Read the Paper

OpenStar Technologies has published a new study in Fusion Engineering and Design, outlining the blueprint for a Deuterium-Tritium (DT) fueled levitated dipole fusion power plant. The levitated dipole’s simplicity makes it a compelling choice for high-availability, competitive fusion power, a case now recognized by the fusion community through peer review. This places OpenStar among the exclusive group of private companies with peer-reviewed DT fusion power plant designs.

The levitated dipole is not a new concept. The late Prof. Akira Hasegawa, former Chairman of the American Physical Society Division of Plasma Physics, proposed the levitated dipole as a candidate for fusion power generation in his 1987 paper titled “A Dipole Field Fusion Reactor”, citing its simplicity as a core advantage. Later work by J. Kesner et al. 2003 expanded on the concept and proposed the levitated dipole as a possible candidate for advanced fuel fusion.

Professor Akira Hasegawa: “The proposal presented by OpenStar deserves serious support as an attempt to construct a realistic and most desirable fusion device.”

DT is the fuel cycle that gets fusion to the grid fastest. With the lowest ignition temperature and highest reactivity of any known fusion fuel, it enables smaller, cheaper power plants and the most viable near-term path to fusion at scale.

Dennis G. Whyte, Professor of Nuclear Science and Engineering at the Plasma Science and Fusion Center, MIT: “Achieving a fusion power plant design with a simpler and faster maintenance and component replacement has been a central challenge to the development of commercially viable fusion. OpenStar’s concept delivers a solution to maintenance, based on the fundamental geometry of their fusion confinement, that appears both distinct and attractive. With their First-Of-A-Kind levitated dipole reactor design, they present a defined and credible path to de-risk its innovative confinement physics and magnet technology that deserves serious attention from the fusion community.“

In this peer-reviewed study, OpenStar offers solutions to the key challenges associated with the levitated dipole:

Onboard thermal management:

A cryogenic solid-liquid slush is used as an on-board thermal reservoir for the superconducting systems on the levitating core magnet. This is a constant temperature system, which allows the removal of thermal energy to happen at the speed of pumping a fluid instead of the speed of thermal diffusion. This greatly increases the fraction of time producing electricity, known as duty cycle, and will allow OpenStar to build more practical power plants.

Optimized coil geometry:

The shape of the levitating high-temperature superconducting coil has been optimized to both reduce magnetic forces and increase plasma confinement performance. This allows the core magnet to produce a strong magnetic field (>20 T) while only requiring standard steels to contain the induced magnetic forces.

Neutron shielding:

The preliminary design of a radiatively-cooled layered tungsten-boron carbide neutron shield for the levitating core magnet was presented. This shield effectively protects the sensitive components of the levitating core magnet from the high energy neutrons generated by the fusing plasma.

Modular maintenance:

The best-in-class simplicity and modularity of the levitated dipole was applied to allow for a practical maintenance procedure. As the levitating core magnet is not coupled to the vacuum vessel as in other confinement schemes, the core magnet can be periodically swapped out and maintained outside of the reaction chamber. This allows for power to be produced while maintenance is carried out on damaged components, allowing OpenStar to accept shorter lifetimes on key components and making the levitated dipole ideally suited for reliable, high-availability power generation.

OpenStar has developed the levitated dipole from a promising experiment to a commercial contender. The publication of this technical paper marks a significant milestone and serves as an industry signal that the levitated dipole is a viable path forward.

Thomas Berry, OpenStar’s Chief Product Officer said: “A publication pushes you toward a real deadline. It’s its own version of a product, something we have to ship, and that forces us to bring rigor and clarity to our designs.”

Read the Paper

OpenStar is the only company developing a levitated dipole reactor for commercial purposes, and this collaboration is the next step on our mission to revolutionise renewable energy by harnessing fusion - the same process powering our sun. 

The twelve-month agreement will see researchers at both MIT and OpenStar use advanced physics simulations to test methods of overcoming a core hurdle: heating a plasma to a hundred million degrees in order to initiate a fusion reaction.  

“The collaboration will allow us to lean on some of the best brains in the business, and for this first phase, will give us essential insights into how we build the larger version of our reactor,” said Dr Darren Garnier, OpenStar’s Director of Plasma Science and a visiting scientist at the PSFC.  

And while this collaboration is new, MIT and OpenStar are connected through history.  

From 1998 to 2014, MIT PSFC and Columbia University worked on the first Levitated Dipole Experiment (LDX) which saw a low-temperature superconducting magnet levitate in a vacuum chamber and confine a plasma. The shape of this plasma resembles the dipole magnetosphere of many planets, including Earth.  

