Hasil untuk "Plasma physics. Ionized gases"

A. Fridman, L. Kennedy

PART 1. FUNDAMENTALS OF PLASMA PHYSICS AND PLASMA CHEMISTRY. CHAPTER 1. Introduction CHAPTER 2. ELEMENTARY PROCESSES OF CHARGED SPECIES IN PLASMA. 2.1. Elementary Charged Particles In Plasma, And Their Elastic And Inelastic Collisions. 2.2. Ionization Processes. 2.3. Mechanisms Of Electron Losses: The Electron-Ion Recombination. 2.4. The Electron Losses Due To Formation Of Negative Ions: Electron Attachment And Detachment Processes. 2.5. The Ion-Ion Recombination Processes. 2.6. The Ion-Molecular Reactions. 2.7. Problems and Concept Questions. CHAPTER 3. ELEMENTARY PROCESSES OF EXCITED MOLECULES AND ATOMS IN PLASMA. 3.1. Electronically Excited Atoms And Molecules In Plasma. 3.2. Vibrationally And Rotationally Excited Molecules. 3.3. Elementary Processes Of Vibrational, Rotational And Electronic Excitation Of Molecules In Plasma. 3.4. Vibrational (VT) Relaxation, Landau-Teller Formula. 3.5. Vibrational Energy Transfer Between Molecules, VV-Relaxation Processes. 3.6. Processes Of Rotational And Electronic Relaxation Of Excited Molecules. 3.7. Elementary Chemical Reactions Of Excited Molecules, Fridman - Macheret a-Model. 3.8. Problems and Concept Questions. CHAPTER 4. PLASMA STATISTICS AND KINETICS OF CHARGED PARTICLES. 4.1. Statistics And Thermodynamics Of Equilibrium And Non-Equilibrium Plasmas, The Boltzmann, Saha And Treanor Distributions. 4.2. The Boltzmann And Fokker-Planck Kinetic Equations, Electron Energy Distribution Functions. 4.3. Electric And Thermal Conductivity In Plasma, Diffusion Of Charged Particles. 4.4. Breakdown Phenomena: The Townsend And Spark Mechanisms, Avalanches, Streamers And Leaders. 4.5. Steady-State Regimes Of Non-Equilibrium Electric Discharges. 4.6. Problems and Concept Questions. CHAPTER 5. KINETICS OF EXCITED PARTICLES IN PLASMA. 5.1.Vibrational Distribution Functions In Non-Equilibrium Plasma, The Fokker-Planck Kinetic Equation. 5.2. Non-Equilibrium Vibrational Kinetics: eV-Processes, Polyatomic Molecules, Non-Steady-State Regimes. 5.3. Macrokinetics Of Chemical Reactions And Relaxation Of Vibrationally Excited Molecules. 5.4. Vibrational Kinetics In Gas Mixtures, Isotopic Effect In Plasma Chemistry. 5.5. Kinetics Of Electronically And Rotationally Excited States, Non-Equilibrium Translational Distributions, Relaxation And Reactions Of Hot Atoms In Plasma. 5.6. Energy Efficiency, Energy Balance And Macrokinetics Of Plasma-Chemical Processes. 5.7. Energy Efficiency Of Quasi-Equilibrium Plasma-Chemical Systems, Absolute, Ideal And Super-Ideal Quenching. 5.8. Problems and Concept Questions. CHAPTER 6. ELECTROSTATICS, ELECTRODYNAMICS AND FLUID MECHANICS OF PLASMA. 6.1. Electrostatic Plasma Phenomena: Debye-Radius And Sheaths, Plasma Oscillations And Plasma Frequency. 6.2. Magneto-Hydrodynamics Of Plasma. 6.3. Instabilities Of Low Temperature Plasma. 6.4. Non-Thermal Plasma Fluid Mechanics In Fast Subsonic And Supersonic Flows. 6.5. Electrostatic, Magneto-Hydrodynamic And Acoustic Waves In Plasma. 6.6. Propagation Of Electro-Magnetic Waves In Plasma. 