An overview is presented of electric propulsion research carried out in U.S. academic institution... more An overview is presented of electric propulsion research carried out in U.S. academic institutions. Universities in the U.S. are engaged in a wide range of research, varying from fundamental studies in micro thruster concepts, to future flight involving magneto plasma sails. I.
The Maecker formula has long been used to explain the scaling of the thrust of self-field magneto... more The Maecker formula has long been used to explain the scaling of the thrust of self-field magnetoplasmadynamic thrusters (MPDTs) with the total current. The formula is shown to be too simplistic to account for the trends in measured thrust data which exhibit departures from the model especially at low current. We show that these departures cannot simply all be attributed to electrothermal effects. Instead, we find that at high currents, the departures can be explained by the evolution of the current densities over the electrode surfaces which influence the spatial distribution of the volumetric Lorentz force densities. At low current levels the departures are attributed to the scaling of gasdynamic pressure distributions induced by the pinching components of the volumetric electromagnetic forces. The insight was used to formulate a more accurate empirically-based model for the scaling of the thrust of an MPDT.
The second Ablative Z-Pinch Pulsed Plasma Thruster (AZPPT2) is a 2.5kg device employing a recent ... more The second Ablative Z-Pinch Pulsed Plasma Thruster (AZPPT2) is a 2.5kg device employing a recent electromagnetic propulsion design to achieve speci c impulses of 468s. The magnetic eld induced by the current-carrying Te on plasma causes the current to contract towards the axis of symmetry of the cylindrical device, e ectively squeezing the Te on particles out the exhaust hole at highly accelerated velocities. A problem in the present design of the AZPPT2 is in the oscillatory current patterns of the thruster circuit, characteristic of underdamped RLC circuits. This ringing poses problems to the lifetime of the capacitor and to the e ciency of the thruster. In this project, we have built a Rogowski coil to better characterize the current ow in the thruster and have modi ed the thruster to reduce the current ringing e ect; the theory behind these e orts is also discussed. The results of this project are a Rogowski coil which measures current changes of 10A/s and sine wave frequencies ...
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the date needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of informatio including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferso Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing comply with a collection of information if it does not display a currently valid OMB control number. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON a. REPORT b.
For numerical simulations to be effective tools in plasma propulsion research, a higher order acc... more For numerical simulations to be effective tools in plasma propulsion research, a higher order accurate solver that captures MHD shocks monotonically and works reliably for strong magnetic fields is needed. For this purpose, a characteristics based scheme for the MHD equations, with flux limiters to improve spatial accuracy, has been developed. In this method, the symmetric form of the MHD equations, accounting for waves propagating in all directions, is solved. The required eigensystem of axisymmetric MHD equations, with appropriate normalization, is presented. This scheme was validated against unsteady (Riemann problem) and force-free equilibrium (Taylor state) test cases. The capability of this method to simulate resistive plasma flows is demonstrated using a simple example.
48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2012
The heating of ions in a magnetized plasma by two electrostatic waves whose frequencies differ by... more The heating of ions in a magnetized plasma by two electrostatic waves whose frequencies differ by the ion cyclotron frequency is experimentally and analytically characterized. An analytical model is presented for the power absorption by the two waves, and it is shown that the two-wave process will yield superior heating to a single electrostatic wave only in the event that the total wave energy density exceeds a threshold value. An experimental investigation of the increase in ion temperature as a function of the fraction of total energy density in one of the propagating modes subsequently reveals that for a low temperature plasma, heating with a single electrostatic wave is superior to employing two beating electrostatic waves. This result is consistent with the analytical prediction that the available wave energy density in the experiment is below the required threshold for the superiority of the two-wave process.
46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2010
A new concept for plasma propulsion that relies on using beating electrostatic wave (BEW) direct ... more A new concept for plasma propulsion that relies on using beating electrostatic wave (BEW) direct ion acceleration to augment the linear ion current produced in a plasma by a rectilinear, magnetic slope configuration is presented and analyzed. The types of particle trajectories possible in a magnetic slope configuration are identified and shown to produce a net flow in a thermalized ion ensemble. The ability of BEW to augment this flow in the magnetic null direction by direct acceleration, as opposed to ion heating, is subsequently demonstrated and a thruster concept that relies on this process is described. It is expected that the direct ion acceleration would yield a propulsive performance that is superior to that obtained by concepts that rely on plasma heating, which suffer from relatively high wall losses.
