The occurrence of magnetism in the universe

March 13, 2018, Helmholtz Association of German Research Centres
A precession driven flow is supposed to power magnetic field self-excitation in a planned liquid metal dynamo experiment at HZDR. Credit: HZDR

Flows of molten metal can generate magnetic fields. This so-called dynamo effect creates cosmic magnetic fields, like those found on planets, moons and even asteroids. In the coming years, researchers are conducting a unique experiment in which a steel drum containing several tons of liquid sodium rotates around two axes in order to demonstrate this effect. It will be carried out in the new DRESDYN facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), an independent German research laboratory. A study, recently published in Physical Review Letters, reports the experiment's chances of success.

Similarly to a bicycle dynamo converting motion into electricity, moving conductive fluids can generate magnetic fields. The so-called magnetic Reynolds number (the product of the fluid's flow velocity, expansion and conductivity) primarily determines whether a is actually generated.

During the experiment, scientists in Frank Stefani's team at the HZDR's Institute of Fluid Dynamics aim to achieve the critical value required for the occurrence of the dynamo effect. For this purpose, a two-meter diameter steel cylinder containing eight tons of liquid sodium will rotate around one axis up to 10 times per second and once per second around another axis that is tilted with respect to the first. The technical term for this movement, which is often compared to a tilted spinning top, is precession.

"Our experiment at the new DRESDYN facility is intended to demonstrate that precession, as a natural driver of flow, is sufficient to create a magnetic field," says André Giesecke, lead author of the study. In his simulations and during accompanying water experiments using a mock-up six times smaller than the experimental setup, the scientists examined the structure of precession-driven flow.

"To our surprise, we observed a symmetrical double role structure in a specific range of the precession rate, which should provide a dynamo effect at a magnetic Reynolds number of 430," says the physicist.

The center of the Earth consists of a solid core surrounded by a layer of molten iron. "The molten metal induces an electric current, which in turn generates a magnetic field," explains Giesecke. The common belief is that buoyancy-driven convection, together with Earth's rotation, is responsible for this geodynamo. However, the role played by precession in the formation of Earth's magnetic field is still completely unclear.

The Earth's rotational axis is tilted by 23.5 degrees from its orbital plane. The rotational axis changes position over a period of approximately 26,000 years. This precessing motion through space is thought to be one of the possible sources of energy for the geodynamo. Millions of years ago, the moon also had a powerful magnetic field, as indicated by rock samples from the Apollo missions. According to experts, precession could have been the main cause.

The liquid sodium experiments at HZDR are expected to start in 2020. Unlike earlier geodynamo laboratory experiments, there will be no propeller inside the steel drum, as was used in the first successful dynamo experiment in Riga, Latvia, in 1999, in which HZDR scientists participated. This and other experiments in Karlsruhe, Germany and Cadarache, France, provided ground-breaking research for a better understanding of the geodynamo.

"In principle, we can define three different parameters for the experiments at DRESDYN: rotation, precession and the angle between the two axes," says Giesecke. He and his colleagues expect to get answers to the fundamental question of whether precession actually produces a magnetic field in a conductive fluid. Additionally, they are interested in finding out which flow components are responsible for the creation of the magnetic field, and the point at which saturation occurs.

Double role in the Container

"In simulations, we discovered that stationary inertia waves occur in a wide parameter range. Within a certain range, however, we have now noticed a characteristic double role structure that proves to be extremely efficient for the dynamo effect. In principle, we are already aware of such a velocity structure thanks to the French dynamo experiment, in which it was artificially produced by two propellers, while in our experiment it should emerge naturally."

The HZDR researchers used special ultrasound technology to measure the flow structure. "We were very surprised at how well the data from the experiment matches the results of the simulation. We therefore have an extremely robust prediction for the major DRESDYN experiment. For example, we know at which rotational rates the dynamo effect occurs and which magnetic structures we can expect," says Giesecke.

The scientific community involved with dynamos is eagerly awaiting the results of the planned experiment, which will operate at the limits of technical feasibility in many respects. "We also expect detailed insights into the general dynamics of liquid metal flows under the influence of magnetic fields. This will allow us to draw conclusions about flows in the industrial sector," according to Giesecke.

And last but not least, the magnetic tomography developed at the HZDR as part of its research is of interest to many areas of steel casting and crystal growing.

Explore further: Understanding stars: How tornado-shaped flow in a dynamo strengthens the magnetic field

More information: André Giesecke et al, Nonlinear Large Scale Flow in a Precessing Cylinder and Its Ability To Drive Dynamo Action, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.120.024502

Related Stories

Creation of a magnetic field in a turbulent fluid

March 10, 2007

Understanding the origin and behavior of the magnetic fields of planets and stars is the goal of research being carried out by many teams from all over the world. The VKS collaboration (CEA, CNRS, Ecole normale supérieure ...

Ancient lunar dynamo may explain magnetized moon rocks

November 9, 2011

The presence of magnetized rocks on the surface of the moon, which has no global magnetic field, has been a mystery since the days of the Apollo program. Now a team of scientists has proposed a novel mechanism that could ...

Recommended for you

How community structure affects the resilience of a network

June 22, 2018

Network theory is a method for analyzing the connections between nodes in a system. One of the most compelling aspects of network theory is that discoveries related to one field, such as cellular biology, can be abstracted ...

