Fusion energy calorimeter for the tokamak fusion test reactor Page: 2 of 7
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the TR geometry, are described in Ref. 3. It is
wortnwhi'e to implement a caTorimeter of the type
distusse' herein when the 0-, fusion neutron flu-
ence becc-es as large as 10'2 n/cm per oulse. This
level )f ,eutron production may be reached in the
TFP in the mid-1980s, but only in a small number
o oulses, However, fluences of the order of 1011
to 10' Pocm2 per Pulse can be expected in the TFTR
in the :ate-1980s, and in a rather large number of
-haracteristics of an Ideal Adiabatic Calorimeter
The neutron moderating medium where the tem-
perature increase is measured is referred to as
the "working medium." An ideal neutron calorimeter
(which cannot be built) would have the following
t views oni virginn" *usion neutrons.
:2: The incident fusion neutrons are completely
Tner-alzed in the calorimeter working medi-Im.
3 'here is negligible degradation or enhancem-
ent o' neutron energy n the material inter-
1ised Between the Plasoa and the workNf
*" he working medium has perfect thermal isol-
5 'he Working medium has both low density and
Tow specific heat, thereby providing high
6} The calorimeter is insensitive to ambient
2) The neutrons do not excite exothermic reac-
'ions in the working medium.
i All gamma rays Produces ry inelastic collis-
inns 'n t'e working medium are captured in
' te nbOve conditIOns are satisfied, teen
Te average tenoerature change. ,T, in the working
medium -niuCed av a 'sOn Pulse of length r 's
c f t)dt)
> 7 5 L
where 's the density, S is tee specific heat,
ard s one lengtn of the working medium (see
rig. wnicn absorbs essentially all the neutron
energy, : is the fusaon neutron flue at the cal-
pr'meter entrance, and E is the fusion neutron
energy. 'ote that ,AT> is independent of the
area of the entrance window.
Choice Of Heutron Moderator
The preferred moderator has (i) low density,
(ii) low specific heat, ;iii) high cross section
for elastic neutron moderation, and 'i icw heat
Conduction. These requirements imply that moder-
ators with low-2 atom constituents are favored.
Table i shows the relevant properties of can-
dfdate neutron moderating media. Liquid hydrogen
has the highest sensitivity, but it would require
.n elaborate cryogenic facility, and would always
present the danger of explosion. From the points
of view of sensitivity, safety, ease of handling
and cost, certain oils that are pure hydrocarbons
appear to be the most suitable liquid moderating
media. Polyethylene (CH ) is a favorable solid
Candidate. These materials have a sensitivity as
large as 2.5 to 3 times that of water. Here sen-
sitivity is defined as T/(oSXt; where the energy
absorption length AE is the distance over which
900 of the incident neutron energy is given ..
(However, the neutron flux at a distance iE from
the front face will be considerably larger than
1l% of the incident flux and will result in sig-
nificant energy deposition by gama rays at dis-
tances beyond :E.)
A solid working medium would be free of :oe
potential problem of convection, which could affect
the measurements of AT. On the other hard, a lia-
oid medium has the advantages that the temperature
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Jassby, D.L. & Imel, G.R. Fusion energy calorimeter for the tokamak fusion test reactor, report, April 1, 1981; New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc1211995/m1/2/: accessed March 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.