An innovative accelerator-driven inertial electrostatic confinement device using converging ion beams Page: 4 of 8
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of many technical barriers, we note that the threshold energy needed for the p-"1B reaction is far
too high for thermonuclear ignition but readily achievable with beams.
Inertial Electrostatic Confinement
In the 1960's, P. Farnsworth (inventor of electronic television) invented a beam approach known
as Inertial Electrostatic Confinement (IEC) and developed the first concepts (Farnsworth, 1966;
Hirsch, 1967). Basically, the IEC concept uses electrostatic fields to inject multiple ion beams
toward a central spot in a background plasma. Spherical symmetry allowed and encouraged ion
recirculation. Electrons were introduced near the central spot to neutralize positive space charge
and permitted ion densities high enough to achieve significant fusion rates.
However, beyond simple cancellation of space charge, Farnsworth also asserted that the
convergence of ion beams and electrons toward a central spot could create not only a high-
density interaction zone but an ion trap as well. Solving the coupled Vlasov-Poisson equations
to account for particle inertia as well as space charge, he deduced that converging electrons and
ions would not simply neutralize one another but would, instead, form multiple layers of
alternating charge as the central focus is approached. Farnsworth associated these charged layers
with configurations of potential "wells" that would be deep enough to trap high densities of
energetic ions. Such a configuration would significantly amplify an ion's probability of
undergoing fusion before succumbing to parasitic loss and ultimately lead to energy out > energy
into beam.
The existence of these predicted deep potential wells is arguably the single key physics question
that determines the long-term viability of the IEC concept. Demonstrating that such potential
wells actually form near the focus of a spherical device and uncovering scaling laws governing
their properties are needed to validate any IEC concept with potential for scale-up to power
generation. Features of the highly non-equilibrium, non-neutral, high ion-current plasma created
near the central focus of an IEC device are doubtless more complex than described by
Farnsworth's initial analyses. (For instance, two-body scatterings tending to drive particle beams
into Maxwellian velocity distributions were ignored.) However, as long as postulated charge-
separation between ions and electrons is significant, Farnsworth's approach is self-consistent and
remains highly plausible. Significant improvements to understanding arguably require input
from experimental studies.
Experimental confirmation of the predicted deep potential wells has been encouraging but not
definitive. R Hirsch (1968), working with Farnsworth, performed experiments with an ion-gun-
injected IEC device and reported measurements of fusion reaction products emerging from a
potential well in the center of the IEC sphere. By the late '60s, after Farnsworth's death, the IEC
approach was generally abandoned by the fusion community in favor of much larger-scale
thermonuclear projects, such as tokamaks. As hopes for quick technical success of large-scale
fusion gradually faded, interest in the IEC approach revived. However, fundamental
experimental work was not resumed until the 1990's when collimated proton measurements from
a low-intensity IEC neutron source performed at UIUC confirmed the early Hirsch results (Gu
and Miley, 1997 and Gu et al., 1997).2
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Bauer, T. H. & Wigeland, R. A. An innovative accelerator-driven inertial electrostatic confinement device using converging ion beams, article, December 8, 1999; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc705793/m1/4/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.