Experimental investigation of isotope scaling of anomalous ion thermal transport

There is a significant divergence between tokamak experimental results and most theoretical predictions in isotopic mass scaling of transport. It indicates a fundamental open physics issue of great importance, as well as a serious question for magnetic fusion. This divergence has motivated a series of basic physics experiments in the Columbia Linear Machine (CLM) [R. Scarmozzino et al., Phys. Rev. Lett. 57, 1729 (1986)], which are reported here. The experimental focus is on the anomalous ion thermal conduction due to ion temperature gradient driven modes in two different gases: hydrogen and deuterium. Unlike in tokamaks, all plasma parameters are kept nearly identical in the CLM for both gases. The results indicate inverse dependence of ion thermal conductivity on the isotopic mass close to K⊥∼Ai−0.5 to −0.8, where Ai is the mass number of the isotope of hydrogen. This is close to the tokamak results, but in contradiction to most theoretical models, especially of the Bohm/gyro-Bohm-types.