Bulletin of the American Physical Society
49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007; Orlando, Florida
Session BO5: Processing, Plasma Antennas, and Electric Propulsion |
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Chair: Igor Alexeff, University of Tennessee Room: Rosen Centre Hotel Salon 11/12 |
Monday, November 12, 2007 9:30AM - 9:42AM |
BO5.00001: Optimization of Extreme Ultra-Violet Emission from Laser-produced Tin Plasmas by Radiation Hydrodynamic Simulations Atsushi Sunahara, Akira Sasaki, Katsunobu Nishihara, Hirofumi Ueda, Tatsuya Aota, Shinsuke Fujioka, Michiteru Yamaura, Yoshinori Shimada, Hiroaki Nishimura, Noriaki Miyanaga, Yasukazu Izawa, Kunioki Mima Extreme Ultra-Violet (EUV) emission from laser-produced tin plasmas is a candidate for the light source used in lithography of the next generation semi-conductors. In order to simulate the EUV emission from laser-produced tin plasma, we have developed the radiation hydrodynamic code ``Star-1D'' and ``Star-2D,'' respectively. The calculated x-ray spectrum and EUV conversion efficiency from 1-D simulations qualitatively agree with experimental results. Calculated spectrum by 2-D code for the long scale length plasma is good agreement with experimentally measured results. Also, calculated density profiles are verified by the interferometry observations. We will show the optimized conditions and its physical interpretation for the high conversion efficiency and high power EUV light source. [Preview Abstract] |
Monday, November 12, 2007 9:42AM - 9:54AM |
BO5.00002: Role of inert gas in the low-temperature CVD nano-crystalline diamond process. Paresh Ray, Jelani Griffin We report a systematic investigation of the effect of different inert gases on chemical vapour deposition (CVD) of nano-crystalline diamond. \textit{In situ} optical emission measurement was employed to monitor the plasma chemistry, which possibly influences the film growth. Our result indicates that C$_{2}$ is not necessarily the key growth species for nano-crystalline diamond and we will demonstrate here that the nano-crystalline diamond film can be grown under conditions where the C$_{2}$ concentration is very small. Modelling results support the trend in number density changes for intermediate radicals with the volume percentage of argon variation for CH$_{4}$/H$_{2}$/Ar plasma. [Preview Abstract] |
Monday, November 12, 2007 9:54AM - 10:06AM |
BO5.00003: Electroluminescence of Carbon-Implanted Silicon Marcel Risch, Michael Bradley Silicon, being the staple semiconductor of integrated circuits and microchips, features an indirect band gap which limits its application in photonic devices. However, there is a large demand for an interface between electric circuits and optical circuits and therefore light-emitting silicon-compatible devices. A possible approach to enhance the room-temperature light properties of silicon is carbon ion implantation. We compute the absolute number of implanted ions using the Lieberman model for the ion current. Subsequently, SRIM calculations yield the concentration distribution, which has great influence on the emission spectrum. We produced Schottky diodes from the processed samples and found the most stable and efficient operation at a current density of about 2.5 A/cm$^{2}$. The observed electroluminescence, caused by compositional and structural disorder, appears orange-white to the eye. The discussed method has limitations for the quantum efficiency but shows some potential for cost-effective on-chip light emitting diodes (LED). [Preview Abstract] |
Monday, November 12, 2007 10:06AM - 10:18AM |
BO5.00004: Plasma Antenna Shielding Esmaeil Farshi, Igor Alexeff, Ted Anderson A method and calculation have been developed to protect space based antennas using plasma Frequency selective surfaces radom. The antennas we are trying to protect are currently metal but could be plasma. The scattering process of the electromagnetic waves has been investigated in a plasma antenna tube; this process is of self-important value from the point of view of studying wave propagation and absorption. When electromagnetic waves propagate in media with random inhomogeneities, there appear waves with frequencies and wave vectors which are different from the frequency and wave vector of the fundamental wave. Here, the so-called scattering process occurs. If the medium is spatially homogeneous but parameters defining its electromagnetic properties experience fluctuations, then scattering must occur on these fluctuations, the latter being random inhomogeneities. Induced charges and currents leading to radiating new scattered waves emerge in a medium under the influence of the fundamental wave, thereby initiating the appearance of scattered waves. However, within the linear approximation induced charges and currents in the homogeneous medium represent only the modification of wave propagation characteristics in a medium, as compared to vacuum, i.e., modification of the complex refractive index. The results may be generalized for physical understanding of the scattering process in plasma. [Preview Abstract] |
