Quodon Current in Tungsten and Consequences for Tokamak Fusion Reactors

Abstract

Tokamak fusion reactors produce energetic He ions that penetrate surfaces less than 20 micron and neutrons that spread throughout the reactor. Experiments with similar swift He ions in heavy metals show that the vibronic coupling of nonlinear lattice excitations creates mobile lattice excitations, called quodons. These are decoupled from phonons, move ballistically at near sonic speed and propagate easily in metals and insulators. They can couple to and transport electric charge, which allows their observation in experiments. They rapidly disperse heat throughout a fusion reactor and carry charge through electrical insulators. In this paper we present an experimental design that separates quodon current and conduction current and therefore makes it possible to measure the former. We also present time-of-flight experiments that lead to an estimation of the quodon speed which is of the order of the sound velocity and therefore much faster than the drift of electrons or holes in conduction currents. We present results on quodon current in tungsten, a material widely used in nuclear fusion technology, showing that many quodons will be produced in fusion reactors. It is predicted that at high output powers, quodons created by He ions and neutrons might adversely impact on cryogenic systems.