by samshort25
 P: 1 Hello! I'm reading into the LHC and the "bunch structure", and I'm confused in general, and I think knowing what the radio frequency acceleration scheme is might help?! As in, how does it work? And does it actually use radio waves? Any help would be greatly appreciated! Thanks, Samantha
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P: 29,238
 Quote by samshort25 Hello! I'm reading into the LHC and the "bunch structure", and I'm confused in general, and I think knowing what the radio frequency acceleration scheme is might help?! As in, how does it work? And does it actually use radio waves? Any help would be greatly appreciated! Thanks, Samantha
The name "RF" is a bit misleading. For example, the proposed International Linear Collider will have accelerating structures in what is known as the "L-Band". I will guess that it will be around either 1.3 GHz, or 13 GHz.

In any case, what is done is like this. You send an EM wave into a standing wave cavity. The mode of the EM wave is in such a way that you will get an axial E-field along the axis of the cavity (such as the TM01 mode). This is the accelerating field that is responsible in accelerating the charged particle. There can be many of these structures stacked together in series. However, because it is an oscillating field, you need to do 2 things:

1. You need to know just the right timing to inject the particles into the cavities.

2. You need to have the field in each cavity to NOT be at the same phase with each other. The phase difference depends on the nature of each cavity. In any case, you need to time the entry of the charge particle just right so that as it goes into one cavity, the field is building in the right direction, and as it leave that cavity and goes into the next cavity, the field in that cavity will also start building in the right direction. How fast these fields build up has to depend on the group velocity and how fast the charge particles are moving through it.

Typical accelerating structures are called "linac", made with several cavities or cells of copper. These are what we call iris-loaded structure. The ILC will have structures made of superconducting material.

Zz.

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