Blog Posts


SEMI-THERM Symposium 2024

In late March 2024, I attended the SEMI-THERM symposium held at San Jose, CA. In this conference, I presented our research work on thermal modeling and testing of the Load Switch that we had built under our APRA-E GAMOW project.

The short course by Prof. Alfonso Ortega, James R. Birle Professor of Energy Technology and Mechanical and Sustainability Engineering from Villanova University, and Dr. Luca Amalfi, CEO of Seguente Inc., was refreshing. A part of the presentation that was eye-opening was the physics behind liquid cooling and the do’s and don’ts for liquid cooling systems.

Short course on Direct to Chip Liquid Cooling: Single Phase water and Two Phase Refrigerant cooling with Pumped and Passive systems
Lieven Vervecken giving a presentation about the unique qualities of the software developed by Diabetix.

It was a pleasure to meet David L. Saums, Lieven Vervecken (CEO of Diabetix), Wendy Luiten a thermal consultant, and Bob Schuch who took care of the SEMI-THERM registrations and helped with all the information I needed. During my presentation I got to meet Kiran Hota from Advanced Cooling Technologies. There were many people whom I met during the symposium, we had great discussions about thermal modeling of PCBs and cooling of Data Centers. A few other people I met included Azad Aziz from Honeywell, Yasmin Khakpour from RTX Research Center, Chau Ho who is the Principal Thermal Architect of Meta and previously at Microsoft, Intel, & Boeing Corporation, and Ajinkya Mahahjan from Smiths Interconnect.

Sangeeta Vinoth giving the presentation at the SEMI-THERM symposium
Sangeeta Vinoth giving the presentation at the SEMI-THERM symposium
Wendy Luiten receiving the THERMI AWARD

It was great to learn from Wendy Luiten on linear regression. She has won the Thermi Award for her work in various roles in Philips R&D for 30+ years. It was a delight to hear her presentation about her research on Thermal Analysis and building a Flat TV.

Another interesting lunch talk was by Sarah da Silva Andrade. She discussed on Professional Approaches to Scientific Communication and Digital Engagement.

Sarah da Silva Andrade giving a lunch talk

Additionally, there was a panel discussion on Artificial Intelligence and its implication for Thermal Engineers.

Panelists at the SEMI-THERM symposium
Sreekant Narumanchi from NREL attending the lunch talk

Princeton Fusion Systems Selected for DOE SBIR Contract

We have been selected by the Department of Energy (DOE) Office of Science for a 2024 Phase I Small Business Innovation Research (SBIR) Grant! The title of our project is “High-Efficiency RF Amplifiers with Plasma Accommodation for Fusion Plasma Heating”.

The Fiscal Year 2024 Awards list can be viewed here. There you can find a concise summary of our proposed project:

“Radio frequency systems used to heat plasmas in fusion power plants will need to be highly efficient and adaptable to changes in the plasma over time. This proposal is for the scaling of an innovative radiofrequency amplifier which produces less heat waste and can follow the changes in the plasma.”

This work leverages our prior experience with and development of high-efficiency radiofrequency amplifiers under our ARPA-E GAMOW contract. The scaling towards application in a plasma fusion reactor would require power-combining of 10’s-100’s of RF boards. The RF amplifiers utilize a Reactance Steering Network (RSN) developed by our collaborators at Princeton University to handle variations in the impedance of a load, which in our case is a plasma. Experiment testing and simulation will be performed to assess the power-combining of multiple RSNs so that we can scale up to high-power operation on the scale of 0.1 – 1 MegaWatts, that is, 100,000-1,000,000 Watts!

ARPA-E -GAMOW staff visit to Princeton Fusion Systems

We had the pleasure to welcomeARPA-Estaff Eric Carlson, Robert Ledoux, Carpenter Gene, Sam Wurzel, Guinevere Shaw (virtual), and Igor Cvetkovic (virtual) toPrinceton Fusion Systemson December 19th, 2023.

During their visit, we demonstrated our working Class-E amplifier, and Load switch with the water cooling chassis. We presented our latest Quarterly work performed in the ARPA-E GAMOW project titled “Wide-Bandgap Semiconductor Amplifiers for Plasma Heating and Control“. We had a great time of discussion, with helpful feedback for advancing and commercializing our technology!

Pillsbury fusion chocolate

One of the unexpected perks of connecting with the Pillsbury law firm through our fusion endeavors and the Fusion Industry Association, is the massive chocolate bar that now arrives for the holidays. This giant dark chocolate bar comes with its own hammer for smashing it into edible-size bits! Thank you Vince and Sid!!

Pillsbury dark chocolate bar comes with its own hammer

The sugar and caffeine is much appreciated for fueling our continued development of the PFRC fusion microreactor!

ARPA-E Energy Innovation Summit 2023

At the end of March, we attended the ARPA-E Energy Innovation Summit in National Harbor, MD. At the Summit we presented our work on power electronics tailored for fusion systems under an ARPA-E GAMOW grant. It was a great experience to network with many other awardees of ARPA-E grants working on innovative energy projects and learn about the power electronics needs of potential customers so we could design our boards to these specifications. Shown below is our Summit booth which was run by PFS Mike Paluszek and me.

Our booth contains prototype circuit boards developed by PSS and our collaborators at Princeton University (the Princeton Power Electronics Research Lab), along with flyers and other learning materials. The posters mounted behind us describe the work done by us and our collaborators: the Princeton Power Electronics Research Lab, UnitedSiC (now Qorvo), and the National Renewable Energy Laboratory (NREL).

Breakout sessions included panels on: future plans for inertial fusion energy, nuclear & materials, rethinking the nuclear waste challenge, and scaling up innovations for impact in the private sector with the ARPA-E SCALEUP program. Dr. Neil deGrasse Tyson gave a talk at the Summit!

The pdfs of the trifold and posters at our Summit booth are shown below. If you have any power electronics requirements for your systems, please contact us at!

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)