A. Leigh Winfrey

Modeling of an Ablation-Free Electrothermal Plasma Pellet Accelerator

Abstract Electromagnetic and electrothermal launch devices can provide high acceleration and inject pellets with speeds in excess of 3 km/s for masses up to 3gm. However, the ablation of the bore adds impurities to the plasma. An ablation-free electrothermal pellet accelerator is a concept that utilizes an ablation-free capillary discharge in which a quartz capillary is coated with a nanocrystalline diamond film (NCD). The ablation-free capillary connects to an extension tube, which is also an ablation-free quartz tube coated with NCD that serves as the acceleration barrel. An ablation-free capillary discharge computer code has been developed to model plasma flow and acceleration of pellets for fusion fueling in magnetic fusion reactors. The code incorporates ideal and non-ideal conductivity models and has a set of governing equations for the capillary, the acceleration tube, and the pellet. The capillary generates the plasma from hydrogen/deuterium gas when the discharge current flows through the capillary. The pellet starts moving in the extension tube when the pressure of the plasma flow from the capillary reaches the release limit. The code results show an exit velocity of 2.7 km/s for a 20 mg deuterium pellet when using a capillary and barrel each 9 cm long where the source and barrel diameters are 0.4cm and 0.6cm, respectively, with a discharge current of 20 kA over a 300 both the capillary and the barrel to 12 cm increases the pellet exit velocity to 2.9 km/s, and a further increase to 18cm results in a 3.15km/s pellet exit velocity. Increasing the barrel length to 36 cm, while keeping the source length at 18 cm, results in an increase in the pellet velocity to 3.32 km/s. The pellet starts moving at 35 μs reaches 3.32 km/s in 100 this velocity until exiting the acceleration tube.

Study of High-Enthalpy Electrothermal Energetic Plasma Source Concept

The electrothermal (ET) energetic plasma source (ETEPS) is a different concept in which the ablation mechanism is forced inside of the open-ended capillary that has energetic liner, a propellant. The generation of the ET plasma results from Joule heating and radiant heat transport to the liner. The discharge initiates erosive burn of the propellant, and the mixed plasma-propellant gasification produces high-enthalpy energetic flow. In the ablation-dominated source, the eroded materials from the solid propellant liner are mixed inside the source before they flow out as a result of the large pressure gradient. The energetic ET source also has another concept in which no ablation occurs and the plasma is generated from the injection of energetic gasses or liquids into the confined open-ended capillary. The ablation-free source generates the plasma from the dissociation of the gaseous/liquid components, which in turn releases the chemical energy of these propellants and mixes the energy with the electrical energy of the plasma. This concept is different from ET chemical (ETC) sources; it generates the propellant or energetic flow without requiring a combustion chamber. It also provides mixing at the ionic level not available in current configurations of ETC launchers, igniters, or thrusters. The ET plasma code ETFLOW-EN was developed to computationally simulate the plasma generation and flow in energetic ET capillary discharges to predict the behavior of the energetic source with the use of lined solid propellants. Operation with liquid/gaseous energetic forms in a nonablative capillary is also a character of this concept and is part of the ETFLOW code. The results of using different forms of energetic materials in solid, liquid, and gaseous mixtures have shown the applicability of ETEPS to produce high-enthalpy energetic plasma flows with sufficient parameters suitable for ETC launch applications. Plasma and flow parameters at the capillary exit were investigated at different mixing ratios.

A comparative study of different low-z liner materials in an ablation-dominated electrothermal mass accelerator for fusion fueling

A low-z ablation-dominated capillary with an ablation-free extension barrel is a concept that provides a plasma flow sufficient to propel fuel pellets into the tokamak fusion plasma chamber. The acceleration barrel is made from a non-ablating material to eliminate mixing the propelling plasma with any impurities evolving from the barrel ablation.

Hyper Jet Focused-Injection Tapered Capillary Plasma Source Concept

The concept of tapered capillary is introduced as a method of injecting focused plasma jet into the breach of bulk-loaded electrothermal-chemical (ETC) launcher. Tapered capillaries will operate in the confined controlled arc regime, and they can provide the advantage of producing focused hyper plasma jets useful for ignition of ETC systems at controlled plasma temperatures and pressures. The concept is also useful for focused implantation of plasma ions on substrates with desired patterns. Such tapered capillaries can inject plasmas at peak kinetic temperatures in the range of 14000-21000 K (~1.2-1.8 eV) and considerable jet pressures of 10-70 MPa for an input discharge current of 20-30 kA over a short pulselength of 100-150 μs. A tapered geometry made of Lexan polycarbonate with 16.8-mm inlet and 8.8-mm outlet radii produces a plasma jet with a plasma temperature of 14253 K (1.23 eV) at a peak bulk velocity of 4.027 km/s with a 10.38-MPa exit pressure, and a total ablated mass of 10.56 mg. Reducing the tapering to 12.6-mm inlet and 6.6-mm outlet radii produces a plasma jet with a plasma temperature of 16382-K (1.411 eV) at a bulk velocity of 4.34 km/s and a total of 23.27-mg ablated mass. Further reduction in the tapering to 8.4-mm inlet and 4.4-mm outlet radii produces a plasma jet with a plasma temperature of 20954 K (1.8 eV) at a bulk velocity of 4.89 km/s with a 70.78-MPa exit pressure, and a total ablated mass of 15.09 mg. The preliminary study shows that the narrow tapering angle produces higher pressure, temperature, velocity, and more ablated mass. Radiant heat flux at the taper exit varies from 2.2 GW/m2 for the wider tapers to 6.24 GW/m2 for the narrower ones.

FEM Optimization of Energy Density in Tumor Hyperthermia Using Time-Dependent Magnetic Nanoparticle Power Dissipation

General principles are developed using a finite element model regarding how time-dependent power dissipation of magnetic nanoparticles can be used to optimize hyperthermia selectivity. To make the simulation more realistic, the finite size and spatial location of each individual nanoparticle is taken into consideration. When energy input into the system and duration of treatment is held constant, increasing the maximum power dissipation of nanoparticles increases concentrations of energy in the tumor. Furthermore, when the power dissipation of magnetic nanoparticles rises linearly, the temperature gradient on the edge of the tumor increases exponentially. With energy input held constant, the location and duration of maximum power dissipation in the treatment time scheme will affect the final energy concentration inside the tumor. Finally, connections are made between the simulation results and optimization of the design of nanoparticle power dissipation time-schemes for hyperthermia.

Modeling and Analysis of a Dual-Channel Plasma Torch in Pulsed Mode Operation for Industrial, Space, and Launch Applications

Dual-channel thermal plasma torch can operate with air, argon, or combustible gases to produce high-temperature plasma flow. This plasma torch can be used in various important applications such as metal industry recycling, surface coating and hardening, space operations using controlled thrust, and macroparticle acceleration based on the electrothermal nature of thermal torches and electrical-to-thermal energy conversion. Power for this torch is supplied from the electric mains and the voltage is stepped up to 6 kV. However, the torch can also operate on dc or pulsed mode. The electrical operation is characterized by the voltampere relationship to determine the power rating of the torch as well as diagnosing the dynamic behavior of the plasma. Experiments on the torch using air and argon have shown plasma temperatures in the range of 0.4-0.6 eV with plasma number density in the range of 1024-1025/m3, indicating a dense plasma regime with the plasma tends to be weakly nonideal. Plasma kinetic temperature and electron number density were obtained from optical emission spectroscopy using the relative line method as the plasma is near local thermodynamic equilibrium condition. Plasma temperature has its peak for low flow rates and decreases for increased flow rates. The torch modeling was conducted using an electrothermal plasma code to simulate and predict the parameters for pulsed mode operation. Simulation was conducted on a single channel as the dual torch is symmetric. Code results for extended pulselength show a plasma temperature between 0.6 and 0.8 eV for nitrogen, oxygen, and helium; which are in good correlation with plasma temperatures obtained from optical emission spectra and measured plasma resistivity. A set of computational experiments using short pulses at higher discharge currents has shown temperature in the range of 2.0-2.5 eV for nitrogen and helium.

