Response to “Comment on ’Electron collection by a
negatively charged sphere in a collisionless
magnetoplasma"
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Citation
Patacchini, L., I. H. Hutchinson, and G. Lapenta. “Response to
``Comment on `Electron collection by a negatively charged
sphere in a collisionless magnetoplasma' '' [Phys. Plasmas [bold
16], 014701 (2009)].” Physics of Plasmas 16.1 (2009): 014702-1.
As Published
http://dx.doi.org/10.1063/1.3057487
Publisher
American Institute of Physics
Version
Original manuscript
Accessed
Thu May 26 08:25:17 EDT 2016
Citable Link
http://hdl.handle.net/1721.1/57430
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Detailed Terms
Response to “Comment on ’Electron collection by a negatively
charged sphere in a collisionless magnetoplasma”’ [Phys. Plasmas
16, 14701, (2009)]
L. Patacchini and I. H. Hutchinson
Plasma Science and Fusion Center, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, USA
G. Lapenta
Centrum voor Plasma-Astrofysica, Departement Wiskunde, Katholieke Universiteit Leuven,
Celestijnenlaan 200B, 3001 Leuven, Belgium
May 5, 2010
We do not think that there is significant dispute here [1]. We fully agree that the problem we
have formulated [2] is to solve for the electron distribution, governed by Liouville’s theorem, and
account for the populated and unpopulated orbits. We also agree and have made clear that there is
an important problem we do not solve, namely the cross-field transport of both electrons and ions.
The transport problem is widely recognized in the magnetized probe literature, but not resolved.
Our practical definition of the “neighborhood” of the probe is the region of the plasma in which the
electron orbits can in fact be taken as governed by Liouville’s theorem (which excludes cross-field
transport). What we show, and calculate in detail, is that there is an important local electron
flux reduction arising in that neigborhood due to the magnetic field, actually within one Larmor
radius of the probe, not previously quantified. This effect must be accounted for in addition to any
other effects on electron (or for that matter ion) collection arising from the transport region. In
particular, if the transport problem is assumed to give a known local neighborhood electron density
(locally Maxwellian), then the localized solution we give enables the electron flux density to the
probe to be related to that local density.
References
[1] J.E. Allen, Phys.Plasmas 16, 14701 (2009).
[2] L. Patacchini, I.H. Hutchinson and G. Lapenta, Phys.Plasmas 14, 062111 (2007).
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