46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2010
An experimental investigation of plasma heating by a single electrostatic wave (SEW) in a magneti... more An experimental investigation of plasma heating by a single electrostatic wave (SEW) in a magnetized, rf-sustained plasma was carried out to establish the existence of an optimal wave frequency for maximized heating, which we recently predicted theoretically. A variable tuning network was constructed for electrostatic ion cyclotron wave launching, and laser-induced fluorescence measurements were made of ion heating and its dependence on SEW frequency over the tunable range of the second to the sixth harmonic of the ion cyclotron frequency. The measurements revealed a dependence of heating on frequency as predicted by the theory and the existence of an optimal frequency that is within one cyclotron harmonic from the theoretically predicted value. The findings establish a fundamental prescription for optimizing plasma heating by electrostatic waves, that is particularly useful for plasma propulsion where efficiency is of prime importance.
39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 2003
Thermal effects on direct measurements of the thrust produced by steady-state, high-power (≥ 10s ... more Thermal effects on direct measurements of the thrust produced by steady-state, high-power (≥ 10s of kWs) plasma thrusters using inverted-pendulum thrust stands are addressed. Three major sources of systematic error exist in the determination of thrust using an inverted-pendulum thrust stand; tare forces, thermal drifts, and thermal deflections. It is shown that thermal deflections, due to changes in the temperature of the flexures used to carry the thruster current, can be the most significant of these effects. The response of the flexural elements to changing thermal loads can produce stand displacements on the order of the expected thrust (100s of mN at thruster currents of 300-500 A). Thermal deflections were reduced by at least 80% by conducting the thruster current to the stand via mercury pots rather than the flexural elements.
An evaluation of previously proposed least-squares multi-color pyrometry methods was carried out ... more An evaluation of previously proposed least-squares multi-color pyrometry methods was carried out to determine their highest achievable accuracy. The study was limited to the visible spectrum and the temperature range of 1700 to 3000 K, typical of electrode surfaces in high-power electric propulsion thrusters. A Monte-Carlo simulation of the various methods showed the eects that the number of colors of the pyrometer, the errors associated with noise and calibration, and the number of measurements have on the uncertainty of the predicted temperature. Some of these methods were found to lead to inaccurate results, an underestimate of the uncertainty of the predicted temperature, or yield larger uncertainties than single-color pyrometry. The two methods that were found to yield the highest accuracy without underestimating the uncertainty are based on tting the intensity versus wavelength data with three free parameters (temperature and the two coecien ts of the emissivity versus wavelen...
30th Joint Propulsion Conference and Exhibit, 1994
The nature of oscillations in the 1 kHz-60 MHz frequency range that have been observed during ope... more The nature of oscillations in the 1 kHz-60 MHz frequency range that have been observed during operation of closed drift thrusters (CDT), such as the stationary plasma thruster (SPT) and the anode layer thruster (ALT), is quantitatively discussed. We use contours of various plasma parameters measured inside the accelerating channel of an SPT[1, 2] as the starting point of our investigation and calculate the magnitude and spatial distribution of various associated natural and collision frequencies, characteristic lengths and velocities. This leads to a thorough characterization of the plasma in the channel under typical operation. This detailed picture is then used to evaluate the stability criteria and dispersion relations of oscillations that are suspected to occur. Using various dispersion relations, we present a band by band overview of the oscillations with a description of their observed behavior and discuss their nature and dependencies through comparison of the calculated contours to reported observations. In particular we discuss the excitation of low frequency azimuthal drift waves that can form a rotating spoke at lower values of B * r , axially propagating "transit-time" oscillations, high frequency azimuthal drift waves, ionization instability-type waves, and wave emission peculiar to weakly ionized inhomogeneous plasma in crossed electric and magnetic fields.
28th Joint Propulsion Conference and Exhibit, 1992
In the present paper the linear stability description and weak turbulence theory are used to deve... more In the present paper the linear stability description and weak turbulence theory are used to develop a second order description of wave-particle transport and anomalous dissipation. The goal is to arrive at anomalous transport coefficients that can be readily included in fluid flow codes. In particular, expressions are derived for the heating rates of ions and electrons by the unstable
48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2012
An analytical model is derived to study the two-dimensional character of axisymmetric, collisionl... more An analytical model is derived to study the two-dimensional character of axisymmetric, collisionless plasma flow along a guiding magnetic field. This is accomplished using a transformation from cylindrical to magnetic coordinates, which enables the separate treatment of the flow-averaged plasma parameters from their spatial non-uniformities. The result gives analytical solutions for the spatial variation of the potential, plasma density, and ion Mach number. Application of the model to the problem of supersonic plasma expansion from a magnetic nozzle shows good agreement with both numerical simulations and experimental measurements. Notably, the development of a downstream radial electric field to preserve quasi-neutrality is the main factor that drives non-uniformities within the plasma. This result is used to explain experimentally observed focusing of the plasma exhaust with respect to the applied magnetic field. Finally, the competition in the expansion process, between the conversion of thermal energy into kinetic energy and the loss to plume divergence of the kinetic energy useful for propulsion yields an expression for the maximum thrust coefficient of a magnetic nozzle in terms of the parameters of the plasma source.
