Power balance in the smallest tokamak

The ion temperature of the smallest tokamak, the major radius of 0.1 m, is measured using Doppler broadening spectroscopy. Experiments are performed for helium discharge. Ion temperature T i = 0.7eV is obtained from the Doppler broadened line spectrum of the helium ion. The electron temperature and density measured using line emission intensities of the helium atom are T e = 4.7eV and n e = 3.2 × 10 18 m −3 . The major radius R 0 = 0.11m and the minor radius a = 0.03m are obtained from magnetic measurements. Then, the energy flow from the electron to the ion is evaluated as well as ohmic heating and power losses due to atomic processes. The main loss channel for electron stored energy is conduction even though the tokamak is immersed in the residual neutral gas. Total energy confinement time τ E = 2.3 µs is determined from the power balance, which is comparable with that deduced from the neo-Alcator scaling law.