A Liquid Wall in a Fusion Energy Device

A liquid wall in a fusion energy device has improved the performance of fusion fuel, and may lead to more resilient fusion devices. At last month's American Physical Society Division of Plasma Physics meeting in Albuquerque, Princeton Plasma Physics Laboratory researchers (Dick Majeski, PPPL, 609-243-3112 and Bob Kaita, PPPL, 609-243-3275) described how they tested this idea on the Current Drive Experiment-Upgrade (CDX-U). CDX-U is a spherical torus, a more rotund version of the well-known tokamak. Like the donut-shaped tokamak, the device uses magnetic fields to confine hot plasma. At the bottom of their tubby tokamak, the researchers placed a pool of liquid lithium. Meanwhile, they applied electrical current to the plasma both to create strong magnetic fields that confine it and also to heat the plasma to desired hot temperatures. In contact with the fusion plasma, the liquid lithium increased the efficiency of transferring the current to the plasma, leading to less wasted energy. It also does an excellent job of absorbing impurities, such as carbon and oxygen, which could otherwise cool the plasma. What's more, it absorbs hydrogen plasma that reaches it, requiring the researchers continually to pump in hydrogen gas. This is actually a good thing, as it prevents an undesirable buildup of cool hydrogen at the plasma boundary which could return to the plasma and lower its temperature. Finally, since the liquid surface can be continually replenished, the liquid wall is not subject to the same degradation and damage that would occur by neutrons that bombard a solid metal wall. The liquid wall can conceivably be applied to future magnetic fusion reactors, whether a spherical torus, a tokamak, or another design. (Meeting paper RI1.004; see picture; also see R. Majeski et al., Journal of Nuclear Materials, March 2003.)