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Xiang Cheng - Internship at Princeton Plasma Physics Laboratory

Internship at Princeton Plasma Physics Laboratory - Princeton, USA
Reported by Xiang Cheng. Powered by FuseNet.

Starting on the 15th of June last summer, I stayed at Princeton Plasma Physics Laboratory (PPPL) for a 3-month internship. During this internship I have investigated the non-adiabatic behavior of charged particles in the magnetic field of a mirror trap and its effects on plasma transport and plasma heating.

Non-adiabatic behaviour and particle loss in magnetic mirror traps

The magnetic moment μ is usually considered to be an adiabatic invariant, but in mumerous situations, especially in fusion devices, this is not actually the case. Adiabatic conditions require that the gyro radius is much smaller than the radius of curvature of the magnetic field lines. However, when the charged plasma particle have a high velocity or when the magnetic induction intensity is low, the gyro radius can be rather large in comparison to the radius of curvature of the magnetic field lines, in the case of which the magnetic moment cannot be treated as an invariant.


The left image shows a schematic of a simple mirror trap configuration (1 denotes the coils, whereas 2 indicates the magnetic field lines). The right image shows the (normalised) magnetic moment evolving in time.

During my internship, I have simulated the motion of an electron in a mirror trap, while observing the changing magnetic moment μ as function of the temperature and position in the magnetic trap. The result showed that the behaviour of the electron is non-adiabitc in the vicinity of the center of the trap and each time the electron passes through this region, there is a jump in μ. Since μ changes in time, it can be expected that an initially trapped particle can eventually escape the mirror device once its μ drops below a certain small value. As such, this mechanism contributes to the loss of particles in magnetic mirror traps, which is a critical issue for these kind of fusion devices and, therefore, deserves a thorough investigation.


A versatile life in Princeton

Princeton is a small and peaceful town, which was no problem for me. In fact, I liked it, because it allowed me to focus on the things I really wanted to do without any distractions. However, peaceful doesn’t mean that it’s boring: you can always find something interesting to do. For instance, a couple of summer concerts were organised at the main campus of Princeton University during my stay, hosting many famous bands and musicians. Princeton also has a nice museum which owns numerous collections and is freely open to everyone. Finally, there are lots of barbecues during summer, which seems to be a big part of the American culture. And if that's not enough, Princeton is quite close to New York, which is definitely the best place to go when you want to have fun. I will never get tired of exploring New York city.

My 3-month internship has been a very valuable experience, during which I have learned a lot. Therefore, I would like to thank Fusenet for their support, which has made this internship possible for me. Thanks!