User talk:Schaffermj

The Wikipedia entry on "betatron" has some serious errors.

1. The first sentence states that "A betatron is a cyclotron," which is wrong; the two classes of accelerators operate on two fundamentally different principles.

2. A bit later, "In a betatron, the magnetic field spins the injected electrons and accelerates them at the center, ..." The magnetic field guides the electrons. It is the induced electric field that accelerates the electrons. They are accelerated around an evacuated toroidal tube at the outer cirmference of the device; nothing is accelerated near the center. The rest of this sentence is so written that the intended logical dependences can not be deciphered.

3. Finally, the sentence "Because the mass of the electron increases at relativistic speeds, the cyclotron becomes less efficient at higher energies," is wrong. The main betatron advantage is that they naturally accomodate relativistic particles. The author of this article is speaking of the inability of the simple cyclotron to accomodate relativistic particles instead.

Halliday & Resnick, "Fundamentals of Physics," correctly describes the betatron (2nd ed. 1986, pp232-234) but the presentation is more confusing than it should be. H&R has a good cross sectional figure of a betatron.

M. Zahn, "Electromagnetic field theory, a problem solving approach," has a more rigorous presentation than H&R, but it seems to me to have one unexplained inconsistency. Zahn does touch on "betatron oscillations", one thing I wanted to learn about.

Schaffermj (talk) 23:59, 26 March 2009 (UTC)