  Radio relics are extended radio emission features which trace shock waves in
the periphery of galaxy clusters originating from cluster mergers. Some radio
relics show a highly polarised emission, which make relics an excellent probe
for the magnetisation of the intra-cluster medium. The origin of the relic
polarisation is still debated. It could be a result of tangentially stretching
the magnetic field at the shock surface. This scenario would naturally explain
the alignment of the polarisation (E-vectors) with the shock normal. We have
implemented a toy model for the relic polarisation according to this scenario.
We find that the magnetic field strength itself crucially affects the
fractional polarisation. Moreover, we find that the shock strength has
surprisingly little effect on the overall polarisation fraction. Finally, we
find that the fractional polarisation may decrease downstream depending on the
magnetic field strength. Our results demonstrates that the shock compression
scenario provides a very plausible explanation for the radio relic polarisation
which specific features permitting to test the origin of radio relic
polarisation.
