Rotamaks: Yet Another Ignored Fusion Technology
Note: This article was written between March and May of 2017. My goal here is to communicate as simply and as accurately as I can. For this post, I did some fact checking with folks inside Dr. Cohens’ group at Princeton. Still, it is not perfect. But, nothing ever is. If we want to see this field develop, the US needs to fully fund this research. Make no mistake: we are leading on this. Enjoy.
Though they have many advantages, plasma structures do have a few problems. First and foremost, they are tricky to make. A loop of plasma can arise in many different ways [33 - 46]. In the figure below, I have drawn out the four methods to make a Field Reversed Configuration [56, 30].
In the foothills of Los Angeles, there is company known as Tri Alpha Energy. This is a fast moving startup. The company’s goal is to try and change everything about the energy world. Tri Alpha has raised over half a billion dollars to build a fusion power plant . At the heart of their approach is an FRC made by colliding spheromaks . The company is extending work in this field which stretches back to the mid-eighties [17, 24, 25]. It knows it must get the delicate process of making these plasma structures right. They have to generate two spheromaks, move them together, merge them, stabilize them and then keep them spinning. This fragile operation is shown below and modelled here .
Using metal rings, you setup fields which oppose each another. Then you release plasma. The field pivots. It switches from being made by the metal rings; to being made by the plasma donuts. These are the spheromaks. They can then be moved by varying magnetic fields around them . These fields guide the spheromaks into the center, where they merge, forming a new structure. Next, the company tries to hold the structure by keeping it spinning. This is done by firing particle beams along its’ edge . This is like kicking the loop, to keep it spinning. The CEO of the company describes it as “keeping a top spinning, by continuously flicking it” . Maintaining the spin is key. If not, deadly instabilities can come in the center or along the edge to kill it [41, 3]. It is generally accepted that the FRC can only live for a hundred microseconds, or less, before collapsing [3, 20, 55 – 62]. But as of today, Tri Alpha is ahead of all of its’ competitors, in its’ ability, to hold a large, long lasting FRC stable [57, 68].
It is at this point that Sam Cohen re-enters our story. At about the same time the Redmond lab was being shut down, Sam started making plans to build a Rotamak at Princeton [3, 4]. His idea was simple: stabilize, generate and heat the plasma in a FRC, with a rotating magnetic field. He did this, by making a column of plasma . The plasma bounced back and forth inside a Pyrex tube, reflected at each end . Technically he used a magnet mirror to do this. Around the pyrex would be a rotating magnetic field. The north and south poles spin around the plasma forming, heating and stabilizing the structure. This mechanism shown below [1, 13, 14, 27, 57].
Like so many fusion approaches, the rotamak has been hurt by a lack of US government funding. The US is not leading in fusion research. This is dangerous and I have been repeating this for 9 years. The US dominance in military, economic and political matters is underpinned by our scientific advancement. If we fail to hold the edge, we will fail this country. Our lack of funding for fusion has already killed off the ecosystem of researchers needed to develop it. If humanity invented net power today, the US military would be caught completely off-guard. It would be a disaster. They would have no scientific talent to turn too to jump-start a program. It would take years, and would leave our country dangerously vulnerable. Net power is the next milestone in this field. This could come at any time and from any direction. Do not assume it is decades away. Today, there are several companies who see a path to a commercial power plant . Today, China has invested tens of millions into an advanced fusion-fission center, which that years ahead of the Americans . What is our government doing? Where is the leadership? This must change.