Mass Spectrometric Analysis of the Electrospray Plume from an Externally Wetted Tungsten Ribbon Emitter

Ticknor, Brian W.; Miller, Shawn W.; Chiu, Yu‐Hui

doi:10.2514/6.2009-5088

Cited by 18 publications

(20 citation statements)

References 11 publications

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“…Previous work on externally wetted emitters has shown that the emission mode of a single emitter can be shifted by changing ('"" which in turn affects the rate of liquid transport to the tip. 7 The difference in V, xl for the two emitters here likely indicates a similar shift in propellant flow rate and subsequently in the emission mode of the thruster.…”

Section: Discussionmentioning

confidence: 73%

“…Angles of approximately ± 40 degrees are achieved, which allows for the measurement of the ion emission properties of the Taylor cone-jet as a function of emitter angle. The entire ion extraction source is held in vacuum of-1 x I0" 7 Torr. Extraction voltages (f'",) of ± 1200 -1500 V are used, operated in alternating polarity (AC) mode.…”

Section: Methodsmentioning

confidence: 99%

“…16 Ribbon emitters, which have a larger surface area than the needles, have been studied for their potential to support larger levels of current emission, but difficulties in controlling the higher flow rate, and thus the electrospray mode, have sometimes prevented their use in the ion-only emission regime. 7 Constructing an array of emitters is an obvious choice to bolster the total thrust produced, 15 "' 7 but reproducibility creating many identical tips is technologically challenging. Recently, the Space Propulsion Laboratory at the Massachusetts Institute of Technology (MIT) has reported a method for the fabrication of linear arrays of emitters made of porous tungsten.'…”

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confidence: 99%

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Effect of Aspect Ratio on the Wettability and Electrospray Properties of Porous Tungsten Emitters with the Ionic Liquid [Emim][Im]

Ticknor¹,

Anderson²,

Fritz³

et al. 2010

46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Section: Discussionmentioning

confidence: 73%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Effect of Aspect Ratio on the Wettability and Electrospray Properties of Porous Tungsten Emitters with the Ionic Liquid [Emim][Im]

Ticknor¹,

Anderson²,

Fritz³

et al. 2010

46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

Self Cite

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“…The elevated baseline reading between ±15°, which has been observed previously in needle mass spectra, is attributed to large m/q species that are not completely filtered out by the mass filter and reach the detector. 22,23 It is possible to use the intensity trend of each species to approximate the location of origin of that species in the Taylor cone. Maximum n = 0 cation intensities are observed at high angle values.…”

Section: Resultsmentioning

confidence: 99%

Capillary Extraction of the Ionic Liquid [Bmim][DCA] for Variable Flow Rate Operations

Miller¹,

Prince²,

Rovey

2012

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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The ionic liquid [Bmim][DCA] is a propellant candidate in a standalone electrospray thruster or in a dual-mode propulsion system consisting of a chemical system and an electrospray system. Since limited published data exists for [Bmim][DCA], the electrospray characteristics are relatively unknown. Emission testing of the ionic liquid has been conducted to characterize the [Bmim][DCA] electrospray plume for both an external flow titanium needle and internal flow capillary. Mass spectrometric, retarding potential, and angle distribution measurements were collected for the positive polarity ions emitted from [Bmim][DCA] wetted emitters with nominal extraction voltages between ~1 kV to ~2.5 kV. The titanium needle operated at a sizably reduced liquid flow rate in comparison to the capillary. As such, only the major species of Bmim + ([Bmim][DCA]) n with n=0,1 were identifiable in the quadrupole measurement range of 0-1000 amu and were formed at or near the needle potential. A typical needle angle distribution was found in these measurements. For the capillary emitter, flow rates from 0.27 nL/s to 2.18 nL/s were used to investigate corresponding alterations in the electrospray beam. The aim of the investigation was to ascertain the ability to "tune" or "dial-in" an electrospray thruster to specific ion or droplet sizes and thus specific performance levels. Unlike the limited species observed from the needle emission, the capillary measurements indicated the presence of n=0,1,2,3,4 cation species with large mass droplet contributions. The lowest flow rates indicated the highest levels of ions in the measurement range of 0-1000 amu with a mix of large mass droplets. For increasing flow rate, species < 500 amu ceased to exist leaving only the n=2,3,4 species mixed with large mass droplets in the electrospray beam. All ion species exceeded the quadrupole mass range at the upper flow rates. Ions emitted from the capillary were formed at levels below the emitter potential. Ohmic losses in the ionic liquid are likely the cause for the less energetic ions. Angular distribution measurements indicated broadening of the beam current and mass distribution for increasing flow rates. Nomenclature D c = transport capillary inner diameter (µm) D n = capillary needle emitter inner diameter (µm) K = ionic liquid electrical conductivity (S/m) L c = transport capillary length (cm) L n = capillary needle emitter length (cm) P 0 = reservoir pressure (Torr) P VC = vacuum chamber pressure (Torr) 2 P n = capillary needle emitter pressure (Torr) q/m = specific charge (C/kg) Q = ionic liquid volumetric flow rate (nL/s) V N = emitter voltage (V) V Ext = extractor plate voltage (V) β n = capillary length/diameter ratio coefficient γ = ionic liquid surface tension (N/m) ε = ionic liquid dielectric constant µ l = ionic liquid viscosity (cP) ρ = ionic liquid density (kg/m 3 )

