PFRC Article in the Journal of Fusion Energy

Our latest paper, The Princeton Field-Reversed Configuration for Compact Nuclear Fusion Power Plants, is now available in the Journal of Fusion Energy, Volume 42, Issue 1, June 2023. This paper is the first released in “The emergence of Private Fusion Enterprises” collection. A view-only version is available for free here.

Our paper gives an overview of the Princeton Field-Reversed Configuration (PFRC) fusion reactor concept and includes the status of development, the proposed path toward a reactor, and the commercialization potential of a PFRC reactor.

The Journal of Fusion Energy features papers examining the development of thermonuclear fusion as a useful power source. It serves as a journal of record for publication of research results in the field. This journal provides a forum for discussion of broader policy and planning issues that play a crucial role in energy fusion programs.

NIF: Net (Scientific) Gain Achieved in Inertial Fusion! What is the impact on PFRC?

The internet was abuzz last week with the news that the National Ignition Facility had achieved that elusive goal: a fusion experiment that achieved net (scientific) energy gain. This facility, which uses 192 lasers to compress a peppercorn-sized pellet of deuterium and tritium, released 3 MJ of energy from 2 MJ of input heat.

We have to use the caveat that this is “scientific” gain because it does not account for the total amount of energy needed to make the laser pulse. As a matter of fact, the lasers require 400 MJ to make those 2 MJ that reach the plasma. If we account for this energy, we can call it the “wall plug” gain or “engineering” gain since it includes all the components needed. This gain for laser-induced fusion is still less than 1%, because the lasers are very inefficient.

Nonetheless, this is great news for all fusion researchers. Since we often get asked: Has anyone achieved net (scientific) gain yet? Now we can say: Yes! It is physically possible to release net energy from a fusing plasma, to get more energy output than direct energy input. This advance has been achieved through various new technology: machine learning to select the best fuel pellets, wringing more energy from the lasers, more exact control over the laser focusing. Modern technology, especially computing for predicting plasma behavior, explains why progress in fusion energy development is now accelerating.

Tokamaks have also come close to net gain, and in fact the JT-60 tokamak achieved conditions that could have produced net gain, if it had used tritium [1].

The reason JT-60 did not use tritium in those shots is very relevant to our fusion approach, the PFRC. Tritium is radioactive, rare, expensive to handle, and releases damaging neutrons during fusion. Tritium is also part of the easiest fusion reaction to achieve in terms of plasma temperature, the deuterium-tritium reaction. It makes sense for fusion experiments to use such a reaction, but this reaction presents many difficulties to a future working power reactor.

The PFRC is being designed to burn deuterium with helium-3, rather than with tritium, precisely to make the engineering of a reactor easier. The deuterium-helium-3 reaction releases no neutrons directly. Some deuterium will fuse with other deuterium to produce neutrons and tritium, but the PFRC is small enough easily expel tritium ash. This results in orders of magnitude less neutrons per square meter reaching the walls. Once we have scientific gain, like the NIF has now demonstrated for laser fusion, we have an easier path to engineering gain — that is, net electricity.

So while the laser fusion milestone doesn’t directly impact our work on the PFRC, it is important to the field. We will continue to follow the progress of all our peers as we work to achieve higher plasma temperatures in our own experiments!

[1] T. Fujita, et al. “High performance experiments in JT-60U reversed shear discharges,” Nuclear Fusion 39 1627 (1999). DOI: 10.1088/0029-5515/39/11Y/302

Bright RMF pulses at 1.8 MHz

We have commenced operations at 1.8 MHz in PFRC-2, after installing new capacitors over the summer to allow us to lower the frequency from the previous value of 4.3 MHz. A lower frequency should allow the RF system to directly heat the plasma ions, not just the lighter electrons.

With each new operating frequency, we need to explore how the plasma responds: to fill pressure, RMF power, magnetic field, mirror ratio, and more. We have now achieved “big bright flashes” with Argon plasmas in PFRC-2! The seed plasma, on the left, is a dimly glowing column. The RMF heated plasma, on the right, produces a bright flash.

