Experimental Study of the Principles Governing Tokamak Transport

Both in Ohmically and beam-heated $L$-mode discharges of ASDEX, the electron-temperature (${T}_{e}$) profile shape can be varied over a wide range by the choice of the safety factor ${q}_{a}$. The power-deposition profile, on the contrary, has no effect on the ${T}_{e}$ profile shape. In current-free W-VII-A stellarator plasmas, no such invariance property is found. An independent constraint seems to fix the current distribution $j(r)$ of the tokamak, which defines the conditions of electron heat transport.