LASL INTENSE 14-MeV NEUTRON SOURCE. Page: 9 of 12
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w = h = R = 1 cm
I = 1 amp
M = 3.5
T = 2000 K.
In this case the required plenum conditions are
no = 4.0 x 1020 cm-3, T = 2000 K, and p = 1610
psi. The upstream test conditions arc M = 3.5, n =
1.82 x 1019 cm-3, T1 = 580 K, p1 = 21.1 psi, v =
4.52 x 105 cm/sec and F = 8.23 x 1024 molecules/sec.
After the heat addition at 220 kW, the downstream
test conditions are M = 2.04, n = 2.02 x 1019
cm 3, T2 = 1400 K, p2 = 56.8 psi, and v2 = 4.08 x
It is important to note that flow of 8.23 x
1024 = 13 moles/sec from a plenum at 1610 psi to a
static temperature of 1400 K are within the experi-
ence of the LASL Rover Program. Design of the flow
system would borrow from that experience. Also cer-
tain test facilities, adequate to these conditions,
could be used for gas target testing.
With the values chosen, the neutron production
would be 7.9 x 1014 neutrons/sec with the flux at
the top and bottom being f = 2.5 x 1014 neutrons/
cm2sec. While this is within our design goal of
10'" to 1015, better figures may be possible through
the choice of a bigger current, smaller dimensions,
or both. The iteration of this calculation, subject
to the requirement of reasonable plenum and flow
conditions, needs to be undertaken in a systematic
Continuing with the closed deuterium flow cir-
cuit, the supersonic flux must be brought to rest
as adiabatically as possible, cooled, compressed,
and reheated to the plenum stagnation conditions.
Such calculations are standard in the design of
closed circuit hypersonic wind tunnels. The recov-
ery of supersonic flow usually uses a second throat
in order to partially choke the recompression shock
to a lower Mach number,1" but in this numerical ex-
ample the flow is already thermally choked to M =
2.04 and the pump power saved does not appear to be
worth the complexity. Accepting a normal shock at
M = 2.14, the stagnation pressure is further reduced
to 330 psi. The supersonic deuterium is then brought
to rest and cooled, probably in a large quench tank
so that the heat exchange surfaces do not have to
work at the 2550 K stagnation temperature. After
cooling, the gas is recompressed and returned to the
plenum where it is reheated to T before expansion
into the reaction volume. Some regeneration of heat
between the quench tank and plenum is possible, but
not a great deal unless the quench tank is to oper-
ate very hot. The deuterium circuit is summarized
in Fig. 10. Again, the details of this calculation
are not meant to indicate any kind of optimum or
final design, but only to show that a practical de-
sign is possible.
The point of using a supersonic target is,
after all, to minimize the gas lost out the beam
holes. This loss may be separated into two parts:
the boundary layer which is all lost, and the poten-
tial flow which turns outwa-d. In order to minimize
the boundary layer, which grows from near zero at
the throat, the expansion nozzle will be made short-
er than standard in wind-tunnel design. This would
make a somewhat two dimensional flow at the test
volume which is bad for aerodynamics but not very
important here. According to wind-tunnel design-
ers,12 the boundary layer loss will be less than the
potential flow loss, which is easier to calculate.
We have estimated this loss from a Prandtl-Meyer
turning calculation and conclude that it would be
practical to deflect the downstream walls to catch
all but about 2% of the deuterium flow. This miss-
ing fraction of the flow can be pumped out to re-
gain the necessary base pressure of about one
TO COOLING TOWER
p.i6pi p*1610ps1 p"330p1
M"3.5 UM2.0 HOS
VOLUM 25 HP
HEATER 22W PUMP
, -DEUTERIUM GAS RETURN, 420 POUNDS/HOUR
Fig. 10. Schematic of gas circuit.
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Henderson, D.B. LASL INTENSE 14-MeV NEUTRON SOURCE., report, January 1, 1972; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1026021/m1/9/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.