Antihydrogen trapping and plasma control - RESUBMISSION 8/5/07

Antihydrogen was the first, and so far the only, atom made entirely of antimatter to be produced. In 2002 two teams of scientists independently produced the first cold antimatter atoms at the European centre for nuclear physics, CERN. Antihydrogen is neutral, and is therefore relatively unperturbed by electric and magnetic fields. Measurements on antihydrogen can therefore, in principle, reach the highest level of precision of any man-made measurements via spectroscopic comparison with its normal matter counterpart hydrogen. This comparison is intended to help explain the antimatter/matter asymmetry in the Universe. The current standard model of particle physics, and the underlying quantum theories, imply that there is perfect symmetry between matter and antimatter. This symmetry means that when energy is transformed into matter (following Einstein's famous equation E=mc^2) / exactly equal amounts of matter and antimatter will be formed. However, the Universe of today seems not to contain significant amounts of antimatter, in particular is there no evidence of antimatter stars or planets, nor that the so-called dark-matter should be antimatter. Thus, to put it popularly, we currently miss 50% of the Universe. The research into antimatter, which this project is all about, aims to help resolve this mystery.An important step towards precision comparison of antihydrogen and hydrogen, is to trap the neutral antihydrogen. (Anti)hydrogen can only be trapped in a magnetic trap, which is very shallow, only allowing trapping of atoms with temperatures below about one degree above absolute zero. This means that it is not enough to just make the antihydrogen cold, it has to be very cold. The aim of this project is exactly that; make very cold antihydrogen and trap it. Antihydrogen is normally made by merging plasmas of its constituents: antielectrons (positrons) and antiprotons. In earlier work by the principal investigator and others it was found that up until now, the somewhat brute-force approach used makes antihydrogen which is significantly warmer than the surroundings. So, even with cryogenic surroundings at four degrees above absolute zero, very few trappable antiatoms would be produced. In this project a range of plasma physics techniques will be implemented. These techniques offer detailed control over the shape and density of the plasmas, as well as diagnostics for these parameters. Although the techniques have been applied elsewhere, the challenge here is to make them into work horses in the complex experimental setup that is used for antihydrogen formation. Furthermore, the techniques have not been applied to the extent proposed here in multi-species plasmas. Using these techniques, it is expected that detailed control of the antihydrogen internal states and their temperature can be obtained. These two parameters are both crucial for the success of magnetic trapping, and the future goal of antihydrogen spectroscopy.