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To Brian from Tim

>3. This maser thing.  What exactly is a maser?  A microwave beam generator? 
> Is there a way to reflect these microwaves with good efficiency?  Perhaps 
>we could somehow rig a reflector to detact from our ship and reflect back 
>the beam and do away with a linear accelerator.

Indeed it is laser with microwaves. Thus making highly directional
monochromic microwaves. I remember a college-demonstration where wax (where
candles are made of) where used as a lens for microwaves. (There we just
used a magnetron and waveguide to generate microwaves)

>4. Has anyone figured out just how long the accelerator needs to be since it 
>has to be linear?  More to the point, can we keep the linear accelerator 
>short enough and, therefore, light enough to produce relativistic exhaust 

Some long time ago I figured out that it would probably be too long, the
formulas are not so easy to integrate so at that time I used some repeating
summation. I assumed that we would not have a constant acceleration of the
mass, but a constant power input. This means that initially it accelerates
fast but at the end much slower. Relativistic effects do make this
difference worse.
But as Kevin corrected me a week ago, why not use a torus instead a lineac?
You seem to have a reason for not liking a torus, could you tell me what
that reason is?

>5. Can we even produce the magnetic fields in an accelerator necessary to 
>get an exhaust velocity of .9996c for .62kg/sec. or even a .75c exhaust 
>velocity using say a 1km long accelerator?  My understanding is that field 
>generators that confine magnetics fields have a tendency to blow up.  I hope 
>I'm wrong but I thought you might know if this concern applies to the 
>designs we've discussed.

I think we should not worry about that too much, for me this is just a
problem for the gigantic-energy stack (i.e. problems involving creation and
containment of gigangtic energies).