Simulation of main plasma parameters of a cylindrical asymmetric capacitively coupled plasma micro-thruster using computational fluid dynamics

Greig, Amelia D.; Charles, Christine; Boswell, Roderick

doi:10.3389/fphy.2014.00080

Cited by 16 publications

(22 citation statements)

References 34 publications

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“…The Pocket Rocket discharge is a gamma discharge, driven by ion-induced secondary electrons [12], and the intermediate heating could potentially be caused by thermionic secondary electron emission becoming more dominant as the wall temperatures rises, increasing plasma density and heating from ion-neutral charge exchange collisions. However, a Langmuir probe measurement using a 1 mm diameter circular flat probe tip inserted through the rear plenum viewport and positioned on the central axis of the discharge tube at the axial midpoint shows no change in ion saturation current (hence ion density) throughout the first 100 s of continuous thruster operation.…”

Section: Discussionmentioning

confidence: 99%

“…However, the plasma density is an over an order of magnitude higher at the axial midpoint of the tube in a region covering only about 2 mm axial length [12], and the majority of light emission captured is from this region. Therefore, the radial cross sections stated above are those located at the axial midpoint of the discharge tube.…”

Section: Rovibrational Spectroscopy Methodsmentioning

confidence: 99%

“…Computational fluid dynamics (CFD) simulations of the Pocket Rocket thruster have shown the discharge operates in a gamma mode and is driven by ion-induced secondary electrons ejected from the inner alumina tube walls [12]. The large asymmetry of the device creates a direct current (DC) self bias on the alumina tube in the vicinity of the powered electrode, acting to accelerate the ion-induced secondary electrons into the center of the discharge bulk.…”

Section: Introductionmentioning

confidence: 99%

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Spatiotemporal study of gas heating mechanisms in a radio-frequency electrothermal plasma micro-thruster

2015

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A spatiotemporal study of neutral gas temperature during the first 100 s of operation for a radio-frequency electrothermal plasma micro-thruster operating on nitrogen at 60 W and 1.5 Torr is performed to identify the heating mechanisms involved. Neutral gas temperature is estimated from rovibrational band fitting of the nitrogen second positive system. A set of baffles are used to restrict the optical image and separate the heating mechanisms occurring in the central bulk discharge region and near the thruster walls. For each spatial region there are three distinct gas heating mechanisms being fast heating from ion-neutral collisions with timescales of tens of milliseconds, intermediate heating with timescales of 10 s from ion bombardment on the inner thruster tube surface creating wall heating, and slow heating with timescales of 100 s from gradual warming of the entire thruster housing. The results are discussed in relation to optimizing the thermal properties of future thruster designs.

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Section: Discussionmentioning

confidence: 99%

Section: Rovibrational Spectroscopy Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spatiotemporal study of gas heating mechanisms in a radio-frequency electrothermal plasma micro-thruster

2015

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“…Computational fluid dynamics (CFD) simulations have shown the discharge operates in a gamma mode and is driven by ion-induced secondary electrons ejected from the inner alumina tube walls. 38 The large asymmetry of the device creates a DC self bias on the alumina tube in the vicinity of the powered electrode, acting to accelerate the ion-induced secondary electrons into the center of the discharge bulk. This results in a peak ion density within the center of the tube, both axially and radially, which has also been observed in experiments.…”

Section: Apparatusmentioning

confidence: 99%

Neutral gas temperature estimates and metastable resonance energy transfer for argon-nitrogen discharges

2016

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Rovibrational spectroscopy band fitting of the nitrogen (N2) second positive system is a technique used to estimate the neutral gas temperature of N2 discharges, or atomic discharges with trace amounts of a N2 added. For mixtures involving argon and N2, resonant energy transfer between argon metastable atoms (Ar*) and N2 molecules may affect gas temperature estimates made using the second positive system. The effect of Ar* resonance energy transfer is investigated here by analyzing neutral gas temperatures of argon-N2 mixtures, for N2 percentages from 1% to 100%. Neutral gas temperature estimates are higher than expected for mixtures involving greater than 5% N2 addition, but are reasonable for argon with less than 5% N2 addition when compared with an analytic model for ion-neutral charge exchange collisional heating. Additional spatiotemporal investigations into neutral gas temperature estimates with 10% N2 addition demonstrate that although absolute temperature values may be affected by Ar* resonant energy transfer, spatiotemporal trends may still be used to accurately diagnose the discharge.

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“…Neutral gas heating in Pocket Rocket mostly results from ion-neutral collisions in the bulk plasma (charge-exchange and elastic) and from heating at the plasma cavity radial walls [11]. While propellant heating and thrust production has now been demonstrated [12] and complemented by computational studies (computer fluid dynamics [13] and particle in cell [14] codes) following earlier analytical studies [15], Pocket Rocket's viability for space use will only be achieved by refinements to the radiofrequency [16] and gas [17] delivery systems to improve overall efficiency and footprint. Optimum operation and viability in space would require achieving pulsed plasma operation combined with pulsed gas operation.…”

Section: Introductionmentioning

confidence: 99%

Vacuum Testing of a Miniaturized Switch Mode Amplifier Powering an Electrothermal Plasma Micro-Thruster

et al. 2017

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A structurally supportive miniaturized low-weight (≤150 g) radiofrequency switch mode amplifier developed to power the small diameter Pocket Rocket electrothermal plasma micro-thruster called MiniPR is tested in vacuum conditions representative of space to demonstrate its suitability for use on nano-satellites such as "CubeSats." Argon plasma characterization is carried out by measuring the optical emission signal seen through the plenum window vs. frequency (12.8-13.8 MHz) and the plenum cavity pressure increase (indicative of thrust generation from volumetric gas heating in the plasma cavity) vs. power (1-15 Watts) with the amplifier operating at atmospheric pressure and a constant flow rate of 20 sccm. Vacuum testing is subsequently performed by measuring the operational frequency range of the amplifier as a function of gas flow rate. The switch mode amplifier design is finely tuned to the input impedance of the thruster (∼16 pF) to provide a power efficiency of 88% at the resonant frequency and a direct feed to a low-loss (∼10 %) impedance matching network. This system provides successful plasma coupling at 1.54 Watts for all investigated flow rates (10-130 sccm) for cryogenic pumping speeds of the order of 6,000 l.s −1 and a vacuum pressure of the order of ∼2 × 10 −5 Torr during operation. Interestingly, the frequency bandwidth for which a plasma can be coupled increases from 0.04 to 0.4 MHz when the gas flow rate is increased, probably as a result of changes in the plasma impedance.

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Simulation of main plasma parameters of a cylindrical asymmetric capacitively coupled plasma micro-thruster using computational fluid dynamics

Cited by 16 publications

References 34 publications

Spatiotemporal study of gas heating mechanisms in a radio-frequency electrothermal plasma micro-thruster

Spatiotemporal study of gas heating mechanisms in a radio-frequency electrothermal plasma micro-thruster

Neutral gas temperature estimates and metastable resonance energy transfer for argon-nitrogen discharges

Vacuum Testing of a Miniaturized Switch Mode Amplifier Powering an Electrothermal Plasma Micro-Thruster

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