Technical Design Report Super Fragment Separator

DRAFT
material) and received the anticipated good results. The material is routinely manufactured with
optical quality and exhibits a surface roughness of less than 10 nm, a maximum shape deviation of
less than 1 µm and a material inhomogeneity less than 10 -4 . Thus an areal weight homogeneity
better than 0.2 mg/cm 2 is reached. Together with the prototype stepper motors and linear drives, a
minimum thickness variation of 200 µg/cm 2 per step is achieved.
Concerning the ion-beam interaction with the degrader material, thermal and radiation damage
issues are to be considered. The degrader unit of the pre-separator will receive the strongest load,
and the worst case is a maximum intensity of 10 10 uranium ions per second (resp. spill). Our calculations
show that aluminium material will be heated by 8 K when the beam spot size has the
expected dimensions of 4 cm 2 . With 45 MPa, the pressure stays well below the cyclic stress limit of
290 MPa. The thermal diffusion time is of the order of 250 ms, thus well below the cycle time of
the synchrotron. This time decreases linearly with the beam spot area, so that also for slow extractions
no problems are expected. However, the numbers show that under continuous running
conditions water cooling of the degrader of the Pre-Separator is required. The conditions will be
similar to those which are presently prevailing in the FRS target area. In the considered energy
domain of several 100 MeV/u elastic collisions leading to displacements and thus to radiation
damage are of minor importance. Nevertheless it will be necessary to study whether such effects
(like swelling, formation of bubbles, etc.) may occur after high-dose irradiations. This is an issue
for the ongoing and coming development program.
For the degrader systems R&D is needed in order to further develop the existing technologies, e.g.
to develop vacuum-compatible high-precision linear and rotational drives for degrader with areas
which are larger than the ones which are operational now. Also the manufacturing and quality
control of quartz-type degraders of the required dimensions is required.
2.4.11.2.1 Degrader system in the Pre-Separator
Width
(cm)
Height
(cm)
Thickness
(g/cm 2 )
Wedge angle
(mrad)
Tolerances
(µm)
15 5 1-10 0-120 120
2.4.11.2.2 Degrader system in the Main-Separator
Width
(cm)
Height
(cm)
Thickness
(g/cm 2 )
Wedge angle
(mrad)
Tolerances
(µm)
30 6 0.5-10 0-80 60
2.4.11.2.3 Degrader system in combination with the energy buncher
At the entrance of the Low-Energy-Branch a particular and novel application using degraders is
realized, an energy buncher system. Its main components are a dispersive magnetic dipole stage
and a monoenergetic degrader. It reduces the momentum spread of in-flight separated ion beams,
usually of the order of several percent (± 3 % in the case of the Super-FRS), down to values
comparable to slowly extracted primary beams. Thus this scheme will be used to compress ("cool")
the longitudinal emittance on a nanosecond timescale. It opens a new window to physics experi-
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