Does an electron beam bending lose energy by photon emission

[houlahound]

A beam of electron in vacuum with velocity v enter a region of spa e with a electric field E. The field is such the electrons circle with radius r. The electrons are now accelerating at constant tangential speed.

Because this is not an atomic orbital then by classical physics the electrons radiate photons of frequency f.

Does this radiation make the electrons lose energy and spiral inward.

The answer is no because such circular beams can be created and are stable, so what compensates for the radiated energy loss?

 

[Jon B]

The 2.45 Ghz frequency generated by the electron beam circling(bending) in the Magnetron in a microwave oven produces no light and therefore no photons.
Visable light is associated with photons is within the frequency range of ~405 - 790 THz. It is not usually associated with electron beams.

 

[Drakkith]

The 2.45 Ghz frequency generated by the electron beam circling(bending) in the Magnetron in a microwave oven produces no light and therefore no photons.
Visable light is associated with photons is within the frequency range of ~405 - 790 THz. It is not usually associated with electron beams.

That is incorrect. ALL electromagnetic radiation is composed of photons, not just visible light.

The answer is no because such circular beams can be created and are stable, so what compensates for the radiated energy loss?

The radiation would indeed lead to an in-spiraling of the electron beam. Stable electron beams, such as in circular particle accelerators, have to keep supplying energy to keep them in a steady path.

 

[houlahound]

I never implied visible photons.

So in a lab bench set up where the beam of electrons is bent by the field from Helmholtz coils which I assume anyone reading are familiar with in most undergrad labs, is the energy removed from the magnetic field measurable. Shouldn't we see a fluctuations in the coil current?? Or should the coils draw more power when the beam is present?

 

[Drakkith]

So in a lab bench set up where the beam of electrons is bent by the field from Helmholtz coils which I assume anyone reading are familiar with in most undergrad labs, is the energy removed from the magnetic field measurable. Shouldn't we see a fluctuations in the coil current?? Or should the coils draw more power when the beam is present?

I don't think energy is removed from the magnetic field. Those beams are probably not stable. The in-spiraling of the electron beam just probably isn't noticeable since the beam isn't moving relativistically or being curved hard enough.

 

[houlahound]

Not wanting to mention manufacturers names but these beams are clearly stable in bench top devices. You can visually measure the radius. The coil currents are only a few amps.

 

[Drakkith]

Not wanting to mention manufacturers names but these beams are clearly stable in bench top devices. You can visually measure the radius. The coil currents are only a few amps.

I'd need a link to such a device to see it and help answer your question.

 

[houlahound]

Both Teltron and Pasco Scientific sell such devices. I used a Pasco its called e/m experiment.

Will link if that's not spamming.

 

[Drakkith]

Lol, no. It's not spamming.

 

[houlahound]

Results are awesome;

https://www.pasco.com/prodCompare/electron-charge-to-mass-ratio-system/index.cfm

 

[Drakkith]

Okay, we just had one of those in my E&M class the other week. I can't guarantee anything, but I was under the impression that the electrons are emitted at a low velocity, in a low-strength magnetic field, and the reaction force from the radiation they release isn't measurable at this scale.

 

[davenn]

Results are awesome;

https://www.pasco.com/prodCompare/electron-charge-to-mass-ratio-system/index.cfm

cool, never played with anything so fun my uni physics classes

 

[jtbell]

Look up "synchrotron radiation" and try calculating the rate of energy loss for electrons in that apparatus. The accelerating voltage is typically a few 1000 V (in our setup it was about 1500 to 5000 V), so the initial kinetic energy is a few keV. The radius of curvature is maybe 5 cm.

 

[houlahound]

I think it is a (non relativistic) cyclotron not a synchrotron, unless a sync and cyc are the same.

Formula is here;

https://en.m.wikipedia.org/wiki/Cyclotronand

If this equals hf then

f= (q^2 B^2 R^2)/(h 2m)

I'm not sure it is valid to assume the kinetic energy of the electrons all turns into photons and can be equated to hf though??

 

[ZapperZ]

1. There IS energy loss when an electron beam moves in a circular path.

2. For a tabletop experiment shown in a typical e/m experiment, the loss is VERY SMALL, because the charge on each electron is very small, and the speed of these electrons is "small".

3. Evidence for such energy loss can seen in when the electron beam are in MeV and GeV energy range. Synchrotron radiation is a clear example of this. It is also why the LHC is so large in diameter, so as to minimize the bending radius.

