Re: ADDITIONAL USES FOR LINEAR ACCELERATORS UP TO 21MEV

As for all possible uses of a Linear Accelerator, I have no idea. 
However, your question about their use as thrusters in the vacuum of 
space, the answer is yes they could be used in this manner. Plasma 
propulsion is already in use. The XIPS, Xenon Ion Propulsion System, has 
just been proven in interplanetary space to be very effective and 
reliable. It is also extremely efficient, providing a great deal of 
propulsion for the small amount of propellant used. It is however, not 
known for its high levels of thrust, providing about a tenth of a Newton 
or less. But since there is no opposing force (drag) in deep space a small 
amount of thrust can provide a great deal of velocity change - you just 
have to be patient! Whereas a liquid propellant engine, such as 
hydrazine, need only burn a few 10's of seconds or less to change the 
spacecrafts velocity vector, a XIP engine may need to burn for hours, or 
even days. 

For more detailed information about plasma propulsion, check out this 
site:
http://nmp.jpl.nasa.gov/ds 1/tech/sep.html