Neutral-beam design options. [Design and cost optimization] Page: 4 of 11
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neutralizer choices could minimize the gas
load on the system; they would, however, be
a possible source of higher 2 impurity for
the fusion plasma.
A computer code has been written to nu-
merically integrate the equations that de-
scribe the populations of the beam consti-
tuents (Ref. 3). The cross sections of
Table I are stored in this code; the input
parameters for the code are the beam energy
E and the population mixture of the ion beam
(e.g. 120 keV, 1001 0%; 200 keV, 75% e. 15%
02, 105 03.). The appropriate cross sec-
tions are determined by interpolation of
the entries of Table I and the populations
of all beam constituents (W'. Do, and D at
E. 1/2E, and 1/3E; 020 and D20 at E and
2/3E; and 0" at E) are obtained as a func-
tios of the target thickness n moleculess/
cm2) by numerical integration.
we have not carried out a systematic
error analysis by propagating the cross-
section uncertainties through the calcula-
tions. ie note, however, that the equili-
brium- (thick-target) Do fractions agree
within about "2? with the measurements
listed in the review article by Allison and
Garcia-inoz. and that the growth curves
for total-neutral-power production from 62
and D,+ agree well with measurements re-
ported by us at the higher energies.(6)
There is, of course, no single parameter
that can fully summarize the results of
these calculations; however, much of the
information can be sunnarized with a
parameter that we call the neutralization
efficiency. in our earlier paper we
defined this as
[p n neutral bem [1
Owr nn i n am '
in this definition all emerging neutrals,
including molecules and fractional-energy
atoms, were included in determining the
efficiency. For many design applications,
however, only the atoms of the prescribed
energy are of interest; the molecules and
lower-energy atoms may be considered waste
power becausS (a) they do not penetrate
very deep into the target-plasma or (b)
they dilute the tritium target-plasma. In
the present paper. therefore, we use the
efficiency for the production of atoms of
the prescribed energy E. which is defined
(power in atoms of energy E)
( power in initial inn beam F 12"'
less recovered power, if any;
For a positive-ion beam containing a meatur
of 0. D+ and 03+ of energy E only the
"full-energy- 00 of energy E are included
in the calculation of n'. For a -pure" beam
of 02 of energy 2E or D3' of energy 3E,
is calculated for the Ge fragments of energy
E, since these are the only atoms produced
to figures 3 and 4 we give examples of
the neutralization efficiency n' vs 02-
target thikkness for '"pure" 1co beams (1001
D, 5', 02. or D3) for energies currently
of interest to the WFE program, The energy
label un each graph identifies the energy
E of the resulting atom beam; e.g. to
obtain 20-keV 0', the appropriate ion beams
would be 20-keV 0 or D, 40-keV D2'.
or 60-keV 03 . Since the cross sections
depend only on the relative velocity. the
20-keV-00 graph is also appropriate for
10-keV He. At energies above 180 keV/D the
desirability of D- beams is immediately
obvious from the figures; not only do these
have the largest conversion efficiency, but
they also require less neutralizer thickness
to attain maximum efficiency. (At very
thick targets all beams reach collisional
equilibrium and the distinction between
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Stearns, J. W.; Berkner, K. H. & Pyle, R. V. Neutral-beam design options. [Design and cost optimization], article, April 1, 1976; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1450193/m1/4/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.