Cyclotron Motion: Does Charge Require Energy to Move?

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    Cyclotron Motion
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Discussion Overview

The discussion revolves around the energy requirements for a charged particle in cyclotron motion, particularly focusing on whether the magnetic field does work on the charge and how the charge is initially set into motion. The scope includes theoretical considerations of magnetic fields, energy conservation, and the mechanics of particle accelerators.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states that in cyclotron motion, the equation qvB=mv^2/R suggests that energy is required to initiate motion, but questions if the energy remains constant once in motion.
  • Another participant claims that the magnetic field does no work on a moving charge, implying that the particle maintains constant speed and energy if radiation is ignored.
  • A participant challenges the assertion that the magnetic field does no work by asking how the charge is initially set into motion.
  • Further clarification is provided that the charge must be accelerated by an external means, such as an electric field, before entering the magnetic field, or through segments that accelerate the charge while it is circulating.

Areas of Agreement / Disagreement

Participants express differing views on the role of the magnetic field in doing work on the charge and how the charge is initially set into motion. The discussion remains unresolved regarding the implications of these points.

Contextual Notes

The discussion highlights assumptions about the nature of work done by magnetic fields and the mechanisms of particle acceleration, which may depend on specific definitions and contexts.

Kolahal Bhattacharya
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We know in a cyclotron motion, qvB=mv^2/R
Can you please tell me if the charge requires energy as it moves...
It is obvious that when it starts it requires energy provided by only the magnetic field. As it starts, it has constant velocity...no dissipation.Does it mean its energy remains constant?Then is Lorentz force is conservative?
 
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The B field does no work on a moving charge.
The particle would circle at constant speed and energy if radiation is neglected.
 
If B field does not do any work,how the charge sets into motion?
 
Kolahal Bhattacharya said:
If B field does not do any work,how the charge sets into motion?

One must set the charge in motion by some means other than the B field. For example, one can accelerate the charges along a straignt line in an electric field and then "inject" the beam into the B field.

Or, while the charges are circulating in the B field, they can pass through short accelerating segments that produce an electric field. As the particles gain momentum, one increases the B field in step so as to keep the radius of the orbit constant. A modern large ring-accelerator like the ones at CERN and Fermilab has alternating accelerating and bending segments.
 

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