An overview is presented of electric propulsion research carried out in U.S. academic institution... more An overview is presented of electric propulsion research carried out in U.S. academic institutions. Universities in the U.S. are engaged in a wide range of research, varying from fundamental studies in micro thruster concepts, to future flight involving magneto plasma sails. I.
The Maecker formula has long been used to explain the scaling of the thrust of self-field magneto... more The Maecker formula has long been used to explain the scaling of the thrust of self-field magnetoplasmadynamic thrusters (MPDTs) with the total current. The formula is shown to be too simplistic to account for the trends in measured thrust data which exhibit departures from the model especially at low current. We show that these departures cannot simply all be attributed to electrothermal effects. Instead, we find that at high currents, the departures can be explained by the evolution of the current densities over the electrode surfaces which influence the spatial distribution of the volumetric Lorentz force densities. At low current levels the departures are attributed to the scaling of gasdynamic pressure distributions induced by the pinching components of the volumetric electromagnetic forces. The insight was used to formulate a more accurate empirically-based model for the scaling of the thrust of an MPDT.
The second Ablative Z-Pinch Pulsed Plasma Thruster (AZPPT2) is a 2.5kg device employing a recent ... more The second Ablative Z-Pinch Pulsed Plasma Thruster (AZPPT2) is a 2.5kg device employing a recent electromagnetic propulsion design to achieve speci c impulses of 468s. The magnetic eld induced by the current-carrying Te on plasma causes the current to contract towards the axis of symmetry of the cylindrical device, e ectively squeezing the Te on particles out the exhaust hole at highly accelerated velocities. A problem in the present design of the AZPPT2 is in the oscillatory current patterns of the thruster circuit, characteristic of underdamped RLC circuits. This ringing poses problems to the lifetime of the capacitor and to the e ciency of the thruster. In this project, we have built a Rogowski coil to better characterize the current ow in the thruster and have modi ed the thruster to reduce the current ringing e ect; the theory behind these e orts is also discussed. The results of this project are a Rogowski coil which measures current changes of 10A/s and sine wave frequencies ...
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the date needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of informatio including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferso Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing comply with a collection of information if it does not display a currently valid OMB control number. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON a. REPORT b.
For numerical simulations to be effective tools in plasma propulsion research, a higher order acc... more For numerical simulations to be effective tools in plasma propulsion research, a higher order accurate solver that captures MHD shocks monotonically and works reliably for strong magnetic fields is needed. For this purpose, a characteristics based scheme for the MHD equations, with flux limiters to improve spatial accuracy, has been developed. In this method, the symmetric form of the MHD equations, accounting for waves propagating in all directions, is solved. The required eigensystem of axisymmetric MHD equations, with appropriate normalization, is presented. This scheme was validated against unsteady (Riemann problem) and force-free equilibrium (Taylor state) test cases. The capability of this method to simulate resistive plasma flows is demonstrated using a simple example.
48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2012
The heating of ions in a magnetized plasma by two electrostatic waves whose frequencies differ by... more The heating of ions in a magnetized plasma by two electrostatic waves whose frequencies differ by the ion cyclotron frequency is experimentally and analytically characterized. An analytical model is presented for the power absorption by the two waves, and it is shown that the two-wave process will yield superior heating to a single electrostatic wave only in the event that the total wave energy density exceeds a threshold value. An experimental investigation of the increase in ion temperature as a function of the fraction of total energy density in one of the propagating modes subsequently reveals that for a low temperature plasma, heating with a single electrostatic wave is superior to employing two beating electrostatic waves. This result is consistent with the analytical prediction that the available wave energy density in the experiment is below the required threshold for the superiority of the two-wave process.
46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2010
A new concept for plasma propulsion that relies on using beating electrostatic wave (BEW) direct ... more A new concept for plasma propulsion that relies on using beating electrostatic wave (BEW) direct ion acceleration to augment the linear ion current produced in a plasma by a rectilinear, magnetic slope configuration is presented and analyzed. The types of particle trajectories possible in a magnetic slope configuration are identified and shown to produce a net flow in a thermalized ion ensemble. The ability of BEW to augment this flow in the magnetic null direction by direct acceleration, as opposed to ion heating, is subsequently demonstrated and a thruster concept that relies on this process is described. It is expected that the direct ion acceleration would yield a propulsive performance that is superior to that obtained by concepts that rely on plasma heating, which suffer from relatively high wall losses.