Zz.

 

[Kevin McHugh]

Yes, it is called Bremsstrahlung radiation. It is how X-Rays are generated in your doctor's X-ray machine.

 

[sophiecentaur]

Ifaik, Bremsstrahlung radiation happens due to close interaction of high speed electrons with atoms in a target. X rays are very high energy but the photons produced by larger structures are surely a lot lower energy because the acceleration of the charges is lower. Would they be classed as Bremsstrahlung radiation?

 

[houlahound]

Quite not, doctors xray is by high energy collision knocking k-shell electrons out of atoms in a solid target. Not even close to this phenomena.

 

[Kevin McHugh]

I stand corrected. I was told by the X-ray tech the X-rays were from Bremsstrahlung. I guess I was misinformed. Thanks Houlahound.

 

[houlahound]

It could be called bremss. in Xrays. I don't know the names I just happen to know the process of medical xray production in dentist and doctor surgeries.

 

[Jon B]

In the original question there is no reference to an electromagnetic frequency being generated. An electron beam is a current traveling without a conductor. The stream of electrons can be influenced by electrostatic charges and magnetic forces to focus and maintain a minimum of loss to the body of the containing device. The beam can be velocity modulated to provide radio waves.

 

[houlahound]

The electron beam is going in a circle = acceleration = EM radiation.

There is no way it can't happen in my view.

 

[ZapperZ]

I stand corrected. I was told by the X-ray tech the X-rays were from Bremsstrahlung. I guess I was misinformed. Thanks Houlahound.

Actually, you are correct.

Medical x-rays are created via both processes. However, the Bremsstrahlung x-ray usually dominates over the characteristics x-ray. See, for example, Pg. 4 of this presentation:

http://www.desy.de/~garutti/LECTURES/BioMedical/Lecture3_FG.pdf

I also believe that Bremsstrahlung x-rays are more directional than the characteristic x-ray which makes them more useful for medical imaging.

Zz.

 

[ZapperZ]

In the original question there is no reference to an electromagnetic frequency being generated. An electron beam is a current traveling without a conductor. The stream of electrons can be influenced by electrostatic charges and magnetic forces to focus and maintain a minimum of loss to the body of the containing device. The beam can be velocity modulated to provide radio waves.

But this is a completely different scenario!

If you put electrons in a circular path and let them stay in that circular path without any additional "booster", they will "decay" their "orbit" since they will lose its energy. This is not an unknown, mysterious, or puzzling phenomenon.

Zz.

 

[Jon B]

The electron beam is going in a circle = acceleration = EM radiation.

There is no way it can't happen in my view.

It is the same as if the DC current was in a conductor. A magnetic field would be established.

 

[Jon B]

But this is a completely different scenario!

If you put electrons in a circular path and let them stay in that circular path without any additional "booster", they will "decay" their "orbit" since they will lose its energy. This is not an unknown, mysterious, or puzzling phenomenon.

Zz.

I was thinking the power supply would remain on and the flow of electrons would continue.

 

[ZapperZ]

I was thinking the power supply would remain on and the flow of electrons would continue.

What "power supply"?

Look at a cyclotron. You have a magnetic field perpendicular to the plane of motion. Without any other external forces, the circular path will eventually decay.

If you add other sources (what I called "booster"), then the OP's question will not matter, will it? That is what we do in many circular accelerators around the world to keep up the energy of the electron beams!

Zz.

 

[Jon B]

What "power supply"?

Look at a cyclotron. You have a magnetic field perpendicular to the plane of motion. Without any other external forces, the circular path will eventually decay.

If you add other sources (what I called "booster"), then the OP's question will not matter, will it? That is what we do in many circular accelerators around the world to keep up the energy of the electron beams!

Zz.

A typical electron beam has a high voltage supply to sustain it. I guess this is an electron torpedo then.

 

[ZapperZ]

A typical electron beam has a high voltage supply to sustain it. I guess this is an electron torpedo then.

Just in case you are not aware of it, I'm an accelerator physicist.

This question isn't about particle accelerator, but the concept of charged particle in a circular path.

Zz.

 

[houlahound]

A non varying DC current in a wire would not emit EM but if the level changed then I expect it would.

A constant level DC current in a loop would not I expect emit EM but then I get tripped up because a circle motion implies acceleration and accelerating electrons radiate??

The device mentioned supplies a power to both the B field and the electrons, this power must compensate for radiative losses or the electrons would spiral out of a fixed radius...I'm so confused.