Historical research guide · 0582 · 2023
The Princeton Field-Reversed Configuration for Compact Nuclear Fusion Power Plants
Christopher Galea · Stephanie Thomas · Michael Paluszek · Samuel Cohen
In one minute
Fusion reactors are usually imagined as buildings. Christopher Galea, Stephanie Thomas and Michael Paluszek of Princeton Fusion Systems, with Samuel Cohen of the Princeton Plasma Physics Laboratory, describe one you could put on a truck. The Princeton Field-Reversed Configuration holds its plasma inside a ring of closed magnetic field lines that the plasma largely makes for itself, in a tube four to eight metres long and a metre and a half across, and heats it with a single radio-frequency trick: an odd-parity rotating magnetic field, which their modelling says keeps those field lines closed instead of letting the plasma leak out along open ones. The fuel is deuterium and helium-3, which returns its energy mostly as charged particles rather than neutrons, so the design aims for about a thousand times less neutron loading on the wall than a deuterium-tritium tokamak. Two machines already exist. PFRC-2 has heated electrons past 500 electronvolts and held plasmas for 300 milliseconds, and the paper names exactly what the next two machines have to reach.
Connection
Chapter 12 argues that every scheme in this book needs the same thing first — a small source of very large energy — and the PFRC is the compact, aneutronic-leaning, hardware-in-the-lab version of that requirement. It also belongs to chapter 9, because a field-reversed configuration is a self-organising plasma structure holding its own closed field lines, the same physics family as the plasmoid.
From the source
An odd-parity rotating magnetic field, RMFo, drives current, heats the plasma, improves confinement and provides stability with a single radio-frequency system, and unlike the even-parity picture-frame antennas used before it, it maintains a field-reversed configuration with closed magnetic field lines rather than open ones that let the plasma escape — first theorised in 2000, since reproduced by an analytical model and by particle-in-cell simulation.Section 1, Introduction; Section 2.2, RMFo Heating Method
In the second-generation PFRC-2 experiment, with an 8 centimetre flux-conserver radius, minority electron populations have reached temperatures of 500 electronvolts and maximum energies above 1.5 kiloelectronvolts, with pulse lengths up to 300 milliseconds — more than 10⁴ times longer than the predicted growth time of the tilt instability — at radio frequencies from 4.3 to 12 megahertz, forward power to 100 kilowatts and coupling efficiency to the plasma of 60 percent.Abstract; Section 3, Status of Development, and Table 1
Scaled to fusion parameters, a PFRC power reactor would be 4 to 8 metres long and 1.5 metres in diameter and produce 1 to 10 megawatts of fusion power, making it suitable for submarines, urban sites and space propulsion.Abstract; Section 2, Overview of the PFRC Reactor Concept
Burning deuterium and helium-3 in a high-beta configuration, where beta is plasma pressure over magnetic-field energy density, gives about 1000 times lower neutron power flux on the inner wall than a deuterium-tritium tokamak, because the main reaction produces no damaging neutrons and the machine is small enough to exhaust the tritium made by deuterium-deuterium side reactions before it burns.Section 2.3, Power Flow and Neutron Loads, Equations 1 to 3
A one-dimensional power-flow model of a 2 megawatt thermal reactor, drawing 0.79 megawatts of rotating-magnetic-field power produced at better than 90 percent amplifier efficiency and converting heat through a 50 percent efficient Brayton cycle, returns 0.57 megawatts of net electric power.Section 2.3, Figure 7
The step that decides the concept is energy confinement near classical at reactor scale: PFRC-2 is being upgraded to a 2 megahertz rotating field at up to 200 kilowatts, where single-particle simulations predict explosive ion heating above 1 kiloelectronvolt, and PFRC-3 must then reach 1.5 tesla, 10 kiloelectronvolt ions and a one-second pulse — with a new supply of helium-3, from natural gas, CANDU reactors, breeding or lunar mining, needed before widespread use.Section 3, Table 1; Section 5, Summary and Next Steps
The way in
https://doi.org/10.1007/s10894-023-00342-2How to cite it
Christopher Galea, Stephanie Thomas, Michael Paluszek, Samuel Cohen (2023) The Princeton Field-Reversed Configuration for Compact Nuclear Fusion Power Plants doi:10.1007/s10894-023-00342-2