RMF pulse at 1.8 MHz with Argon

This bright light is atomic or molecular line emission, depending on the fill gas. This occurs in the PFRC when the plasma gets dense and energetic due to the RMF current drive. With Argon, we have achieved bright discharges at about 50 kW, or 1/4 of the total RF power available. Argon gas produces a higher density plasma in the PFRC because it has a lower ionization energy.

We are now working to find the parameters which will produce these bright, energetic discharges in our target operating gas of hydrogen. The hydrogen gas must dissociate as well as get ionized. We can experiment with other gases too, like helium and neon, to learn more about the system.

Great article from National Academy of Sciences on PFRC

We recently learned of this great article written on FRCs and the PFRC in particular: “Small-scale fusion tackles energy, space applications”. It was posted on the website for the Proceedings of the National Academy of Sciences (PNAS) in 2020.

The article is well written and provides information on the PFRC innovation, fusion fuel choice, and development plan. It does a great job explaining the heating methods of the main FRC approaches in industry today: the RF-heated PFRC, the beam-heated TAE approach, and the merged-and-compressed Helion Energy approach. Dr. Sam Cohen, Stephen Dean, Michl Binderbauer (TAE), and Michael Paluszek are quoted.

Cohen, for his part, has been pursuing his Princeton Field Reversed Configuration (PFRC) design since 2002, with a strong emphasis on simplicity and compactness… The idea, says Cohen, is to drive oscillating currents through these coils in a way that sets up a rotating magnetic field inside the tube: a loop of flux that whirls through the plasma like a flipped coin and drags the plasma particles around and around the waist of the cylinder. In the process, he says, “the fields create, stabilize, and heat the FRC”—all in a single deft maneuver.

Small-scale fusion tackles energy, space applications, M. Mitchell Waldrop, January 28, 2020, 117 (4) 1824-1828

Read and enjoy!

New FRC Journal Paper is an Editor’s Pick at Physics of Plasmas

PFRC inventor Dr. Sam Cohen and his student Taosif Ahsan have published a new journal paper, “An analytical approach to evaluating magnetic-field closure and topological changes in FRC devices,” in Physics of Plasmas (Phys. Plasmas 29, 072507 (2022)). The paper is an Editor’s Pick and has important implications for confining plasma in Field-Reversed Configurations (FRCs).

We describe mathematical methods based on optimizing a modified non-linear flux function (MFF) to evaluate whether odd-parity perturbations affect the local closure of magnetic field lines in field-reversed configurations. Using the MFF methodology, quantitative formulas are derived that provide the shift of the field minimum and the threshold for field-line opening, a discontinuous change in field topology.

Paper Abstract

This paper follows up on a 2000 paper by Cohen and Milroy, which made qualitative assertions about changes in magnetic field topology, e.g., movement of the center of separatrix, separator line, and other geometric parameters. Ahsan and Cohen developed the modified flux function (MFF) mathematical tool to quantitatively understand the effects of perturbations on a Solov’ev FRC field structure.  The analytical results from this function have reproduced the previous numerical observation that small odd-parity perturbation preserves FRC field structure. In particular, the contours around the equilibrium stay closed.

Closure of magnetic field lines limits plasma losses that would occur due to charged particles leaving the FRC by traveling along open field lines. The paper points out that in a reactor-scale FRC where ions have a large gyroradius relative to the field structure, but electrons have a small radius and follow the field lines, particle and energy losses on the open field lines outside the FRC will be significant. Hence, ensuring closure of field lines is a crucial step toward improved plasma confinement in FRCs.

3D contours of a perturbed FRC using the modified flux function (MFF)

Princeton Fusion Systems Awarded Three DOE INFUSE 2022a Grants

The Department of Energy announced the First Round of the FY 2022 Public-Private Partnership Awards to Advance Fusion Energy. The awards list contains 18 awardees. Princeton Fusion Systems, also known as Princeton Satellite Systems, received three awards:

Electron density profiles on PFRC with USPR: Ultrashort Pulse Reflectometry (USPR) is a plasma diagnostic technique that would be used on the Princeton Field-Reversed Configuration (PFRC) to measure electron density profiles. Such profile measurements provide insight into the structure of PFRC plasma and can improve our estimates of confinement time. Our University partner is University of California, Davis, PI Dr. Neville Luhmann.

