Undergrad What are the differences between Ion Linac and Electron Linac?

[dRic2]

Hi, I've been reading out of curiosity about linear accelerators to get a general ideal of the principles behind them. My main concern is that, as far as I could tell, there are two different types (I'm sure there are more than two, but I want to keep things simple) of Linear Accelerators (Linac).

The first type, usually used for electrons, is simply a cylindrical waveguide where an EM wave is propagating (generally TM_010). Irises are added to "slow down" the phase velocity of the wave to match the velocity of the electrons (http://web.mit.edu/course/22/22.09/ClassHandouts/Charged Particle Accel/CHAP12.PDF pag 393):

(taken from a YT video)
This type of Linac is used for electrons since they posses a very high velocity (due to their low mass) and relativistic speed are easely achieved.

The second type of Linac, used for ions, is the made by a lots of cavities connected to an alternating potential source as sketched below:

(http://web.mit.edu/course/22/22.09/ClassHandouts/Charged Particle Accel/CHAP14.PDF pag 453)
Here, each cavity is an equipotential surface so no E field is inside. The ion is accelerated only in gaps between cavities and the whole structure support a standing wave (not a propagating wave as in the first case). I see no waveguide here, but probably the whole structure could be enclosed in a cylindrical conductor (thus forming a waveguide)... I don't know.

Is what I said correct ? Because I am really confused. If I keep reading those document I run into Traveling wave Linac and Standing wave Linac, but I don't understand if they are referring to what I already said or if there are other types of Linac which I am neglecting... I am pretty confused right now.

 

[mfb]

If the ions are slow the wavelength would be too large to make a cavity feasible. Here is a picture of the UNILAC at GSI.

You can make a linac as long combination of RF cavities. Standing waves in cavities.

 

[JonasKK]

It seems to me that you've got the basic right.
I think a better and more accessible resource than those MIT handouts is the lecture notes from the major accelerator schools, e.g. the CERN Accelerator School (CAS) or the Joint Universities Accelerator School (JUAS). In [1,2] you have the lectures from JUAS on linacs. The names traveling wave and standing wave are pretty descriptive of what's going on, but the linked lecture slides gives a very nice overview of the different kinds. Also contains nicer pictures! (The MIT handout you linked is woeful, in my opinion).

[1] https://indico.cern.ch/event/850755/contributions/3576234/
[2] https://indico.cern.ch/event/850755/contributions/3576063/

 

[nsaspook]

A small industrial RF linac (1 MeV) for ions used in semiconductor manufacturing. 10 RF cavities.
https://www.physicsforums.com/threads/whats-inside-the-box.813916/

 

[dRic2]

Sorry, I was very busy yesterday... couldn't reply. Anyway, thanks for the resources.