<p>They can, but it would be called cyclotron emission. The difference is that cyclotron emission occurs at a discrete frequency for a given B-field, whereas the relativistic electrons emit at a broad spread of frequencies that form a continuum under realistic conditions.</p>
<p>Hence this is a terminology thing as well as a physics thing. Cyclotron radiation becomes synchrotron radiation as the electrons become relativistic.</p>

CC BY-SA 4.0
2022-07-09T19:01:42.840Z
And cyclotron radiation is beamed with a certain opening angle, which is a purely relativistic effect.
AtmosphericPrisonEscape
CC BY-SA 4.0
2022-07-09T19:19:54.357Z
@AtmosphericPrisonEscape Synchrotron radiation can be beamed (if the B-field is spatially uniform). Cyclotron radiation is not.
ProfRob
CC BY-SA 4.0
2022-07-09T21:01:10.407Z
This is really interesting decades ago I worked at a cyclotron lab, these days at a synchrotron lab. I never thought about cyclotron radiation at the former and make great use of the forward-emitted synchrotron radiation (and the narrow and coherent beams from [wigglers and undulators](https://physics.stackexchange.com/q/480966/83380) and now I can't stop wondering what happens between the two limits. It seems that the mechanisms are pretty different, so both happen to some extent even in both limits, it's just a question of amplitudes. Now I'll go off and think about it...
uhoh
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2022-07-10T10:32:42.080Z
Thank you @ProfRob for the answer!
Loika
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2022-07-10T10:34:28.470Z
@uhoh that is quite an interesting question!
Loika
CC BY-SA 4.0
2022-07-10T10:47:53.773Z
@uhoh It's called gyro-synchrotron radiation.
ProfRob
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2022-07-09T15:59:48.480Z
2022-07-09T19:22:22.110Z
2022-07-09T19:22:22.110Z
ProfRob
<p>I'm reading <a href="https://www.cv.nrao.edu/%7Esransom/web/Ch4.html" rel="noreferrer">this</a> chapter of <em>Essential Radio Astronomy</em>.</p>
<p>It says that we can divide bremsstrahlung into electric or magnetic breaking radiation, depending on which field is the source of the acceleration of electrons. <strong>Synchrotron radiation</strong> is another name for magnetic breaking radiation, and it is usually non-thermal, because the relativistic electrons creating the emissions tend to have a power-law distribution.</p>
<p><strong>My question</strong> would be: why does synchrotron radiation only occur in the case of relativistic electrons? Why cannot any non-relativistic electron that is moving in the presence of a magnetic field emit synchtron radiation?</p>

<radiation>
Why does sychrotron radiation only involve relativistic electrons?
Loika
# Why does sychrotron radiation only involve relativistic electrons?

(Asked by: username_0 on 2022-07-09)

I'm reading [this](https://www.cv.nrao.edu/%7Esransom/web/Ch4.html) chapter of *Essential Radio Astronomy*.

It says that we can divide bremsstrahlung into electric or magnetic breaking radiation, depending on which field is the source of the acceleration of electrons. **Synchrotron radiation** is another name for magnetic breaking radiation, and it is usually non-thermal, because the relativistic electrons creating the emissions tend to have a power-law distribution.

**My question** would be: why does synchrotron radiation only occur in the case of relativistic electrons? Why cannot any non-relativistic electron that is moving in the presence of a magnetic field emit synchtron radiation?

**Tags:** radiation

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## 1 answers

### Answer by username_1 on 2022-07-09. Score: 8 | Accepted answer

They can, but it would be called cyclotron emission. The difference is that cyclotron emission occurs at a discrete frequency for a given B-field, whereas the relativistic electrons emit at a broad spread of frequencies that form a continuum under realistic conditions.

Hence this is a terminology thing as well as a physics thing. Cyclotron radiation becomes synchrotron radiation as the electrons become relativistic.

> **Comments:**
> **username_2**: And cyclotron radiation is beamed with a certain opening angle, which is a purely relativistic effect.  
> **username_1**: @AtmosphericPrisonEscape Synchrotron radiation can be beamed (if the B-field is spatially uniform). Cyclotron radiation is not.  
> **username_3**: This is really interesting decades ago I worked at a cyclotron lab, these days at a synchrotron lab. I never thought about cyclotron radiation at the former and make great use of the forward-emitted synchrotron radiation (and the narrow and coherent beams from [wigglers and undulators](https://physics.stackexchange.com/q/480966/83380) and now I can't stop wondering what happens between the two limits. It seems that the mechanisms are pretty different, so both happen to some extent even in both limits, it's just a question of amplitudes. Now I'll go off and think about it...  
> **username_0**: Thank you @ProfRob for the answer!  
> **username_0**: @uhoh that is quite an interesting question!  
> **username_1**: @uhoh It's called gyro-synchrotron radiation.  

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