In more traditional fusion machines, multiple superconducting magnets are used to produce a complex magnetic field. In contrast, the levitated dipole uses a single magnet to confine a plasma in a much simpler configuration.  

OpenStar has revived elements of the original LDX design with the addition of novel onboard power supplies and high-temperature superconducting (HTS) magnets, with the aim of bringing fusion power to the renewable energy market.  

To support these ambitious goals, the company recruited LDX’s former Chief Experimentalist, Dr Garnier, to become Openstar’s Director of Plasma Science.  

“When the LDX project lost its funding in 2010, it felt like we had left a lot on the table. We’d achieved a lot, and I felt there was a huge amount of potential for the levitated dipole,” said Dr Garnier.  

“A year ago I received an out of the blue email from OpenStar CEO Ratu Mataira telling me he was revisiting the dipole all the way in New Zealand. When they offered me the job a few months later, it was a no-brainer.”  

Prior to joining Openstar, Garnier was a research scientist at MIT working on a collaboration with another fusion company.  

With his ties to the institute, Garnier recognised the value of collaborating alongside world-leading experts to investigate ion cyclotron resonance heating (ICRH) for OpenStar’s Levitated Dipole, a common heating method in other fusion devices.  

The collaboration agreement sees researchers from both sides pooling resources to test using advanced physics models to simulate this possibility.  

“This first phase of the collaboration is essentially to answer the ‘does it work’ question. We can use validated computer codes to decide whether we use ICRH for future dipoles.” 

MIT’s Dr Gregory Wallace and Dr John Wright are leading this collaboration.  

For Dr Wallace, the collaboration means a chance to explore a new, innovative reactor configuration.   

“The LDX project never tested if hot ions can be produced and confined in a dipole field.  We’re hoping to show that this is possible through computational modelling, which will give us the confidence we need to design and build a high-power ICRH system going forward,” said Dr Wallace. 

A key component of proving the viability of dipoles as power plant devices is plasma performance. To briefly understand this in the context of fusion devices, and more specifically, levitated dipoles, read on.

Fusion is the process that powers the stars. Inside our sun, nuclei of hydrogen fuse to become helium, releasing huge amounts of energy. These nuclei are held together by gravitational confinement, something only possible in stars. When recreating this process here on Earth, we must deploy alternative confinement methods, the main ones for fusion being magnetic and inertial confinement.  

Here at OpenStar, we use magnetic confinement. This method uses a magnetic field to confine a plasma consisting of fuels upwards of 100 million degrees Celsius. In conventional machines such as tokamaks and stellarators, powerful magnets form a hollow donut shape, and the plasma is confined within. OpenStar’s levitated dipole is the opposite.  

In the levitated dipole configuration, the magnet is located in the core of the reactor, and the plasma is confined on the outside of the magnet. This configuration is reminiscent of the dipole magnetospheres seen around planets such as Earth, Jupiter and Uranus. Here on Earth, the magnetosphere helps to protect us from the solar winds ejected from the Sun. When these high-energy particles enter the magnetosphere, they follow Earth’s magnetic field lines and crash into the upper layers of the atmosphere at the north and south poles, forming the aurora borealis and australis. 

In 1986, Akira Hasegawa observed Voyager 2’s encounter with Uranus, prompting him to consider dipoles as a viable fusion confinement method.  Since this discovery, multiple laboratories around the world have investigated levitated dipoles as plasma confinement devices. OpenStar is currently the only company developing this concept for commercial purposes.  

For the levitated dipole, all necessary components, including the superconducting coils that produce the magnetic field, are contained inside the donut-shaped magnet. To further ensure no interruption of the field lines emanating from the magnet, the device must levitate inside a vacuum chamber entirely disconnected from all external power supplies.  

A major reason why dipole fields are among the most ideal for plasma confinement comes down to one of the most fundamental principles of physics: entropy. More specifically, entropy as it pertains to a phenomenon called the turbulent pinch. In this occurrence, convective cells drive peaked pressure rather than dispersing them, and as the energy in the plasma increases, so does the entropy. This not only increases the stability of the plasma itself, reducing some of the risks present in other system designs but also gives rise to plasma pressures far above the magnetic pressures being used to confine them, enabling the use of smaller, cheaper magnets to achieve fusion.  

OpenStar’s current prototype device is Junior. The purpose of this magnet is to prove the viability of our novel superconducting power supplies housed onboard the floating magnet itself, a world-first application method. While developing this device, our team has also been working on our next machine, Tahi. Tahi is all about plasma performance. Not only will it be the largest levitated dipole device in the world but aims to prove that this production method of fusion energy is scalable to power plants.

