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In this paper we present a detailed numerical investigation of the hypothesisthat a rotation of astrophysical jets can be caused by magnetohydrodynamicshocks in a helical magnetic field. Shock compression of the helical magneticfield results in a toroidal Lorentz force component which will accelerate thejet material in toroidal direction. This process transforms magnetic angularmomentum (magnetic stress) carried along the jet into kinetic angular momentum(rotation). The mechanism proposed here only works in a helical magnetic fieldconfiguration. We demonstrate the feasibility of this mechanism by axisymmetricMHD simulations in 1.5D and 2.5D using the PLUTO code. In our setup the jet isinjected into the ambient gas with zero kinetic angular momentum (no rotation).Different dynamical parameters for jet propagation are applied such as the jetinternal Alfven Mach number and fast magnetosonic Mach number, the densitycontrast of jet to ambient medium, or the external sonic Mach number of thejet. The mechanism we suggest should work for a variety of jet applications,e.g. protostellar or extragalactic jets, and internal jet shocks (jet knots) orexternal shocks between the jet and ambient gas (entrainment). For typicalparameter values for protostellar jets, the numerically derived rotationfeature looks consistent with the observations, i.e. rotational velocities of0.1-1 percent of the jet bulk velocity.

Jet rotation driven by MHD shocks in helical magnetic fields