Doing high school level physics and I got stuck at a question regarding a cyclotron. I need to know how does it work and the reason alternating current is used and the structure of the two semi circle of the cyclotron.
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2$\begingroup$ Your question is rather vague at the moment. Have you Googled for articles on cyclotrons? If so, are there specific issues you don't understand? For example, if you want to know how RF cavities accelerate particles see Accelerating electrons via microwaves $\endgroup$– John RennieCommented Jun 5, 2014 at 9:45
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1$\begingroup$ I wanted to understand better the basic principles the cyclotron uses to accelerate a charged particle, reasons for the narrow gap between the two Dees and the usage of an alternating current instead of a direct current. I tried Wikipedia, but the article was rather technical for my level. Do tell me how can I improve the way I ask questions. $\endgroup$– ZhaoCommented Jun 6, 2014 at 1:43
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1 Answer
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I'll try to make it short: (Try looking at a diagram of a cyclotron before reading )
- There are two semicircular Dees connected to an alternating voltage source
- There is space between the dees
- Due to the potential difference, there is an electric field generated between the two dees
- A magnetic field that is perpendicular to the Dees is also present
- So, when for example a positively charged particle $Q$ is in the space, it is accelerated in the direction of the electric field from one Dee to the other (Note, it gains energy of $QV$)
- When the particle is inside the Dee, it moves in a circular path (remember, a moving charged particle in a magnetic field feels a force)
- By the time it finishes a semicircle in one Dee and reaches the space between them, the polarity of the Dees changes as the voltage is alternating.
- Thus, the electric field is in the oppsite direction to what it was previously
- This is necessary so that the particle is accelerated to the other Dee and again gains an energy of $QV$
- However, it is important to note that the time taken for the charged particle to finish its path in one dee has to equal to half time period of the alternating voltage source so that the polarity of the Dees change just in time when the charged particle reaches the gap between the dees
What if the source is not alternating?
By the time the charged particle finishes its path in one Dee, it will be repelled by the other Dee as the electric field vector is in the opposite direction of the particle's velocity and thus preventing any further gain in energy
You might try reading about the Linac and the synchrotron, similar concepts are used