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“…[7] Alteration of the needle emitter surface has been shown to impact the intensity ratio of ion species as well as the quantity and mass-to-charge of droplets emitted, again determined through the use of near-field measurements. [8,9] This alteration is likely the result of flow rate modification of the ionic liquid propellant, although no direct measurement of the flow rate was possible. We have previously reported on the effects of volumetric flow rate on the emitted ion species from a capillary-style emitter employing the ionic liquid BMI-DCA (1-butyl-3methylimidazolium dicyanamide).…”

Section: Introductionmentioning

confidence: 99%

Mass Spectrometry of Selected Ionic Liquids in Capillary Electrospray at Nanoliter Volumetric Flow Rates

Miller

Prince²,

Bemish³

et al. 2016

52nd AIAA/SAE/ASEE Joint Propulsion Conference

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Capillary-based electrospray thrusters allow user-enabled control of the volumetric flow rate of the propellant. This control, coupled with mass spectrometry techniques spanning a large mass-to-charge range, enables elucidation of the composition of the electrospray beam and through further analyses, a better understanding of the physics occurring at the liquid/vacuum interface. In this work, mass spectra of selected ionic liquids electrosprayed from a capillary emitter are measured, using time-of-flight mass spectrometry, over a wide range of volumetric flow rates. The time-of-flight mass spectrometer enables simultaneous acquisition over a mass-to-charge range of 20 amu/q to ~500,000 amu/q in a single pulse cycle. Additionally, the use of orthogonal extraction enables direct determination of the kinetic energies of ions present in the electrosprayed beam. The presented data reveal a complex emission process occurring for ionic liquid capillary-based electrospray at nanoliter volumetric flow rates. The electrospray beam mass-to-charge composition includes a sequence of singly-charged ions and doubly-charged ions at nearly all sampled flow rates for all electrosprayed ionic liquids. In addition to the small ion-clusters, two Maxwell-Boltzmann distributions from approximately 10,000 amu/q to 500,000 amu/q exist in the spectra each with mass-to-charge distribution sensitive to the volumetric flow rate. The volumetric flow rate dependence of the largest charge-to-mass ratio droplets appears to be consistent with previously measured scaling laws, although exhibiting a wide mass-to-charge distribution. The flow rate dependence of the lower mass-to-charge distribution is more complex and is discussed in some detail. Measurement of the time-of-flight mass spectrum for a number of different ion kinetic energy defects over a number of different volumetric flow rates results in a more thorough understanding of kinetic energy losses experienced in the jet structure of the Taylor cone, with direct impacts to the thrust performance of these types of devices. The appearance of these ions and distributions alter the thought on the emission mechanism at work in the electrospray system. No longer is electrospray defined and easily explained by the Iribarne emission mechanism and droplet generation by the Rayleigh instability.

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Mass Spectrometric Analysis of the Electrospray Plume from an Externally Wetted Tungsten Ribbon Emitter

Cited by 18 publications

References 11 publications

Effect of Aspect Ratio on the Wettability and Electrospray Properties of Porous Tungsten Emitters with the Ionic Liquid [Emim][Im]

Effect of Aspect Ratio on the Wettability and Electrospray Properties of Porous Tungsten Emitters with the Ionic Liquid [Emim][Im]

Capillary Extraction of the Ionic Liquid [Bmim][DCA] for Variable Flow Rate Operations

Mass Spectrometry of Selected Ionic Liquids in Capillary Electrospray at Nanoliter Volumetric Flow Rates

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