[ExI] Electromagnetic launcher efficiency

[Anders Sandberg]

Just a quick question I hope Spike, Keith or some of you others already 
know the answer to:

What is the theoretical limit to electromagnetic launcher efficiency?

As far as I can tell from the literature, the quenchgun people seem to 
claim that a superconducting coilgun storing all its energy in the coils 
is optimal:

    "The quenchgun is analogous to the Carnot engine in thermodynamics
    the ideal launcher capable of achieving the maximum theoretically
    possible efficiency. "

http://adsabs.harvard.edu/full/1992NASSP.509B.117S
However, presumably the magnetic fields will not all couple to the 
projectile. And I would really need to get a number of that efficiency - 
I cannot find the old papers cited, since they are all 80s conference 
proceedings.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900012490_1990012490.pdf 

claims "nearly all energy is transmitted", but I cannot figure out how 
nearly the nearly is.

Normal railguns obviously have energy losses from ohmic resistance. The 
calculations in
http://ilin.asee.org/Conference2008/SESSIONS/Lumped%20Parameter%20Modeling%20of%20the%20Ideal%20Railgun.pdf
seem to imply that if everything was superconducting the efficiency 
would be 1, which I find doubtful.

Real electromagnetic launchers have far bigger energy losses of course, 
but I am interested in the theoretical limit. Assume you can get as much 
superconductors, perfect timing and energy as you like.

-- 
Anders Sandberg,
Future of Humanity Institute
Philosophy Faculty of Oxford University

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