Experimental Study of Isotope Scaling of Radial Ion Thermal Transport in Axisymmetric Magnetic Field

A series of basic transport physics experiments are performed in Columbia Linear Machine, which generates a steady-state collisionless cylindrical plasma column in uniform axial magnetic field. The focus is on the isotopic scaling of ion thermal conductivity due to ion temperature gradient-driven modes. The experiments are performed using two different gases: Hydrogen and Deuterium. The results indicate reduction of thermal transport with increasing isotopic mass leading to a scaling K_{[perpindicular]} ~ A_i^-0.5, where A_i is the mass number of the isotope of hydrogen. This inverse gyro-Bohm scaling is similar to the tokamak results, but is in stark contradiction to most present theoretical models predicting Bohm (A_i⁰) or gyro-Bohm (A_i^0.5) scaling. A series of experiments to explore the physics basis of this scaling has been also performed.