Monday, November 12, 2007 10:18AM - 10:30AM |
BO5.00005: Experimental Validation of a Hydromagnetic Rankine-Hugoniot Model for Pulsed Plasma Thrusters Flavio Poehlmann, Nicolas Gascon, Mark Cappelli The most commonly used model for the Pulsed Plasma Thruster (PPT) is based on an electric circuit analysis, which provides only little physical insight to the mechanism by which the discharge accelerates the propellant. We present a model for the acceleration mechanism in gas-fed PPTs that is derived from early work on coaxial plasma deflagration guns$^1$ and is based on an analogy to chemical combustion waves. More specifically, the Rankine-Hugoniot theory for detonations and deflagrations can be extended to include magnetohydrodynamics in plasmas. Equations have been derived for the exhaust velocity and a mode transition to the so-called plasma deflagration mode that was independently observed by several researchers$^{1,2}$ can be explained based on this model. Experimental data was taken at Stanford to verify the validity of the derived equations. \newline \newline $^{1}$Cheng, D.Y., ``Plasma Deflagration and the Properties of a Coaxial Plasma Deflagration Gun'', Nuclear Fusion 10, 1970 \newline $^{2}$Woodall, D.M., Len, L.K. ``Observation of current sheath transition from snowplow to deflagration'' J. Appl. Phys. 57 (3), Feb 1985 [Preview Abstract] |
Monday, November 12, 2007 10:30AM - 10:42AM |
BO5.00006: High Resolution Spectral Measurements of Electrical Propulsion Plasmas Murat Celik, Oleg Batishchev, Manuel Martinez-Sanchez Among various diagnostics methods in studying the EP thrusters' plasma, emission spectroscopy provides a non-invasive, fast and economical diagnostics allowing also the ability to access hard to reach locations. This study presents the spectral measurement results of SPT (BHT-200) and TAL (MHT-9) Hall Effect thrusters and mini-Helicon (mHTX@MIT) thruster plasmas. The measurements were conducted using a 750mm focal length spectrometer with a spectral resolution of up to $\sim $0.01 nm in the UV-VIS-NIR wavelength range, 200-1000nm. For one set of the measurements, collection optics was placed on a portable optical shelf attached to the window port of the vacuum chamber. For another set of measurements the thruster plasma radiation emission was collected using a collimating lens inside the vacuum chamber and the signal was brought out of the chamber to the spectrometer by the use of UV-rated optical fibers. Accurate spectral characterization was done for Xe and Ar plasma in a broad operational range. Additionally, emission spectroscopy was used to detect line radiation due to wall erosion products in SPT, to study the effect of thruster operational parameters on the ceramic lining erosion rate, subsequently of the thruster's lifetime. [Preview Abstract] |
Monday, November 12, 2007 10:42AM - 10:54AM |
BO5.00007: Optical Diagnostic Development of a Bismuth Hall Thruster David Scharfe, Mark Cappelli As the heaviest of all stable isotopes, bismuth is a uniquely efficient propellant option for certain plasma-based electric propulsion (E.P.) applications. In general, E.P. systems offer significant benefits over conventional chemical propulsion rockets; however, current E.P. technologies are still lacking in the efficiency and power handling required for feasible Nuclear-Electric Propulsion missions to the outer planets. One option to accommodate the requirements of such missions is an advanced bismuth-fueled Hall thruster. In preparation for development of an advanced Bi-fed Hall thruster, a laboratory-model Hall thruster has been modified to run on bismuth propellant and optical diagnostics have been developed for analyzing the bismuth plasma in the thruster exhaust. For ion velocity measurements, the Bi II 680.86 nm transition will be probed with a New Focus brand Velocity class TLB-6309 laser, and phase sensitive LIF collection will be recorded at 660.02 nm. The design of the laboratory thruster, as well as recordings of the emission and LIF signals from these transitions in the thruster, will be presented. [Preview Abstract] |
Monday, November 12, 2007 10:54AM - 11:06AM |
