What Is the Role of J x B in Rotating Magnetic Field Current Drives?

[Jdo300]

Hello All,

I have had some interest in the effects of rotating magnetic fields and was doing some research on the subject when I came across the following paper published from the University of Washington:;

http://wsx.lanl.gov/Publications/RSI-RMF-Tobin-paper.pdf

The paper discusses some experiments involving a high power, high speed rotating magnetic field. I didn't read through the entire paper but there was one spot on the first page that really caught my attention:

"The Translation, Confinement and Sustainment (TCS) Experiment located at the Redmond Plasma
Physic Laboratory (RPPL) of the University of Washington was designed to apply, for the first time, a
rotating magnetic field (RMF) to a high-temperature field reversed configuration (FRC) plasma (Te ~ 100
eV and Ti ~ 300 eV) [1]. The RMF current drive technique is a special case of the more general j x B
current drive scheme, by which electrons are “pulled” along with the rotating magnetic field [2]. Unlike
inductive current drive systems, RMF current drive is steady state. The RMF is used for the purpose of
building up and sustaining the magnetic flux of the FRC. The exp erimental goal is to benchmark this
current drive technique against theoretical predictions, and to determine the robustness of the FRC plasma
to this external perturbation. An initial goal for the RMF system was to extend the lifetime of the FRC by a
factor of ~3; this goal has already been achieved with pulses lasting 1 ms. It was anticipated that a 1 ms
pulse would become limited by particle inventory rather than resistive flux losses. At present particle
inventory is not limiting lifetime, exactly why is not yet understood."

I am particularly interested in the part that I highlighted in boldface. I was wondering if anyone here may know anything about "rotating magnetic field current drive" systems, and how the J x B equations fits into this? I am very interested in learning more about this. Does it only apply to plasmas or could the effect take place in regular wires too?

Thank you,
Jason O

 

[Almsco]

Hi Jason,

I'm not an expert on rotating magnetic fields, but I do know a bit about the J x B equations. The J x B equations are used to describe a current that is driven in a conductor by a changing magnetic field, which results in a force that is perpendicular to both the current and the magnetic field. This type of force can be used to drive the plasma contained in your experiment, which describes the rotation of the magnetic field. I'm not sure if this effect can be applied to regular wires, but it definitely applies to plasma.

 

[charng]

.

Dear Jason O.,

Thank you for sharing your interest in rotating magnetic fields and the paper from the University of Washington. The special case of J x B mentioned in the paper refers to the use of a rotating magnetic field (RMF) for current drive in plasmas. In this technique, the rotating magnetic field induces a current in the plasma, which in turn generates magnetic fields that can confine and sustain the plasma.

The J x B term refers to the force experienced by a charged particle in a magnetic field. In this case, the RMF causes the electrons in the plasma to move along with the rotating magnetic field, resulting in a net current. This is different from inductive current drive systems, where the current is induced by changing the magnetic field.

The use of rotating magnetic fields for current drive has been studied in various plasma experiments, including fusion research. It is not limited to plasmas, as it can also be used to induce currents in regular wires. However, the specific effects and applications may differ depending on the system.

I hope this helps to answer your questions and provides some insight into the special case of J x B in the context of rotating magnetic fields. It is a fascinating area of research, and I encourage you to continue exploring and learning more about it.