Note: Flowing ion population from a resonance cavity source

Gayetsky, Lisa; Lynch, K. A.

doi:10.1063/1.3584969

Cited by 4 publications

(6 citation statements)

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“…29 In our system, the ion beam velocity is !8c s , where c s is the ion sound speed. 18 We do know that the magnitude of the ion beam velocity from the source did not change over the course of our data collection. 17 Given these facts, we approximated the ion current to the sphere as n o ev ib A xs , where v ib is the ion beam velocity and A xs is the cross sectional area of the sphere.…”

Section: Resultsmentioning

confidence: 96%

“…The stream of ions has an energy of approximately 13 eV (Ref. 18), but we do not exactly know how the flow of ions interacts with the sheath of the sphere to give the total magnitude of ion current density to the sphere's surface. Other authors show that when k D % a, for subsonic ion velocities, more ions are collected on the side of the sphere away from the ion source than on the side facing it.…”

Section: Resultsmentioning

confidence: 99%

“…A microwave Argon plasma source is connected to the vacuum chamber. 18,19 This setup generates plasmas with electron temperature (typically tenths of eV), density (10 4 cm À3 ), and Debye length (in the centimeter range) similar to those in the regions on interest in the ionosphere (hundreds of km in altitude). 19 The plasma source ions enter the chamber with flow energies between 12 and 15 eV (Ref.…”

Section: Experimental Setup and Diagnosticsmentioning

confidence: 99%

“…19 The plasma source ions enter the chamber with flow energies between 12 and 15 eV (Ref. 18). It should be stated that in the ionosphere, the ions are typically from atomic Nitrogen, Hydrogen, and Oxygen, not Argon.…”

Section: Experimental Setup and Diagnosticsmentioning

confidence: 99%

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A laboratory experiment to examine the effect of auroral beams on spacecraft charging in the ionosphere

et al. 2011

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A 2.54 cm diameter conducting electrically isolated Copper sphere is suspended in a low density (10 4 cm À3 ), low temperature (T e ¼ 0.5 eV) Argon plasma, which mimics a spacecraft in an ionospheric plasma. An electron beam with current density of approximately 10 À10 A=cm 2 and beam spot of 10.2 cm diameter, which mimics an auroral electron beam, is fired at the sphere while varying the beam energy from 100 eV to 2 keV. The plasma potential in the sheath around the sphere is measured using an emissive probe as the electron beam energy is varied. To observe the effects of the electron beam, the experimental sheath potential profiles are compared to a model of the plasma potential around a spherically symmetric charge distribution in the absence of electron beams. Comparison between the experimental data and the model shows that the sphere is less negative than the model predicts by up to half a volt for beam energies that produce high secondary electron emission from the surface of the sphere. It is shown that this secondary emission can account for changes in potential of spacecraft in the ionosphere as they pass through auroral beams and thus helps to improve interpretations of ionospheric thermal ion distributions.

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

Section: Experimental Setup and Diagnosticsmentioning

confidence: 99%

Section: Experimental Setup and Diagnosticsmentioning

confidence: 99%

See 2 more Smart Citations

A laboratory experiment to examine the effect of auroral beams on spacecraft charging in the ionosphere

et al. 2011

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“…The high count rate cutoff occurs when the instrument is saturated by the large particle fluxes. We have quantified the saturation limit of the HT by testing a flight spare detector in the Dartmouth ELEPHANT (Experimental Low Energy Plasma for Hemispherical Analyzer Nominal Testing) calibration chamber facility [ Frederick‐Frost and Lynch , ; Gayetsky and Lynch , ; Siddiqui et al , ]. Count rates greater than 130 kHz in our example detector cause distortion in pitch angle imaging due to saturation.…”

Section: Example Instrumentationmentioning

confidence: 99%

Electrostatic analyzer measurements of ionospheric thermal ion populations

Fernandes

Lynch

2016

JGR Space Physics

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We define the observational parameter regime necessary for observing low‐altitude ionospheric origins of high‐latitude ion upflow/outflow. We present measurement challenges and identify a new analysis technique which mitigates these impediments. To probe the initiation of auroral ion upflow, it is necessary to examine the thermal ion population at 200–350 km, where typical thermal energies are tenths of eV. Interpretation of the thermal ion distribution function measurement requires removal of payload sheath and ram effects. We use a 3‐D Maxwellian model to quantify how observed ionospheric parameters such as density, temperature, and flows affect in situ measurements of the thermal ion distribution function. We define the viable acceptance window of a typical top hat electrostatic analyzer in this regime and show that the instrument's energy resolution prohibits it from directly observing the shape of the particle spectra. To extract detailed information about measured particle population, we define two intermediate parameters from the measured distribution function, then use a Maxwellian model to replicate possible measured parameters for comparison to the data. Liouville's theorem and the thin‐sheath approximation allow us to couple the measured and modeled intermediate parameters such that measurements inside the sheath provide information about plasma outside the sheath. We apply this technique to sounding rocket data to show that careful windowing of the data and Maxwellian models allows for extraction of the best choice of geophysical parameters. More widespread use of this analysis technique will help our community expand its observational database of the seed regions of ionospheric outflows.

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Measuring the seeds of ion outflow: Auroral sounding rocket observations of low‐altitude ion heating and circulation

et al. 2016

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We present an analysis of in situ measurements from the MICA (Magnetosphere‐Ionosphere Coupling in the Alfvén Resonator) nightside auroral sounding rocket with comparisons to a multifluid ionospheric model. MICA made observations at altitudes below 325 km of the thermal ion kinetic particle distributions that are the origins of ion outflow. Late flight, in the vicinity of an auroral arc, we observe frictional processes controlling the ion temperature. Upflow of these cold ions is attributed to either the ambipolar field resulting from the heated electrons or possibly to ion‐neutral collisions. We measure trueE→×trueB→ convection away from the arc (poleward) and downflows of hundreds of m s−1 poleward of this arc, indicating small‐scale low‐altitude plasma circulation. In the early flight we observe DC electromagnetic Poynting flux and associated ELF wave activity influencing the thermal ion temperature in regions of Alfvénic aurora. We observe enhanced, anisotropic ion temperatures which we conjecture are caused by transverse heating by wave‐particle interactions (WPI) even at these low altitudes. Throughout this region we observe several hundred m s−1 upflow of the bulk thermal ions colocated with WPI; however, the mirror force is negligible at these low energies; thus, the upflow is attributed to ambipolar fields (or possibly neutral upwelling drivers). The low‐altitude MICA observations serve to inform future ionospheric modeling and simulations of (a) the need to consider the effects of heating by WPI at altitudes lower than previously considered viable and (b) the occurrence of structured and localized upflows/downflows below where higher‐altitude heating rocesses are expected.

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Note: Flowing ion population from a resonance cavity source

Cited by 4 publications

References 6 publications

A laboratory experiment to examine the effect of auroral beams on spacecraft charging in the ionosphere

A laboratory experiment to examine the effect of auroral beams on spacecraft charging in the ionosphere

Electrostatic analyzer measurements of ionospheric thermal ion populations

Measuring the seeds of ion outflow: Auroral sounding rocket observations of low‐altitude ion heating and circulation

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