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

反氢原子是第一个，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）独立制造出第一个冷反物质原子。反氢是中性的，因此相对不受电场和磁场的干扰。因此，原则上，通过与正常物质氢的光谱比较，反氢的测量可以达到任何人造测量的最高精度。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和量子理论都暗示物质和反物质之间存在完美的对称性。这种对称性意味着当能量转化为物质时（遵循爱因斯坦著名的方程E=mc^2），将形成完全等量的物质和反物质。然而，今天的宇宙似乎并不包含大量的反物质，特别是没有反物质恒星或行星的证据，也没有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%。反物质的研究，也就是这个项目的全部，旨在帮助解决这个谜团。精确比较反氢和氢的重要一步是捕获中性反氢。（反）氢只能被捕获在磁阱中，磁阱非常浅，只允许捕获温度低于绝对零度1度的原子。这意味着仅仅使反氢冷却是不够的，它必须非常冷。这个项目的目标正是：制造非常冷的反氢并捕获它。反氢通常是通过合并其组成部分的等离子体：反电子（正电子）和反质子来制造的。在早期的工作中，主要研究者和其他人发现，到目前为止，使用的有点蛮力的方法使反氢明显比周围环境温暖。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，将实施一系列等离子体物理技术。这些技术提供了对等离子体的形状和密度的详细控制，以及对这些参数的诊断。虽然这些技术已经在其他地方得到应用，但这里的挑战是使它们成为用于反氢形成的复杂实验装置中的工作马匹。此外，该技术还没有应用到这里提出的多物种等离子体的程度。使用这些技术，预计可以得到详细的控制反氢的内部状态和它们的温度。这两个参数对于磁俘获的成功以及反氢光谱学的未来目标都至关重要。

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.