Spatial uniformity of the current emitted by an array of passively fed electrospray porous emitters

Guerra-Garcia, Carmen; Krejci, David; Lozano, Paulo

doi:10.1088/0022-3727/49/11/115503

Cited by 55 publications

(28 citation statements)

References 16 publications

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“…was lower than −87 V or higher than 89 V, the collector current began to be detected and reached −1.0 A at −92 V and 0.6 A at 92 V. Since the starting voltage of ion extraction is a function of the surface tension of the ionic liquid, the curvature radius of the emitter tip, and the distance between the emitters and the extractor, 30) the absolute value of the starting voltage is estimated to be approximately equal for both cation and anion extraction, which was true for the present experiments and the previous ones. 17,21,31) We could demonstrate that ions were extracted from the sub-m scale capillaries of the high-density emitter array when EMI-DCA was utilized as the propellant. Note that the sum of the extractor current and the collector current was approximately equal to the emitter current, indicating the current conservation via emitted ions, and thus the plots of the emitter current at the voltage amplitude of 92 V were out of range of the graph.…”

Section: Resultsmentioning

confidence: 97%

“…A at 900 V with the same ionic liquid of EMI-DCA, 17,31) resulting in the current density of −0.31 mA/cm 2 at −900 V and 0.25 mA/cm 2 at 900V. In comparison, our high-density emitter array obtained a few times higher current density for both polarities than the S-iEPS and showed a similar tendency that the anion produced higher absolute value of the current than the cation at the same absolute value of the emitter voltage owing to the lighter mass of DCA (66 g/mol)…”

Section: Resultsmentioning

confidence: 99%

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Fabrication of a high-density emitter array for electrospray thrusters using field emitter array process

Inoue

Nagao

Murakami

et al. 2019

Jpn. J. Appl. Phys.

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To improve the thrust density of electrospray thrusters using ionic liquids as the propellant, we have fabricated a high-density emitter array utilizing the fabrication technique of a field emitter array (FEA) or gated nano electron sources. The density of the emitter array can reach approximately 4 million/cm 2 , which is four orders of magnitude higher than that of conventional electrospray thrusters. Performing deep reactive ion etching from the back side of the same 2 structure as FEAs and removing their Ni cones by dilute nitric acid, we have successfully fabricated sub-m scale capillary emitters with self-aligned extractor electrodes and ionic liquid reservoirs behind them. Current measurements were also conducted with EMI-BF4 and EMI-DCA as the propellant. Although the ion was not extracted with EMI-BF4 owing to its electrochemical reaction with the electrodes, both positive and negative ion currents were detected using EMI-DCA, where the current density exceeded that of conventional electrospray thrusters.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Fabrication of a high-density emitter array for electrospray thrusters using field emitter array process

Inoue

Nagao

Murakami

et al. 2019

Jpn. J. Appl. Phys.

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“…Furthermore, in the devices presented here, 100's of emission sites are likely present over the emitter arrays each making a small contribution towards the total beam current and characterized by an onset field (/voltage) dependent on local conditions. At a single polarity and emitting 100's of µA, individual emission site onset and collapse is likely to occur during beam current amplitude modulation yet at sufficiently distributed potentials to avoid large, discreet, steps in current [32]. Regardless, minimum onset times may differ between polarities (as observed in Ref.…”

Section: Active Charge Neutralizationmentioning

confidence: 92%

Charge Neutralization and Direct Thrust Measurements from Bipolar Pairs of Ionic Electrospray Thrusters

Courtney¹,

Shea²,

Dannenmayer³

et al. 2018

Journal of Spacecraft and Rockets

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Electrospray (ES) thrusters are unique in their ability to emit both positive and negative beams, each contributing similarly to thrust. Spacecraft charging could be prevented without a dedicated neutralizer if currents of simultaneously emitted opposing polarity beams were matched; despite a lack of implicit coupling between them. We discuss and evaluate experimentally both an active current-balance control circuit and a passive self-balancing configuration. Our highly ionic ES source includes a pair of machined porous glass ES emitter arrays in a single holder. In the passive configuration, unbalanced charge collection on a common floating extractor yields rapid charging towards artificially imposed 200 V limits without means for charge suppression, showing the unsuitability of that architecture. Active balancing of emitted currents was fully effective at charge neutralization during stable periods of emission, yet insufficient during potential alternations. We present methods to improve this approach, including demonstrating beam current modulation at up to 450 Hz. Direct thrust measurements when simultaneously emitting opposing polarity beams of the ionic liquid 1-ethyl-3-methylimidazolium tetrauoroborate are presented. Direct thrust measurements up to 35 µN were in excellent agreement with commanded levels and computations based on measured currents (up to 190 µA) and voltages (up to 2100 V).

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“…For an array of 480 porous emitters, measurements of the spatial uniformity and estimations of the fraction of tips emitting have been reported by MIT. 90 The propellant in this device was supplied passively, 91 and the thruster was operated in an ambipolar mode with a change in polarity every thirty seconds. Whether the alternating ambipolar operation of an entire microthruster array is preferable to the parallel operation of two microthruster arrays of opposite polarity, possibly also operated alternatingly, 92 is a topic currently under investigation.…”

Section: -13mentioning

confidence: 99%

Space micropropulsion systems for Cubesats and small satellites: From proximate targets to furthermost frontiers

Levchenko

Bazaka

Ding

et al. 2018

Applied Physics Reviews

271

104

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Rapid evolution of miniaturized, automatic, robotized, function-centered devices has redefined space technology, bringing closer the realization of most ambitious interplanetary missions and intense near-Earth space exploration. Small unmanned satellites and probes are now being launched in hundreds at a time, resurrecting a dream of satellite constellations, i.e., wide, all-covering networks of small satellites capable of forming universal multifunctional, intelligent platforms for global communication, navigation, ubiquitous data mining, Earth observation, and many other functions, which was once doomed by the extraordinary cost of such systems. The ingression of novel nanostructured materials provided a solid base that enabled the advancement of these affordable systems in aspects of power, instrumentation, and communication. However, absence of efficient and reliable thrust systems with the capacity to support precise maneuvering of small satellites and CubeSats over long periods of deployment remains a real stumbling block both for the deployment of large satellite systems and for further exploration of deep space using a new generation of spacecraft. The last few years have seen tremendous global efforts to develop various miniaturized space thrusters, with great success stories. Yet, there are critical challenges that still face the space technology. These have been outlined at an inaugural International Workshop on Micropropulsion and Cubesats, MPCS-2017, a joint effort between Plasma Sources and Application Centre/Space Propulsion Centre (Singapore) and the Micropropulsion and Nanotechnology Lab, the G. Washington University (USA) devoted to miniaturized space propulsion systems, and hosted by CNR-Nanotec—P.Las.M.I. lab in Bari, Italy. This focused review aims to highlight the most promising developments reported at MPCS-2017 by leading world-reputed experts in miniaturized space propulsion systems. Recent advances in several major types of small thrusters including Hall thrusters, ion engines, helicon, and vacuum arc devices are presented, and trends and perspectives are outlined.

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Spatial uniformity of the current emitted by an array of passively fed electrospray porous emitters

Cited by 55 publications

References 16 publications

Fabrication of a high-density emitter array for electrospray thrusters using field emitter array process

Fabrication of a high-density emitter array for electrospray thrusters using field emitter array process

Charge Neutralization and Direct Thrust Measurements from Bipolar Pairs of Ionic Electrospray Thrusters

Space micropropulsion systems for Cubesats and small satellites: From proximate targets to furthermost frontiers

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