6.7. Emission And Absorption Of Radiation In Plasma, Continuous Spectrum. 6.8. Spectral Line Radiation In Plasma. 6.9. Non-Linear Phenomena In Plasma. 6.10. Problems and Concept Questions. PART 2. PHYSICS AND ENGINEERING OF ELECTRIC DISCHARGES. CHAPTER 7. GLOW DISCHARGE. 7.1. Structure And Physical Parameters Of Glow Discharge Plasma. Current-Voltage Characteristics, Comparison Of Glow And Dark Discharges. 7.2. Cathode And Anode Layers Of A Glow Discharge. 7.3. Positive Column Of Glow Discharge. 7.4. Glow Discharge Instabilities. 7.5. Different Specific Glow Discharge Plasma Sources. 7.6. Problems and Concept Questions. CHAPTER 8. ARC DISCHARGES. 8.1. Physical Features, Types, Parameters And Current-Voltage Characteristics Of Arc Discharges. 8.2. Mechanisms Of Electron Emission From Cathode. 8.3. Cathode And Anode Layers In Arc Discharges. 8.4. Positive Column Of Arc Discharges. 8.5. Different Configurations Of Arc Discharges. 8.6. Gliding Arc Discharge. 8.7. Problems and Concept Questions. CHAPTER 9. NON-EQUILIBRIUM COLD ATMOSPHERIC PRESSURE PLASMAS: CORONA, DIELECTRIC BARRIER AND SPARK DISCHARGES. 9.1. The Continuous Corona Discharge. 9.2. The Pulsed Corona Discharge. 9.3. Dielectric-Barrier Discharge. 9.4. Spark Discharges. 9.5. Problems and Concept Questions. CHAPTER 10. PLASMA CREATED IN HIGH FREQUENCY ELECTROMAGNETIC FIELDS: RADIO-FREQUENCY (RF), MICROWAVE AND OPTICAL DISCHARGES. 10.1. Radio-Frequency (RF) Discharges At High Pressures, Inductively Coupled Thermal RF Discharges. 10.2. Thermal Plasma Generation In Microwave And Optical Discharges. 10.3. Non-Equilibrium Radio-Frequency (RF) Discharges, General Features Of Non-Thermal Capacitively-Coupled (CCP) Discharges. 10.4. Non-Thermal Capacitively-Coupled (CCP) Discharges Of Moderate Pressure. 10.5. Low Pressure Capacitively-Coupled RF Discharges. 10.6. Asymmetric, Magnetron And Other Special Forms Of Low Pressure Capacitive RF-Discharges. 10.7. Non-Thermal Inductively-Coupled (ICP) Discharges. 10.8. Non-Thermal Low-Pressure Microwave And Other Wave-Heated Discharges. 10.9. Non-Equilibrium Microwave Discharges Of Moderate-Pressure. 10.10. Problems and Concept Questions. CHAPTER 11. DISCHARGES IN AEROSOLS, DUSTY PLASMAS. 11.1. Photo-Ionization Of Aerosols. 11.2.Thermal Ionization Of Aerosols. 11.3. Electric Breakdown Of Aerosols. 11.4. Steady-State Dc Electric Discharge In Heterogeneous Medium. 11.5. Dusty Plasma Formation, Evolution Of Nano-Particles In Plasma. 11.6. Critical Phenomena In Dusty Plasma Kinetics. 11.7. Non-Equilibrium Clusterization In Centrifugal Field. 11.8. Dusty Plasma Structures: Phase Transitions, Coulomb Crystals, Special Oscillations. 11.9. Problems and Concept Questions. CHAPTER 12. ELECTRON BEAM PLASMAS. 12.1.Generation And Properties Of Electron-Beam Plasmas. 12.2. Kinetics Of Degradation Processes, Degradation Spectrum. 12.3. Plasma-Beam Discharge. 12.4. Non-Equilibrium High-Pressure Discharges Sustained By High-Energy Electron Beams. 12.5. Plasma In Tracks Of Nuclear Fission Fragments, Plasma Radiolysis. 12.6. Dusty Plasma Generation By A Relativistic Electron Beam. 12.7. Problems and Concept Questions.

