Magnetic field and refocusing paraxial electrons

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Discussion Overview

The discussion revolves around the technical meaning of refocusing paraxial electrons in the context of magnetic fields. Participants explore concepts related to electron behavior in magnetic fields, particularly in applications such as Cathode Ray Tubes (CRTs) and particle accelerators. The conversation includes mathematical reasoning and attempts to clarify the underlying physics.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants suggest that refocusing paraxial electrons involves making the electrons bunch up as they travel through a magnetic field.
  • There is a discussion about the definition of paraxial electrons, with references to their similarity to paraxial rays in optics, indicating they travel nearly parallel to the system's axis.
  • One participant raises a question about the context of the term "refocusing," asking for sources and whether it relates to CRTs or particle accelerators.
  • A mathematical approach is presented involving the pitch of electrons and their motion in a magnetic field, with equations provided to describe the relationship between velocity, radius, and period of motion.
  • Another participant questions the use of the Lorentz force in the calculations, indicating uncertainty about the equations presented.
  • Links to external resources are shared, suggesting that they may contain useful explanations regarding the use of magnetic fields to focus electron beams.
  • Clarifications are made regarding the absence of an electric field and its implications for the Lorentz force in this context.

Areas of Agreement / Disagreement

Participants express uncertainty about the technical meaning of refocusing paraxial electrons and whether the equations presented are correctly applied. There is no consensus on the interpretation of the term or the correctness of the mathematical approach.

Contextual Notes

Participants mention the need for definitions and context regarding the term "refocusing," indicating that assumptions about the magnetic field's role and the absence of electric fields may influence the discussion.

paulina
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what is the technical meaning of refocusing paraxial electrons along the direction of magnetic field?
 
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I'm not quite sure. It sounds like making the electrons bunch up as they travel through a magnetic field. In optics, paraxial rays are rays which travel nearly parallel to the optical axis, so I assume that paraxial electrons are electrons that are traveling nearly parallel to the axis of the system. I'm not quite sure what "along the direction of the magnetic field" means, as I'm not well versed in EM theory.
 
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paulina said:
what is the technical meaning of refocusing paraxial electrons along the direction of magnetic field?

Can you show us the source of this comment? Either post a link or list where you have read it? Was it in the context of Cathode Ray Tube (CRT) displays, or in the context of particle accelerators?
 
berkeman said:
Can you show us the source of this comment? Either post a link or list where you have read it? Was it in the context of Cathode Ray Tube (CRT) displays, or in the context of particle accelerators?

there was a question related to this which i although solved but could not find its true meaning...
"In a region of space a uniform magnetic field Bis along the positive X-axis.Electrons are emitted from the origin with a speed 'v' at different angles.Show that the paraxial electrons are refocused on the x-axis at a distance (2.pi..m.v/Be). Here, m is the mass of electron and e the charge on it."
i found the answer by finding the pitch of an electron which has velocity v along x and y-axis ( v i +v j)...
i have no idea if my attempt was right or wrong.
 
Can you post your work on this question? Did you use the Lorentz force in your calculatons?
 
berkeman said:
Can you post your work on this question? Did you use the Lorentz force in your calculatons?

(mv^2)/r = B.e.v
r = m.v/B.e
so, T = 2.pi.m/B.e
now, p = v.T (p= pitch)
p = 2.pi.m.v/ B.e

i did not use Lorentz force
now answer to my question please... :(
 
paulina said:
(mv^2)/r = B.e.v
r = m.v/B.e
so, T = 2.pi.m/B.e
now, p = v.T (p= pitch)
p = 2.pi.m.v/ B.e

i did not use Lorentz force
now answer to my question please... :(

I'm not tracking exactly what you did with those equations (they may be related to the Lorentz Force, but I'm not sure). In any case, I did a quick Google search on this:

refocusing paraxial electrons along the direction of magnetic field

and got this hit list: https://www.google.com/search?sourc...tic+field&gs_l=hp...0.0.0.427...0.ZfAOzJjBBpA

The first 2 hits are to this PF thread of yours, but the rest look to be good explanations of using magnetic fields to focus electron beams. Please see if the first couple explanation hits are useful for you. :-)
 
berkeman said:
I'm not tracking exactly what you did with those equations (they may be related to the Lorentz Force, but I'm not sure). In any case, I did a quick Google search on this:

refocusing paraxial electrons along the direction of magnetic field

and got this hit list: https://www.google.com/search?sourceid=navclient&aq=&oq=refocusing paraxial electrons along the direction of magnetic field&ie=UTF-8&rlz=1T4GGLL_enUS301US302&q=refocusing paraxial electrons along the direction of magnetic field&gs_l=hp...0.0.0.427...0.ZfAOzJjBBpA

The first 2 hits are to this PF thread of yours, but the rest look to be good explanations of using magnetic fields to focus electron beams. Please see if the first couple explanation hits are useful for you. :)
well there is no electric field, so no lorentz force...
anyway thanks for the link...
 
paulina said:
well there is no electric field, so no lorentz force...
anyway thanks for the link...

There are 2 parts to the Lorentz Force equation, after all... :-)
 
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