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Tamiya Fujiwara - One of the best experts on this subject based on the ideXlab platform.
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Voltage-current characteristics of high-current glow Discharges
Applied Physics Letters, 2001Co-Authors: Koichi Takaki, D. Taguchi, Tamiya FujiwaraAbstract:The voltage–current characteristics of glow Discharges in gas mixture (N2:O2=8:2) at a pressure of 10 Torr were obtained with the Discharge current up to 150 A. Parallel-plane electrodes with a diameter of 10.7 cm and a Discharge Chamber with co-axial geometry were used to produce glow Discharge with high current. The glow Discharge voltage was almost constant until the whole surface of the cathode was covered with glow, i.e., until the Discharge current became 3.7 A in our experimental condition (a normal glow Discharge mode). The voltage, however, increased with the current when the glow covered over the cathode (an abnormal glow Discharge mode). The electron density in positive column of the high-current glow Discharge was obtained to be 3×1011 cm−3 from Langmuir probe measurements.
Xiaolin Wang - One of the best experts on this subject based on the ideXlab platform.
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performance investigation of a pressure pulsation dampener applied in the Discharge Chamber of a twin screw refrigeration compressor
International Journal of Refrigeration-revue Internationale Du Froid, 2018Co-Authors: Xiaokun Wu, Ziwen Xing, Wenqing Chen, Xiaolin WangAbstract:Abstract Intermittent gas flow generates pressure oscillations in the twin-screw refrigeration compressor that cause serious problems such as structural vibration and noise. In order to reduce the amplitude of this pressure pulsation, a pressure pulsation dampener (PPD) applied in the Discharge Chamber of a twin screw refrigeration compressor was proposed based on the theory of Helmholtz resonator. A mathematical model was developed to design an optimal PPD by incorporating the R134-oil mixture sound speed model and the pressure pulsation simulation model. A comprehensive experimental study was then performed to validate the model and evaluate the effect of key parameters such as oil flow rate and cavity volume on attenuation performance of the PPD. Vibrational characteristics of the compressor equipped with and without the PPD were also measured and compared. Under the design frequency of 250 Hz, the vibrational acceleration of compressor under-chassis reduced by 36.2% to 41.1% when the compressor was fitted with the proposed PPD.
Alec D Gallimore - One of the best experts on this subject based on the ideXlab platform.
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performance and flatness of a multiple cathode rectangular ion thruster Discharge Chamber
Journal of Propulsion and Power, 2007Co-Authors: Joshua L Rovey, Alec D GallimoreAbstract:Results from the extended life test of the Deep Space One flight spare ion engine show that enlargement of the Discharge cathode assembly orifice due to erosion of the orifice by ion bombardment limits the throughput of the Ion thruster, and therefore limits its operational lifetime to approximately three years. Future deep-space missions will require significantly longer operational lifetime, perhaps as long as 7-14 years. In an effort to increase lifetime, an ion thruster Discharge Chamber designed for operation with multiple Discharge cathode assemblies was investigated. The multiple-cathode Discharge Chamber approach attempts to incase lifetime by operating three Discharge cathode assemblies sequentially. Simulated ion thruster operation of the multiple-cathode Discharge Chamber with the active Discharge cathode assembly located on centerline and off centerline for a variety of magnetic field configurations was accomplished. Results indicate that the configuration with permanent magnets and 0 A electromagnet current provided the best performance and flatness with optimum values of 194 ± 6 W/A at 0.89 ± 0.03 propellant efficiency and 0.55 ± 0.02, respectively. Finally, operation of the dormant cathodes with propellant flow is suggested to reduce preoperation erosion of those units.
