Ion Beams in Multi-Species Plasma

Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas

Database of ion temperature maps during geomagnetic storms

Ion temperatures as a function of the x and y axes in the geocentric solar magnetospheric (GSM) coordinate system and time are available for 76 geomagnetic storms that occurred during the period July 2008 to December 2013 on CDAWeb. The method for mapping energetic neutral atom data from the Two Wide‐angle Imaging Spectrometers (TWINS) mission to the GSM equatorial plane and subsequent ion temperature calculation are described here. The ion temperatures are a measure of the average thermal energy of the bulk ion population in the 1–40 keV energy range. These temperatures are useful for studies of ion dynamics, for placing in situ measurements in a global context, and for establishing boundary conditions for models of the inner magnetosphere and the plasma sheet

Spatial Structure of Ion Beams in an Expanding Plasma

We report spatially resolved perpendicular and parallel, to the magnetic field, ion velocity distribution function (IVDF) measurements in an expanding argon helicon plasma. The parallel IVDFs, obtained through laser induced fluorescence (LIF), show an ion beam with v ≈ 8000 m/s flowing downstream and confined to the center of the discharge. The ion beam is measurable for tens of centimeters along the expansion axis before the LIF signal fades, likely a result of metastable quenching of the beam ions. The parallel ion beam velocity slows in agreement with expectations for the measured parallel electric field. The perpendicular IVDFs show an ion population with a radially outward flow that increases with distance from the plasma axis. Structures aligned to the expanding magnetic field appear in the DC electric field, the electron temperature, and the plasma density in the plasma plume. These measurements demonstrate that at least two-dimensional and perhaps fully three-dimensional models are needed to accurately describe the spontaneous acceleration of ion beams in expanding plasmas

Mini-conference on helicon plasma sources

The first two sessions of this mini-conference focused attention on two areas of helicon source research: The conditions for optimal helicon source performance and the origins of energetic electrons and ions in helicon sourceplasmas. The final mini-conference session reviewed novel applications of helicon sources, such as mixed plasma source systems and toroidal helicon sources. The session format was designed to stimulate debate and discussion, with considerable time available for extended discussion.E.E.S. and A.M.K. acknowledge support for this work from NSF award No. PHY- 0611571

Storm time equatorial magnetospheric ion temperature derived from TWINS ENA flux

The plasma sheet plays an integral role in the transport of energy from the magnetotail to the ring current. We present a comprehensive study of the equatorial magnetospheric ion temperatures derived from Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) energetic neutral atom (ENA) measurements during moderate to intense (Dstpeak < −60 nT) storm times between 2009 and 2015. The results are validated using ion temperature data derived from the Geotail low‐energy particle energy analyzer and the Los Alamos National Laboratory magnetospheric plasma analyzer. The ion temperatures are analyzed as a function of storm time, local time, and L shell. We perform a normalized superposed epoch analysis of 48 geomagnetic storms and examine the spatial and temporal evolution of the plasma as a function of storm phase. This analysis illustrates the spatial and temporal variation of the ions from the plasma sheet into the inner magnetosphere. We find that the ion temperature increases approaching the storm peak. This enhancement has the largest magnetic local time extent near 12 RE distance downtail.Key PointsWe derive and statistically examine storm time equatorial magnetospheric ion temperatures from TWINS ENA fluxThe TWINS ion temperature data are validated using Geotail and LANL ion temperature dataFor moderate to intense storms the widest (in MLT) peak in nightside ion temperature is found to exist near 12 REPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137478/1/jgra53387.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137478/2/jgra53387_am.pd