Wow, Pete, way to go! You're in the history books now. Really cool! You and your family, no doubt, are very proud.
I thought you were in Japan when the breakthrough occurred--sending neutrinos site to site, was it? Lost the email, and a whole slate of others when we did a virus scan after installing high speed internet. Thanks for the step by step account of the process. I will reread it, of course, but it is clear as I go along. Once I get to the end, the most crystalline thing is that the work is mind-bogglingly microscopic. We'd heard about the Ministry putting the muzzle on scientists round the climate change issue. I guess that isn't their only area of concern? Congrats again! Natalia On 11/19/2010 8:50 PM, pete wrote: > On Thu, 18 Nov 2010, D and N wrote: > >> Most of you have probably heard the news out of CERN that hydrogen >> anti-matter has finally been /captured /in a container for about a second. >> >> The reports have varied, but the mention of the Canadian team, including >> physicists from Triumf, rang a bell. Congratulations to your colleagues, >> Pete! >> >> If you could, enlighten us on the real story. >> >> Natalia > > Sure. I've been out of the loop with this experiment for a while, and as > is common with big impact papers these days, there was a tight embargo > on the news until the public announcement. People on authors list gave > no hint how well things were progressing. Art Olin managed to sneak a > mini-seminar into a regular science division meeting yesterday, > simultaneous to the announcement; his talk was scheduled but there was > no indication he had anything new to reveal. I would have gone to see > what he had to say, anyway, except that it was at 10am. Just as I missed > the ALPHA Canada group picture a couple of years ago, which was taken at > about 10:15. Oh, well, Makoto emailed me my copy of the paper this > morning, and there's my name in the acknowledgements. > > I haven't seen any of the group around since then, as I have a few > questions myself on the details. Basically, as I described last time, > the trick to this process is convincing the antihydrogen (Hbar, in > physics jargon) to have quite low energy after being formed (equivalent > to heat for large numbers of atoms, or simply velocity for numbers down > in the double digits or less), so it can be held by the very weak force > generated by a strong magnetic field acting on the magnetic dipole of > the atom. The paper points out the problems which the initial group had > a decade ago (I can't tell if the paper is publically accessible, as we > have a blanket site-licence subscription to such websites here) as they > were feeding antiprotons (Pbars) into the reaction vessel at a few eV, > which was still too energetic to capture. > > The paper then goes on to describe a trick whereby the Pbars, which are > initially collected in a standard charged particle trap, after some > clever tricks to remove much of their energy, are gently nudged into > oscillating over through a low potential barrier into the region where > the antielectrons aka positrons (e+) are held, in a similar trap. > Counterintuitively, a "chirping" (frequency dropping) oscillation > applied to the field strength in the Pbar trap, across the frequency > range corresponding to the oscillation time of the Pbars as they bounce > back and forth within the confines of the trap, induces the antiprotons > to match the dropping frequency by travelling a little farther in each > oscillation, gaining a small amount of energy as they do so. Eventually, > in a couple of hundred microseconds, they've acquired sufficient energy > to just slip out of the trap, and across into the neighbouring space > where the e+ are held. > > The positrons, of which there are generally more (in this case two > million per cycle vs 30,000 Pbars), as they are easier to > generate and collect, coming in this case from a radioactive decay > source, are much colder than the Pbars, having been cooled by repeatedly > allowing the fastest ones to escape their trap in brief intervals, > separated by intervals where the remaining particles "rethermalize", ie > reforming the upper tail of the statistic distribution of their > energies. (It is planned in future to collect more Pbars per instance, > so that this trick can be applied to them as well, thus increasing > overall production efficiency. This is possible because the collection > time can be extended somewhat. The duration for the trapped Hbars can > also be extended far beyond the milliseconds of the current specimens, > as well, by the way. The short capture time was simply a feature of > the proof-of-principle nature of this particular trial.) > > The trick at this point is for the Pbars and e+ to combine into neutral > atoms without zinging off out of the trap (which has now shifted into > neutral particle magnetic trap mode). I'm not sure exactly how this > part works, as the deionization is highly exothermic. I rather suspect > that the reason they can do it is that they are only catching one Hbar > for every ten cycles, so there is only one Hbar there at a time. The > exothermic nature may only be a problem when there are a large number > of atoms each giving off the energy of formation as radiation, which > then gets scattered and degraded off the neighbouring atoms, being > absorbed as kinetic energy. With only a small number of candidate > atoms, the radiation may simply escape to deposit its heat in the > containment vessel instead. The other possibility is that there is > a considerable amount of Hbar being formed in each cycle, with all > the atoms initially acquiring sufficient energy to escape, but that > they then thermalize, off each other, before escaping, so that one in > ten times one of them is knocked just the right way to leave it with > a low velocity relative to the lab frame, and thus it gets snagged by > the trap. > > I will get this cleared up the next time I see one of the authors > wandering about, maybe next week. > > -Pete > > > _______________________________________________ > Futurework mailing list > [email protected] > https://lists.uwaterloo.ca/mailman/listinfo/futurework > _______________________________________________ Futurework mailing list [email protected] https://lists.uwaterloo.ca/mailman/listinfo/futurework
