  The spatial scales of relativistic radio jets, probed by relativistic
magneto-hydrodynamic jet launching simulations (RMHDs) and by most
very-long-baseline interferometry (VLBI) observations differ by an order of
magnitude. Bridging the gap between these RMHD simulations and VLBI
observations requires selecting nearby active galactic nuclei (AGN), the
parsec-scale region of which can be resolved. 3C 84 is a nearby bright AGN
fulfilling the necessary requirements: it is launching a powerful, relativistic
jet powered by a central supermassive black hole, while also being very bright.
Using 22 GHz global VLBI measurements of 3C 84 we aim to study its sub-parsec
region in both total intensity and linear polarisation, to explore the
properties of this jet, with a linear resolution of $\sim0.1$ parsec. We test
different simulation setups by altering the bulk Lorentz factor $\Gamma$ of the
jet, as well as the magnetic field configuration (toroidal, poloidal, helical).
We confirm the persistence of a limb brightened structure, which reaches deep
into the sub-parsec region. The corresponding electric vector position angles
(EVPAs) follow the bulk jet flow inside but tend to be orthogonal to it near
the edges. Our state-of-the-art RMHD simulations show that this geometry is
consistent with a spine-sheath model, associated with a mildly relativistic
flow and a toroidal magnetic field configuration.
