OpenStar Technologies, a New Zealand-based fusion research company, has reached a key milestone by generating its first plasma. Nuclear fusion research is exploding across the globe. OpenStar has adopted a novel approach to achieving commercial fusion energy that does not utilize a tokamak or stellarator design for its device. It is working on a levitated dipole reactor (LDR).
     Nuclear fusion on Earth works by replicating the process that stars use to generate energy. Inside a star, high temperature and pressure force nuclei of lighter atoms to fuse into larger atoms and release tremendous amounts of energy.
     Replicating the stellar fusion process on Earth would generate energy without any carbon emissions or radioactive waste. Nuclear fusion research has been going on for decades but has recently accelerated. Multiple approaches are being attempted to attain a net energy gain from this process.
     Tokamaks and stellarators are popular designs for nuclear fusion reactors and have shown great promise. However, OpenStar has taken a riskier approach by opting for an LDR design.
     A dipole system contains separated positive and negative charges. Such systems can be built in the lab, and they also occur naturally in nature. Nuclear fusion reactions require temperatures of several hundred million degrees. OpenStar researchers believe that dipoles can accommodate this heat and be scaled to build a fusion machine.
     Many fusion researchers utilize a magnetic field to confine the high-temperature plasma in a fusion reactor from hitting the walls. OpenStar’s approach achieves the same goal by constructing a magnetosphere similar to the one that exists around planets.
     In the magnetosphere, the highest-energy particles find their way toward the poles (in this case, the support system of the reactor). OpenStar avoids this problem by using levitation to keep the plasma within its doughnut-shaped reactor. The advantage of the LDR is that it does not have a lot of stored energy or “plasma current” that can potentially blow up the reactor in the case of other designs.
     OpenStar magnets utilize high-temperature superconductors (HTS). These are made of rare earth barium and copper oxides (REBCO) and can produce magnetic fields as strong as 20 Tesla. The Earth’s natural magnetic field is about fifty microteslas.
     OpenStar uses a helium gas loop to achieve temperatures of fifty Kelvin (-223 degrees Celsius) for the HTS magnets to operate in and create dipoles for the fusion reaction. The advantage of using an HTS magnet in this design is that it can be built faster and iterated quickly.
     Since the plasma in an LDR is stable and turbulence is not much of an issue, the team at OpenStar can create long pulse lengths for it. In the five trial shots they recently ran, the pulse length was between five and twenty seconds.
     Limiting pulse lengths to this time was necessary to gather the data required for their analysis. The LDR reactor is only at a prototype stage. However, achieving first plasma sets the stage for further technological advances in the years to come.
     OpenStar is hopeful that its LDR reactor can begin generating electricity as early as 2030.

OpenStar Technologies

     The Princeton Plasma Physics Laboratory (PPPL) has just announced the completion of the complex process of building the first quadrant of the magnet at the heart of the National Spherical Torus Experiment-Upgrade (NSTX-U) nuclear fusion reactor. This is a major milestone for the PPPL’s nuclear fusion project, which comes under the U.S. Department of Energy (DOE).
     PPPL said that “it is assembling two high-current magnets to create the toroidal field-ohmic heating coil (TF-OH) bundle. The magnets make up the core of the NSTX-U, similar to the core of an apple. They are designed to produce the highest magnetic field strength of any large spherical torus.”
     The toroidal field (TF) coil is a nineteen-foot-tall inner magnet which resembles a telephone pole. The TF carries up to four million amps of electric current to stabilize and confine the hot plasma in fusion experiments, according to a press release by PPPL.
     There will also be an outer magnet called the ohmic heating (OH) coil. It is a four-kilovolt magnet that wraps around the TF coil like thread around a bobbin.
     The press release stated that “It uses up to twenty four thousand amps to induce an electric field that drives an electric current within the vessel and helps heat the plasma”.
     Steve Cowley is the PPPL director. He said that “These magnets are critical to the NSTX-U experiment, and the team has been laser focused on this assembly. Constructing the first quadrant is a big achievement.”
     The PPPL states that the quadrants are going through a process called vacuum pressure impregnation (VPI). In this process, pieces of the TF coil “pie” are baked together into one very tall, solid piece of pie.
     The quadrant was constructed by technicians at Elytt Energy in Bilbao, Spain in July. Preliminary electrical tests conducted on the quadrant in August showed that the process was successful.
     Dave Micheletti is the division director of major science and engineering projects at the PPPL. He said that the team is now looking forward to the time “when the entire magnet is complete.”
     The NSXT-U recovery team has completed many critical components of the nuclear fusion device. Once the center stack magnets are installed, the team can start focusing on reassembling and testing the NSTX-U.
     Engineers have designed the TF coil and OH coil so the strong magnets will be powerful enough to confine the plasma during nuclear fusion experiments, which can occur every 20 minutes while the experiment is operating.
     The NSTX-U is currently the primary nuclear fusion experiment at PPPL. The spherical fusion device is shaped more like a cored apple than the doughnut-like shape of conventional tokamaks. It can produce high-pressure plasmas with relatively low and cost-effective magnetic fields.
     Using both neutral beams and high-power radio waves, the NSTX-U will heat the plasma to one hundred million degrees Celsius. This is seven times hotter than the Sun.
     According to the PPPL, the NSTX-U’s compact design makes it an ideal candidate to serve as the model for a nuclear fusion pilot plant followed by a commercial fusion reactor.
     The NSTX-U recovery project is eighty-four percent complete, and it has seen participation from scientists around the globe.
     PPPL’s end goal is to seek assistance from around the globe to help PPPL and the world figure out the best way to build commercial nuclear fusion reactors.

Princeton Plasma Physics Laboratory