SPS rectennae energy conversion questions

I browsed the SLAC site and found a lot of interesting references there.

www.slac.stanford.edu

> >Greg Loeh
> >The Stanford Linear Accelerator Center uses about 480 klystron tubes rated
> >at
> >50 megawatts peak energy. Greg is head of the group that designs these
> >tubes.
> >...
> >Greg is very familiar with producing microwaves and he could not see any
> >way to
> >directly convert that energy back into electrical power. In the
> >accelerator
> >very little of the microwave energy goes into moving the electrons in the
> >beam,
> >the rest goes into resitors at the end of each accelerator section. If
> >there
> >was a practical way to recover this energy it would be used.

Recovering the energy is apparently not important from the SLAC perspective.

The Standard SLAC S-Band Klystron has a power output of 65 MW, and it only has
an efficiency of 45 %.

And a lot of the time when the accelerator is not operating they keep the
Klystrons running and dump the power into a water bath.

Energy efficiency is just not that important to them.