L. Spitzer

D. E. Kerr

Joel G. Rogers, Andrew A. Egly, Yoon S. Roh et al.

In this study, particle-in-cell (PIC) simulation was used to validate a conceptual design for a quasi-spherical, net power, hydrogen-plus-boron-11-fueled fusion reactor incorporating high-temperature superconducting (HTS) magnets. By burning a fully thermalized plasma, our proposed MET6 reactor uses the principles of the 1980 magneto-electrostatic trap design of Yushmanov to improve the classic Polywell design. Because the input power consumed by the reactor will barely balance the waste bremsstrahlung radiation, future research must focus on reducing the bremsstrahlung losses to reach practical net power levels. The first step to reducing bremsstrahlung, explored in this paper, is to tune the reactor parameters to reduce the energies of trapped electrons. We assume the quality factor Q can be approximated as the ratio of fusion power output divided by bremsstrahlung power loss. Thus, assuming the particles’ power loss is negligible compared to bremsstrahlung power loss, the resulting quality factor is estimated to be Q ≈ 1.3.

Richard Morrow

An implicit flux-corrected transport (FCT) and diffusion algorithm was developed and used in many gas discharge calculations. Such calculations require the use of a fine mesh where the electric field changes rapidly; that is, near electrodes or in a streamer front. If diffusion is included using an explicit method, then the von Neumann stability condition severely limits the time-step that can be used; however, this limitation does not apply to implicit methods. Further, for gas discharge calculations including space-charge effects, it is necessary to solve the continuity equations with no negative number densities nor point-by-point oscillation in the number density. This is because the electron number densities are finely balanced with the ion number densities to determine the space-charge distribution and hence the electric field which drives the motion of the particles. An efficient way to solve the particle transport equation, with the required properties, is to use FCT. The most accurate form of FCT developed by the author is implicit fourth-order FCT; hence, the method presented incorporates implicit diffusion into the implicit fourth-order FCT scheme to produce a robust algorithm that has been successfully used in many calculations.

Katherine A. Schreiber, Katrina E. Koehler, Katrina E. Koehler et al.

Ultra-high energy resolution microcalorimeter gamma-ray spectroscopy—with energy resolution 5 to 10 times better than observed in spectra obtained by commercial-off-the-shelf high purity germanium detectors—is an enabling technology for ultra-precise isotope identification and quantification. Microcalorimeter gamma spectroscopy complements measurements requiring high-accuracy mass spectrometry, a costly, destructive analysis technique, and may offer benefits over mass spectrometry in the future. Microcalorimeter detectors are fabricated from superconducting materials and operate at ultra-low temperatures (<0.1 K), properties which permit measurement of spectra with peak full width half maximum (FWHM) of less than 100 eV at 100 keV. The microcalorimeter collaboration between Los Alamos National Laboratory, National Institute of Standards and Technology, and University of Colorado, Boulder has deployed three microcalorimeter gamma-ray spectrometers to nuclear facilities and analytical laboratories so far. These are the Spectrometer Optimized for Facility Integrated Applications (SOFIA), a portable system that can be moved to any facility, and two instruments called the High Efficiency and Resolution Microcalorimeter Spectrometers (HERMES) intended for permanent installation at Idaho National Laboratory and Pacific Northwest National Laboratory. Each spectrometer was customized to satisfy requirements for their specific applications. This work describes samples examined by microcalorimeter gamma-ray spectrometers, including recently irradiated materials, nuclear material from various stages of the fuel cycle, and medical isotope products. It also highlights useful signatures from actinide and fission product gamma-rays that are otherwise infeasible to observe or use for analysis without costly chemical separations and mass spectrometric assay. Microcalorimeter technology provides additional spectral signatures to existing techniques to better constrain the origin and intended use of nuclear and radioactive materials.

Luke R. Sadergaski, Robert J. Lascola, Kyle C. Hartig

Nicolas Bente, Alfredo Cuellar Valencia, Hubert Piquet

A system-level study of a NO_x abatement process by means of non-thermal plasma (NTP) generated with dielectric barrier discharges (DBDs) is the framework of this article. With the goal of system improvement, the kinetic reaction simulation software ZdPlaskin is considered to select the most favorable operating conditions in order to optimize NO_x abatement (deNO_x). A parametric exploration of the performance, through variations in operating conditions (temperature, power injection pattern, and input gas mixture composition), requires highly numerous simulations; thus, the shortest possible computation times with robust results are of significant interest. As such, an analysis and filtering method is proposed and detailed to build a minimized chemical kinetic reaction set, allowing us to reliably analyze the impact of the selected operating conditions for the DBD reactor on treatment performance.

