Radiation issues in the Fermilab booster magnets Page: 2 of 3
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In fact, the lost beam is divided between the top and
bottom faces, but as we will see, beam loss on either face
leads to similar integrated dose on the top and bottom
coils, so for the sake of simplicity, we deposit the entire
beam loss in the top face in the simulation.Total Dose
Recalling the total proton rate that we started with, the
instantaneous energy deposition above corresponds to an
energy deposition on the order of 1-2x 10-7 Gy per
accelerated proton. The Booster has accelerated about
1x10 protons in its years of operation [5], so this
corresponds to roughly 10-20 kGy of total dose.
Recalling that Booster was significantly less efficient for
most of its life and the fact that beam loss is different in
different periods, it is reasonable to assume that some
areas of insulation may have received as much as 100-200
kGy.7W
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..
m
"II
i " F - i I
Figure 3: Longitudinal energy deposition in Gy/sec
at 500 MeV (top) and 5 GeV (bottom) incident
energy.
RESULTS
Instantaneous Energy Deposition
Figure 3 shows the longitudinal profile of the energy
deposition at both energies. Based on this, the first 50 cm
are taken as the shower maximum and used to determine
the peak of the energy deposition in the insulator. Figure
4 shows then rate of energy deposition in this region. We
see that both energies result in peak energy losses of
about 1.x 10-3 Gy/sec in the volume of the epoxy resin.
As a cross check of our assumptions, Figure 5 shows
the MARS calculation of the residual radiation at the front
face after 30 days of operation and 1 day of cool down.
This is consistent with surveys done in the Booster.Figure 4: Cross sectional energy distribution,
showing the energy deposited in the coil packs at
500 MeV (top) and 5 GeV (bottom) incident
energy.
Projected Dose
The Booster is expected to deliver on the order of
5 -10x 10" protons over the next 10 years [6]. The abilityI now
L.
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Prebys, E. Radiation issues in the Fermilab booster magnets, article, May 1, 2005; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc874008/m1/2/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.