Simulations of antihydrogen
The ALPHA antihydogen experiment was in November 2010 able to report the first successful attempt to catch antiatoms in a magnetic trap. This achievement, reported in Nature, has received a lot of attention, both in news media, popular since, and within the physics community. For example, Physics World listed this as the most important progress in Physics 2010, and the American Physical Society had in on its top ten list. More recently we made the first antimatter spectroscopy between hyperfine states of antihydrogen. The long-term goal of ALPHA and other antihydrogen experiments is to test fundamental symmetries of nature by comparing matter and antimatter atoms. Primarily, ALPHA aims at high-resolution spectroscopy of antihydrogen, for instance on the 1s-2s line which has been measured to an accuracy of one part in 10^14 in ordinary hydrogen. Another possibility is to compare the gravitational interaction of matter and antimatter. All studies of this sort require the antiatoms to be held in an atom trap for times long enough to perform the studies. This is a challenge since antimatter is destroyed when it meets ordinary matter. Therefore the atom trap consists of varying magnetic fields, where the atoms are confined near the minimum of the field. However, the trap is very shallow, antiatoms with an energy greater than about 0.5 Kelvin will escape from the trap. Since typical energies in the experiment are much higher than this, only a small fraction of the antihydrogen atoms created can actually be trapped. Presently a new experimental apparatus is being built at CERN. The goal of these simulations is to understand the behavior of both charged particle and antihydrogen dynamics in the trap. To reach the final goal of detailed studies of antihydrogen the trapping efficiency has to be increased. The most important factor is to reduce the temperature of the antihydrogen atoms formed. This is where my theoretical simulations come in. I calculate classical trajectories of antiprotons inserted in a plasma of positrons (antielectrons). The antiprotons go back and forth through the plasma many times, each time with some probability of forming an antihydrogen atom. The antiprotons also interact in other ways, leading for instance to a gradual thermalization with the positrions, and to loss processes. The temperature of the anithydrogen depends on a lot of factors: the density, temperature and number of the antiprotons and positrons before forming the antihydrogen, and the configuration of electric and magnetic fields inside the trap. Taken together this becomes a very complicated problem, requiring extensive numerical simulations. Dynamics of trapped ground-state antihydrogen may also be studied. This is necessary to understand how the antiatoms react to applied fields, such as microwaves or lasers. Additionally, I perform calculations of antihydrogen and antiprotons interacting with ordinary atoms and ions. This is important since, even though one strives to create a good vacuum in the trapping region, there is always some background gas present.