K12 Bent Crystal XBCV Description
A bent crystal is used in the K12 beam to split off a small
fraction of the primary proton beam, after traversal of the
KL target, and transport it
cleanly towards the KS target.
The crystal has several advantages compared to the more
'classical' solution of a bending magnet followed by a pinhole:
- In case a dipole magnet were used, also the
muons produced in the target and the
collimators/dumps following it would be
deflected. The crystal selects such a
well-defined small phase space that only protons
have a chance to be transported further down the
beam line,
- The wanted fraction of protons to be
transported is so small (less than 10-4)
that a very small pin hole would be required.
The edges of the hole (skin depth) would be at
least comparable to the size of the hole itself.
- Our way of using the crystal limits quite
sharply the emittance of the outgoing proton
beam in both the horizontal and vertical plane.
Note that the crystal bends 450 GeV/c protons over an angle of
7.2 mrad. Using typical bending
magnets, a 5 metres long magnet would be required to obtain
this kind of angles. The crystal is only a few centimetres long.
In the picture above we show the goniometer that holds the
crystal.
A
detailed description of the specific application of a bent
crystal in the K12 beam has been published.
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