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

反氢是第一个，也是迄今为止唯一一个完全由反物质构成的原子。2002年，两组科学家在欧洲核子研究中心（CERN）独立制造了第一批冷反物质原子。反氢是中性的，因此相对来说不受电场和磁场的干扰。因此，对反氢的测量，原则上可以达到任何人造测量的最高精度，通过光谱与它的正常物质对应氢进行比较。这种比较旨在帮助解释宇宙中反物质/物质的不对称性。目前粒子物理学的标准模型，以及基础的量子理论，暗示着物质和反物质之间存在着完美的对称性。这种对称性意味着，当能量转化为物质（遵循爱因斯坦著名的方程E=mc^2）时，将形成数量完全相等的物质和反物质。然而，今天的宇宙似乎并不包含大量的反物质，特别是没有证据表明反物质恒星或行星存在，也没有证据表明所谓的暗物质应该是反物质。因此，通俗地说，我们目前错过了宇宙的50%。对反物质的研究，也就是这个项目的全部内容，旨在帮助解开这个谜团。精确比较反氢和氢的一个重要步骤是捕获中性反氢。（反）氢只能被困在一个非常浅的磁阱中，只允许在温度低于绝对零度的情况下捕获原子。这意味着仅仅使反氢变冷是不够的，它必须非常冷。这个项目的目的就是；制造非常冷的反氢并将其捕获。反氢通常是由反电子（正电子）和反质子组成的等离子体合并而成。在首席研究员和其他人的早期工作中发现，到目前为止，使用的某种蛮力方法产生的反氢比周围环境要热得多。因此，即使在绝对零度以上4度的低温环境中，也很少会产生可捕获的反原子。在这个项目中，一系列的等离子体物理技术将被实现。这些技术提供了对等离子体形状和密度的详细控制，以及对这些参数的诊断。尽管这些技术已经在其他地方得到了应用，但这里的挑战是将它们应用到用于反氢形成的复杂实验装置中。此外，这些技术还没有应用到本文提出的多种等离子体的程度。利用这些技术，有望获得对反氢内部态及其温度的详细控制。这两个参数对于磁捕获的成功和反氢光谱的未来目标都是至关重要的。

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.