SPS rectennae energy conversion questions

>
> the method of turning the microwaves to power on the
> ground, and they
> maintained that the preferred method was to boil
> water to turn turbines.
>

Not in any study that I am familiar with.

Ask them to provide references and/or sources for this
claim.

> Any thoughts on this exchange (below)?
> Are currently floated proposals still using
> microwaves?

Some yes. Some propose lasers instead.

> I refered them to the following site. Any more
> current information online?
> http://permanent.com/p-sps.htm
>

Plenty of places, but that is a good start.

>
> >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.

Klystrons are still about the most efficient means
of generating microwaves.

> >...
> >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

This is surprising. Most microwave engineers
are familiar with Schottky barrier diodes, which have
efficiencies in the high 90's for converting
microwaves
into electricity.

> >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.
>

That is an interesting observation, however
I think the author may be confusing his use of the
word "practical". It is more a question of
economics.

The Stanford folks could possibly recover the unused
microwaves if they wanted to, but electricity is
fairly cheap, and the capital cost of the conversion
system might not be economic.

Microwave power transmission has been demonstrated,
there is no doubt that it works and has high
efficiences. You need a receiving array of dipole
antennas each connected to a Schottky barrier diode.

Demonstrations include an experiment with the
Goldstone dish ( I think there are links to that at
the SSI web site ) where a rack of floodlights was
powered by a microwave beam. And an aircraft flew
powered by a microwave beam.

I believe there has been a demo a Reunion Island, but
I had difficulty getting hard data from those folks.

It might be interesting to get more info about the
Stanford Accelerator, and ask them if they have
considered using dipoles with Schottky barrier diodes
to recycle the microwaves, and if they did a cost
analysis of that versus dissipating the microwaves in
resistors.

Cheers,

Charles R.