From: magnus@thep.lu.se (Magnus Olsson)
Newsgroups: sci.space
Subject: Re: Anti-atoms (was Re: Making Antimatter)
Date: 9 Jan 93 09:58:53 GMT
Organization: Theoretical Physics, Lund University, Sweden

In article <1993Jan8.192720.1@fnalnl.fnal.gov> higgins@fnalnl.fnal.gov (Bill Higgins-- Beam Jockey) writes:
>In article <Jan08.193145.59326@yuma.ACNS.ColoState.EDU>, wallacen@ColoState.EDU (nathan wallace) writes:
>> Presumably the "cold" AP mentioned in the recent Sci Am article would
>> be part of such a system.
>
>The U. of Washington ion traps are suitable for keeping only small
>numbers of antiprotons, or other charged particles, so far as I know.

I quote from the Sci. Am. article (Gabrielse: Extremely Cold
Antiprotons, December 1992):

"In this way, during one hour, more than 100,000 cold antiprotons have
been stacked, or added to one another, in the trap. We estimate that
our current apparatus is capable of capturing and cooling up to one
million antiprotons"

One million antiprotons isn't a big lot; the total energy released
when they annihilate with protons is on the order of 0.1 millijoule.
By comparison, the kinetic energy of a two-ton space probe travelling
at the modest speed of 10 km/s is 100 gigajoules. We're talking about
fifteen orders of magnitude even in this very conservative estimate -
hardly a Trivial Matter of Engineering...

[...]

>Well, I would apply the word "antimatter" to any antiparticle, but I
>understand what you mean:  matter made of neutral anti-atoms has not
>been fabricated.  H. Poth and collaborators have done work on
>antiprotonic atoms, where a negative antiproton orbits a positive
>nucleus for a short time (it's a nice probe of nuclear physics).  

And to clarify a little: "A short time" in this context is very short
indeed. I don't know the lifetime for an antiproton-proton system, but
the analogous electron-positron system, the positronium "atom", only
lives for about a microsecond before the electron and positron
annihilate each other.

>They
>would like to make antihydrogen (positron plus antiproton), but as far
>as I know they haven't managed it yet.  

I quote again from the Sci. Am. article:

"Antihydrogen production is an ambitious and difficult undertaking
that will take some time to realize. Estimated production rates are
very low." 

"Very low" means in this context that they'll be lucky to produce even
a single antiatom within the next five years or so.

>If somebody is
>planning to do this, it's certainly at CERN's Low Energy Antiproton
>Ring, where the action is in this field.  Fermilab has no facilities
>for work with "cold" antiprotons.

Yes. Gabrielse specifically mentions moving his experiment to CERN
from the States for that reason. 


NOTE: I'm *not* dismissing antimatter as an energy source for
spaceships. I'm only saying that it will take a very long time before
it becomes even remotely practical.


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