Ion Joule Heating as a Function of Electric Field Scale Size*

Details Ion Joule Heating as a Function of Electric Field Scale Size* Ion Joule Heating as a Function of Electric Field Scale Size*

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm32a..13w&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SM32A-13

Physics

2467 Plasma Temperature And Density, 7807 Charged Particle Motion And Acceleration, 7831 Laboratory Studies

Scientific paper

We have demonstrated in earlier work the ability to control the magnitude and direction of the electric field (or the sign of potential change) in space in a simulated ionospheric environment as part of a laboratory-based experimental series related to ion heating. In that work we showed the transition from velocity-shear-driven ion cyclotron wave heating to ion Joule heating as a function of ion-neutral collision frequency1. In results presented here2, we present heating data using electric fields determined by differentiation of a fit to the potential profile obtained by an emissive probe, and have used the full-width-at-half-maximum (fwhm) of this field to characterize the size of the region. Both emissive probe and temperature measurements are derived from radial traversals of the respective probes across a cylindrical chamber. In the case of the ion temperature measurements, which are derived from energy analyzer data by conventional techniques, we demonstrate increased ion temperature consistent with increasing electric field length. We point out that measured ion temperature broadening is much less than directed energy which would be derived solely from the electric field acceleration. As in the earlier work, we observe a peak in the ion temperature and the Joule heating rate when the ion neutral collision frequency approaches the ion cyclotron frequency. The data suggest that for approximately constant pressure and electric field strength, the normalized ion temperature increase will be limited for a given scale size. For the data sets used, we argue that these observations are consistent with the notion of a limit to ion heating based on a comparison of the scale length of the electric field region to the mean free path for ion-neutral collisions. *work supported by ONR 1J. Geophys. Res.,106, 1807, Feb 2001, 2J. Geophys. Res., accepted, Jan 2002

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