Influence of transient behavior on the determination of the energy confinement time in a tokamak
Abstract
The disregard of fast processes (e.g., the L-H transition) in a tokamak plasma can lead to large errors in the determination of the energy confinement time τE. A major upgrade in the electromagnetic diagnostic system for the analysis of plasma parameters and in the collection system has made it possible to take into account the influence of the transient character of the radial profile and the value of the plasma current I P as well as the stored energy W on the determination of τE from diamagnetic measurements and to investigate fast processes involved in the L-H transition. The energy confinement time τE is calculated from the equation τ E=W/[U PIP-d/dt(LI P 2 /2)-dW/dt] where U P is the plasma loop voltage (V), I P is the plasma current (A), and L is the total internal inductance (H). The total inductance L of the plasma column has been determined from measurements of the quantity β J+I i/2, where β J is the ratio between the gas-kinetic pressure and the pressure of the poloidal magnetic field, and I i is the internal inductance. The inclusion of transient behavior in the determination of τ E from diamagnetic measurements gives a correction of up to 50%.