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design and operation of a multiple cathode high power rectangular Discharge Chamber
41st AIAA ASME SAE ASEE Joint Propulsion Conference and Exhibit, 2005Co-Authors: Joshua L Rovey, Alec D GallimoreAbstract:A high-power, rectangular Discharge Chamber is being designed by the University of Michigan for operation with multiple Discharge cathode assemblies (DCAs). The multiple cathode approach attempts to increase thruster lifetime by operating three DCAs sequentially, possibly providing a threefold increase in Discharge life. The baseline multiplecathode Discharge Chamber (MCDC) magnetic field topology is developed based on the NASA Evolutionary Xenon Thruster (NEXT) magnetic field. The selected MCDC magnetic field consists of permanent magnet rings, an electromagnet, and magnetic iron c-channels to augment the field. Experimental results are obtained by operating the MCDC with an ion collection grid (without beam extraction) in the University of Michigan Large Vacuum Test Facility. Operation of the MCDC with the active DCA located on centerline and offcenterline is accomplished, as well as operation with the dormant cathodes floating and connected to cathode common. Different magnetic field configurations are experimentally tested by adjusting the electromagnet current or adding the iron c-channels. Discharge stability is analyzed by measuring Discharge voltage oscillations, and 13 button probes are placed on the ion collection grid to determine uniformity. MCDC grid-plane plasma properties, backplate electron current, and dormant cathode current and voltage characteristics are also monitored. A stable Discharge is obtained for all operational configurations. Results indicate that the 0 A electromagnet configuration provides the best performance and flatness with optimum values of 194 W/A at 0.89 propellant efficiency and 0.55, respectively. Backplate electron current ratios indicate that the majority of the Discharge current is deposited in the corners of the rectangular MCDC. Finally, operation of the dormant cathodes with propellant flow is suggested to reduce potential erosion of those units.
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internal plasma potential profiles in a laboratory model hall thruster
Physics of Plasmas, 2001Co-Authors: James M Haas, Alec D GallimoreAbstract:The Plasmadynamics and Electric Propulsion Laboratory High-speed Axial Reciprocating Probe system is used in conjunction with a floating emissive probe to measure plasma potential in the Discharge Chamber of the P5 Hall thruster. Plasma potential measurements are made at a constant voltage, 300 V, at two different Discharge current conditions: 5.4 and 10 A. The plasma potential contours for the 5.4 A case indicate that the acceleration region begins several millimeters upstream of the exit plane, extends several centimeters downstream, and is uniform across the width of the Discharge Chamber. The 10 A case is similar to the 5.4 A case with the exception that the acceleration region is shifted downstream on centerline. Axial electric field profiles, computed from the measured potential, show a double peak structure in the 5.4 A case, indicating a zone of ion deceleration. Perturbations to the Discharge current are shown to correspond spatially with the location of the peak electric field indicating that th...
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an investigation of internal ion number density and electron temperature profiles in a laboratory model hall thruster
36th AIAA ASME SAE ASEE Joint Propulsion Conference and Exhibit 2000, 2000Co-Authors: James M Haas, Alec D GallimoreAbstract:Experiments have been conducted at the University of Michigan Plasmadynamics and Electric Propulsion Laboratory (PEPL) to investigate the acceleration and ionization mechanisms in the P5 laboratory-model Hall thruster. A cylindrical, double Langmuir probe was used to measure electron temperature and ion number density in the Discharge Chamber of the PS. Probe residence times inside the thruster, and hence thruster perturbation, were minimized by use of PEPL's High-Speed Axial Reciprocating Probe (HARP) system. Discharge voltage for this experiment was fixed at 300 V and two Discharge current settings were considered: 5.4 A (1.6 kW) and 10 A (3 kW). Axial profiles of temperature and number density at multiple radial positions spanning the width of the Discharge channel are presented for the two cases along with previously measured profiles of the radial magnetic field and plasma potential. At 1.6 kW, the number density exhibited a dual-peak axial profile indicating two regions of ionization. The maximum temperature and number density was approximately 38 eV and 2.1xlO m", respectively. This structure essentially disappeared at 3 kW, with a single number density peak of 2.8el0. Electron temperature reached a maximum of 32 eV at roughly the same axial location. INTRODUCTION The role of the Hall thruster as a primary propulsion device continues to expand and evolve as new missions are developed which can benefit directly from the Hall thruster's unique combination of thrust and specific impulse. Along with this changing role comes the need to scale