Magnetorotational instability (PROMISE Experiment)
Cosmic magnetic fields play a surprisingly active role in cosmic structure formation by fostering outward angular momentum transport and inward mass accretion onto central objects, like protostars or black holes, by means of the magnetorotational instability (MRI). At the PROMISE experiment, two special versions of MRI, the helical MRI and the azimuthal MRI, are investigated.
PROMISE is basically a TaylorCouette experiment with a gap width of 4 cm and a height of 40 cm (Figure 1). The utilized fluid is the eutectic alloy GaInSn which is liquid at room temperatures. Figure 2 shows the present setup, including a 20 kA power supply for the central rod and a pentagonshaped returncurrent system for the homogenization of the azimuthal field component.
The TaylorCouette experiment is usually carried out in the hydrodynamically stable regime, when the angular momentum is increasing outward. The helical MRI (HMRI) appears as an axisymmetric travelling wave when the azimuthal field acquires an amplitude that is comparable with that of the axial field (Figure 3). For purely or strongly dominant azimuthal field, the nonaxisymmtric azimuthal MRI (AMRI) shows up (Figure 4).
Figure 1: Sketch of the PROMISE facility, comprising a TaylorCouette cell with inner radius of 4 cm, outer radius of 8 cm, and a height of 40 cm, filled with GaInSn, an external coil and a central copper rod for the generation of the axial and the azimuthal magnetic field, respectively.  Figure 2: Present configuration of PROMISE with a 20 kA power supply (right) for the central rod and a pentagonshaped returncurrent system for the homogenization of the azimuthal field component. 
Figure 3: Results for HMRI. Measured velocity structure when increasing the current through the central rod, for a fixed current of 76 A in the coil (top). Approximately at 5000 A, HMRI emerges as an upward travelling wave. Experimentally and numerically determined dependence of the mean squared of the velocity perturbations on the applied rod current (bottom). 
Figure 4: Results for AMRI. Axial velocity perturbation for Re = 1480 and Ha = 124: (a) simulation for an idealized axisymmetric field. (b) Simulation for the realistic field geometry. (c) Measured velocity. (d) Numerically predicted growth rate. (e) Simulated and measured mean squared velocity perturbation. (f) Angular drift frequency. 
Press releases
Publications

Mamatsashvili, G., Stefani, F., Guseva, A., Avila, M.
Quasitwodimensional nonlinear evolution of helical magnetorotational instability in a magnetized Taylor–Couette flow
New J. Phys. 20 (2018), 013012 
Mamatsashvili, G., Stefani, F.
Linking dissipationinduced instabilities with nonmodal growth: The case of helical magnetorotational instability
Physical Review E 94 (2016), 051203 
Seilmayer, M., Gundrum, T., Stefani, F.
Noise reduction of ultrasonic Doppler velocimetry in liquid metal experiments with high magnetic fields
Flow Meas. Instrum. 48 (2016), 7480. 
Stefani, F., Kirillov, O.N.
Destabilization of rotating flows with positive shear by azimuthal magnetic fields
Phys. Rev. E 92 (2015), 051001(R). 
Rüdiger, G., Gellert, M., Schultz, M., Hollerbach, R., Stefani, F.
Astrophysical and experimental implications from the magnetorotational instability of toroidal fields
Mon. Not. R. Astron. Soc. 438 (2014), 271277. 
Kirillov, O.; Stefani, F.; Fukumoto, Y.
Local instabilities in magnetized rotational flows: A shortwavelength approach
Journal of Fluid Mechanics 760(2014), 591633 
Kirillov, O.; Stefani, F.; Fukumoto, Y.
Instabilities of rotational flows in azimuthal magnetic fields of arbitrary radial dependence
Fluid Dynamics Research 46(2014)3, 031403 
Seilmayer, M.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Stefani, F.; Gellert, M.; Rüdiger, G.; Schultz, M.; Hollerbach, R.
Experimental evidence for nonaxisymmetric magnetorotational instability in a rotating liquid metal exposed to an azimuthal magnetic field
Physical Review Letters 113(2014), 024505 
Kirillov, O.; Stefani, F.
Extending the range of the inductionless magnetorotational instability
Phys. Rev. Lett. 111 (2013), Art. No. 061103; arXiv:1303.4642  Kirillov, O.N., Stefani, F.
Standard and helical magnetorotational instability: How singularities create paradoxal phenomena in MHD
Acta Appl. Math. 120 (2012), 177198 
Kirillov, O.N., Stefani, F., Fukumoto, Y.
A unifying picture of helical and azimuthal MRI, and the universal significance of the Liu limit
Astrophys. J. 756 (2012), 83. 
Kirillov, O.N., Stefani, F.
Paradoxes of magnetorotational instability and their geometrical resolution
Phys. Rev. E 84 (2010), 036304  Kirillov, O.N., Stefani, F.
On the relation of helical and standard magnetorotational instability Astrophys. J. 712 (2010), 5268. 
Stefani, F., Gerbeth, G., Gundrum, Th., Hollerbach, R., Priede, J., Rüdiger, G., Szklarski, J.
Helical magnetorotational instability in a TaylorCouette flow with strongly reduced Ekman pumping
Phys. Rev. E 80 (2009), Art. No. 066303; arXiv:0904.1027 
Stefani, F., Gundrum, Th., Gerbeth, G., Rüdiger, G., Szklarski, J., Hollerbach, R.
Experiments on the magnetorotational instability in helical magnetic fields
New J. Phys. 9 (2007), Art. No. 295 
Stefani, F., Gundrum, Th., Gerbeth, G., Rüdiger, G., Schultz, M., Szklarski,
J., Hollerbach, R.
Experimental evidence for magnetorotational instability in a TaylorCouette flow under the influence of a helical magnetic field
Phys. Rev. Lett. 97 (2006), Art. No. 184502; astroph/0606473