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In article <C0IB07.BBL@zoo.toronto.edu>, henry@zoo.toronto.edu (Henry Spencer) writes:
> In article <93007.120340DOCTORJ@SLACVM.SLAC.STANFORD.EDU> Jon J Thaler <DOCTORJ@SLACVM.SLAC.STANFORD.EDU> writes:
>>> Kilogram quantities of antimatter are quite adequate for early interstellar
>>> probes, given modest vehicles... it looks plausible.
>>
>>A reality check:
>>This is about 13 orders of magnitude larger than the total number of
>>antiprotons ever created and stored (about 10**14)

A quick call to the Main Control Room disclosed that the largest
"p-bar stack" ever stored at Fermilab was 121 milliamps in the
Accumulator (1.21E12 antiprotons) on 7 January 1991.  I don't know if
CERN in Geneva has exceeded this, but if they have, it's not by much.
(The largest stack ever dumped by accident, in a power glitch, was 81
mA, by the way.)

As for Henry, most of what he says is true but you gotta take it with
a big grain of salt:

> Reality check right back at you:  plot human antimatter production capacity
> versus time.  Interesting graph, no?  Sure, it's limited right now... but
> it's growing fast.

I would have to look at antiproton production projections for the new
120-GeV Main Injector which we are planning to build.  But I wouldn't
say it's growing all that fast, especially since *nobody* is planning
to build any new antimatter sources outside Fermilab and CERN, any
time in the next decade or more.  These two labs will continue to
tinker with modest improvements in the existing sources.  

The big demand for antiprotons-- to come up with fat negative
particles you can run backwards through the Tevatron and SPS
synchrotrons, and collide with protons-- has gone away.  Future
machines, such as the Superconducting Supercollider (how I hate that
name), the Large Hadron Collider, and the UNK lab, will have dual
rings circulating protons.  P-bars have proved to be just too much
hassle.  And outside of high-energy physics experiments, nobody can
afford them.
 
> If we mounted a major effort, we could probably be test-firing antimatter
> rocket engines within ten years.  There are *NO* fundamental barriers that
> anyone has been able to find.  It's purely a matter of scaling up and
> optimizing the hardware -- the existing accelerators are optimized for
> production of Nobel prizes, not bulk antimatter -- and solving assorted
> straightforward engineering problems of handling and storage.  The idea
> has been investigated in depth; no show-stoppers have appeared.

I don't appreciate the gratuitous sneer at the people who sweated to
get the production rates *this* high.  They solved difficult
engineering problems and had to make use of technology available at
HEP labs rather than some blue-sky paper scheme.  And, yes, Simon van
der Meer did win a Nobel prize for stochastic cooling, an essential
process in the storage of antiprotons.  So what?

Stack rate this afternoon is 2.35E10 p-bars per hour; Fermilab's
record is near 4E10, about 111 million per second or 3.3E15 per year. 
We can get you a milligram in 200,000 years if you bring your own
bag-- our storage system won't preserve antiprotons that long.
 
> A production setup the size of the Hanford works could make enough
> antimatter to open up the solar system.  Interstellar propulsion is
> harder.  

Interstellar propulsion is very hard using any technique.  I concede
that making and storing kilograms of antimatter is pretty easy
compared to making a workable ramscoop, or (the original subject of
discussion) causing p-p fusion in a stream of hydrogen flowing through
your reactor at relativistic speeds.

> Kilogram quantities are probably going to have to be made in
> space, not so much for handling reasons (although those aren't trivial)
> as because of the sheer amounts of *energy* needed.  

At the moment, to make one antiproton, we buy from Commonwealth Edison
as much electrical energy as you'd get from annihilating a billion
antiprotons.  It's a lousy way to store energy.

> It would be a huge
> project, but there's no fundamental problem; we could start designing
> hardware tomorrow if it were urgent enough.

I've got stuff to do tomorrow.  How about Saturday?

[I guess I should add that opinions expressed are not those of
Fermilab, Universities Research Association, or the Department of
Energy.]

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