existing thrusters to both higher and lower power levels without sacrificing the thruster's inherent performance characteristics. Central to this idea of efficient scaling is the need to fully understand the Hall thruster ionization and acceleration mechanisms. This will be accomplished by a thorough mapping of plasma parameters inside the Discharge Chamber. The resulting data will enable the development of accurate computer models, which will be invaluable in generating the next generation of high-efficiency Hall thrusters. Toward this end, the University of Michigan Plasmadynamics and Electric Propulsion Laboratory (PEPL) has developed a comprehensive experimental program aimed at fully exploring the underlying physics of the Hall thruster. The centerpiece of this effort is the P5, a 5 kW laboratory-model Hall thruster. The P5 has been shown to have performance characteristics very similar to commercially available, state-of-the-art thrusters. It was designed specifically to facilitate internal plasma parameter measurements. As part of the same program, a High-Speed Axial Reciprocating Probe (HARP) system was assembled to allow rapid positioning of electrostatic probes inside the thruster. Using the HARP, probe residence times under 100 ms are routinely and consistently achieved. Correspondingly, perturbations to the Discharge current during data collection are generally less than 10%. Graduate Student, Student Member, AIAA. Associate Professor, Director of Lab, Associate Fellow, AIAA. Copyright © 2000 by James M. Haas Published by the American Institute of Aeronautics and Astronautics with permission. (c)2000 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. OBJECTIVE The objective of this research is to measure the electron temperature and ion number density inside the Discharge Chamber of a Hal! thruster while avoiding significant perturbation to thruster operation. The resulting data are combined with previous measurements of the axial electric field and radial magnetic field to further extend our understanding of the magnitude and spatial structure of the ionization and acceleration regions. EXPERIMENTAL SET-UP Thruster The thruster used is the University of Michigan/Air Force Research Laboratory P5 5 kW laboratory-model Hall thruster. This throster was developed specifically to provide extensive diagnostic access to the Discharge Chamber. Compared to smaller thrusters, the P5 provides a larger Discharge Chamber for better spatial resolution for electrostatic probes as well as a lower power density to reduce heat flux to the probe. Thrust, specific impulse, and efficiency have been measured and correspond very closely to commercially available thrusters. Performance characteristics and plasma parameter profiles in the plume have been reported in a previous work. The P5 incorporates a lanthanum hexahoride (LaB6) cathode. Thruster Discharge voltage was fixed at 300 V for all experiments. Two Discharge current levels were considered: 5.4 A and 10 A. These corresponded to anode mass flow rates of 63 seem and 112 seem, respectively. Cathode mass flow rate remained constant at 6 seem. Vacuum Chamber All experiments were conducted in the University of Michigan's 6 m diameter by 9 m long Large Vacuum Test Facility (LVTF). The pumping system consists of four CVI model TM-1200 ReEntrant Cryopumps providing a measured xenon pumping speed of 140,000 1/s. The ultimate base pressure of the facility is 2xlO"7 Torr. The operating pressures for this experiment were S.SxlO" Torr and 9.6X10"6 Torr when corrected for xenon and corresponded to Discharge currents of 5.4 A and 10.0 A, respectively. Details of the facility have been presented in a previous work. Positioning System The double probe is positioned inside the Hall thruster Discharge Chamber using the PEPL HARP system. The HARP system allows the probe to be inserted into, and removed from, the thruster on a time scale under 100 ms. This allows measurements to be made with very little perturbation to thruster operation. The extent of thruster perturbation is determined by monitoring the Discharge current during probe movement. Use of the double probe caused a slight perturbation in the Discharge current but this remained less than 10% of the nominal Discharge current value during all measurements. Double probe data were collected during both insertion and removal of the probe and agreed reasonably well for most sets of data. However, data from the outward sweep generally exhibited more noise due to the presence of the probe insulator body in the channel. It was concluded that the inward sweep was more representative of the true data. Therefore all data presented, unless otherwise noted, are from the inward sweep. Figure 1 shows the area inside the Discharge Chamber where electron temperature and ion number density were measured. The exit plane is defined as the end of the Discharge channel. Radial movement is accomplished by mounting the thruster on a linear table. Between axial sweeps with the HARP system, the thruster is moved radially such that a 2-D cross section of the Discharge Chamber and near-field region is covered. Note that the axial position throughout this paper corresponds to the tip of the double probe electrodes.