Isao Murata, Alexander Winkler, Fuminobu Sato

Jonmoni Dutta, Ahmed Atteya, Pralay Kumar Karmakar

The presence of diverse negative ions is well-known to modify different collective waves and instabilities in diverse space and astrophysical environments. We herein investigate the stability dynamics of the spherical nonthermal (kappa-modified) pulsational mode of gravitational collapse (PMGC) excitable in astrophysical dust molecular clouds (DMCs). It primarily explores the impact of the realistic nonthermal negative ionic effects on the PMGC stability features. The high-energetic lighter constituents, such as the electrons, positive ions, and negative ions, are modelled with their respective nonthermal kappa (κ)-distribution laws. The inertial dust particulates are treated in the viscous fluid fabric. Application of spherical normal mode treatment results in a generalized linear quartic (degree-4) dispersion relation. A computational illustrative platform illuminates the underlying stabilizing and destabilizing factors. It is seen that the cloud size, dust mass, dust charge, nonthermality parameters, equilibrium charged dust number density, and neutral dust viscosity play stabilizing roles. It counters the destabilizing scenarios caused by the equilibrium electron number density, positive ion number density, negative ion number density, neutral dust density, and charged dust viscosity. The fundamental physical mechanisms responsible herein are substantiated and compared in light of the previous predictions. The nontrivial avenues of our study in realizing the Jeans-driven galactic structural unit formation processes, moderated actively with the presence of negative ions in diverse real astronomical circumstances are summarily indicated.

Stuart Reyes, Shirshak Kumar Dhali

Some of the popular and successful atmospheric pressure fuel/air plasma-assisted combustion methods use repetitive ns pulsed discharges and dielectric-barrier discharges. The transient phase in such discharges is dominated by transport under strong space charge from ionization fronts, which is best characterized by the streamer model. The role of the nonthermal plasma in such discharges is to produce radicals, which accelerates the chemical conversion reaction leading to temperature rise and ignition. Therefore, the characterization of the streamer and its energy partitioning is essential to develop a predictive model. We examine the important characteristics of streamers that influence combustion and develop some macroscopic parameters. Our results show that the radicals’ production efficiency at an applied field is nearly independent of time and the radical density generated depends only on the electrical energy density coupled to the plasma. We compare the results of the streamer model to the zero-dimensional uniform field Townsend-like discharge, and our results show a significant difference. The results concerning the influence of energy density and repetition rate on the ignition of a hydrogen/air fuel mixture are presented.

Zhigang Pu, Kun Xu

The Unified Gas-Kinetic Wave-Particle (UGKWP) method is constructed for partially ionized plasma (PIP). This method possesses both multiscale and unified preserving (UP) properties. The multiscale property allows the method to capture a wide range of plasma physics, from the particle transport in the kinetic regime to the two-fluid and magnetohydrodynamics (MHD) in the near continuum regimes, with the variation of local cell Knudsen number and normalized Larmor radius.The unified preserving property ensures that the numerical time step is not limited by the particle collision time in the continuum regime for the capturing of dissipative macroscopic solutions of the resistivity, Hall-effect, and all the way to the ideal MHD equations.The UGKWP is clearly distinguishable from the classical single scale Particle-in-Cell/Monte Carlo Collision (PIC/MCC) methods.The UGKWP method combines the evolution of microscopic velocity distribution with the evolution of macroscopic mean field quantities, granting it UP properties. Moreover, the time step in UGKWP is not constrained by the plasma cyclotron period through the Crank-Nicolson scheme for fluid and electromagnetic field interactions. The momentum and energy exchange between different species is approximated by the Andries-Aoki-Perthame (AAP) model. Overall, the UGKWP method enables a smooth transition from the PIC method in the rarefied regime to the MHD solvers in the continuum regime. This method has been extensively tested on a variety of phenomena ranging from kinetic Landau damping to the macroscopic flow problems, such as the Brio-Wu shock tube, Orszag-Tang vortex, and Geospace Environmental Modeling (GEM) magnetic reconnection. These tests demonstrate that the proposed method can capture the fundamental features of PIP across different scales seamlessly.

Luke R. Sadergaski, Jeffrey D. Einkauf, Laetitia H. Delmau et al.

