Digitiser to help generate record-breaking magnetic fields

The International MegaGauss Science Laboratory, part of the Institute Solid State Physics (ISSP) at the University of Tokyo, is attempting to set a new world record for the highest ever indoor magnetic field. Looking to improve the precision of the firing processes with subnanosecond measurements, the ISSP installed a digitiser from Spectrum Instrumentation.

To optimise the magnetic fields generated by the laboratory’s MegaGauss machine, the trigger events that fire banks of large capacitors have to be triggered within 10 ns of each other. To achieve this high level of precision, the trigger signals for each capacitor have to be examined to determine their key characteristics and timing relationships to ensure optimal firing every time, as the physical parameters of the MegaGauss machine restrict firing to just a few shots per day.

The large capacitor banks that are used to generate the ultrahigh magnetic fields of the MegaGauss machine.

In order to capture and analyse the trigger signals, ISSP required a fully synchronous, 10-channel digitiser system that delivers a single shot sampling rate in excess of 1 GS/s. The high sampling rate allows the shape and frequency content of individual trigger pulses to be revealed, while fully synchronous sampling ensures interchannel timing measurements can be consistently made with subnanosecond precision.

A further complication is the fact that the MegaGauss machine generates dangerously high magnetic fields that are potentially unsafe and can easily interfere with the measuring instrumentation. Great care needs to be taken to shield both equipment and operators. The measurement system needs to be located in the laboratory while the operator adjusts and monitors the experiments from the safety of a control room. As such, the digitiser system must be able to operate remotely and controlled over the laboratory’s network.

The solution was to use a DN6.221-12 digitizerNETBOX system from Spectrum Instrumentation. The unit met all the necessary technical requirements, offering 12 fully synchronous channels, each sampling at 1.25 GS/s.

The Spectrum Instrumentation DN6-221-12 digitizerNETBOX.

As digitizerNETBOX units are LXI compliant instruments, they allow full remote control and data transfer over a Gigabit Ethernet connection. The system also provides a turnkey solution to multichannel acquisition, with users simply selecting the desired number of digitiser channels as well as fundamental specifications such as the sampling rate, resolution and onboard acquisition memory.

The Spectrum digitizerNETBOX is located close to the large capacitors and housed in a shielded enclosure to avoid EMI. LXI control allows easy operation with a notebook PC or via a connection to the laboratory network.

The unit also comes with SBench 6-Pro software that allows the user to quickly set up the system and start making measurements. SBench 6-Pro features an easy-to-use graphical user interface that allows multichannel waveform display, data analysis and documentation. Acquired and analysed signals can be stored and exported to other devices, or other software programs, in a number of formats such as MATLAB, ASCII, binary and wave.

An acquisition showing 10 independent trigger signals (used to fire the capacitors) but captured synchronously by the digitzerNETBOX. Signal characteristics are easily identified and critical timing measurements can be made. Data is also exported for further analysis and documentation.

The laboratory is now able to further optimise the performance of the MegaGauss machine, with the expectation that it will be able to generate the world’s highest ever indoor magnetic fields later this year.

Top image credit: ©stock.adobe.com/au/sakkmesterke