Casey C. Farnell - One of the best experts on this subject based on the ideXlab platform.
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extracted current bias voltage and ion production of cathodic hollow cathode driven plasma contactors
Journal of Spacecraft and Rockets, 2015Co-Authors: Kan Xie, John D. Williams, Qimeng Xia, Rafael A Martinez, Casey C. FarnellAbstract:Plasma properties on extracted electron current–bias voltage characteristics are presented for three selected plasma contactor configurations: a hollow-cathode-only concept, a motive Discharge Chamber concept, and a passive Discharge Chamber concept. Measurements were used to demonstrate how one could achieve low impedance performance without being affected by space plasma properties or by consuming significant propellant mass and power. A one-dimensional model was applied to describe the plasma expansion process that occurs downstream of a cathodic contactor. The model matched well with experimental trends and indicated that the plasma ion production rate within and nearby the plasma contactor dominated the emission-bias behavior of the devices. High ion production rate at a given total mass flow resulted in high propellant utilization and low Discharge loss. However, plasma potential measurements showed that an anode sheath limited the maximum propellant unitization to less than ∼75% and led to a foldba...
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comparison of hollow cathode Discharge plasma configurations
Plasma Sources Science and Technology, 2011Co-Authors: John D. Williams, Casey C. FarnellAbstract:Hollow cathodes used in plasma contactor and electric propulsion devices provide electrons for sustaining plasma Discharges and enabling plasma bridge neutralization. Life tests show erosion on hollow cathodes exposed to the plasma environment produced in the region downstream of these devices. To explain the observed erosion, plasma flow field measurements are presented for hollow cathode generated plasmas using both directly immersed probes and remotely located plasma diagnostics. Measurements on two cathode Discharge configurations are presented: (1) an open, no magnetic field configuration and (2) a setup simulating the Discharge Chamber environment of an ion thruster. In the open cathode configuration, large amplitude plasma potential oscillations, ranging from 20 to 85 V within a 34 V Discharge, were observed using a fast response emissive probe. These oscillations were observed over a dc potential profile that included a well-defined potential hill structure. A remotely located electrostatic analyzer (ESA) was used to measure the energy of ions produced within the plasma, and energies were detected that met, and in some cases exceeded, the peak oscillatory plasma potentials detected by the emissive probe. In the ion thruster Discharge Chamber configuration, plasma potentials from the emissive probe again agreed with ion energies recorded by the remotely located ESA; however, much lower ion energies were detected compared with the open configuration. A simplified ion-transit model that uses temporal and spatial plasma property measurements is presented and used to predict far-field plasma streaming properties. Comparisons between the model and remote measurements are presented.