Partial least squares regression (PLSR) and support vector regression (SVR) models were optimized for the quantification of U(VI) (10–320 g L−1) and HNO3 (0.6–6 M) by Raman spectroscopy with optimized calibration sets chosen by optimal design of experiments. The designed approach effectively minimized the number of samples in the calibration set for PLSR and SVR by selecting sample concentrations with a quadratic process model, despite complex confounding and covarying spectral features in the spectra. The top PLS2 model resulted in percent root mean square errors of prediction for U(VI), HNO3, and NO3− of 3.7%, 3.6%, and 2.9%, respectively. PLS1 models performed similarly despite modeling an analyte with a majority linear response (i.e., uranyl symmetric stretch) and another with more covarying vibrational modes (i.e., HNO3). Partial least squares (PLS) model loadings and regression coefficients were evaluated to better understand the relationship between weaker Raman bands and covarying spectral features. Support vector machine models outperformed PLS1 models, resulting in percent root mean square error of prediction values for U(VI) and HNO3 of 1.5% and 3.1%, respectively. The optimal nonlinear SVR model was trained using a similar number of samples (11) compared with the PLSR model, even though PLS is a linear modeling approach. The generic D-optimal design presented in this work provides a robust statistical framework for selecting training set samples in disparate two-factor systems. This approach reinforces Raman spectroscopy for the quantification of species relevant to the nuclear fuel cycle and provides a robust chemometric modeling approach to bolster online monitoring in challenging process environments.

Y. Qiu

Geant4 offers constructive solid geometry (CSG) for modeling detector geometries, but representing intricate computer-aided design (CAD) structures can be cumbersome. This article presents a novel approach that overcomes this limitation. A new CSG solid type called “half-space solid” enables the equivalent representation of complex CAD solids within Geant4. An automatic program utilizes optimized decomposition algorithms to convert CAD solids into half-space solids. The geometry description markup language (GDML) has been extended to accommodate the half-space solid type alongside the development of interfaces for exporting converted geometries and their subsequent import into Geant4. These advancements establish a fully automated workflow for converting CAD geometries into CSG-based representations suitable for Geant4 simulations. The reliability of the half-space solid-based modeling approach has been verified through comparisons with established Geant4 solids for both simple shapes and a complex fusion reactor model. The excellent agreement obtained from these comparisons demonstrates the efficiency of this new approach.

Mobish A. Shaji, Mikaela J. Surace, Alexander Rabinovich et al.

Per-and Polyfluoroalkyl substances (PFASs) are recalcitrant organofluorine contaminants, which demand urgent attention due to their bioaccumulation potential and associated health risks. While numerous current treatments technologies, including certain plasma-based treatments, can degrade PFASs, their complete destruction or mineralization is seldom achieved. Extensive aqueous PFAS mineralization capability coupled with industrial-level scaling potential makes gliding arc plasma (GAP) discharges an interesting and promising technology in PFAS mitigation. In this study, the effects of GAP discharge’s thermal and reactive properties on aqueous perfluorooctanesulfonic acid (PFOS) mineralization were investigated. Treatments were conducted with air and nitrogen GAP discharges at different plasma gas temperatures to investigate the effects of plasma thermal environment on PFOS mineralization; the results show that treatments with increased plasma gas temperatures lead to increased PFOS mineralization, and discharges in air were able to mineralize PFOS at relatively lower plasma gas temperatures compared to discharges in nitrogen. Studies were conducted to identify if GAP-based PFOS mineralization is a pure thermal process or if plasma reactive chemistry also affects PFOS mineralization. This was done by comparing the effects of thermal environments with and without plasma species (air discharge and air heated to plasma gas temperatures) on PFOS mineralization; the results show that while GAP discharge was able to mineralize PFOS, equivalent temperature air without plasma did not lead to PFOS mineralization. Finally, mineralization during treatments with GAP discharges in argon and air at similar gas temperatures were compared to investigate the role of plasma species in PFOS mineralization. The results demonstrate that treatments with argon (monoatomic gas with higher ionization) lead to increased PFOS mineralization compared to treatments with air (molecular gas with lower ionization), showing the participation of reactive species in PFOS mineralization.

