10 research outputs found
Alfv\'en wave experiments with liquid rubidium in a pulsed magnetic field
Magnetic fields are key ingredients for heating the solar corona to
temperatures of several million Kelvin. A particularly important region with
respect to this is the so-called magnetic canopy below the corona, where sound
and Alfv\'en waves have roughly the same speed and can, therefore, easily
transform into each other. We present the results of an Alfv\'en-wave
experiment with liquid rubidium carried out in a pulsed field of up to 63 T. At
the critical point of 54 T, where the speeds of Alfv\'en waves and sound
coincide, a new 4 kHz signal appears in addition to the externally excited 8
kHz torsional wave. This emergence of an Alfv\'en wave with a doubled period is
in agreement with the theoretical predictions of a parametric resonance between
the two wave types. We also present preliminary results from numerical
simulations of Alfv\'en and magneto-sonic waves using a compressible MHD code.Comment: 7 pages, 4 figure
Mode Conversion and Period Doubling at Plasma- Unity in an Alfv\'en-Wave Experiment with Liquid Rubidium
We report Alfv\'en-wave experiments with liquid rubidium at the Dresden High
Magnetic Field Laboratory (HLD). Reaching up to 63 T, the pulsed magnetic field
exceeds the critical value of 54 T at which the Alfv\'en speed becomes equal to
the sound speed (plasma- unity). At this threshold we observe a period
doubling of an applied 8 kHz CW excitation, a clear footprint for a parametric
resonance between magnetosonic waves and Alfv\'en waves.Comment: 5 pages, 4 figure
Results of a modified PROMISE experiment
Key words magnetic fields – magnetohydrodynamics (MHD) The PROMISE experiment relies on the fact that the critical Reynolds number for the appearance of the magnetorotational instability (MRI) in liquid metal flows drastically decreases when the purely axial magnetic field is replaced by a helical one. We report the results of a modified version of this experiments in which the radial electrical boundary conditions are changed. Special focus is laid on the role of the radial jet region where the two Ekman vortices from the top and the bottom meet each other. c ○ 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim