Technical Design Report Super Fragment Separator

DRAFT
Figure 2.4.122: Left: Von-Mises-stress in the graphite wheel irradiated with a 238 U beam (same parameters
as in Figure 2.4.120) according to an ANSYS simulation. Right: The same calculated for the connection
between INCONEL spoke and graphite ring.
The need to strip heavy fragments after their creation in the target, such that the maximum yield of
fully- stripped fragments is obtained, requires a layer of a suitable stripper material (e.g. titanium)
deposited on the downstream face of the target wheel. A technical solution that is compatible with
the high temperatures of the graphite wheel is presently under discussion.
In order to estimate the useful life time of the graphite target wheel due to radiation damage, we
have tried to relate the radiation damage at high energies and in transmission mode to experimentally
observed radiation damage at low energies (11 A MeV) where the specific energy loss is
much higher and the ions are stopped in the graphite. Tomut et al. [69] have found a critical fluence
value of about 10 13 238 U ions/cm 2 for low-energy uranium beams. At this critical fluence, the 3 nm-
diameter tracks produced by uranium ions start to overlap, giving rise to the observed changes in
graphite properties. According to Liu et al. [70] the track density at the high beam energies in the
Super-FRS target are about a factor of 10 3 lower. Another factor of 10 3 can be gained from annealing
of radiation damage at temperatures above 800 K [54]. Consequently, the track density
resulting from one year of Super-FRS operation with 238 U (10 7 pulses with 10 12 ions/s impinging
on a wheel rotating with 1 Hz) is estimated to be 10 11 /cm 2 , well be below the critical limit given
above. A more critical situation can be foreseen, however, for the beam catchers where the specific
energy loss and, therefore, the track density are much higher.
Target area layout and infrastructure
Following the concepts realized at all current high-power target systems, the Super-FRS target-area
elements (target assembly, pillow seals, diagnostic detectors etc.) consist of individual
modules ("plugs") that combine the respective element with a tight local iron shielding. The plugs
can be removed and inserted vertically by a crane (see Figure 2.4.123). They are inserted in a target
box that is connected to the beam line via inflatable all-metal seals which do not require any
clamping (so-called "pillow seals" [71]). In addition, all inserts together with their respective
shielding are sealed from ambient air at working-platform level by organic-material seals that are
operated manually during target service periods. The local shielding of each plug ensures that the
neutron dose at platform level during beam-on periods is low enough to allow the use of polymer
seals.
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