The pho­to­elec­tric ef­fect in stereo

June 22, 2018

In the photoelectric effect, a photon ejects an electron from a material. Researchers at ETH have now used attosecond laser pulses to measure the time evolution of this effect in molecules. From their results they can deduce ...

Water can be very dead, electrically speaking

June 21, 2018

In a study published in Science this week, the researchers describe the dielectric properties of water that is only a few molecules thick. Such water was previously predicted to exhibit a reduced electric response but it ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (10) Mar 13, 2018
The common belief is that buoyancy-driven convection, together with Earth's rotation, is responsible for this geodynamo. However, the role played by precession in the formation of Earth's magnetic field is still completely unclear.

This is indeed the common belief used to explain why smaller planets still do have a magnetic field in spite of billions of years of existence.
One should, however, be fully aware that that is all it is. A BELIEF. There is no confirmation of this belief being the actual supplier of earth's magnetic field. The current model is woefully super complex and impractical to test ( hence this simplified precessionary attempt ).

The clearest indication to date is that the magnetic field of the earth is decaying exponentially as if it models or represents a single impulse response to an initial input only thousands of years ago. There is absolutely no sign of an alternating "dynamo" effect except in the minds of those who want billions of years.
1 / 5 (2) Mar 13, 2018
We currently don't have a good explanation to what metallic hydrogen actually is and this is what most people say is the cause of the magnetism for stars and large gas planets like Jupiter (and no reason to say its not also the cause for planets like Earth).

First with Hydrogen I think the proton spin that we call charge is the cause (and this is made up of 3 x quark charges and 1 x gluon singlet charge), the effect is the S and P orbitals the electron field must follow (gluon singlet likely causing the S orbits, red, green and blue quarks causing the P orbits).

We also have to remember spacetime will be very dense (max curvature) near the center of mass for the star/planet and this could make the protons act as a bose-einstein condensate (and superconductor) so all the effective positive charge is in the core and negative charge on the outside - making it one huge rotating battery.
1 / 5 (2) Mar 13, 2018
This brings up a point of what the electron field actually is with any atom, rather than being a seperate particle the motion is actually a mirror of how the quarks and gluons are moving inside the proton.

So if we can think of the electron field being in shells and S, P, D orbitals, etc. We can also think of protons (and neutrons) also moving in those same S, P, D orbitals and shells as well.

Hydrogen being the simplest atom likely only fills the 1s orbital by default (which mirrors the gluon singlet and uniform charge distribution in the proton itself). Add a neutron and it then fills the 2s orbital for deuterium, helium would fill 1s, 2s, 2p3 orbitals (so full 1 and 2 shells) and why it is very stable and unreactive.
1 / 5 (1) Mar 14, 2018
Hydridic Earth seems another viable option.
1 / 5 (1) Mar 14, 2018
The conductive core of Earth consists of vertical plumes of heated magma in roughly dodecahedral arrangement, which induce the magnetic currents. This arrangement can be affected by distribution of dark matter around Earth, which would be subject of dodecahedral symmetry of most effective packing geometry of dark matter fluctuations. The dark matter catalyzes nuclear reactions, which heat the mantle and power their convective currents. When large cloud of dark matter will hit the solar system from outside, then this geometry would get broken, which is why we have both global warming with geothermal origin, both traveling magnetic pole at the same moment.
1 / 5 (3) Mar 14, 2018
All the current stories and theories about magnetism and gravity are unsuccessful, because science neither knows nor understands what matter is, how and from what it originates, and especially gentle about what gravity and magnetism are. To solve these phenomena, science has, up to now, spent a few million dollars dollars basically. If he wants to find out the truth about these phenomena, I have a solution that will not be much expensive, for example, to ask for a millionth of the previous futile expenses. But here's just a warning. Magnetism and gravity can not occur without the existence of the AETHER substance, from which matter is formed. And magnetism does not exist without a neutron. Why, the answer costs only $ 100 billion.
1 / 5 (1) Mar 14, 2018
The dodecahedral distribution of dark matter has its predecessor in dodecahedral Earth hypothesis or Russian geologists, who connected the mantle plumes with geological artifacts at the surface or Earth. But it's not the only possible geometry as many people already noted, that the geometry of continents reflecs the geometry of CMBR fluctuations, which would assign the terrestrial origin to CMBR observations. IMO both geometries rather share their common packing geometry so that this similarity is coincidental - but who knows? There are many hidden secrets in hyperdimensional geometry of Universe and AdS/CFT correspondence in it.
not rated yet Mar 14, 2018
There is only one way to make a magnetic dipole, ... charge rotation. Rub a glass ring on a cat. Spin it. Measure dipole flowing thru center. And because of the earth's dipole polarity, we have excess negative charge internally.
1 / 5 (2) Mar 15, 2018
How exactly does this 10x1/sec precession of a 2m not oblate sphere relate to the 26,000-year precession of the oblate sphere Earth? The scales seem slightly skewed.
1.5 / 5 (2) Mar 15, 2018
If you put salt water in a blender, will it create a magnetic field?
not rated yet Mar 15, 2018
Salt water in a blender will give you 2 magnetic dipoles.....they oppose each other. If you can separate the charge with velocity or should get a net dipole.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.