artis said:
I just read in LHC page that LHC also uses klysrons and cavities, why semiconductors are not used , is it because they can't handle the very high energies required for these applications? Or is there a specific need for a physical electron beam which I doubt?
Is there a schematic anywhere where one could see in detail how the klystron and cavity work more precisely?
thanks.
As Vanadium has asked, when you ask why not use such-and-such, you need to explain why, rather than wait for someone to give contrary views.
In producing accelerating structures, one must consider not just the physics, but also the engineering and economic aspects. Machining copper structures is easier (Cu is a rather soft metal), and it is quite robust for what they are used for. And remember when I mentioned about these structures having divots and also us being able to slightly change their temperatures to get the exact frequency or most power into the structure that we need. You can't do that with semiconductors, at least not as easily and not as cheaply. You also need them to be large, and it is often difficult to have a uniform, homogeneous solid semiconductor of such size (you can't braise them the way you can Cu or other metals).
But the other issue that we have with semiconductor structures is that, the RF pulse from the klystron is typically long (order of ms). From our experience, long RF pulses at very high gradient tend to induce not only breakdown in these structures, but also have ample opportunities to create multipactor events on the semiconductor surfaces, which is not something that we want (semiconductors tend to have a higher secondary emission than metals).
Having said all of that, there are advanced accelerator concepts that used semiconducting structures to generate wakefields that are then used to accelerate bunches of electrons. The wakefields are generated by very short and very large charge electron bunches. Such technique is still in research and development stage, although we have seen several proof-of-principle demonstrations.
But the workhorse of normal accelerating structures is still Cu, with Nb being the superconducting counterpart.
Zz.