BO5.00008: Plasma Flow Characterization of a mini-Helicon Thruster Nareg Sinenian, Oleg Batishchev, Manuel Martinez-Sanchez We present experimental analysis of the plasma flow produced by the mini-Helicon Thruster Experiment, currently under development at the MIT Space Propulsion Laboratory. It can efficiently ionize $\sim$1mg of Ar or N at a nominal 1kW RF power. Possible electric propulsion applications require high ($\sim $20-30km/s) exhaust velocity. Our current goal is to optimize thruster design and beam efficiency. Plasma flow is primarily measured using 2-pin Mach probes and Retarding Potential Analyzers. Several issues are addressed including RF-compensation, the effects of non-equilibrated plasma and very high energy fluxes (4MW/m$^2$). Measurement results from these diagnostics over the radius of the plasma jet are presented and yield an indirect measurement of the total axial thrust force. A direct measurement of the thermal component of the total axial thrust force is accomplished using a feedback controlled thrust balance, capable of measurements within a range of 0.1-20mN with a resolution of approximately .1mN. Comparison of the indirect measurements of the total axial thrust and direct measurements of the thermal component of the total axial thrust yields the magnetic component of the total thrust. The latter originates from the magnetic nozzle effect and can be varied by altering the topology of the field in the rear exhaust region. [Preview Abstract] |
Monday, November 12, 2007 11:06AM - 11:18AM |
BO5.00009: Studies of a Pure Electron Plasma to Investigate Electron Mobility in Hall Thrusters Emily Fossum, Lyon King Excessive cross-field electron mobility in Hall thrusters has a negative effect on thruster efficiency and has been shown experimentally to be much larger than predicted by classical theory. An electron trapping apparatus was constructed in order to study electron dynamics in the defining electric and magnetic fields of a Hall-effect thruster in a highly controlled environment. Electrons are confined using only electric and magnetic fields without ions and dielectric walls, which are present in a typical Hall thruster. Mobility studies on a non-neutral plasma provide several advantages over a Hall thuster's quasi-neutral plasma, including a well-defined electric field and the ability to take internal electrostatic probe measurements. Cross-field electron mobility was investigated in response to magnetic and electric field strengths and background neutral density. Experimental design considerations including loading mechanisms, trapping potential, field design, and diagnostic techniques are presented along with experimental results. In this investigation, measured cross-field mobility appears to be consistent with Bohm-like mobility rather than classical mobility. [Preview Abstract] |
Monday, November 12, 2007 11:18AM - 11:30AM |
BO5.00010: Fluctuations, Electron Transport, and Flow Shear in 2D Axial, Azimuthal (z-$\theta )$ Hybrid Hall Thruster Simulations. Eduardo Fernandez, Nicolas Gascon, Aaron Knoll, Michelle Scharfe, Mark Cappelli Motivated by the inability of radial-axial (r-z) simulations to properly treat cross-field electron transport in Hall thrusters, a novel 2D z-$\theta $ model has been implemented. In common with many r-z descriptions, the simulation is hybrid in nature and assumes quasi-neutrality. Unlike r-z models, electron transport is not enhanced with an ad-hoc mobility coefficient; instead it is given by collisional or ``classical'' terms as well as ``anomalous'' contributions associated with azimuthal electric field fluctuations. Results indicate that anomalous transport dominates classical transport for most of the channel and near field, \textit{except} in a strong electron flow shear region near the channel exit. The correlation between flow shear, fluctuation behavior, and electron transport will be examined, along with experimental data from the Stanford Hall Thruster. Our findings make a strong link to the turbulent transport suppression mechanism by flow shear seen in fusion devices. The scheme for combining the r-z and z-$\theta $ descriptions into an upcoming 3D hybrid model will be presented. [Preview Abstract] |
Monday, November 12, 2007 11:30AM - 11:42AM |