Junior - OpenStars Fusion Magnet

OpenStar Technologies

OpenStar Technologies is building a Levitated Dipole Reactor (LDR), uniquely integrating novel power supplies and leveraging High-Temperature Superconductors (HTS) onboard a levitating electromagnet. This half-tonne device, affectionately named Junior,  houses a complex arrangement of systems unlike anything else in the world. 

For more traditional fusion machines, a plasma is confined inside a fixed configuration of superconductors. For the levitated dipole, the superconductors are contained within a donut-shaped magnet with field lines emanating outwards, confining a plasma around the magnet in a dipole shape. We can observe this same shape in nature with Earth’s magnetosphere.   

Though our founding in 2021 came from modern innovations here in New Zealand, it would not have been possible without the foundations laid by institutions such as MIT, Columbia University, and Tokyo University. MIT, alongside Columbia, began their Levitated Dipole Experiment, or LDX, in 1998 and officially ceased research in 2014. Over this time, they studied the quirks and benefits of Low-Temperature Superconductors for Dipole application and successfully confined a plasma. The University of Tokyo began experiments on RT-1,  another levitated dipole device using HTS, in the early 2000s and they continue to extract findings from its operation today. 

As opposed to Low-Temperature Superconductors which operate close to absolute zero, High-Temperature Superconductors are more forgiving for fusion devices. Their ability to operate at liquid nitrogen levels (77K) makes a wealth of operations more accessible. HTS can carry more current or higher critical current densities; this is a key factor in driving better performance for plasma confinement. The higher thermal tolerance also increases power recirculation efficiency, as less energy is required to keep the coils cool. 

As the world invests heavily in conventional fusion devices, OpenStar is proving the viability of an alternative machine with our key enabling technologies. The fusion industry is united with the common goal of commercialising the process that powers the stars, and Junior is a stepping stone in achieving that with dipole devices. Our current milestone includes confining a plasma with a magnet charged by a flux pump. So far we have designed, built and tested such a magnet in less than 2 years, a feat in and of itself. 

Coils

The magnet itself comprises 14 non-insulated coils utilising ReBCO superconductor. Each coil is wound with up to 100 turns, alternating layers of HTS tape and solder paste. The coil is then placed into a temperature-controlled oven to evenly distribute the solder. For quality assurance, they are tested in liquid nitrogen (77 K). The use of FEM (Finite Element Modelling) is used for final validation.

The coils operate at 1440 A within a temperature range of 30 - 50 K and can reach a peak value of 5.6 T, storing 0.5 MJ of energy. This field strength is not enough for power plant-level fusion, however, this is not the purpose of Junior. This device is designed to test the integration of HTS power supplies in a levitated dipole magnet.

Subsystems

As Junior levitates, it does so while completely disconnected from any external power supplies. This is in part because the confined plasma will be upwards of 100 million degrees Celsius, a temperature that no physical material can withstand. More crucially though, particles must move at great speeds and extreme temperatures for fusion to occur and should the magnetic field lines have mechanical elements obstructing their path, the plasma would never reach its critical temperature. 

Levitating the magnet is relatively easy. Junior is initially hoisted into position with mechanical support, then held in its floating position by a second, smaller magnet atop the chamber. The challenges arise in integrating the power supply, electronics, and communication equipment on board the floating magnet in a cavity that is not penetrated by the magnetic fields. Additionally, all subsystems equipment must maintain their room temperature operating state, a far cry from the cryogenic coils and scalding plasma. 

To identify the optimal arrangement of the coils and subsystems, a type of genetic algorithm known as differential evolution was deployed. Junior now boasts a near-zero field region in the magnet cavity where the onboard power supplies live. 

A key component of this assembly is the power supply that is responsible for charging the magnet.  Such energy demand would usually warrant a large, heavy power source that cannot sit onboard a levitating magnet. The development of novel HTS power supplies for dipole application sets OpenStar apart from our fusion competitors.

Structure

Designed to withstand 74 tonnes of compressive force, the structure of Junior resists stresses that would otherwise cause self-implosion. Approximately half of the ReBCO conductor is used in the inner coils which form the mid-coil pack. The remaining coils sit at the top and bottom of the magnet. Crucially, the structure must also protect the zero field region which houses the onboard power supplies. 

To reach cryogenic operating temperatures for the magnet, we use conduction cooling with a helium gas loop. As the power supplies on board only offer a finite amount of power, the magnet must be redocked and recharged intermittently, the cold loop comes into play during this time to maintain cryogenic temperatures. 

Conclusion

This trip to Salt Lake City will allow us to share the process of developing Junior and the subsequent findings from various experimental campaigns amongst some of the brightest minds in the superconducting industry. Attendees will hear from a handful of OpenStar crew who have been a part of the development process from design to test. We encourage you to introduce yourself should you be in attendance and stay tuned as further developments unfold.