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direct and remote measurements of plasma properties nearby hollow cathodes
2005Co-Authors: Russell H Martin, Casey C. Farnell, John D. WilliamsAbstract:Measurements are presented of plasma properties near a hollow cathode made using a rapidly actuating Langmuir probe. The probe's x-y positioning system is designed to allow characterization of the intense plasma region commonly present within a few millimeters of a hollow cathode orifice. Of major concern for the Langmuir probe is the probe surface temperature, which should remain below ~1500 K during use to avoid electron emission and possible corruption of the current/voltage characteristics it is intended to measure. To avoid excessive temperatures, the probe is afforded minimum time in intense plasma regions via use of a motion system traveling at an average speed of ~1 m/s. The system is used to execute a complete Langmuir trace every 0.5 mm over ~6 cm of travel. A combined electrostatic analyzer (ESA) and Wein Filter (ExB) probe is also described. The ESA/ExB system is used to remotely measure the energy and charge state of ions produced within a prototype NSTAR Discharge Chamber. The ESA portion of the probe is employed to measure the ion distribution as a function of energy per charge state (E/z). The ExB probe section is then used to measure the charge state (z) of the ions with the ESA portion set to an E/z of interest. Detailed measurements are reported along various lines-of-sight where the remotely located probe is aimed (relative to the axis of the Discharge Chamber). Plans are described where future correlations between direct and remote measurements will be performed.
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Characteristics of Energetic Ions Emitted from Hollow Cathodes
2003Co-Authors: Casey C. Farnell, John D. Williams, Paul J. WilburAbstract:The behavior of a hollow cathode operated within an ion thruster Discharge Chamber is characterized using a remotely located, charged-particle analyzer. A very complex structure of the ion energy distribution function is revealed that is in general agreement with previous observations from many earlier works. Observations, which are in general agreement with the literature, include the measurement of ions that have “through anode” energies and beyond, that have higher ion energies occurring as flow rate is reduced, and that have higher Discharge currents inducing more energetic ion production. All of these observations are also in line with results from long term life tests of hollow cathode-equipped ion thruster systems, which show erosion of hollow cathodes and components located nearby that is presumably caused by sputtering due to energetic ion bombardment. Most studies of hollow cathodes have concentrated on devices operated outside of Discharge Chambers where they are more readily accessible. This study is different in that it was performed with the hollow cathode located within a specially designed, 30-cm diameter Discharge Chamber. The measurements were made using a collimated electrostatic energy analyzer (ESA) that was sighted through a slot cut in the Discharge Chamber wall and pseudo grid surface. The hollow cathode/Discharge Chamber system could be rotated about an axis centered at the cathode orifice, and this enabled measurement of the ion energy distribution functions at zenith angles ranging from 0 o to 90 o with respect to the hollow cathode centerline. The ESA lateral position was also varied to look at regions located [in a line-of-sight (LOS) sense] on either side of the hollow cathode. Results are presented which show the effects of zenith angle variation, Discharge current, and cathode flow rate on the ion energy distribution. Very interesting results obtained in recent experiments at high Discharge currents are presented that show the ion energy distribution varying widely when measured at different zenith angles and at different positions near the hollow cathode. Specifically, few high-energy ions are seen on-axis, but many are seen at moderate (~20° and higher) zenith angles and from regions up to 5 cm from the cathode. This observation is different than those made on hollow cathodes operated outside of a Discharge Chamber.
Koichi Takaki - One of the best experts on this subject based on the ideXlab platform.
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Voltage-current characteristics of high-current glow Discharges
Applied Physics Letters, 2001Co-Authors: Koichi Takaki, D. Taguchi, Tamiya FujiwaraAbstract:The voltage–current characteristics of glow Discharges in gas mixture (N2:O2=8:2) at a pressure of 10 Torr were obtained with the Discharge current up to 150 A. Parallel-plane electrodes with a diameter of 10.7 cm and a Discharge Chamber with co-axial geometry were used to produce glow Discharge with high current. The glow Discharge voltage was almost constant until the whole surface of the cathode was covered with glow, i.e., until the Discharge current became 3.7 A in our experimental condition (a normal glow Discharge mode). The voltage, however, increased with the current when the glow covered over the cathode (an abnormal glow Discharge mode). The electron density in positive column of the high-current glow Discharge was obtained to be 3×1011 cm−3 from Langmuir probe measurements.
