# Creating a magnetic field?

by nickdk
Tags: creating, field, magnetic
 P: 15 Is it possible to create a strong enough (artificial) magnetic field to stop high energy particles? Much like the earth's magnetic field stops high energy particles.
 P: 1,160 Yes, in TOKAMAKs and Stellarators they create strong magnetic fields to confine high energy charged particles.
 Mentor P: 11,744 "Confining" and "stopping" are not the same thing. If by "stopping", nickdk means "bringing to rest" or "making stationary", it's impossible for a magnetic field (by itself) to do that, because the magnetic force on a (charged) particle is always perpendicular to the particle's motion. It cannot change the particle's speed, only its direction of motion.
P: 1,160
Creating a magnetic field?

 Quote by jtbell "Confining" and "stopping" are not the same thing. If by "stopping", nickdk means "bringing to rest" or "making stationary", it's impossible for a magnetic field (by itself) to do that, because the magnetic force on a (charged) particle is always perpendicular to the particle's motion. It cannot change the particle's speed, only its direction of motion.
You are right, the total velocity cannot be put to zero by a magnetic field but there are magnetic "bottles" where a non-uniform magnetic field prevents particles from escaping (it "reflects" particles axially in the throat area). In certain sense it "stops" particles at some moment of reflection (I mean the axial part of motion).
 P: 4,663 Think of the betatron accelerator using the Faraday induction law to accelerate electrons to relativistic energies. The highest energy betatron ever built was over 300 MeV. Could the betatron dB/dt be reversed to decelerate 300 MeV electrons? See http://en.wikipedia.org/wiki/Betatron The only requirement for the betatron magnetic field is that the guide field on the vacuum chamber be half the average field inside the area of the orbit (easy physics 201 problem). If B(t) stops increasing (it is a sine wave) and starts decreasing while maintaining this ratio with accelerated electrons in the vacuum chamber, the electrons will decelerate. Bob S
 P: 1,160 We speak of a constant magnetic field, not of varying one. dB/dt = rotE, so it is E that actually makes this work.
P: 4,663
 Quote by Bob_for_short We speak of a constant magnetic field, not of varying one. dB/dt = rotE, so it is E that actually makes this work.
The OP asked Is it possible to create a strong enough (artificial) magnetic field to stop high energy particles?, not strong enough constant magnetic field.
Bob S
 P: 1,160 You are right.
 P: 15 Interesting stuff. Thank you all :)

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