Shirshak Kumar Dhali

In the transient phase of an atmospheric pressure discharge, the avalanche turns into a streamer discharge with time. Hydrodynamic fluid models are frequently used to describe the formation and propagation of streamers, where charge particle transport is dominated by the creation of space charge. The required electron transport data and rate coefficients for the fluid model are parameterized using the local mean energy approximation (LMEA) and the local field approximation (LFA). In atmospheric pressure applications, the excited species produced in the electrical discharge determine the subsequent conversion chemistry. We performed the fluid model simulation of streamers in nitrogen gas at atmospheric pressure using three different parametrizations for transport and electron excitation rate data. We present the spatial and temporal development of several macroscopic properties such as electron density and energy, and the electric field during the transient phase. The species production efficiency, which is important to understand the efficacy of any application of non-thermal plasmas, is also obtained for the three different parametrizations. Our results suggest that at atmospheric pressure, all three schemes predicted essentially the same macroscopic properties. Therefore, a lower-order method such as LFA, which does not require the solution of the energy conservation equation, should be adequate to determine streamer macroscopic properties to inform most plasma-assisted applications of nitrogen-containing gases at atmospheric pressure.

Mangaljit Singh, Muhammad Ashiq Fareed, Ramin Ghahri Shirinabadi et al.

High-order harmonic generation is a nonlinear optical frequency conversion process that occurs during intense ultrafast laser-matter interaction. At the Advanced Laser Light Source laboratory, we use ultrafast laser pulses having diverse wavelengths, spanning visible, near- and mid-infrared ranges, to generate high-order harmonics from laser-ablated plumes in the extreme ultraviolet or soft X-ray region of the electromagnetic spectrum. The Advanced Laser Light Source Laboratory is situated within the Énergie Matériaux Télécommunications Center of the Institut national de la recherche scientifique in Montréal, Quebec, Canada. We focus on generating bright and broadband harmonics by exploiting various types of ultrafast resonances in different species within the laser-ablated plume, and use them for applications in ultrafast spectroscopy, imaging, and AMO science. We are also actively exploring previously unknown physics governing the harmonic generation from different resonances. In this review article, we provide an overview of the recent advancements made in these directions.

N. Dianne Bull Ezell

NASA and the Department of Defense are planning for a mission to Mars in the 2030s–2040s using nuclear thermal propulsion (NTP). NTP uses a nuclear reactor to heat flowing hydrogen and create thrust. A serious concern for crewed and uncrewed missions to Mars is the loss of reactor control. The reactor startup and initial rocket impulse are initiated in cislunar or near-earth orbital regions; therefore, radio communications between ground control and the NTP engine should occur in real time. However, radio communications can take more than 20 min, depending on planet positions, to reach Mars orbiters from ground control. To address this delay, local autonomous controls are implemented onboard the NTP engine to ensure acceptable operation. However, autonomous controls have not been demonstrated or implemented in research or power reactor contexts because of safety and reliability concerns. To enable autonomous controls development, demonstration, and validation, Oak Ridge National Laboratory has created a nonnuclear hardware-in-the-loop test bed. Sensors throughout the test bed relay system status and hardware response to the user control algorithm, including measurements of temperature, flow, pressure of a loop, control drum position, and drum speed. This paper discusses the development of this facility and user accessibility.

Z. Pu, Chang Liu, K. Xu

Most plasmas are only partially ionized. To better understand the dynamics of these plasmas, the behaviors of a mixture of neutral species and plasma in ideal magnetohydrodynamic states are investigated. The current approach is about the construction of coupled kinetic models for the neutral gas, electron, and proton, and the development of the corresponding gas-kinetic scheme (GKS) for the solution in the continuum flow regime. The scheme is validated in the 1D Riemann problem for an enlarged system with the interaction from the Euler waves of the neutral gas and magnetohydrodynamic ones of the plasma. Additionally, the Orszag-Tang vortex problem across different ionized states is tested to examine the influence of neutrals on the MHD wave evolution. These tests demonstrate that the proposed scheme can capture the fundamental features of ideal partially ionized plasma, and a transition in the wave structure from the ideal MHD solution of the fully ionized plasma to the Euler solution of the neutral gas is obtained.

J. Watrous, David Seidel, Christopher Moore et al.

Problems of frequent interest in the application of SNL's multiphysics plasma modeling code, EMPIRE, involve intense electron flows in an environment that includes a background gas. Collisional ionization of the background gas can lead to rapid increases in the particle population. This can occur on a timescale and with an intensity that can result in extreme performance degradation even in the presence of sophisticated parallization capabilities. An approach to dealing with phenomena of this sort is to replace a specific subset of macroparticles, such as that which resulted from the ionization avalanche, with a set that contains significantly fewer macroparticles, yet conserves essential aspects of the original particle distribution. Algorithms that perform this task are referred to as merge algorithms.