Writing about Fusion

Hi! I’m Paige, and I’m an undergraduate at Princeton interested in physics and science communications. This January, I got to work as an intern here at Princeton Satellite Systems. These past few weeks, I’ve been writing about the fusion-related projects PSS is working on, such as their Princeton Field-Reversed Configuration (PFRC) fusion reactor concept and plans for a space propulsion engine.

My first task was to write a four-page report on the PFRC, including its design, market demand, and development timeline. I knew very little about fusion coming into this internship, so first I had to learn all I could about the process that powers the sun and has the potential to supply the earth with clean, practically limitless energy.

Various types of fusion reactors are under development by companies and coalitions all over the world; they differ in the reactors they use and their methods of confining and heating plasma. ITER, for instance, is an example of a tokamak under construction in France; it uses superconducting magnets to confine plasma so that the reaction of tritium and deuterium can occur. 

The PFRC, currently in the second stage of experiments at the Princeton Plasma Physics Laboratory, uses radio frequency waves to create a rotating magnetic field that spins and heats the plasma inside, which is contained by closed magnetic field lines in a field-reversed configuration resulting from the opposition of a background solenoidal magnetic field to the field created by the rotating plasma current. The fusion reaction within the PFRC is that of helium-3 and deuterium, which offers multiple advantages over reactions involving tritium. Compared with other fusion reactors, the PFRC is incredibly compact.  It will be about the size of a minivan, 1/1000th the size of ITER; this compactness makes it ideal for portable or remote applications.

After learning about the design and market applications of the PFRC, I created a four page brochure about PFRC, writing for a general audience. I included the basics of the reactor design and its advantages over other reactors, as well as market estimates and the research and development timeline. I went on to write four page brochures about PSS’s Direct Fusion Drive engine, which will use PFRC technology for space propulsion purposes, and GAMOW, the program under which PSS is collaborating on developing various power electronics for fusion reactors.

These past few weeks have been quite informative to me, and I realized how much I loved writing about science and technology! I learned all about fusion, and I especially loved learning the details of the PFRC reactor design. To summarize the design, research, and development of the PFRC and other technologies within four page flyers, I had to learn how to write about technology and research comprehensively and engagingly for a general audience, which improved my science communication skills.

10 thoughts on “Writing about Fusion

  1. Will you be able to build a fusion reactor with a power output of 30mw within mid to late 2030s? I plan to create a nuclear fusion powered airplane startup. For aviation safety it may need 2 reactors just in case one stops working in mid air. The inner fuselage width is 4.8m with a length of 35m.

    • Thanks for the comment. 15 MWe per machine is feasible. The schedule depends on how much funding we receive. Our next test device is PFRC-3. It will cost about $50M USD. It will take 2 years to build. We would operate it for a least 3 years to learn all we can about the physics so that we would be in a position to build PFRC-4 that would burn the plasma. Nobody has burned a plasma for very long, and not a deuterium-helium-3 plasma so we expect that PFRC-4 will teach us more physics. That will be a 4-year program. Since we don’t need new materials for the first wall or divertor and we can use conventional superconducting coils, our engineering challenges are not quite as tough as for D-T machines. With sufficient funding 2035 is not out of the question. That said, complex engineering projects all have delays and unforeseen issues that drag out their schedules.

      • Thanks for the reply! On second thought it may require more power for a longer version. This one would need 80 mw. If you can’t do 40mw per machine Christopher Galea said that multiple of this can be pack together by applying oppositely-directed currents for neighboring reactors. Is there any technical issues for packaging them together like that?

  2. I too was wandering about the brochures mentioned in the blog post that Paige just wrote.

    I have been watching the development of fusion in general and the DFD specifically. Progress does seem rather slow with a long time between posts. I am not a physicist so I have to ask naive questions, but I am very curious as to what it is that makes progress so slow.

    A few theories.
    1. No enough money or personnel. (always true)
    2. Or is it more technical
    The heating requires a lot of power and it is only possible to create a short burst. The only way to get continuous operation is to already have the whole system at a break even point. (understanding this is not a burning type device and that it must be driven)
    3. The tilt mode collapses and only allows a very short pulse.

    I am trying to read the papers, but the dates on them are 10-20 years old.

    • Thanks for the comments! For fusion in general there are still many challenging physics and engineering problems that need to be solved. For example, D-T machines have very high energy neutrons that damage the reactor. No solutions currently exist. Also in D-T machines, tritium needs to be bred which is a major engineering challenge. A D-T machine would have a large chemical plant attached to the reactor to breed and extract tritium.

      For PFRC our machine runs continuously. It is a driven machine so all heating is through the RF system. Our engineering analyses show that a net power gain is possible.

      The tilt mode is not a problem with oblate FRCs. PFRC will have an active control system for position control and possible rotation damping. We’ve demonstrated pulses as long as 200 ms. The limitation was the power drive system, not the plasma dynamics.

      • How far do the magnetic fields extend.
        If the drive is ~2m in diameter, how many could you put in a cylinder ~9m in diameter?

        • The magnetic fields rapidly drop off with radius to about 1% of the maximum magnetic field within the first 50 centimeters outside of the coils. One can additionally choose to apply oppositely-directed currents for neighboring DFD engines so that the magnetic dipole fields are subtracted in the region between the engines, even cancelling out completely in a portion of this region.

          We can hence place DFD engines right next to each other, so we consider the packing problem of how many circles you can fit within a larger circle (see, e.g., https://www.engineeringtoolbox.com/smaller-circles-in-larger-circle-d_1849.html, for a calculator). Up to 14 DFD’s that are 2 meters in diameter can fit in a 9 meter diameter cylinder.

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