RE: starship-design: HOTOL SeaDragon idea.

["L. Parker" <lparker@cacaphony.net>]

As far as I am aware, the reports below are the most recent published on
creation of antimatter in significant numbers. It is one of the ones I said
was under review. CERN and others have been manufacturing "antihydrogen" for
several years, but not in a way that was useful for study or in any
significant numbers. This year they have actually been able to contain them
long enough to do something with them. The containment device is a modified
Penning Trap.

Note, if you read the full paper, you will find that this just barely
qualifies as an atom - there is only an antiproton and a positron. Here is
the text of the news articles from AIP:


Number 611 #1, October 29, 2002 by Phil Schewe, James Riordon, and Ben Stein
The Internal States of Anti-Hydrogen

The internal states of anti-hydrogen have been studied, for the first time,
by the ATRAP collaboration, working at CERN where antiprotons are slowed and
then joined with positrons to form anti-hydrogen atoms within a detector-
and electrode-filled enclosure (a nested Penning trap) over the past year.
This work suggests that anti-hydrogen is preferentially formed in an excited
state via a three-body process when two positrons and an anti-proton
collide.

Only a month ago the ATHENA collaboration, working at the same CERN
facility, made the first report of cold anti-H atom detection (Update 605)
using techniques largely pioneered by ATRAP (the antiproton accumulation
techniques, the nested Penning trap used, the positron cooling approach,
etc.) So what has changed since then? Three things:


(1) First of all, the ATHENA detection of anti-atoms is indirect. The
presumed presence of the anti-atom (positron plus antiproton) is registered
by a dual annihilation of the positron with an electron and the antiproton
with a nearby proton.

Complicating the detection scenario is the fact that the proton-antiproton
annihilation itself sometimes spawns positrons which (when they annihilate
in their turn) could falsely indicate the prior presence of an anti-atom.

This class of events constitutes a background which must be subtracted out
in the analysis process, and it precludes one from identifying any
particular double-annihilation event as having been a genuine anti-hydrogen
(sometimes written as an H with a bar over it).


By contrast, the ATRAP direct detection process unambiguously identifies
H-bar in a process called field ionization, which works as follows. Having
formed in the center of the enclosure, neutral anti-atoms are free to drift
in any direction.

Some of them annihilate but others move into an "ionization well," a region
where strong electric fields tear the H-bar apart. Negatively charged
antiprotons not in the company of a positively charged positron cannot reach
the well.

Once there, though, the field sunders the atom, and the antiprotons are
trapped in place, leaving the positron to move off and annihilate elsewhere.
By counting the number of antiprotons one knows how many anti-atoms had
arrived at the well. Every event represents an anti-atom. (See figure.)


(2) Moreover, one can now make a statistical study of the electric field
needed to ionize the positron and deduce from this, in a rudimentary way,
some information about the internal energy states of the H-bar. Thus the
internal properties of an anti-atom have been studied for the first time.
The observed range in principal quantum number n (n=1 corresponding to the
ground state, or lowest level) goes from 43 up to 55.


(3) Finally, another thing that is different in this experiment is the much
higher rate of anti-H production. The collaboration spokesperson, Gerald
Gabrielse of Harvard (617-495-4381, CERN 41-22-767-9813,
gabrielse@physics.harvard.edu) says that more anti-H atoms can be recorded
in a few hours than have been reported in all previous experiments.


The ultimate goal of these experiments will be to trap neutral cold
anti-hydrogen atoms and to study their spectra with the same precision
(parts per 1014 for an analysis of the transition from the n=2 to the n=1
state) as for plain hydrogen. One could then tell whether the laws of
physics apply the same or differently to atoms and anti-atoms. (Gabrielse et
al., Physical Review Letters, 18 November; other ATRAP contacts are Walter
Oelert at Forschungszentrum Julich, 49-2461-61-4156, CERN 41-22-767-1758;
Jochen Walz at the Max Planck Institute for Quantum Physics,
49-89-32905-281, CERN 41-22-767-9813; Eric Hessels at York University, CERN
41-22-767-9813; ATRAP website).


In recent work ATRAP sees a further increase in the antihydrogen production
rate by using a small radio transmitter to heat antiprotons into making
repeated collisions with cold positrons. With this higher production rate,
they are able to make the first measurements of a distribution (not just the
range) of excited states of antihydrogen. (For an early background article,
by Gabrielse, see Scientific American, Dec 1992.)


There is also an earlier article of interest:



Number 577 #1, February 20, 2002 by Phil Schewe, James Riordon, and Ben
Stein

Cold Antihydrogen Atoms

Cold antihydrogen atoms might have been made, for the first time, in an
experiment at the CERN lab, where positrons and antiprotons are brought
together in a bottle made of electric and magnetic fields.

Nature allows the existence of antiparticles but hasn't seen fit to make a
lot of them. Modest amounts of antiprotons show up in cosmic ray showers,
and positrons (antielectrons) are forged in certain high-energy regions of
the sky such as galactic nuclei.

But if larger forms of anti-matter like anti-atoms, anti-stars, and
anti-galaxies were plentiful in the visible part of the universe then we
would see the catastrophic gamma ray glare from places where matter brushes
up against antimatter. Such radiation has not been seen and scientists must
make their own anti-atoms artificially.

Making antihydrogen is difficult, however, because positrons and
antiprotons, even when they can be marshaled and brought near each other,
are usually going past each other too quickly for neutral atoms to form.

A few years ago a dozen or so hot antihydrogen atoms were made on the fly
amid violent scattering interactions at CERN and Fermilab (Updates 253,
297). These did not dally long enough to be studied, but instead expired
quickly when they crashed into detectors that established the antihydrogen's
brief existence.


At CERN several experiments are devoted to making cold anti-atoms in a
controlled environment amenable to detailed studies. The main goal here is
to determine whether the laws of physics (gravity, quantum mechanics,
relativity, etc.) apply to anti-atoms the same as they do to regular atoms.

At this week's meeting of the American Association for the Advancement of
Science (AAAS) in Boston, Gerald Gabrielse of Harvard, spokesperson for the
Antihydrogen Trap Collaboration (ATRAP), reported new results.

In this experiment 6-MeV antiprotons (themselves made by smashing a beam of
protons into a target) are slowed by a factor of 10 billion (to an
equivalent temperature of 4 K), partly by mixing them with cold electrons,
and then collected in a trap. Positrons from the decay of sodium-22 nuclei
are cooled and collected at the other end of the device. Eventually about
300,000 positrons are electrically nudged into the vicinity of about 50,000
antiprotons.


Gabrielse believes that what sits in the trap isn't entirely a neutral
plasma consisting of coincident positron and antiproton clouds, and that
cold antihydrogen atoms might have formed. More diagnostic equipment being
installed now may settle the issue in the coming months. A larger version of
the ATRAP apparatus, which might be in operation as early as this fall,
should allow the researchers to introduce some lasers for the purpose of
studying the spectroscopy of prospective anti-hydrogen atoms in the trap.