BO5.00011: Introduction of Shear-Based Transport Mechanisms in Radial-Axial Hybrid Hall Thruster Simulations Michelle Scharfe, Nicolas Gascon, David Scharfe, Mark Cappelli, Eduardo Fernandez Electron diffusion across magnetic field lines in Hall effect thrusters is experimentally observed to be higher than predicted by classical diffusion theory. Motivated by theoretical work for fusion applications and experimental measurements of Hall thrusters, numerical models for the electron transport are implemented in radial-axial hybrid simulations in order to compute the electron mobility using simulated plasma properties and fitting parameters. These models relate the cross-field transport to the imposed magnetic field distribution through shear suppression of \newline turbulence-enhanced transport. While azimuthal waves likely enhance cross field mobility, axial shear in the electron fluid may reduce transport due to a reduction in turbulence amplitudes and modification of phase shifts between fluctuating properties. The sensitivity of the simulation results to the fitting parameters is evaluated and an examination is made of the transportability of these parameters to several Hall thruster devices. [Preview Abstract] |
Monday, November 12, 2007 11:42AM - 11:54AM |
BO5.00012: Effects of gyrocenter shift on the retrograde motion of cathode spots and plasma transports K.C. Lee The gyrocenter shift phenomenon explained the mechanism of radial electric field formation at the boundary of fusion devices [K. C. Lee, \textit{Phys. Plasmas }\textbf{13}, 062505 (2006)]. The theory of gyrocenter shift is also applicable to low temperature high collisional plasmas by the generalization of the theory resulting from short mean free path comparing to gyroradius. Introducing the expanded formula of gyrocenter shift, the retrograde motion of cathode spots in the arc discharge is investigated through a model with similar parameters to an experimental study. It is found that a reversed electric field is formed in front of cathode spots when they are under magnetic field parallel to the cathode surface and this reversed electric field generates the rotation of cathode spots opposite to Amperian direction of the whole discharge. The ion drift velocity profiles calculated from the model are in agreement to the experimental results as functions of magnetic flux density and gas pressure. Also, the effect of the gyrocenter shift on the plasma transport will be discussed. [Preview Abstract] |
Monday, November 12, 2007 11:54AM - 12:06PM |
BO5.00013: Adaptive Kinetic Model for the Ultrafast Laser Ablation Propulsion Oleg Batishchev, Alla Batishcheva, Jean-Luc Cambier Modern ultrafast femtosecond Ti:Sa lasers are capable of delivering tera-watt powers to a 1-10$\mu $m size volumes at 1-10KHz repletion rates. Though the energy per single pulse is limited to 0.01-1J, due to the unparallel energy density, the material in a focal spot ablates with high energy, instantly forming T$\sim $0.01-1MeV plasma, which corresponds to the extremely high specific impulse Isp$\sim $0.01-1Msec. Amount of the ablated material is controlled by the focal spot size. Average thrust could be controlled in the broad range by varying the atomic weight of the irradiated material and the laser repetition rate, effectively varying average power in the 10W -- 10kW interval. Various practical configurations are considered. One of the possibilities is ablating micro-droplets in the strong diverging magnetic field. In this way most of the 1.5kT random energy could be directed into a half-space, thus forming an exhaust plume. The efficiency of laser energy absorption, ablated plasmas energy spectra, plume divergence, net thrust production are difficult questions to be answered. For analysis we deploy an adaptive kinetic model that solves strongly couple sets of non-linear Boltzmann-Maxwell equations. Results of the numerical simulations for a range of physical parameters -- laser pulse durations, flux densities, target dimensions -- will be discussed. [Preview Abstract] |
Monday, November 12, 2007 12:06PM - 12:18PM |
BO5.00014: Micro-propulsion in space via dust - plasma thruster Gary Zank, Khare Avinash A new scheme of micro propulsion in space i.e. the dust -- plasma thruster is proposed. The scheme uses plasma thermal energy to charge externally injected sub micron sized particles and simultaneously create electric fields in the plasma which accelerates them. Particles are subsequently charge stripped and exhausted to produce electrically neutral thrust obviating the need of a charge neutralizer. For reasonable plasma and particle parameters, thrust and specific impulse over a broad range may be produced. The dependence of thrust on particle size and other plasma parameters allows for a better thruster precision. The scheme is shown to have modest power requirements. It may be realized in a simple design where there are no high voltage grids or electrodes, charge neutralizer, valves, pressurized gases etc and can operate in space or vacuum. A layout for the possible configuration is described. [Preview Abstract] |
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