Evaluating RF antenna designs for PFRC plasma heating and sustainment: We intend to analyze RF antenna performance parameters critical to the validity of robust PFRC-type fusion reactor designs. Team member University of Rochester will support TriForce simulations and contractor Plasma Theory and Computation, Inc. will support RMF code simulations. Our national lab partner is Princeton Plasma Physics Laboratory, PI Dr. Sam Cohen.

Stabilizing PFRC plasmas against macroscopic low frequency instabilities: This award will use the TriForce code to simulate several plasma stabilization techniques for the PFRC-2 experiment. Our lab partner is PPPL and the team again includes the University of Rochester.

These awards will help us advance PFRC technology. Contact us for more information!

TriForce model of the PFRC-1 experiment

A Cutting Edge Modular Nuclear Fusion Power Plant Using PFRC Reactors

The following movie is by Woodruff Scientific, Inc. It was developed under an ARPA-E Grant. The movie shows a five PFRC modular power plant. The technician is shown for scale. Modular power plants are ideal for power systems because they allow for incremental capital investment. Modules would be added as needed. You can read more about PFRC here.

Experimental work on PFRC-2 was funded by an ARPA-E OPEN 2018 grant. ARPA-E is funding many cutting edge fusion projects including new mirror machines, stellarators and many others.

5 PFRC Modular Power Plant

ARPA-E 2022 Summit

We will be at the 2022 ARPA-E Summit in Denver, CO next week, May 23-25! PFS will have booths for both of our projects, WIDE BAND GAP SEMICONDUCTOR AMPLIFIERS FOR PLASMA HEATING AND CONTROL and Next-Generation PFRC. This post has links to the documents that we will have at our booth both physically and on the summit mobile app!

Wide Band Gap Amplifiers (GAMOW)

Next-Generation PFRC (OPEN 2018)

PFRC video including animation of how it works
7-minute tech demo video of PFRC-2 experiment from 2021 Virtual Summit

The ARPA-E 2022 Nuclear Fusion Annual Meeting in San Francisco

I attended the ARPA-E 2022 Fusion Annual Meeting at the Westin St. Francis hotel in San Francisco. This is a meeting for all companies that have ARPA-E grants and are working on nuclear fusion technology. Below is the poster for our Princeton Field Reversed Configuration ARPA-E OPEN 2018 grant. The poster gives an overview of the technology and the latest results from the work.

Below is our ARPA-E GAMOW poster on power electronics. It includes work by Princeton Fusion Systems, Princeton University, Qorvo and the National Renewable Energy Laboratory (NREL). The first panel explains the benefits of wide bandgap semiconductors. The second panel shows the latest results on Class-E amplifiers for plasma heating. The next panel shows Qorvo’s latest 2 V SiC cascodes. The final panel shows the cooling systems being designed by NREL.

The meeting had two days of interesting talks by distinguished speakers. Dr. Robert Mumgaard of Commonwealth Fusion Systems talked about their work on advanced high-temperature superconducting magnets and the theory behind high field Tokamaks. Dennis Stone of NASA discussed NASA COTS programs. Dr. Wayne Sullivan of General Atomic talked about their research programs. General Atomics has been operating a Tokamak possibly longer than anyone else. We heard talks on the Centrifugal Mirror at the University of Maryland and WHAM, the high field mirror, at the University of Wisconsin. Andrew Holland of the Fusion Industry Association gave an overview of funding resources for fusion research. He said FIA had verified 31 companies that were developing fusion power technology. This is a huge change from just a few years ago when only large government entities were conducting fusion research.

We talked to several organizations in need of high voltage and high current power electronics. We plan to pivot our GAMOW work to meet the needs of these potentially near-term customers.

The meeting had breakout sessions in which we discussed funding for fusion research and how to help gain social acceptance for nuclear fusion power. Both are challenging.

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.