![PFRC 2 pulse](https://upload.wikimedia.org/wikipedia/commons/e/e4/PFRC_2_pulse.jpg)
The Princeton field-reversed configuration (PFRC) is a series of experiments in
, an experimental program to evaluate a configuration for a
fusion power
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices de ...
reactor, at the
Princeton Plasma Physics Laboratory
Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science. Its primary mission is research into and development of fusion as an energy source. It is known ...
(PPPL). The experiment probes the dynamics of long-pulse, collisionless, low s-parameter
field-reversed configuration
A field-reversed configuration (FRC) is a type of plasma device studied as a means of producing nuclear fusion. It confines a plasma on closed magnetic field lines without a central penetration. In an FRC, the plasma has the form of a self-stabl ...
s (FRCs) formed with odd-parity rotating magnetic fields.
It aims to experimentally verify the physics predictions that such configurations are globally stable and have transport levels comparable with classical magnetic diffusion.
It also aims to apply this technology to the
Direct Fusion Drive
Direct Fusion Drive (DFD) is a conceptual low radioactivity, nuclear- fusion rocket engine designed to produce both thrust and electric power for interplanetary spacecraft. The concept is based on the Princeton field-reversed configuration reacto ...
concept for spacecraft propulsion.
History
The PFRC was initially funded by the
United States Department of Energy
The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United Stat ...
. Early in its operation it was contemporary with such RMF-FRCs as the
Translation Confinement Sustainment experiment The Translation Confinement Sustainment experiment (TCS) was a plasma physics experiment at the University of Washington's Redmond Plasma Physics Laboratory from 2002 until 2009. The experiment studied magnetic plasma confinement to support contro ...
(TCS) and the
Prairie View Rotamak
The Prairie View (PV) Rotamak is a Plasma (physics), plasma physics experiment at Prairie View A&M University. The experiment studies magnetic Plasma (physics), plasma confinement to support controlled nuclear fusion experiments. Specifically, the ...
(PV Rotamak).
At PPPL, the experiment PFRC-1 ran from 2008 through 2011.
PFRC-2 is running . PFRC-3 is scheduled next. PFRC-4 is scheduled for the mid-2020s.
Odd-parity rotating magnetic field
The electrical current that forms the
field-reversed configuration
A field-reversed configuration (FRC) is a type of plasma device studied as a means of producing nuclear fusion. It confines a plasma on closed magnetic field lines without a central penetration. In an FRC, the plasma has the form of a self-stabl ...
(FRC) in the PFRC is driven by a rotating magnetic field (RMF). This method has been well-studied and produced favorable results in the Rotamak series of experiments. However, rotating magnetic fields as applied in these and other experiments (so-called ''even parity RMFs'') induce opening of the magnetic field lines. When a transverse magnetic field is applied to the axisymmetric equilibrium FRC magnetic field, rather than magnetic field lines closing on themselves and forming a closed region, they spiral around in the azimuthal direction and ultimately cross the separatrix surface which contains the closed FRC region.
![PFRC-2 discharge](https://upload.wikimedia.org/wikipedia/commons/6/69/PFRC-2_discharge.gif)
The PFRC uses RMF antennae which produce a magnetic field which changes direction about a symmetry plane oriented with its normal along the axis, half-way along the length of the axis of the machine. This configuration is called an ''odd parity'' rotating magnetic field. Such magnetic fields, when added in small magnitude to axisymmetric equilibrium magnetic fields, do not cause opening of the magnetic field lines and overall topology is preserved.
The critical threshold magnitude of 'odd parity' rotating magnetic field, which opens up the axisymmetric equilibrium magnetic field lines, and fundamentally changes field topology is rather high. Thus, the RMF is not expected to contribute to transport of particles and energy out of the core of the PFRC.
Low s-parameter
In an FRC, the name s-parameter is given to the ratio of the distance between the magnetic null and the separatrix, and the thermal ion Larmor radius. That is how many ion orbits can fit between the core of the FRC and where it meets the bulk plasma.
A high-s FRC would have very small ion gyroradii compared to the size of the machine. Thus, at high s-parameter, the model of
magnetohydrodynamics
Magnetohydrodynamics (MHD; also called magneto-fluid dynamics or hydromagnetics) is the study of the magnetic properties and behaviour of electrically conducting fluids. Examples of such magnetofluids include plasmas, liquid metals, ...
(MHD) applies.
MHD predicts that the FRC is unstable to the "n=1 tilt mode," in which the reversed field tilts 180 degrees to align with the applied magnetic field, destroying the FRC.
A low-s FRC is predicted to be stable to the tilt mode.
An s-parameter less than or equal to 2 is sufficient for this effect. However, only two ion radii between the hot core and the cool bulk means that on average only two scattering periods (velocity changes of on average 90 degrees) are sufficient to remove a hot, fusion-relevant ion from the core of the plasma. Thus the choice is between high s-parameter ions that are ''classically'' well confined but ''convectively'' poorly confined, and low s-parameter ions that are ''classically'' poorly confined but ''convectively'' well confined.
The PFRC has an s-parameter between 1 and 2.
Stabilizing the tilt-mode is predicted to aid confinement more than the small number of tolerable collisions will hurt confinement.
Spacecraft propulsion
Scientists from Princeton Satellite Systems are working on a new concept called
Direct Fusion Drive
Direct Fusion Drive (DFD) is a conceptual low radioactivity, nuclear- fusion rocket engine designed to produce both thrust and electric power for interplanetary spacecraft. The concept is based on the Princeton field-reversed configuration reacto ...
(DFD) that is based on the PFRC. It would produce electric power and propulsion from a single compact fusion reactor. The first concept study and modeling (Phase I) was published in 2017,
and was proposed to power the propulsion system of a
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...
orbiter and lander.
Adding propellant to the cool plasma flow results in a variable thrust when channeled through a magnetic nozzle. Modeling suggests that the DFD might produce 5
Newtons of thrust per each
megawatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
of generated fusion power.
About 35% of the fusion power goes to thrust, 30% to electric power, 25% lost to heat, and 10% is recirculated for the
radio frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the ...
(RF) heating.
The concept has advanced to Phase II
to further advance the design and shielding.
References
External links
*, Princeton Plasma Physics Laboratory
Professor Samuel A. Cohen
{{Fusion power
Magnetic confinement fusion devices
Princeton Plasma Physics Laboratory