershman and M. B. Harreguy and S. Yatom and Y. Raitses and P. Efthimion and G. Haspel},

url = {https://www.nature.com/articles/s41598-021-84086-z.pdf},

doi = {https://doi.org/10.1038/s41598-021-84086-z},

year  = {2021},

date = {2021-02-25},

journal = {Scientific Reports},

volume = {11},

number = {4626},

abstract = {There is an urgent need for disinfection and sterilization devices accessible to the public that can be fulfilled by innovative strategies for using cold atmospheric pressure plasmas. Here, we demonstrate a successful novel combination of a flexible printed circuit design of a dielectric barrier discharge (flex-DBD) with an environmentally safe chemical reagent for surface decontamination from bacterial contaminants. Flex-DBD operates in ambient air, atmospheric pressure, and room temperature without any additional gas flow at a power density not exceeding 0.5 W/cm2. The flex-DBD activation of a 3% hydrogen peroxide solution results in the reduction in the bacterial load of a surface contaminant of > 6log10 in 90 s, about 3log10 and 2log10 better than hydrogen peroxide alone or the flex-DBD alone, respectively, for the same treatment time. We propose that the synergy between plasma and hydrogen peroxide is based on the combined action of plasma-generated OH· radicals in the hydrogen peroxide solution and the reactive nitrogen species supplied by the plasma effluent. A scavenger method verified a significant increase in OH· concentration due to plasma treatment. Novel in-situ FTIR absorption spectra show the presence of O3, NO2, N2O, and other nitrogen species. Ozone dissolving in the H2O2 solution can effectively generate OH· through a peroxone process. The addition of the reactive nitrogen species increases the disinfection efficiency of the hydroxyl radicals and other oxygen species. Hence, plasma activation of a low concentration hydrogen peroxide solution, using a hand-held flexible DBD device results in a dramatic improvement in disinfection.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zhao2021,

title = {High hydrogen coverage on graphene via low temperature plasma with applied magnetic field},

author = {F. Zhao and Y. Raitses and X. Yang and A. Tan and C. G. Tully},

url = {https://www.sciencedirect.com/science/article/pii/S0008622321002773/pdfft?isDTMRedir=true&download=true},

doi = {https://doi.org/10.1016/j.carbon.2021.02.084},

year  = {2021},

date = {2021-02-22},

journal = {Carbon},

volume = {117},

pages = {244-251},

abstract = {The chemical functionalization of two-dimensional materials is an effective method for tailoring their chemical and electronic properties with encouraging applications in energy, catalysis, and electronics. One exemplary 2D material with remarkable properties, graphene, can be exploited for hydrogen storage and large on/off ratio devices by hydrogen termination. In this work, we describe a promising plasma- based method to provide high hydrogen coverage on graphene. A low pressure (~10 mtorr) discharge generates a fine-tunable low-temperature hydrogen-rich plasma in the applied radial electric and axial magnetic fields. Post-run characterization of these samples using Raman spectroscopy and X-ray photoelectron spectroscopy demonstrates a higher hydrogen coverage, 35.8%, than the previously re- ported results using plasmas. Plasma measurements indicate that with the applied magnetic field, the density of hydrogen atoms can be more than 10 times larger than the density without the magnetic field. With the applied electric field directed away from the graphene substrate, the flux of plasma ions to- wards this substrate and the ion energy are insufficient to cause measurable damage to the treated 2D material. The low damage allows a relatively long treatment time of the graphene samples that con- tributes to the high coverage obtained in these experiments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Shneider2021,

title = {Cavitation model of the inflationary stage of Big Bang},

author = {M. N. Shneider and M. Pekker},

url = {https://aip.scitation.org/doi/pdf/10.1063/5.0035458},

doi = {https://doi.org/10.1063/5.0035458},

year  = {2021},

date = {2021-01-25},

journal = {Phys. Fluids},

volume = {33},

number = {017116},

abstract = {In this paper, we propose a model for the initial stage of the development of the universe analogous to cavitation in a liquid in a negative pressure field. It is assumed that at the stage of inflation, multiple breaks of the metric occur with the formation of areas of physical vacuum in which the generation of matter occurs. The proposed model explains the large-scale isotropy of the universe without ultrafast inflationary expansion and the emergence of a large-scale cellular (cluster) structure, as a result of the development of cavitation ruptures of a false vacuum. It is shown that the cavitation model can be considered on par with (or as an alternative to) the generally accepted inflationary multiverse model of the Big Bang.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Starikovskiy2021,

title = {Simulation of decelerating streamers in inhomogeneous atmosphere with implications for runaway electron generation},

author = {A. Yu. Starikovskiy and N. L. Aleksandrov and M. N. Shneider},

url = {https://scholar.google.com/scholar_url?url=https://aip.scitation.org/doi/pdf/10.1063/5.0037669&hl=en&sa=T&oi=ucasa&ct=usl&ei=OsE_YNXjCMnJsQK99J7gAw&scisig=AAGBfm2GutV3f5blVsHClApv2itx6BXblg},

doi = { https://doi.org/10.1063/5.0037669},

year  = {2021},

date = {2021-01-22},

journal = {J. Appl. Phys.},

volume = {129},

number = {063301},

abstract = {The dynamics of positive and negative streamers is numerically simulated in atmospheric pressure air in the range of parameters corresponding to the streamer deceleration and termination in the middle of the discharge gap. A detailed comparison with experiments in air at constant and variable density demonstrates good agreement between the 2D simulation results and the observations. It is shown that positive and negative streamers behave in radically different ways when decelerating and stopping. When the head potential drops, the negative streamer transits to the mode in which the propagation is due to the forward electron drift. In this case, the radius of the ionization wave front increases, whereas the electric field at the streamer head decreases further and the streamer stops. Its head diameter continues to increase due to the slow drift of free electrons in the residual under-breakdown field. On the contrary, the only advancement mechanism for a positive streamer with a decreasing head potential is a decrease in the effective radius of the ionization wave, leading to a local increase in the electric field. This mechanism makes it possible to compensate for the reduction in the efficiency of gas photoionization at small head diameters. A qualitative 1D model is suggested to describe streamer deceleration and stopping for different discharge polarities. Estimates show that, during positive streamer stopping, the local electric field at the streamer head can exceed the threshold corresponding to the transition of electrons to the runaway mode when the head potential (relative to the surrounding space) decreases to ∼1.2 kV in atmospheric pressure air. In this case, pulsed generation of a beam of runaway electrons directed into the channel of a stopping positive streamer can occur. The energy of the formed pulsed electron beam depends on the intensity of photoionization in front of the streamer head. This energy can vary from 700 V (when increasing the photoionization rate by a factor of 10 with respect to the value in atmospheric pressure air) to 2.6 kV (when decreasing the photoionization rate by a factor of 1000). It is possible that this behavior of decelerating positive streamers can explain the observed bursts of x-ray radiation during the streamer propagation in long air gaps.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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{Efthimion2020,

title = {Critical Need for a National Initiative in Low Temperature Plasma Research},

author = {P. Efthimion and I. Kaganovich and Y. Raitses and M. Keidar and H. -C. Lee and M. 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 = {C. A. Galea and M. N. Shneider and M. Gragston and Z. 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}

}