46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2010
An experimental investigation of plasma heating by a single electrostatic wave (SEW) in a magneti... more An experimental investigation of plasma heating by a single electrostatic wave (SEW) in a magnetized, rf-sustained plasma was carried out to establish the existence of an optimal wave frequency for maximized heating, which we recently predicted theoretically. A variable tuning network was constructed for electrostatic ion cyclotron wave launching, and laser-induced fluorescence measurements were made of ion heating and its dependence on SEW frequency over the tunable range of the second to the sixth harmonic of the ion cyclotron frequency. The measurements revealed a dependence of heating on frequency as predicted by the theory and the existence of an optimal frequency that is within one cyclotron harmonic from the theoretically predicted value. The findings establish a fundamental prescription for optimizing plasma heating by electrostatic waves, that is particularly useful for plasma propulsion where efficiency is of prime importance.
39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 2003
Thermal effects on direct measurements of the thrust produced by steady-state, high-power (≥ 10s ... more Thermal effects on direct measurements of the thrust produced by steady-state, high-power (≥ 10s of kWs) plasma thrusters using inverted-pendulum thrust stands are addressed. Three major sources of systematic error exist in the determination of thrust using an inverted-pendulum thrust stand; tare forces, thermal drifts, and thermal deflections. It is shown that thermal deflections, due to changes in the temperature of the flexures used to carry the thruster current, can be the most significant of these effects. The response of the flexural elements to changing thermal loads can produce stand displacements on the order of the expected thrust (100s of mN at thruster currents of 300-500 A). Thermal deflections were reduced by at least 80% by conducting the thruster current to the stand via mercury pots rather than the flexural elements.
An evaluation of previously proposed least-squares multi-color pyrometry methods was carried out ... more An evaluation of previously proposed least-squares multi-color pyrometry methods was carried out to determine their highest achievable accuracy. The study was limited to the visible spectrum and the temperature range of 1700 to 3000 K, typical of electrode surfaces in high-power electric propulsion thrusters. A Monte-Carlo simulation of the various methods showed the eects that the number of colors of the pyrometer, the errors associated with noise and calibration, and the number of measurements have on the uncertainty of the predicted temperature. Some of these methods were found to lead to inaccurate results, an underestimate of the uncertainty of the predicted temperature, or yield larger uncertainties than single-color pyrometry. The two methods that were found to yield the highest accuracy without underestimating the uncertainty are based on tting the intensity versus wavelength data with three free parameters (temperature and the two coecien ts of the emissivity versus wavelen...
30th Joint Propulsion Conference and Exhibit, 1994
The nature of oscillations in the 1 kHz-60 MHz frequency range that have been observed during ope... more The nature of oscillations in the 1 kHz-60 MHz frequency range that have been observed during operation of closed drift thrusters (CDT), such as the stationary plasma thruster (SPT) and the anode layer thruster (ALT), is quantitatively discussed. We use contours of various plasma parameters measured inside the accelerating channel of an SPT[1, 2] as the starting point of our investigation and calculate the magnitude and spatial distribution of various associated natural and collision frequencies, characteristic lengths and velocities. This leads to a thorough characterization of the plasma in the channel under typical operation. This detailed picture is then used to evaluate the stability criteria and dispersion relations of oscillations that are suspected to occur. Using various dispersion relations, we present a band by band overview of the oscillations with a description of their observed behavior and discuss their nature and dependencies through comparison of the calculated contours to reported observations. In particular we discuss the excitation of low frequency azimuthal drift waves that can form a rotating spoke at lower values of B * r , axially propagating "transit-time" oscillations, high frequency azimuthal drift waves, ionization instability-type waves, and wave emission peculiar to weakly ionized inhomogeneous plasma in crossed electric and magnetic fields.
28th Joint Propulsion Conference and Exhibit, 1992
In the present paper the linear stability description and weak turbulence theory are used to deve... more In the present paper the linear stability description and weak turbulence theory are used to develop a second order description of wave-particle transport and anomalous dissipation. The goal is to arrive at anomalous transport coefficients that can be readily included in fluid flow codes. In particular, expressions are derived for the heating rates of ions and electrons by the unstable
48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2012
An analytical model is derived to study the two-dimensional character of axisymmetric, collisionl... more An analytical model is derived to study the two-dimensional character of axisymmetric, collisionless plasma flow along a guiding magnetic field. This is accomplished using a transformation from cylindrical to magnetic coordinates, which enables the separate treatment of the flow-averaged plasma parameters from their spatial non-uniformities. The result gives analytical solutions for the spatial variation of the potential, plasma density, and ion Mach number. Application of the model to the problem of supersonic plasma expansion from a magnetic nozzle shows good agreement with both numerical simulations and experimental measurements. Notably, the development of a downstream radial electric field to preserve quasi-neutrality is the main factor that drives non-uniformities within the plasma. This result is used to explain experimentally observed focusing of the plasma exhaust with respect to the applied magnetic field. Finally, the competition in the expansion process, between the conversion of thermal energy into kinetic energy and the loss to plume divergence of the kinetic energy useful for propulsion yields an expression for the maximum thrust coefficient of a magnetic nozzle in terms of the parameters of the plasma source.
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Papers by Edgar Choueiri