26 tesla! High field magnet exceeds everyone’s expectations

In january 2014, the HFM was just delivered to HZB.

In january 2014, the HFM was just delivered to HZB. © P. Dera/HZB

Insertion of the resistive Bitter coil into the superconducting coil.

Insertion of the resistive Bitter coil into the superconducting coil. © HZB

These strong copper lines provide current.

These strong copper lines provide current. © HZB

The screenshot testifies: 26,2 Tesla with a current of 19997 Amps.

The screenshot testifies: 26,2 Tesla with a current of 19997 Amps.

It’s done! The high field magnet is consistently producing magnetic fields of approx. 26 tesla and staying at this value over extended periods of time. And all this in spite of the fact that 26 tesla exceeds the original 25-tesla goal; in other words, the magnet turns out to be even stronger than anyone had hoped for. On Thursday afternoon, October 16, 2014, Dr. Peter Smeibidl who heads the HFM’s team of eight was able to report on their success and thank everyone involved with setting up the complex high field magnet with its own cooling systems and 4-megawatt power supply.

The new high field magnet is what’s known as a hybrid system consisting of one normally conducting and one superconducting coil that are connected in series. This new approach was developed at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida, USA. The goal was to build a high field magnet capable of producing the most powerful magnetic fields anywhere in the World for neutron scattering experiments.

New insights into quantum phenomena in matter

This is something not only HZB scientists but researchers from around the World have been waiting for – because certain quantum physical phenomena in matter can only be clearly visualized in the presence of extreme magnetic fields and, in many cases, neutrons are the ideal probes to use, a combination only the HZB will be able to offer. In the presence of these extreme, 20-tesla and greater magnetic fields, new order states and phase transitions in high temperature superconductors, new IT materials, and other samples could, for the first time ever, be experimentally investigated.

Fast progress

Overall, the first implementation of the HZB’s high field magnet went comparatively smoothly. “We were able to address most of the issues, which arose during testing really quickly,“ says project coordinator Dr. Hartmut Ehmler. This shows that quality control measurements during production of the coils and the set-up of the magnet system did work well.  

Some weeks ago, the HFM team did start testing the two magnets in series: Ramping up power from zero to only 1,000 Amperes and greater. In the process, the team tested how the system would respond to changes in current intensity (induction), which forces and voltage spikes occurred in the process, and whether or not this was consistent with previous calculations of the magnet’s performance.

The HZB team was supported by engineers from the National High Field Laboratory in Tallahassee, Florida, where both the superconducting outer coil and the inner resistance coil had been developed and built specifically for the HZB.

Until the end, everyone was on the edge

For security reasons, performance of the whole facility during an emergency shutdown and other incidents were tested. At approx. 14,000 Amperes, which corresponds to one-half the total power, unexpected difficulties arose: The energy liberated during a controlled shutdown exceeded prior calculations and resulted in a greater-than-intended rise in the helium coolant’s temperature and pressure. To minimize the risk, over the course of the next several weeks, the cryo facility’s valves were adjusted before the tests could be continued at higher currents. Until the very end, everyone was on edge to see whether or not the last several thousand Amperes would make for additional surprises before the finish-line could be crossed. Luckily, all systems cooperated without further incidents, so that the current could be incrementally increased up to a final value of 20,000 Amperes.

Over the next few weeks, a number of final tests will still need to be performed before the magnet will assume its place in Neutron Hall II by year-end.

For additional information:
We have gone ahead and documented the HFM’s setup for you at: www.hzbzlog.com. You’ll be able to read about the team’s experiences and about the various problems they were faced with and had to overcome in the process. Keep checking in with us to follow the challenges that will still have to be addressed during the 25-ton magnet’s move.

Read an Interview mit Prof. Dr. Bella Lake about the scientific motivation.

Construction of the HFM