Electrothermal energetic plasma source concept for high-enthalpy flow and electrothermal-chemical applications

The electrothermal energetic plasma source (ETEPS) is a new concept in which the ablative mechanism is forced inside of the capillary which has energetic liner, i.e. a chemical propellant. The generation of the electrothermal plasma results from Joule heating and radiant heat transport to the liner. The discharge initiates erosive burn of the propellant and the mixed plasma-propellant gasification produces high enthalpy energetic flow. In the ablation-dominated capillary discharge the eroded materials from the solid propellant liner are mixed inside the source before flowing out as a result of the large pressure gradient. The energetic electrothermal source may also be used in a regime where no ablation occurs, where the plasma is generated from the injection of energetic gasses or liquids into the confined capillary. The ablation-free source generates the plasma from the dissociation of the gaseous/liquid components, which in turn releases the chemical energy of these propellants and mixing the energy with the electrical energy of the plasma. This concept is different from electrothermal chemical sources; it generates the propellant or energetic flow without requiring a combustion chamber. It also provides mixing at the ionic level not available in current configurations of electrothermal chemical launchers, igniters, or thrusters. The electrothermal plasma code ETFLOW-EN was developed to computationally simulate the plasma generation and flow in energetic ET capillary discharges to predict the behavior of the energetic source with the use of lined solid propellants. Operation with liquid/gaseous energetic forms in a non-ablative capillary is also a character of this concept and is part of the ETFLOW code. Results of using different forms of energetic materials in solid, liquid and gaseous mixtures have shown the applicability of ETEPS to produce high enthalpy energetic plasma flows with sufficient parameters suitable for ETC launch applications.

Investigation of Geometry and Current Density Effects in a Pulsed Electrothermal Plasma Source Using a 2-D Simulation Model

Electrothermal (ET) plasma discharges have application to mass acceleration technologies relevant to military ballistics and magnetic confinement fusion reactor operation. ET plasma discharges are initiated in capillary geometries by passing large currents (order of tens of kiloamperes) along the capillary axis. A partially ionized plasma then forms and radiates heat to the capillary walls inducing ablation. Ablated particles enter the capillary plasma source and cause a pressure surge that can propel pellets to velocities exceeding 2 km/s. These devices present several advantages over other mass accelerator technologies due to their simple design and ability to achieve high projectile launch frequencies. In order to investigate the operation of ET plasma discharges in more detail than previously possible, a 2-D, multifluid model has been developed to simulate the plasma-fluid dynamics that develop in these devices during operation. In this paper, the 2-D simulation model is used to investigate the effect of source geometry and current density on discharge characteristics. Peak pressure and electric field magnitudes for pulsed discharge operation are shown to scale well with theoretical and empirical scaling laws for steady-state discharge operation. The pulse shape of the source internal pressure is shown to change significantly with increasing source radius. The behavior of other plasma parameters is investigated. In addition, observations of the departure from the ablation-controlled arc regime are presented. This analysis suggests that, for the current pulse length investigated, source radii higher than 4 mm require significantly more current density in order to produce sufficient ablation to stabilize the plasma discharge.

An electric field model developed for multi-physics plasma-fluid simulation for atmospheric dielectric barrier discharge actuators

Summary form only given. Immersed bodies such as struts and vanes in gas turbine flow systems will, except at the lowest of flow velocities, shed separated wakes. One means to mitigate this is through active flow control by the use of pulsed DC plasma actuation. A two-dimensional, plasma-fluid model and code, multi-PHysics Analysis of Fluid-plasma Numerical Integration algoRithm (PHAFNIR), that couples electrodynamics, plasma reaction kinetics, and fluid mechanics has been developed and validated extensively to experiment. Further, numerical verification has also been performed on this code.

Review of past, present, and future plasma models for electrothermal plasma discharge simulation

Summary form only given. Electrothermal (ET) plasma discharges have captured the interest of researchers due to their wide range of applicability. They have been investigated for their application to solid propellant ignition, electric propulsion, high heat flux experiments, and fusion fuel pellet injection. ET plasma discharges involve the passage of high currents (order of tens of kA) through narrow channels (usually millimeters in diameter and centimeters in length). The plasma arc that forms inside the discharge radiates heat to the channels walls and ablation is induced. The partially ionized plasma that results is then ejected into an exit chamber. The history of the simulation and modeling capabilities of ET plasma discharge devices is a history that spans nearly three decades. During this time, numerical models have progressed from 0D and steady state models to 2D and timedependent models. This progression has not been a steady progression, and recent studies have utilized 0D models even though 1D models are relatively prevalent. Semi-2D models have also been developed in an attempt to better understand the radial gradients inside ET plasma discharges. Twodimensional simulations of boundary layer flow inside ET plasma discharges have also been performed. More recently, fully-2D simulations of ET plasma discharges have appeared. In this work, a review of the history of the simulation and modeling capabilities of ET plasma discharges is presented. Some models are selected to discuss in detail. In addition, speculations are made regarding likely future models that will advance capabilities, enhance model consistency, and combine many of the fundamental physics involved inside these devices.