Technical Design Report Super Fragment Separator

Pre-Separator
DRAFT
In order to access the exotic nuclei created via projectile fission and fragmentation a high-energy
separator with substantially increased acceptance, compared to the FRS, is required. The design of
the Super-FRS has been based upon this criterion [3]. In Table 2.4.1 the main parameters of the
FRS and the Super-FRS are compared. The phase-space acceptance of the Super-FRS has been
substantially increased by means of larger apertures and fields in the magnets. Besides the technical
layout of the production target, the separation and dump of the primary beam are major
technical challenges to be solved in the Pre-Separator [4]. The projectile beam emerging from the
production target has to be separated from the selected fragments and dumped in a special catcher
system. One major requirement is that the high-intensity primary beam should not impinge on the
first degrader to maintain the high-quality separation power of the two achromatic degrader stages.
Keeping in mind that the intensity and such the energy deposition of the primary beam is about two
orders of magnitude larger than the fragments the conditions and properties for the material and the
high radiation field require special considerations implemented in the optical layout.
The dipole magnets have been divided into three 11-degree parts. The space in between these
different dipole magnets (2.4 m) accommodates position-sensitive detectors and primary beam
catchers, i.e. the primary beam will not be dumped inside any magnet but in localized external
beam catchers. An extra dispersive focus is required directly behind the first dipole magnet system,
i.e. in total the Pre-Separator has three dispersive focal planes to form an overall achromatic system.
The division of the dipole magnets into three parts gives also advantages for the technical production
which reduces the costs of the magnets. The six beam catchers positioned on both sides of
the optical axis will stop the primary beam completely. In the target and in these beam catchers the
primary beam will be slowed down by atomic interaction and will be partially converted into heavy
projectile fragments and light particles, such as protons and neutrons which will even penetrate
through the 1 m thick material used for the beam catchers. Therefore, one has to consider if the
superconducting magnets right after an interaction zone (target, beam catcher) can survive the high
radiation field and how much temperature rise is acceptable to avoid quenching of a superconducting
magnet. From detailed Monte Carlo simulations using the PHITS code [41] we can conclude
that in principle all superconducting magnets stay below the quench limit. However, due to
high radiation load the cryogenic power exceeds the practical limits. Taken this into account and to
have a long term save and reliable operation, the first quadrupole and dipole magnets including the
hexapole magnet directly behind the focal plane PF1 are produced as normal conducting systems
with radiation-hard insulation.
Figure 2.4.5: Layout of the Pre-Separator. The focal planes (PF1-PF4) and beam catcher (BC1-BC6) are
indicated. In the standard separation mode of the Super-FRS a shaped degrader will be installed at PF2. All
hexapole magnets are placed outside of the quadrupole magnets.
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