Measuring fusion reactions in real time

To produce the same kind of clean energy that powers the sun and the stars, scientists and researchers have long tried to build nuclear fusion devices that would work here on Earth. A recent design from research and development firm Sorlox uses a unique spiral-shaped chamber to compress fuel into a plasma state, which then ignites and generates huge pulses of energy.

 To build an optimal device, the company needed to measure—in real time—data such as the currents and voltages of the electromagnetic cage used to control the plasma as it floats past the accelerator walls. This posed a design problem because the extremely hot and highly electrically charged plasma reacts so quickly it could potentially be difficult to measure. In developing its device, the firm used a Genesis high-speed data acquisition (DAQ) system from HBM.


Sorlox accelerator and HBM Genesis shown in action

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Basic physics

Nuclear fusion is a process that differs from fission, the type of atomic reactions harnessed by existing nuclear power plants. Basically, fission produces energy by fracturing atoms while fusion generates energy through miniscule acts of atomic coupling. In the sun’s core, thermonuclear temperatures reach 15 million degrees C, high enough to cause protons to slam together and unite. Each time this happens, a tiny amount of mass is lost. As Einstein’s famous equation E = MC2 states, the mass is released in the form of energy. The released energy is explosive and totals huge amounts—thousands of times the amount it took to bind the atoms together in the first place.  

Engineers, scientists, and physicists have long attempted to develop a fusion device or accelerator that would work here on earth. Many think that the devices could help end the environmental destruction being caused by harmful byproducts from traditional energy sources. The fear is backed up by recent statistics that claim by mid-century the atmosphere will likely contain 500 parts per million of CO2 while toward the end of this century, the effects of this will cause major ecological harm. Renewable sources like solar and wind won’t play a significant part in solving the problem because they fluctuate too much and are difficult to store. The hope is to harness the immense energy produced by fusion reactions. 

Researchers already have built lab devices that cause fusion reactions by compressing a fuel pellet that contains deuterium, an isotope of hydrogen easily extracted from seawater, and tritium, made from lithium, also available from sea water. Similar to what happens in the sun or a star, when deuterium and tritium nuclei are fused at high temperatures and pressures, they form a helium nucleus, a neutron—and huge amounts of energy. At such high temperatures, matter exists in a plasma state where electrically neutral atoms or molecules have been converted to electrically charged ions. The hot plasma must be confined for a sufficiently long period so that it does not cool down and for fusion to occur and produce energy. Because the plasma is electrically charged and extremely hot, it has been found that the optimal mechanism to cage it is a strong magnetic field in the shape of a torus. 

Scientists have built devices that produce temperatures more than 10 times higher than in the sun and cause fusion reactions which produce megawatts of power for a few seconds. One project trains lasers on a tiny fuel pellet of the hydrogen isotopes deuterium and tritium. The pressure from the lasers compresses the fuel pellet which is inside a cylinder until the deuterium and tritium fuse together, releasing a huge burst of energy. The ongoing challenge has been to create a device where the amount of energy released by the fusion reaction is greater than the amount of energy that went into creating the fuel pellet. The next step is creating a fusion reaction that—like the reactions in the sun or stars—is self-sustaining, a point called “ignition.” In other words, the challenge is to create a self-sustaining, synthetic star. 

In developing its accelerator, Sorlox attacked the problem from another direction. The first innovation was developing a spiral-shaped compressor made from cast metal, which the company dubbed the Nautilus, for a compact device about the size of a refrigerator. Sorlox makes a plasma by ionizing deuterium gas using a high-strength magnetic field. The plasma is in the form of a current ring called a compact toroid. The magnetized plasma is launched into the Nautilus compressor and squished down from 1015 ions/cubic centimeter to 1018 ions/cubic centimeter. This is hot and dense enough to facilitate ignition.  

 

Sorlox accelerator screenshot of HBM’s Perception software showing good RF drive run pickup and timers

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Measuring the process

In running the math needed to develop the device, the scientists realized they needed a DAQ system that could measure about 100 million samples per second. The Genesis system employs a fast card that could handle those rates. The first iteration of the nuclear accelerator required the use of a four-channel DAQ system, and the next-generation machine needed a 12-channel system.   

According to project lead Brent Freeze, Sorlox used the DAQ system to measure the electromagnetic fields that control the plasma. A special magnetic sensor in the unit reads currents over a distance—important because of the pressures and temperatures involved. The sensor is an inductive device wrapped around an electrical conductor. Its output is a small voltage that represents the current induced as the plasma passes by. The scientists also used the DAQ system to measure the density of the plasma and its speed while it is being ejected into this compressor. A separate high-speed camera system allowed viewing the propagation of plasma—how it forms and is compressed.

The DAQ system took data continuously. This was important, because when each pulse is run, it must be controlled, which requires a feedback mechanism. With all the measurement data available, it was possible to determine the excitation and the responses from the different sensors to correlate all the data together. 

“Everything was being recorded by the DAQ system,” says Freeze. “Not only was the unit taking the data from the sensors, it also was digitally duplicating what’s coming in on the cameras into linked files. The DAQ system actually is doing double duty here. It’s both taking the data while we’re running and also backing up all of the imaging data on a hard drive. The system lets us explore what happens when you take a plasma up to these extreme temperatures and magnetic fields.” 

 

Application implications

According to Sorlox, the biggest application for its latest generation fusion accelerator potentially is electric power generation. Based on the annual fuel costs for a 1-GW coal-fired power plant, estimates say that a 90% fuel cost saving is feasible using the new technology. Also, the technology is environmentally friendly because it does not emit greenhouse gases. Other newer models of the pulsed plasma device work in applications including medical isotope and Helium-3 production. The DAQ system continues to be useful to Sorlox in developing next-generation machines by helping engineers get better models of fusion reactions and how they work. 


About the author

Dirk Eberlein graduated from the Leipzig University of Applied Sciences in Germany with a degree in engineering. He started his career at HBM Test and Measurement in 1998 and has held various positions. Since 2011, Eberlein has been the product and application manager for Genesis HighSpeed measurement systems. dirk.eberlein@hbm.com

More in Home